Method for improving uniformity of high-temperature gas permeation layer on surface of large nuclear stainless steel base material

Abstract

The invention discloses a method for improving the uniformity of a high-temperature gas permeation layer on the surface of a large nuclear stainless steel base material. The method comprises the following steps that firstly, the surface of the stainless steel base material is soaked and then washed clean; 2, carrying out surface treatment to obtain a large nuclear stainless steel base material with a metal coating; and 3, high-temperature gas rapid permeation is conducted, and the large nuclear stainless steel base material with the high-temperature gas permeation layer is obtained. The metal coating is firstly prepared on the surface of the stainless steel base material, so that the surface activation energy during high-temperature gas permeation tends to be consistent, the initial state of gas permeation is close, the prepared metal coating reduces the diffusion rate of gas in a solid, the difference of the diffusion rates of the gas in different directions is reduced, and even under long-time heat preservation, the diffusion rate of the gas in the solid is reduced. And the diffusion thickness values in different directions are basically consistent, so that the diffusion uniformity and repeatability in the stainless steel base material are improved, finally, gas atom reinforced phases which are uniformly distributed are obtained in the coating, the coating performance can be improved, and the method is suitable for the field of material surface strengthening.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas diffusion infiltration layers, and particularly relates to a method for improving the uniformity of a high-temperature gas infiltration layer on the surface of a large-sized nuclear-grade stainless steel substrate. Background Art

[0002] Large-sized stainless steel substrates are important basic components necessary for major engineering construction and major technical equipment. Large-sized parts usually require the aid of handling tools and have the characteristics of huge mass and volume, long production cycle, complex process, high product price, long service life and difficult replacement, and high performance index requirements. For large-sized stainless steel components, the service environment conditions are complex and persistent, and surface treatment is usually required. However, the non-uniformity of the structure and composition of the large-sized stainless steel component substrates often seriously affects the stability of coating preparation and reduces the reliability of the quality of large-sized stainless steel products. Thermodynamically speaking, the surface diffusion initiation process of gas atoms is mainly determined by the thermal diffusion temperature and the activation energy of the diffusion surface. The higher the thermal diffusion temperature and the lower the activation energy of the diffusion surface, the easier the diffusion initiation process. Kinetically speaking, the diffusion rate of gas atoms after entering the surface is mainly determined by the interdiffusion intrinsic coefficient of the two and the diffusion channel blocking effect. The diffusion coefficient is determined by the temperature and the characteristics of the diffusing atoms themselves, and the diffusion channel blocking state is closely related to the composition of the substrate, the grain boundary distribution, the grain size of the structure, the orientation, etc. The diffusion process is extremely complex and it is difficult to guide the actual production process through scientific calculations. The gas diffusion process is usually parabolic. After the gas atom diffusion time reaches a certain value, time actually has little effect on the performance and the thickness of the infiltration layer. Under low-temperature diffusion conditions, it is uncertain whether the diffusion reaction can be initiated. After initiation, the diffusion rate of gas atoms is usually low, and in actual production, an ideal thickness state of the infiltration layer is often obtained through a long holding time. However, during long-term holding, precipitates will form at the grain boundaries, greatly reducing the toughness of the material and decreasing the wear resistance and corrosion resistance of the material. Under high-temperature diffusion conditions, the diffusion reaction is likely to occur, and the diffusion rate of gas atoms is usually high. However, the difference in the initial diffusion state and diffusion rate on the surface of the substrate material in different directions is obvious, and can reach an order-of-magnitude difference, resulting in a large difference in the infiltration layer thickness in different directions of the substrate, thus affecting the stability of the product quality. The high-temperature diffusion mechanism is unclear and there is no theoretical basis for process formulation, resulting in inconsistent performance of some products.

