High-strength and high-corrosion-resistance super austenitic stainless steel and preparation method thereof

Abstract

The invention relates to the technical field of austenitic stainless steel, in particular to high-strength and high-corrosion-resistance super austenitic stainless steel and a preparation method thereof.The high-strength and high-corrosion-resistance super austenitic stainless steel comprises, by mass, not larger than 0.02% of C, 0.30%-0.45% of Si, 6.00%-12.50% of Mn, not larger than 0.03% of P, not larger than 0.002% of S, 19.00%-23.00% of Cr, 1.00%-10.00% of Ni, 4.00%-6.00% of Mo, 0.30%-0.55% of Cu, 0.85%-1.60% of N, not larger than 0.07% of Nb, not larger than 0.03% of RE, not larger than 0.02% of Al, not larger than 0.003% of O and the balance Fe. RE is one or a combination of more of Ce, La and Y, and the balance is Fe and inevitable impurities. The raw material cost is greatly reduced by reducing the molybdenum element and the nickel element, and the manganese element and the nitrogen element are added to synergistically improve the comprehensive mechanical property and the corrosion resistance of the super austenitic stainless steel, so that the super austenitic stainless steel with the outstanding cost advantage is obtained; and the super austenitic stainless steel is more excellent in strength and corrosion resistance.

Description

Technical Field

[0001] The invention relates to the technical field of austenitic stainless steel, and in particular to a high-strength and high-corrosion-resistant super austenitic stainless steel and a preparation method thereof. Background Art

[0002] As a material with excellent corrosion resistance and good comprehensive mechanical properties, super austenitic stainless steel has become one of the key materials in the field of high-end equipment manufacturing. With the rapid development of key fields such as petrochemicals, marine engineering, energy conservation and environmental protection, the demand for high-performance, low-cost key materials is growing, and the service environment of super austenitic stainless steel has put forward higher requirements on the corrosion resistance and mechanical properties of the material.

[0003] In the current existing technology, super austenitic stainless steel has the problems of high cost, difficulty in hot working, insufficient corrosion resistance and comprehensive mechanical properties. The main sources of raw material costs are Ni and Mo; the main reason for the difficulty in hot working is that higher Mo, Cr and Ni will lead to the precipitation of carbides, nitrides, Cr-rich intermetallic phases and Mo-rich phases; the insufficient comprehensive mechanical properties and corrosion resistance are due to the limited solubility of N element in steel, and it is necessary to further increase the N content to improve the strength and corrosion resistance of steel.

[0004] To sum up, there is an urgent need to develop a new type of super austenitic stainless steel with lower cost and manufacturing difficulty, better strength and corrosion resistance, to achieve leapfrog substitution, reduce costs and increase efficiency, and fundamentally solve and break through the key problems that hinder the rapid development, industrial production and widespread application of super austenitic stainless steel.

[0005] To this end, the present application provides a high-strength and high-corrosion-resistant super austenitic stainless steel and a preparation method thereof. Summary of the invention

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a high-strength and high-corrosion-resistant super austenitic stainless steel and a preparation method thereof, thereby solving the technical problems of high cost, difficulty in hot working, and insufficient corrosion resistance and comprehensive mechanical properties of super austenitic stainless steel in the prior art.

[0007] In order to achieve the above-mentioned object, the first aspect of the present invention provides a high-strength and high-corrosion-resistant super austenitic stainless steel, which comprises the following chemical components, measured by mass percentage: C: ≤0.02%, Si: 0.30%~0.45%, Mn: 6.00%~12.50%, P: ≤0.03%, S: ≤0.002%, Cr: 19.00%~23.00%, Ni: 1.00%~10.00%, Mo: 4.00%~6.00%, Cu: 0.30%~0.55%, N: 0.85%~1.60%, Nb: ≤0.07%, RE: ≤0.03%, Al: ≤0.02%, O: ≤0.003%, and the rest are Fe and unavoidable impurities, wherein RE is one or a combination of Ce, La or Y.

[0008] Optionally, in the above chemical composition, the relationship between nitrogen element N and chromium element Cr and manganese element Mn needs to satisfy:

[0009] W N ≤0.19×W Cr +0.11×W Mn

[0010] Among them, W N is the mass percentage of nitrogen in super austenitic stainless steel, W Cr is the mass percentage of chromium in super austenitic stainless steel, W Mn It is the mass percentage of manganese element in super austenitic stainless steel.

[0011] Optionally, the chromium-nickel equivalent ratio Cr eq / Ni eq , and control 0.40≤Cr eq / Ni eq ≤0.80; the chromium-nickel equivalent ratio Cr eq / Ni eq The expression is:

[0012]

[0013] Among them, W Cr is the mass percentage of chromium in super austenitic stainless steel, W Mo is the mass percentage of molybdenum element in super austenitic stainless steel, W Si is the mass percentage of silicon in super austenitic stainless steel, W Ni is the mass percentage of nickel element in super austenitic stainless steel, W C is the mass percentage of carbon element in super austenitic stainless steel, W N is the mass percentage of nitrogen in super austenitic stainless steel, W Mnis the mass percentage of manganese in super austenitic stainless steel, W Cu It is the mass percentage of copper element in super austenitic stainless steel.

