Steel sheet, hot-dip galvanized steel sheet and galvannealed steel sheet

Patent metadata

Field	Value
Publication number	US-11274356-B2
Application number	US-201716772692-A
Country	US
Kind code	B2
Filing date	Dec 15, 2017
Priority date	Dec 15, 2017
Publication date	Mar 15, 2022
Grant date	Mar 15, 2022

Abstract

A steel sheet having a chemical composition of the base metal including, in mass %, C: 0.17 to 0.40%, Si: 0.10 to 2.50%, Mn: 1.00 to 10.00%, P: 0.001 to 0.03%, S: 0.0001 to 0.02%, Al: 0.001 to 2.50%, N: 0.0001 to 0.010%, O: 0.0001 to 0.010%, Ti: 0 to 0.10%, Nb: 0 to 0.10%, V: 0 to 0.10%, B: 0 to 0.010%, Cr: 0 to 2.00%, Ni: 0 to 2.00%, Cu: 0 to 2.00%, Mo: 0 to 2.00%, Ca: 0 to 0.50%, Mg: 0 to 0.50%, REM: 0 to 0.50%, the balance: Fe and impurities, wherein the steel sheet has an internal oxidized layer in which at least one part of a crystal grain boundary is covered by oxides, and in which a grain boundary coverage ratio of oxides is 60% or more in a region from the surface of the base metal to a depth of 5.0 μm.

First claim

The invention claimed is:

1. A steel sheet in which a chemical composition of a base metal comprises, in mass %,
C: 0.17 to 0.40%,
Si: 0.10 to 2.50%,
Mn: 1.00 to 10.00%,
P: 0.001 to 0.03%,
S: 0.0001 to 0.02%,
Al: 0.001 to 2.50%,
N: 0.0001 to 0.010%,
O: 0.0001 to 0.010%,
Ti: 0 to 0.10%,
Nb: 0 to 0.10%,
V: 0 to 0.10%,
B: 0 to 0.010%,
Cr: 0 to 2.00%,
Ni: 0 to 2.00%,
Cu: 0 to 2.00%,
Mo: 0 to 2.00%,
Ca: 0 to 0.50%,
Mg: 0 to 0.50%,
REM: 0 to 0.50%, and
the balance: Fe and impurities,
wherein the steel sheet has, from a surface of the base metal to a depth of 5.0 μm or more, an internal oxidized layer in which at least one part of a crystal grain boundary is covered with oxides, and wherein:
in a region from the surface of the base metal to a depth of 5.0 μm, a grain boundary coverage ratio of the oxides is 60% or more.

2. The steel sheet according to claim 1 , comprising:
a decarburization layer from the surface of the base metal to a depth of 50 μm or more.

3. A hot-dip galvanized steel sheet, comprising:
a hot-dip galvanized layer on a surface of the steel sheet according to claim 2 .

4. The hot-dip galvanized steel sheet according to claim 3 , wherein:
a coating mass of the hot-dip galvanized layer is not more than 70 g/m 2 .

5. A galvannealed steel sheet, comprising:
a galvannealed layer on a surface of the steel sheet according to claim 2 .

6. The galvannealed steel sheet according to claim 5 , wherein:
a coating mass of the galvannealed layer is not more than 70 g/m 2 .

7. The galvannealed steel sheet according to claim 5 , wherein:
the galvannealed layer contains, in mass %, Fe: 7.0 to 15.0%.

8. The steel sheet according to claim 1 , comprising:
a nickel electroplating layer on the surface of the base metal.

9. A hot-dip galvanized steel sheet, comprising:
a hot-dip galvanized layer on a surface of the steel sheet according to claim 8 .

10. The hot-dip galvanized steel sheet according to claim 9 , wherein:
a coating mass of the hot-dip galvanized layer is not more than 70 g/m 2 .

11. A galvannealed steel sheet, comprising:
a galvannealed layer on a surface of the steel sheet according to claim 8 .

12. The galvannealed steel sheet according to claim 11 , wherein:
a coating mass of the galvannealed layer is not more than 70 g/m 2 .

13. The galvannealed steel sheet according to claim 11 , wherein:
the galvannealed layer contains, in mass %, Fe: 7.0 to 15.0%.

14. The steel sheet according to claim 1 , wherein the steel sheet has a tensile strength of 980 MPa or more.

15. A hot-dip galvanized steel sheet, comprising:
a hot-dip galvanized layer on a surface of the steel sheet according to claim 1 .

16. The hot-dip galvanized steel sheet according to claim 15 , wherein:
a coating mass of the hot-dip galvanized layer is not more than 70 g/m 2 .

17. A galvannealed steel sheet, comprising:
a galvannealed layer on a surface of the steel sheet according to claim 1 .

18. The galvannealed steel sheet according to claim 17 , wherein:
a coating mass of the galvannealed layer is not more than 70 g/m 2 .

19. The galvannealed steel sheet according to claim 17 , wherein:
the galvannealed layer contains, in mass %, Fe: 7.0 to 15.0%.

Assignees

• Nippon Steel Corp

Inventors

• Takeda Kengo
• Hayashi Kunio
• Uenishi Akihiro
• Kawata Hiroyuki
• YOSHINAGA Chisato
• Miyazaki Yasunobu
• Nakamura Toyomitsu

Classifications

• C23C2/024

  by cleaning or etching · CPC title

• C23C2/0224

  Two or more thermal pretreatments · CPC title

• C23C2/02

  Pretreatment of the material to be coated, e.g. for coating on selected surface areas (C23C2/30 takes precedence) · CPC title

• C21D6/008

  containing Si · CPC title

• C23C28/028

  Including graded layers in composition or in physical properties, e.g. density, porosity, grain size · CPC title