# US 8,273,191 B2 · High-strength stainless steel material and production process of the same

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- Number: US 8,273,191 B2
- Document ID: US8273191B2
- Status: Granted
- Kind: B2
- Application number: 12/811,617
- Filed: 2009-02-02
- Published: 2010-11-11
- Granted: 2012-09-25
- Earliest claimed: 2008-02-07
- Assignees: Nisshin Steel Co., Ltd.
- Inventors: Naoki Hirakawa; Hiroshi Fujimoto; Satoshi Suzuki
- Web page: https://patentgrep.com/patent/US8273191B2

## CPC

- C22C 38/18: containing chromium
- C21D 6/00: Heat treatment of ferrous alloys
- C21D 9/46: for sheet metals
- C22C 38/001: {containing N}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/40: with nickel
- C22C 38/42: with copper
- 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

Provided is a high-strength stainless steel material having less deterioration in mechanical strength and improved workability, particularly bending workability compared with conventional steel materials. The high-strength stainless steel material of the present invention has a specific composition, has a metal microstructure composed of two phases, that is a ferrite phase and a martensite phase, has a γmax of from 50 to 85, the γmax being represented by the following equation (1): γmax=420Wc+470WN+23WNi+7WMn−11.5WCr−11.5WSi+189 (1) wherein, Wc, WN, WNi, WMn, WCr, and WSi; represent contents (unit: mass %) of C, N, Ni, Mn, Cr, and Si relative to the total mass of the stainless steel material, respectively; and has a difference of 300 HV or less in hardness between the ferrite phase and the martensite phase.

## Claims

### Claim 1

A high-strength stainless steel material having a composition comprising, as essential components thereof, greater than 0.00 mass % but not greater than 0.15 mass % of C, greater than 0.0 mass % but not greater than 2.0 mass % of Si, greater than 0.0 mass % but not greater than 4.0 mass % of Mn, greater than 0.00 mass % but not greater than 0.04 mass % of P, greater than 0.00 mass % but not greater than 0.03 mass % of S, greater than 0.0 mass % but not greater than 4.0 mass % of Ni, from 10.0 to 20.0 mass % of Cr, and greater than 0.00 mass % but not greater than 0.12 mass % of N with a balance of Fe and inevitable impurities;
having a metal microstructure composed of two phases, one of the phases being a ferrite phase and the other of the phases being a martensite phase;
having a γmax of from 50 to 85, the γmax being represented by the following equation (1):
γmax=420Wc+470WN+23WNi+7WMn−11.5WCr−11.5WSi+189 (1)
(in the equation (1), Wc, WN, WNi, WMn, WCr and WSi represent contents (unit: mass %) of C, N, Ni, Mn, Cr, and Si relative to the total mass of the stainless steel material, respectively; and
having a difference of 300 HV or less in hardness between the ferrite phase and the martensite phase and wherein the high-strength steel material has a hardness of 397 HV or less.

### Claim 2 (depends on 1)

The high-strength stainless steel material according to claim 1, which has yield elongation.

### Claim 3 (depends on 1)

The high-strength stainless steel material according to claim 1, further comprising greater than 0.0 mass % but not greater than 3.0% of Cu and having a γmax of from 50 to 85, the γmax being represented by the following equation (2):
γmax=420Wc+470WN+23WNi+9WCu+7WMn−11.5WCr−11.5WSi+189 (2)
(in the equation (2), Wc, WN, WNi, WCu, WMn, WCr, and Ws; represent contents (unit: mass %) of C, N, Ni, Cu, Mn, Cr, and Si relative to the total mass of the stainless steel material, respectively.

### Claim 4

A production process of a high-strength stainless steel material comprising a step of subjecting, to a dual-phase formation treatment, a steel piece having a composition comprising, as essential components, greater than 0.00 mass % but not greater than 0.15 mass % of C, greater than 0.0 mass % but not greater than 2.0 mass % of Si, greater than 0.0 mass % but not greater than 4.0 mass % of Mn, greater than 0.00 mass % but not greater than 0.04 mass % of P, greater than 0.00 mass % but not greater than 0.03 mass % of S, greater than 0.0 mass % but not greater than 4.0 mass % of Ni, from 10.0 to 20.0 mass % of Cr, and greater than 0.00 mass % but not greater than 0.12 mass % of N with a balance of Fe and inevitable impurities; and having a γmax of from 50 to 85, the γmax being represented by the following equation (1):
γmax=420Wc+470WN+23WNi+7WMn−11.5WCr−11.5WSi+189 (1)
(in the equation (1), Wc, WN, WNi, WMn, WCr, and WSi represent contents (unit: mass %) of C, N, Ni, Mn, Cr, and Si relative to the total mass of the steel piece, respectively); and
subjecting the steel piece obtained by the dual-phase formation treatment to an aging treatment,
wherein the high-strength stainless steel material has a difference of 300 HV or less in hardness between a ferrite phase and a martensite phase and wherein the high-strength steel material has a hardness of 397 HV or less.

### Claim 5 (depends on 4)

The production process of a high-strength stainless steel material according to claim 4, wherein the steel piece further contains greater than 0.0 mass % but not greater than 3.0 mass % of Cu and has γmax of from 50 to 85, the γmax being represented by the following equation (2):
γmax=420Wc+470WN+23WNi+9WCu+7WMn−11.5WCr−11.5WSi+189 (2)
(in the equation (2), Wc, WN, WNi, WMn, WCr, and WSi represent contents (unit: mass %) of C, N, Ni, Cu, Mn, Cr, and Si relative to the total mass of the steel piece, respectively).

### Claim 6 (depends on 4)

The production process of producing a high-strength stainless steel material according to claim 4, wherein a maximum temperature in the aging treatment step is less than 600° C.

### Claim 7 (depends on 2)

The high-strength stainless steel material according to claim 2, further comprising greater than 0.0 mass % but not greater than 3.0% of Cu and having a γmax of from 50 to 85, the γmax being represented by the following equation (2):
γmax=420Wc+470WN+23WNi+9WCu+7WMn−11.5WCr−11.5WSi+189 (2)
(in the equation (2), Wc, WN, WNi, WCu, WMn, WCr, and WSi represent contents (unit: mass %) of C, N, Ni, Cu, Mn, Cr, and Si relative to the total mass of the stainless steel material, respectively.

### Claim 8 (depends on 5)

The production process of producing a high-strength stainless steel material according to claim 5, wherein a maximum temperature in the aging treatment step is less than 600° C.