High-nitrogen HK30 heat-resistant austenitic stainless steel and preparation method thereof

Abstract

The invention relates to the technical field of metal materials, in particular to high-nitrogen HK30 heat-resistant austenitic stainless steel and a preparation method thereof, and the high-nitrogen HK30 heat-resistant austenitic stainless steel is prepared by adding niobium and nitrogen elements on the basis of traditional HK30 stainless steel. By regulating and controlling components and heat treatment conditions, the phenomena of plastic deformation instability and sawtooth yield in the HK30 heat-resistant austenitic stainless steel are inhibited, and surface roughening is reduced; according to the method, the work hardening capacity of the HK30 heat-resistant austenitic stainless steel is enhanced, and the yield strength and the tensile strength are improved.

Description

Technical Field

[0001] The invention relates to the technical field of metal materials, and in particular to a high-nitrogen HK30 heat-resistant austenitic stainless steel and a preparation method thereof. Background Art

[0002] The main problems facing the automotive industry at present include fuel efficiency, greenhouse gas emissions and automobile collision safety. With the introduction of the "National VI" standard, it is inevitable to improve engine emission indicators, and thus the application of automotive turbochargers has become increasingly widespread. The introduction of turbocharger technology has greatly improved the fuel economy and efficiency of modern automobile engines. Variable geometry technology (VGT) controls the flow of engine exhaust gas by adjusting the geometry of the turbine blades to maintain the best performance of the engine at low and high speeds. Due to the harsh working environment of turbocharger components, the selected materials need to have good high temperature fatigue, creep strength and micro-stability in addition to adapting to continuous high temperature and corrosive environments. HK30 stainless steel has good heat resistance, wear resistance and fatigue resistance, so it is very suitable for certain fields that require high temperature wear, corrosion resistance and a certain degree of fatigue resistance, and is often selected as the material for preparing turbocharger blades. The service temperature of this material is 350℃~650℃, which is just in the sensitive temperature range of dynamic strain aging of HK30 material.

[0003] However, a large number of experimental studies have shown that austenitic heat-resistant stainless steel with excellent mechanical properties often suffers from severe plastic instability during deformation, which mainly manifests in two forms on the local deformation band, namely, the Luders band and the Portevin–Le Chatelier (PLC) band. The Luders band refers to the area where local deformation occurs at the beginning of the yield point drop, which corresponds to the yield platform on the engineering stress-strain curve during the propagation process; the PLC band represents various irregular and uneven deformation bands, which correspond to different forms of stress serrations on the tensile curve. Local deformation plastic instability will cause surface roughening of the material after deformation, resulting in weakened structural stability of the material and even premature failure in some cases. At the same time, the PLC effect can occur along with the work hardening process, and there is currently no effective way to eliminate its negative impact. This has become a key factor restricting the promotion and application of austenitic heat-resistant steel, and has also become a hot issue in the field of basic research on austenitic heat-resistant stainless steel.

[0004] The microscopic mechanism of the PLC effect is generally believed to be dynamic strain aging (DSA), that is, the interaction between solute atoms and mobile dislocations. It is generally believed that dynamic strain aging is usually related to substitutional atoms (such as Cr and Nb) at high temperatures, while the occurrence of dynamic strain aging at lower temperatures is related to interstitial atoms (such as C and N). For HK30 heat-resistant austenitic stainless steel, Cr, Mn, Nb, C, N, etc. are all important factors that trigger DSA. At the same time, the Cr precipitated in the alloy 23 Second phases such as C6, Cr2N, and NbC will also have a significant impact on the atomic diffusion and dislocation movement of stainless steel.