[0003] Therefore, there is an urgent need to develop a method that can control the initial state of high-temperature gas infiltration on the surface of a large-sized nuclear-grade stainless steel substrate and reduce the high-temperature diffusion rate, so as to improve the uniformity and repeatability during high-temperature gas diffusion. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the uniformity of the high-temperature gas permeation layer on the surface of a large-scale nuclear stainless steel substrate in view of the shortcomings of the above-mentioned prior art. The method adopts a surface treatment method to first prepare a layer of high-melting-point single-phase uniform metal coating on the surface of a large-scale nuclear stainless steel substrate. The single-phase and uniform structure is good. Since the concentration difference of the diffused atoms is greatly reduced, the diffusion rate is greatly reduced, thereby improving the uniformity of the high-temperature gas permeation layer on the surface of the large-scale nuclear stainless steel substrate.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for improving the uniformity of the high-temperature gas permeation layer on the surface of a large nuclear stainless steel substrate, characterized in that the method comprises the following steps:

[0006] Step 1: Soak the surface of the stainless steel substrate for large nuclear use in warm water and an alkaline metal cleaning agent and then rinse it clean to obtain a clean stainless steel substrate for large nuclear use;

[0007] Step 2: surface treating the clean large-scale nuclear stainless steel substrate obtained in step 1 to obtain a large-scale nuclear stainless steel substrate with a metal coating;

[0008] Step 3: Place the large nuclear stainless steel substrate with metal coating obtained in step 2 into a heat treatment furnace, then introduce gas to perform high-temperature gas rapid infiltration to obtain a large nuclear stainless steel substrate with a high-temperature gas infiltration layer.

[0009] The present invention first cleans the surface of a large nuclear stainless steel substrate that requires rapid high-temperature gas penetration, soaks it in warm water and an alkaline metal cleaning agent, and then rinses it to remove the oxide layer on the surface, thereby preventing the oxide layer from causing uneven gas penetration.

[0010] Low-temperature diffusion has low gas decomposition efficiency, and a long time of diffusion is required to prepare a reliable diffusion layer, and the stability is poor, which has a significant impact on the physical properties of the base material. Therefore, in practical applications, increasing the diffusion temperature for preparing the gas diffusion layer is often used to improve production efficiency. However, the higher the diffusion temperature, the faster the diffusion rate of the gas atoms, and the more difficult it is to control the uniformity and repeatability of the gas atom diffusion. Therefore, when the diffusion temperature is increased, it is necessary to minimize the difference in diffusion thickness caused by anisotropy and high diffusion rate in the diffusion process. Therefore, in the present invention, a metal coating, i.e., a diffusion barrier layer, is prepared by surface treatment to reduce the diffusion rate of the gas, thereby ensuring that the start-up state of the gas diffusion is basically consistent. Even if the diffusion rate in this state of high-temperature diffusion is reduced, it is much greater than the low-temperature diffusion rate. The diffusion process is usually parabolic. The saturation state can be reached in a very short time under high-temperature diffusion. The thickness of the gas diffusion layer remains basically unchanged with the increase in the insulation time. The problems of uniformity and repeatability of the gas diffusion layer prepared in this state are solved.

[0011] The above method for improving the uniformity of the high-temperature gas infiltration layer on the surface of a large-scale nuclear-use stainless steel substrate is characterized in that the surface treatment in step two is pack cementation or vapor deposition. The present invention uses surface treatment means such as pack cementation and vapor deposition to prepare a metal coating with a certain thickness on the surface of the large-scale nuclear-use stainless steel substrate, and the chemical composition and organizational structure have good consistency.

[0012] The above method for improving the uniformity of the high-temperature gas infiltration layer on the surface of a large-scale nuclear-use stainless steel substrate is characterized in that the component of the metal coating in step two has good compatibility with Fe and a high melting point, and the component of the metal coating is chromium. In the present invention, high-temperature gas diffusion is used, and the diffusion rate of the gas is reduced by preparing a high-melting-point diffusion barrier layer. The diffusion barrier layer should be capable of forming a stable and simple solid solution structure, having good thermal stability, and matching the thermal expansion coefficient of the substrate. Most importantly, it has the ability to hinder the diffusion of gas atoms at high temperatures; the metal chromium coating has characteristics such as a high melting point, good stability, and easy preparation, and also has good wear resistance and corrosion resistance, and can be used as a diffusion barrier layer material, and the thickness uniformity of the gas infiltration layer is good.

