# US 2023/0399728 A1 · Austenite stainless steel material, method for producing same, and plate spring

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- Number: US 2023/0399728 A1
- Document ID: US20230399728A1
- Status: Published application
- Kind: A1
- Application number: 18/250,278
- Filed: 2021-05-19
- Published: 2023-12-14
- Earliest claimed: 2021-02-24
- Assignees: Nippon Steel Stainless Steel Corporation
- Applicants: Nippon Steel Stainless Steel Corporation
- Inventors: Masaya TANAKA; Naoki HIRAKAWA
- Web page: https://patentgrep.com/patent/US20230399728A1

## CPC

- C22C 38/58: with more than 1.5% by weight of manganese
- C21D 6/004: {containing Cr and Ni}
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0247: characterised by the heat treatment
- 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 38/06: containing aluminium
- C22C 38/34: with more than 1.5% by weight of silicon
- C22C 38/42: with copper
- C22C 38/44: with molybdenum or tungsten
- C22C 38/46: with vanadium
- C22C 38/48: with niobium or tantalum
- C22C 38/50: with titanium or zirconium
- C22C 38/54: with boron
- C22C 38/60: containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
- F16F 1/18: Leaf springs {(planar springs in general F16F1/027; "Belleville"-type springs with generally radial arms F16F1/324)}
- C21D 2211/001: Austenite
- 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)
- F16F: SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION

## Abstract

An austenitic stainless steel material comprises, on a mass basis, 0.200% or less of C, 4.00% or less of Si, 5.00% or less of Mn, 4.00 to 10.00% of Ni, 12.00 to 18.00% of Cr, 3.50% or less of Cu, 1.00 to 5.00% of Mo, and 0.200% or less of N, a total amount of C and N of 0.100% or more, and the balance being Fe and impurities; wherein the austenitic stainless steel material has a value of Md30 of −40.0 to 0° C., wherein the value of Md30 is represented by the following equation (1): Md30=551−462(C+N)−9.2Si−8.1Mn−29(Ni+Cu)−13.7Cr−18.5Mo (1) in which the symbols of the elements each represents a content (% by mass) of each element.

## Claims

### Claim 1

An austenitic stainless steel material,
wherein the austenitic stainless steel material comprises, on a mass basis, 0.200% or less of C, 4.00% or less of Si, 5.00% or less of Mn, 4.00 to 10.00% of Ni, 12.00 to 18.00% of Cr, 3.50% or less of Cu, 1.00 to 5.00% of Mo, and 0.200% or less of N, a total amount of C and N of 0.100% or more, and the balance being Fe and impurities;
wherein the austenitic stainless steel material has a value of Md30 of −40.0 to 0° C., the value of Md30 being represented by the following equation (1):
Md30=551−462(C+N)−9.2Si−8.1Mn−29(Ni+Cu)−13.7Cr−18.5Mo (1)
in which the symbols of the elements each represents a content (% by mass) of each element; and
wherein the austenitic stainless steel material has a metallographic structure having a dislocation density of a strain-induced martensite phase of 8.0×1016 m−2 or less, a dislocation density of a retained austenite phase of 1.5×1016 to 6.0×1016 m−2, and a content of the strain-induced martensite phase of 20 to 55% by volume.

### Claim 2 (depends on 1)

The austenitic stainless steel material according to claim 1, further comprising, on a mass basis, one or more selected from 0.100% or less of Al, 0.010% or less of O, 0.0001 to 0.500% of V, and 0.0001 to 0.0150% of B.

### Claim 3 (depends on 1)

The austenitic stainless steel material according to claim 1, further comprising, on a mass basis, one or more selected from 0.0001 to 0.500% of Ti, 0.010 to 0.500% of Co, 0.010 to 0.100% of Zr, 0.010 to 0.100% of Nb, 0.0005 to 0.0030% of Mg, 0.0003 to 0.0030% of Ca, 0.010 to 0.200% of Y, 0.001 to 0.100% of Ln, 0.001 to 0.500% of Sn, 0.001 to 0.500% of Sb, 0.010 to 0.100% of Pb, and 0.010 to 0.500% of W.

### Claim 4 (depends on 1)

The austenitic stainless steel material according to claim 1, wherein the austenitic stainless steel material has a tensile strength (TS) of 1400 MPa or more and an elongation at break (EL) of 2.0% or more

### Claim 5 (depends on 1)

The austenitic stainless steel material according to claim 1, wherein the austenitic stainless steel material has a stress relaxation percentage of 1.00% or less, the stress relaxation percentage being represented by the following equation (2):
stress relaxation percentage=(σ1−σ2)/σ1 (2)
in which σ1 is a stress less than 0.2% yield strength, and σ2 is a stress on 180 seconds after applying the stress of σ1.

### Claim 6

A method for producing an austenitic stainless steel material, the method comprising:
subjecting a rolled material to a solution treatment, followed by cold rolling at a rolling reduction ratio to obtain a dislocation density of a strain-induced martensite phase of 8.0×1016 m−2 or less, a dislocation density of a retained austenite phase of 1.5×1016 to 6.0×1016 m−2, and a content of the strain-induced martensite phase of 20 to 55% by volume, wherein the rolled material comprises, on a mass basis, 0.200% or less of C, 4.00% or less of Si, 5.00% or less of Mn, 4.00 to 10.00% of Ni, 12.00 to 18.00% of Cr, 3.50% or less of Cu, 1.00 to 5.00% of Mo, and 0.200% or less of N, a total amount of C and N being 0.100% or more, and the balance being Fe and impurities, and wherein the rolled material has a value of Md30 of −40.0 to 0° C., the value of Md30 being represented by the following equation (1):
Md30=551−462(C+N)−9.2Si−8.1Mn−29(Ni+Cu)−13.7Cr−18.5Mo (1)
in which the symbols of the elements each represents a content (% by mass) of each element.

### Claim 7 (depends on 6)

The method according to claim 6, further comprising a step of performing a heat treatment after the cold rolling.

### Claim 8 (depends on 6)

The method according to claim 6, wherein the rolled material further comprises, on a mass basis, one or more selected from 0.100% or less of Al, 0.010% or less of O, 0.0001 to 0.500% of V, and 0.0001 to 0.0150% of B.

### Claim 9

(canceled)

### Claim 10 (depends on 1)

A plate spring, comprising the austenitic stainless steel material according to claim 1.

### Claim 11 (depends on 2)

A plate spring, comprising the austenitic stainless steel material according to claim 2.

### Claim 12 (depends on 2)

The austenitic stainless steel material according to claim 2, further comprising, on a mass basis, one or more selected from 0.0001 to 0.500% of Ti, 0.010 to 0.500% of Co, 0.010 to 0.100% of Zr, 0.010 to 0.100% of Nb, 0.0005 to 0.0030% of Mg, 0.0003 to 0.0030% of Ca, 0.010 to 0.200% of Y, 0.001 to 0.100% of Ln, 0.001 to 0.500% of Sn, 0.001 to 0.500% of Sb, 0.010 to 0.100% of Pb, and 0.010 to 0.500% of W.

### Claim 13 (depends on 7)

The method according to claim 7, wherein the rolled material further comprises, on a mass basis, one or more selected from 0.100% or less of Al, 0.010% or less of O, 0.0001 to 0.500% of V, and 0.0001 to 0.0150% of B.