CN111607759A - A kind of method for high pressure chromizing of austenitic stainless steel surface - Google Patents

Abstract

The invention discloses a method for high-pressure chromizing on the surface of austenitic stainless steel. The method comprises the following steps: 1. grinding, cleaning and drying the austenitic stainless steel step by step; 2. placing the austenitic stainless steel in a The center of the chromed tank is filled with a chromizing agent, and the chromed tank is covered to obtain a filled chromed tank; 3. The filled chromed tank is subjected to chromizing treatment to obtain a surface with chromizing layer of austenitic stainless steel. The invention provides a stronger driving force for active chromium atoms by performing chromizing treatment on austenitic stainless steel under high pressure conditions, improves the diffusion rate of active chromium atoms generated by the reaction, and thus increases the thickness and thickness of the chromizing layer. The chromizing rate improves the production efficiency of the chromizing treatment, and the chromizing agent will not agglomerate after the chromizing treatment, which reduces the workload of taking out. The structure of the chromed layer is uniform and dense, and the surface hardness is high.

Description

A kind of method for high pressure chromizing of austenitic stainless steel surface

technical field

The invention belongs to the technical field of preparation of stainless steel surface hardening coatings, in particular to a method for high-pressure chromizing on the surface of austenitic stainless steel.

Background technique

Austenitic stainless steel is a stainless steel with an austenitic structure at room temperature. When it contains about 18% of Cr, about 8% to 10% of Ni, and about 0.1% of C, it has a stable austenite structure. Austenitic stainless steel has high toughness and plasticity, but low strength. Austenitic stainless steel is the most important type of stainless steel. This type of stainless steel has excellent corrosion resistance, non-magnetic properties and biocompatibility. It has little response to temperature changes, and its production and usage account for about 70% of the total production and usage of stainless steel. It is widely used in chemical, marine, petrochemical, instrument manufacturing, food biology, medicine and other industries. Although austenitic stainless steels are widely used, there are still some challenges that need to be overcome. Its corrosion resistance requires a very low carbon content (the carbon content is generally less than 0.03%), so that the intergranular corrosion resistance can be significantly improved; its performance is determined by its unique structure, and its surface properties cannot be strengthened through phase transformation. The characteristics of these austenitic stainless steels lead to low hardness (200HV5 ~ 250HV5) in practical application, extremely soft surface, difficult to withstand friction damage, and poor wear resistance, which restricts the application of severe friction environment under special working conditions.

In order to improve the hardness of austenitic stainless steel, the usual practice is to protect the surface, strengthen the surface by chemical heat treatment methods such as nitriding, carburizing or chromizing, and keep the hardness of the core unchanged, which can greatly improve the surface hardness. The wear resistance has also been greatly improved. The nitriding and carburizing with the precipitation of Cr carbon and nitrogen compounds, the surface corrosion resistance is significantly reduced, and the thickness of the obtained coating is thin, which is difficult to meet the harsh conditions. Using, and chromizing can get a thicker layer, which can meet the requirements of complex working conditions.

At present, the existing invention patents and the chromizing process used in the thesis have a low rate of formation of layers or the thickness of the obtained layer is relatively thin. The patent with publication number CN101168833A discloses a solid-state chromizing process. The thickness of the infiltrated layer obtained by the process of chromizing for 3h to 6h is 10 μm to 20 μm, and the average growth rate of the infiltrated layer is about 3 μm/h; the patent with publication number CN105177596A discloses a tool steel gas chromizing and quenching combined process, the process The thickness of the infiltrated layer obtained by holding for 10h is 10 μm～20 μm, and the average growth rate of the infiltrated layer is about 1 μm/h～2 μm/h.

Chromizing in the prior art mainly enriches the surface of stainless steel by active chromium atoms, which produces a concentration difference with the interior of the stainless steel, thereby providing a diffusion driving force for the penetration of active chromium atoms into the stainless steel, but this diffusion driving force is often small. , resulting in the long time of chromizing and the shortage of low thickness of chromizing layer. Therefore, there is a need for a chromizing method that can improve the driving force for the diffusion of active chromium atoms.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a method for high-pressure chromizing on the surface of austenitic stainless steel in view of the above-mentioned deficiencies of the prior art. The method provides a stronger driving force for the active chromium atoms to the direction of the austenitic stainless steel in the chromizing treatment by chromizing the austenitic stainless steel under high pressure conditions, and improves the diffusion rate of the active chromium atoms generated by the reaction. , so that the active chromium atoms enriched on the surface of the austenitic stainless steel can more easily penetrate into the austenitic stainless steel, thereby increasing the thickness of the chromizing layer and the chromizing rate, and improving the production efficiency of the chromizing treatment.

