High-yield-ratio high-strength steel sheet having excellent workability

Patent metadata

Field	Value
Publication number	US-9611524-B2
Application number	US-201313800561-A
Country	US
Kind code	B2
Filing date	Mar 13, 2013
Priority date	Mar 30, 2012
Publication date	Apr 4, 2017
Grant date	Apr 4, 2017

Abstract

A steel sheet according to the present invention has tensile strength of 980 MPa or more, exerts a high-yield ratio, and has excellent workability (in detail, strength-ductility balance). The steel sheet contains: C: 0.06-0.12% (excluding 0.12%); Si: 0.2% or less; Mn: 2.0-3.5%; at least one element selected from the group consisting of Ti, Nb, and V of 0.01-0.15% in total; B: 0.0003-0.005%; P: 0.05% or less; S: 0.05% or less; Al: 0.005-0.1%; N: 0.015% or less; and the balance is iron and unavoidable impurities, in which the content of ferrite is more than 5% to 15% or less, that of martensite is 25-55%, and the total content of bainite and tempered martensite is 30% or more to less than 70%, based on the whole microstructure, and in which the average crystal grain size of the ferrite is 3.0 μm or less.

First claim

What is claimed is:

1. A steel sheet comprising:
C of 0.06 mass % or more to 0.112 mass % or less;
Si of 0.2 mass % or less;
Mn of 2.0 to 3.5 mass %;
at least one element selected from the group consisting of Ti, Nb, and V of 0.01 to 0.15 mass % in total;
B of 0.0003 to 0.005 mass %;
P of 0.05 mass % or less;
S of 0.05 mass % or less;
Al of 0.005 to 0.1 mass %;
N of 0.015 mass % or less; and
the balance being iron and unavoidable impurities,
wherein a microstructure of the steel sheet contains ferrite, martensite, bainite, and tempered martensite,
wherein a content of ferrite is more than 5 area % to 15 area % or less, a content of martensite is 31 to 55 area %, and a total content of bainite and tempered martensite is 30 area % or more to less than 70 area %, based on the whole microstructure,
wherein an average crystal grain size of the ferrite is 3.0 μm or less, and
wherein a tensile strength is 980 MPa or more.

2. The steel sheet according to claim 1 , further comprising, as another element, at least one element selected from the group consisting of Cr and Mo of 1.0 mass % or less in total, excluding 0 mass %.

3. The steel sheet according to claim 1 , having a hot-dip galvanizing-coated layer or a hot-dip galvannealing-coated layer on a surface of the steel sheet.

4. The steel sheet according to claim 1 , wherein the amount of C is 0.06 mass % or more to 0.110 mass % or less.

5. The steel sheet according to claim 1 , wherein the amount of C is 0.06 mass % or more to 0.100 mass % or less.

6. The steel sheet according to claim 1 , wherein the content of martensite is 36 to 55 area %.

7. The steel sheet according to claim 1 , wherein the content of martensite is 40 to 55 area %.

8. The steel sheet according to claim 2 , having a hot-dip galvanizing-coated layer or a hot-dip galvannealing-coated layer on a surface of the steel sheet.

9. A steel sheet consisting of:
C of 0.06 mass % or more to less than 0.112 mass %;
Si of 0.2 mass % or less;
Mn of 2.0 to 3.5 mass %;
at least one element selected from the group consisting of Ti, Nb, and V of 0.01 to 0.15 mass % in total;
B of 0.0003 to 0.005 mass %;
optionally at least one element selected from the group consisting of Cr and Mo of 1.0 mass % or less;
P of 0.05 mass % or less;
S of 0.05 mass % or less;
Al of 0.005 to 0.1 mass %;
N of 0.015 mass % or less; and
the balance being iron and unavoidable impurities,
wherein a microstructure of the steel sheet contains ferrite, martensite, bainite, and tempered martensite,
wherein a content of ferrite is more than 5 area % to 15 area % or less, a content of martensite is 31 to 55 area %, and a total content of bainite and tempered martensite is 30 area % or more to less than 70 area %, based on the whole microstructure,
wherein an average crystal grain size of the ferrite is 3.0 μm or less, and
wherein a tensile strength is 980 MPa or more.

10. The steel sheet according to claim 9 , wherein the amount of C is 0.06 mass % or more to 0.110 mass % or less.

11. The steel sheet according to claim 9 , wherein the amount of C is 0.06 mass % or more to 0.100 mass % or less.

Assignees

• Kobe Steel Ltd

Inventors

• Hamada Kazuyuki
• Asai Tatsuya

Classifications

• C22C38/04

  containing manganese · CPC title

• B32B15/013

  one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium · CPC title

• C22C38/28

  with titanium or zirconium · CPC title

• C21D9/46

  for sheet metals · CPC title

• C22C38/22

  with molybdenum or tungsten · CPC title