Hot-pressed steel sheet member

Patent metadata

Field	Value
Publication number	US-10273555-B2
Application number	US-201315101772-A
Country	US
Kind code	B2
Filing date	Dec 27, 2013
Priority date	Dec 27, 2013
Publication date	Apr 30, 2019
Grant date	Apr 30, 2019

Abstract

A hot-pressed steel sheet member includes a specific chemical composition and further includes a steel structure in which an area ratio of ferrite in a surface layer portion ranging from a surface to 15 μm in depth is greater than 1.20 times an area ratio of ferrite in an inner layer portion being a portion excluding the surface layer portion, and the inner layer portion contains a steel structure represented, in area %, ferrite: 10% to 70%, martensite: 30% to 90%, and a total area ratio of ferrite and martensite: 90% to 100%. A tensile strength of the hot-pressed steel sheet member is 980 MPa or more.

First claim

The invention claimed is:

1. A hot-pressed steel sheet member, comprising:
a chemical composition represented by, in mass %:
C: 0.10% to 0.34%;
Si: 0.5% to 2.0%;
Mn: 1.0% to 3.0%;
sol. Al: 0.001% to 1.0%;
P: 0.05% or less;
S: 0.01% or less;
N: 0.01% or less;
Ti: 0% to 0.20%;
Nb: 0% to 0.20%;
V: 0% to 0.20%;
Cr: 0% to 1.0%;
Mo: 0% to 1.0%;
Cu: 0% to 1.0%;
Ni: 0% to 1.0%;
Ca: 0% to 0.01%;
Mg: 0% to 0.01%;
REM: 0% to 0.01%;
Zr: 0% to 0.01%;
B: 0% to 0.01%;
Bi: 0% to 0.01%; and
balance: Fe and impurities; and

a steel structure in which:
an area ratio of ferrite in a surface layer portion ranging from a surface to 15 μm in depth is greater than 1.20 times an area ratio of ferrite in an inner layer portion being a portion excluding the surface layer portion starting at a depth greater than 15 μm; and
the inner layer portion comprises a steel structure represented, in area %:
ferrite: 10% to 70%;
martensite: 30% to 90%; and
a total area ratio of ferrite and martensite: 90% to 100%,

wherein a tensile strength of the hot-pressed steel sheet member is 980 MPa or more.

2. The hot-pressed steel sheet member according to claim 1 , wherein the chemical composition comprises one or more selected from the group consisting of, in mass %:
Ti: 0.003% to 0.20%;
Nb: 0.003% to 0.20%;
V: 0.003% to 0.20%;
Cr: 0.005% to 1.0%;
Mo: 0.005% to 1.0%;
Cu: 0.005% to 1.0%; and
Ni: 0.005% to 1.0%.

3. The hot-pressed steel sheet member according to claim 1 , wherein the chemical composition comprises one or more selected from the group consisting of, in mass %:
Ca: 0.0003% to 0.01%;
Mg: 0.0003% to 0.01%;
REM: 0.0003% to 0.01%; and
Zr: 0.0003% to 0.01%.

4. The hot-pressed steel sheet member according to claim 1 , wherein the chemical composition comprises, in mass %, B: 0.0003% to 0.01%.

5. The hot-pressed steel sheet member according to claim 1 , wherein the chemical composition comprises, in mass %, Bi: 0.0003% to 0.01%.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Hayashi Koutarou

Classifications

• C21D8/04

  to produce plates or strips for drawing, e.g. for deep-drawing · CPC title

• C21D8/0457

  with diffusion of elements, e.g. decarburising, nitriding · CPC title

• C21D1/18

  Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62) · CPC title

• C21D2211/005

  Ferrite · CPC title

• C22C38/002

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