In order to solve the above-mentioned technical problems, the technical solution provided by the present invention is: a method for high-pressure chromizing on the surface of austenitic stainless steel, the method comprises the following steps:

Step 1: Grinding, cleaning and drying the austenitic stainless steel step by step;

Step 2: Put the austenitic stainless steel that has been dried in the first step into the center of the chromizing tank, fill the chromizing tank with a chromizing agent, and then cover the chromizing tank to obtain a filled chromed tank;

Step 3: Perform chromizing treatment on the chromed tank after filling in step 2 to obtain austenitic stainless steel with a chromizing layer on the surface; the process of chromizing treatment is as follows: chromizing the filled chrome tank After being placed in the resistance furnace, high-purity Ar gas was introduced into the resistance furnace to make the pressure in the resistance furnace reach 0.15MPa~0.40MPa, then the temperature was raised to 1050℃~1120℃, and then kept for 10h~20h, and then cooled to room temperature. Austenitic stainless steel with a chromed layer on the surface is obtained in the chrome tank; the thickness of the chromed layer is 90 μm˜220 μm.

The invention removes the oxide scale and other impurities on the surface of the austenitic stainless steel by grinding, cleaning and drying the austenitic stainless steel step by step, ensures that the surface of the austenitic stainless steel is smooth and clean, and is beneficial to the active chromium atoms in the austenitic stainless steel. The surface of the austenitic stainless steel is enriched, so as to ensure the smooth progress of the chromizing treatment; in the present invention, the austenitic stainless steel is put into the chromizing tank, filled and capped with the chromizing agent, so that the austenitic stainless steel and the chromizing agent are In the same small space, the chromium halide gas generated by the subsequent chromizing treatment reaction can fully contact the austenitic stainless steel, which ensures the smooth progress of the chromizing reaction and prevents the chromizing agent from entering the mechanical pump during subsequent vacuuming. The pump body is damaged; the high-purity Ar gas is introduced into the chromizing treatment to prevent the austenitic stainless steel from being oxidized and ensure the smooth progress of the chromizing reaction. By controlling the pressure, temperature and holding time in the resistance furnace, the In the chromizing treatment, the active chromium atoms provide a stronger driving force to the direction of the austenitic stainless steel, which increases the diffusion rate of the active chromium atoms generated by the reaction, and makes the active chromium atoms enriched on the surface of the austenitic stainless steel easier to penetrate into the stainless steel. In austenitic stainless steel, the thickness of the chromizing layer and the chromizing rate are increased, and at the same time, the austenitic stainless steel has a suitable grain structure, which prevents the grains from being too coarse due to excessive temperature, and the mechanical properties of austenitic stainless steel. The deficiency of performance reduction prevents the deficiency of low reaction efficiency caused by too low temperature, avoids the deficiency of low chromizing efficiency caused by too small pressure, and avoids the deficiency of unbearable resistance of the resistance furnace caused by too large pressure; The process parameters of the chromizing treatment ensure that the chromizing agent will not agglomerate after the chromizing treatment, reduce the workload of taking out the austenitic stainless steel with a chromizing layer on the surface, and improve the work efficiency.

The above-mentioned method for high-pressure chromizing on the surface of austenitic stainless steel, characterized in that, the cleaning process described in step 1 is: ultrasonically sonicating the austenitic stainless steel that has been polished step by step in an acetone solution and an ethanol solution in turn. the ultrasonic time is 10min-30min; the mass fraction of the acetone solution is 50%-65%, and the mass fraction of the ethanol solution is 75%-99%. The invention completely removes the impurities on the surface of the austenitic stainless steel by performing ultrasonic waves in the acetone solution and the ethanol solution, ensures that the surface of the austenitic stainless steel is smooth and clean, is conducive to the enrichment of active chromium atoms on the surface of the austenitic stainless steel, and realizes The chromizing treatment can be carried out smoothly; the invention adopts the acetone solution and the ethanol solution of the mass fraction, which has the advantages of cheap and easy to obtain.

