阅读说明：本技术 临界固溶和始于高温多次变温交变时效与退火热处理方法 (Critical solid solution and high-temperature multiple variable-temperature alternating aging and annealing heat treatment method ) 是由 李志广 靳峰 赵伟 李姝颖 白泽兵 李荣军 于 2020-12-07 设计创作，主要内容包括：本发明提供一种临界固溶和始于高温多次变温交变时效与退火热处理方法,包括：临界固溶热处理过程和临界始于高温多次变温交变时效与退火热处理过程。本发明的方案具有技术可行性、工艺适应性、质量可靠性、经济合理性、使用安全性,可有效扬长避短了奥氏体不锈钢传统主流热处理方法的优缺点,从根本上解决了现有奥氏体不锈钢热处理“质量稳定性差、合格品率低、硬度偏低、力学性能低与一致性差、抗变色锈蚀能力差、加热时间长、效率低、热处理设备加热可靠性差与高温元器件使用寿命低以及成本高”等“一长一高四差五低”特有热处理技术难题,尤其适用于奥氏体不锈钢在钢厂和制造厂所涉及的冶炼、轧钢、锻造和热处理等热加工工程技术领域。(The invention provides a method for critical solid solution and high-temperature multiple variable-temperature alternating aging and annealing heat treatment, which comprises the following steps: the critical solution heat treatment process and the critical solution heat treatment process start from the high-temperature multiple-temperature-changing alternating aging and annealing heat treatment process. The scheme of the invention has technical feasibility, process adaptability, quality reliability, economic rationality and use safety, can effectively make good use of the advantages and disadvantages of the traditional mainstream heat treatment method of austenitic stainless steel, fundamentally solves the unique heat treatment technical problems of poor quality stability, low qualified product rate, low hardness, low mechanical property, poor consistency, poor anti-tarnishing resistance, long heating time, low efficiency, poor heating reliability of heat treatment equipment, low service life of high-temperature components, high cost and the like, namely one long step, one high step, four steps, five steps, and the like of the conventional heat treatment of austenitic stainless steel, and is particularly suitable for the heat treatment engineering technical fields of smelting, steel rolling, forging, heat treatment and the like of austenitic stainless steel in steel factories and manufacturing plants.)

1. A critical solid solution and high-temperature multiple variable-temperature alternating aging and annealing heat treatment method is characterized by comprising the following steps:

a critical solution heat treatment process, the critical solution heat treatment process comprising: firstly, carrying out pre-solid solution critical preheating heating and heat preservation when the austenitic stainless steel is heated to the preheating temperature from room temperature at a medium speed in a heating furnace within a set time, then continuously carrying out pre-solid solution critical stabilizing heating and heat preservation when the austenitic stainless steel is heated to the stabilizing temperature, then continuously carrying out critical solid solution minimum temperature heating and heat preservation when the austenitic stainless steel is heated to the solid solution minimum temperature, then continuously carrying out critical solid solution maximum temperature heating and heat preservation when the austenitic stainless steel is heated to the solid solution maximum temperature, and finally continuously carrying out solid solution cooling when the austenitic stainless steel is cooled to the room temperature by adopting a specific cooling mode;

after the critical solution heat treatment is finished, the first half part of the temperature-changing alternating aging heat treatment which starts from high temperature for multiple times is continuously carried out, and the method comprises the following steps: the 1 st critical process is started in the high-temperature variable-temperature alternating aging process: the method specifically comprises the following steps that 1, the first half part of the critical process is started at high temperature and ended at low temperature without variable temperature alternating aging: firstly heating and preserving the austenite stainless steel at the critical aging highest temperature when the temperature of the austenite stainless steel is raised to the aging highest temperature from room temperature at a medium speed in a heating furnace within a specified time, then continuing heating and preserving the austenite stainless steel at the critical aging intermediate temperature when the temperature of the austenite stainless steel is rapidly lowered to the aging intermediate temperature, then continuing heating and preserving the austenite stainless steel at the critical aging lowest temperature when the temperature of the austenite stainless steel is rapidly lowered to the final aging lowest temperature, and then continuing the second half of the 1 st time, starting from the low temperature and ending in the high-temperature variable-temperature alternating aging process: firstly, continuously heating and preserving heat at critical aging intermediate temperature when the austenitic stainless steel is rapidly heated from the critical aging minimum temperature to the aging intermediate temperature in a heating furnace within the specified time, and then continuously heating and preserving heat at critical aging maximum temperature when the austenitic stainless steel is rapidly heated from the critical aging intermediate temperature to the critical aging maximum temperature in the heating furnace within the specified time; after the 1 st critical starting from the high-temperature-changing alternating aging process is ended, then the 2 nd, 3 rd or 4 th critical temperature-changing alternating aging process is carried out again: sequentially and reversely repeating the second half critical starting from low temperature to high temperature for 1 time, the critical temperature varying and alternating aging for 3 times, sequentially and reversely repeating the critical temperature varying and alternating aging for 2 times, the critical temperature varying and alternating aging for 4 times, and sequentially and reversely repeating the critical temperature varying and alternating aging for 3 times for 1 time;

after the 2 nd, 3 rd or 4 th critical temperature starting from the high-temperature multiple temperature-changing alternating aging process is completely finished, finally, cooling is carried out when the austenitic stainless steel is rapidly cooled to the critical annealing temperature by adopting a specific cooling mode;

after the first half part is critical and begins to be subjected to high-temperature multiple variable-temperature alternating aging heat treatment, the second half part critical annealing heat treatment is finally carried out, and the method comprises the following steps: the method comprises the steps of critical heating and heat preservation of austenitic stainless steel at a critical annealing temperature in a heating furnace within a set time, and cooling of austenitic stainless steel by rapid cooling in a specific cooling mode.

2. The method of claim 1, wherein the total aging time from the high temperature critical multiple temperature swing alternate aging heat treatment is 1, and each temperature swing alternate aging process comprises at least 1 heating and 1 cooling simultaneously.

3. The method for critical solution treatment and high-temperature multiple temperature-varying alternating aging and annealing heat treatment according to claim 1, wherein the temperature range of critical multiple temperature-reducing temperature-varying alternating aging is as follows: the 1 st critical temperature reduction, temperature change, alternating aging temperature interval: n staged temperature reduction and heating temperature intervals which are started from a temperature reduction and aging highest heating temperature interval Tacmax-1, sequentially pass through n-2 aging intermediate heating temperature intervals Tacm-1 and finally end to a time effect lowest heating temperature interval Tacmin-1, wherein n is more than or equal to 3 and less than or equal to 7;

critical temperature reduction, temperature variation and alternating aging temperature intervals of 2 nd time, 3 rd time or 4 th time: the cooling aging process is sequentially repeated, and the relation of the numerical values of the critical cooling temperature variation alternating aging lowest temperature interval of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmin-1 > Tacmin-2 > Tacmin-3 > Tacmin-4;

the relation of the numerical values of the intermediate heating temperature intervals of the critical temperature reduction, temperature variation, alternation and aging at the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacm-1 is more than Tacm-2 is more than Tacm-3 is more than Tacm-4;

the relation of the numerical values of the critical temperature reduction, temperature change, alternating aging highest temperature intervals of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmax-1 is more than Tacmax-2 is more than Tacmax-3 is more than Tacmax-4;

any one of a cooling aging minimum heating temperature range, a cooling aging middle heating temperature range and a cooling aging maximum temperature range is not repeatedly generated in a critical multi-time cooling variable temperature alternating aging temperature range, and any one of a heating aging minimum heating temperature range, a heating aging middle heating temperature range and a heating aging maximum temperature range is not repeatedly generated.

4. The method for critical solution treatment and high-temperature multiple temperature-varying alternating aging and annealing heat treatment according to claim 1, wherein the temperature range of critical multiple temperature-increasing temperature-varying alternating aging is as follows: the 1 st critical temperature rise and temperature change alternating aging temperature interval: starting from a heating and aging minimum heating temperature interval Tacmin-1, sequentially passing through n-2 aging intermediate heating temperature intervals Tacm-1, and finally ending n staged heating and heating temperature intervals of a time-effect maximum heating temperature interval Tacmax-1, wherein n is more than or equal to 3 and less than or equal to 7;

critical temperature rise, temperature change, alternating aging temperature interval for the 2 nd time, the 3 rd time or the 4 th time: the temperature-rise aging process is sequentially repeated, and the relation of the numerical values of the critical temperature-rise temperature-change alternating aging lowest temperature interval of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmin-1 > Tacmin-2 > Tacmin-3 > Tacmin-4;

the relation of the numerical values of the intermediate heating temperature intervals of the critical heating aging of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacm-1 is more than Tacm-2 is more than Tacm-3 is more than Tacm-4;

the relation of the numerical values of the critical temperature-raising, temperature-changing, alternating aging highest temperature intervals of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmax-1 is more than Tacmax-2 is more than Tacmax-3 is more than Tacmax-4;

the critical multiple temperature rise and temperature change alternating aging temperature range does not repeatedly generate any temperature rise aging minimum heating temperature range, temperature rise aging middle heating temperature range and temperature rise aging maximum temperature range, and any temperature fall aging minimum heating temperature range, temperature fall aging middle heating temperature range and temperature fall aging maximum temperature range.

5. The method for critical solution treatment and multiple variable temperature alternating aging and annealing heat treatment from high temperature according to claim 1, wherein the mathematical relationship between the maximum heating temperature Tacmax of the critical multiple variable temperature alternating aging and the maximum theoretical heating temperature Tactmax of the aging is as follows:

Tacmax＝Tactmax–(20～30)℃

wherein Tacmax is the highest heating temperature of high-temperature multiple-time variable-temperature alternating aging, and the unit is; tactmax is the maximum theoretical heating temperature for aging, in degrees C.

6. The method for critical solution treatment and high-temperature multiple variable-temperature alternating aging and annealing heat treatment according to claim 1, wherein the mathematical relationship between the minimum heating temperature Tacmin for critical high-temperature multiple variable-temperature alternating aging and the minimum theoretical heating temperature Tactmin for aging is as follows:

Tacmin＝Tactmin+(20～30)℃

wherein Tacmin is the minimum heating temperature of high-temperature multiple-time temperature change alternating aging at the critical point, and the unit is; tactmin is the lowest theoretical heating temperature for aging, and the unit is ℃.

