CN118048581A

CN118048581A - High-nitrogen austenitic stainless steel and preparation method thereof

Info

Publication number: CN118048581A
Application number: CN202410183439.6A
Authority: CN
Inventors: 牛广斌; 王大鹏; 傅万堂; 张国利; 张金珠; 吕知清; 王振华
Original assignee: TIANJIN HEAVY EQUIPMENT ENGINEERING RESEARCH CO LTD; Yanshan University; China First Heavy Industries Co Ltd
Current assignee: TIANJIN HEAVY EQUIPMENT ENGINEERING RESEARCH CO LTD; Yanshan University; China First Heavy Industries Co Ltd
Priority date: 2024-02-19
Filing date: 2024-02-19
Publication date: 2024-05-17

Abstract

The invention discloses high-nitrogen austenitic stainless steel and a preparation method thereof, belongs to the technical field of stainless steel, and solves the problem of insufficient strength of high-nitrogen austenitic stainless steel alloy after hot forging and solution treatment in the prior art. The high-nitrogen austenitic stainless steel comprises the following components in percentage by mass, wherein the balance of ：C0.08％～0.11％,Si 0.40％～1.2％,Mn 18.5％～21.0％,Cr 18％～19.5％,Ni0.5％～2.3％,V 0.35％～0.95％,N 0.68％～0.75％,Nb 0.01％～0.05％,Cu≤0.01％,Al≤0.01％,P≤0.020％,S≤0.010％, is Fe and unavoidable trace impurities. The high-nitrogen austenitic stainless steel of the present invention is excellent in strength after hot forging and solution treatment.

Description

High-nitrogen austenitic stainless steel and preparation method thereof

Technical Field

The invention relates to the technical field of stainless steel, in particular to high-nitrogen austenitic stainless steel and a preparation method thereof.

Background

The high-nitrogen austenitic stainless steel is a novel engineering material which appears in recent years, the nitrogen content of the high-nitrogen austenitic stainless steel is more than 0.40%, and the nitrogen content of the high-nitrogen ferritic and martensitic stainless steel is more than 0.08%. Nitrogen is adopted as an alloy element, so that not only can the austenite structure be stabilized, the strength be improved, the toughness is not obviously reduced, but also the corrosion resistance can be improved. The austenitic stainless steel with high nitrogen, chromium and manganese is one of materials with the best combination of toughness in the existing metal materials, has the advantages of high yield strength and plasticity, good corrosion resistance, low magnetic permeability and the like, and is widely applied to various fields such as generator rotor guard rings, biomedicine, automobile manufacturing industry, chemical industry, ocean engineering and the like. Because of the austenitic structure of such steels, the strength cannot be increased by heat treatment, usually by work hardening, which occurs during cold deformation or warm forging, the strength of the material is greatly increased by sacrificing part of the plasticity. In the engineering production process, along with the increasing demand of the product size of the austenitic stainless steel forgings with high nitrogen, chromium and manganese, especially the production of large forgings, the large equipment, the space field and the special die are needed for cold deformation or warm forging deformation, and the manufacturing period and the production cost are influenced. In order to reduce the deformation amount of the work hardening or to eliminate the need for the work hardening by cold deformation or warm forging, it is a need to provide a high-nitrogen austenitic stainless steel alloy having a high base yield strength (for example, after hot forging or solution treatment).

Disclosure of Invention

In view of the above, the present invention aims to provide a high-nitrogen austenitic stainless steel and a preparation method thereof, which are used for solving the problem of insufficient strength of the existing high-nitrogen austenitic stainless steel alloy after hot forging and solution treatment.

The aim of the invention is mainly realized by the following technical scheme:

the invention provides high-nitrogen austenitic stainless steel, which comprises the following components in percentage by mass, wherein the balance of ：C 0.08％～0.11％,Si 0.40％～1.2％,Mn18.5％～21.0％,Cr 18％～19.5％,Ni 0.5％～2.3％,V 0.35％～0.95％,N0.68％～0.75％,Nb 0.01％～0.05％,Cu≤0.01％,Al≤0.01％,P≤0.020％,S≤0.010％, is Fe and unavoidable trace impurities.

