Cold-rolled steel plate for hot forming, having excellent corrosion-resistance and spot-weldability, hot-formed member, and method for manufacturing same

Patent metadata

Field	Value
Publication number	US-12049679-B2
Application number	US-202318242140-A
Country	US
Kind code	B2
Filing date	Sep 5, 2023
Priority date	Sep 26, 2016
Publication date	Jul 30, 2024
Grant date	Jul 30, 2024

Abstract

An aspect of the present invention relates to 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 %).

First claim

The invention claimed is:

1. A method of manufacturing a cold-rolled steel plate for hot-forming, comprising:
heating a slab to 1000˜1300° C., the slab 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 %;
obtaining a hot-rolled steel plate by hot-rolling the heated slab at finishing rolling temperature of Ar3 to 1000° C.;
coiling the hot-rolled steel plate within a temperature range of higher than Ms to 750° C. or less;
obtaining a cold-rolled steel plate by cold-rolling the coiled hot-rolled steel plate; and
continuously annealing the cold-rolled steel plate to satisfy equation (2) and equation (3) below:
1≤exp[0.07*DP(I)+(0.6*Cr+3*Si)]≤100  equation (2)

50*exp[0.05*DP(I)−(1.2*Cr+6*Si)]≤2.5  equation (3)

where each element symbol is a value of a content of each element measured by weight %, and DP(I) is a dew point temperature (° C.) when the continuous annealing is performed,
wherein the slab 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 %.

2. The method of claim 1 , wherein the slab comprises one or more elements selected from between a) and b) below by weight %:
a) one or more elements selected from among Ti, Nb, Zr, and V: 0.001 to 0.4%
b) B: 0.0001 to 0.01%.

3. The method of claim 1 , wherein the slab comprises one or more elements selected from among c) to e) below by weight %:
c) one or more elements selected from between Mo and W: 0.001 to 1.0%
d) a sum of contents of Cu and Ni: 0.005 to 2.0%
e) one or more elements selected from between Sb and Sn: 0.001 to 1.0%.

4. The method of claim 1 , wherein the cold-rolling is performed at a reduction ratio of 30 to 80%.

5. The method of claim 1 , wherein the continuous annealing is performed within a temperature range of 700 to 900° C.

Assignees

• Posco Co Ltd

Inventors

• Oh Jin-Keun
• Cho Yeol-Rae
• Cho A-Ra
• Cha Jin-Ho
• Heo Si-Myoung
• Seo Jeong-Won
• Kim Seong-Woo

Classifications

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C22C38/54

  with boron · CPC title

• C22C38/50

  with titanium or zirconium · CPC title

• C22C38/26

  with niobium or tantalum · CPC title

• C22C38/24

  with vanadium · CPC title