High-strength galvanized steel sheet

Patent metadata

Field	Value
Publication number	US-10370737-B2
Application number	US-201515543271-A
Country	US
Kind code	B2
Filing date	Nov 24, 2015
Priority date	Jan 15, 2015
Publication date	Aug 6, 2019
Grant date	Aug 6, 2019

Abstract

A high-strength galvanized steel sheet and method for producing the same. The high-strength galvanized steel sheet including a specified chemical composition and a microstructure comprising, in terms of area fraction, a tempered martensite phase: 30% or more and 73% or less, a ferrite phase: 25% or more and 68% or less, a retained austenite phase: 2% or more and 15% or less, and other phases: 10% or less (including 0%), the other phases comprising a martensite phase: 3% or less (including 0%) and a bainitic ferrite phase: less than 5% (including 0%), the tempered martensite phase having an average grain size of 8 μm or less, the ferrite phase having an average grain size of 5 μm or less, and the retained austenite phase having a C content less than 0.7% by mass.

First claim

The invention claimed is:

1. A high-strength galvanized steel sheet having a chemical composition comprising, by mass %:
C: 0.15% or more and 0.25% or less;
Si: 0.50% or more and 2.5% or less;
Mn: 2.3% or more and 4.0% or less;
P: 0.100% or less;
S: 0.02% or less;
Al: 0.01% or more and 2.5% or less;
at least one element selected from the group consisting of Nb: 0.005% or more and 0.1% or less, Ti: 0.005% or more and 0.1% or less, V: 0.01% or more and 1.0% or less, and Mo: 0.005% or more and 2.0% or less; and
the balance being Fe and inevitable impurities,
wherein the steel sheet has a microstructure comprising, in terms of area fraction, a tempered martensite phase: 30% or more and 73% or less, a ferrite phase: 25% or more and 68% or less, a retained austenite phase: 2% or more and 15% or less, other phases: 10% or less (including 0%) in total, the other phases comprising, in terms of area fraction, a martensite phase: 3% or less (including 0%), and bainitic ferrite phase: 0%,
the tempered martensite phase having an average grain size of 8 μm or less,
the ferrite phase having an average grain size of 5 μm or less, and
the retained austenite phase having a C content less than 0.7% by mass.

2. The high-strength galvanized steel sheet according to claim 1 , wherein the galvanized steel sheet includes a galvannealed steel sheet.

3. The high-strength galvanized steel sheet according to claim 2 , wherein the galvanized steel sheet has a tensile strength of 1180 MPa or more.

4. The high-strength galvanized steel sheet according to claim 1 , wherein the galvanized steel sheet has a tensile strength of 1180 MPa or more.

5. The high-strength galvanized steel sheet according to claim 1 , wherein the chemical composition further comprises at least one group selected from the group consisting of:
group A: by mass %, at least one element selected from the group consisting of Cr: 0.01% or more and 2.0% or less, Ni: 0.01% or more and 2.0% or less, and Cu: 0.01% or more and 2.0% or less,
group B: by mass %, B: 0.0002% or more and 0.0050% or less, and
group C: by mass %, at least one element selected from the group consisting of Ca: 0.001% or more and 0.005% or less and REM: 0.001% or more and 0.005% or less.

6. The high-strength galvanized steel sheet according to claim 5 , wherein the galvanized steel sheet includes a galvannealed steel sheet.

7. The high-strength galvanized steel sheet according to claim 6 , wherein the galvanized steel sheet has a tensile strength of 1180 MPa or more.

8. The high-strength galvanized steel sheet according to claim 5 , wherein the galvanized steel sheet has a tensile strength of 1180 MPa or more.

Assignees

• Jfe Steel Corp

Inventors

• Hasegawa Hiroshi
• Kimura Hideyuki
• Funakawa Yoshimasa
• Makimizu Yoichi
• Suzuki Yoshitsugu

Classifications

• C21D8/02

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

• C22C38/26

  with niobium or tantalum · CPC title

• C22C38/001

  containing N · CPC title

• C21D2211/001

  Austenite · CPC title

• C21D6/001

  containing Ni (C21D6/004 takes precedence) · CPC title