# US 2022/0033941 A1 · High-strength stainless steel

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- Number: US 2022/0033941 A1
- Document ID: US20220033941A1
- Status: Published application
- Kind: A1
- Application number: 17/312,119
- Filed: 2019-08-23
- Published: 2022-02-03
- Earliest claimed: 2018-12-18
- Assignees: Posco
- Applicants: Posco
- Inventors: Jong Jin Jeon; Mi-Nam Park; Sang Seok Kim
- Web page: https://patentgrep.com/patent/US20220033941A1

## CPC

- C22C 38/44: with molybdenum or tungsten
- C21D 6/004: {containing Cr and Ni}
- C21D 6/005: {containing Mn}
- C21D 6/008: {containing Si}
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0263: {following hot rolling}
- C21D 9/46: for sheet metals
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- C22C 38/001: {containing N}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/42: with copper
- C21D 1/18: Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62)
- C21D 8/0436: {Cold rolling}
- C21D 9/48: deep-drawing sheets
- C21D 2211/001: Austenite
- C21D 2211/005: Ferrite
- C21D 2211/008: Martensite
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)

## Abstract

A stainless steel with a yield strength of 2,200 MPa or more is disclosed through the generation of the strain-induced martensite phase and the increase of the martensite phase strength. A high strength stainless steel according to an embodiment of present disclosure includes, in percent (%) by weight of the entire composition, C: 0.14 to 0.20%, Si: 0.8 to 1.0%, Mn: more than 0 and 0.5% or less, Cr: 15.0 to 17.0%, Ni: 4.0 to 5.0%, Mo: 0.6 to 0.8%, Cu: 0.5% or less, N: 0.05 to 0.11%, the remainder of iron (Fe) and other inevitable impurities, and C+N: 0.25% or more and Md30 value satisfies 40° C. or more.

## Claims

### Claim 1

A high strength stainless steel comprising, in percent (%) by weight of the entire composition, C: 0.14 to 0.20%, Si: 0.8 to 1.0%, Mn: more than 0 and 0.5% or less, Cr: 15.0 to 17.0%, Ni: 4.0 to 5.0%, Mo: 0.6 to 0.8%, Cu: 0.5% or less, N: 0.05 to 0.11%, the remainder of iron (Fe) and other inevitable impurities, and
C+N: 0.25% or more and Md30 value represented by a following Equation (1) satisfies 40° C. or more.
Md30(° C.)=551−462*(C+N)−9.2*Si−8.1*Mn−13.7*Cr−29*(Ni+Cu)−18.5*Mo (1)
(Here, C, N, Si, Mn, Cr, Ni, Cu, Mo mean the content (% by weight) of each element)

### Claim 2 (depends on 1)

The high strength stainless steel of claim 1, wherein a Ms value represented by a following Equation (2) satisfies −110° C. or less.
Ms(° C.)=502−810*C−1230*N−13*Mn−30*Ni−12*Cr−54*Cu−46*Mo (2)

### Claim 3 (depends on 2)

The high strength stainless steel of claim 2, wherein the Ms value represented by the Equation (2) satisfies −117° C. or less, or a value of a following Equation (3) satisfies 17.0 or more.
Ni/(C+N) (3)

### Claim 4 (depends on 1)

The high strength stainless steel of claim 1, wherein a matrix structure comprises, as an area fraction, a martensite phase of 45% or more, a residual austenite phase and ferrite phase, and
the ferrite phase is 4% or less.

### Claim 5 (depends on 1)

The high strength stainless steel of claim 1, wherein the stainless steel is a cold rolled material with a reduction ratio of 60% or more, and has a yield strength of 2,200 MPa or more.