阅读说明：本技术 一种获得弥散分布的细小碳化物的真空渗碳方法 (Vacuum carburization method for obtaining dispersed fine carbides ) 是由 丛培武 徐跃明 杜春辉 陆文林 陈旭阳 何龙祥 王赫 薛丹若 杨广文 范雷 凡占 于 2021-09-09 设计创作，主要内容包括：本发明公开了一种获得弥散分布的细小碳化物的真空渗碳方法,包括加热保温阶段、脉冲渗碳阶段、变温阶段、淬火阶段。脉冲渗碳阶段是指渗碳/扩散多次交替的高浓度渗碳过程；变温阶段是指渗碳结束后,停止加热,充气快冷至Ac1线下某一温度,并保温一段时间,随后立即升温至淬火温度,即Ac3或Ac1线以上30-50℃,保温至工件均匀奥氏体化；淬火阶段是指采用高压气淬或油淬中的一种方式进行。能细化组织,同时提高表面含碳量并获得弥散分布的细小碳化物(球状为主),最大程度发挥材料的强韧性,从而提高工件的服役性能。(The invention discloses a vacuum carburizing method for obtaining finely dispersed carbides, which comprises a heating and heat preservation stage, a pulse carburizing stage, a temperature changing stage and a quenching stage. The pulse carburization stage is a high-concentration carburization process of multiple alternation of carburization/diffusion; the temperature-changing stage is that after the carburization is finished, the heating is stopped, the gas is filled for quick cooling to a certain temperature below the Ac1 line, the temperature is kept for a period of time, then the temperature is immediately raised to the quenching temperature, namely 30-50 ℃ above the Ac3 or Ac1 line, and the temperature is kept until the workpiece is evenly austenitized; the quenching stage is carried out by adopting one mode of high-pressure gas quenching or oil quenching. The structure can be refined, the carbon content on the surface is improved, the dispersed fine carbides (mainly spherical) are obtained, the toughness of the material is exerted to the maximum extent, and the service performance of the workpiece is improved.)

1. A vacuum carburization method for obtaining finely dispersed carbides is characterized by comprising a heating and heat-preserving stage, a pulse carburization stage, a temperature changing stage and a quenching stage;

the pulse carburizing stage is a high-concentration carburizing process in which carburizing and diffusion are alternated for multiple times, wherein carburizing gas is filled into a carburizing chamber in a pulse mode, the carbon concentration gradient of the surface layer of a workpiece is adjusted through the carburizing/diffusion time, and the carbon content of the surface is close to the maximum solubility of carbon in austenite at the carburizing temperature;

the temperature changing stage comprises: after the carburization is finished, the workpiece continues to be in the heating chamber, the heating is stopped, nitrogen with set pressure is filled, the fan is started or not started, the surface layer of the workpiece is rapidly cooled to the temperature below the Ac1 line and is stabilized for a period of time, carbides are uniformly precipitated and spheroidized, then high-temperature exhaust is carried out, after the workpiece is pumped to vacuum, the temperature is immediately raised to the quenching temperature, and the temperature is preserved for a period of time, so that the workpiece is uniformly heated and completely austenitized;

any one of the following quenching modes is selected in the quenching stage: direct high-pressure gas quenching, direct oil quenching and gas-oil quenching.

2. The vacuum carburizing method for obtaining the dispersion-distributed fine carbides according to claim 1, wherein the pulse carburizing stage is characterized in that the carburizing temperature is 930-: 2-1: 7, and the carbon content value on the surface is set to be 0.8-1.3%.

3. The vacuum carburizing method for obtaining the dispersion-distributed fine carbides according to claim 1, wherein in the temperature changing stage, the pressure of nitrogen gas filled in the heating chamber is 2-6 x 105Pa, the temperature is reduced to below the Ac1 line, then the temperature is kept for 5-10min, and the temperature is kept for 5-20min after the temperature is raised to the quenching temperature.

4. The vacuum carburizing method for obtaining finely distributed carbides according to claim 3, wherein the temperature change stage requires rapid cooling, the cooling temperature range is between 600 ℃ and 700 ℃, and the temperature change is only performed once.