7. The method for critical solution treatment and multiple temperature-varying alternating aging and annealing heat treatment from high temperature according to claim 1, wherein the mathematical relationship between the intermediate heating temperature Tacm, the aging minimum temperature Tacmin and the aging maximum heating temperature Tacmax in each stage of the critical multiple temperature-varying alternating aging is as follows:

Tacm＝Tacmin+n_i(Tacmax–Tacmin)/(n–1)

wherein Tacm is the intermediate heating temperature of each stage of high-temperature multiple variable-temperature alternating aging, and the unit is; tacmin is the minimum temperature of critical temperature reduction or temperature rise and temperature change alternating aging, and the unit is; n is_iThe specific nth heating temperature interval from high to low or from low to high for the 2 nd to the 2 nd last phases_iNumber of stages, n being not less than 1_iLess than or equal to 5; tacmax is the critical cooling or temperature-raising variable-temperature alternating-aging maximum heating temperature, and the unit is; (Tacmax-Tacmin)/n is a specific numerical value with the unit of constant temperature, wherein the unit is critical temperature reduction or temperature rise descending or temperature rise ascending step difference; n is the total number of stages starting from a critical temperature reduction, temperature change, alternating ageing highest heating temperature Tacmax interval and ending at a critical temperature reduction, temperature change, alternating ageing lowest heating temperature Tacmin or starting from a critical temperature rise, temperature change, alternating ageing lowest temperature Tacmin and ending at a critical temperature rise, temperature change, alternating ageing highest heating temperature Tacmax interval, and n is more than or equal to 3 and less than or equal to 7.

8. The method for critical solid solution and multiple variable temperature alternating aging and annealing heat treatment from high temperature according to claim 1, wherein the mathematical relations between the working heating temperature Tacw of the high temperature multiple variable temperature alternating aging and the working temperature Tw of the workpiece, the minimum heating temperature Tacmin of the high temperature multiple variable temperature alternating aging and the maximum heating temperature Tacmax of the high temperature multiple variable temperature alternating aging are as follows: tacmin is less than Tw + (60-100) DEG C and less than Tacw and less than Tacmax;

wherein, Tacw is the critical temperature starting from the high-temperature multiple-time variable-temperature alternating aging working heating temperature, and the unit is that Tacw at least appears once in each critical middle aging heating temperature Tacm interval; tw is the work piece use temperature, and the unit is; tacmin is the minimum heating temperature of high-temperature multiple variable-temperature alternating aging, and the unit is; tacmax is the highest heating temperature of high-temperature multiple temperature-changing alternating aging, and the unit is ℃.

9. The method of claim 1, wherein the first half of the total time τ of Critical solution and multiple temperature ramp and Alternating aging at high temperature and multiple temperature ramp and annealing is_acNAnd the total time tau of theoretical aging_aNtThe mathematical relationship of (a) is: tau is_acN＝(1/2～1/3)τ_aNt；

Wherein, tau_acNThe total time of high-temperature multiple temperature-changing alternating aging is critical, and is min or h; tau is_aNtThe theoretical total aging time is min or h.

10. The method of critical solution and multiple temperature swing alternate aging and annealing heat treatment from high temperature as claimed in claim 1, wherein the total number of second half critical annealing heat treatments is 1.

Technical Field

The invention relates to the technical field of material heat treatment, in particular to a method for critical solid solution and high-temperature multiple-time variable-temperature alternating aging and annealing heat treatment.

Background

The heat treatment principle of austenitic stainless steel is quite different from that of alloy structural steel: the alloy structural steel can generate high-temperature austenite structure transformation (good heat treatment manufacturability) under the high-temperature condition, so that the alloy structural steel is very easy to greatly improve the hardness (or mechanical property) by quenching and tempering heat treatment methods; however, austenitic stainless steel cannot generate high-temperature austenitic structure transformation (only limited dissolution and precipitation of alloy element strengthening phases, and poor heat treatment manufacturability) under high-temperature conditions, so that the austenitic stainless steel is extremely difficult to greatly improve the hardness (or mechanical property) through heat treatment methods such as solid solution, aging, annealing and the like.

The meaning of solution heat treatment is: the heat treatment process comprises the following steps of heating austenitic stainless steel to a certain temperature, keeping the temperature, fully dissolving excess phases, and then rapidly cooling to obtain a supersaturated solid solution, wherein the heat treatment process mainly has the main functions of obtaining a supersaturated strengthened solid solution, preparing a structure for precipitation hardening treatment, eliminating stress and carrying out work hardening between forming procedures; the meaning of the aging heat treatment is: after the austenitic stainless steel is subjected to solution treatment, keeping at room temperature or a temperature higher than room temperature to form a solute atom segregation area in a supersaturated solid solution and/or separate out a second phase particle, a dispersed and distributed excess phase and separate out the second phase particle, wherein the main effect is to precipitate and harden the austenitic stainless steel; the meaning of the annealing heat treatment is: the heat treatment process comprises the steps of heating the austenitic stainless steel to a proper temperature before, during or after the solid solution or aging treatment process of the austenitic stainless steel, keeping the temperature at a certain temperature, and then slowly cooling, wherein the heat treatment process mainly has the function of removing residual cold and hot processing stress of the austenitic stainless steel.

The austenitic stainless steel has a main strengthening phase of carbide of alloying elements and a weakening phase of intermetallic compounds (such as Fe)₂W、Fe₂Mo, CuO, FeS, FeO, MnS, etc.); due to solid solution and agingEven if the annealing heat treatment method is different, the types, the number, the size, the shape, the distribution, the melting point, the brittleness, the hardness and the like of the strengthening phase and the weakening phase of the same material are different, and the more the austenitic stainless steel alloy elements are, the larger the difference is.

The carbide formed by nickel, chromium, tungsten, molybdenum, vanadium, titanium, aluminum, niobium and other alloy elements has the relative stability in austenitic stainless steel from high to low in the sequence: hf > Zr > Ti > Ta > Nb > V > W > Mo > Cr > Mn > Fe > Co > Ni, so that dissolution of the above-mentioned alloy elements in austenitic stainless steel results in limited dissolution (Fe, Cr)₃C、(Fe，Cr)₇C₃、(W，Mo)₆C and (Fe, Cr, Ni, Mn, W, Mo)₂₃C₆Isoalloyed cementite and fully miscible Mn₃C、Fe₃C、(Fe，Mn)₃C、VC、Ta、NbC、(V，Ta，Nb)C、Mo₂C、W₂C、Fe₃W₃C、Fe₃Mo₃C、Fe₃(W，Mo)₃C, and the like; when the solid solution temperature is more than or equal to 1000 ℃ and more than or equal to 1050 ℃, most carbide phases are respectively basically dissolved and completely dissolved (the aging process is correspondingly influenced); because the solution heating temperature of the existing traditional mainstream austenitic stainless steel is the highest theoretical solution temperature, the unfavorable critical temperature intervals of 700 ℃ -815 ℃ (sensitized intercrystalline corrosion critical temperature region), 940 ℃ (FeS-FeO eutectic melting point and dissolution genetic critical temperature region), 985 ℃ (Fe-FeS eutectic melting point and dissolution genetic critical temperature region), 1083 ℃ (weakened phase copper alloy dissolution critical temperature region), 1164 ℃ (FeS-MnS eutectic melting point and dissolution genetic critical temperature region) and the like can not be quickly avoided, so that the solid solution capacity, range, quality, efficiency and the like of the carbide strengthened phase can not be effectively improved. In fact, the austenitic stainless steel solid solution temperature is not a simple and unchangeable single-point temperature value, but a complex and changeable multi-point temperature range; the existing traditional mainstream solution heat treatment method has the advantages that: the solid solution capability, the range, the quality, the efficiency and the like of one or a few alloy elements in the austenitic stainless steel can be effectively improved; the existing traditional mainstream solution heat treatment method has the following defects: cannot effectively improve the solid solution of most alloy element strengthening phasesThe capacity, range, quality and efficiency, etc. are very small (when the time reaches a certain level, the solid solution capacity, range, quality and efficiency, etc. of one or a few alloying element solid solution strengthening phases reach a limit saturation state), and the alloying element strengthening phases can only reach the limit solid solution capacity, range, quality and efficiency, etc. Therefore, the existing traditional mainstream austenitic stainless steel solution heat treatment method is a one-stage single-point fixed limited solution heat treatment method under the condition that the heating temperature and the heating time are the only conditions, and is a heat treatment method which is considered as a whole under the condition of being not on the whole under the approximate condition.

The aging heat treatment temperature of the austenitic stainless steel is different due to different use requirements such as anti-rust corrosion capability, high-temperature strength, hardness, mechanical property and the like: if the temperature is lower than 500 ℃, the trace amount of needle-shaped carbide with larger grain size is mainly precipitated, and if the temperature is between 550 and 740 ℃, the carbide (Fe, Cr, Ni, Mn, W, Mo) is mainly precipitated₂₃C₆Carbide of the same composite alloy is mainly precipitated (Fe, Cr, Ni, Mn, W, Mo) at 625-670 deg.C₂₃C₆The carbide of the compound alloy is uniformly distributed in the crystal, the carbide begins to grow sharply at the temperature of about 700 ℃, and is mainly precipitated at the temperature of about 800 ℃ (Fe, Cr, Ni, Mn, W, Mo)₇C₆When the temperature of the composite alloy carbide is about 880 ℃, a small amount of (Fe, Cr, Ni, Mn, W, Mo) C composite alloy carbide is mainly precipitated, and when the temperature is higher than 900 ℃, the precipitation amount of the precipitated lamellar carbide is increased to influence the metal hardness and the mechanical property; because the aging heating temperature of the traditional mainstream austenitic stainless steel is the highest aging theoretical temperature, the capability, range, quality, efficiency and the like of precipitating carbide strengthening phases by aging cannot be effectively improved. In fact, the aging temperature of austenitic stainless steel is not a simple and unchangeable single-point temperature value, but a complex and changeable multi-point temperature range; the existing traditional mainstream aging heat treatment method has the advantages that: the aging precipitation capacity, range, quality, efficiency and the like of one or a few alloy element strengthening phases in the austenitic stainless steel can be effectively improved; the prior aging heat treatment method has the following defects: can not effectively improve the strength of most alloy elementsThe aging precipitation capacity, range, quality and efficiency of the chemical phases are very little even if the aging time is increased (after the time reaches a certain degree, the aging capacity, range, quality and efficiency and the like of the one or a few alloy element strengthening phases reach a limit saturation state), and the alloy element strengthening phases can only reach the limited aging precipitation capacity, range, quality and efficiency and the like. Therefore, the existing traditional mainstream austenitic stainless steel aging heat treatment method is a one-stage single-point fixed limited aging heat treatment method under the condition that the heating temperature and the heating time are the only conditions, and is a heat treatment method which is considered as a whole under the condition of being not in a comprehensive mode.