[0013] The above method for improving the uniformity of the high-temperature gas infiltration layer on the surface of a large-scale nuclear-use stainless steel substrate is characterized in that the metal coating in step two is single-phase and has a uniform structure. In the present invention, the barrier layer has basically the same thickness and structure, ensuring that the starting state of gas diffusion is basically the same, and improving the service life and safety reliability of large-scale nuclear-use stainless steel devices.

[0014] The above method for improving the uniformity of the high-temperature gas infiltration layer on the surface of a large-scale nuclear-use stainless steel substrate is characterized in that the thickness of the metal coating in step two is not less than 20 μm. In the present invention, the high-melting-point barrier layer can reduce the diffusion rate to achieve the purpose of improving the diffusion uniformity. If the barrier layer is too thin, when the gas enters the substrate material after completing the diffusion of the barrier layer, the diffusion distance is far from the stable state, which will cause a large difference in the diffusion of the gas in the substrate stage, showing gas diffusion with different thicknesses.

[0015] The above method for improving the uniformity of the high-temperature gas infiltration layer on the surface of a large-scale nuclear-use stainless steel substrate is characterized in that the gas introduced in step three is continuously introduced to keep the working pressure of the gas in the heat treatment furnace at 20 MPa to 45 MPa. In the present invention, the pressure in the heat treatment furnace is mainly determined by the size of the gas inflow and outflow, which will affect the stability of the temperature and atmosphere in the furnace, thereby affecting the uniformity of diffusion. Too small or too large gas flow rates will cause too large differences in all directions in the furnace and uneven gas diffusion.

[0016] The above method for improving the uniformity of the high-temperature gas infiltration layer on the surface of a large-sized nuclear-grade stainless steel substrate is characterized in that in step three, the high-temperature gas rapid infiltration adopts segmented heating. With a heating rate of 50 °C / h to 200 °C / h, it is heated to 500 °C to 600 °C and then held for 0.5 h to 1 h. Then, with a heating rate of 50 °C / h to 200 °C, it is heated to 950 °C to 1100 °C and then held for no more than 15 h. In the present invention, the temperature gradient during the heat treatment heating process increases with the increase of the target temperature. Under the condition of the same treatment temperature, the segmented heating method is more conducive to reducing the temperature gradient inside the material, ensuring that the thickness difference of the gas diffusion infiltration layer is small. And if the heating time at high temperature is too long, the grains will become coarser, increasing the brittleness of the steel and making it prone to cracking. Therefore, the holding time in the second stage is no more than 15 h.

[0017] The above method for improving the uniformity of the high-temperature gas infiltration layer on the surface of a large-sized nuclear-grade stainless steel substrate is characterized in that in the large-sized nuclear-grade stainless steel substrate with a high-temperature gas infiltration layer in step three, the thickness of the high-temperature gas infiltration layer is not less than 20 μm. In the present invention, the thickness of the gas diffusion infiltration is at least the thickness of the metal coating prepared in step two to ensure the bonding performance between the prepared infiltration layer and the substrate.

[0018] The above method for improving the uniformity of the high-temperature gas infiltration layer on the surface of a large-sized nuclear-grade stainless steel substrate is characterized in that after the high-temperature gas rapid infiltration in step three, it is cooled in the furnace to below 300 °C and then taken out of the furnace. In the present invention, cooling in the furnace can avoid stress concentration caused by too large a temperature difference during the cooling process of the material, thereby reducing the risk of embrittlement of the material and improving the service life and performance stability of the material.

[0019] The present invention has the following advantages compared with the prior art:

[0020] 1. The present invention first prepares a metal coating with a high melting point and uniform single-phase structure on the surface of a large-sized nuclear-grade stainless steel substrate by means of surface treatment. The anisotropy of this metal coating is small, so the subsequent high-temperature gas atom diffusion starts in a consistent state. It is single-phase and has good tissue uniformity. The diffusion rate of gas atoms in this layer is also basically the same. At a relatively high temperature, the initial parabolic diffusion process is also basically the same. In the later stage, even if the diffusion process enters the stainless steel substrate from the single-phase metal coating, due to the greatly reduced concentration difference of the diffusing atoms, the diffusion rate is greatly reduced. Even if the time is increased, the material has large anisotropy, and the difference in the diffusion thickness values of gas atoms in different directions of the stainless steel substrate is also negligible, improving the uniformity of the high-temperature gas infiltration layer on the surface of the large-sized nuclear-grade stainless steel substrate.