5. The vacuum carburizing method for obtaining finely dispersed carbides according to any one of claims 1 to 4, wherein the pulse carburizing stage selects an acetylene or propane atmosphere as the carburizing gas.

6. The vacuum carburization method for obtaining finely dispersed carbides according to claim 5, wherein the pulse carburization stage carburizes for 2 hours or more.

Technical Field

The invention relates to a vacuum carburizing heat treatment technology, in particular to a vacuum carburizing method for obtaining fine carbides in dispersion distribution.

Background

The heat treatment is a process technology which gives or improves the service performance of the workpiece and fully exerts the potential of materials by changing the microstructure in the workpiece or changing the chemical components on the surface of the workpiece. The heat treatment is a key core technology in the mechanical manufacturing industry, and with the continuous importance on the heat treatment technology, the heat treatment industry gradually develops from extensive type to fine type, and more importance is placed on a new process and a new technology, the internal quality of a product is improved, energy and material are saved, consumption is reduced, the service life is prolonged, economic benefits are concerned, and the like. The vacuum low-pressure carburization technology gradually replaces controllable atmosphere carburization equipment with the advantages of little or no oxidation, energy conservation, emission reduction, clean heat treatment and the like, and is more and more widely applied to key parts such as gears, transmission shafts and the like.

Key bearing parts such as heavy-duty gears, shafts and the like are widely applied to the industries such as aerospace, wind power, high-speed locomotives, heavy-duty automobiles and the like, the 'hard outside and tough inside' are generally required, and the surface layer strengthening is usually realized by adopting a carburizing and quenching mode. Research shows that the improvement of the carbon content of the carburized layer and the obtainment of fine carbides with good form and distribution are very beneficial to the toughness of a heat-treated workpiece, and the surface hardness is as high as 800-1000HV 1.

As shown in fig. 1 and 3, the above requirements cannot be met by the current vacuum carburization process, effective control of the size and morphology of carbide can only be achieved at a low carbon content (below 0.8%), and once the carbon content of the carburized layer is increased, network carbide which is harmful to product performance often appears, i.e. carbon atoms are always precipitated at austenite grain boundaries, but nucleation, growth and formation of dispersed carbide in the austenite grain are not achieved, so that the toughness of the material is difficult to be exerted to the maximum extent.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention aims to provide a vacuum carburizing method for obtaining dispersed and distributed fine carbides, so as to solve the technical problems in the prior art. The method has the advantages of short process flow, high carburizing efficiency, cleanness, no pollution and strong practicability.

The purpose of the invention is realized by the following technical scheme:

the invention relates to a vacuum carburizing method for obtaining dispersed and distributed fine carbides, which comprises a heating and heat-preserving stage, a pulse carburizing stage, a temperature changing stage and a quenching stage;

the pulse carburizing stage is a high-concentration carburizing process in which carburizing and diffusion are alternated for multiple times, wherein carburizing gas is filled into a carburizing chamber in a pulse mode, the carbon concentration gradient of the surface layer of a workpiece is adjusted through the carburizing/diffusion time, and the carbon content of the surface is close to the maximum solubility of carbon in austenite at the carburizing temperature;

the temperature changing stage comprises: after the carburization is finished, the workpiece continues to be in the heating chamber, the heating is stopped, nitrogen with set pressure is filled, the fan is started or not started, the surface layer of the workpiece is rapidly cooled to the temperature below the Ac1 line and is stabilized for a period of time, carbides are uniformly precipitated and spheroidized, then high-temperature exhaust is carried out, after the workpiece is pumped to vacuum, the temperature is immediately raised to the quenching temperature, and the temperature is preserved for a period of time, so that the workpiece is uniformly heated and completely austenitized;

any one of the following quenching modes is selected in the quenching stage: direct high-pressure gas quenching, direct oil quenching and gas-oil quenching.

Compared with the prior art, the vacuum carburization method for obtaining the finely dispersed carbide provided by the invention obtains the required carbon concentration gradient curve by adjusting the time of multiple alternation of carburization/diffusion in the pulse carburization stage, and rapidly cools the surface layer of the workpiece by pressurizing and inflating in the temperature changing stage so as to uniformly precipitate the carbide and refine the structure. The method has the advantages of short process flow, high carburizing efficiency, cleanness, no pollution and strong practicability, and exerts the toughness of the material to the greatest extent, thereby improving the service performance of the workpiece.