[0014] Optionally, in the above chemical composition, the contribution of the solute elements to the yield strength σ ss ≥590MPa,σ ss The calculation formula is:

[0015] σ ss (MPa)=496[%N]+356.5[%C]+20.1[%Si]+3.7[%Cr]+14.6[%Mo]+12.7[%Al]+40.3[%Nb]

[0016] Optionally, in the above chemical composition, the mass percentages of Cr, Mo and N elements satisfy:

[0017] 60≤W Cr +3.3×W Mo +16×W N

[0018] Among them, W Cr is the mass percentage of chromium in super austenitic stainless steel, W Mo is the mass percentage of molybdenum element in super austenitic stainless steel, W N It is the mass percentage of nitrogen in super austenitic stainless steel.

[0019] The second aspect of the present invention further provides a method for preparing high-strength and high-corrosion-resistant super austenitic stainless steel, which is used to prepare the high-strength and high-corrosion-resistant super austenitic stainless steel provided in the first aspect, and the preparation method comprises:

[0020] S1: Melting, according to the target composition, the raw materials corresponding to the chemical composition except manganese, nickel-magnesium and rare earth are placed in the crucible of the pressurized induction furnace, the manganese raw material, nickel-magnesium alloy and rare earth are placed in the charging bin, the pressurized induction furnace is vacuumed to below 3Pa, argon gas is introduced into the furnace until the pressure is stabilized at 0.02MPa-0.05MPa, and the temperature is increased by power to obtain a stainless steel melt;

[0021] S2: vacuum carbon deoxidation, maintaining the temperature of the above stainless steel melt at 1540°C to 1560°C, and performing vacuum carbon deoxidation for 10min to 15min;

[0022] S3: Manganese alloying: After the vacuum carbon deoxidation of step S2 is completed, the temperature of the stainless steel melt is kept between 1540° C. and 1560° C., and manganese alloying raw materials are added to obtain a manganese alloyed metal melt;

[0023] S4: Nitriding, filling nitrogen into the manganese alloyed metal melt, pressurizing the pressurized induction furnace by top filling nitrogen and bottom blowing nitrogen, the bottom blowing nitrogen flow rate is q 1 When the smelting pressure reaches P 1 After that, the holding time is t, and the nitriding temperature is maintained between 1540℃ and 1560℃;

[0024] S5: Deoxidation. After step S4, the temperature of the manganese alloyed metal melt is lowered to 1480°C to 1500°C, and nickel-magnesium alloy and rare earth are added to perform deoxidation and desulfurization. Subsequently, the bottom blowing nitrogen flow rate is maintained at (1 to 2) × q 1 , to obtain molten steel;

[0025] S6: After casting and deoxidation, stop blowing nitrogen at the bottom and continue to introduce nitrogen into the pressurized induction furnace until the casting pressure P 2 Then, the casting is performed while maintaining the molten steel casting temperature; after the casting is completed, the casting is cooled, the pressure is released, and the high-strength and high-corrosion-resistant super austenitic stainless steel ingot is taken out;

[0026] S7: Hot working and solution treatment. After the high-strength and high-corrosion-resistant super austenitic stainless steel ingot is homogenized, hot working and solution treatment are performed to obtain the final high-strength and high-corrosion-resistant super austenitic stainless steel.

[0027] Optionally, in step S4, the bottom blowing nitrogen flow rate is q 1 The calculation formula is:

[0028] q 1 =γ(100W N -λ),

[0029] When 0.85%≤W N When ≤1.1%, γ=0.896, λ=0.675,

[0030] q 1 =0.896(100W N -0.675);

[0031] When 1.1%<W N When ≤1.3%, γ=0.758, λ=0.863,

[0032] q 1 =0.758(100W N -0.863);

[0033] When 1.3%<W N When, γ=0.656, λ=1.008,

[0034] q 1 =0.656(100W N-1.008);

[0035] Among them, q 1 The unit is Nm 3 / h·t; γ is the bottom blowing flow coefficient; λ is the bottom blowing correction constant.

[0036] Optional, high strength and corrosion resistant super austenitic stainless steel smelting pressure P 1 =0.6MPa~1.3MPa, holding time t is 15min~20min; casting pressure P of high-strength and high-corrosion-resistant super austenitic stainless steel 2 =(1.2~1.7)×P 1 ; Casting temperature T is 1470℃~1520℃.

[0037] Optionally, in step S7, the hot working process of the high-strength and high-corrosion-resistant super austenitic stainless steel includes homogenization, forging, and rolling processes; if the ingot is a round ingot, it is forged first and then rolled; if the ingot is a square ingot, it is directly rolled.

[0038] Optionally, in step S7: when 0.85% ≤ W N ≤1.30%, the homogenization temperature is 1220℃~1280℃, the forging temperature is 1170℃~1200℃, the rolling temperature is 1170℃~1200℃, the solution temperature is 1180℃~1220℃, and the solution time is 1min / mm~7.5min / mm; when 1.30%<W N When ≤1.60%, the homogenization temperature is 1250℃~1280℃, the forging temperature is 1180℃~1200℃, the rolling temperature is 1180℃~1200℃, the solution temperature is 1200℃~1250℃, and the solution time is 1min / mm~7.5min / mm.

[0039] The beneficial effects of the present invention are:

[0040] (1) The high-strength and high-corrosion-resistant super austenitic stainless steel provided by the present invention greatly reduces the cost of raw materials by reducing the molybdenum element Mo and the nickel element Ni.