The existing traditional mainstream austenitic stainless steel annealing heat treatment methods are divided into a high-temperature annealing method, a medium-temperature annealing method and a low-temperature annealing method. The existing high-temperature annealing method has the advantages that: the effect of removing the residual cold and hot processing stress is good; the existing high-temperature annealing method has the following defects: the austenitic stainless steel has large deformation amount, long heating time, newly generated negative effects of solid solution and aging (particularly influencing the type, the number, the size, the shape, the distribution, the melting point, the brittleness, the hardness and the like of strengthening phases after the solid solution of the austenitic stainless steel), and the difficult problems that an independent process is required to be arranged and the process is not suitable as a final process (only suitable as an intermediate process before the aging after the solid solution, or suitable as a process without the solid solution and aging heat treatment), and the like; the prior moderate temperature annealing method has the advantages that: the effect of removing the residual cold and hot processing stress is good; the existing moderate temperature annealing method has the following defects: the austenitic stainless steel has large deformation amount, long heating time, newly generated aging negative effects (particularly influencing the strengthening phase types, the number, the size, the shape, the distribution, the melting point, the brittleness, the hardness and the like after the solid solution and the aging of the austenitic stainless steel) and the problems that an independent process is required to be arranged and is not suitable to be used as a final process (only suitable to be used as an intermediate process before the aging after the solid solution and suitable to be used as an independent process without the solid solution and the aging heat treatment) and the like cannot be solved; the existing low-temperature annealing method has the advantages that: the austenitic stainless steel has extremely small deformation amount, does not newly generate the negative effects of solid solution or aging (particularly does not influence the type, the quantity, the size, the shape, the distribution, the melting point, the brittleness, the hardness and the like of strengthening phases after the solid solution and the aging of the austenitic stainless steel) and is also suitable for any intermediate process and final process; the existing low-temperature annealing method has the following defects: the effect of removing the residual cold and hot processing stress is not as good as that of a high-temperature annealing method and a medium-temperature annealing method, and the problems of independent working procedures, long heating time and the like cannot be solved.

Although austenitic stainless steel belongs to the stainless steel material series, the phenomenon of 'discoloring and rusting a metal surface' is generated to different degrees by 'bright silvery white metal surface' after machining and staying for a certain time, and the main reasons for the generation are considered to be from the conventional mainstream known viewpoints: the chemical components of austenitic stainless steel do not meet the standard of procurement materials; secondly, the content of Cr, Ni, W and other anti-corrosion metals in the austenitic stainless steel is relatively low or the content of C, P, As, Sb, Bi and other metal elements which are easy to discolor and corrode is relatively high; thirdly, the surface of the austenitic stainless steel is discolored or corroded (generally referred to as corrosion) due to chemical reaction or electrochemical reaction between metal on the surface of the austenitic stainless steel and substances such as oxygen, water, acid, alkali, salt and the like in the atmosphere, wherein the original steel surface is a layer of firm, fine and extremely thin silver white light bright chromium-rich oxide film substance which is destroyed to form loose heterogeneous substances; fourthly, the surface roughness of the austenitic stainless steel is caused; fifthly, the austenitic stainless steel part is caused by working at the temperature of 300-800 ℃. In fact, besides the discolored rusting of austenitic stainless steels, it is also involved in a cause that is not yet recognized to be very important: the method is caused by the improper hot working methods of smelting, steel rolling, forging, heat treatment and the like of the austenitic stainless steel in steel mills and manufacturing plants, particularly the comprehensive action of a plurality of hot working complex factors such as material, chemical components, furnace batch, hot working temperature, time, cooling medium and the like to generate more alloy carbides and non-carbides which are easy to discolor and rust, and the like, and the method is one of the most fundamental reasons which directly influence the final effect of the heat treatment of the austenitic stainless steel.

Based on the comprehensive influence of a plurality of complex factors, the existing austenitic stainless steel heat treatment technology is difficult to solve the following special heat treatment technical problems of 'one long, one high, four different and five low':

firstly, the heat treatment quality stability is poor, the qualified product rate is low: when the heat treatment quality stability is good, the primary heat treatment qualified product rate can only reach 99 percent (especially, the hardness value and the mechanical property can only reach the lower limit value even if the primary heat treatment qualified product rate is qualified); when the heat treatment quality stability is poor, the primary heat treatment yield is highly likely to fail by 100%.

Secondly, the hardness (or mechanical property) of the heat treatment is low and the consistency is poor: the solid solution and aging heat treatment can reach the medium and low hardness value of 20.0-26.5 HRC, the medium and high hardness value of 27.0-28.0 HRC, the high hardness value of 28.5-32.0 HRC, and even the paradoxical phenomenon of qualified Brinell hardness and unqualified Rockwell hardness.

Thirdly, the tarnish resistance is poor: the austenitic stainless steel has strong sensitivity and high speed for changing 'bright silvery white' into 'color change rust' after the metal surface is machined and stays for a certain time.

Fourthly, the heating time of the heat treatment is long, and the efficiency is low: the heating time under the highest temperature conditions of solid solution and aging is long, and the requirement of quick batch production is difficult to realize; in order to remove residual cold and hot processing stress generated before, during and after the solid solution and aging process, an independent annealing process with longer heating time is required; in order to solve the problems of unqualified solid solution and aging heat treatment, rework and repair are forced to be carried out.

Fifthly, the heating reliability of the heat treatment equipment is poor: the existing box-type resistance furnace equipment has poor heating reliability (only has the functions of conduction and radiation heat transfer), and is far inferior to equipment such as a fluidized bed furnace, a salt bath furnace, a vacuum furnace and the like (simultaneously has the functions of conduction, radiation and convection heat transfer) in heating reliability.

Sixthly, the service life of the high-temperature component of the heat treatment equipment is short: the service life of the high-temperature components of the equipment is low due to large high-temperature load and long retention time under the conditions of highest temperature of solid solution and aging.

Seventhly, the heat treatment cost is high: the combination of the above disadvantages ultimately results in high heat treatment costs.

In summary, the conventional mainstream austenitic stainless steel heat treatment methods cannot solve the special heat treatment technical problems of poor heat treatment quality stability, low qualified product rate, low hardness (or low mechanical property) and poor consistency, poor anti-tarnishing resistance, long heating time, low efficiency, poor heating reliability of heat treatment equipment, low service life of high-temperature components and parts, high cost and the like of the austenitic stainless steel.

Disclosure of Invention

The invention aims to solve the technical problem of providing a heat treatment method of critical solid solution and high-temperature multiple-time variable-temperature alternating aging and annealing. Solves the special heat treatment technical problems of poor quality stability, low qualified product rate, low hardness, low mechanical property, poor consistency, poor anti-tarnishing capability, long heating time, low efficiency, poor heating reliability of heat treatment equipment, low service life of high-temperature components, high cost and the like in the prior heat treatment of austenitic stainless steel.

In order to solve the technical problems, the technical scheme of the invention is as follows:

a critical solution and high-temperature multiple variable-temperature alternating aging and annealing heat treatment method comprises the following steps:

a critical solution heat treatment process, the critical solution heat treatment process comprising: firstly, carrying out pre-solid solution critical preheating heating and heat preservation when the austenitic stainless steel is heated to the preheating temperature from room temperature at a medium speed in a heating furnace within a set time, then continuously carrying out pre-solid solution critical stabilizing heating and heat preservation when the austenitic stainless steel is heated to the stabilizing temperature, then continuously carrying out critical solid solution minimum temperature heating and heat preservation when the austenitic stainless steel is heated to the solid solution minimum temperature, then continuously carrying out critical solid solution maximum temperature heating and heat preservation when the austenitic stainless steel is heated to the solid solution maximum temperature, and finally continuously carrying out solid solution cooling when the austenitic stainless steel is cooled to the room temperature by adopting a specific cooling mode;

after the critical solution heat treatment is finished, the first half part of the temperature-changing alternating aging heat treatment which starts from high temperature for multiple times is continuously carried out, and the method comprises the following steps: the 1 st critical process is started in the high-temperature variable-temperature alternating aging process: the method specifically comprises the following steps that 1, the first half part of the critical process is started at high temperature and ended at low temperature without variable temperature alternating aging: firstly heating and preserving the austenite stainless steel at the critical aging highest temperature when the temperature of the austenite stainless steel is raised to the aging highest temperature from room temperature at a medium speed in a heating furnace within a specified time, then continuing heating and preserving the austenite stainless steel at the critical aging intermediate temperature when the temperature of the austenite stainless steel is rapidly lowered to the aging intermediate temperature, then continuing heating and preserving the austenite stainless steel at the critical aging lowest temperature when the temperature of the austenite stainless steel is rapidly lowered to the final aging lowest temperature, and then continuing the second half of the 1 st time, starting from the low temperature and ending in the high-temperature variable-temperature alternating aging process: firstly, continuously heating and preserving heat at critical aging intermediate temperature when the austenitic stainless steel is rapidly heated from the critical aging minimum temperature to the aging intermediate temperature in a heating furnace within the specified time, and then continuously heating and preserving heat at critical aging maximum temperature when the austenitic stainless steel is rapidly heated from the critical aging intermediate temperature to the critical aging maximum temperature in the heating furnace within the specified time; after the 1 st critical starting from the high-temperature-changing alternating aging process is ended, then the 2 nd, 3 rd or 4 th critical temperature-changing alternating aging process is carried out again: sequentially and reversely repeating the second half critical starting from low temperature to high temperature for 1 time, the critical temperature varying and alternating aging for 3 times, sequentially and reversely repeating the critical temperature varying and alternating aging for 2 times, the critical temperature varying and alternating aging for 4 times, and sequentially and reversely repeating the critical temperature varying and alternating aging for 3 times for 1 time;

after the 2 nd, 3 rd or 4 th critical temperature starting from the high-temperature multiple temperature-changing alternating aging process is completely finished, finally, cooling is carried out when the austenitic stainless steel is rapidly cooled to the critical annealing temperature by adopting a specific cooling mode;

after the first half part is critical and begins to be subjected to high-temperature multiple variable-temperature alternating aging heat treatment, the second half part critical annealing heat treatment is finally carried out, and the method comprises the following steps: the method comprises the steps of critical heating and heat preservation of austenitic stainless steel at a critical annealing temperature in a heating furnace within a set time, and cooling of austenitic stainless steel by rapid cooling in a specific cooling mode.

