A stainless steel surface composite case and its preparation method and application

Abstract

The application discloses a stainless steel surface composite case and a preparation method and application thereof, and the stainless steel surface composite case comprises a surface CrN+Cr2N layer and a nitrided austenite diffusion layer. The application obtains a new stainless steel surface composite case by combining gradient ion nitriding treatment with chromizing treatment, and compared with a traditional method of nitriding and then chromizing, the composite case has a gradient case structure of the complete and dense CrN+Cr2N layer and the nitrided austenite diffusion layer, the case has more excellent corrosion resistance and wear resistance, the case has high bonding strength with the substrate and good toughness. Meanwhile, the preparation method of the composite case is simple in operation, fast in penetration speed, can prepare a large-thickness case, can realize uniform case on the surface of a complex workpiece, is suitable for large-scale production, and can be widely applied in the fields of stainless steel work dies, ocean platforms, nuclear energy, fuel cells, high-end equipment and sports parts.

Description

Technical Field

[0001] The present invention relates to the technical field of surface treatment, in particular to a composite diffusion layer on the surface of stainless steel, a preparation method thereof and an application thereof. Background Art

[0002] Chromizing refers to a surface treatment method in which the workpiece to be processed is placed in a chromizing medium and, under certain conditions, active chromium atoms are allowed to penetrate into the surface of the workpiece. The main purpose of chromizing is to improve the corrosion resistance and heat resistance of the base material, improve the oxidation resistance of the base material, and enhance the wear resistance and fatigue strength. For stainless steel, due to its very low carbon content, the hardness of the chromized layer formed is relatively low and the wear resistance is insufficient. In addition, the chromizing temperature of stainless steel is very high, and it usually takes a long time of chromizing at more than 1000°C to obtain a sufficient thickness of the chromized layer. This will lead to deterioration of the properties of the base material and severe deformation of the workpiece. Patent CN100567552C uses a method of high-temperature chromizing followed by nitriding to increase the hardness of the chromized layer. Patent CN101195913B uses a method of nitrogen-carbon co-diffusion treatment followed by chromizing to achieve a low-temperature chromizing process at 700°C.

[0003] Although the above-mentioned pre-nitriding or nitrocarburizing methods promote the chromizing speed and reduce the chromizing temperature, or solve the problem of the hardness and temperature of the chromized layer by chromizing first and then nitriding, these methods still cannot obtain a strong and tough chromized layer and cannot be used in high load, strong wear and other environments.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite infiltration layer on the surface of stainless steel, a preparation method and application thereof, and by preparing the composite infiltration layer, a stainless steel material with both strength and toughness can be obtained.

[0006] The present invention is achieved in that:

[0007] In a first aspect, the present invention provides a composite diffusion layer on the surface of stainless steel, which includes a surface CrN+Cr2N layer and a nitrided austenite diffusion layer.

[0008] In some embodiments, the thickness of the surface CrN+Cr2N layer is 15 μm to 150 μm.

[0009] In some embodiments, the thickness of the nitrided austenite diffusion layer is 50 μm to 400 μm.

[0010] In a second aspect, the present invention provides a method for preparing the composite diffusion layer on the surface of stainless steel, which comprises: performing gradient ion nitriding treatment and chromizing treatment on the surface of a stainless steel substrate to obtain the composite diffusion layer.

[0011] In some embodiments, the gradient ion nitriding treatment includes: performing a nitrogen-enriched layer treatment at 480° C. to 600° C., performing an enhanced diffusion treatment at 700° C. to 900° C., and performing a surface enhanced nitrogen-enriched treatment at 500° C. to 600° C.

[0012] In some embodiments, the conditions for nitrogen-rich layer treatment are: treatment temperature of 480°C to 600°C, treatment time of 2h to 5h, nitrogen and hydrogen ratio of 3:1 to 1:3, gas pressure of 400Pa to 800Pa, and voltage of 500V to 700V.

[0013] In some embodiments, the conditions for enhanced diffusion treatment are: treatment temperature of 700°C to 900°C, treatment time of 2h to 10h, nitrogen and hydrogen ratio of 1:1 to 1:3, gas pressure of 300Pa to 600Pa, and voltage of 500V to 700V.