[0041] (2) The high-strength and high-corrosion-resistant super austenitic stainless steel provided by the present invention increases the manganese element Mn and the nitrogen element N, thereby achieving synergistic improvement of the comprehensive mechanical properties and corrosion resistance of the super austenitic stainless steel by Mn and N.

[0042] (3) The preparation method of the high-strength and high-corrosion-resistant super austenitic stainless steel provided by the present invention utilizes the nitrogen alloying method of "top filling nitrogen and bottom blowing nitrogen" to synergistically increase nitrogen, and realizes rapid nitriding and precise nitrogen control by regulating the nitrogen pressure in the furnace and the bottom blowing flow rate.

[0043] In summary, by optimizing the alloy components in the chemical composition, the super austenitic stainless steel prepared by the present invention has outstanding cost advantages and at the same time has better strength and corrosion resistance. DETAILED DESCRIPTION

[0044] In order to better understand the above technical scheme, exemplary embodiments of the present invention will be described in detail below. However, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a clearer and more thorough understanding of the present invention, and to be able to fully convey the scope of the present invention to those skilled in the art.

[0045] Example:

[0046] A high-strength and high-corrosion-resistant super austenitic stainless steel comprises the following chemical components, calculated by mass percentage: C: ≤0.02%, Si: 0.30%-0.45%, Mn: 6.00%-12.50%, P: ≤0.03%, S: ≤0.002%, Cr: 19.00%-23.00%, Ni: 1.00%-10.00%, Mo: 4.00%-6.00%, Cu: 0.30%-0.55%, N: 0.85%-1.60%, Nb: ≤0.07%, RE: ≤0.03%, Al: ≤0.02%, O: ≤0.003%, and the rest are Fe and unavoidable impurities, wherein RE is one or more combinations of Ce, La and Y.

[0047] "W" in the examples represents the mass percentage corresponding to different chemical elements.

[0048] Both Mn and Cr can increase the solubility of nitrogen in the material. In order to ensure the stability of austenite and avoid the precipitation of nitrides, the optimal amount of nitrogen added needs to be determined by the mass percentage of manganese and chromium in the above chemical composition. N is the mass percentage of nitrogen in super austenitic stainless steel, and its formula is:

[0049] W N ≤0.19×W Cr +0.11×W Mn

[0050] Among them, W N is the mass percentage of nitrogen in super austenitic stainless steel, W Cr is the mass percentage of chromium in super austenitic stainless steel, W Mn is the mass percentage of manganese element in super austenitic stainless steel;

[0051] Since the high-strength and high-corrosion-resistant super austenitic stainless steel of the present invention has a high nitrogen content, it is necessary to increase the nitrogen solubility in the steel by adding elements such as manganese and chromium that have strong nitrogen solubility capabilities in controlling the nitrogen content.

[0052] Among them, N, Mn, and Ni are all austenite stabilizing elements, especially N, which has a stronger ability to stabilize austenite, about 30 times that of Ni. Therefore, as the content of N and Mn increases, the content of Ni in steel can be appropriately reduced to reduce the cost of raw materials. However, in order to ensure that super austenitic stainless steel has a complete austenitic structure, the chromium-nickel equivalent ratio Cr is introduced. eq / Ni eq , and control 0.40≤Cr eq / Ni eq ≤0.80, thereby ensuring the stability of the austenite structure in the system; the expression of chromium-nickel equivalent is:

[0053]

[0054] Among them, W Cr is the mass percentage of chromium in super austenitic stainless steel, W Mo is the mass percentage of molybdenum element in super austenitic stainless steel, W Si is the mass percentage of silicon in super austenitic stainless steel, W Ni is the mass percentage of nickel element in super austenitic stainless steel, W C is the mass percentage of carbon element in super austenitic stainless steel, W N is the mass percentage of nitrogen in super austenitic stainless steel, W Mn is the mass percentage of manganese in super austenitic stainless steel, W Cu is the mass percentage of copper element in super austenitic stainless steel;

[0055] N and C are both solid solution elements that have a very obvious effect on improving yield strength, especially N, which has a stronger improvement effect. Therefore, by increasing the content of N and adjusting solid solution elements such as C, Si, Cr, Mo, Al, and Nb, the yield strength can be improved while reducing the cost. The contribution value of solid solution elements to yield strength is σ ss ≥590MPa,σ ss The calculation formula is:

[0056] o SS(MPa) = 496 [% N] + 356.5 [% C] + 20.1 [% Si] + 3.7 [% Cr] + 14.6 [% Mo] + 12.7 [% Al] + 40.3 [% Nb] The present invention ensures that the corrosion resistance of the high-strength and high-corrosion-resistant super austenitic stainless steel is improved by controlling the mass percentage of the chemical composition of chromium element Cr, molybdenum element Mo and nitrogen element N in the super austenitic stainless steel. The mass percentages of Cr, Mo and N elements meet the following requirements:

[0057] 60≤W Cr +3.3×W Mo +16×W N .