Optionally, the total aging time of the high-temperature critical multiple temperature-varying alternating aging heat treatment is 1 time, and each temperature-varying alternating aging process simultaneously comprises at least 1 time of temperature rise and 1 time of temperature drop.

Optionally, the critical multiple temperature reduction, temperature variation, alternating aging temperature interval means: the 1 st critical temperature reduction, temperature change, alternating aging temperature interval: n staged temperature reduction and heating temperature intervals which are started from a temperature reduction and aging highest heating temperature interval Tacmax-1, sequentially pass through n-2 aging intermediate heating temperature intervals Tacm-1 and finally end to a time effect lowest heating temperature interval Tacmin-1, wherein n is more than or equal to 3 and less than or equal to 7;

critical temperature reduction, temperature variation and alternating aging temperature intervals of 2 nd time, 3 rd time or 4 th time: the cooling aging process is sequentially repeated, and the relation of the numerical values of the critical cooling temperature variation alternating aging lowest temperature interval of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmin-1 > Tacmin-2 > Tacmin-3 > Tacmin-4;

the relation of the numerical values of the intermediate heating temperature intervals of the critical temperature reduction, temperature variation, alternation and aging at the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacm-1 is more than Tacm-2 is more than Tacm-3 is more than Tacm-4;

the relation of the numerical values of the critical temperature reduction, temperature change, alternating aging highest temperature intervals of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmax-1 is more than Tacmax-2 is more than Tacmax-3 is more than Tacmax-4;

any one of a cooling aging minimum heating temperature range, a cooling aging middle heating temperature range and a cooling aging maximum temperature range is not repeatedly generated in a critical multi-time cooling variable temperature alternating aging temperature range, and any one of a heating aging minimum heating temperature range, a heating aging middle heating temperature range and a heating aging maximum temperature range is not repeatedly generated.

Optionally, the critical multiple temperature rise and temperature change alternating aging temperature interval means: the 1 st critical temperature rise and temperature change alternating aging temperature interval: starting from a heating and aging minimum heating temperature interval Tacmin-1, sequentially passing through n-2 aging intermediate heating temperature intervals Tacm-1, and finally ending n staged heating and heating temperature intervals of a time-effect maximum heating temperature interval Tacmax-1, wherein n is more than or equal to 3 and less than or equal to 7;

critical temperature rise, temperature change, alternating aging temperature interval for the 2 nd time, the 3 rd time or the 4 th time: the temperature-rise aging process is sequentially repeated, and the relation of the numerical values of the critical temperature-rise temperature-change alternating aging lowest temperature interval of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmin-1 > Tacmin-2 > Tacmin-3 > Tacmin-4;

the relation of the numerical values of the intermediate heating temperature intervals of the critical heating aging of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacm-1 is more than Tacm-2 is more than Tacm-3 is more than Tacm-4;

the relation of the numerical values of the critical temperature-raising, temperature-changing, alternating aging highest temperature intervals of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmax-1 is more than Tacmax-2 is more than Tacmax-3 is more than Tacmax-4;

the critical multiple temperature rise and temperature change alternating aging temperature range does not repeatedly generate any temperature rise aging minimum heating temperature range, temperature rise aging middle heating temperature range and temperature rise aging maximum temperature range, and any temperature fall aging minimum heating temperature range, temperature fall aging middle heating temperature range and temperature fall aging maximum temperature range.

Optionally, the mathematical relation between the maximum heating temperature Tacmax of the high-temperature multiple-temperature-change alternating aging and the maximum theoretical heating temperature Tactmax of the aging is as follows: tacmax is Tactmax- (20-30) DEG C;

wherein Tacmax is the highest heating temperature of high-temperature multiple-time variable-temperature alternating aging, and the unit is; tactmax is the maximum theoretical heating temperature for aging, in degrees C.

Optionally, the mathematical relation between the minimum heating temperature Tacmin of high-temperature multiple-temperature-change alternating aging and the minimum theoretical heating temperature Tactmin of aging is as follows: tacmin + (20-30) DEG C;

wherein Tacmin is the minimum heating temperature of high-temperature multiple-time temperature change alternating aging at the critical point, and the unit is; tactmin is the lowest theoretical heating temperature for aging, and the unit is ℃.

Optionally, the mathematical relation between the intermediate heating temperature Tacm, the aging minimum temperature Tacmin and the aging maximum heating temperature Tacmax in each stage of the critical multiple temperature-changing alternating aging is as follows:

Tacm＝Tacmin+n_i(Tacmax–Tacmin)/(n–1)

wherein Tacm is the intermediate heating temperature of each stage of high-temperature multiple variable-temperature alternating aging, and the unit is; tacmin is the minimum temperature of critical temperature reduction or temperature rise and temperature change alternating aging, and the unit is; n is_iThe specific nth heating temperature interval from high to low or from low to high for the 2 nd to the 2 nd last phases_iNumber of stages, n being not less than 1_iLess than or equal to 5; tacmax is the critical cooling or temperature-raising variable-temperature alternating-aging maximum heating temperature, and the unit is; (Tacmax-Tacmin)/n is a specific numerical value with the unit of constant temperature, wherein the unit is critical temperature reduction or temperature rise descending or temperature rise ascending step difference; n is the total number of stages starting from a critical temperature reduction, temperature change, alternating ageing highest heating temperature Tacmax interval and ending at a critical temperature reduction, temperature change, alternating ageing lowest heating temperature Tacmin or starting from a critical temperature rise, temperature change, alternating ageing lowest temperature Tacmin and ending at a critical temperature rise, temperature change, alternating ageing highest heating temperature Tacmax interval, and n is more than or equal to 3 and less than or equal to 7.

Optionally, the mathematical relation between the critical operating heating temperature Tacw starting from the high-temperature multiple-time variable-temperature alternating aging and the workpiece use temperature Tw, the critical minimum heating temperature Tacmin starting from the high-temperature multiple-temperature variable-temperature alternating aging and the critical maximum heating temperature Tacmax starting from the high-temperature multiple-temperature variable-temperature alternating aging is as follows: tacmin is less than Tw + (60-100) DEG C and less than Tacw and less than Tacmax;

wherein, Tacw is the critical temperature starting from the high-temperature multiple-time variable-temperature alternating aging working heating temperature, and the unit is that Tacw at least appears once in each critical middle aging heating temperature Tacm interval; tw is the work piece use temperature, and the unit is; tacmin is the minimum heating temperature of high-temperature multiple variable-temperature alternating aging, and the unit is; tacmax is the highest heating temperature of high-temperature multiple temperature-changing alternating aging, and the unit is ℃.

Optionally, the first half part of the aging time tau is critical and begins from high temperature multiple temperature change and alternation_acNAnd the total time tau of theoretical aging_aNtThe mathematical relationship of (a) is: tau is_acN＝(1/2～1/3)τ_aNt；

Wherein, tau_acNThe total time of high-temperature multiple temperature-changing alternating aging is critical, and is min or h; tau is_aNtThe theoretical total aging time is min or h.

Alternatively, the number of the second half critical annealing heat treatments is 1.

The scheme of the invention at least comprises the following beneficial effects:

(1) the method for high-temperature multiple variable-temperature alternating aging and annealing heat treatment of the invention has the advantages of technical feasibility, process adaptability, quality reliability, economic rationality and use safety, effectively takes advantage of and avoids the advantages and disadvantages of the traditional mainstream austenitic stainless steel heat treatment method, and fundamentally solves the problems of the existing austenitic stainless steel, such as poor heat treatment quality stability, low qualified product rate, low hardness (or low mechanical property) and consistency, poor tarnish resistance capability, long heating time, low efficiency, poor heating reliability of heat treatment equipment, low service life of high-temperature components, high cost and the like.

(2) The method for the high-temperature multiple-temperature-change alternating aging and annealing heat treatment of the invention has the advantages of good heat treatment manufacturability, effective increase of solid solution and aging strengthening phases, reduction or inhibition of solid solution and aging weakening phases, reduction of residual cold and hot processing stress and deformation, and capability of meeting the service performance requirements of austenitic stainless steel.

(3) The method for the critical solid solution and critical temperature-changing alternating aging and annealing heat treatment of the invention starts from high temperature multiple times, has good quality stability and high reliability, can accurately, effectively and quickly obtain the optimized heat treatment hardness (or mechanical property) with the distribution range of the middle limit or the upper limit and the tolerance less than or equal to 2.5HRC, and the qualified product rate of the one-time heat treatment hardness (or mechanical property) reaches 100 percent.

(4) The method for the critical solid solution and critical temperature-variable alternating aging and annealing heat treatment of the invention starts from high temperature for multiple times, and can effectively improve the surface tarnish resistance of the austenitic stainless steel after machining.

(5) The method for the critical solid solution and critical temperature-changing alternating aging and annealing heat treatment of the invention starts from high temperature for multiple times, and can effectively improve the heat treatment efficiency (especially can be used for full-load furnace charging and rapid production, and can reduce the total time of solid solution, aging and annealing heat treatment by at least 40 percent, etc.).

(6) The critical solid solution and critical temperature start from a high-temperature multiple-temperature-change alternating aging and annealing heat treatment method can effectively prolong the service life of high-temperature components of heating equipment.

(7) The method for the heat treatment of the austenitic stainless steel by the alternating aging and annealing at the critical solid solution and critical temperature for multiple times can effectively reduce the heat treatment cost of the austenitic stainless steel.

Drawings

FIG. 1 is a schematic diagram of the prior austenitic stainless steel showing the solution, aging and annealing heat treatment processes (including the heating, heat preservation, cooling processes, time used and the like of the solution, aging and annealing heat treatment) consisting of 1 time 1-stage solution treatment under the condition of the highest solution temperature, 1 time 1-stage aging under the condition of the highest aging temperature and 1 time 1-stage annealing under the condition of medium-temperature annealing or low-temperature annealing temperature;

FIG. 2 is a schematic flow diagram of the critical solution and critical multiple temperature swing alternate aging and annealing heat treatment process of the present invention;

FIG. 3 is a schematic diagram of the austenitic stainless steel consisting of 1 time of 4-stage critical solution treatment under the condition of critical solution temperature by a decreasing time method, 2 times of 3 times of each critical solution treatment under the condition of critical aging temperature by an equal time method (wherein, the 1 st time of 3-stage cooling is not alternated, the 2 nd time of 3-stage heating is alternated, and the 3 rd time of 3-stage cooling is alternated), critical solution treatment starting from high temperature multiple variable temperature alternating aging, and critical solution treatment and annealing heat treatment process (including the heating, heat preservation, cooling processes and the used time of critical solution treatment, critical aging and critical annealing heat treatment) which are carried out 1 time of 1-stage critical annealing under the condition of critical low temperature annealing temperature.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

As shown in fig. 2, an embodiment of the present invention provides a method for critical solution and multiple temperature-varying alternating aging and annealing heat treatment starting at high temperature, comprising: step 21, critical solution heat treatment process; and step 22, the critical process starts from the high-temperature multiple temperature-changing alternating aging and annealing heat treatment process.