Drawings

FIG. 1 is a graph illustrating a conventional vacuum low pressure carburization process curve in the prior art;

FIG. 2 is a schematic diagram of a process curve of a vacuum carburizing method for obtaining finely dispersed carbides according to an embodiment of the invention;

FIG. 3 is a schematic view of a prior art medium vacuum low pressure carburization conventional process surface carbide structure (x 500);

FIG. 4a is a schematic view of the surface carbide structure (x 500) of the vacuum carburization process of the dispersed fine carbides in the example of the present invention.

FIG. 4b is a SEM spherical carbide structure diagram of the vacuum carburization process of the dispersed fine carbides in the embodiment of the present invention.

Detailed Description

The technical scheme in the embodiment of the invention is clearly and completely described below by combining the attached drawings in the embodiment of the invention; it is to be understood that the described embodiments are merely exemplary of the invention, and are not intended to limit the invention to the particular forms disclosed. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.

The terms that may be used herein are first described as follows:

the term "and/or" means that either or both can be achieved, for example, X and/or Y means that both cases include "X" or "Y" as well as three cases including "X and Y".

The terms "comprising," "including," "containing," "having," or other similar terms of meaning should be construed as non-exclusive inclusions. For example: including a feature (e.g., material, component, ingredient, carrier, formulation, material, dimension, part, component, mechanism, device, process, procedure, method, reaction condition, processing condition, parameter, algorithm, signal, data, product, or article of manufacture), is to be construed as including not only the particular feature explicitly listed but also other features not explicitly listed as such which are known in the art.

The term "consisting of … …" is meant to exclude any technical feature elements not explicitly listed. If used in a claim, the term shall render the claim closed except for the inclusion of the technical features that are expressly listed except for the conventional impurities associated therewith. If the term occurs in only one clause of the claims, it is defined only to the elements explicitly recited in that clause, and elements recited in other clauses are not excluded from the overall claims.

Unless expressly stated or limited otherwise, the terms "mounted," "connected," and "secured," etc., are to be construed broadly, as for example: can be fixedly connected, can also be detachably connected or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms herein can be understood by those of ordinary skill in the art as appropriate.

When concentrations, temperatures, pressures, dimensions, or other parameters are expressed as ranges of values, the ranges are to be understood as specifically disclosing all ranges formed from any pair of upper, lower, and preferred values within the range, regardless of whether ranges are explicitly recited; for example, if a numerical range of "2 ~ 8" is recited, then the numerical range should be interpreted to include ranges of "2 ~ 7", "2 ~ 6", "5 ~ 7", "3 ~ 4 and 6 ~ 7", "3 ~ 5 and 7", "2 and 5 ~ 7", and the like. Unless otherwise indicated, the numerical ranges recited herein include both the endpoints thereof and all integers and fractions within the numerical range.

The terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," and the like are used in an orientation or positional relationship that is indicated based on the orientation or positional relationship shown in the drawings for ease of description and simplicity of description only, and are not intended to imply or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting herein.

Details which are not described in detail in the embodiments of the invention belong to the prior art which is known to the person skilled in the art. Those not specifically mentioned in the examples of the present invention were carried out according to the conventional conditions in the art or conditions suggested by the manufacturer. The reagents or instruments used in the examples of the present invention are not specified by manufacturers, and are all conventional products available by commercial purchase.

The invention relates to a vacuum carburizing method for obtaining dispersed and distributed fine carbides, which comprises a heating and heat-preserving stage, a pulse carburizing stage, a temperature changing stage and a quenching stage;

the pulse carburizing stage is a high-concentration carburizing process in which carburizing and diffusion are alternated for multiple times, wherein carburizing gas is filled into a carburizing chamber in a pulse mode, the carbon concentration gradient of the surface layer of a workpiece is adjusted through the carburizing/diffusion time, and the carbon content of the surface is close to the maximum solubility of carbon in austenite at the carburizing temperature;

the temperature changing stage comprises: after the carburization is finished, the workpiece continues to be in the heating chamber, the heating is stopped, nitrogen with set pressure is filled, the fan is started or not started, the surface layer of the workpiece is rapidly cooled to the temperature below the Ac1 line and is stabilized for a period of time, carbides are uniformly precipitated and spheroidized, then high-temperature exhaust is carried out, after the workpiece is pumped to vacuum, the temperature is immediately raised to the quenching temperature, and the temperature is preserved for a period of time, so that the workpiece is uniformly heated and completely austenitized;

any one of the following quenching modes is selected in the quenching stage: direct high-pressure gas quenching, direct oil quenching and gas-oil quenching.