[0005] Studies have shown that the solid solution strengthening effect of nitrogen can significantly improve the yield strength of steel, which can reach 200-350% of the yield strength of traditional steel. The strengthening principle of nitrogen-strengthened steels disclosed in patents CN116574868A, CN115369301A, and CN101429621A is that nitrogen is evenly distributed in the matrix through solid solution and nitriding treatment. The solid solution strengthening of nitrogen is mainly manifested in two aspects: (1) interstitial nitrogen atoms are dissolved in the matrix, causing lattice distortion, interacting with dislocations, hindering dislocation movement, and increasing the strength of stainless steel; (2) nitrogen atoms are concentrated on dislocation lines, pinning dislocations and increasing strength. Summary of the invention

[0006] In view of the above-mentioned shortcomings of the prior art, the present invention provides a solution for suppressing the plastic instability of HK30 heat-resistant austenitic stainless steel, which can simultaneously suppress the nucleation and propagation of Luders bands and PLC bands during tensile deformation of this type of steel, and can improve the work hardening ability and tensile strength while ensuring a certain plasticity.

[0007] Technical Solution

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] The invention provides a high nitrogen HK30 heat-resistant austenitic stainless steel. The HK30 heat-resistant austenitic stainless steel with a nitrogen content of 0.4-0.6% is prepared by adding niobium and nitrogen elements to traditional HK30 stainless steel.

[0010] Furthermore, the composition of the heat-resistant austenitic stainless steel includes, by mass percentage, 24-26% Cr, 19-22% Ni, 0.5-1.0% Mn, 0.25-0.35% C, 1.20-1.50% Nb, 0.4-0.6% N, O≤0.10%, and the balance is Fe.

[0011] Furthermore, the yield strength at room temperature is 420-468 MPa, the tensile strength is 707-806 MPa, and the elongation is 12-17%.

[0012] A method for preparing high-nitrogen HK30 heat-resistant austenitic stainless steel comprises the following steps: raw material preparation - pressing or injection molding - sintering nitriding - heat treatment.

[0013] Further, the raw material is prepared by a gas atomization method, the atomization pressure is 2-8 MPa of nitrogen, and the powder particle size after preparation is D10=3-12 μm, D50=9-18 μm, D90=15-30 μm, and the powder nitrogen content is 0.3-0.5% N.

[0014] The raw material is powdered by nitrogen atomization, and the atomization pressure is 2-8MPa. The raw material is melted, blown and atomized in a nitrogen-containing atmosphere, so that the escape of nitrogen in the alloy steel melt can be suppressed, and the obtained high nitrogen steel powder has a high nitrogen content and a low oxygen content. At the same time, during the atomization process, the alloy steel melt is broken into small droplets under the impact of the nitrogen-containing atmosphere, and solidified into fine powder, so that the obtained high nitrogen steel powder has a finer particle size and a uniform particle size distribution. After the preparation is completed, the powder particle size is D10=3-12μm, D50=9-18μm, D90=15-30μm, and the powder nitrogen content is 0.3-0.5%N.

[0015] Further, the powder is formed by pressing or injection molding, and then sintered by nitrogen to obtain products with different nitrogen contents. The powder metallurgy process is powder pressing.

[0016] Furthermore, the powder is molded by injection molding, and the metal injection molding process includes feeding--injection molding--debinding;

[0017] Feed material preparation: The feed material preparation uses 90% by mass of metal powder and 10% by mass of binder, and mixes them on an open mill for 1.5 hours at a mixing speed of 30 r / min and a temperature of 180°C;

[0018] Injection molding degreasing: The injection process is that the mold temperature is 90-100℃, the maximum injection temperature is 175-185℃, and the injection pressure is 80-90Mpa;

[0019] Debonding: The injection molded product is catalytically degreased in a fuming nitric acid atmosphere at a temperature of 110-120°C for 4-6 hours.

[0020] The catalytic debinding process cannot completely debind the binder, and thermal debinding is required in the early stage of atmosphere sintering.

[0021] Furthermore, the sintering nitriding process includes negative pressure debinding (i.e., hot debinding), partial pressure sintering, and forced cooling;

[0022] The temperature of negative pressure degreasing stage is ≥600℃, and the holding time is ≥30min;

[0023] The pressure of sintering and nitriding in the partial pressure sintering stage is 20-80Kpa, the temperature of sintering and nitriding is 1290-1340°C, and the time of sintering and nitriding is 1-3h;

[0024] Forced cooling stage, cooling rate ≥ 10℃ / min;

[0025] Among them, the protective gas used in the sintering and nitriding stage is nitrogen. After sintering, the product density is 7.77-7.80g / cm 3 , the nitrogen content is 0.4-0.6wt.%.