Further, the high nitrogen austenitic stainless steel may comprise ：C0.09％～0.11％,Si 0.50％～1.2％,Mn 18.5％～20.0％,Cr 18.5％～19.4％,Ni 0.5％～2.3％,V 0.40％～0.95％,N 0.68％～0.75％,Nb 0.01％～0.03％,Cu≤0.008％,Al≤0.009％,P≤0.010％,S≤0.010％, parts by mass of Fe and unavoidable trace impurities in balance.

Further, in the components of the high-nitrogen austenitic stainless steel, the mass percentage of C is as follows: 0.095% -0.11%.

Further, in the components of the high-nitrogen austenitic stainless steel, the mass percentage of Mn is as follows: 18.6 to 19.5 percent.

Further, in the components of the high-nitrogen austenitic stainless steel, the mass percentage of Cr is as follows: 18.7 to 19.2 percent.

Further, in the components of the high-nitrogen austenitic stainless steel, the mass percentage of Ni is as follows: 0.5 to 2.1 percent.

Further, the microstructure of the high-nitrogen austenitic stainless steel is austenite and nitride which is dispersed.

Furthermore, the grain size of the high-nitrogen austenitic stainless steel reaches more than 6 grades, and the grains are uniform.

Further, the grain size difference is 0.5 or less.

The invention also provides a preparation method of the high-nitrogen austenitic stainless steel, which comprises the following steps:

Step 1: smelting a steel ingot;

step 2: homogenizing the steel ingot;

step 3: forging and cogging the steel ingot, and water-cooling after forging;

step 4: and carrying out solution treatment on the forging stock to obtain the high-nitrogen austenitic stainless steel.

Further, in step 2, the homogenization treatment includes the following steps:

S201, heating the steel ingot to 600-650 ℃ and preserving heat;

S202, heating to 800-850 ℃ and preserving heat;

S203, heating to 1150-1180 ℃ and preserving heat; wherein the temperature rise rate in S202 is smaller than the temperature rise rate in S203.

Further, the temperature rise rate in S202 is less than 40 ℃/h.

Further, the temperature rise rate in S203 is 70 ℃/h or more.

Further, in the step3, the initial forging temperature is controlled to be 1150-1180 ℃.

In step 3, the final forging temperature is controlled to 950 ℃ or higher.

Compared with the prior art, the invention can at least realize one of the following beneficial effects:

a) According to the high-nitrogen austenitic stainless steel, the solid solution strengthening effect of the alloy is improved by accurately controlling the contents of carbon, silicon, vanadium, niobium and nickel in the alloy; and the epsilon-phase precipitation temperature is controlled by cooperatively controlling the matching of manganese, chromium and other alloy elements, so that hot forging cracks are reduced; in addition, the solid solubility of nitrogen in the matrix can be improved under normal pressure smelting by adding each alloy element, so that the nitrogen content in normal pressure smelting can reach more than 0.68%; by accurately controlling the content of O, S, P, al, the content of inclusions in the alloy is reduced, the purity of the alloy can be improved, the occurrence probability of hot forging cracks is reduced, and the uniformity of crystal grains and the precipitation and distribution of crystal boundaries are ensured.

B) The high-nitrogen austenitic stainless steel composition is favorable for forming dispersed nitrides in an austenitic structure, and plays a role in refining grains and improving matrix strength.

C) The preparation method of the high-nitrogen austenitic stainless steel adopts smelting, forging and solution treatment, combines the steps of precisely controlling homogenization treatment and parameters of each step through precise control of components, and combines the precise control of forging technological parameters, so that the basic strength of the high-nitrogen austenitic stainless steel can be remarkably improved, the performance use requirements can be met, the deformation quantity of the high-nitrogen austenitic stainless steel for processing and strengthening can be reduced, even the cold deformation or warm forging deformation is not needed for processing and strengthening, and the manufacturing procedures and cost are reduced.

D) The high-nitrogen austenitic stainless steel of the present invention is excellent in strength after hot forging and solution treatment, for example, the properties of a forged blank are as follows: the tensile strength σ _b is 950MPa or more, for example 956 to 1110MPa; the yield strength sigma _0.2 is more than 690MPa, for example 690-840 MPa; the elongation is more than 35%, such as 35% -46%; the surface shrinkage is more than 60%, for example 60% -69%; the impact energy is 56J or more, for example, 56 to 135J. The properties after solid solution were as follows: the tensile strength sigma _b is more than 920MPa, for example, 920-984 MPa; the yield strength sigma _0.2 is more than 620MPa, for example, 620-675 MPa; the elongation is more than 38%, such as 38% -52%; the surface shrinkage is more than 59%, for example, 59% -70%; the impact energy is 70J or more, for example, 70 to 138J.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, like reference numerals being used to refer to like parts throughout the several views.