[0014] In some embodiments, the conditions for enhanced nitrogen enrichment treatment are: treatment temperature of 500°C to 600°C, treatment time of 2h to 5h, nitrogen and hydrogen ratio of 2:1 to 1:2, gas pressure of 400Pa to 800Pa, and voltage of 500V to 700V.

[0015] In some embodiments, the thickness of the nitrided layer is 15 μm to 300 μm.

[0016] In some embodiments, the chromizing treatment comprises a solid chromizing treatment.

[0017] In some embodiments, the chromizing treatment includes a salt bath chromizing treatment.

[0018] In some embodiments, the chromizing treatment conditions are: chromizing temperature is 840° C. to 1050° C., and chromizing time is 2 h to 10 h.

[0019] In some embodiments, the components and mass fractions of the chromizing agent in the chromizing treatment are: chromium powder 40% to 50%, NH4Cl 3% to 7%, rare earth 2% to 10%, and Al2O3 powder as the balance.

[0020] In some embodiments, the rare earth is selected from one or more of yttrium oxide, cerium oxide, or lanthanum oxide.

[0021] In some embodiments, the preparation method further includes pre-treating the surface of the substrate before performing the gradient ion nitriding treatment, and sequentially performing fine grinding, ultrasonic cleaning, and drying on the substrate before performing the chromizing treatment.

[0022] In some embodiments, the pretreatment includes: performing ultrasonic degreasing, rust removal cleaning, drying, and ion sputtering cleaning on the substrate in sequence.

[0023] In a third aspect, the present invention provides a high-strength and high-toughness material, which includes a substrate, and the surface of the substrate is further provided with the above-mentioned stainless steel surface composite diffusion layer.

[0024] In a fourth aspect, the present invention also provides the use of the above-mentioned high-strength and high-toughness materials in the preparation of molds, anti-corrosion parts in the marine, energy and chemical industries, and moving parts of high-end equipment.

[0025] The present invention has the following beneficial effects:

[0026] The present invention combines gradient ion nitriding with chromizing to obtain a new composite nitrided layer on the surface of stainless steel. Compared with the traditional nitriding followed by chromizing method, the composite nitrided layer of the present invention has a complete and dense gradient nitrided layer structure of CrN+Cr2N layer and nitrided austenite diffusion layer. The nitrided layer has better corrosion resistance and wear resistance, high bonding strength between the nitrided layer and the substrate, and good toughness. At the same time, the preparation method of the composite nitrided layer of the present invention is simple to operate, has a fast nitriding rate, can prepare a thick nitrided layer, and can achieve a uniform nitrided layer on the surface of complex workpieces. It is suitable for large-scale production and can be widely used in the fields of stainless steel molds, offshore platforms, nuclear energy, fuel cells, and high-end equipment moving parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 This is the cross-sectional morphology of the nitrided layer after gradient ion nitriding and chromizing in Example 1, where from left to right are the CrN+Cr2N layer, the nitrided austenite diffusion layer, and the matrix;

[0029] Figure 2 This is the surface indentation morphology of the nitrided layer after gradient ion nitriding and chromizing in Example 1;

[0030] Figure 3 The surface morphology of the nitrided layer after gradient ion nitriding and chromizing in Example 1;

[0031] Figure 4 The cross-sectional morphology of the chromized layer in Comparative Example 1, where from left to right are the substrate and the chromized layer;

[0032] Figure 5 This is the surface morphology of the chromized layer after ion nitriding in comparative example 3. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0034] The present invention provides a composite diffusion layer on the surface of stainless steel, and the preparation method thereof is as follows:

[0035] S1. Substrate surface pretreatment

[0036] The surface of the substrate is sequentially subjected to ultrasonic degreasing, rust removal, and drying to prevent rust and grease from affecting the subsequent ion nitriding effect.

[0037] Before gradient ion nitriding, ion sputtering cleaning pretreatment is performed to remove the oxide scale on the surface of the stainless steel substrate so that ion nitriding can proceed smoothly.

[0038] S2. Gradient ion nitriding treatment

[0039] The stainless steel substrate is nitrided using plasma nitriding technology.

[0040] Gradient ion nitriding treatment is performed on the surface of the stainless steel substrate: first, a nitrogen-rich layer treatment is performed at 480℃~600℃, then an enhanced diffusion treatment is performed at 700℃~900℃, and then a surface enhanced nitrogen-rich treatment is performed at 500℃~600℃.