The method comprises the following steps: firstly, carrying out a first part of critical solution heat treatment, and finally, continuously carrying out a second part of critical composite heat treatment of high-temperature multiple variable-temperature alternating aging and critical annealing.

The first part of the critical solution heat treatment process: the critical solution heat treatment process comprises the steps of critical solution heat treatment process comprising critical preheating heating and heat preservation before solid solution when the temperature of austenitic stainless steel is raised from room temperature to the preheating temperature at a medium speed in a heating furnace within a specified time, critical stabilizing heating and heat preservation before solid solution when the temperature of austenitic stainless steel is raised to the stabilizing temperature, critical solution lowest temperature heating and heat preservation when the temperature of austenitic stainless steel is raised to the solution lowest temperature, critical solution highest temperature heating and heat preservation when the temperature of austenitic stainless steel is raised to the solution highest temperature, solid solution cooling when the temperature of austenitic stainless steel is lowered to room temperature by a specific cooling mode, and the like;

the second part of critical treatment starts from the high-temperature multiple-temperature-changing alternating aging and critical annealing composite heat treatment process: after the first part of critical solution heat treatment is finished, the second part of first half part critical temperature-variable alternating aging heat treatment which starts from high temperature to low temperature and starts from low temperature to high temperature is continued, and the 1 st critical temperature-variable alternating aging process comprises the following steps: the method specifically comprises the following steps that 1, the first half part of the critical process is started at high temperature and ended at low temperature without variable temperature alternating aging: firstly heating and preserving the austenite stainless steel at the critical aging highest temperature when the temperature of the austenite stainless steel is raised to the aging highest temperature from room temperature at a medium speed in a heating furnace within a specified time, then continuously heating and preserving the austenite stainless steel at the critical aging intermediate temperature when the temperature of the austenite stainless steel is rapidly lowered to the aging intermediate temperature, and then continuously heating and preserving the austenite stainless steel at the critical aging lowest temperature when the temperature of the austenite stainless steel is rapidly lowered to the final aging lowest temperature (the first half part of the 1 st time is critical and begins at a high temperature and ends at a low temperature and does not change the temperature and alternate the aging process), and then continuing the second half part of the 1 st time, beginning at a low temperature and ends at a high temperature and changes the temperature and: firstly, continuously heating and preserving the critical aging middle temperature when the austenitic stainless steel is rapidly heated from the critical aging lowest temperature to the aging middle temperature in a heating furnace within the specified time, and then continuously heating and preserving the critical aging highest temperature when the austenitic stainless steel is rapidly heated from the critical aging middle temperature to the critical aging highest temperature in the heating furnace within the specified time (the first half of the critical temperature starts from the low temperature and ends at the high-temperature variable-temperature alternating aging process, and the first half of the critical temperature starts at the high-temperature variable-temperature alternating aging process and also ends at all at the 1 st time); after the 1 st critical starting from the high-temperature-changing alternating aging process is ended, then the 2 nd, 3 rd or 4 th critical temperature-changing alternating aging process is carried out again: sequentially and reversely repeating the second half critical starting from low temperature to high temperature variable temperature alternating aging process for 1 time (the 2 nd critical variable temperature alternating aging process is finished) for the 2 nd time critical variable temperature alternating aging, or sequentially and reversely repeating the 2 nd critical variable temperature alternating aging process for 1 time (the 3 rd variable temperature alternating aging process is finished) for the 3 rd time critical variable temperature alternating aging process for 1 time (the 4 th critical variable temperature alternating aging process is finished); after the 2 nd, 3 rd or 4 th critical starting from the high-temperature multiple temperature-changing alternating ageing process is completely finished, finally, continuously adopting a specific cooling mode to rapidly cool the austenitic stainless steel to the critical annealing temperature, and starting from the critical starting from the high-temperature multiple temperature-changing alternating ageing heat treatment process; and finally, continuing the second half-half critical annealing heat treatment after the second half-half critical treatment is started at the high-temperature multiple-temperature-changing alternating aging heat treatment, wherein the critical annealing heat treatment process comprises the following steps: the method comprises the critical annealing heat treatment process which comprises the steps of critical heating and heat preservation of austenitic stainless steel at the critical annealing temperature in a heating furnace within a specified time, cooling of austenitic stainless steel by rapid cooling in a specific cooling mode, and the like.

In an embodiment of the present invention, the first partial critical solution heat treatment method is a 4-stage critical solution heat treatment method performed under conditions such as a 4-stage heating temperature range, a 4-stage heating sequence, a 4-stage heating time, a 4-stage heating frequency, a specific cooling method, and the like.

In an embodiment of the present invention, the total number of solid solutions of the first part of the critical solid solution heat treatment is 1.

In an embodiment of the present invention, the first part critical solid solution heating temperature interval refers to: and a 4-stage critical solid solution heating temperature interval which starts from the stage of raising the temperature from room temperature to the pre-critical solid solution preheating temperature Tsccp, continues to raise the temperature to the critical pre-solid solution stabilizing temperature Tscs, continues to raise the temperature to the critical solid solution lowest temperature Tcmin, and finally ends at the stage of raising the temperature to the critical solid solution highest temperature Tcmax.

In the invention, the number of the first part solution heating temperature interval stages is moderate: for example, the solid solubility in the 1 stage is too poor, the solid solubility in the 2 stage is good, and the solid solubility in the 6 or more stages is excessive, so in this embodiment, a 4-stage critical solid solubility heating temperature range is set in which the preheating temperature before solid solubility Tscp, the stabilization temperature before solid solubility Tscs, the minimum solid solubility temperature Tscmin, and the maximum solid solubility temperature Tscmax are different: the preheating temperature Tsccp interval before solid solution in the critical solid solution first stage is the most favorable heating temperature interval for effectively overcoming the low thermal conductivity and serious high-temperature expansion of austenitic stainless steel below 700-800 ℃ and reducing the thermal stress and deformation, and also can quickly avoid 450-5 ℃ in the temperature rise stage00 ℃ (chromium-poor precipitation critical temperature zone and large-particle-size needle-rod-shaped carbide precipitation critical temperature zone), 475 ℃ (cold brittleness critical temperature zone and large-particle-size needle-rod-shaped carbide precipitation critical temperature zone), 550 ℃ -670 ℃ (graphitization, intergranular corrosion or along crystal brittleness critical temperature zone) and other most favorable heating temperature zones; the stabilizing temperature Tscs interval before solid solution of the second stage of critical solid solution is not only used for reducing the deformation and residual stress of the workpiece and facilitating the solid solution of Cr but also used for dissolving Cr without forming Cr₂₃C₆The steel is characterized in that the steel forms a stable TiC or NbC most favorable heating and heat preservation temperature interval by the aid of the strengthening phase (the strengthening phase is not precipitated in the intergranular region and does not lean chromium in the grain boundary), and also quickly avoids 700-815 ℃ (a sensitized intercrystalline corrosion critical temperature region), 940 ℃ (a FeS-FeO eutectic melting point and a dissolution genetic critical temperature region), 985 ℃ (a Fe-FeS eutectic melting point and a dissolution genetic critical temperature region) and a most favorable heating temperature interval close to an effective solid solution minimum temperature Tcmc and the like in a temperature raising stage; the solid solution minimum temperature Tcmc interval of the critical solid solution third stage is an effective solid solution minimum temperature interval, and is also an optimum heating temperature interval which rapidly avoids 940 ℃ (FeS-FeO eutectic melting point and dissolution inheritance critical temperature zone), 985 ℃ (Fe-FeS eutectic melting point and dissolution inheritance critical temperature zone), 1083 ℃ (weakening phase copper alloy dissolution and inheritance critical temperature zone), 1164 ℃ (FeS-MnS eutectic melting point and dissolution inheritance critical temperature zone) and the like in the temperature rising stage; the solid solution highest temperature Tsccax interval of the critical solid solution fourth stage is an effective solid solution highest temperature interval, and is also an optimal heating temperature interval which rapidly avoids 1083 ℃ (a weakened phase copper alloy dissolution and heredity critical temperature area), 1164 ℃ (a FeS-MnS eutectic melting point and dissolution heredity critical temperature area), 1193 ℃ (a FeS compound melting point and a dissolution heredity critical temperature area) and the like in the temperature rising stage. The final results show that: the critical solid solution is set to be in the temperature intervals with different stages 4, so that the potential special function of solid solution can be fully excavated, the solid solution capacity, the quality, the efficiency and the like can be greatly improved, and particularly, the solid solution strengthening phase can be greatly increased, the solid solution weakening phase can be reduced or inhibited, the heating stress can be reduced, the high-temperature heating time can be reduced, the tarnish resistance can be improved, the efficiency can be improved, and the high temperature of heating equipment can be improvedThe service life of the temperature components and the like.

In the embodiment of the invention, the mathematical relation between the critical pre-solid solution preheating temperature Tsccp and the solid solution minimum theoretical heating temperature Tcmin is as follows: ttscp is Tsctmin- (330-350) DEG C;

wherein Tsscp is the preheating temperature before critical solid solution, DEG C, and is also the heating temperature of the first stage of critical solid solution; tsctmin is the critical solution minimum theoretical heating temperature, DEG C.

In the embodiment of the invention, the mathematical relation between the critical pre-solid solution stabilizing heating temperature Tscs and the solid solution minimum theoretical heating temperature Tcmin is as follows: tscs is Tsctmin- (120-150) DEG C;

wherein Tscs is the stabilizing heating temperature before critical solid solution, DEG C, and is also the heating temperature of the second stage of critical solid solution; tsctmin is the critical solution minimum theoretical heating temperature, DEG C.

In the embodiment of the invention, the mathematical relation between the critical solid solution minimum heating temperature Tcmin, the solid solution minimum theoretical heating temperature Tsctmin and the copper alloy dissolution critical temperature is as follows:

Tsctmin+(5～10)℃≤Tscmin≤1083℃–(13～15)℃

tscomin is the critical solid solution minimum heating temperature, DEG C, and is the heating temperature of the critical solid solution third stage; tsctmin is the critical solution minimum theoretical heating temperature, DEG C; 1083 ℃ is the copper alloy dissolution critical temperature, DEG C.