[0026] During the nitriding process, the dissolution of nitrogen atoms starts from the sample surface and gradually diffuses into the interior of the sample. As the nitriding process progresses, the nitrogen content on the surface will always be higher than that on the interior until the surface nitrogen content reaches equilibrium. However, at this time, the nitriding rate will drop sharply, so it is difficult to achieve nitrogen equilibrium inside the sample, and thus it is difficult for the entire sample to achieve nitrogen equilibrium.

[0027] Furthermore, the heat treatment process is as follows: the nitrided sample is subjected to a solution treatment, the temperature of the solution treatment is 1100° C. to 1150° C., and the holding time of the solution treatment is 2 to 4 hours.

[0028] After solution treatment, a relatively uniform nitrogen content and austenite structure are obtained. The HK30 heat-resistant austenite stainless steel product obtained by the method of the present invention has white round dot precipitates dispersed in the crystal and block precipitates precipitated along the grain boundary in the structure after solution treatment, and the block precipitates have a size of 2 to 4 μm and a spacing of 20 to 50 μm.

[0029] After the solution treatment, a large amount of nitrogen elements are dissolved in the matrix, which plays a role of solid solution strengthening; further, with the increase of nitrogen content, the collective grain diameter decreases, resulting in a certain degree of fine grain strengthening; further, there are colored dot precipitates dispersed in the crystal and blocky precipitates precipitated along the grain boundary in the matrix, which play a role of precipitation strengthening. These three kinds of strengthening are combined to make the high nitrogen HK30 heat-resistant austenitic stainless steel obtained by the present invention have high strength and more excellent high temperature performance.

[0030] The high nitrogen HK30 heat-resistant austenitic stainless steel prepared by the method described above can weaken the dynamic strain aging of HK30 heat-resistant austenitic stainless steel.

[0031] The high nitrogen HK30 heat-resistant austenitic stainless steel has a room temperature yield strength of 420-468 MPa, a tensile strength of 707-806 MPa, and an elongation of 12-17%.

[0032] The high-temperature mechanical properties of the product are less affected by dynamic strain aging. After conventional HK30 is stretched at 650°C, rough stripes appear on the surface caused by dynamic strain aging. The HK30 prepared by the method has a yield strength of 260-316MPa, a tensile strength of 588-667MPa, and an elongation of 13-26% at 650°C. After stretching, the surface of the sample is smooth without any roughness.

[0033] The nucleation and propagation of local deformation bands of the high nitrogen HK30 heat-resistant austenitic stainless steel are suppressed. The sample is heated to 2.5×10 -4 -1×10 -2 1s -1 There is no serration fluctuation during strain rate stretching. At 550-650℃, conventional HK30 shows C-type serration with a larger amplitude, while HK30 prepared by this method shows only A+B-type serration with a smaller amplitude, and the critical strain of dynamic strain aging is significantly improved.

[0034] The present invention affects the interaction between the key solute atoms and dislocations in dynamic strain aging in HK30 by adding certain Nb and N elements, and inhibits the nucleation and propagation of local deformation bands. Nb microalloying can promote the precipitation of nanometer-level second phase particles Nb (C, N) during rolling, which plays a role in pinning austenite grain boundaries and preventing grain growth, and on the other hand, the Nb (C, N) dispersedly distributed in the matrix also plays a role in pinning dislocations and hindering dislocation slip; the nitrogen content will affect the strength of stainless steel. Compared with other austenitic stainless steels that do not contain nitrogen, the strength of high-nitrogen austenitic stainless steel is significantly increased. Under the condition of maintaining excellent fracture toughness, its strength value is 2 to 4 times higher than that of AISI 200 and 300 series stainless steels. At the same time, in terms of corrosion resistance, 1% of nitrogen can achieve the corrosion resistance of 20% chromium, and in terms of stabilizing austenite, 1% of nitrogen in stainless steel is equivalent to 18% of nickel. In addition, nitrogen has better biocompatibility than nickel and is low in price. At the same time, reasonable selection of solid solution treatment conditions can make N, C and Cr, Nb and other elements attract each other and even combine to form compounds, reducing the probability of the appearance of solute elements that trigger DSA.