[0041] Specifically, the conditions for the nitrogen-rich layer treatment are: treatment temperature of 480°C to 600°C, treatment time of 2h to 5h, nitrogen and hydrogen ratio of 3:1 to 1:3, gas pressure of 400Pa to 800Pa, and voltage of 500V to 700V.

[0042] The conditions for the enhanced diffusion treatment are: 700° C. to 900° C., treatment time 2 h to 10 h, nitrogen to hydrogen ratio 1:1 to 1:3, gas pressure 300 Pa to 600 Pa, and voltage 500 V to 700 V.

[0043] The conditions for the surface enhanced nitrogen enrichment treatment are: 500°C to 600°C, treatment time of 2h to 5h, nitrogen and hydrogen ratio of 2:1 to 1:2, gas pressure of 400Pa to 800Pa, and voltage of 500V to 700V.

[0044] Through the above gradient ion nitriding treatment, a composite nitriding layer combining a surface nitrogen-rich layer and a diffused austenite nitriding layer can be obtained, and the thickness of the nitriding layer is 15μm to 300μm.

[0045] The present invention obtains a composite nitriding layer combining a surface nitrogen-rich layer and a diffused austenite nitriding layer through a three-step nitriding treatment, which provides sufficient nitrogen source and nitriding influence layer for subsequent chromizing treatment, thereby improving the chromizing speed and forming a complete CrN+Cr2N layer to obtain a high-hardness and high-strength chromizing layer.

[0046] By strengthening the diffusion treatment, the thickness of the nitriding layer is increased, and a high nitrogen content austenite structure is obtained. The nitrogen can be fixed in the austenite, delaying the ineffective loss of nitrogen inward during chromizing, and finally obtaining a gradient structure chromizing and nitriding composite layer, thereby improving the strength and toughness of the nitriding layer.

[0047] S3. Surface finishing of nitriding layer

[0048] After the stainless steel substrate is subjected to gradient ion nitriding, the substrate is finely ground to eliminate surface deposits and contamination, and then ultrasonically degreased and dried.

[0049] S4. Chrome treatment

[0050] The chromizing treatment of the present invention is a solid chromizing treatment, and more preferably, the chromizing treatment is a salt bath chromizing treatment.

[0051] The conditions of the chromizing treatment are as follows: the chromizing temperature is 840° C. to 1050° C., and the chromizing time is 2 h to 10 h.

[0052] The composition of the chromizing agent used in the chromizing treatment of the present invention is as follows: 40% to 50% chromium powder, 3% to 7% NH4Cl, 2% to 10% rare earth, and the balance Al2O3 powder, wherein the rare earth is selected from one or more of yttrium oxide, cerium oxide, or lanthanum oxide.

[0053] Based on the nitriding treatment and then the chromizing treatment, a composite nitriding layer of surface CrN+Cr2N layer and nitrided austenite diffusion layer can be obtained on the surface of the stainless steel. This gradient structure of the nitriding layer has high surface hardness and good hardness gradient. The bonding strength between the nitriding layer and the matrix is ​​high, the nitriding layer has good toughness, and has the performance characteristics of both strength and toughness.

[0054] The method for preparing a composite chromized and nitrided layer on the surface of stainless steel disclosed herein can produce a complete and dense chromized and nitrided layer. This composite chromized layer exhibits excellent wear resistance and corrosion resistance, improving the toughness and corrosion resistance of the stainless steel substrate. The stainless steel obtained with this composite chromized layer can be used in the manufacture of stainless steel tools and molds, key moving parts, and corroded components, significantly improving the performance of these components.

[0055] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0056] S1. Substrate surface pretreatment

[0057] The stainless steel substrate is cleaned by ultrasonic degreasing and rust removal, and then dried. The cleaned substrate is placed in an ion nitriding furnace, vacuumed to below 5 Pa, and ion sputtering cleaning is performed on the substrate using a mixture of argon and hydrogen at a high bias voltage.

[0058] S2, gradient ion nitriding treatment

[0059] After ion sputtering cleaning, gradient ion nitriding treatment is performed on the surface of the stainless steel substrate.

