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US-20260125785-A1 - AUSTENITIC STAINLESS STEEL HAVING EXCELLENT LOW-TEMPERATURE IMPACT TOUGHNESS AND METHOD FOR MANUFACTURING SAME

US20260125785A1US 20260125785 A1US20260125785 A1US 20260125785A1US-20260125785-A1

Abstract

According to an embodiment of the present invention, an austenitic stainless steel comprising, in weight percentage, C: 0.03% or less (excluding 0), N: 0.15 to 0.25%, Si: 1.0% or less (excluding 0), Mn: 3.3 to 7.5%, Cr: 17.0 to 22.0%, Ni: 6.5 to 9.5%, Cu: 1.2% or less (excluding 0), Mo: 0.8% or less (excluding 0), and the balance being Fe and inevitable impurities, wherein the austenitic stainless steel satisfies formula (1): 70≤(100−ASP)/(Ni/Mn)≤170, and the Charpy impact energy at −196° C. is 120 J or more (where ASP represents the austenite phase stability and ASP is calculated by 551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29 (Ni+Cu)−18.5Mo (Ni and Mn represent the weight percentages of respective elements thereof).

Inventors

  • Seokweon Song
  • Kwangmin KIM
  • Hongju LEE
  • Inho Kim

Assignees

  • POSCO CO., LTD

Dates

Publication Date
20260507
Application Date
20230523
Priority Date
20221011

Claims (13)

  1. 1 . An austenitic stainless steel comprising, in percent by weight (wt %), 0.03% or less (excluding 0) of C, 0.15 to 0.25% of N, 1.0% or less (excluding 0) of Si, 3.3 to 7.5% of Mn, 17.0 to 22.0% of Cr, 6.5 to 9.5% of Ni, 1.2% or less (excluding 0) of Cu, 0.8% or less (excluding 0) of Mo, and the balance of Fe and inevitable impurities, wherein the austenitic stainless steel satisfies Formula (1) below and has a Charpy impact energy at −196° C. of 120 J or more: 7 ⁢ 0 ≤ ( 100 - A ⁢ S ⁢ P ) / ( Ni / Mn ) ≤ 1 ⁢ 7 ⁢ 0 Formula ⁢ ( 1 ) (wherein ASP represents austenite phase stability, ASP is calculated by 551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29 (Ni+Cu)−18.5Mo, and Ni and Mn represent wt % of the respective elements).
  2. 2 . The austenitic stainless steel according to claim 1 , wherein the austenitic stainless steel satisfies Formula (2) below: 1.45 Mn + 10 ⁢ Ni - 9.5 Cu - 175 ⁢ N + 0.32 ( CVN @ 25 ⁢ ° ⁢ C . ) ≥ 120 Formula ⁢ ( 2 ) (wherein Mn, Ni, Cu, and N represent wt % of the respective elements, and CVN@25° C. refers to a Charpy impact energy value at 25° C.).
  3. 3 . The austenitic stainless steel according to claim 1 , wherein the austenitic stainless steel satisfies Formula (3) below: 4 . 4 + 2 ⁢ 3 ⁢ ( C + N ) + 1.3 Si + 0.24 ( Cr + Ni + Mn ) ≥ 1 ⁢ 6 Formula ⁢ ( 3 ) (wherein C, N, Si, Cr, Ni, and Mn represent wt % of the respective elements).
  4. 4 . The austenitic stainless steel according to claim 1 , wherein a yield strength is 300 MPa or more.
  5. 5 . A method for manufacturing an austenitic stainless steel, the method comprising: manufacturing a slab comprising, in percent by weight (wt %), 0.03% or less (excluding 0) of C, 0.15 to 0.25% of N, 1.0% or less (excluding 0) of Si, 3.3 to 7.5% of Mn, 17.0 to 22.0% of Cr, 6.5 to 9.5% of Ni, 1.2% or less (excluding 0) of Cu, 0.8% or less (excluding 0) of Mo, and the balance of Fe and inevitable impurities, and satisfying Formula (1) below; heating and extracting the slab; hot rolling and hot annealing the extracted slab to a hot-rolled steel sheet; and cold rolling and cold annealing the hot-rolled steel sheet, wherein a Charpy impact energy at −196° C. is 120 J or more: 7 ⁢ 0 ≤ ( 100 - A ⁢ S ⁢ P ) / ( Ni / Mn ) ≤ 1 ⁢ 7 ⁢ 0 Formula ⁢ ( 1 ) (wherein ASP represents austenite phase stability, ASP is calculated by 551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29 (Ni+Cu)−18.5Mo, and Ni and Mn represent wt % of the respective elements).
  6. 6 . The method according to claim 5 , wherein the austenitic stainless steel satisfies Formula (2) below: 1.45 Mn + 10 ⁢ Ni - 9.5 Cu - 175 ⁢ N + 0.32 ( CVN @ 25 ⁢ ° ⁢ C . ) ≥ 120 Formula ⁢ ( 2 ) (wherein Mn, Ni, Cu, and N represent wt % of the respective elements, and CVN@25° C. refers to a Charpy impact energy value at 25° C.).
  7. 7 . The method according to claim 5 , wherein the austenitic stainless steel satisfies Formula (3) below and has a yield strength of 300 MPa or more: 4 . 4 + 2 ⁢ 3 ⁢ ( C + N ) + 1.3 Si + 0.24 ( Cr + Ni + Mn ) ≥ 1 ⁢ 6 Formula ⁢ ( 3 ) (wherein C, N, Si, Cr, Ni, and Mn represent wt % of the respective elements).
  8. 8 . The method according to claim 5 , wherein the heating and extracting of the slab is performed at 1080 to 1280° C.
  9. 9 . The method according to claim 5 , wherein the hot rolling is performed at 800° C. or above at a reduction ratio of 70% or more.
  10. 10 . The method according to claim 5 , wherein the hot annealing is performed at 1000 to 1200° C. for 60 minutes or less.
  11. 11 . The method according to claim 5 , further comprising a cooling process after the hot rolling and before the hot annealing, wherein the cooling process is performed at a cooling rate of 50° C./s or less.
  12. 12 . The method according to claim 5 , wherein the cold rolling is performed at room temperature at a reduction ratio of 50% or more.
  13. 13 . The method according to claim 5 , wherein the cold annealing is performed at 1000 to 1200° C. for 10 minutes or less.