FIG. 1 is a grain size of the high nitrogen austenitic stainless steel of example 1;

FIG. 2 is a microstructure of the high nitrogen austenitic stainless steel of example 1.

Detailed Description

Preferred embodiments of the present invention are described in detail below with reference to the attached drawing figures, which form a part of the present invention and are used in conjunction with embodiments of the present invention to illustrate the principles of the present invention.

The invention provides high-nitrogen austenitic stainless steel, which comprises the following components in percentage by mass, wherein the balance of ：C 0.08％～0.11％,Si 0.40％～1.2％,Mn18.5％～21.0％,Cr 18％～19.5％,Ni 0.5％～2.3％,V 0.35％～0.95％,N0.68％～0.75％,Nb 0.01％～0.05％,Cu≤0.01％,Al≤0.01％,P≤0.010％,S≤0.010％, is Fe and unavoidable trace impurities.

The following is a specific description of the action and the selection of the amounts of the components contained in the invention:

N: n has strong solid solution strengthening capability, and the strength of the steel is continuously improved along with the increase of the content of N, but the fracture toughness is not obviously reduced; n is an austenite stabilizing element that inhibits the formation of ferrite and strain-induced martensite in the steel; in addition, N is very advantageous for improving the pitting resistance and the stress corrosion resistance of steel. However, since N is dissolved in austenite under normal pressure and influenced by the alloy components, the present invention ensures that the N content is 0.68% to 0.75% by the ratio of the alloy components.

Cr: cr is one of the most main alloying elements in austenitic stainless steel, cr is added into the high-nitrogen chromium manganese austenitic stainless steel and is dissolved into an iron matrix, so that the electrode potential of the matrix can be effectively improved, a Cr-rich oxide film is formed on the surface under the action of an oxidizing medium, and the anode reaction is prevented, so that the corrosion resistance of the austenitic stainless steel is improved; cr increases the solubility of C and decreases the depletion of Cr, so that it is advantageous to increase the Cr content for the intergranular corrosion resistance of austenitic stainless steel; cr can effectively improve the pitting corrosion resistance and crevice corrosion resistance of steel, and when N exists in the steel at the same time, the effectiveness of Cr is greatly enhanced. The increase in Cr content in austenitic stainless steel can decrease the martensitic transformation temperature (M _s), thereby increasing the stability of the austenitic matrix. Therefore, it is difficult to obtain martensite even through cold working and low temperature treatment of the high-chromium austenitic stainless steel. However, the Cr content cannot be too high because Cr is an element that strongly forms/stabilizes ferrite, i.e., can reduce the austenite region. As the Cr content in the steel increases, a ferrite (δ) structure may appear in austenitic stainless steel. In austenitic stainless steels, as the Cr content increases, the propensity for formation of some intermetallic phases (e.g., sigma phases) increases, which also promotes the formation of χ phases if Mo is included in the steel. The precipitation of these intermetallic phases not only significantly reduces the plasticity and toughness of the steel, but also reduces the corrosion resistance of the steel under some conditions. While the stainless steel maintains a fully austenitic structure without delta ferrite formation, the mechanical properties are not significantly affected if the Cr content is only increased. Therefore, the invention is subjected to intensive research and the Cr content is controlled to be 18-19.5%.

Mn: in high nitrogen chromium manganese austenitic stainless steels, the element Mn acts primarily to stabilize austenite and increase the solubility of N. In Ni-saving stainless steel, mn is a very important alloying element and is mainly added to the steel in combination with an element forming austenite. Mn is a weak austenite forming element, but has a strong effect of stabilizing austenite, and Mn itself contributes little to improvement of corrosion resistance of steel. In order to increase the solubility of N, the Mn content is controlled to be 18.5-21.0%.