In the embodiment of the invention, the mathematical relation between the critical solid solution maximum heating temperature Tcmax and the solid solution maximum theoretical heating temperature Tctmax and the FeS-MnS eutectic dissolution critical temperature is as follows:

Tscmax≤Tsctmax≤1164℃–(12～14)℃

wherein Tsmax is the critical solid solution maximum heating temperature, DEG C, and is also the heating temperature of the fourth stage of the critical solid solution; tstmax is the critical maximum theoretical heating temperature of solid solution, DEG C; the temperature of 1164 ℃ is the dissolution critical temperature of the FeS-MnS eutectic, and the temperature is lower.

In the examples of the present invention, the critical solid solution is divided into 4 stages of heating time: and 4-stage heating time of critical pre-solid solution preheating, critical pre-solid solution stabilizing, critical solid solution lowest temperature and critical solid solution highest temperature corresponding to the critical 4-stage solid solution temperature.

In the embodiment of the present invention, the first part critical solution time is not too long nor too short: when the temperature is too long, the solid solution is sufficient but exceeds the solubility limit degree of the strengthening phase, the weakening phase is increased, and the high-temperature load time of the high-temperature component of the equipment is also increased; if too short, the solid solution strengthening phase is not sufficiently dissolved, and therefore, the 4-stage critical solid solution heating time is performed by a decreasing time method, i.e., preheating before solid solution, stabilizing before solid solution, sufficiently dissolving the lowest temperature, and heating at the highest temperature of solid solution are performed by τ_s1＞τ_s2＞τ_s3＞τ_s4The method can effectively and rapidly dissolve and increase the solid solution strengthening phase, reduce or inhibit the solid solution weakening phase, effectively reduce the heating stress, reduce the heating time under the highest temperature condition, improve the anti-tarnishing capacity, improve the heat treatment efficiency and prolong the service life of high-temperature components of heating equipment.

In the present invention, the critical solid solution time is carried out in accordance with a decreasing time method, the heating time τ being at each stage of the decreasing time method_scnPreheating heating time tau before solid solution_sc1And decreasing the time step difference τ_sc0The mathematical relationship of (a) is:

τ_scn＝[τ_sc1–(n–1)τ_sc0](ii) a In the formula tau_scnHeating time, min or h, tau, at each stage of the critical solid solution decreasing time method_scnIs divided into tau_sc1、τ_sc2、τ_sc3、τ_sc4，τ_sc1＞τ_sc2＞τ_sc3＞τ_sc4；τ_sc1Preheating heating time before solid solution in a critical solid solution first stage, wherein the preheating heating time is min or h; tau is_sc2Stabilizing and heating time before solid solution in a second stage of critical solid solution for min or h; tau is_sc3Heating time is the critical solid solution minimum temperature of the critical solid solution third stage, and min or h; tau is_sc4Heating time of maximum solution temperature in the fourth stage of critical solution treatment, min or h, tau_sc4Less than or equal to 5 min; n is the number of the nth stage of the critical solution heating, and n is 1, 2, 3, 4; tau is_sc0Is critical solution addingThe decreasing time step difference of heat, min or h, is the same constant specific value.

In an embodiment of the present invention, the first part critical solution heat treatment final cooling method is: cooled in room temperature water.

In an embodiment of the present invention, the first part of the critical solution heat treatment process is: the first stage is as follows: austenitic stainless steel is placed in a furnace for a process-defined time τ_sc1Heating from room temperature to the critical preheating temperature Tsccp at medium speed for critical preheating heating before solid solution and heat preservation → the second stage: then the austenitic stainless steel is continuously placed in the heating furnace for the specified time tau_sc2Rapidly raising the temperature from the critical preheating temperature Tspc to the critical stabilization temperature Tscs for critical stabilization heating and heat preservation before solid solution → the third stage: then the austenitic stainless steel is continuously placed in the heating furnace for the specified time tau_sc3Rapidly raising the temperature from the critical stabilization temperature Tscs to the critical solid solution minimum temperature Tcmin for critical solid solution minimum temperature heating and heat preservation → a fourth stage: then the austenitic stainless steel is continuously placed in the heating furnace for the specified time tau_sc4And quickly heating the austenitic stainless steel from the critical solid solution minimum temperature Tcmin to the critical solid solution maximum temperature Tcmax to perform critical solid solution maximum temperature heating and heat preservation → finally, quickly discharging the austenitic stainless steel from the critical solid solution maximum temperature Tcmax to perform quick cooling in cooling medium room temperature water (and placing the cooled austenitic stainless steel on a room temperature working site).

In an embodiment of the present invention, the second part of the critical heat treatment method starts from a high temperature multiple temperature-changing alternating aging and critical annealing composite heat treatment method: the composite heat treatment method of the high-temperature multiple alternating ageing and the critical annealing is characterized in that the critical annealing heat treatment which is performed under the conditions of a first half part of the second part, a first half part, a second half part, a third half part, a fourth half part, a fifth half part, a sixth half part, a seventh half part, a sixth.

In the embodiment of the present invention, the second part of the aging process starts from the high-temperature multiple temperature-varying alternating aging heat treatment, the total aging time is 1 time (including 2, 3 or 4 times), and each temperature-varying alternating aging process should include at least 1 temperature rise and 1 temperature fall at the same time.

In the embodiment of the invention, the critical multiple temperature reduction, temperature change and alternating aging temperature interval refers to: the 1 st critical temperature reduction, temperature change, alternating aging temperature interval: cooling and heating temperature intervals are started from a cooling and aging highest heating temperature interval Tacmax (marked as Tacmax-1), sequentially pass through n-2 aging intermediate heating temperature intervals Tacm (marked as Tacm-1) and finally reach n stages (n is more than or equal to 3 and less than or equal to 7, namely n is 3, 4, 5, 6 or 7) ending from the time-efficiency lowest heating temperature interval Tacmin (marked as Tacmin-1); critical temperature reduction, temperature variation and alternating aging temperature intervals of 2 nd time, 3 rd time or 4 th time: the cooling aging process is sequentially repeated, and the relation of the numerical values of the critical cooling temperature variation alternating aging lowest temperature interval of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmin-1 is more than Tacmin-2 is more than Tacmin-3 is more than Tacmin-4, and the numerical relational expressions of the intermediate heating temperature intervals of the critical temperature reduction, temperature variation, alternating aging and the like for the 1 st time, the 2 nd time, the 3 rd time and the 4 th time are as follows: tacm-1 is more than Tacm-2 is more than Tacm-3 is more than Tacm-4, and the relation of the numerical values of the temperature-changing alternating aging highest temperature interval of critical temperature reduction and temperature change for the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmax-1 is more than Tacmax-2 is more than Tacmax-3 is more than Tacmax-4; the critical multiple temperature-reducing temperature-changing alternating aging temperature range does not repeatedly have any temperature-reducing aging minimum heating temperature range, temperature-reducing aging intermediate heating temperature range and temperature-reducing aging maximum temperature range, and does not repeatedly have any temperature-increasing aging minimum heating temperature range, temperature-increasing aging intermediate heating temperature range and temperature-increasing aging maximum temperature range.

In the invention, the critical multiple temperature rise and temperature change alternating aging temperature interval refers to: the 1 st critical temperature rise and temperature change alternating aging temperature interval: heating temperature rising and heating temperature intervals are started from a heating and aging minimum heating temperature interval Tacmin (marked as Tacmin-1), sequentially pass through n-2 aging intermediate heating temperature intervals Tacm (marked as Tacm-1) and finally end to a time efficiency maximum heating temperature interval Tacmax (marked as Tacmax-1), and are in n stages (n is more than or equal to 3 and less than or equal to 7, namely n is 3, 4, 5, 6 or 7); critical temperature rise, temperature change, alternating aging temperature interval for the 2 nd time, the 3 rd time or the 4 th time: the temperature-rise aging process is sequentially repeated, and the relation of the numerical values of the critical temperature-rise temperature-change alternating aging lowest temperature interval of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmin-1 is more than Tacmin-2 is more than Tacmin-3 is more than Tacmin-4, and the relation of the intermediate heating temperature interval value of the critical temperature rise and aging of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacm-1 is more than Tacm-2 is more than Tacm-3 is more than Tacm-4, the numerical relation of the highest temperature interval of the critical temperature rise, temperature change, alternation and aging of the 1 st time, the 2 nd time, the 3 rd time and the 4 th time is as follows: tacmax-1 is more than Tacmax-2 is more than Tacmax-3 is more than Tacmax-4; the critical multiple temperature rise and temperature change alternating aging temperature range does not repeatedly have any temperature rise aging minimum heating temperature range, temperature rise aging middle heating temperature range and temperature rise aging maximum temperature range, and does not repeatedly have any temperature fall aging minimum heating temperature range, temperature fall aging middle heating temperature range and temperature fall aging maximum temperature range.

In the embodiment of the invention, because the aging temperature range of the austenitic stainless steel is narrow (between 170 ℃ and 230 ℃), the temperature range of the aging temperature of the austenitic stainless steel starting from high temperature multiple temperature change alternating is neither too small nor too large: the aging temperature range of the 1 stage belongs to the prior art (no temperature difference), and the aging capability is too poor; in the aging temperature range of 2 stages (the temperature difference is large), the aging capability is increased but is still insufficient; when the temperature is within the aging temperature range of not less than 8 stages (the temperature difference is too small), the aging capability is excessive (in fact, a certain aging capability is still provided in each temperature rise or decrease transition stage where the temperature difference is too small). Therefore, the temperature range of the high-temperature multiple-time variable-temperature alternating aging is set to be 3-7, namely n is 3, 4, 5, 6 or 7 stages, so that the aging capacity, range, quality, efficiency and the like can be improved.

In the embodiment of the present invention, the second part of critical temperature ranges starting from the high-temperature multiple-temperature-changing alternating aging temperature range mainly have the following functions: the critical aging maximum heating temperature Tacmax interval is the maximum temperature interval of effective aging, and is also the critical temperature area which rapidly avoids 850 ℃ -900 ℃ in the cooling and heating stages (forming a sigma phase critical temperature area, and slightly precipitating (Fe, Cr, Ni, Mn, W, Mo) C composite alloy carbide or lamellar carbide); the critical middle aging n-2 staged temperature Tacm intervals are the optimal heating and heat preservation temperature intervals between the critical aging highest heating temperature Tacmax interval and the critical aging lowest heating temperature Tacmin interval; the minimum heating staged temperature Tacmin interval of critical aging is the minimum temperature interval of effective aging, and is also the most beneficial heating and heat preservation temperature interval which rapidly avoids 450 ℃ -500 ℃ (chromium-poor precipitation critical temperature area and large-particle-size needle-rod-shaped carbide precipitation critical temperature area), 475 ℃ (cold brittleness critical temperature area and large-particle-size needle-rod-shaped carbide precipitation critical temperature area), 550 ℃ -670 ℃ (graphitization, intercrystalline corrosion or crystal-brittle fracture critical temperature area) and the like in the cooling and heating stages. Therefore, the aging strengthening phase can be effectively increased, the aging weakening phase can be reduced or inhibited, the optimized hardness range with good quality stability, high reliability and good consistency of heat treatment hardness can be obtained, the anti-tarnishing resistance is improved, the heat treatment efficiency is improved and the like by setting the temperature range of the high-temperature multiple-time variable-temperature alternating aging as n grading ranges.

