阅读说明：本技术 一种奥氏体不锈钢表面低温氮碳共渗的方法 (Method for low-temperature nitrocarburizing of austenitic stainless steel surface ) 是由 李丹 王伟 吴俊平 马景云 周海鹏 范祥森 刘小海 于 2020-05-29 设计创作，主要内容包括：本发明公开了一种奥氏体不锈钢表面低温氮碳共渗的方法,包括如下步骤：第一步：将奥氏体不锈钢进行固溶处理；第二步：将固溶处理后的奥氏体不锈钢放入真空加热炉中,且所述真空加热炉内放置可热分解的破膜剂,对炉内奥氏体不锈钢进行三段式破膜处理；第三步：待炉内破膜结束后,将所述真空加热炉温度升至430～450℃后,向所述真空加热炉内通入NH<Sub>3</Sub>与CO,且NH<Sub>3</Sub>以1～2L/min,CO以0.5～2L/min的速度通入所述真空加热炉内；且将炉内压力设置为70000～90000Pa,并进行低温氮碳共渗20～30h。解决了现有技术中,奥氏体不锈钢的硬度和耐磨性比较差的技术问题。(The invention discloses a method for low-temperature nitrocarburizing on the surface of austenitic stainless steel, which comprises the following steps: the first step is as follows: carrying out solution treatment on austenitic stainless steel; the second step is that: putting the austenitic stainless steel after the solution treatment into a vacuum heating furnace, placing a thermally decomposable film breaking agent in the vacuum heating furnace, and carrying out three-stage film breaking treatment on the austenitic stainless steel in the furnace; the third step: after the membrane breaking in the furnace is finished, raising the temperature of the vacuum heating furnace to 430-450 DEG CIntroducing NH into the vacuum heating furnace 3 With CO, and NH 3 Introducing CO into the vacuum heating furnace at a speed of 1-2L/min and 0.5-2L/min; and setting the pressure in the furnace to be 70000-90000Pa, and performing low-temperature nitrocarburizing for 20-30 h. The technical problem that the hardness and the wear resistance of the austenitic stainless steel are poor in the prior art is solved.)

1. A method for low-temperature nitrocarburizing on the surface of austenitic stainless steel is characterized by comprising the following steps:

the first step is as follows: carrying out solution treatment on austenitic stainless steel;

the second step is that: putting the austenitic stainless steel subjected to the solution treatment into a vacuum heating furnace, adding a thermally decomposable film breaking agent into the vacuum heating furnace, and performing three-stage film breaking treatment on the austenitic stainless steel in the furnace;

the third step: after the membrane breaking in the furnace is finished, raising the temperature of the vacuum heating furnace to 430-450 ℃, and introducing NH into the vacuum heating furnace₃With CO, and NH₃Introducing CO into the vacuum heating furnace at a speed of 1-2L/min and 0.5-2L/min; and setting the pressure in the furnace to be 70000-90000Pa, and performing low-temperature nitrocarburizing for 20-30 h.

2. The method for low-temperature nitrocarburizing on the surface of austenitic stainless steel according to claim 1, wherein the temperature of the vacuum heating furnace is 420-440 ℃ when the low-temperature nitrocarburizing is performed in the third step.

3. The method for low-temperature nitrocarburizing of the surface of austenitic stainless steel according to claim 1, wherein, in the third step of low-temperature nitrocarburizing, after the temperature of the vacuum heating furnace is raised to 440 ℃, NH is introduced into the vacuum heating furnace₃With CO, and NH₃Introducing CO into the vacuum heating furnace at the speed of 1L/min and 2L/min; and the pressure in the furnace is set to 85000Pa, and low-temperature nitrocarburizing treatment is carried out for 30 h.

4. The method of austenitic stainless steel surface low temperature nitrocarburizing according to claim 1, wherein the three-stage rupture of the membrane comprises:

firstly, before membrane breaking, filling nitrogen into the vacuum heating furnace to enable the pressure in the vacuum heating furnace to reach 2000Pa, adjusting the temperature to 120-250 ℃, and preserving heat for 1-2 hours to enable the membrane breaking agent to be primarily decomposed;

in the second stage, after the first stage is finished, adjusting the temperature in the vacuum heating furnace to 300-400 ℃, and preserving heat for 2-5 hours, wherein the pressure in the vacuum heating furnace reaches 90000-100000 Pa, so that the film breaking agent is further fully decomposed;

and in the third stage, adjusting the temperature in the vacuum heating furnace to 120-250 ℃, preserving the heat for 1-2 hours, and fully removing the passive film on the surface of the austenitic stainless steel.