In the pulse carburization stage, the carburization temperature is 930-980 ℃, the carburization pressure is 800-1500Pa, the times of alternately performing carburization/diffusion and the specific time of each time are determined according to the required effective hardened layer depth or the carbon concentration gradient curve, and the diffusion ratio is 1: 2-1: 7, and the carbon content value on the surface is set to be 0.8-1.3%.

And in the temperature changing stage, the pressure of nitrogen gas filled into the heating chamber is 2-6 multiplied by 105Pa, the temperature is reduced to be below the Ac1 line, the temperature is kept for 5-10min, the temperature is increased to the quenching temperature, and the temperature is kept for 5-20 min.

The temperature changing stage requires rapid cooling, the cooling temperature range is between 600 ℃ and 700 ℃, and the temperature is changed only once.

In the pulse carburizing stage, acetylene or propane atmosphere is selected as carburizing gas.

The carburizing time in the pulse carburizing stage is more than 2 hours.

In summary, in the vacuum carburizing method for obtaining finely dispersed carbides according to the embodiments of the present invention, the required carbon concentration gradient curve is obtained by adjusting the time of multiple alternation of carburizing/diffusing in the pulse carburizing stage, and the surface layer of the workpiece is rapidly cooled by pressurizing and inflating in the temperature changing stage, so that carbides are uniformly precipitated and the structure is refined. The method has the advantages of short process flow, high carburizing efficiency, cleanness, no pollution and strong practicability, and furthest exerts the obdurability of the material, thereby improving the service performance of the workpiece.

In the invention:

the pulse carburizing stage is to introduce acetylene or propane atmosphere under vacuum condition, utilize the diffusion of active carbon atoms in solid under high temperature condition to form carbide, and achieve the purpose of surface hardening after cooling. The pulse carburizing stage is very critical, the carburizing and diffusing time directly influences the carbon concentration gradient curve of the surface layer of the material, and further influences the microstructure and the performance of the material, and whether austenite grains grow up is determined by the carburizing temperature and the total carburizing time.

And in the temperature changing stage, after the pulse carburizing is finished, the workpiece is continuously kept in the vacuum heating chamber, the heating is stopped, nitrogen is filled and the air is exhausted in a pulse mode, so that the surface temperature of the workpiece can be quickly reduced, carbon atoms are precipitated and spheroidized in crystal grains, and then nucleation and growth are carried out, and the formation of dispersed and distributed fine carbides is promoted.

The method is applied to surface layer strengthening of high-end high-performance carburized gear parts and shaft parts.

Compared with the prior art, the invention has the beneficial effects that:

in the invention, the times of carburization/diffusion alternation and the specific process time of each time are designed according to the carbon concentration gradient curve required by a workpiece in the pulse carburization stage, and the carbon content of a carburized layer is accurately controlled; and in the temperature changing stage, the surface layer of the workpiece is rapidly cooled to be below an Ac1 line by virtue of pressurization, inflation and forced circulation, so that carbide is uniformly precipitated and the structure is refined. Martensite and retained austenite (1-2 level) on the surface of the workpiece, and the hardness is more than 62 HRC. The method has the advantages of short process flow, high carburizing efficiency, cleanness, no pollution and strong practicability.

In order to more clearly show the technical solutions and the technical effects provided by the present invention, the following detailed description is provided for the embodiments of the present invention with specific embodiments.