In the embodiment of the invention, the mathematical relation between the highest heating temperature Tacmax of the high-temperature multiple-time variable-temperature alternating aging and the highest theoretical heating temperature Tactmax of the aging is as follows:

Tacmax＝Tactmax–(20～30)℃

wherein Tacmax is the critical temperature starting from the highest heating temperature of high-temperature multiple-time variable-temperature alternating aging at DEG C; tactmax is the maximum theoretical heating temperature of aging at DEG C.

In the embodiment of the invention, the mathematical relation between the lowest heating temperature Tacmin of high-temperature multiple-time temperature change alternating aging and the lowest theoretical heating temperature Tactmin of aging is as follows:

Tacmin＝Tactmin+(20～30)℃

wherein Tacmin is the critical temperature starting from the lowest heating temperature of high-temperature multiple temperature-changing alternating aging at DEG C; tactmin is the lowest theoretical heating temperature of aging at DEG C.

In the embodiment of the invention, the mathematical relation between the intermediate heating temperature Tacm, the aging minimum temperature Tacmin and the aging maximum heating temperature Tacmax of each stage of the second part of critical multiple temperature-changing alternating aging is as follows: tacm ═ Tacmin + n_i(Tacmax–Tacmin)/(n–1)；

Wherein Tacm is the intermediate heating temperature and DEG C of each stage of high-temperature multiple temperature-changing alternating ageing at critical temperature, and is the specific stage temperature from 2 nd stage to 2 nd stage of critical temperature-reducing or temperature-raising temperature-changing alternating ageing; tacmin is the lowest temperature and DEG C of critical temperature reduction or temperature rise and temperature change alternating aging, and is also the heating temperature of the final subsection or the 1 st subsection of the critical temperature reduction or temperature rise and temperature change alternating aging; n is_iThe specific nth heating temperature interval from high to low or from low to high for the 2 nd to the 2 nd last phases_iNumber of stages, n being not less than 1_iN is less than or equal to 5_i1, 2, 3, 4 or 5; tacmax is the highest heating temperature and DEG C of the critical temperature reduction or temperature rise and temperature change alternating aging, and is also the heating temperature of the 1 st stage or the last stage of the critical temperature reduction or temperature rise and temperature change alternating aging; (Tacmax-Tacmin)/n is a specific value with the temperature difference of critical temperature reduction or temperature rise decreasing or increasing and the temperature difference being unchanged; n is the total number of stages starting from a critical temperature-reducing temperature-changing alternating aging highest heating temperature Tacmax interval and ending at a critical temperature-reducing temperature-changing alternating aging lowest heating temperature Tacmin or starting from a critical temperature-increasing temperature-changing alternating aging lowest temperature Tacmin and ending at a critical temperature-increasing temperature-changing alternating aging highest heating temperature Tacmax interval, n is more than or equal to 3 and less than or equal to 7, namely n is 3, 4, 5, 6 or 7.

In the embodiment of the invention, the mathematical relation between the critical starting point of the first half part of the second part and the working temperature Tacw of the high-temperature multiple-time variable-temperature alternating ageing and the workpiece use temperature Tw, the critical starting point of the first half part and the minimum heating temperature Tacmin of the high-temperature multiple-temperature variable-temperature alternating ageing and the critical starting point of the second half part and the maximum heating temperature Tacmax of the high-temperature multiple-temperature variable-temperature alternating ageing are as follows: tacmin is less than Tw + (60-100) DEG C and less than Tacw and less than Tacmax;

wherein Tacw is the critical temperature starting from the high-temperature multiple variable-temperature alternating aging working heating temperature, DEG C, and Tacw at least appears once in each critical middle aging heating temperature Tacm interval; tw is the workpiece use temperature, DEG C; tacmin is the critical temperature starting from the lowest heating temperature of high-temperature multiple-time variable-temperature alternating aging at DEG C; tacmax is the critical temperature starting from the highest heating temperature of high-temperature multiple-time variable-temperature alternating aging at DEG C.

In an embodiment of the present invention, the total time of the second part critical starting from the high temperature multiple temperature-swing alternating ageing cannot be too short or too long: if the time is too short, the alloy element strengthening phase can only reach the limited aging precipitation capacity, range, quality, efficiency and the like; if the aging capacity, range, quality, efficiency and the like of the alloy element strengthening phase are too long, the alloy element strengthening phase can reach a saturated or limit state. The critical starting time is the total time tau of high-temperature multiple temperature-changing alternating ageing_acNAnd the total time tau of theoretical aging_aNtThe mathematical relationship of (a) is: tau is_acN＝(1/2～1/3)τ_aNt；

In the formula tau_acNThe total time of high-temperature multiple temperature-changing alternating aging is critical, and is min or h; tau is_aNtThe theoretical total aging time is min or h.

In the embodiment of the invention, when the critical starting time is carried out according to the equal time method in the high-temperature multiple-temperature-changing alternating ageing time, the critical starting time of the equal time method is the total heating time tau of the high-temperature multiple-temperature-changing alternating ageing time_acNHeating time tau in each stage corresponding to heating temperature intervals of 1 st, 2 nd, 3 rd, … …, and nth stages_acnThe mathematical relationship of (a) is: tau is_acN＝∑τ_acn＝∑τ_acN/N；

In the formula tau_acNThe critical point of the equal time method is the total time of high-temperature multiple variable-temperature alternating aging heating for min or h; tau is_acnHeating time of each stage of aging corresponding to heating temperature intervals of 1 st stage, 2 nd stage, 3 rd stage, … … and nth stage of high-temperature multiple-temperature-changing alternating aging is critical, and is tau/time or h/time respectively_ac1、τ_ac2、τ_ac3、τ_ac4、τ_ac5、τ_ac6、τ_ac7，τ_ac1＝τ_ac2＝τ_ac3＝τ_ac4＝τ_ac5＝τ_ac6＝τ_ac7(ii) a N is the total number of stages of high-temperature multiple variable-temperature alternating aging heating, and is more than or equal to 3 and less than or equal to 7 (namely N is 3, 4, 5, 6 or 7); n is the number of the nth stage starting from the high-temperature multiple variable-temperature alternating aging heating, and n is more than or equal to 1 and less than or equal to 7 (namely n is 1, 2, 3, 4, 5, 6 or 7).

In the embodiment of the invention, when the critical starting time is carried out according to the increasing time method, the critical starting time of the increasing time method is the total heating time tau of the high-temperature multiple-temperature-changing alternating ageing_acNHeating time tau in each stage of aging corresponding to heating temperature intervals of 1 st, 2 nd, 3 rd, … …, and nth stages of heating_acnThe mathematical relationship of (a) is: tau is_acN＝∑τ_acn＝∑[τ_ac1+(n–1)τ_ac0]；

In the formula tau_acNThe critical point of the increasing time method is the total time of high-temperature multiple variable-temperature alternating aging heating for min or h; n is the total number of stages of high-temperature multiple variable-temperature alternating aging heating, and is more than or equal to 3 and less than or equal to 7 (namely N is 3, 4, 5, 6 or 7); tau is_acnHeating time of each stage of high-temperature multiple temperature-changing alternating ageing is critical, min/time or h/time is respectively tau_ac1、τ_ac2、τ_ac3、τ_ac4、τ_ac5、τ_ac6、τ_ac7，τ_ac1＞τ_ac2＞τ_ac3＞τ_ac4＞τ_ac5＞τ_ac6＞τ_ac7(ii) a n is the number of the nth stage of high-temperature multiple variable-temperature alternating aging heating, and n is more than or equal to 1 and less than or equal to 7 (namely n is 1, 2, 3, 4, 5, 6 or 7); tau is_ac1Heating time in a first stage of high-temperature multiple-temperature-changing alternating ageing is critical, and the heating time is min/time or h/time; tau is_ac0The critical point is that the heating time increases the grade difference, min/time or h/time, starting from high temperature multiple temperature change alternating aging, and the specific value is the same and unchanged.

In the embodiment of the invention, when the critical starting time is carried out according to a decreasing time method at high temperature multiple temperature-changing alternating ageing time, the critical starting time of the decreasing time method is the total heating time tau of the high temperature multiple temperature-changing alternating ageing time_acNThe 1 st stage of temperature rising and temperature reducing aging,Heating time tau in each stage of aging corresponding to heating temperature intervals of 2 nd stage, 3 rd stage, … …, and nth stage_acnThe mathematical relationship of (a) is: tau is_acN＝∑τ_acn＝∑[τ_ac1–(n–1)τ_ac0]；

In the formula tau_scNThe criticality of the decreasing time method is started from the total time of high-temperature multiple variable-temperature alternating aging heating for min/time or h/time; n is the total number of stages of high-temperature multiple variable-temperature alternating aging heating, and is more than or equal to 3 and less than or equal to 7 (namely N is 3, 4, 5, 6 or 7); tau is_acnHeating time of each stage of aging corresponding to heating temperature intervals of 1 st stage, 2 nd stage, 3 rd stage, … … and nth stage of high-temperature multiple-temperature-changing alternating aging is critical, and is tau/time or h/time respectively_ac1、τ_ac2、τ_ac3、τ_ac4、τ_ac5、τ_ac6、τ_ac7，τ_ac1＜τ_ac2＜τ_ac3＜τ_ac4＜τ_ac5＜τ_ac6＜τ_ac7(ii) a n is the number of the nth stage of high-temperature multiple variable-temperature alternating aging heating, and n is more than or equal to 1 and less than or equal to 7 (namely n is 1, 2, 3, 4, 5, 6 or 7); tau is_ac1Heating for min/time or h/time at the first stage of high-temperature multiple-temperature-changing alternating ageing for critical time; tau is_ac0The critical point is that the time level difference is decreased by a plurality of times of temperature change, alternating aging and heating at high temperature, and the time level difference is min/time or h/time and is the same and unchangeable specific numerical value.