5. The method of austenitic stainless steel surface low temperature nitrocarburizing according to claim 4, said three-stage rupture of membranes comprising:

firstly, before membrane breaking, nitrogen is filled into the vacuum heating furnace to ensure that the pressure in the vacuum heating furnace reaches 2000Pa, the temperature is adjusted to 150-250 ℃, and heat preservation is carried out for 2 hours to ensure that the membrane breaking agent is primarily decomposed;

a second stage, after the first stage is finished, adjusting the temperature in the vacuum heating furnace to 330-400 ℃, and preserving heat for 4 hours, wherein the pressure in the vacuum heating furnace reaches 95000Pa, so that the film breaking agent is further fully decomposed;

and in the third stage, adjusting the temperature in the vacuum heating furnace to 250 ℃, and preserving the heat for 1.5 hours to fully remove the passive film on the surface of the austenitic stainless steel.

6. The method for low-temperature nitrocarburizing on the surface of austenitic stainless steel according to claim 1, wherein the solution treatment adopts a vacuum gas quenching furnace, the temperature in the vacuum gas quenching furnace is adjusted to 1050-1150 ℃, the temperature is kept for 3-5 h, and after the temperature is kept, nitrogen is introduced into the vacuum gas quenching furnace, and the gas quenching is carried out at the pressure of 5-8 bar.

7. The method of austenitic stainless steel surface low temperature nitrocarburizing according to claim 1, further comprising:

the fourth step: and carrying out surface post-treatment on the austenitic stainless steel after the third step is finished.

8. The method of low temperature nitrocarburizing of an austenitic stainless steel surface according to claim 7, wherein the surface post-treatment employs an electropolishing treatment.

9. The method of low temperature nitrocarburizing of an austenitic stainless steel surface according to claim 8, wherein the electropolishing treatment process comprises: adjusting the temperature of the electrolytic polishing solution to 50-70 ℃, the voltage of 5-9V and the current of 0.5-3A/dm²The electrolysis time is 5-15 min; the electrolytic polishing solution comprises 50-55% of phosphoric acid, 42-46% of sulfuric acid and 3% of trimethylol pentanol polyoxyethylene polyoxypropylene ether.

10. The method of low temperature nitrocarburizing of an austenitic stainless steel surface according to claim 9, wherein the electropolishing treatment process comprises: adjusting the temperature of the electrolytic polishing solution to 65 ℃, the voltage of the electrolytic polishing solution is 9V, and the current of the electrolytic polishing solution is 2A/dm²The electrolysis time is 12 min; wherein the components of the electrolytic polishing solution comprise 52% of phosphoric acid, 46% of sulfuric acid and 3% of trimethylol pentanol polyoxyethylene polyoxypropylene ether.

Technical Field

The invention belongs to the technical field of metal surface treatment, and particularly relates to a low-temperature nitrocarburizing method for the surface of austenitic stainless steel.

Background

Austenitic stainless steel has excellent corrosion resistance, and is increasingly applied to the industries of medical instruments, petrochemical engineering, ocean engineering, transportation and the like. Because the austenitic stainless steel has low carbon content which is less than or equal to 0.03 percent generally, the hardness of the austenitic stainless steel cannot be enhanced through conventional heat treatment, the frictional wear resistance is poor, and the application of the austenitic stainless steel in the industries is limited to a great extent, so that domestic and foreign scholars make a great deal of research on the surface hardening treatment of the austenitic stainless steel.

At present, austenitic stainless steel can obtain good hardness and wear resistance mainly by using an ion nitriding method. However, when the conventional high temperature (t > 450 ℃) ion nitriding is used to perform surface nitriding treatment on austenitic stainless steel, a thicker nitrided layer can be obtained to ensure the wear resistance of the austenitic stainless steel surface, but the high temperature causes precipitation of chromium-containing nitride, which causes chromium depletion of the stainless steel matrix and deterioration of the corrosion resistance.

Disclosure of Invention

The invention aims to provide a method for low-temperature nitrocarburizing on the surface of austenitic stainless steel so as to solve the technical problems of uneven hardness and poor wear resistance of austenitic stainless steel in the prior art.