[0058] A method for preparing high-strength and high-corrosion-resistant super austenitic stainless steel comprises the following steps:

[0059] S1: Melting: According to the target composition, the raw materials corresponding to the chemical composition except manganese, nickel-magnesium and rare earth are placed in the crucible of the pressurized induction furnace, the manganese raw material, nickel-magnesium alloy and rare earth are placed in the charging bin, the pressurized induction furnace is vacuumed to below 3Pa, argon gas is introduced into the furnace until the pressure is stabilized at 0.02MPa-0.05MPa, and the temperature is increased by power to obtain a stainless steel melt;

[0060] S2: Vacuum carbon deoxidation: the temperature of the above stainless steel melt is maintained at 1540°C to 1560°C, and vacuum carbon deoxidation is performed for 10min to 15min;

[0061] S3: Manganese alloying: After the vacuum carbon deoxidation of step S2 is completed, the temperature of the stainless steel melt is kept between 1540° C. and 1560° C., and manganese alloying raw materials are added to obtain a manganese alloyed metal melt;

[0062] S4: Nitriding: Nitrogen is charged into the manganese alloyed metal melt, and the pressurized induction furnace is pressurized by top filling nitrogen and bottom blowing nitrogen. The bottom blowing nitrogen flow rate is q 1 Nm 3 / h·t, when the smelting pressure reaches P1, the holding time is t, and the nitriding temperature is maintained between 1540℃ and 1560℃;

[0063] S5: Deoxidation: After step S4, the temperature of the manganese alloyed metal melt is lowered to 1480°C to 1500°C, and nickel-magnesium alloy and rare earth are added for deoxidation and desulfurization. Subsequently, the bottom blowing nitrogen flow rate is maintained at (1 to 2) × q 1 Nm 3 / h·t, and molten steel is obtained;

[0064] S6: Casting: After deoxidation is completed, stop blowing nitrogen at the bottom and continue to introduce nitrogen into the pressurized induction furnace until the casting pressure P 2Then, the casting is performed while maintaining the molten steel casting temperature T; after the casting is completed, the casting is cooled, the pressure is released, and the high-strength and high-corrosion-resistant super austenitic stainless steel ingot is taken out;

[0065] S7: Hot working and solution treatment: The high-strength and high-corrosion-resistant super austenitic stainless steel ingot is homogenized and then hot worked and solution treated to obtain the final high-strength and high-corrosion-resistant super austenitic stainless steel.

[0066] Furthermore, the smelting pressure P of high-strength and high-corrosion-resistant super austenitic stainless steel 1 =0.6MPa~1.3MPa, holding time t is 15min~20min, among which,

[0067]

[0068]

[0069] Among them, P 1 is the smelting pressure, in MPa; P 0 is the standard atmospheric pressure, in MPa; T is the smelting temperature, in °C; M is the activity coefficient of nitrogen.

[0070] Casting pressure P of high strength and high corrosion resistance super austenitic stainless steel 2 =(1.2~1.7)×P 1 ; Casting temperature T is 1470℃~1520℃.

[0071] This embodiment provides a bottom blowing nitrogen flow rate q for the high strength and high corrosion resistance super austenitic stainless steel smelting process. 1 The calculation formula is:

[0072] q 1 =γ(100W N -λ)

[0073] When 0.85%≤W N When ≤1.1%, γ=0.896, λ=0.675,

[0074] q 1 =0.896(100W N -0.675);

[0075] When 1.1%<W N When ≤1.3%, γ=0.758, λ=0.863,

[0076] q 1 =0.758(100W N -0.863);

[0077] When 1.3%<W NWhen, γ=0.656, λ=1.008,

[0078] q 1 =0.656(100W N -1.008);

[0079] Among them, q 1 The unit is Nm 3 / h·t; γ is the bottom blowing flow coefficient; λ is the bottom blowing correction constant.

[0080] By introducing the bottom blowing flow coefficient γ and the bottom blowing correction constant λ, the calculation formula of the bottom blowing flow in the existing technology was corrected, and a calculation formula more suitable for the nitrogen content of high-strength and high-corrosion-resistant super austenitic stainless steel was obtained, which accelerated the nitrogen dissolution rate and the nitrogen control process.

[0081] Bottom blowing of nitrogen during the nitriding process can stir the molten steel, increase the dissolution rate of nitrogen, and quickly and efficiently bring the nitrogen content in the molten steel close to the target value, greatly improving production efficiency while also ensuring the uniformity and stability of the nitrogen content in high-nitrogen steel.

[0082] In this embodiment, the hot working process of the high-strength and high-corrosion-resistant super austenitic stainless steel includes homogenization, forging, and rolling.

[0083] Among them, if the ingot is a round ingot, it is forged first and then rolled; if the ingot is a square ingot, it is directly rolled.

[0084] In this embodiment, when the tough and highly corrosion-resistant super austenitic stainless steel 0.85%≤W N When ≤1.30%, the homogenization temperature is 1220℃~1280℃, the forging temperature is 1170℃~1200℃, the rolling temperature is 1170℃~1200℃, the solution temperature is 1180℃~1220℃, and the solution time is 1min / mm~7.5min / mm ( / mm represents unit thickness or diameter).

[0085] In the embodiment, when the tough and highly corrosion-resistant super austenitic stainless steel 1.30%<W N When the homogenization temperature is 1250℃~1280℃, the forging temperature is 1180℃~1200℃, the rolling temperature is 1180℃~1200℃, the solution temperature is 1200℃~1250℃, and the solution time is 1min / mm~7.5min / mm ( / mm represents unit thickness or diameter).

[0086] In this embodiment, the homogenization temperature needs to control the complete dissolution of nitrides, the reduction of element segregation and the sufficient ablation of dendrite structure, while avoiding excessive grain growth and excessive oxidation of the ingot and being lower than the solid-liquid phase line, so as to achieve the purpose of full homogenization of composition and structure.