In the embodiment of the invention, the critical starting of the first half part of the second part in the high-temperature multiple alternating ageing heat treatment final cooling mode is as follows: the furnace door is opened or other cooling modes are adopted to rapidly cool along with the furnace.

In the embodiment of the invention, the second half rear half critical low temperature annealing heating temperature Tlac is mathematically related to the low temperature annealing minimum theoretical heating temperature tlactamin and the low temperature annealing maximum theoretical heating temperature Tlacmax by the following formula: tlactmin + (80-90) DEG C is less than or equal to Tlac and less than or equal to Tlacmax- (10-15) DEG C;

in the formula, Tlac is the critical low-temperature annealing heating temperature and is DEG C; tlactmin is the lowest theoretical heating temperature of low-temperature annealing at DEG C; tlacmax is the maximum theoretical heating temperature of low temperature annealing at C.

In an embodiment of the present invention, the second half-half critical annealing temperature cannot be too high or too low: when the annealing temperature is too high, the effect of removing the residual cold and hot processing stress of the material is good when the high-temperature annealing (the annealing temperature Tha is more than 850-1200 ℃) and the medium-temperature annealing (the annealing temperature Tma is 680-850 ℃), but the difficult problems of large deformation of the austenitic stainless steel, long heating time, newly generated negative effects of solid solution and aging, needing to set an independent process and being not suitable for being used as a final process (only being suitable for being used as an intermediate process before aging after solid solution or being suitable for being used as a process without solid solution and aging heat treatment) and the like can not be solved, and the problems of rapidly avoiding 700 ℃ -815 ℃ (a sensitized intercrystalline corrosion critical temperature zone), 850 ℃ -900 ℃ (a critical temperature zone for forming sigma phase, a critical temperature zone for slightly precipitating (Fe, Cr, Ni, Mn, W, Mo) C composite alloy carbide or a layered carbide), and 940 ℃ (FeS-FeO eutectic melting point and a dissolved genetic critical temperature zone, 985 ℃ (Fe-FeS eutectic melting point and dissolution genetic critical temperature region), 1083 ℃ (weakening phase copper alloy dissolution and genetic critical temperature region) or 1164 ℃ (FeS-MnS eutectic melting point and dissolution genetic critical temperature region), and the like; when the annealing temperature is too low, such as the annealing temperature is lower than 275 ℃, although 450 ℃ -500 ℃ (chromium-poor precipitation critical temperature zone and large-particle-size needle-rod-shaped carbide precipitation critical temperature zone), 475 ℃ (cold-brittleness critical temperature zone and large-particle-size needle-rod-shaped carbide precipitation critical temperature zone), 550 ℃ -670 ℃ (graphitization, intergranular corrosion or along-crystal-brittle-cracking critical temperature zone) and the like can be effectively and quickly avoided, and the novel negative effects of solid solution or aging heat treatment are not generated while the low-temperature annealing heat treatment is carried out, the deformation of austenitic stainless steel is extremely small, the strengthening effect of discoloration and rust resistance after the solid solution or aging heat treatment is favorably kept, the method is also suitable for any intermediate process and final process, but an independent low-temperature annealing process is needed, the heating time is long, the effect of removing the residual cold and hot processing stress of the material is poor, therefore, the critical low-temperature annealing method is continuously adopted, the method is finally more favorable for obtaining the optimized heat treatment hardness range of the austenitic stainless steel, reducing the residual cold and hot processing stress and deformation, meeting the service performance requirement, improving the anti-tarnishing capacity and improving the heat treatment efficiency.

In the invention, the second half of the second part is subjected to critical low temperature annealing for a heating time tau_lacHeating time tau of low-temperature annealing theory_latThe mathematical relationship of (a) is: tau is_lac＝τ_lat(ii) a In the formula tau_lacCritical low temperature annealing heating time, min or h; tau is_latThe heating time is the theoretical heating time of low-temperature annealing, min or h.

In the embodiment of the present invention, the heating time of the critical low-temperature annealing should not be too short in principle but should not be too long: if the time is too short, the effects of reducing the residual cold and hot processing stress capability and quality of the austenitic stainless steel are poor although the annealing efficiency can be improved and the heat energy consumption can be reduced; when the temperature is too long, the capability of reducing the residual cold and hot processing stress of the austenitic stainless steel is good, the quality is good, but the annealing efficiency is low and the heat energy consumption is large. In fact, the heating time of the critical low-temperature annealing is beneficial to improving the capability and quality of reducing the residual cold and hot processing stress of the austenitic stainless steel, and the annealing efficiency is not reduced or the heat energy consumption is not related to the heating time of the critical low-temperature annealing, because the heat source of the critical low-temperature annealing is realized by the residual heat after the temperature reduction and the cooling of the previous critical aging process.

In an embodiment of the present invention, the final cooling manner of the second half critical low temperature annealing heat treatment of the second half part is as follows: the furnace is cooled by opening the furnace door or other cooling modes, or directly taken out of the furnace and cooled in room-temperature water or room-temperature air.

In an embodiment of the present invention, the second part of the critical heat treatment starts from the high-temperature multiple temperature-varying alternating aging and critical annealing composite heat treatment, and comprises the following processes: 1) the first half part of the second part begins in a high-temperature multiple variable-temperature alternating aging heat treatment process: after the first part of critical solution heat treatment is finished, continuing to perform a second part of critical temperature-variable alternating aging heat treatment starting from high temperature for multiple times, and depending on the process of critical temperature-variable alternating aging heat treatment starting from high temperature to low temperature and starting from low temperature to high temperature for multiple times, the method comprises the following steps that the 1 st critical temperature-variable alternating aging process starting from high temperature: the method specifically comprises the following steps of 1, starting from high temperature to low temperature non-variable temperature alternating aging process in the first half part of the time: firstly heating and preserving the austenite stainless steel at the critical aging highest temperature when the temperature of the austenite stainless steel is raised to the aging highest temperature from room temperature at a medium speed in a heating furnace within a specified time, then continuously heating and preserving the austenite stainless steel at the critical aging intermediate temperature when the temperature of the austenite stainless steel is rapidly lowered to the aging intermediate temperature, and then continuously heating and preserving the austenite stainless steel at the critical aging lowest temperature when the temperature of the austenite stainless steel is rapidly lowered to the final aging lowest temperature (the first half of the 1 st time is started from high temperature and ended from the low temperature non-variable temperature alternating aging process), and then continuing the second half of the 1 st time, which is started from low temperature and ended from the high temperature variable temperature alternating aging process: firstly, continuously heating and preserving the critical aging middle temperature when the austenitic stainless steel is rapidly heated from the critical aging lowest temperature to the aging middle temperature in a heating furnace within the specified time, and then continuously heating and preserving the critical aging highest temperature when the austenitic stainless steel is rapidly heated from the critical aging middle temperature to the critical aging highest temperature in the heating furnace within the specified time (the first half of the critical temperature starts from the low temperature and ends at the high-temperature variable-temperature alternating aging process, and the first half of the critical temperature starts at the high-temperature variable-temperature alternating aging process and also ends at all at the 1 st time); then, the 2 nd, 3 rd or 4 th critical temperature-changing alternating aging process is carried out again: after the 1 st critical starting high-temperature-changing alternating ageing process is finished, continuing the 2 nd critical temperature-changing alternating ageing process, sequentially and reversely repeating the 1 st half critical starting low-temperature and high-temperature-changing alternating ageing process for 1 time (the 2 nd critical temperature-changing alternating ageing process is finished), or sequentially and reversely repeating the 3 rd critical temperature-changing alternating ageing process for 1 time (the 3 rd critical temperature-changing alternating ageing process is finished), or sequentially and reversely repeating the 4 th critical temperature-changing alternating ageing process for 1 time (the 4 th critical temperature-changing alternating ageing process is finished); after the 2 nd, 3 rd or 4 th critical starting from the high-temperature multiple temperature-changing alternating aging process is completely finished, finally, the specific cooling mode is continuously adopted to rapidly cool the austenitic stainless steel to the critical annealing temperature, and the critical starting from the high-temperature multiple temperature-changing alternating aging heat treatment process is formed by the process steps (the first half of the second part of the critical starting from the high-temperature multiple temperature-changing alternating aging heat treatment process is completely finished); 2) a third part of critical annealing heat treatment, comprising the following processes: critical annealing and heating process: after the first half part of the second part is critical and begins to be completely finished in the high-temperature multiple-temperature-changing alternating aging heat treatment process, the second half part critical annealing heat treatment is continued: heating and preserving heat of austenitic stainless steel within a range of critical annealing temperature Tlac within a heating furnace within a specified time; critical annealing and final cooling process: after the critical annealing heating process is finished, a furnace door is opened or other cooling modes are adopted to cool the austenitic stainless steel along with the furnace from the critical annealing temperature Tlac or directly taken out of the furnace to be cooled in room temperature water or room temperature air (the second half of the second part of the critical annealing heat treatment process is completely finished, and all processes of high-temperature multiple-temperature-changing alternating aging and annealing heat treatment of one critical solution and critical solution are also completely finished).

According to the technical scheme, the invention fundamentally solves the problems of the special heat treatment technology theory and practice that the traditional mainstream austenitic stainless steel technical method cannot solve the problems of poor quality stability, low qualified product rate, low hardness (or low mechanical property) and poor consistency, poor anti-tarnishing capacity, long heating time, low efficiency, poor heating reliability of heat treatment equipment, low service life of high-temperature components and parts, high cost and the like.

Although the invention is researched by taking the heat treatment method of austenitic stainless steel (the used heating equipment is the conventional box-type resistance heating furnace) as a research object, the invention is also applicable to heat treatment methods of other types of stainless steel, high-temperature alloy and the like (the heating equipment can also be selected from other types of resistance heating furnaces, high-medium and low-frequency heating furnaces, salt bath heating furnaces, gas-fuel oil heating furnaces, fluid particle heating furnaces, vacuum heating furnaces and the like); similarly, the method is also suitable for heat treatment methods related in the technical fields of hot working engineering such as austenitic stainless steel smelting, steel rolling, forging, heat treatment and the like related in steel mills and manufacturing plants; meanwhile, it should be noted that: it will be apparent to those skilled in the art that several arrangements, combinations, modifications, improvements (especially, the heating temperatures and times for solution, aging, and annealing, and the cooling media can be properly adjusted or changed according to the grades, the use properties, and the heating equipment of austenitic stainless steel) and the like can be made without departing from the technical principle of the present invention.