In order to realize the purpose, the invention adopts the following technical scheme:

a method for low-temperature nitrocarburizing on the surface of austenitic stainless steel comprises the following steps:

the first step is as follows: carrying out solution treatment on austenitic stainless steel;

the second step is that: putting the austenitic stainless steel subjected to solution treatment into a vacuum heating furnace, placing a decomposable film breaking agent in the vacuum heating furnace, and performing three-section film breaking treatment on the austenitic stainless steel in the furnace;

the third step: after the membrane breaking in the furnace is finished, raising the temperature of the vacuum heating furnace to 430-450 ℃, and introducing NH into the vacuum heating furnace₃Introducing NH3 into the vacuum heating furnace at a speed of 1-2L/min and CO at a speed of 0.5-2L/min; and setting the pressure in the furnace to be 70000-90000Pa, and performing low-temperature nitrocarburizing for 20-30 h. Preferably, when the low-temperature nitrocarburizing is carried out in the third step, the temperature of the vacuum heating furnace is 420-440 ℃.

Preferably, when the low-temperature nitrocarburizing is performed in the third step, after the temperature of the vacuum heating furnace is raised to 440 ℃, NH is introduced into the vacuum heating furnace₃With CO, and NH₃Introducing CO into the vacuum heating furnace at the speed of 1L/min and 2L/min; and the pressure in the furnace is set to 85000Pa, and low-temperature nitrocarburizing is carried out for 30 h.

Preferably, the three-stage membrane rupture includes:

firstly, before membrane breaking, filling nitrogen into the vacuum heating furnace to enable the pressure in the vacuum heating furnace to reach 2000Pa, adjusting the temperature to 120-250 ℃, and preserving heat for 1-2 hours to enable the membrane breaking agent to be primarily decomposed;

in the second stage, after the first stage is finished, adjusting the temperature in the vacuum heating furnace to 300-400 ℃, and preserving heat for 2-5 hours, wherein the pressure in the vacuum heating furnace reaches 90000-100000 Pa, so that the film breaking agent is further fully decomposed;

and in the third stage, adjusting the temperature in the vacuum heating furnace to 120-250 ℃, preserving the heat for 1-2 hours, and fully removing the passive film on the surface of the austenitic stainless steel.

Preferably, the three-stage membrane rupture includes:

firstly, introducing nitrogen into the vacuum heating furnace before film breaking to ensure that the pressure in the vacuum heating furnace reaches 2000Pa, adjusting the temperature to 250 ℃, and preserving heat for 2 hours to ensure that the film breaking agent is preliminarily decomposed;

a second stage, after the first stage is finished, adjusting the temperature in the vacuum heating furnace to 400 ℃, and preserving heat for 4 hours, wherein the pressure in the vacuum heating furnace reaches 95000Pa, so that the film breaking agent is further fully decomposed;

and in the third stage, adjusting the temperature in the vacuum heating furnace to 250 ℃, and preserving the heat for 1.5 hours to fully remove the passive film on the surface of the austenitic stainless steel.

Preferably, the solid solution treatment is performed by using a vacuum gas quenching furnace, the temperature in the vacuum gas quenching furnace is adjusted to 1050-1150 ℃, the temperature is kept for 3-5 hours, and after the heat preservation is finished, nitrogen is introduced into the vacuum gas quenching furnace, and the gas quenching is performed at the pressure of 5-8 bar.

Preferably, the method further comprises the following steps:

the fourth step: and carrying out surface post-treatment on the austenitic stainless steel after the third step is finished.

Preferably, the surface post-treatment is an electrolytic polishing treatment.

Preferably, the electrolytic polishing treatment process comprises: adjusting the temperature of the electrolytic polishing solution to 50-70 ℃, the voltage is 5-9V, the current is 0.5-3A/dm 2, and the electrolytic time is 5-15 min; the electrolytic polishing solution comprises 50-55% of phosphoric acid, 42-46% of sulfuric acid and 3% of trimethylol pentanol polyoxyethylene polyoxypropylene ether.

Preferably, the electrolytic polishing treatment process comprises: adjusting the temperature of the electrolytic polishing solution to 65 ℃, the voltage is 9V, the current is 2A/dm2, and the electrolytic time is 12 min; wherein the components of the electrolytic polishing solution comprise 52% of phosphoric acid, 46% of sulfuric acid and 3% of trimethylol pentanol polyoxyethylene polyoxypropylene ether.