[0087] In this embodiment, the forging temperature and the rolling temperature need to be as high as possible above the precipitation temperature of chromium nitride to reduce the cracking tendency during the hot working process.

[0088] In this embodiment, the solution temperature should ensure that the intermetallic phases such as chromium nitride and σ phase are completely dissolved back to avoid the precipitation phase affecting the comprehensive mechanical properties and corrosion resistance of austenitic stainless steel.

[0089] In this embodiment, the tensile strength of the high-strength and high-corrosion-resistant austenitic stainless steel is ≥950 MPa, the yield strength is ≥550 MPa, the elongation is ≥45%, and the pitting corrosion resistance equivalent index is:

[0090] (PREN=W Cr +3.3×W Mo +16×W N )≥60.

[0091] In this embodiment, the smelting process of high-strength and high-corrosion-resistant super austenitic stainless steel preferably adopts a pressurized induction furnace, and uses a nitrogen alloying method of "top nitrogen filling and bottom nitrogen blowing" to synergistically increase nitrogen. The smelting pressure is controlled to P by controlling the top nitrogen filling and bottom nitrogen blowing. 1 , and use the bottom blowing nitrogen flow rate to increase the nitrogen addition rate and melt nitrogen content.

[0092] In addition, nitrogen is easy to segregate and precipitate during the solidification process of super austenitic stainless steel, and pressurized solidification can effectively inhibit the segregation and precipitation of nitrogen. Therefore, the present invention adopts the technical means of pressurized solidification to reduce the segregation of nitrogen and inhibit the precipitation of nitrogen pores; at the same time, pressurization can also strengthen cooling, thereby refining the solidification structure and improving the quality of the ingot.

[0093] This embodiment adopts the nitrogen alloying method of "top filling with nitrogen and bottom blowing with nitrogen", and provides a matching pressure casting method.

[0094] In this embodiment, the crucible material used for pressurized induction melting is preferably MgO material.

[0095] In this embodiment, the smelting raw materials of super austenitic stainless steel can be ferroalloys and high-purity metals, preferably high-purity metals (impurity elements ≤ 0.01%). Unless otherwise specified, the remaining raw materials or reagents are commercially available products well known to those skilled in the art.

[0096] The technical principle of the alloy composition in the present invention is as follows:

[0097] Control of nitrogen (N) element content: N is a strong austenite-forming element, which can also stabilize austenite and expand the austenite phase area. In stainless steel, N can be used to replace Ni to ensure austenite structure while maintaining excellent performance and saving costs; at the same time, N is an interstitial atom with strong solid solubility, which can improve the strength of the material without reducing the toughness of the material. In addition, N can synergize with elements such as Cr and Mo, and its ability to improve corrosion resistance is 5 times that of Mo and 16 times that of chromium (PREN = %Cr + 3.3×%Mo + 16×%N). Therefore, increasing the N content can effectively improve the comprehensive mechanical properties and corrosion resistance of the material. The super austenitic stainless steel of the present invention controls the N element content to 0.85% to 1.60%, preferably 1.00% to 1.60%, and more preferably 1.25 to 1.60%.

[0098] Control of manganese (Mn) content: As one of the austenite-forming elements, Mn can further improve the solubility of N and enhance the stability of austenite structure; at the same time, a high content of Mn can reduce the driving force for nitride precipitation and reduce the amount of nitride precipitation. Therefore, Mn and N are often added in combination to replace expensive Ni. Therefore, as the N content increases, the Mn content also needs to be increased to enhance the nitrogen solubility of the material. The super austenitic stainless steel of the present invention controls the Mn content to 6.00% to 12.50%, preferably 8.50% to 10.00%.

[0099] Manganese can increase the solubility of nitrogen in stainless steel, and nitrogen as an interstitial atom has a strong solid solution strengthening ability, which can improve the strength of the material without reducing the toughness of the material. At the same time, the improvement effect of nitrogen on corrosion resistance is 16 times that of chromium and 5 times that of molybdenum. Increasing nitrogen solubility can also significantly improve the corrosion resistance of the material. In addition, a higher mass fraction of Ni will reduce the solubility of C and N in stainless steel and increase the tendency of carbides and nitrides to precipitate. Therefore, manganese and nitrogen are often added in combination to replace expensive nickel in steel to achieve cost reduction and efficiency improvement. Furthermore, when the chromium content is too high, it is not easy to maintain a single-phase austenite structure, and it will promote the precipitation of Cr-rich intermetallic phases, deteriorating hot working properties, comprehensive mechanical properties and corrosion resistance; and molybdenum is very easy to segregate into the liquid phase during solidification, resulting in a large amount of precipitation of molybdenum-rich phases at grain boundaries and dendrites, and Mo-depleted zones will appear around the molybdenum-rich phases, deteriorating the corrosion resistance of the material. Therefore, chromium and molybdenum elements can be appropriately reduced to reduce the precipitation of harmful phases.

[0100] Nickel (Ni) element content control: A higher Ni element mass fraction will reduce the solubility of C and N in stainless steel and increase the tendency of carbides and nitrides to precipitate; at the same time, N, Mn, and Ni are all austenite stabilizing elements, especially N has a stronger ability to stabilize austenite, which is about 30 times that of Ni. Therefore, as the content of N and Mn elements increases, the Ni content in the steel can be appropriately reduced to reduce the cost of raw materials and avoid the precipitation tendency of nitrides in high nitrogen steel. The super austenitic stainless steel of the present invention controls the Ni content to 1.00% to 10.00%, preferably 4.00 to 7.00%.