[0021] 2. The diffusion infiltration process adopted by the present invention is significantly different from the conventional process. By means of structural design, on the one hand, the single-phase metal coating is used as the starting diffusion layer to make the thermodynamic conditions the same, so that the starting state of gas diffusion is basically the same. On the other hand, the existence of the high-melting-point single-phase metal coating can significantly reduce the gas diffusion rate. Under the same environmental and time conditions, the difference in gas diffusion in each direction is reduced, and finally the uniformity and stability of coating preparation are guaranteed.

[0022] 3. The present invention realizes the control of the gas infiltration process of large stainless steel substrates through structural design, improves the stability and repeatability of the gas infiltration process, and the preparation process is simple and easy to implement in practical applications.

[0023] 4. The idea for solving problems provided by the present invention can be applied to similar coating preparation technologies and extended to more practical application fields, such as the electronic field, etc.

[0024] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the metallographic structure of the large nuclear-grade stainless steel substrate with a metal chromium coating in the second step of Embodiment 1 of the present invention.

[0026] Figure 2 It is the metallographic structure of the large nuclear-grade stainless steel substrate with a high-temperature gas infiltration layer in the third step of Embodiment 1 of the present invention.

[0027] Figure 3 It is the metallographic structure of the large nuclear-grade stainless steel substrate with a high-temperature gas infiltration layer in the second step of Comparative Example 1 of the present invention.

[0028] Figure 4 It is the metallographic structure of the large nuclear-grade stainless steel substrate with a metal chromium coating in the second step of Embodiment 2 of the present invention

[0029] Figure 5 It is the metallographic structure of the large nuclear-grade stainless steel substrate with a high-temperature gas infiltration layer in the third step of Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] Embodiment 1

[0031] This embodiment includes the following steps:

[0032] Step 1: Immerse the surface of the large nuclear-grade stainless steel substrate in warm water at 40°C to 50°C and an alkaline metal cleaning agent for 10 minutes, then clean it with clean water, and then rinse it thoroughly with deionized water to obtain a clean large nuclear-grade stainless steel substrate;

[0033] Step 2: The cleaned large-sized nuclear-use stainless steel substrate obtained in Step 1 is subjected to surface treatment by pack cementation to obtain a large-sized nuclear-use stainless steel substrate with a metallic chromium coating;

[0034] Step 3: The large-sized nuclear-use stainless steel substrate with a metallic coating obtained in Step 2 is placed in a heat treatment furnace, and then nitrogen is introduced. With a heating rate of 200 °C / h, it is heated to 600 °C and held for 1 h. After the holding ends, it is again heated to 1070 °C at a heating rate of 200 °C / h and held for 15 h. During the operation, the working state pressure of the gas in the heat treatment furnace is 45 MPa. After the holding ends, it is cooled in the furnace to below 300 °C and then taken out of the furnace to obtain a large-sized nuclear-use stainless steel substrate with a high-temperature gas infiltration layer.

[0035] After testing, the thickness of the metallic chromium coating in the large-sized nuclear-use stainless steel substrate with a metallic chromium coating in this embodiment is 80 μm. The metallic chromium coating has good compatibility with Fe, a high melting point, is single-phase and has a uniform structure. The thickness of the high-temperature gas infiltration layer in the large-sized nuclear-use stainless steel substrate with a high-temperature gas infiltration layer is 83 μm. The interface between the high-temperature gas infiltration layer and the stainless steel substrate is obvious, the thickness of the high-temperature gas infiltration layer is basically consistent, and the tissue distribution state of the high-temperature gas infiltration layer is the same in all directions.

[0036] Figure 1 This is the metallographic structure of the large-sized nuclear-use stainless steel substrate with a metallic chromium coating in Step 2 of this embodiment. From Figure 1 it can be seen that the interface between the metallic chromium coating and the stainless steel substrate is obvious, the thickness of the metallic chromium coating is 80 μm, the thickness of each part is basically consistent, and the coating tissue is evenly distributed.

