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、碳化物析出球化阶段、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,形成所需的表面碳浓度梯度；碳化物析出球化阶段是指立即充气使工件表面快冷至Ac1线以上某一温度并保温一段时间,促使碳化物在奥氏体中析出并形成弥散分布,同时利用心部余热使工件达到淬火温度。该方法兼顾组织性能和变形量,一方面获得了高含碳量(1％-1.5％)的弥散分布的细小碳化物,实现了“外硬内韧”,另一方面减小了淬火畸变,实现了尺寸控制。是一种工艺时间短,渗碳效率高,设备运行成本低,产品表面性能优,变形小的方法,最大程度发挥了材料的强韧性,从而提高工件的服役性能。(The invention discloses a vacuum carburizing method for obtaining dispersed and distributed fine carbides, which comprises a heating and heat-preserving stage, a pulse carburizing stage, a carbide precipitation and spheroidization stage and a quenching stage. The pulse carburization stage is a high-concentration carburization process with multiple alternation of carburization/diffusion to form a required surface carbon concentration gradient; the carbide precipitation and spheroidization stage is to immediately inflate the workpiece surface to quickly cool the workpiece surface to a certain temperature above the Ac1 line and preserve heat for a period of time to promote the carbide to precipitate in austenite and form dispersion distribution, and simultaneously utilize the residual heat of the center to make the workpiece reach the quenching temperature. The method gives consideration to the structure performance and the deformation, obtains the dispersedly distributed fine carbide with high carbon content (1-1.5 percent) on one hand, realizes 'external hardness and internal toughness', reduces quenching distortion on the other hand, and realizes size control. The method has the advantages of short process time, high carburizing efficiency, low equipment operation cost, excellent product surface performance and small deformation, and furthest exerts the obdurability of the material, thereby improving the service performance of the workpiece.)

1. A vacuum carburization method for obtaining dispersed and distributed fine carbides is characterized by comprising a heating and heat-preserving stage, a pulse carburization stage, a carbide precipitation and spheroidization stage and a quenching stage;

the pulse carburizing stage is a high-concentration carburizing process with multiple alternation of carburizing and diffusing, wherein the carburizing gas is filled into the carburizing chamber in a pulse mode, the carbon concentration gradient of the surface layer of the workpiece is adjusted by the carburizing and diffusing time, and the carbon content of the surface is close to the maximum solubility of carbon in austenite at the carburizing temperature;

the carbide precipitation and spheroidization stage comprises the following steps: after the carburization is finished, stopping heating, immediately filling nitrogen with set pressure, rapidly cooling the surface of the workpiece to be above an Ac1 line, preserving heat, rapidly precipitating carbide in austenite grains, inhibiting diffusion of alloy elements and alloy carbide, reducing the diffusion rate of carbon atoms, and improving the form of the carbide;

and the quenching stage is high-pressure gas quenching or 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 1-1.5%.

3. The vacuum carburizing method for obtaining the dispersion-distributed fine carbides according to claim 1, wherein in the carbide precipitation and spheroidization stage, nitrogen is filled in a heating chamber or an oil quenching chamber, the pressure is 0.5-6 x 105Pa, the time interval between the filling of the nitrogen and the stop of the heating is within 15s, and the heat preservation time when the temperature is reduced to be above the Ac1 line is 5-20 min.

4. The vacuum carburization method for obtaining finely dispersed carbides according to claim 1, characterized in that the quenching stage:

if a high-pressure gas quenching mode is adopted, the cooling speed in the quenching process is adjusted by controlling the gas quenching pressure and the rotating speed of the fan;

if the oil quenching mode is adopted, the cooling speed in the quenching process is adjusted through oil temperature setting, stirring or not and stirring frequency, and the deformation of the workpiece is reduced to the greatest extent by controlling the cooling speed.

5. The vacuum carburizing method for obtaining finely dispersed carbides according to any one of claims 1 to 4, wherein the pulse carburizing step is performed by introducing acetylene or propane atmosphere under vacuum conditions, diffusing activated carbon atoms in a solid under high temperature conditions to form carbides, and cooling to achieve surface hardening.

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.