[0060] The nitrogen and hydrogen ratio was 2:1, the pressure was 400Pa, the bias was 580V, the temperature was 480℃, and the temperature was kept warm for 2 hours to obtain a surface nitrogen-rich layer; the nitrogen and hydrogen ratio was adjusted to 1:1, the pressure was 350Pa, the bias was 580V, the temperature was 700℃, and the temperature was kept warm for 2 hours to obtain an enhanced diffusion layer; the nitrogen and hydrogen ratio was adjusted to 2:1, the pressure was 600Pa, the bias was 550V, the temperature was 540℃, and the temperature was kept warm for 2 hours to obtain a surface enhanced nitrogen-rich layer.

[0061] S3, nitriding layer surface fine grinding treatment

[0062] After the stainless steel substrate is subjected to gradient ion nitriding, the substrate is finely ground to eliminate surface deposits and contamination, and then ultrasonically degreased and dried.

[0063] S4, chromizing treatment

[0064] After fine grinding and ultrasonic cleaning, the substrate is chromized. The chromization treatment is solid chromization at a temperature of 840°C for 4 hours. The chromizing agent is 45% chromium powder, 3% NH4Cl, 2% yttrium rare earth oxide, and the balance Al2O3 powder.

[0065] After gradient ion nitriding, the thickness of the nitriding layer is 50μm, the thickness of the CrN+Cr2N layer after nitriding and chromizing composite treatment is 28μm, the thickness of the nitrided austenite diffusion layer is 80μm, the surface hardness is HV1801, and the Rockwell indentation grade reaches HF1, with good strength, toughness and bonding strength.

[0066] Figure 1 This is the cross-sectional morphology of the nitrided layer after gradient ion nitriding and chromizing. It can be seen from the figure that a good gradient structure is formed on the interface.

[0067] Figure 2 The indentation morphology of the surface of the carburized layer after gradient ion nitriding and chromizing is shown. There is no peeling mark on the carburized layer at the edge of the indentation, and the indentation grade reaches HF1, which proves that the carburized layer of this embodiment has good toughness and bonding strength.

[0068] Figure 3This is the surface morphology of the nitrided layer after gradient ion nitriding and chromizing. It can be seen from the figure that a dense CrN+Cr2N structure is formed on the surface of the substrate.

[0069] Example 2

[0070] This embodiment differs from Example 1 in that a nitrogen-to-hydrogen ratio of 1:1 is introduced, the pressure is 500 Pa, the bias voltage is 600 V, the temperature is 540°C, and the temperature is maintained for 3 hours to obtain a surface nitrogen-enriched layer; the nitrogen-to-hydrogen ratio is adjusted to 1:3, the pressure is 500 Pa, the bias voltage is 650 V, the temperature is 800°C, and the temperature is maintained for 4 hours to obtain a reinforced diffusion layer; and the nitrogen-to-hydrogen ratio is adjusted to 1:1, the pressure is 800 Pa, the bias voltage is 650 V, the temperature is 580°C, and the temperature is maintained for 2 hours to obtain a surface reinforced nitrogen-enriched layer. After fine grinding and ultrasonic cleaning, the substrate is chromized. The chromization treatment is a solid chromization treatment, the chromization temperature is 950°C, the chromization time is 8 hours, and the chromizing agent is 50% chromium powder, 5% NH4Cl, 8% cerium rare earth oxide, and the balance Al2O3 powder.

[0071] After gradient ion nitriding, the thickness of the nitrided layer is 130μm, the thickness of the CrN+Cr2N layer after nitriding and chromizing composite treatment is 70μm, the thickness of the nitrided austenite diffusion layer is 180μm, the surface hardness is greater than HV1924, and the Rockwell indentation grade reaches HF1, with good strength, toughness and bonding strength.

[0072] Example 3

[0073] This embodiment differs from Example 1 in that a nitrogen-to-hydrogen ratio of 1:2, a pressure of 600 Pa, a bias voltage of 600 V, a temperature of 580°C, and a holding time of 3 hours are used to obtain a surface nitrogen-enriched layer; a nitrogen-to-hydrogen ratio of 1:2, a pressure of 600 Pa, a bias voltage of 600 V, a temperature of 880°C, and a holding time of 3 hours are used to obtain a reinforced diffusion layer; and a nitrogen-to-hydrogen ratio of 1:2, a pressure of 600 Pa, a bias voltage of 650 V, a temperature of 600°C, and a holding time of 2 hours are used to obtain a surface reinforced nitrogen-enriched layer. After fine grinding and ultrasonic cleaning, the substrate is chromized. The chromization treatment is a solid chromization treatment with a chromization temperature of 1050°C and a chromization time of 10 hours. The chromizing agent is 50% chromium powder, 7% NH4Cl, 7% lanthanum rare earth oxide, and the balance Al2O3 powder.

