Cold-rolled steel sheet, galvanized cold-rolled steel sheet and method of manufacturing the same

Patent metadata

Field	Value
Publication number	US-2016130680-A1
Application number	US-201414891889-A
Country	US
Kind code	A1
Filing date	Jul 1, 2014
Priority date	Jul 1, 2013
Publication date	May 12, 2016
Grant date	—

Abstract

A cold-rolled steel sheet includes a predetermined chemical composition, and includes a structure expressed by: an area fraction of ferrite: 95% or more; an area fraction of retained austenite and an area fraction of martensite: 1% to 3% in total; a product of the area fraction of retained austenite and a carbon concentration in retained austenite: 1 or more; a value of I(111)/{I(100)+I(110)} at a region where a depth from a surface is ¼ of a thickness of the cold-rolled steel sheet when intensity of a (hkl) plane is expressed by I(hkl): 2 or less.

First claim

1 . A cold-rolled steel sheet; comprising:
a chemical composition expressed by, in mass %:
Si: 0.01% to 0.50%;
Mn or Cr, or both thereof: 0.70% to 1.50% in total;
C: 0.030% to 0.060% when Cr: “0” (zero)% or more and less than 0.30%,
0.030% to 0.080% when Cr: 0.30% or more and 1.50% or less;

Al: 0.800% to 2.000%;
P: 0.030% or less;
S: 0.0100% or less;
Mo: 0.10% to 0.50%;
O: 0.0070% or less;
N: 0.0070% or less;
B: “0” (zero)% to 0.0020%;
Ti: “0” (zero)% to 0.050%;
Nb: “0” (zero)% to 0.050%;
V: “0” (zero)% to 0.050%;
Ni: “0” (zero)% to 1.00%;
Cu: “0” (zero)% to 1.00%;
Ca or REM, or both thereof: “0” (zero)% to 0.0300% in total;
W: “0” (zero)% to 1.000%;
Mg: “0” (zero)% to 0.010%;
Zr: “0” (zero)% to 0.200%;
As: “0” (zero)% to 0.500%;
Co: “0” (zero)% to 1.000%;
Sn: “0” (zero)% to 0.200%;
Pb: “0”(zero)% to 0.200%;
Y: “0” (zero)% to 0.200%;
Hf: “0” (zero)% to 0.2000%; and
the balance: Fe and impurities; and
a structure expressed by:
an area fraction of ferrite: 95% or more;
an area fraction of retained austenite and an area fraction of martensite: 1% to 3% in total;
a product of the area fraction of retained austenite and a carbon concentration in retained austenite: 1 or more;
a value of I(111)/{I(100)+I(110)} at a region where a depth from a surface is ¼ of a thickness of the cold-rolled steel sheet when intensity of a (hkl) plane is expressed by I(hkl): 2 or less.

2 . The cold-rolled steel sheet according to claim 1 , wherein the chemical composition satisfies:
Cr: 0.30% to 0.80%; or Mn: 0.40% to 1.00%; or both thereof.

3 . The cold-rolled steel sheet according to claim 1 , wherein the chemical composition satisfies:
B: 0.0003% to 0.0020%; Ti: 0.005% to 0.050%; Nb: 0.005% to 0.050%; or V: 0.005% to 0.050%; or any combination thereof.

4 . The cold-rolled steel sheet according to claim 1 , wherein the chemical composition satisfies:
Ni: 0.01% to 1.00%; or Cu: 0.01% to 1.00%; or both thereof.

5 . The cold-rolled steel sheet according to claim 1 , wherein the chemical composition satisfies
Ca or REM, or both thereof: 0.0005% to 0.0300% in total.

6 . The cold-rolled steel sheet according to claim 1 , wherein the chemical composition satisfies:
W: 0.001% to 1.000%; Mg: 0.0001% to 0.010%; Zr: 0.0001% to 0.200%; As: 0.0001% to 0.500%; Co: 0.0001% to 1.000%; Sn: 0.0001% to 0.200%; Pb: 0.0001% to 0.200%; Y: 0.0001% to 0.200%; or Hf: 0.0001% to 0.2000%; or any combination thereof.

7 . A galvanized cold-rolled steel sheet, comprising:
the cold-rolled steel sheet according to claim 1 ; and a hot-dip galvanized layer or an alloyed hot-dip galvanized layer on a surface of the cold-rolled steel sheet.