[0035] While significantly suppressing dynamic strain aging, the purpose of improving high-temperature performance is achieved, thereby expanding the application scope of the alloy and having important application value in industry.

[0036] High nitrogen powder with high nitrogen content and high fine powder yield is obtained by nitrogen atomization powder making. The MIM process is introduced into the production of turbocharger blades, which effectively solves the manufacturing needs of blade precision casting process; at the same time, the Nb element improves the mechanical properties of steel through fine grain strengthening and precipitation strengthening. By adding Nb and N elements, on the one hand, the high-temperature comprehensive performance of the alloy can be improved; on the other hand, the interaction between interstitial atoms and dislocations is affected, and combined with the regulation of heat treatment process, N, C and Cr, Nb and other elements can attract each other and even combine to form compounds, reducing the probability of the appearance of solute elements that cause DSA. While significantly suppressing the PLC effect, the purpose of improving mechanical properties is achieved, thereby expanding the application range of the alloy, which has important application value in industry.

[0037] Beneficial Effects

[0038] Compared with the known public technology, the technical solution provided by the present invention has the following beneficial effects:

[0039] 1. The present invention suppresses the plastic deformation instability and serration yielding phenomenon in HK30 heat-resistant austenitic stainless steel by regulating the composition and heat treatment conditions, and reduces the occurrence of surface roughening.

[0040] 2. The method adopted by the present invention enhances the work hardening ability of HK30 heat-resistant austenitic stainless steel and improves the yield strength and tensile strength.

[0041] 3. The present invention can manufacture high-temperature parts with complex shape features, and the process is simple, which has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 The microstructure morphology of high nitrogen HK30 heat-resistant austenitic stainless steel after solution treatment in Example 1 (a), Example 2 (b), and Example 3 (c) of the present invention.

[0044] Figure 2 The present invention is for the HK30 heat-resistant austenitic stainless steel before modification (a), and after modification to obtain different nitrogen contents of 0.4% N (b), 0.5% N (c), and 0.6% N (d). After high-temperature uniaxial tensile deformation, the stress serration fluctuation is weakened or even disappears, indicating that the modification treatment of the present invention significantly inhibits the plastic instability behavior of high-nitrogen HK30 heat-resistant austenitic stainless steel.

[0045] Figure 3 These are pictures of tensile test pieces of high nitrogen HK30 heat-resistant austenitic stainless steel after fracture according to Comparative Example (a), Example 1 (b), Example 2 (c), and Example 3 (d) of the present invention. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] The present invention will be further described below in conjunction with the embodiments.

[0048] (I) Preparation of HK30 austenitic stainless steel

[0049] Embodiment 1:

[0050] The preparation process of high nitrogen HK30 heat-resistant austenitic stainless steel is raw material preparation - pressing or injection molding - sintering nitriding - heat treatment process. The details are as follows:

[0051] (1) Raw material preparation:

[0052] HK30 heat-resistant austenitic stainless steel powder, with a certain amount of Nb element added, the specific composition includes 25.16% Cr, 20.89% Ni, 1.46% Nb, 0.76% Mn, 0.73% Si, 0.34% C, 0.042% O, and the balance is Fe;

[0053] The HK30 heat-resistant austenitic stainless steel powder is prepared by gas atomization, and the gas atomization pressure is 3MPa of nitrogen, so that the powder has low oxygen content and good fluidity. After the preparation, the powder particle size is D10=3-12μm, D50=9-18μm, D90=15-30μm, and the powder particle size distribution is relatively concentrated. Under the combined effect of the atomization medium nitrogen and the alloy elements at high temperature, a certain amount of nitrogen is dissolved in the powder, and the content is about 0.096%. The powder composition is as follows: 25.16% Cr, 20.89% Ni, 1.46% Nb, 0.76% Mn, 0.73% Si, 0.34% C, 0.096% N, 0.042% O, and the balance is Fe.