[0101] Chromium (Cr) content control: Cr can increase the nitrogen solubility of stainless steel and further improve the corrosion resistance of steel; at the same time, at high temperatures, Cr can promote the protective Cr 2 O 3 The formation of Cr significantly improves the high-temperature oxidation resistance of stainless steel. However, when the Cr content is too high, it is not easy to maintain a single-phase austenite structure, and it will promote the precipitation of Cr-rich intermetallic phases, deteriorating hot working properties and corrosion resistance. Therefore, for steels with high N content, it is necessary to take into account nitrogen solubility, corrosion resistance and oxidation resistance as well as the angle of not promoting the precipitation of intermetallic phases and nitrides, and appropriately reduce the Cr content. The super austenitic stainless steel of the present invention controls the Cr content to 19.00% to 23.00%, preferably 20.00% to 22.00%.

[0102] Control of molybdenum (Mo) element content: Mo is an important component of super austenitic stainless steel. Mo can promote the formation of a passivation film on the surface of stainless steel and improve corrosion resistance. Its improvement capacity is 3 times that of Cr. However, too high a Mo content will aggravate the segregation and precipitation of Mo elements during solidification, resulting in a long homogenization time, causing problems such as overheating, overburning, and coarse grains; severe Mo segregation will lead to the precipitation of hard and brittle intermetallic phases, reduce organizational stability, reduce thermoplasticity, and cause serious hot working cracking; at the same time, Mo elements are very easy to oxidize and volatilize, causing serious catastrophic oxidation. Therefore, it is necessary to appropriately reduce the content of Mo elements, and it also plays a role in reducing the cost of steel preparation. Therefore, the present invention proposes to increase nitrogen and manganese elements to improve steel strength, and improve the stability of austenite structure, while reducing nickel, chromium, and molybdenum elements, inhibiting the precipitation of harmful phases and reducing raw material costs, so as to achieve the improvement of strength, plasticity, and corrosion resistance of super austenitic stainless steel. The super austenitic stainless steel of the present invention controls the content of Mo elements to 4.00% to 6.00%, preferably 4.50% to 5.50%.

[0103] In order to further explain the technical effect of the present invention, Example 1, Example 2 and Example 3, as well as Comparative Example 1 and Comparative Example 2 are given below. The specific chemical compositions and related parameters are shown in Tables 1 to 3. The corrosion resistance of the prepared super austenitic stainless steel is shown in Table 4, and the tensile strength, yield strength and elongation are shown in Table 5.

[0104] Table 1 shows the chemical compositions of Examples 1 to 3 and Comparative Examples 1 to 2

[0105]

[0106] In the above-mentioned Examples 1 to 3, composition design was performed on steels with different nitrogen mass percentages, and suitable systems were obtained under corresponding nitrogen mass percentages.

[0107] Table 2 Composition design index of super austenitic stainless steel of Examples 1 to 3

[0108] Design indicators Example 1 Example 2 Example 3 <![CDATA[Cr eq / In eq ]]> 0.66 0.58 0.46 <![CDATA[σ ss (MPa)]]> 724.51 817.91 947.15 <![CDATA[W Cr +3.3×W Mo +16×W N ]]> 60.08 61.91 62.73 <![CDATA[W N (%)]]> 1.11 1.52 1.75

[0109] The preparation of super austenitic stainless steel with different nitrogen mass percentages in Examples 1 to 3 follows the above formula of the present invention, which improves the stability of the super austenitic stainless steel and improves the comprehensive mechanical properties and corrosion resistance.

[0110] Table 3 shows the smelting parameters of Examples 1 to 3 and Comparative Examples 1 to 2

[0111] Smelting parameters Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Argon gas pressure (MPa) 0.03 0.02 0.04 0.02 0.03 Vacuum carbon deoxidation time (min) 11 12 14 11 12 Vacuum carbon deoxidation temperature (℃) 1549 1556 1551 1550 1546 Manganese alloying temperature (℃) 1541 1560 1556 1540 1550 <![CDATA[Smelting pressure P 1 (MPa)]]> 0.68 0.85 1.05 0.53 0.08 <![CDATA[P 1 Holding time t(min)]]> 15 17 19 15 16 Nitriding temperature(℃) 1542 1559 1555 1541 1549 <![CDATA[Bottom blowing flow rate q 1 (Nm 3 / h·t)]]> 0.36 0.32 0.38 - - Deoxidation temperature(℃) 1486 1489 1495 1482 1491 <![CDATA[Casting pressure P 2 (MPa)]]> 1.01 1.22 1.67 0.78 0.12 Casting temperature(℃) 1490 1500 1505 1485 1490 Homogenization temperature (℃) 1243 1261 1279 1276 1254 Forging temperature(℃) 1177 1181 1192 1185 1171 Rolling temperature(℃) 1175 1186 1194 1192 1184 Solution temperature(℃) 1192 1225 1247 1201 1194

[0112] In order to prevent the smelting process and heat treatment process from affecting the performance of Examples 1 to 3 and Comparative Examples 1 to 2, the entire smelting process was carried out on Examples 1 to 3 and Comparative Examples 1 to 2 according to the same standard.