[0074] After gradient ion nitriding, the thickness of the nitriding layer is 200μm, the thickness of the CrN+Cr2N layer after nitriding and chromizing composite treatment is 120μm, the thickness of the nitrided austenite diffusion layer is 350μm, the surface hardness is greater than HV2123, and the Rockwell indentation grade reaches HF1, with good strength, toughness and bonding strength.

[0075] Comparative Example 1

[0076] This comparative example is basically the same as Example 1, except that it is not subjected to gradient ion nitriding treatment and is directly subjected to chromizing treatment. The chromizing treatment results show that the thickness of the chromized layer is 2 μm at 840°C, there is no nitrided diffusion layer, and the surface hardness is HV398. Figure 4 As shown in the figure, it is the cross-sectional morphology of the chromized layer. It can be seen from the figure that there is no gradient structure on the interface and the chromized layer is very thin.

[0077] Comparative Example 2

[0078] This comparative example is essentially the same as Example 1, except that only the nitrogen-enriched layer was treated during nitriding. Chromizing was then performed after the nitrogen-enriched layer treatment. Results showed that the thickness of the nitrided layer after the nitrogen-enriched layer treatment was 15 μm, the thickness of the CrN+Cr2N layer after the combined nitriding and chromizing treatment was 12 μm, and the thickness of the nitrided austenite diffusion layer was 28 μm.

[0079] Comparative Example 3

[0080] This comparative example is basically the same as Example 1, except that the nitriding treatment is only for enhanced diffusion treatment. After enhanced diffusion treatment, chromization is performed. The results show that the thickness of the nitrided layer after enhanced diffusion treatment is 30 μm, the thickness of the CrN+Cr2N layer after nitriding and chromization combined treatment is 17 μm, and the thickness of the nitrided austenite diffusion layer is 53 μm. Figure 5 As shown in the figure, it is the surface morphology of the diffusion layer. No continuous diffusion layer is formed on the CrN+Cr2N surface, and the structure is loose.

[0081] Comparative Example 4

[0082] This comparative example is essentially the same as Example 1, except that only the surface strengthening nitrogen-rich layer treatment was performed during the nitriding treatment. The results show that after the strengthening nitrogen-rich layer treatment, the nitrided layer thickness is 18 μm, the CrN+Cr2N layer thickness is 13 μm after the combined nitriding and chromizing treatment, and the nitrided austenite diffusion layer thickness is 31 μm.

[0083] Comparative Example 5

[0084] This comparative example is essentially the same as Example 1, except that the nitriding treatment does not include a nitrogen-enriched layer. The results show that the thickness of the nitrided layer after ion nitriding is 35 μm, the thickness of the CrN+Cr2N layer after the combined nitriding and chromizing treatment is 20 μm, and the thickness of the nitrided austenite diffusion layer is 55 μm.

[0085] Comparative Example 6

[0086] This comparative example is essentially the same as Example 1, except that the nitriding treatment does not include enhanced diffusion treatment. The results show that the thickness of the nitrided layer after ion nitriding is 20 μm, the thickness of the CrN+Cr2N layer after the combined nitriding and chromizing treatment is 15 μm, and the thickness of the nitrided austenite diffusion layer is 33 μm.

[0087] Comparative Example 7

[0088] This comparative example is essentially the same as Example 1, except that the nitriding treatment does not include a surface-strengthening nitrogen-rich layer. The results show that after ion nitriding, the nitrided layer thickness is 38 μm, while after the combined nitriding and chromizing treatment, the CrN+Cr2N layer thickness is 18 μm. The nitrided austenite diffusion layer thickness is 50 μm, and the density of the CrN+Cr2N layer is reduced.

[0089] Comparative Example 8

[0090] This comparative example is basically the same as Example 1, except that the temperature for the nitrogen-rich layer treatment is 400° C. At this time, the nitrogen-rich nitriding effect is not ideal, and the result is similar to that of Comparative Example 5.