C: c is an element in the stainless steel which strongly forms, stabilizes and enlarges austenite region, and remarkably improves the strength of the austenitic stainless steel through interstitial solid solution strengthening. C can also improve the stress corrosion resistance of austenitic stainless steel in high concentration chlorides (e.g., 42% MgCl ₂ boiling solution). However, C is also sometimes considered a detrimental element in austenitic stainless steel. For example, C may form high chromium M ₂₃C₆ type carbides with Cr in the steel, resulting in localized chromium depletion in the steel, degrading the corrosion resistance, particularly intergranular corrosion resistance, of the steel. Therefore, the content of C should be controlled as low as possible in the smelting process of austenitic stainless steel, and the increase of C on the surface of the stainless steel is prevented in the subsequent processes of heat treatment, cold working, heat treatment and the like, so as to avoid the precipitation of Cr carbide. Therefore, through intensive research, the content of C is controlled to be 0.08-0.11%, the strength of austenitic stainless steel is improved, and M ₂₃C₆ type carbide can be eliminated through solution treatment.

V: the atomic size of V is equivalent to that of Fe, the solid solubility is large, the addition amount is easy to control, and the V is insensitive to segregation bands. In high nitrogen chromium manganese austenitic stainless steel, V can play a role in nitrogen fixation because V has a strong affinity with nitrogen in the steel, the formation of V (C, N) greatly reduces the content of free N in the steel, and V mainly influences the structure and the performance of the steel by precipitating and separating out V (C, N). Can inhibit austenite recrystallization and prevent grain growth in the hot working process, thereby refining the grains and improving the strength and toughness of the steel. In addition, the strain timeliness of the steel can be effectively avoided. Nitrogen in the steel can enhance the strengthening effect of V. The more the nitrogen content in the steel increases, the more remarkable the V (C, N) precipitation strengthening effect is. At higher temperatures (above 1000 ℃), V (C, N) can dissolve in gamma-Fe, so vanadium is mainly inter-phase precipitation during gamma-alpha transformation and precipitation strengthening in ferrite. Through intensive research, the V content is controlled to be 0.35-0.95%.

Nb: since Nb has a larger atomic size than Fe and a larger diffusion coefficient in austenite, nb tends to be biased at high energy such as grain boundaries and dislocation lines. This produces a strong dragging effect on dislocation climb and grain boundary movement, inhibiting recrystallization nucleation, thereby increasing material recrystallization time. Nb is an austenite stabilizing element, and can form carbon/nitride with elements such as C/N in steel, thereby preventing or reducing the formation of M ₂₃C₆ carbide and preventing the generation of sensitization-state intergranular corrosion. The Nb compounds have high complete solid solution temperature, generally above 1100 ℃, and play roles in pinning dislocation and preventing grain boundary migration, and refine austenite grains. Generally, the larger the addition amount, the higher the complete solid solution temperature. Therefore, when the processing technology of Nb microalloyed steel is formulated, the solid solution quantity and precipitation quantity proportion of Nb and the size range of precipitated phase particles are strictly controlled, so that the effect of refining grains is achieved, and the Nb content is controlled to be 0.01% -0.05% by being used as microalloying elements through intensive research.

Si: si is an element that strongly forms ferrite. As the Si content increases, the ferrite content will increase, and the formation of intermetallic phases will also accelerate and increase. But an increase in Si will increase the yield strength. Through intensive research, the Si content is controlled to be 0.40% -1.2%.

Ni: ni is an important alloy element in austenitic stainless steel, and has the main functions of forming and stabilizing austenite, improving the thermodynamic stability of the steel, and simultaneously, ni and Si can also jointly influence the precipitation temperature of high Wen-Fe; nickel and iron can be infinitely dissolved, and nickel enlarges the austenite region of iron and is a main alloy element for forming and stabilizing austenite. Nickel and carbon do not form carbide, nickel can improve the strength of steel, the plasticity and toughness of the steel are not affected, and the corrosion resistance of the steel can be improved. Although the nickel element can be replaced by increasing the N content in the high-nitrogen steel, the high-nitrogen steel can be increased to 0.68-0.75 percent, and then the high-nitrogen steel can be increased by special modes such as pressurization and the like, and a certain amount of nickel element is needed. Through intensive research, the content of Ni element is controlled to be 0.5% -2.3%.