[0113] First, the theoretical pitting corrosion resistance equivalent index (PREN = %Cr + 3.3 × %Mo + 16 × %N) of each heat of steel was calculated, wherein the larger the PREN value, the better the pitting corrosion resistance of the steel. Secondly, the super austenitic stainless steels of Examples 1 to 3 and Comparative Examples 1 to 2 were subjected to heat processing and heat treatment, and several samples of 50 mm × 25 mm × 5 mm were cut from the rolled plates. The surfaces of the samples were polished to 2000 meshes step by step with sandpaper and weighed. The samples were placed in a simulated flue gas desulfurization environment (solution: 11.4 wt% H 2 SO 4 +1.2wt%HCl+1.0wt%FeCl 3 +1.0wt%CuCl 2 , temperature: slightly boiling) for 60 days. After the experiment, the sample was cleaned and weighed, and the uniform corrosion rate was calculated. The results are shown in Table 4. The lower the corrosion rate, the better the corrosion resistance.

[0114] Table 4 Corrosion resistance of super austenitic stainless steel prepared in Examples 1 to 3 and Comparative Examples 1 to 2

[0115] Furnace No. Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 PREN 60.08 61.91 62.73 56.75 44.23 Uniform corrosion rate (mm / y) 0.0071 0.0064 0.0059 0.0106 0.0168

[0116] It can be seen from Table 4 that compared with the comparative examples 1 to 2, the PREN values ​​and uniform corrosion rates of the steels of Examples 1 to 3 are improved to a certain extent.

[0117] Samples for comprehensive mechanical properties test were obtained from the steel plates of the super austenitic stainless steel prepared in Examples 1 to 3 and Comparative Examples 1 to 2, respectively. The tensile strength, yield strength and elongation of the super austenitic stainless steel were tested at room temperature, and the comprehensive mechanical properties of the super austenitic stainless steel prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were evaluated.

[0118] Table 5 Tensile strength, yield strength and elongation of super austenitic stainless steel prepared in Examples 1 to 3 and Comparative Examples 1 to 2

[0119] Comprehensive mechanical properties Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Tensile strength(MPa) 1055.54 1150.61 1195.29 855.95 752.64 Yield strength(MPa) 650.25 760.21 802.36 420.11 301.21 Elongation(%) 70.57 61.54 57.25 67.13 46.69

[0120] It can be seen from Table 5 that, compared with Comparative Example 1, the tensile strength of Examples 1 to 3 is increased from 855.95 MPa to 1055.54 MPa to 1195.29 MPa, and the yield strength is increased from 420.11 MPa to 650.25 MPa to 802.36 MPa, while the elongation results are similar, with only a slight decrease in Examples 2 and 3 compared with Comparative Example 1.

[0121] Compared with Comparative Example 2, the tensile strength of Examples 1 to 3 is increased from 752.64MPa to 1055.54MPa to 1195.29MPa, the yield strength is increased from 301.21MPa to 650.25MPa to 802.36MPa, and the elongation is increased by 20% to 50% compared with Comparative Example 2. The above comparison shows that the preparation method of the high-strength and high-corrosion-resistant super austenitic stainless steel of the present invention enables the super austenitic stainless steel prepared in this embodiment to obtain more excellent comprehensive mechanical properties.

[0122] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A high-strength and high-corrosion-resistant super austenitic stainless steel, characterized in that: Calculated in mass percentage, it includes the following chemical components: C: ≤0.02%, Si: 0.30%~0.45%, Mn: 6.00%~12.50%, P: ≤0.03%, S: ≤0.002%, Cr: 19.00%~23.00%, Ni: 1.00%~10.00%, Mo: 4.00%~6.00%, Cu: 0.30%~0.55%, N: 0.85%~1.60%, Nb: ≤0.07%, RE: ≤0.03%, Al: ≤0.02%, O: ≤0.003%, and the rest are Fe and unavoidable impurities, among which RE is one or a combination of Ce, La or Y.

2. The high-strength and high-corrosion-resistant super austenitic stainless steel according to claim 1, characterized in that: In the chemical composition, the relationship between nitrogen element N and chromium element Cr and manganese element Mn needs to satisfy: IN N ≤0.19×W Cr +0.11×W Mn Among them, W N is the mass percentage of nitrogen in super austenitic stainless steel, W Cr is the mass percentage of chromium in super austenitic stainless steel, W Mn It is the mass percentage of manganese element in super austenitic stainless steel.

3. The high-strength and high-corrosion-resistant super austenitic stainless steel according to claim 1, characterized in that: The introduction of chromium-nickel equivalent ratio Cr eq / Ni eq , and control 0.40≤Cr eq / Ni eq ≤0.80; the chromium-nickel equivalent ratio Cr eq / Ni eq The expression is: Among them, W Cr is the mass percentage of chromium in super austenitic stainless steel, W Mo is the mass percentage of molybdenum element in super austenitic stainless steel, W Si is the mass percentage of silicon in super austenitic stainless steel, W Ni is the mass percentage of nickel element in super austenitic stainless steel, W C is the mass percentage of carbon element in super austenitic stainless steel, W N is the mass percentage of nitrogen in super austenitic stainless steel, W Mn is the mass percentage of manganese in super austenitic stainless steel, W Cu It is the mass percentage of copper element in super austenitic stainless steel.