The above-mentioned method for high-pressure chromizing on the surface of austenitic stainless steel is characterized in that the chromizing agent in step 2 is mixed with the following raw materials by mass percentage: 50% of chromium, 48% of aluminum oxide, 2% of ammonium chloride %. The chromizing agent used in the present invention has the advantages of good chromizing effect, low cost and easy availability.

The above-mentioned method for high-pressure chromizing on the surface of austenitic stainless steel is characterized in that the mass purity of the high-purity Ar gas in step 3 is not less than 99.999%, and the temperature increase rate of heating and the cooling temperature in the chromizing treatment The rate is 3℃/min～10℃/min. By controlling the mass purity of the Ar gas, the present invention ensures that no other impurities are brought into the process of introducing the Ar gas, thereby avoiding the influence of impurities on the chromizing treatment; The temperature of the body stainless steel is uniform during the heating and cooling process, so that the whole austenitic stainless steel has the same temperature, thus ensuring that the chromed layer is evenly distributed on the surface of the austenitic stainless steel.

The above-mentioned method for high-pressure chromizing on the surface of austenitic stainless steel is characterized in that the surface hardness of the chromizing layer described in step 3 is greater than 500HV5. The surface hardness of the chromed layer of the austenitic stainless steel with the chromized layer on the surface of the invention is greater than 500HV5, which significantly improves the wear resistance of the base austenitic stainless steel.

Compared with the prior art, the present invention has the following advantages:

1. The present invention provides a stronger driving force for the active chromium atoms in the chromizing treatment to the austenitic stainless steel by performing chromizing treatment on the austenitic stainless steel under high pressure conditions, and improves the efficiency of the active chromium atoms generated by the reaction. The diffusion rate makes it easier for the active chromium atoms enriched on the surface of austenitic stainless steel to penetrate into the austenitic stainless steel, so that the thickness of the chromed layer reaches 90 μm to 220 μm, and the average chromed rate reaches 6 μm/h to 16 μm/h. , the production efficiency of chromizing treatment is improved, and the life of parts made of austenitic stainless steel with a chromizing layer on the surface is also significantly improved.

2. The chromed layer of the present invention is well combined with the interface of the austenitic stainless steel, the structure of the chromed layer is uniform and dense, the layers are distinct and the interface is continuous, and the coating has high hardness and good wear resistance.

3. The embedding method chromizing of the present invention is a mature and widely used preparation method, the process is simple, the performance is stable, the repeatability is good, and the chromizing agent will not agglomerate after the reaction, which reduces the work of taking out It is suitable for large-scale promotion and use.

The technical solutions of the present invention will be further described in detail below through the accompanying drawings and embodiments.

Description of drawings

FIG. 1 is an optical microscope view of the cross-section of the 316H austenitic stainless steel having a chromizing layer on the surface of Example 1 of the present invention after being corroded with aqua regia for 10 s.

2 is a schematic diagram of an energy spectrum line scan of a 316H austenitic stainless steel with a chromizing layer on the surface of Example 1 of the present invention.

3 is an X-ray diffraction diagram of a chromed layer of 316H austenitic stainless steel having a chromed layer on the surface of Example 1 of the present invention.

Detailed ways

Example 1

This embodiment includes the following steps:

Step 1. Use 180#, 400#, 1200# sandpaper to grind the 316H austenitic stainless steel step by step, then ultrasonically clean it in acetone solution with a mass fraction of 60% for 10 minutes, and then in an ethanol solution with a mass fraction of 99%. Ultrasonic cleaning for 10min, and then drying treatment;

Step 2: Put the 316H austenitic stainless steel that has been dried in the first step into the center of the chromizing tank, fill the chromizing tank with a chromizing agent, and then cover the chromizing tank to obtain the filling After the chromizing tank; the chromizing agent is mixed with the following raw materials by mass percentage: 50% of chromium, 48% of alumina, and 2% of ammonium chloride;

Step 3: Perform chromizing treatment on the filled chromizing tank in step 2 to obtain 316H austenitic stainless steel with a chromizing layer on the surface; the process of chromizing treatment is as follows: After the tank was placed in the resistance furnace, Ar gas with a mass purity of 99.999% was introduced into the resistance furnace to make the pressure in the resistance furnace reach 0.15MPa, and then heated to 1090 °C at a heating rate of 10 °C/min, and then kept for 15 hours. The cooling rate of 10°C/min was cooled to room temperature, and a 316H austenitic stainless steel with a chromizing layer on the surface was obtained in the chromizing tank.