For key parts such as gears, bearings and the like, the key to improve the service performance of parts is to obtain fine carbides in a dispersed distribution on the surface layer. Currently, a conventional heat treatment process of solution treatment/normalizing, high-temperature tempering, quenching and low-temperature tempering is generally adopted to obtain a spherical pearlite structure, so that carbides are fine, round and distributed in a dispersed manner. The production process has long process flow, low efficiency and high energy consumption, and is difficult to meet the requirements of times on the development of heat treatment technology.

As shown in figure 1, the newly developed vacuum low-pressure carburizing and high-pressure gas quenching technology makes up the defect, has the advantages of cleanness, high efficiency and precision, has the characteristics of flexible process control and wide application range, and provides a new feasible process path for obtaining the dispersed and distributed fine carbides.

However, the vacuum low-pressure carburization high-pressure gas quenching technology in the prior art still has the defects of long process time, high equipment operation cost, poor product surface performance, large deformation and the like.

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 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 carbide precipitation and spheroidization stage and a quenching stage;

the pulse carburizing stage is a high-concentration carburizing process with multiple alternation of carburizing and diffusing, wherein the carburizing gas is filled into the carburizing chamber in a pulse mode, the carbon concentration gradient of the surface layer of the workpiece is adjusted by the carburizing and diffusing time, and the carbon content of the surface is close to the maximum solubility of carbon in austenite at the carburizing temperature;

the carbide precipitation and spheroidization stage comprises the following steps: after the carburization is finished, stopping heating, immediately filling nitrogen with set pressure, rapidly cooling the surface of the workpiece to be above an Ac1 line, preserving heat, rapidly precipitating carbide in austenite grains, inhibiting diffusion of alloy elements and alloy carbide, reducing the diffusion rate of carbon atoms, and improving the form of the carbide;

and the quenching stage is high-pressure gas quenching or oil quenching.

Compared with the prior art, the vacuum carburization method for obtaining the dispersed fine carbides, provided by the invention, has the advantages that the required carbon concentration gradient curve is obtained by adjusting the time of multiple alternation of carburization/diffusion in the pulse carburization stage, so that the carbon content of the surface is increased; in the carbide precipitation and spheroidization stage, the surface layer of the workpiece is rapidly cooled through inflation, so that the carbide is precipitated in austenite grains, and the diffusion of the carbide is inhibited to form dispersion distribution; the deformation of the workpiece is reduced to the maximum extent through the control of the cooling speed in the quenching stage. The method has the advantages of short process time, high carburizing efficiency, low equipment operation cost, excellent product surface performance and small deformation.

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 vacuum carburizing method for obtaining finely dispersed carbides according to an 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 carbide precipitation and spheroidization stage and a quenching stage;

the pulse carburizing stage is a high-concentration carburizing process with multiple alternation of carburizing and diffusing, wherein the carburizing gas is filled into the carburizing chamber in a pulse mode, the carbon concentration gradient of the surface layer of the workpiece is adjusted by the carburizing and diffusing time, and the carbon content of the surface is close to the maximum solubility of carbon in austenite at the carburizing temperature;

the carbide precipitation and spheroidization stage comprises the following steps: after the carburization is finished, stopping heating, immediately filling nitrogen with set pressure, rapidly cooling the surface of the workpiece to be above an Ac1 line, preserving heat, rapidly precipitating carbide in austenite grains, inhibiting diffusion of alloy elements and alloy carbide, reducing the diffusion rate of carbon atoms, and improving the form of the carbide;

and the quenching stage is high-pressure gas quenching or 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 1-1.5%.

And in the carbide precipitation and spheroidization stage, nitrogen is filled into the heating chamber or the oil quenching chamber, the pressure is 0.5-6 multiplied by 105Pa, the time interval between gas filling and heating stopping is within 15s, and the heat preservation time with the temperature reduction temperature above the Ac1 line is 5-20 min.

The quenching stage comprises the following steps:

if a high-pressure gas quenching mode is adopted, the cooling speed in the quenching process is adjusted by controlling the gas quenching pressure and the rotating speed of the fan;

if the oil quenching mode is adopted, the cooling speed in the quenching process is adjusted through oil temperature setting, stirring or not and stirring frequency, and the deformation of the workpiece is reduced to the greatest extent by controlling the cooling speed.