P, S is used as a harmful element, and in consideration of actual manufacturing cost and technology, the invention is controlled to be less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, simultaneously, the Cu content is controlled to be less than or equal to 0.010 percent, the Al content is strictly controlled, alN inclusion formed in high-nitrogen steel is prevented from being easily cracked in hot forging, and the Al content is required to be less than or equal to 0.010 percent.

In order to further improve the comprehensive performance of the high-nitrogen austenitic stainless steel, the high-nitrogen austenitic stainless steel comprises the following components in percentage by mass, wherein the balance of the high-nitrogen austenitic stainless steel is ：C 0.09％～0.11％,Si0.50％～1.2％,Mn 18.5％～20.0％,Cr 18.5％～19.4％,Ni 0.5％～2.3％,V0.40％～0.95％,N 0.68％～0.75％,Nb 0.01％～0.03％,Cu≤0.008％,Al≤0.009％,P≤0.010％,S≤0.010％, and unavoidable trace impurities.

In order to further improve the comprehensive performance of the high-nitrogen austenitic stainless steel, the high-nitrogen austenitic stainless steel comprises the following components in percentage by mass: 0.095% -0.11%.

In order to further improve the comprehensive performance of the high-nitrogen austenitic stainless steel, the high-nitrogen austenitic stainless steel comprises the following Mn in percentage by mass: 18.6 to 19.5 percent.

In order to further improve the comprehensive performance of the high-nitrogen austenitic stainless steel, the high-nitrogen austenitic stainless steel comprises the following Cr in percentage by mass: 18.7 to 19.2 percent.

In order to further improve the comprehensive performance of the high-nitrogen austenitic stainless steel, the high-nitrogen austenitic stainless steel comprises the following components in percentage by mass: 0.5 to 2.1 percent.

Specifically, the microstructure of the high-nitrogen austenitic stainless steel is austenite and nitride distributed in a dispersed manner, the grain size can reach more than 6 grades, for example, 6-9 grades, and the grains are uniform, for example, the grain size difference is less than 0.5 grade.

The invention provides a preparation method of the high-nitrogen austenitic stainless steel, which comprises the following steps:

Step 1: smelting a steel ingot;

step 2: homogenizing the steel ingot;

step 3: forging and cogging the steel ingot, and water-cooling after forging;

Specifically, in the step 1, an arc furnace is adopted to smelt and cast electrode blanks and electroslag remelting is adopted to prepare steel ingots. In the step 1, normal pressure smelting is adopted.

Specifically, in the step 1, the arc furnace smelting and casting electrode blank may include the following steps: refining molten steel in an arc furnace; refining molten steel in a refining ladle, adjusting alloy components, performing VOD operation, blowing nitrogen and stirring, adding manganese metal nitride to adjust N in batches, adjusting N by utilizing Cr metal nitride in the residual insufficient mode, and finally adjusting manganese and chromium by using manganese metal and chromium metal; stirring the components after the components are qualified by argon, wherein the tapping temperature is 1460-1490 ℃; and (5) pouring the electrode blank under the protection of argon.

Specifically, in the step 1, the electroslag remelting may include the following steps: and (3) electroslag remelting a group of electrode blanks in a crystallizer, wherein 20-40% of CaF ₂ 50％～70％,Al₂O₃ and 0-20% of CaO are selected for slagging, and the melting speed of the electroslag remelting is 0.8-1.2T/h.

Specifically, in the step1, the surface of the steel ingot needs to be peeled, and surface cracks and slag skin are removed.

Specifically, in the step 2, the homogenization treatment includes the following steps:

s201, heating the steel ingot to 600-650 ℃, and performing heat preservation according to 1-1.2 h/100 mm;

S202, raising the temperature to 800-850 ℃ at a heating rate of less than 40 ℃/h for the first time, and performing heat preservation for 1-1.2 h/100 mm;

S203, heating to 1150-1180 ℃ at a speed of not less than 70 ℃ per hour for the second time, and homogenizing at a speed of 2-3 h/100 mm.