After testing, the thickness of the 316H austenitic stainless steel with a chromizing layer on the surface of this example is 100 μm, the hardness is 570HV5, and the average chroming rate is 8 μm/h. Austenitic stainless steel is well bonded without cracks and spalling.

Fig. 1 is an optical microscope view of the cross-section of the 316H austenitic stainless steel with a chromizing layer on the surface of the present embodiment after being corroded by aqua regia for 10s. It can be seen from Fig. 1 that the chromizing layer in this embodiment has clear layers and a continuous interface. , the thickness of the chromed layer is 100 μm.

The 316H austenitic stainless steel with chromizing layer on the surface of this example was observed with a scanning electron microscope, and a scanning electron microscope image was obtained, and then EDS line scanning was performed on the basis of the scanning electron microscope image, and Figure 2 was obtained. It can be seen from Fig. 2 that the chromium element content in the chromizing layer of the 316H austenitic stainless steel with a chromizing layer on the surface of the present embodiment is very high and evenly distributed, and the contents of other elements such as carbon, nickel, molybdenum and manganese are relatively low , has no effect on the characterization of the chromed layer.

Fig. 3 is the X-ray diffraction diagram of the chromed layer of the 316H austenitic stainless steel with a chromed layer on the surface of this embodiment. It can be seen from Fig. 3 that the main phase in the chromed layer of this embodiment is Cr ₂₃ Phase C ₆ .

Comparative Example 1

This comparative example includes the following steps:

Step 1. Use 180#, 400#, 1200# sandpaper to grind the 316H austenitic stainless steel step by step, then ultrasonically clean it in acetone solution with a mass fraction of 60% for 10 minutes, and then in an ethanol solution with a mass fraction of 99%. Ultrasonic cleaning for 10min, and then drying treatment;

Step 2: Put the 316H austenitic stainless steel that has been dried in the first step into the center of the chromizing tank, fill the chromizing tank with a chromizing agent, and then cover the chromizing tank to obtain the filling After the chromizing tank; the chromizing agent is mixed with the following raw materials by mass percentage: 50% of chromium, 48% of alumina, and 2% of ammonium chloride;

Step 3: Perform chromizing treatment on the filled chromizing tank in step 2 to obtain 316H austenitic stainless steel with a chromizing layer on the surface; the process of chromizing treatment is as follows: After the tank is placed in the resistance furnace, Ar gas with a mass purity of 99.999% is introduced into the resistance furnace to make the pressure in the resistance furnace reach 0.1MPa, and then heated to 1090 °C at a heating rate of 10 °C/min, and then kept for 15 hours. The cooling rate of 10°C/min was cooled to room temperature, and a 316H austenitic stainless steel with a chromizing layer on the surface was obtained in the chromizing tank.

After testing, the thickness of the chromizing layer of the 316H austenitic stainless steel with a chromizing layer on the surface of this comparative example is 30 μm, the hardness is 380HV5, and the average chromizing rate is 2 μm/h. Cracks, loose and brittle.

It can be seen from the comparison between Comparative Example 1 and Example 1 that when the pressure in the chromizing treatment is less than 0.15MPa, the thickness of the obtained chromizing layer is small, the chromizing rate is slow, and many cracks appear on the surface of the chromizing layer, which is relatively Loose and crisp.

Example 2

This embodiment includes the following steps:

Step 1. Use 180#, 400#, 1200# sandpaper to polish the 316L austenitic stainless steel step by step, then ultrasonically clean it in acetone solution with a mass fraction of 50% for 10 minutes, and then clean it in an ethanol solution with a mass fraction of 80%. Ultrasonic cleaning for 10min, and then drying treatment;

Step 2: Put the 316L austenitic stainless steel dried in the first step into the center of the chromizing tank, fill the chromizing tank with a chromizing agent, and then cover the chromizing tank to get the filling After the chromizing tank; the chromizing agent is mixed with the following raw materials by mass percentage: 50% of chromium, 48% of alumina, and 2% of ammonium chloride;

Step 3: Perform chromizing treatment on the filled chromizing tank in step 2 to obtain 316L austenitic stainless steel with a chromizing layer on the surface; the process of chromizing treatment is as follows: After the tank is placed in the resistance furnace, Ar gas with a mass purity of 99.999% is introduced into the resistance furnace to make the pressure in the resistance furnace reach 0.20MPa, and then heated to 1050 °C at a heating rate of 5 °C/min, and then kept for 15 hours. The cooling rate of 5°C/min was cooled to room temperature, and a 316L austenitic stainless steel with a chromizing layer on the surface was obtained in the chromizing tank.

