# US 11,441,205 B2 · Cold-rolled steel plate for hot forming, having excellent corrosion-resistance and spot-weldability, hot-formed member, and method for manufacturing same

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- Number: US 11,441,205 B2
- Document ID: US11441205B2
- Status: Granted
- Kind: B2
- Application number: 16/336,645
- Filed: 2017-09-26
- Published: 2020-12-10
- Granted: 2022-09-13
- Earliest claimed: 2016-09-26
- Assignees: Posco
- Applicants: Posco
- Inventors: Jin-Keun Oh; Yeol-Rae Cho; A-Ra Cho; Jin-Ho Cha; Si-Myoung Heo; Jeong-Won Seo; Seong-Woo Kim
- Web page: https://patentgrep.com/patent/US11441205B2

## CPC

- C21D 9/46: for sheet metals
- C21D 9/56: Continuous furnaces for strip or wire
- B21B 3/02: Rolling special iron alloys {, e.g. stainless steel}
- B21D 22/022: {by heating the blank or stamping associated with heat treatment (C21D takes precedence)}
- 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 8/0231: {Warm rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0247: characterised by the heat treatment
- C21D 8/0263: {following hot rolling}
- C21D 8/0273: {Final recrystallisation annealing}
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- C22C 38/001: {containing N}
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/008: {containing tin}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/20: with copper
- C22C 38/22: with molybdenum or tungsten
- C22C 38/24: with vanadium
- C22C 38/26: with niobium or tantalum
- C22C 38/50: with titanium or zirconium
- C22C 38/54: with boron
- C21D 2211/003: Cementite
- C21D 2211/005: Ferrite
- C22C 38/34: with more than 1.5% by weight of silicon
- C22C 38/38: with more than 1.5% by weight of manganese
- 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)
- B21B: ROLLING OF METAL (auxiliary operations used in connection with metal-working operations covered in B21, see B21C; bending by rolling B21D; manufacture of particular objects, e.g. screws, wheels, rings, barrels, balls, by rolling B21H; pressure welding by means of a rolling mill B23K20/04)
- B21D: WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL (working or processing of wire B21F)
- C22C: ALLOYS (treatment of alloys C21D, C22F)

## Abstract

Provided is a cold-rolled steel plate for hot forming, which is excellent in corrosion-resistance and spot-weldability, contains, by weight %, C: 0.1-0.4%, Si: 0.5-2.0%, Mn: 0.01-4.0%, Al: 0.001-0.4%, P: 0.001-0.05%, S: 0.0001-0.02%, Cr: 0.5% to less than 3.0%, N: 0.001-0.02%, and a balance of Fe and inevitable impurities, satisfying formula (1) below, and includes an Si amorphous oxidation layer continuously or discontinuously formed at a thickness of 1 nm-100 nm on the surface thereof. Formula (1): 1.4≤0.4*Cr+Si≤3.2 (wherein element symbols denote measurements of respective element contents by weight %).

## Claims

### Claim 1

A cold-rolled steel plate for hot-forming, having excellent corrosion-resistance and spot-weldability, comprising:
C: 0.1 to 0.4%, Si: 0.5 to 2.0%, Mn: 0.01 to 4.0%, Al: 0.001 to 0.4%, P: 0.001 to 0.05%, S: 0.0001 to 0.02%, Cr: 0.5% or higher and less than 3.0%, N: 0.001 to 0.02%, and a balance of Fe and inevitable impurities by weight %,
wherein the cold-rolled steel plate satisfies equation (1) below:
1.4≤0.4*Cr+Si≤3.2 equation (1):
where each element symbol is a value of a content of each element measured by weight %;
wherein an Si-based amorphous oxide layer having a thickness of 1 nm to 100 nm is continuously or discontinuously formed on a surface of the cold-rolled steel plate; and
wherein an Fe, Mn, and Cr oxide layer is formed to a thickness of 2.5 μm or less on the Si-based amorphous oxide layer.

### Claim 2 (depends on 1)

The cold-rolled steel plate of claim 1, wherein the cold-rolled steel plate further includes one or more selected from a) one or more selected from Ti, Nb, Zr, and V: 0.001 to 0.4% by weight %, and b) B: 0.0001 to 0.01% by weight %.

### Claim 3 (depends on 1)

The cold-rolled steel plate of claim 1, wherein the cold-rolled steel plate further includes one or more selected from c) one or more of Mo and W: 0.001 to 1.0% by weight %, d) a sum of contents of Cu and Ni: 0.005 to 2.0% by weight %, and e) one or more of Sb and Sn: 0.001 to 1.0% by weight %.

### Claim 4 (depends on 1)

The cold-rolled steel plate of claim 1, wherein a microstructure of the cold-rolled steel plate includes ferrite and cementite.