Specifically, in S202, considering that the low-temperature heat conduction of the high-nitrogen austenitic stainless steel is small, the steel ingot is slowly transferred from the outer surface to the core, and the phenomenon that the temperature difference in the steel ingot is large, internal tensile stress is generated and steel ingot cracking is easily caused due to the fact that the temperature rising rate is too fast is avoided; the temperature rising rate is properly reduced, so that the temperature uniformity of the steel ingot after the first temperature rising can be ensured, and the generation of cracks is avoided, and therefore, the temperature rising rate is controlled to be less than 40 ℃/h, for example, 30-35 ℃/h.

Specifically, in S203, after the heat preservation at 800-850 ℃ is completed, the internal and external temperatures of the steel ingot are uniform, and the temperature is continuously raised because of good high-temperature plasticity, even if the temperature difference exists between the internal and external temperatures in the temperature raising process, the influence of temperature stress is not worried, and the rapid temperature raising can be performed. In addition, the high-nitrogen austenitic stainless steel can quickly pass through a sensitive temperature range in which brittle phases are separated out, so that the brittle phases in the high-nitrogen austenitic stainless steel are reduced, the plasticity of the stainless steel is improved, and surface cracks or edge cracks generated in the hot working process are reduced. Therefore, the temperature rise rate is 70 ℃/h or more, for example, 80 to 100 ℃/h.

Specifically, in the step 2, the homogenization treatment is performed at 1150-1180 ℃ for a long time to melt back the harmful phase in the solidification process of the steel ingot, and the alloy elements which are easy to segregate are diffused at high temperature. Therefore, the heat preservation is carried out for homogenization treatment according to the speed of 2 to 3 hours per 100 mm.

Specifically, in the step 3, since cracking and overheating and overburning of the grain boundaries are likely to occur in consideration of the precipitation temperature of the high-temperature hazardous phase δ, the initial forging temperature is controlled to 1150 to 1180 ℃. In addition, the final forging temperature is controlled to 950 ℃ or higher, for example, 960 to 970 ℃ in consideration of precipitation of a low-temperature harmful phase epsilon, poor low-temperature plasticity, deformation resistance to elongation and the like.

Specifically, in the step 3, considering that the high-nitrogen austenitic forging of the invention has poor high-temperature plasticity, the forging temperature interval is narrow, and the cracking tendency is serious; and carrying out thermal deformation in a mode of multiple times and small deformation. Considering that the deformation is too large, the alloy grain structure has the risk of mixed crystals in a large deformation area and also has the risk of cracking; if the deformation is too small, the alloy is insufficiently deformed, and the purpose of grain breakage and recrystallization cannot be achieved. Therefore, the deformation amount of each upsetting is controlled to be 30-50%, and the deformation amount of each drawing is controlled to be 15-20%. The specific process of hot forging and the pass of deformation can be designed according to the final shape and size of the forging, and will not be described in detail here. And immediately after the completion of the forging hot forging forming, water cooling is performed.

Specifically, in the step 4, the solution treatment includes: charging the forging stock into a furnace at the furnace temperature of less than or equal to 500 ℃ and rapidly (70-100 ℃/h) heating to 1050-1080 ℃, preserving heat according to 2h/100mm, discharging and water-cooling.

Specifically, in the step 4, the heating rate is 70 ℃/h or more.

Specifically, the high-nitrogen austenitic stainless steel is excellent in strength after hot forging and solution treatment, and for example, the forging stock has the following properties: the tensile strength σ _b is 950MPa or more, for example 956 to 1110MPa; the yield strength sigma _0.2 is more than 690MPa, for example 690-840 MPa; the elongation is more than 35%, such as 35% -46%; the surface shrinkage is more than 60%, for example 60% -69%; the impact energy is 56J or more, for example, 56 to 135J. The properties after solid solution were as follows: the tensile strength sigma _b is more than 920MPa, for example, 920-984 MPa; the yield strength sigma _0.2 is more than 620MPa, for example, 620-675 MPa; the elongation is more than 38%, such as 38% -52%; the surface shrinkage is more than 59%, for example, 59% -70%; the impact energy is 70J or more, for example, 70 to 138J.

Examples 1 to 4

The advantages of the high nitrogen austenitic stainless steel of the present invention for improvement of the base yield strength are demonstrated below in specific examples and comparative examples.

