High-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet having excellent formability and small material anisotropy with ultimate tensile strength of 980 MPa or more

Patent metadata

Field	Value
Publication number	US-9540720-B2
Application number	US-201214347269-A
Country	US
Kind code	B2
Filing date	Sep 28, 2012
Priority date	Sep 30, 2011
Publication date	Jan 10, 2017
Grant date	Jan 10, 2017

Abstract

Disclosed is a high-strength hot-dip galvanized steel sheet having small material anisotropy and excellent formability with an ultimate tensile strength of 980 MPa or more. The hot-dip galvanized steel sheet includes a hot-dip galvanized layer formed on a surface of a base steel plate. The base steel plate contains C, Si, Mn, O, P, S, Al and N within predetermined ranges and a balance including Fe and inevitable impurities. The hot-dip galvanized layer contains Fe at less than 7 mass % or 7 to 15 mass % and a balance including Zn, Al, and inevitable impurities.

First claim

The invention claimed is:

1. A high-strength hot-dip galvanized steel sheet having small material anisotropy and excellent formability with an ultimate tensile strength of 980 MPa or more, the hot-dip galvanized steel sheet comprising a hot-dip galvanized layer formed on a surface of a base steel sheet,
wherein the base steel sheet contains: by mass %,
C: 0.1 to less than 0.40%;
Si: 0.5 to 3.0%;
Mn: 1.5 to 3.0%;
O: 0.0001 to 0.006%;
P: 0.0001 to 0.04%;
S: 0.0001 to 0.01%;
Al: 0.0005 to 2.0%;
N: 0.0005 to 0.01%; and
a balance including Fe and inevitable impurities,
a microstructure of the base steel sheet contains ferrite of 40% or more, contains residual austenite of 8 to 27%, by volume fraction, and contains bainite and a balance being martensite or less than 10% of pearlite,
an average value of pole densities of orientation groups {100} <011> to {223} <110> represented by each of crystal orientations {100} <011>, {116} <110>, {114} <110>, {113} <110>, {112} <110>, {335} <110>, and {223} <110> in a sheet thickness range of ⅝ to ⅜ from the surface of the base steel sheet is 6.5 or less and a pole density of a crystal orientation {332} <113> is 5.0 or less, and
the hot-dip galvanized layer contains Fe: less than 7 mass % and a balance including Zn, Al, and inevitable impurities.

2. The high-strength hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to claim 1 , wherein the base steel sheet further contains one or two or more of: by mass %,
Cr: 0.05 to 1.0%;
Mo: 0.01 to 1.0%;
Ni: 0.05 to 1.0%;
Cu: 0.05 to 1.0%;
Nb: 0.005 to 0.3%;
Ti: 0.005 to 0.3%;
V: 0.005 to 0.5%; and
B: 0.0001 to 0.01%.

3. The high-strength hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to claim 1 , wherein the base steel sheet further contains, by mass %, 0.0005 to 0.04% in total of one or two or more selected from Ca, Mg, and REM.

4. A high-strength alloyed hot-dip galvanized steel sheet having small material anisotropy and excellent formability with an ultimate tensile strength of 980 MPa or more, the alloyed hot-dip galvanized steel sheet comprising an alloyed hot-dip galvanized layer formed on a surface of a base steel sheet,
wherein the base steel sheet contains: by mass %,
C: 0.10 to less than 0.4%;
Si: 0.5 to 3.0%;
Mn: 1.5 to 3.0%;
O: 0.0001 to 0.006%;
P: 0.0001 to 0.04%;
S: 0.0001 to 0.01%;
Al: 0.0005 to 2.0%;
N: 0.0005 to 0.01%; and
a balance including Fe and inevitable impurities,
a microstructure of the base steel sheet contains ferrite of 40% or more, contains residual austenite of 8 to 27%, by volume fraction, and contains bainite and a balance being martensite or less than 10% of pearlite,
an average value of pole densities of orientation groups {100} <011> to {223} <110> represented by each of crystal orientations {100} <011>, {116} <110>, {114} <110>, {113} <110>, {112} <110>, {335} <110>, and {223} <110> in a sheet thickness range of ⅝ to ⅜ from the surface of the base steel sheet is 6.5 or less and a pole density of a crystal orientation {332} <113> is 5.0 or less, and
the alloyed hot-dip galvanized layer contains Fe: 7 to 15 mass % and a balance including Zn, Al, and inevitable impurities.

5. The high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to claim 4 , wherein the base steel sheet further contains one or two or more of: by mass %,
Cr: 0.05 to 1.0%;
Mo: 0.01 to 1.0%;
Ni: 0.05 to 1.0%;
Cu: 0.05 to 1.0%;
Nb: 0.005 to 0.3%;
Ti: 0.005 to 0.3%;
V: 0.005 to 0.5%; and
B: 0.0001 to 0.01%.

6. The high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to claim 4 , wherein the base steel sheet further contains, by mass %, 0.0005 to 0.04% in total of one or two or more selected from Ca, Mg, and REM.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Azuma Masafumi
• Wakabayashi Chisato
• Nozaki Takayuki
• Fujita Nobuhiro
• Takahashi Manabu

Classifications

• Y10T428/12972

  Containing 0.01-1.7% carbon [i.e., steel] · CPC title

• Y10T428/12958

  Next to Fe-base component · CPC title

• Y10T428/12799

  Next to Fe-base component [e.g., galvanized] · CPC title

• Y10T428/12792

  Zn-base component · CPC title

• Y10T428/12757

  Fe · CPC title