8 . A method of manufacturing a cold-rolled steel sheet, comprising:
performing hot-rolling of a slab heated to a temperature of 1250° C. or less to obtain a hot-rolled sheet; coiling the hot-rolled sheet at a temperature of 650° C. or less; then, performing cold-rolling of the hot-rolled sheet with a reduction ratio of 70% or more to obtain a cold-rolled sheet; and performing continuous annealing of the cold-rolled sheet at a temperature of 750° C. to 900° C., wherein the performing the hot-rolling comprises performing finish-rolling at a temperature of 850° C. to 1000° C. under a state in which two phases of ferrite and austenite exist, a total reduction ratio at last three stands is 60% or more in the finish-rolling, cooling is started within one second from an end of the finish-rolling, and the slab comprises a chemical composition expressed by, in mass %,
Si: 0.01% to 0.50%;
Mn or Cr, or both thereof: 0.70% to 1.50% in total;
C: 0.030% to 0.060% when Cr: “0” (zero)% or more and less than 0.30%,
0.030% to 0.080% when Cr: 0.30% or more and 1.50% or less;

Al: 0.800% to 2.000%;
P: 0.030% or less;
S: 0.0100% or less;
Mo: 0.10% to 0.50%;
O: 0.0070% or less;
N: 0.0070% or less;
B: “0” (zero)% to 0.0020%;
Ti: “0” (zero)% to 0.050%;
Nb: “0” (zero)% to 0.050%;
V: “0” (zero)% to 0.050%;
Ni: “0” (zero)% to 1.00%;
Cu: “0” (zero)% to 1.00%;
Ca or REM, or both of them: “0” (zero)% to 0.0300% in total;
W: “0” (zero)% to 1.000%;
Mg: “0” (zero)% to 0.010%;
Zr: “0” (zero)% to 0.200%;
As: “0” (zero)% to 0.500%;
Co: “0” (zero)% to 1.000%;
Sn: “0” (zero)% to 0.200%;
Pb: “0” (zero)% o to 0.200%;
Y: “0” (zero)% to 0.200%;
Hf: “0” (zero)% to 0.2000%; and
the balance: Fe and impurities.

9 . The method of manufacturing the cold-rolled steel sheet according to claim 8 , wherein in the chemical composition satisfies:
Cr: 0.30% to 0.80%; or Mn: 0.40% to 1.00%; or both thereof.

10 . The method of manufacturing the cold-rolled steel sheet according to claim 8 , wherein the chemical composition satisfies:
B: 0.0003% to 0.0020%; Ti: 0.005% to 0.050%; Nb: 0.005% to 0.050%; or V: 0.005% to 0.050%; or any combination thereof.

11 . The method of manufacturing the cold-rolled steel sheet according to claim 8 , wherein the chemical composition satisfies:
Ni: 0.01% to 1.00%; or Cu: 0.01% to 1.00%; or both thereof.

12 . The method of manufacturing the cold-rolled steel sheet according to claim 8 , wherein the chemical composition satisfies
Ca or REM, or both thereof: 0.0005% to 0.0300% in total.

13 . The method of manufacturing the cold-rolled steel sheet according to claim 8 , wherein the chemical composition satisfies:
W: 0.001% to 1.000%; Mg: 0.0001% to 0.010%; Zr: 0.0001% to 0.200%; As: 0.0001% to 0.500%; Co: 0.0001% to 1.000%; Sn: 0.0001% to 0.200%; Pb: 0.0001% to 0.200%; Y: 0.0001% to 0.200%; or Hf: 0.0001% to 0.2000%; or any combination thereof.

14 . A method of manufacturing a galvanized cold-rolled steel sheet, comprising:
manufacturing a cold-rolled steel sheet by the method according to claim 8 ; and forming a hot-dip galvanized layer or an alloyed hot-dip galvanized layer on a surface of the cold-rolled steel sheet.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Kawasaki Kaoru
• Kameda Masaharu
• Sano Kohichi
• Okamoto Riki

Classifications

• C21D8/02

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

• C22C38/002

  containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60 · CPC title

• C22C38/005

  containing rare earths, i.e. Sc, Y, Lanthanides · CPC title

• C22C38/10

  containing cobalt · CPC title

• C22C38/22

  with molybdenum or tungsten · CPC title