Examples 1-4 of the present invention provide a high nitrogen austenitic stainless steel and a method for preparing the same. The chemical composition of the examples is shown in Table 1. The microstructure of the high nitrogen austenitic stainless steels of examples 1-4 are shown in Table 2; FIG. 1 is a grain size of the high nitrogen austenitic stainless steel of example 1; fig. 2 is a microstructure of the high nitrogen austenitic stainless steel of example 1. The results of the primary performance measurements of the examples are shown in Table 3.

The preparation method of the example 1 comprises the following steps:

step 1: smelting and casting an electrode blank by adopting an arc furnace, and then smelting 5000kg of steel ingot by adopting electroslag remelting;

The arc furnace smelting and casting electrode blanks can comprise the following steps: refining molten steel in an arc furnace; refining molten steel in a refining ladle, adjusting alloy components, performing VOD operation, blowing nitrogen and stirring, adding manganese metal nitride to adjust N in batches, adjusting N components to 0.7% by utilizing Cr metal nitride, and finally adjusting manganese and chromium by using manganese metal and chromium metal; stirring the components after the components are qualified by argon, wherein the tapping temperature is 1470 ℃; completing casting of the electrode blank under the protection of argon;

The electroslag remelting may include the steps of: electroslag remelting is carried out on a group of electrode blanks in a crystallizer, caF ₂60％,Al₂O₃ percent and CaO 20 percent are selected for slagging, and the melting speed of the electroslag remelting is 1T/h;

peeling the surface of the electroslag ingot to remove surface cracks and slag skin;

step 2: homogenizing the steel ingot:

s201, heating the steel ingot to 650 ℃, and preserving heat for 9 hours;

S202, heating to 850 ℃ at 35 ℃/h for the first time, and preserving heat for 9h;

s203, raising the temperature to 1180 ℃ at 80 ℃/h for the second time, and carrying out homogenization treatment at the temperature of 24 h;

Step 3: forging and cogging the steel ingot, heating, upsetting, drawing and deforming for many times, wherein the heating temperature is 1180 ℃, the final forging temperature is 960 ℃, and the forged billet with the thickness of 200mm is obtained, and water cooling is carried out after forging; the deformation of each upsetting is controlled to be 30-50% and the deformation of each drawing is controlled to be 15-20%.

Step 4: and (3) placing the forging stock into a 500 ℃ kiln, heating at 70 ℃/h, heating to 1050 ℃, preserving heat for 4 hours, discharging, and cooling with water to obtain the high-nitrogen austenitic stainless steel solid solution state blank.

The preparation method of example 2 is substantially the same as that of example 1, except that:

In step 2: homogenizing the steel ingot:

S201, heating the steel ingot to 600 ℃, and preserving heat for 8 hours;

s202, heating to 830 ℃ at 30 ℃/h for the first time, and preserving heat for 8h;

s203, heating to 1180 ℃ at 100 ℃/h for the second time, and carrying out homogenization treatment at 20h by heat preservation.

The preparation method of example 3 is substantially the same as that of example 1, except that:

step 1: smelting and casting an electrode blank by adopting an arc furnace, and then smelting 7000kg of steel ingot by adopting electroslag remelting;

Step 3: forging and cogging the steel ingot, heating, upsetting, drawing and deforming for many times, wherein the heating temperature is 1180 ℃, the final forging temperature is 970 ℃, and the forged billet with the thickness of 300mm is obtained, and water cooling is carried out after forging;

Step 4: and (3) placing the forging stock into a 500 ℃ kiln, heating at 70 ℃/h, heating to 1080 ℃, preserving heat for 6h, discharging, and cooling with water to obtain the high-nitrogen austenitic stainless steel solid solution state blank.

The preparation method of example 4 is substantially the same as that of example 1, except that:

Step 1: smelting and casting an electrode blank by adopting an arc furnace, and smelting 8000kg of steel ingot by adopting electroslag remelting;

Step 3: forging and cogging the steel ingot, heating, upsetting, drawing and deforming for multiple times, wherein the heating temperature is 1150 ℃, the final forging temperature is 960 ℃, and obtaining a forging stock with the thickness of 250mm, and cooling by water after forging;

step 4: and (3) putting the forging stock into a furnace kiln at 300 ℃ to be heated at 100 ℃/h, heating to 1060 ℃, preserving heat for 5h, discharging, and cooling with water to obtain the high-nitrogen austenitic stainless steel solid solution state blank.