[0054] (2) Injection molding degreasing:

[0055] Feed material preparation: The feed material preparation uses 90% by mass of metal powder and 10% by mass of binder; the materials are mixed on an open mill for 1.5 hours at a mixing speed of 30 r / min and a temperature of 180°C.

[0056] The binder composition is polyoxymethylene (POM) 87.5wt.%, polyethylene (PE) 5wt.%, ethylene-vinyl acetate copolymer (EVA) 2wt.%, paraffin (PW) 2wt.%, stearic acid (SA) 2wt.%, antioxidant (B215) 1.5wt.%;

[0057] Injection molding: The specific injection process is mold temperature 100℃, nozzle temperature 180℃, first-stage injection temperature 180℃, second-stage injection temperature 180℃, third-stage injection temperature 175℃, and injection pressure 90MPa.

[0058] Debonding: The injection molded product is subjected to catalytic degreasing in a fuming nitric acid atmosphere at a temperature of 120°C for 7 hours.

[0059] (3) Sintering nitriding: The sintering process is mainly divided into three parts: negative pressure degreasing (i.e. hot degreasing), partial pressure sintering, and forced cooling.

[0060] Negative pressure degreasing stage: the temperature was raised to 350℃ at 10℃ / min and kept for 30min, then raised to 600℃ at 10℃ / min and kept for 30min, the gas pressure was 0 and the gas flow rate was 20L / min;

[0061] Partial pressure sintering stage: increase the temperature to 1050℃ at a rate of 10℃ / min and keep it for 30min, then increase the temperature to 1250℃ at a rate of 5℃ / min and keep it for 60min, finally increase the temperature to 1320℃ at a rate of 5℃ / min and keep it for 210min, after sintering, reduce the temperature to 950℃ at a rate of 10℃ / min, during the whole partial pressure sintering stage, the gas pressure is maintained at 20KPa, and the gas flow rate is 20L / min;

[0062] Forced cooling stage: Start the fan, force cool to 70℃ at 5℃ / min, open the furnace door to obtain the sintered billet.

[0063] Among them, the protective gas used in the sintering nitriding stage is nitrogen.

[0064] (4) Heat treatment process: The process is 1100℃ insulation for 4 hours for solid solution treatment and oil cooling.

[0065] The nitrogen content of the sample after sintering and nitriding is 0.4093wt.%, the oxygen content is 0.0006wt.%, and the carbon content is 0.3064wt.%.

[0066] The density of stainless steel parts can exceed 7.7g / cm 3, the nitrogen content can reach 0.4.wt%. The alloy needs to be heat treated.

[0067] After solution treatment, the sample with 0.4% N has white dots dispersed in the crystal and blocky precipitates precipitated along the grain boundary. The size of the blocky precipitates is 2 to 4 μm, and the spacing is 20 to 50 μm.

[0068] Embodiment 2:

[0069] The only difference from Example 1 is that the gas pressure is maintained at 50 KPa during the entire partial pressure sintering stage.

[0070] The nitrogen content of the sample obtained after sintering and nitriding was 0.4908wt.%, the oxygen content was 0.0042wt.%, and the carbon content was 0.3007wt.%.

[0071] The density of stainless steel parts can exceed 7.7g / cm 3 , the nitrogen content can reach 0.5.wt%. The alloy needs to be heat treated.

[0072] After solution treatment, the sample with 0.4908wt.%N has white dot precipitates dispersed in the crystal and block precipitates precipitated along the grain boundary. The size of the block precipitates is 2-4μm and the spacing is 20-50μm.