In the pulse carburizing stage, acetylene or propane atmosphere is introduced under the vacuum condition, activated carbon atoms are diffused in solid under the high-temperature condition to form carbide, and the carbide is cooled to achieve surface hardening.

In summary, in the vacuum carburizing method for obtaining the dispersion-distributed fine carbides according to the embodiment of the present invention, the pulse carburizing stage is a high-concentration carburizing process in which carburizing/diffusion is alternated for multiple times, so as to form a required surface carbon concentration gradient; the carbide precipitation and spheroidization stage is to immediately inflate the workpiece surface to quickly cool the workpiece surface to a certain temperature above the Ac1 line and preserve heat for a period of time to promote the carbide to precipitate in austenite and form dispersion distribution, and simultaneously utilize the residual heat of the center to make the workpiece reach the quenching temperature. The process method gives consideration to the structure performance and the deformation, obtains the dispersedly distributed fine carbide with high carbon content (1-1.5 percent) on one hand, realizes 'external hardness and internal toughness', reduces quenching distortion on the other hand, and realizes size control. The method has the advantages of short process time, high carburizing efficiency, low equipment operation cost, excellent product surface performance and small deformation, and furthest exerts the obdurability of the material, thereby improving the service performance of the workpiece.

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.

(2) Carbide precipitation and spheroidization stage: and determining the inflation pressure and the cooling temperature according to the material and the size of the workpiece, and compiling in a process curve. And after the pulse carburizing is finished, stopping heating, immediately filling nitrogen with the pressure of 0.5-6 multiplied by 105Pa, rapidly cooling the surface layer of the workpiece to a certain temperature above the Ac1 line, and preserving the heat for 5-20 min.

(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 parts such as high-end high-performance carburized gear parts, bearings and the like.

The invention relates to a vacuum carburization method for obtaining dispersed fine carbides, which obtains a required carbon concentration gradient curve by adjusting the time of multiple alternation of carburization/diffusion in a pulse carburization stage, and improves the carbon content of the surface; in the carbide precipitation and spheroidization stage, the surface layer of the workpiece is rapidly cooled through inflation, so that the carbide is precipitated in austenite grains, and the diffusion of the carbide is inhibited to form dispersion distribution; the deformation of the workpiece is reduced to the maximum extent through the control of the cooling speed in the quenching stage. The method has the advantages of short process time, high carburizing efficiency, low equipment operation cost, excellent product surface performance and small deformation, 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 carbide precipitation and spheroidization stage, after pulse carburizing is finished, heating is stopped, nitrogen with certain pressure is immediately filled, the surface of the workpiece is quickly reduced to about a certain temperature above an Ac1 line, heat preservation is carried out for a period of time, carbon atoms are precipitated in austenite grains, the diffusion of alloy elements and alloy carbides is inhibited, the diffusion rate of the carbon atoms is reduced, and the finely dispersed carbides are formed. Meanwhile, the workpiece reaches the quenching temperature by using the residual heat of the core part, the process time is shortened, and the heat treatment power consumption is reduced.

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 designs the times of carburization/diffusion alternation and the specific process time of each time according to the carbon concentration gradient curve required by a workpiece in the pulse carburization stage, and accurately controls the carbon content of the carburized layer; in the carbide precipitation and spheroidization stage, the surface of a workpiece is rapidly reduced to about a certain temperature above an Ac1 line by virtue of immediate aeration, so that the carbide is precipitated in austenite grains, and the diffusion of the carbide is inhibited to form dispersion distribution; the deformation of the workpiece is reduced to the maximum extent through the control of the cooling speed in the quenching stage. Martensite and retained austenite (grade 1-2) on the surface of the workpiece, a core structure (grade 1-2), hardness of more than 63HRC, and deformation amount of less than 0.15%. The method has the advantages of short process time, high carburizing efficiency, low equipment operation cost, excellent product surface performance and small deformation. The toughness of the material is exerted to the maximum extent, so that the service performance of the workpiece 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.