# US 11,299,799 B2 · Austenitic stainless steel product having excellent surface properties and manufacturing method of the same

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- Number: US 11,299,799 B2
- Document ID: US11299799B2
- Status: Granted
- Kind: B2
- Application number: 16/472,973
- Filed: 2017-12-04
- Published: 2020-06-18
- Granted: 2022-04-12
- Earliest claimed: 2016-12-23
- Assignees: Posco
- Applicants: Posco
- Inventors: Hyung Gu Kang; Jae-Hong Shim; Gyu Jin Jo; Dong Chul Chae
- Web page: https://patentgrep.com/patent/US11299799B2

## CPC

- C22C 38/42: with copper
- C22C 38/44: with molybdenum or tungsten
- C21D 1/18: Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62)
- C21D 6/004: {containing Cr and Ni}
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0273: {Final recrystallisation annealing}
- 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 38/16: containing copper
- C22C 38/58: with more than 1.5% by weight of manganese
- 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)

## Abstract

An austenitic stainless steel product having excellent surface characteristics and a manufacturing method therefor are disclosed. The disclosed austenitic stainless steel product comprises an austenitic stainless steel comprising, by weight percent, 0.005 to 0.15% of C, 0.1 to 1.0% of Si, 0.1 to 2.0% of Mn, 6.0 to 8.0% of Ni, 16 to 18% of Cr, 0.1 to 4.0% of Cu, 0.005 to 0.2% of N, 0.01 to 0.2% of Mo, and the remainder comprising iron (Fe) and other unavoidable impurities, and a Ni surface negative segregation thereof defined by the following formula (1) is 0.6 to 0.9 and the martensite fraction thereof is 10 to 30%. (CNi-Min)/(CNi-Ave) formula (1) Here, CNi-min is the minimum concentration of Ni on the surface and CNi-Ave is the average concentration of Ni on the surface.

## Claims

### Claim 1

An austenitic stainless steel product, the stainless steel comprising:
by weight percent, 0.005 to 0.15% of C, 0.1 to 1.0% of Si, 0.1 to 2.0% of Mn, 6.0 to 8.0% of Ni, 16 to 18% of Cr, 0.1 to 4.0% of Cu, 0.005 to 0.2% of N, 0.01 to 0.2% of Mo, and the remainder comprising iron (Fe) and other unavoidable impurities, and a surface degree of negative segregation of Ni defined by the following formula (1) is in the range of 0.6 to 0.9 and the martensite fraction thereof is 10 to 30%
(CNi-Min)/(CNi-Ave) Formula (1)
Where CNi-Min is the minimum concentration of Ni at the surface and CNi-Ave is the average concentration of Ni at the surface, and
wherein a surface hardness ratio defined by the following formula (2) is in the range of 1.1 to 1.6
A/B Formula (2)
where A is the average value of the upper 10% of the product surface hardness, and B is the average value of the lower 10% the product surface hardness.

### Claim 2 (depends on 1)

The austenitic stainless steel product according to claim 1, wherein cracks having a depth of 20 μm or more from the surface is 10 or less.

### Claim 3 (depends on 1)

The austenitic stainless steel product according to claim 1, wherein a Ni surface segregation portion is less than 60% in area fraction and a Ni surface negative segregation portion is more than 5%.

### Claim 4

A method of manufacturing an austenitic stainless steel product, the method comprising:
processing the austenitic stainless steel product, comprising:
by weight percent, 0.005 to 0.15% of C, 0.1 to 1.0% of Si, 0.1 to 2.0% of Mn, 6.0 to 8.0% of Ni, 16 to 18% of Cr, 0.1 to 4.0% of Cu, 0.005 to 0.2% of N, 0.01 to 0.2% of Mo, and the remainder comprising iron (Fe) and other unavoidable impurities; and
heat treating the austenitic stainless steel product at a temperature of 900-1,150° C. for 10 minutes or less; and
cooling the heat-treated austenitic stainless steel to 500° C. within 30 minutes;
wherein the austenitic stainless steel product has a surface degree of negative segregation of Ni defined by the following formula (1) is in the range of 0.6 to 0.9 and the martensite fraction thereof is 10 to 30%
(CNi-Min)/(CNi-Ave) Formula (1)
Where CNi-Min is the minimum concentration of Ni at the surface and CNi-Ave is the average concentration of Ni at the surface, and
wherein a surface hardness ratio defined by the following formula (2) is in the range of 1.1 to 1.6
A/B Formula (2)
where A is the average value of the upper 10% of the product surface hardness, and B is the average value of the lower 10% the product surface hardness.

### Claim 5 (depends on 4)

The method of claim 4, wherein the martensite fraction of the austenitic stainless steel product before the heat treatment is 10 to 50%.

### Claim 6 (depends on 5)

The method of claim 5, wherein the martensite fraction of the austenitic stainless steel product after cooling is 10 to 30%.