After testing, the thickness of the 316L austenitic stainless steel with a chromizing layer on the surface of this example is 90 μm, the hardness is 580HV5, and the average chroming rate is 6 μm/h. Austenitic stainless steel is well bonded without cracks and spalling.

Example 3

This embodiment includes the following steps:

Step 1. Use 180#, 400#, 1200# sandpaper to grind 316H austenitic stainless steel step by step, then ultrasonically clean it in 65% acetone solution for 10 minutes, and then use 75% ethanol solution Medium ultrasonic cleaning for 20min, and then drying treatment;

Step 2: Put the 316H austenitic stainless steel that has been dried in the first step into the center of the chromizing tank, fill the chromizing tank with a chromizing agent, and then cover the chromizing tank to obtain the filling After the chromizing tank; the chromizing agent is mixed with the following raw materials by mass percentage: 50% of chromium, 48% of alumina, and 2% of ammonium chloride;

Step 3: Perform chromizing treatment on the filled chromizing tank in step 2 to obtain 316H austenitic stainless steel with a chromizing layer on the surface; the process of chromizing treatment is as follows: After the tank was placed in the resistance furnace, Ar gas with a mass purity of 99.999% was introduced into the resistance furnace to make the pressure in the resistance furnace reach 0.40MPa, and then heated to 1120 °C at a heating rate of 3 °C/min, and then kept for 20 hours. The cooling rate of 3°C/min was cooled to room temperature, and a 316H austenitic stainless steel with a chromizing layer on the surface was obtained in the chromizing tank.

After testing, the thickness of the 316H austenitic stainless steel with a chromizing layer on the surface of this example is 220 μm, the hardness is 550HV5, and the average chroming rate is 16 μm/h. The austenitic stainless steel is well bonded without cracks and spalling.

The above descriptions are only preferred embodiments of the present invention, and do not limit the present invention in any way. Any simple modifications, changes and equivalent changes made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solutions of the present invention.

Claims (5)

1. a method for high pressure chromizing of austenitic stainless steel surface, is characterized in that, this method comprises the following steps: Step 1: Grinding, cleaning and drying the austenitic stainless steel step by step; Step 2: Put the austenitic stainless steel that has been dried in the first step into the center of the chromizing tank, fill the chromizing tank with a chromizing agent, and then cover the chromizing tank to obtain a filled chromed tank; Step 3: Perform chromizing treatment on the chromed tank after filling in step 2 to obtain austenitic stainless steel with a chromizing layer on the surface; the process of chromizing treatment is as follows: chromizing the filled chrome tank After being placed in the resistance furnace, high-purity Ar gas was introduced into the resistance furnace to make the pressure in the resistance furnace reach 0.15MPa~0.40MPa, then the temperature was raised to 1050℃~1120℃, and then kept for 10h~20h, and then cooled to room temperature. Austenitic stainless steel with a chromed layer on the surface is obtained in the chrome tank; the thickness of the chromed layer is 90 μm˜220 μm. 2. the method for a kind of high pressure chromizing of austenitic stainless steel surface according to claim 1, is characterized in that, the process of cleaning described in step 1 is: the austenitic stainless steel after step by step grinding is successively in acetone. Ultrasound is carried out in the solution and the ethanol solution; the ultrasonic time is 10min-30min; the mass fraction of the acetone solution is 50%-65%, and the mass fraction of the ethanol solution is 75%-99%. 3. a kind of method for high pressure chromizing of austenitic stainless steel surface according to claim 1, is characterized in that, the chromizing agent described in step 2 is mixed by the raw material of following mass percentage: chromium 50%, alumina 48%, Ammonium Chloride 2%. 4. the method for high-pressure chromizing of austenitic stainless steel surface according to claim 1, is characterized in that, the mass purity of the high-purity Ar gas described in the step 3 is not less than 99.999%, in the described chromizing treatment, the temperature rises The heating rate and the cooling rate are both 3°C/min to 10°C/min. 5 . The method for high-pressure chromizing on the surface of austenitic stainless steel according to claim 1 , wherein the surface hardness of the chromizing layer described in step 3 is greater than 500HV5. 6 .

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