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

the method comprises the steps of performing low-temperature nitrocarburizing treatment on the surface of the austenitic stainless steel, forming nitrogen or carbon rich on the surface of the austenitic stainless steel by permeating nitrogen and carbon atoms, keeping the original austenite phase structure, and avoiding a surface uniform hardened layer separated from chromium nitride and chromium carbide. Firstly, carrying out solid solution treatment on the surface of austenitic stainless steel, then putting the austenitic stainless steel after the solid solution treatment into a vacuum heating furnace, placing a decomposable film breaking agent in the vacuum heating furnace, carrying out three-stage film breaking treatment on the austenitic stainless steel in the furnace, and carrying out the three-stage film breaking treatment on the austenitic stainless steel in the furnace, so that a passivation film on the surface of the austenitic stainless steel is completely removed, and nitrogen atoms and carbon atoms can smoothly enter during the subsequent low-temperature nitrocarburizing treatment. After the membrane rupture in the furnace is finished, low-temperature nitrocarburizing treatment is carried out in the same vacuum heating furnace, so that the austenitic stainless steel is prevented from contacting oxygen in the air after the membrane rupture; therefore, by the preparation method, nitrogen or carbon with uniform thickness is formed on the surface of the austenitic stainless steel, the original austenite phase structure is kept, and the surface of the austenitic stainless steel is free of a surface hardening layer formed by precipitation of chromium nitride and chromium carbide, so that the treated austenitic stainless steel has excellent wear resistance and corrosion resistance. Solves the technical problems of uneven hardness and poorer wear resistance of austenitic stainless steel in the prior art.

Drawings

FIG. 1 is a metallographic picture of the sample of example 1 of the present invention;

FIG. 2 is a metallographic picture of the sample of example 2 of the present invention;

FIG. 3 is a metallographic picture of the sample in example 3 of the present invention;

FIG. 4 is a metallographic picture taken in accordance with example 4 of the present invention;

FIG. 5 is a metallographic picture taken in accordance with example 5 of the present invention;

FIG. 6 is a metallographic picture taken in accordance with example 6 of the present invention;

FIG. 7 is a metallographic picture taken in accordance with example 7 of the present invention;

FIG. 8 is a metallographic picture taken in accordance with example 8 of the present invention;

FIG. 9 is a metallographic picture 1 of the surface of austenitic stainless steel obtained by rupture of the film outside the comparative example;

FIG. 10 is a metallographic picture 2 of the surface of austenitic stainless steel obtained by rupture of the film outside the comparative example;

FIG. 11 is a metallographic picture of the surface of austenitic stainless steel obtained by rupture of a film in a furnace according to the present invention;

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

According to the invention, the surface of the austenitic stainless steel is subjected to low-temperature nitrocarburizing treatment, so that a nitrogen or carbide layer with a certain thickness and uniform thickness is formed on the surface of the austenitic stainless steel. The processing method mainly comprises three steps: firstly, carrying out solution treatment on austenitic stainless steel; secondly, putting the austenitic stainless steel subjected to the solution treatment into a vacuum heating furnace, putting a decomposable film breaking agent into the vacuum heating furnace, and performing three-stage film breaking treatment on the austenitic stainless steel in the furnace; thirdly, after the film breaking in the vacuum heating furnace is finished, raising the temperature of the vacuum heating furnace to 400-450 ℃, and introducing NH into the vacuum heating furnace₃With CO, and NH₃Introducing CO into the vacuum heating furnace at a speed of 1-2L/min and 0.5-2L/min; and setting the pressure in the furnace to be 70000-90000Pa, and performing low-temperature nitrocarburizing for 15-30 h.

Specifically, in the first step, when the austenitic stainless steel is subjected to solution treatment, the adopted equipment is a vacuum gas quenching furnace, the temperature is heated to 1050-1150 ℃, heat preservation is carried out for 3-5 hours, nitrogen is introduced for gas quenching after the heat preservation is finished, and the nitrogen pressure is 5-8 bar.