TABLE 1 chemical composition, wt%

TABLE 2 microstructure

Examples	Grain size of	Solid solution structure
			1	7.5～8.0	Austenite-dispersed nitrides
2	8.5～9.0	Austenite-dispersed nitrides
			3	6.0～6.5	Austenite-dispersed nitrides
4	7.5～8.0	Austenite-dispersed nitrides

TABLE 3 Performance test results

The inventors have conducted a number of experimental studies during the course of the study, and now consider some schemes with lower base yield strength as comparative examples.

Comparative example 1

This comparative example provides a high nitrogen austenitic stainless steel having the composition shown in table 4 below, prepared in the same manner as in example 1, and will not be described in detail herein.

Comparative example 2

Comparative example 3

Comparative example 4

The results of the main property detection of the comparative example steel are shown in Table 5.

TABLE 4 chemical composition, wt%

Comparative example	C	Si	Mn	S	P	Cr	Ni	Nb	V	N	Cu	Al
													1	0.10	0.08	20.23	0.009	0.020	19.44	0.02	0.003	0.02	0.7	0.03	0.005
2	0.078	0.074	18.86	0.008	0.020	19.45	0.02	0.003	0.005	0.68	0.008	0.008
													3	0.10	0.055	18	0.006	0.025	18.17	0.02	0.003	0.005	0.5	0.007	0.006
4	0.11	0.45	17.5	0.002	0.012	18.7	0.17	0.003	0.005	0.58	0.06	0.002

Table 5 comparative example performance test results

The comparative examples and comparative examples show that the high-nitrogen austenitic stainless steel of the present invention is excellent in strength after hot forging and solution treatment.

The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present invention are intended to be included in the scope of the present invention.

Claims

1. The high-nitrogen austenitic stainless steel is characterized by comprising the following components in percentage by mass, wherein the balance of ：C 0.08％～0.11％,Si 0.40％～1.2％,Mn18.5％～21.0％,Cr 18％～19.5％,Ni 0.5％～2.3％,V 0.35％～0.95％,N0.68％～0.75％,Nb 0.01％～0.05％,Cu≤0.01％,Al≤0.01％,P≤0.020％,S≤0.010％, is Fe and unavoidable trace impurities.

2. The high nitrogen austenitic stainless steel according to claim 1, wherein the components of the high nitrogen austenitic stainless steel may be, in mass percent: c0.09-0.11%, si

0.50％～1.2％,Mn 18.5％～20.0％,Cr 18.5％～19.4％,Ni 0.5％～2.3％,V0.40％～0.95％,N 0.68％～0.75％,Nb 0.01％～0.03％,Cu≤0.008％,Al

Less than or equal to 0.009%, less than or equal to 0.010% of P, less than or equal to 0.010% of S, and the balance of Fe and unavoidable trace impurities.

3. The high nitrogen austenitic stainless steel according to claim 1, wherein the high nitrogen austenitic stainless steel comprises the following components in mass percentage: 0.095% -0.11%.

4. The high nitrogen austenitic stainless steel according to claim 1, wherein the high nitrogen austenitic stainless steel comprises the following components in mass percent Mn: 18.6 to 19.5 percent.

5. The high nitrogen austenitic stainless steel according to claim 1, wherein the high nitrogen austenitic stainless steel comprises the following Cr in mass percent: 18.7 to 19.2 percent.

6. The high nitrogen austenitic stainless steel according to claim 1, wherein the high nitrogen austenitic stainless steel comprises the following Ni in mass percent: 0.5 to 2.1 percent.

7. The high nitrogen austenitic stainless steel according to any of claims 1 to 6, wherein the microstructure of the high nitrogen austenitic stainless steel is austenite + diffusion distributed nitrides.

8. The high nitrogen austenitic stainless steel according to claim 7, wherein the grain size of the high nitrogen austenitic stainless steel reaches 6 or more grades.

9. The high nitrogen austenitic stainless steel of claim 8, wherein the grain size fraction difference is below 0.5.

10. A method of producing the high nitrogen austenitic stainless steel according to any one of claims 1 to 9, characterized by comprising:

Step 1: smelting a steel ingot;

step 2: homogenizing the steel ingot;

step 3: forging and cogging the steel ingot, and water-cooling after forging;