[0037] Figure 2 This is the metallographic structure of the large-sized nuclear-use stainless steel substrate with a high-temperature gas infiltration layer in Step 3 of Embodiment 1 of the present invention. From Figure 2 it can be seen that the interface between the high-temperature gas infiltration layer and the stainless steel substrate is obvious, the thickness of the high-temperature gas infiltration layer is 83 μm, the thickness of the high-temperature gas infiltration layer is basically consistent, and the tissue distribution state of the high-temperature gas infiltration layer is the same in all directions.

[0038] Comparative Example 1

[0039] This comparative example includes the following steps:

[0040] Step 1: The surface of the large-sized nuclear-use stainless steel substrate is soaked in warm water at 40 °C to 50 °C and an alkaline metal cleaning agent for 10 min, then cleaned with clean water, and then rinsed thoroughly with deionized water to obtain a cleaned large-sized nuclear-use stainless steel substrate;

[0041] Step 2: Put the cleaned large-scale nuclear-use stainless steel substrate obtained in Step 1 into a heat treatment furnace, then introduce nitrogen, heat it at a heating rate of 200 °C / h to 600 °C, hold for 1 h, and then heat it again at a heating rate of 200 °C / h to 1070 °C and hold for 15 h. During the operation, the working pressure of the gas in the heat treatment furnace is 45 MPa. After holding, cool it in the furnace to below 300 °C and then take it out of the furnace to obtain a large-scale nuclear-use stainless steel substrate with a high-temperature gas infiltration layer.

[0042] After testing, the interface between the high-temperature gas infiltration layer and the stainless steel substrate of the large-scale nuclear-use stainless steel substrate with a high-temperature gas infiltration layer in this comparative example is wavy, and the thickness uniformity of the gas infiltration coating in different directions is poor, with a large thickness difference at different positions, showing an obvious difference.

[0043] Figure 3 This is the metallographic structure of the large-scale nuclear-use stainless steel substrate with a high-temperature gas infiltration layer in Step 2 of this comparative example. From Figure 3 it can be seen that the interface between the high-temperature gas infiltration layer and the stainless steel substrate is wavy, and the thickness uniformity of the gas infiltration coating in different directions is poor, with a large thickness difference at different positions, showing an obvious difference.

[0044] By comparing Example 1 and Comparative Example 1, it can be seen that in Example 1, the stainless steel substrate was first surface-treated to obtain a large-scale nuclear-use stainless steel substrate with a metal chromium coating, and the metal chromium coating played a role in making the high-temperature gas infiltration layer uniform and stable. In Comparative Example 1, high-temperature gas rapid infiltration was directly carried out, and the obtained high-temperature gas infiltration layer was uneven.

[0045] Example 2

[0046] This example includes the following steps:

[0047] Step 1: Immerse the surface of the large-scale nuclear-use stainless steel substrate in warm water at 40 °C to 50 °C and an alkaline metal cleaning agent for 10 min, then clean it with clean water, and then rinse it thoroughly with deionized water to obtain a cleaned large-scale nuclear-use stainless steel substrate;

[0048] Step 2: Carry out surface treatment on the cleaned large-scale nuclear-use stainless steel substrate obtained in Step 1 by pack cementation to obtain a large-scale nuclear-use stainless steel substrate with a metal chromium coating;

[0049] Step 3: Place the large-sized nuclear-grade stainless steel substrate with a metal coating obtained in Step 2 into a heat treatment furnace, then introduce nitrogen. Heat it at a heating rate of 50 °C / h to 600 °C and hold for 0.5 h. After the holding is completed, heat it again at a heating rate of 50 °C / h to 1100 °C and hold for 10 h. During the operation, the working pressure of the gas in the heat treatment furnace is 20 MPa. After the holding is completed, cool it in the furnace to below 300 °C and then take it out of the furnace to obtain a large-sized nuclear-grade stainless steel substrate with a high-temperature gas penetration layer.

[0050] After testing, the thickness of the metal chromium coating in the large-sized nuclear-grade stainless steel substrate with a metal chromium coating in this embodiment is 48 μm. The metal chromium coating has good compatibility with Fe, a high melting point, is single-phase and has a uniform structure. The thickness of the high-temperature gas penetration layer in the large-sized nuclear-grade stainless steel substrate with a high-temperature gas penetration layer is 450 μm. The interface between the high-temperature gas penetration layer and the stainless steel substrate is obvious, the thickness of the high-temperature gas penetration layer is basically the same, and the tissue distribution state of the high-temperature gas penetration layer is the same in all directions.