And secondly, performing membrane rupture treatment on the austenitic stainless steel. Specifically, the austenitic stainless steel after the solution treatment is placed in a vacuum heating furnace, a decomposable film breaking agent is placed in the vacuum heating furnace, the film breaking agent can be one or a mixture of chloride or fluoride, the furnace is vacuumized until the vacuum degree in the furnace is less than or equal to 10Pa, nitrogen is introduced to 90000Pa, the vacuumizing and the nitrogen filling are repeated for 3 times, oxygen in the vacuum heating furnace is fully diluted and discharged, and the situation that the oxygen in the vacuum heating furnace secondarily oxidizes the austenitic stainless steel after the film breaking to influence the subsequent low-temperature hardening treatment is avoided. Specifically, the austenitic stainless steel in the vacuum heating furnace is subjected to three-stage film breaking treatment, so that a passivation film with a compact surface of the austenitic stainless steel is completely removed, and nitrogen atoms and carbon atoms can smoothly enter during subsequent low-temperature nitrocarburizing treatment.

More specifically, the three-stage rupture of membranes includes: firstly, before membrane breaking, nitrogen is flushed into the vacuum heating furnace, so that the pressure in the vacuum heating furnace reaches 2000Pa, the temperature is adjusted to 120-250 ℃, and heat preservation is carried out for 1-2 hours, so that the membrane breaking agent is subjected to preliminary decomposition; in the second stage, after the first stage is finished, adjusting the temperature in the vacuum heating furnace to 300-400 ℃, and preserving heat for 2-5 hours, wherein the pressure in the vacuum heating furnace reaches 90000-100000 Pa, so that the film breaking agent is further fully decomposed; and in the third stage, adjusting the temperature in the vacuum heating furnace to 120-250 ℃, preserving the heat for 1-2 hours, and fully removing the passive film on the surface of the austenitic stainless steel. Therefore, by adopting the three-stage film breaking method, the compact passivation film on the surface of the austenitic stainless steel in the furnace is completely removed after the film breaking in the third stage is finished, and nitrogen atoms and carbon atoms can smoothly enter the furnace during the subsequent low-temperature nitrocarburizing treatment.

And thirdly, after the membrane breaking in the furnace is finished, performing low-temperature nitrocarburizing treatment in the same vacuum heating furnace, thereby avoiding the contact of the austenitic stainless steel after the membrane breaking and oxygen in the air. Specifically, the temperature in the vacuum heating furnace is raised to 430-450 ℃, then low-temperature nitrocarburizing treatment is carried out, and the temperature control accuracy of the adopted equipment is +/-2 ℃. Meanwhile, low-temperature nitrocarburizing treatment is adopted, so that the phenomenon that the corrosion resistance of the austenitic stainless steel is influenced by chromium nitride or chromium carbide separated out from the surface due to overhigh temperature is avoided. Introducing NH into the vacuum heating furnace₃With CO, and NH₃Introducing CO into the vacuum heating furnace at a speed of 1-2L/min and 0.5-2L/min; and setting the pressure in the furnace to be 70000-90000Pa, and performing low-temperature nitrocarburizing for 15-30 h. The equipment adopts automatic control pressure control, the pressure in the furnace is set to be 70000-90000Pa, and the activity of the atmosphere in the furnace is ensured. And after the low-temperature nitrocarburizing is finished, opening the outer fan to cool and discharge.

Further, the method also comprises a fourth step of carrying out surface post-treatment on the surface of the austenitic stainless steel. Specifically, the austenitic stainless steel after low-temperature nitrocarburizing treatment is subjected to electrolytic polishing to remove non-S phases with the surface of 2-3 um. The electrolytic polishing solution comprises 50-55% of phosphoric acid, 42-46% of sulfuric acid and 3% of trimethylol pentanol polyoxyethylene polyoxypropylene ether. The temperature of the electrolyte is 50-70 ℃, the voltage is 5-9V, and the current is 0.5-3A/dm²The electrolysis time is 5-15 min, the metal bright color is recovered on the surface of the austenitic stainless steel after the electrolytic polishing treatment, the S phase is uniform and continuous, the S phase is not fractured, the salt spray resistance test time of the austenitic stainless steel after the electrolytic polishing is more than or equal to 500h, and the austenitic stainless steel has excellent corrosion resistance

In order to better illustrate a method for low-temperature nitrocarburizing the surface of austenitic stainless steel, the following description will be given in detail with reference to comparative examples and examples.