[0073] Embodiment 3:

[0074] The only difference from Example 1 is that the gas pressure is maintained at 80 KPa during the entire partial pressure sintering stage.

[0075] The nitrogen content of the sample after sintering and nitriding is 0.6069wt.%, the oxygen content is 0.0010wt.%, and the carbon content is 0.2989wt.%.

[0076] The density of stainless steel parts can exceed 7.7g / cm3 and the nitrogen content can reach 0.6.wt%. The alloy needs to be heat treated.

[0077] After solution treatment, the sample with 0.6% N has white dots dispersed in the crystal and blocky precipitates precipitated along the grain boundary. The size of the blocky precipitates is 2 to 4 μm, and the spacing is 20 to 50 μm.

[0078] With the increase of nitrogen sintering pressure, the fine strengthening phase dispersed in HK30 sample has no obvious change.

[0079] Comparative Example:

[0080] The difference from Example 1 is that the gas pressure is maintained at 15 KPa during the entire partial pressure sintering stage and the sintering atmosphere is argon. Since there is no nitriding during the sintering process, the obtained product has almost no nitrogen residue and the nitrogen content is 0.015%.

[0081] (II) Performance test

[0082] Test method: A standard tensile specimen with a diameter of 5 mm was used at a strain rate of 1.8×10 -3 s -1 , tensile tests were carried out on an American Instron 3369 mechanical testing machine within the temperature range of 300-650°C (100°C interval).

[0083] The results of normal temperature and high temperature tensile tests under the same conditions show that:

[0084] Embodiment 1:

[0085] Under room temperature stretching, the sample has a yield strength of 420 MPa, a tensile strength of 707 MPa, and an elongation of 17.05%.

[0086] Under high temperature tensile conditions, at 300-500℃, the nucleation and propagation of the local deformation band of the modified HK30 heat-resistant austenitic stainless steel are suppressed, and the stress-strain curve is smooth or has slight sawtooth fluctuations. At 550℃, obvious sawtooth yielding phenomenon begins to appear, and the critical strain of sawtooth yielding increases compared with the control group. The surface of the sample is smooth after fracture, and no roughness occurs; further, the high temperature mechanical properties are improved, the yield strength at 650℃ is 260-285MPa, the tensile strength is 590-643MPa, and the elongation is 14.51-21.04%.

[0087] Embodiment 2:

[0088] Under room temperature stretching, the sample has a yield strength of 450 MPa, a tensile strength of 804 MPa, and an elongation of 13.02%.

[0089] Under high temperature tensile conditions, the nucleation and propagation of the local deformation band of the modified HK30 heat-resistant austenitic stainless steel are suppressed. At 300-500°C, the stress-strain curve is smooth or has slight serrated fluctuations. The surface of the sample is smooth after fracture, and no roughness occurs. Sawtooth yield will only appear in the stress-strain curve at 650°C, and the critical strain of serrated yield is increased compared with the comparative example and Example 1. The yield strength at 650°C at each strain rate is 298-316MPa, the tensile strength is 632-661MPa, and the elongation is 6.50%-21.12%.

[0090] Embodiment 3:

[0091] Under room temperature stretching, the yield strength of the sample is 468MPa, the tensile strength is 806MPa, and the elongation is 12.83%.

[0092] Under high temperature tensile conditions, the nucleation and propagation of the local deformation band of the modified HK30 heat-resistant austenitic stainless steel are suppressed. At 300-550℃, the stress-strain curve is smooth or has slight serrated fluctuations. The surface of the sample is smooth after breaking, and no roughness occurs. Sawtooth yield will appear in the stress-strain curve at 650℃, and the critical strain of serrated yield is increased compared with the comparative example, example 1, and example 2. 284-305MPa, the tensile strength is 588-667MPa, and the elongation is 12%-21%.

[0093] Comparative Example:

[0094] The uniaxial tensile test was carried out at room temperature: the yield strength of the comparison sample was 258.74 MPa, the tensile strength was 644 MPa and the elongation was 23.43%.