[0091] Comparative Example 9

[0092] This comparative example is basically the same as Example 1, except that the diffusion temperature for enhanced diffusion is 650° C. At this time, the enhanced diffusion effect is not ideal, and the result is similar to that of Comparative Example 6.

[0093] Comparative Example 10

[0094] This comparative example is basically the same as Example 1, except that the diffusion temperature for enhanced diffusion is 1000°C, resulting in severe nitrogen inward diffusion loss, reduced surface nitrogen concentration, and decreased density of the CrN+Cr2N layer.

[0095] Comparative Example 11

[0096] This comparative example is basically the same as Example 1, except that the temperature of the surface enhanced nitrogen-rich layer is 400°C, and the enhanced nitriding effect is not ideal. The result is similar to that of Comparative Example 7.

[0097] Comparative Example 12

[0098] This comparative example is basically the same as Example 1, except that the temperature of the surface strengthened nitrogen-rich layer is 700°C; as a result, the surface nitrogen concentration is reduced and the density of the CrN+Cr2N layer is reduced, which is similar to Comparative Example 7.

[0099] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A composite diffusion layer on the surface of stainless steel, characterized in that: The composite diffusion layer on the surface of the stainless steel comprises a surface CrN+Cr2N layer and a nitrided austenite diffusion layer; The thickness of the surface CrN+Cr2N layer is 15µm~150µm; The thickness of the nitrided austenite diffusion layer is 50µm to 400µm; The method for preparing the composite nitriding layer on the surface of stainless steel comprises: performing gradient ion nitriding treatment and chromizing treatment on the surface of the stainless steel substrate to obtain the composite nitriding layer; The gradient ion nitriding treatment includes: nitrogen-enriched layer treatment at 480°C to 600°C, enhanced diffusion treatment at 700°C to 900°C, and surface enhanced nitrogen-enriched treatment at 500°C to 600°C; The thickness of the nitriding layer after ion nitriding is 15µm~300µm; The chromizing treatment includes solid chromizing treatment; The chromizing treatment conditions are as follows: the chromizing temperature is 840° C. to 1050° C., and the chromizing time is 2 h to 10 h; The components and mass fractions of the chromizing agent in the chromizing treatment are: 40% to 50% chromium powder, 3% to 7% NH4Cl, 2% to 10% rare earth, and the balance Al2O3 powder; the rare earth is selected from one or more of yttrium oxide, cerium oxide, or lanthanum oxide.

2. The composite diffusion layer on the surface of stainless steel according to claim 1, characterized in that: The nitrogen-rich layer treatment conditions are as follows: treatment temperature of 480°C to 600°C, treatment time of 2h to 5h, nitrogen to hydrogen ratio of 3:1 to 1:3, pressure of 400Pa to 800Pa, and voltage of 500V to 700V; The conditions of the enhanced diffusion treatment are: treatment temperature of 700°C to 900°C, treatment time of 2h to 10h, nitrogen to hydrogen ratio of 1:1 to 1:3, gas pressure of 300Pa to 600Pa, and voltage of 500V to 700V; The conditions for the enhanced nitrogen enrichment treatment are: treatment temperature of 500°C to 600°C, treatment time of 2h to 5h, nitrogen to hydrogen ratio of 2:1 to 1:2, gas pressure of 400Pa to 800Pa, and voltage of 500V to 700V.

3. The composite diffusion layer on the surface of stainless steel according to claim 1, characterized in that: The preparation method further comprises pre-treating the surface of the substrate before the gradient ion nitriding treatment, and sequentially performing fine grinding, ultrasonic cleaning and drying on the substrate before the chromizing treatment.

4. The composite diffusion layer on the surface of stainless steel according to claim 3, characterized in that: The pretreatment comprises: performing ultrasonic degreasing, rust removal cleaning, drying and ion sputtering cleaning on the substrate in sequence.

5. A high-strength and high-toughness material, characterized in that: The method comprises a substrate, wherein the surface of the substrate is further provided with the stainless steel surface composite diffusion layer as claimed in any one of claims 1 to 4.

6. Use of the high-strength and high-toughness material according to claim 5 in the preparation of molds, anti-corrosion parts in the marine, energy and chemical industries, and moving parts of high-end equipment.

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