Example 1

Referring to fig. 2, in an embodiment of the present invention, a vacuum carburizing method for obtaining fine carbides in a dispersed distribution includes the following stages:

(1) heating and heat preservation: and determining whether the heating process is segmented or not according to the material and the size of the workpiece, setting the heating temperature, the heating time and the heat preservation time of each segment, drawing a process curve, putting the workpiece in a vacuum furnace for vacuumizing, and heating in operation. The final stage carburization temperature is usually 930-.

(2) A pulse carburizing stage: according to the carburized layer depth of the workpiece or the carbon concentration gradient requirement of the carburized layer, the times of carburized/diffused alternate operation and the time of each operation are set and compiled in a process curve. The carburizing gas is filled into the carburizing chamber in a pulse mode, the gas type is usually acetylene or propane, the carburizing pressure is usually 800-1500Pa, and after the carburizing/diffusing is finished, the carbon content of the workpiece surface is usually close to the maximum solubility of carbon in austenite at the carburizing temperature.

(3) A temperature changing stage: and determining the cooling temperature, the inflation pressure, the cooling and heat preservation time, the heating temperature, the heating time and the heating and heat preservation time according to the material and the size of the workpiece, and compiling the temperature, the inflation pressure, the cooling and heat preservation time, the heating temperature, the heating time and the heating and heat preservation time into a process curve. And after the pulse carburizing is finished, continuing to heat the workpiece in the heating chamber, stopping heating, filling nitrogen with the pressure of 2-6 multiplied by 105Pa, starting a fan to perform forced circulation if necessary, rapidly cooling the surface layer of the workpiece to a certain temperature below an Ac1 line, preserving heat for 5-10min, then exhausting at high temperature, vacuumizing, immediately heating to the quenching temperature, and preserving heat for 5-20min for soaking.

(4) And (3) quenching: according to the requirements of material quality, structure property and size control of the workpiece, the quenching mode and technological parameters are determined, such as high-pressure gas quenching (6-20bar), oil quenching (oil temperature is 50-80 ℃, oil stirring), gas oil quenching (inflation pressure, inflation time, oil temperature and oil stirring) and the like, and the step mainly comprises solidification and further grain refinement.

The method is applied to surface layer strengthening of high-end high-performance carburized gear parts and shaft parts.

Example 2 shaft

Dimension (mm) shaft diameter phi 38 and length 150mm

Materials: 18CrNiMo 7-6.

The technical requirements of heat treatment are as follows: after vacuum carburization, standard JB/T6141.3-1992 carburizes the carbide of the carburized layer to be less than or equal to 2 grades, the surface martensite and the retained austenite to be less than or equal to 2 grades, the carburized layer to be 0.9-1.2 mm and the surface hardness to be HRC 62.

And (3) carburizing process: compared with the vacuum carburization process for obtaining the dispersed and distributed fine carbides, the vacuum low-pressure carburization traditional process is adopted.

By adopting the traditional vacuum low-pressure carburization process, the surface hardness of a test piece is HRC58.5, the surface carbon content is 1.5 percent, the effective hardened layer depth is 1.1mm, and the microstructure shows that martensite is 4 grade, retained austenite is 4 grade, and surface carbide is 4 grade, and is in a net shape, as shown in figure 3.

By adopting the traditional vacuum low-pressure carburization process, once the carbon content of a carburized layer is increased, a harmful structure of net-shaped carbide is often formed on the surface, the phenomenon that the retained austenite is too much and the martensite is thick often appears on a near surface layer, and the surface layer strengthening requirement of high-end high-performance carburized gear parts and shaft parts is difficult to meet.

By adopting the vacuum low-pressure carburization process of the invention, the hardness of the surface of a test piece is HRC63.7, the carbon content of the surface is 1.2 percent, the depth of an effective hardening layer is 1.1mm, the microstructure of the test piece shows 2 grades of martensite, an aphanitic or fine needle-like structure, 1 grade of residual austenite and 1 grade of carbide, the test piece is distributed in a dispersion way, as shown in figure 4a, the carbide is 200 nm-500 nm, and the shape is mainly spherical, as shown in figure 4 b.

The vacuum low-pressure carburizing process of the dispersion distributed fine carbides can improve the carbon content of the carburized layer and obtain fine carbide tissues with good shape and distribution, the strength and toughness of the material are exerted to the best degree, and the overall heat treatment level is improved.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.