Description

TECHNICAL FIELD The present disclosure relates to an austenitic stainless steel, and more specifically, to an austenitic stainless steel having high strength and excellent low-temperature impact properties applicable to parts, equipment, and tanks for the purpose of storage, transportation, and use of LNG, liquefied ammonia, liquid nitrogen, liquefied CO2, liquefied hydrogen, and the like. BACKGROUND ART Stainless steels with excellent corrosion resistance are advantageous materials for use in various parts, equipment, and structural materials directly exposed to external environments because they do not require separate investment in facilities for improving corrosion resistance. Particularly, in the case of austenitic stainless steels, excellent formability and elongation thereof enable formation of shapes according to various customer requirements and provide aesthetically pleasing appearances. In addition, because austenitic stainless steels do not embrittle at low temperature due to inherent properties thereof, excellent impact properties may be obtained at low temperature and austenitic stainless steels are used in the industry as materials suitable for use in cryogenic environments such as LNG, liquefied ammonia, liquid nitrogen, liquefied CO2, and liquefied hydrogen. However, general austenitic stainless steels have a yield strength of 250 MPa or less, which limits application thereof in various uses, and martensite phase transformation observed in metastable austenitic stainless steels causes deterioration in impact properties, thereby acting as a factor hindering use in cryogenic environments. In conventional products, high-priced elements were used to improve austenite phase stability and prevent martensite phase transformation, and Ni has been actively used to improve austenite phase stability. However, excessive addition of Ni, a high-priced element with unstable supply and extreme price fluctuation, has limitations in terms of price competitiveness. Therefore, there is a need to develop austenitic stainless steels having high yield strength and excellent impact properties with high austenite phase stability compared to manufacturing costs by overcoming problems of conventional general-purpose austenitic stainless steels. DISCLOSURE Technical Problem The present disclosure has been proposed to solve the above-described problems, and provided are an austenitic stainless steel having high yield strength and excellent impact properties with high austenite phase stability compared to manufacturing costs and a method for manufacturing the same. However, the technical problems to be solved by the present disclosure are not limited to the aforementioned problems, and any other technical problems not mentioned herein will be clearly understood from the following description by those skilled in the art to which the present disclosure pertains. Technical Solution An austenitic stainless steel according to an embodiment of the present disclosure to achieve the above-described object includes, in percent by weight (wt %), 0.03% or less (excluding 0) of C, 0.15 to 0.25% of N, 1.0% or less (excluding 0) of Si, 3.3 to 7.5% of Mn, 17.0 to 22.0% of Cr, 6.5 to 9.5% of Ni, 1.2% or less (excluding 0) of Cu, 0.8% or less (excluding 0) of Mo, and the balance of Fe and inevitable impurities, wherein the austenitic stainless steel satisfies Formula (1) below and has a Charpy impact energy at −196° C. of 120 J or more: Formula (1): 70≤(100−ASP)/(Ni/Mn)≤170 (wherein ASP represents austenite phase stability, ASP is calculated by 551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29 (Ni+Cu)−18.5Mo, and Ni and Mn represent wt % of the respective elements). In addition, in the austenitic stainless steel according to an embodiment of the present disclosure, austenitic stainless steel may satisfy Formula (2) below. Formula (2): 1.45Mn+10Ni−9.5Cu−175N+0.32(CVN(@25° C.)≥120 (wherein Mn, Ni, Cu, and N represent wt % of the respective elements, and CVN(@25° C. refers to a Charpy impact energy value at 25° C.). In addition, in the austenitic stainless steel according to an embodiment of the present disclosure, the austenitic stainless steel may satisfy Formula (3) below. 4.4+2⁢3⁢(C+N)+1.3 Si+0.24(Cr+Ni+Mn)≥1⁢6Formula⁢ (3) (wherein C, N, Si, Cr, Ni, and Mn represent wt % of the respective elements.) In addition, in the austenitic stainless steel according to an embodiment of the present disclosure, a yield strength may be 300 MPa or more. A method for manufacturing an austenitic stainless steel according to an embodiment of the present disclosure includes: manufacturing a slab including, in percent by weight (wt %), 0.03% or less (excluding 0) of C, 0.15 to 0.25% of N, 1.0% or less (excluding 0) of Si, 3.3 to 7.5% of Mn, 17.0 to 22.0% of Cr, 6.5 to 9.5% of Ni, 1.2% or less (excluding 0) of Cu, 0.8% or less (excluding 0) of Mo, and the balance of Fe and inevitable impurities, and satisfying Formula (1) below: heating and extracting the slab; hot ro