[0095] In the high temperature tensile test: the samples stretched at 350-650℃ all showed serrated yield, and the morphology of the samples after fracture showed obvious surface roughening. The high temperature stretching at 650℃ at various strain rates showed a large C-shaped serration, and the yield strength of the comparative example was 221MPa-225MPa, the tensile strength was 468MPa-486MPa, and the elongation was 19.17%-27.82%.

[0096] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high nitrogen HK30 heat-resistant austenitic stainless steel, characterized in that: HK30 heat-resistant austenitic stainless steel with a nitrogen content of 0.4-0.6% is prepared by adding niobium and nitrogen elements to traditional HK30 stainless steel.

2. The high nitrogen HK30 heat-resistant austenitic stainless steel according to claim 1, characterized in that: Measured by mass percentage, the composition of the heat-resistant austenitic stainless steel includes: 24-26% Cr, 19-22% Ni, 0.5-1.0% Mn, 0.25-0.35% C, 1.20-1.50% Nb, 0.4-0.6% N, O≤0.10%, and the balance is Fe.

3. The high nitrogen HK30 heat-resistant austenitic stainless steel according to claim 1, characterized in that: The yield strength at room temperature is 420-468MPa, the tensile strength is 707-806MPa, and the elongation is 12-17%.

4. A method for preparing high nitrogen HK30 heat-resistant austenitic stainless steel as claimed in claim 1, characterized in that: The preparation process route is raw material preparation-pressing or injection molding-sintering nitriding-heat treatment process.

5. The method for preparing high nitrogen HK30 heat-resistant austenitic stainless steel according to claim 4, characterized in that: Raw material preparation: The raw material is prepared by atomization method, and the atomization pressure is 2-8 MPa of nitrogen. After preparation, the powder particle size is D10=3-12 μm, D50=9-18 μm, D90=15-30 μm, and the powder nitrogen content is 0.3-0.5% N.

6. The method for preparing high nitrogen HK30 heat-resistant austenitic stainless steel according to claim 5, characterized in that: The powder is formed by pressing or injection molding, and then sintered by nitrogen to obtain products with different nitrogen contents.

7. The method for preparing high nitrogen HK30 heat-resistant austenitic stainless steel according to claim 6, characterized in that: The powder is molded by injection molding method. The metal injection molding process includes feeding-injection molding-debonding; Feed material preparation: The feed material preparation uses 90% by mass of metal powder and 10% by mass of binder, and mixes them on an open mill for 1.5 hours at a mixing speed of 30 r / min and a temperature of 180°C; Injection molding degreasing: The injection process is that the mold temperature is 90-100℃, the maximum injection temperature is 175-185℃, and the injection pressure is 80-90Mpa; Debonding: The injection molded product is catalytically degreased in a fuming nitric acid atmosphere at a temperature of 110-120°C for 4-6 hours.

8. The method for preparing high nitrogen HK30 heat-resistant austenitic stainless steel according to claim 4, characterized in that: The sintering nitriding process includes negative pressure degreasing, partial pressure sintering, and forced cooling; The temperature of negative pressure degreasing stage is ≥600℃, and the holding time is ≥30min; The pressure of sintering and nitriding in the partial pressure sintering stage is 20-80Kpa, the temperature of sintering and nitriding is 1290-1340°C, and the time of sintering and nitriding is 1-3h; Forced cooling stage, cooling rate ≥ 10℃ / min; Among them, the protective gas used in the sintering nitriding stage is nitrogen.

9. The method for preparing high nitrogen HK30 heat-resistant austenitic stainless steel according to claim 4, characterized in that: The heat treatment process comprises: performing a solution treatment on the nitrided sample, wherein the temperature of the solution treatment is 1100° C. to 1150° C., and the holding time of the solution treatment is 2 to 4 hours.

10. The high nitrogen HK30 heat-resistant austenitic stainless steel prepared by the method according to claims 4-9 can reduce the dynamic strain aging of HK30 heat-resistant austenitic stainless steel.

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