4. The high-strength and high-corrosion-resistant super austenitic stainless steel according to claim 1, characterized in that: In the chemical composition, the contribution of the solute elements to the yield strength is ss ≥590MPa,σ ss The calculation formula is: σ SS (MPa)=496[%N]+356.5[%C]+20.1[%Si]+3.7[%Cr]+14.6[%Mo]+12.7[%Al]+40.3[%Nb]。 5. The high-strength and high-corrosion-resistant austenitic stainless steel according to claim 1, characterized in that: In the chemical composition, the mass percentages of Cr, Mo and N elements satisfy: 60≤W Cr +3.3×W Mo +16×W N Among them, W Cr is the mass percentage of chromium in super austenitic stainless steel, W Mo is the mass percentage of molybdenum element in super austenitic stainless steel, W N It is the mass percentage of nitrogen in super austenitic stainless steel.

6. A method for preparing high-strength and high-corrosion-resistant super austenitic stainless steel, preparing the high-strength and high-corrosion-resistant super austenitic stainless steel as claimed in any one of claims 1 to 5, characterized in that: The preparation method comprises: S1: Melting, according to the target composition, the raw materials corresponding to the chemical composition except manganese, nickel-magnesium and rare earth are placed in the crucible of the pressurized induction furnace, the manganese raw material, nickel-magnesium alloy and rare earth are placed in the charging bin, the pressurized induction furnace is vacuumed to below 3Pa, argon gas is introduced into the furnace until the pressure is stabilized at 0.02MPa-0.05MPa, and the temperature is increased by power to obtain a stainless steel melt; S2: vacuum carbon deoxidation, maintaining the temperature of the above stainless steel melt at 1540°C to 1560°C, and performing vacuum carbon deoxidation for 10min to 15min; S3: Manganese alloying: After the vacuum carbon deoxidation of step S2 is completed, the temperature of the stainless steel melt is kept between 1540° C. and 1560° C., and manganese alloying raw materials are added to obtain a manganese alloyed metal melt; S4: Nitriding, filling nitrogen into the manganese alloyed metal melt, pressurizing the pressurized induction furnace by top filling nitrogen and bottom blowing nitrogen, the bottom blowing nitrogen flow rate is q1, when the smelting pressure reaches P1, the pressure is maintained for t, and the nitriding temperature is maintained between 1540℃ and 1560℃; S5: Deoxidation. After step S4, the temperature of the manganese alloyed metal melt is lowered to 1480°C to 1500°C, and nickel-magnesium alloy and rare earth are added to perform deoxidation and desulfurization treatment. Subsequently, the bottom blowing nitrogen flow rate is maintained at (1 to 2)×q1 to obtain molten steel; S6: Casting, after deoxidation is completed, stop blowing nitrogen at the bottom, continue to introduce nitrogen into the pressurized induction furnace to the casting pressure P2, and then maintain the molten steel casting temperature for casting; after the casting is completed, cool, release the pressure, and take out the high-strength and high-corrosion-resistant super austenitic stainless steel ingot; S7: Hot working and solution treatment. After the high-strength and high-corrosion-resistant super austenitic stainless steel ingot is homogenized, hot working and solution treatment are performed to obtain the final high-strength and high-corrosion-resistant super austenitic stainless steel.

7. The method for preparing high-strength and high-corrosion-resistant super austenitic stainless steel according to claim 6, characterized in that: In step S4, the calculation formula of the bottom blowing nitrogen flow rate q1 is: q1=γ(100W N -l), When 0.85% ≤ W N ≤ 1.1%, γ = 0.896, λ = 0.675, q1=0.896(100W N -0.675); When 1.1% < W N ≤ 1.3%, γ = 0.758, λ = 0.863, q1=0.758(100W N -0.863); When 1.3% < W N , γ = 0.656, λ = 1.008, q1=0.656(100W N -1.008); Among them, the unit of q1 is Nm 3 / h·t; γ is the bottom blowing flow coefficient; λ is the bottom blowing correction constant.

8. The method for preparing high-strength and high-corrosion-resistant super austenitic stainless steel according to claim 6, characterized in that: The smelting pressure of high-strength and high-corrosion-resistant super austenitic stainless steel is P1=0.6MPa~1.3MPa, and the pressure holding time t is 15min~20min; The casting pressure of high-strength and high-corrosion-resistant super austenitic stainless steel is P2=(1.2~1.7)×P1; the casting temperature T is 1470℃~1520℃.

9. The method for preparing high-strength and high-corrosion-resistant super austenitic stainless steel according to claim 6, characterized in that: In step S7, the hot working process of the high-strength and high-corrosion-resistant super austenitic stainless steel includes homogenization, forging, and rolling processes; If the ingot is a round ingot, it is forged first and then rolled; If the ingot is a square ingot, it is rolled directly.

10. The method for preparing high-strength and high-corrosion-resistant super austenitic stainless steel according to claim 6, characterized in that: In step S7: When 0.85%≤W N When ≤1.30%, the homogenization temperature is 1220℃~1280℃, the forging temperature is 1170℃~1200℃, the rolling temperature is 1170℃~1200℃, the solution temperature is 1180℃~1220℃, and the solution time is 1min / mm~7.5min / mm; When 1.30%<W N When ≤1.60%, the homogenization temperature is 1250℃~1280℃, the forging temperature is 1180℃~1200℃, the rolling temperature is 1180℃~1200℃, the solution temperature is 1200℃~1250℃, and the solution time is 1min / mm~7.5min / mm.

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