[0051] Figure 4 This is the metallographic structure of the large-sized nuclear-grade stainless steel substrate with a metal chromium coating in Step 2 of this embodiment. As can be seen from Figure 4 it, the interface between the metal chromium coating and the stainless steel substrate is obvious. The thickness of the metal chromium coating is 80 μm, the thickness of each part is basically the same, and the coating tissue is evenly distributed.

[0052] Figure 5 This is the metallographic structure of the large-sized nuclear-grade stainless steel substrate with a high-temperature gas penetration layer in Step 3 of this embodiment. As can be seen from Figure 5 it, the interface between the high-temperature gas penetration layer and the stainless steel substrate is obvious. The thickness of the high-temperature gas penetration layer is 450 μm. The high-temperature gas penetration layer has two layers. The first layer is the nitrogen diffusion inside the chromium penetration layer, the interface is straight and significant. The second layer is the nitrogen diffusion inside the substrate, and the interface is also straight and the thickness is the same. The thickness of the high-temperature gas penetration layer is basically the same, and the tissue distribution state of the high-temperature gas penetration layer is the same in all directions. The introduction of the chromium penetration layer significantly improves the uniformity of nitrogen diffusion.

[0053] Example 3

[0054] This embodiment includes the following steps:

[0055] Step 1: Immerse the surface of the large-sized nuclear-grade stainless steel substrate in warm water at 40 °C to 50 °C and an alkaline metal cleaning agent for 10 min, then clean it with clean water, and then rinse it thoroughly with deionized water to obtain a clean large-sized nuclear-grade stainless steel substrate;

[0056] Step 2: Subject the clean large-sized nuclear-grade stainless steel substrate obtained in Step 1 to surface treatment by vapor deposition to obtain a large-sized nuclear-grade stainless steel substrate with a metal chromium coating;

[0057] Step 3: Place the large-sized nuclear-grade stainless steel substrate with a metal coating obtained in Step 2 into a heat treatment furnace, then introduce nitrogen. Heat it at a heating rate of 100 °C / h to 500 °C and hold for 0.7 h. After the holding is completed, heat it again at a heating rate of 100 °C / h to 950 °C and hold for 10 h. During the operation, the working pressure of the gas in the heat treatment furnace is 25 MPa. After the holding is completed, cool it in the furnace to below 300 °C and then take it out of the furnace to obtain a large-sized nuclear-grade stainless steel substrate with a high-temperature gas infiltration layer.

[0058] After testing, the thickness of the metal chromium coating in the large-sized nuclear-grade stainless steel substrate with a metal chromium coating in this embodiment is 30 μm. The metal chromium coating has good compatibility with Fe, a high melting point, is single-phase and has a uniform structure. The thickness of the high-temperature gas infiltration layer in the large-sized nuclear-grade stainless steel substrate with a high-temperature gas infiltration layer is 33 μm. The interface between the high-temperature gas infiltration layer and the stainless steel substrate is obvious. The thickness of the high-temperature gas infiltration layer is basically consistent, and the tissue distribution state of the high-temperature gas infiltration layer is the same in all directions.

[0059] Example 4

[0060] This embodiment includes the following steps:

[0061] Step 1: Immerse the surface of the large-sized nuclear-grade stainless steel substrate in warm water at 40 °C to 50 °C and an alkaline metal cleaning agent for 10 min, then clean it with clean water, and then rinse it thoroughly with deionized water to obtain a clean large-sized nuclear-grade stainless steel substrate;

[0062] Step 2: Perform surface treatment on the clean large-sized nuclear-grade stainless steel substrate obtained in Step 1 by plasma glow discharge to obtain a large-sized nuclear-grade stainless steel substrate with a metal chromium coating;

[0063] Step 3: Place the large-sized nuclear-grade stainless steel substrate with a metal coating obtained in Step 2 into a heat treatment furnace, then introduce nitrogen. Heat it at a heating rate of 100 °C / h to 550 °C and hold for 0.8 h. After the holding is completed, heat it again at a heating rate of 100 °C / h to 1100 °C and hold for 5 h. During the operation, the working pressure of the gas in the heat treatment furnace is 35 MPa. After the holding is completed, cool it in the furnace to below 300 °C and then take it out of the furnace to obtain a large-sized nuclear-grade stainless steel substrate with a high-temperature gas infiltration layer.

[0064] After testing, the thickness of the metal chromium coating in the large-sized nuclear-grade stainless steel substrate with a metal chromium coating in this embodiment is 20 μm. The metal chromium coating has good compatibility with Fe, a high melting point, is single-phase and has a uniform structure. The thickness of the high-temperature gas infiltration layer in the large-sized nuclear-grade stainless steel substrate with a high-temperature gas infiltration layer is 25 μm. The interface between the high-temperature gas infiltration layer and the stainless steel substrate is obvious. The thickness of the high-temperature gas infiltration layer is basically consistent, and the tissue distribution state of the high-temperature gas infiltration layer is the same in all directions.

[0065] As described above, it is only a preferred embodiment of the present invention and does not impose any limitations on the present invention. Any simple modification, change, and equivalent variation made to the above embodiments based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for improving the uniformity of the high-temperature gas permeation layer on the surface of a large nuclear stainless steel substrate, characterized in that: The method comprises the following steps: Step 1: Soak the surface of the stainless steel substrate for large nuclear use in warm water and an alkaline metal cleaning agent and then rinse it clean to obtain a clean stainless steel substrate for large nuclear use; Step 2: surface treating the clean large-scale nuclear stainless steel substrate obtained in step 1 to obtain a large-scale nuclear stainless steel substrate with a metal coating; Step 3: Place the large nuclear stainless steel substrate with metal coating obtained in step 2 into a heat treatment furnace, then introduce gas to perform high-temperature gas rapid infiltration to obtain a large nuclear stainless steel substrate with a high-temperature gas infiltration layer.

2. A method for improving the uniformity of the high temperature gas permeation layer on the surface of a large nuclear stainless steel substrate according to claim 1, characterized in that: The surface treatment in step 2 is embedding infiltration or vapor deposition.

3. The method for improving the uniformity of the high temperature gas permeation layer on the surface of a large nuclear stainless steel substrate according to claim 1, characterized in that: The component of the metal coating in step 2 has good compatibility with Fe and a high melting point, and the component of the metal coating is chromium.

4. The method for improving the uniformity of the high temperature gas permeation layer on the surface of a large nuclear stainless steel substrate according to claim 1, characterized in that: The metal coating in step 2 is single-phase and has uniform structure.

5. The method for improving the uniformity of the high temperature gas permeation layer on the surface of a large nuclear stainless steel substrate according to claim 1, characterized in that: The thickness of the metal coating in step 2 is not less than 20 μm.

6. The method for improving the uniformity of the high temperature gas permeation layer on the surface of a large nuclear stainless steel substrate according to claim 1, characterized in that: The gas introduced in step 3 is continuously introduced to maintain the working pressure of the gas in the heat treatment furnace at 20MPa to 45MPa.

7. A method for improving the uniformity of the high temperature gas permeation layer on the surface of a large nuclear stainless steel substrate according to claim 1, characterized in that: The high-temperature gas rapid infiltration described in step three adopts staged heating, with a heating rate of 50℃ / h~200℃ / h, heating to 500℃~600℃ and keeping warm for 0.5h~1h, and then heating to 950℃~1100℃ at a heating rate of 50℃ / h~200℃ / h and keeping warm for no more than 15h.

8. The method for improving the uniformity of the high temperature gas permeation layer on the surface of a large nuclear stainless steel substrate according to claim 1, characterized in that: The thickness of the high-temperature gas permeation layer in the large nuclear stainless steel substrate having the high-temperature gas permeation layer described in step 3 is not less than 20 μm.

9. The method for improving the uniformity of the high temperature gas permeation layer on the surface of a large nuclear stainless steel substrate according to claim 1, characterized in that: After the high temperature gas is rapidly infiltrated in step 3, the product is cooled to below 300° C. in the furnace and then taken out of the furnace.

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