Hot-pressed member, cold-rolled steel sheet for hot pressing, and manufacturing methods therefor
AssigneeJfe Steel Corporation
InventorsKatsutoshi TAKASHIMA, Minoru TANAKA, Yoshie OBATA, Michitaka SAKURAI
Life of this patent
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Abstract
Provided is a hot-pressed member that combines both high strength of 1850 MPa or more in TS and excellent delayed fracture resistance. A hot-pressed member comprises: a predetermined chemical composition; a microstructure in which a prior austenite average grain size is 8 μm or less, a volume fraction of martensite is 95% or more, and a volume fraction of granular carbide of 0.1 μm or more in grain size is 0.10% to 4.0%; a Ni diffusion region of 2.0 μm or more in a depth direction in a surface layer; and a tensile strength of 1850 MPa or more.
Claims11
1-10. (canceled)
A hot-pressed member, comprising:
- a chemical composition consisting of, in mass %,
- C:
- 0.31% or more and less than 0.55%,
- Si:
- 0.01% or more and 1.0% or less,
- Mn:
- 1.0% or more and 2.5% or less,
- P:
- 0.05% or less,
- S:
- 0.005% or less,
- Al:
- 0.01% or more and 0.50% or less,
- N:
- 0.01% or less, and
- Cu:
- 0.002% or more and 0.25% or less,
- and optionally one or more one or more selected from the group consisting of
- Mo:
- 0.005% or more and 0.35% or less,
- Cr:
- 0.005% or more and 0.35% or less,
- Nb:
- 0.001% or more and 0.05% or less,
- Ti:
- 0.001% or more and 0.050% or less,
- B:
- 0.0002% or more and 0.0050% or less,
- Ca:
- 0.005% or less,
- V:
- 0.05% or less,
- Sb:
- 0.001% or more and 0.020% or less,
- Ni:
- 0.50% or less, and
- Sn:
- 0.50% or less,
- with a balance consisting of Fe and inevitable impurities;
- a microstructure in which a prior austenite average grain size is 8 μm or less, a volume fraction of martensite is 95% or more, and a volume fraction of granular carbide of 0.1 μm or more in grain size is 0.10% or more and 4.0% or less;
- a Ni diffusion region of 2.0 μm or more in a depth direction in a surface layer;
- and
- a tensile strength of 1850 MPa or more.
The hot-pressed member according to claim 1, further comprising
- a Ni-containing Zn or Zn alloy coating or plating layer at a surface thereof.
A cold-rolled steel sheet for hot pressing, comprising:
- a chemical composition consisting of, in mass %,
- C:
- 0.31% or more and less than 0.55%,
- Si:
- 0.01% or more and 1.0% or less,
- Mn:
- 1.0% or more and 2.5% or less,
- P:
- 0.05% or less,
- S:
- 0.005% or less,
- Al:
- 0.01% or more and 0.50% or less,
- N:
- 0.01% or less, and
- Cu:
- 0.002% or more and 0.25% or less,
- and optionally one or more selected from the group consisting of
- Mo:
- 0.005% or more and 0.35% or less,
- Cr:
- 0.005% or more and 0.35% or less,
- Nb:
- 0.001% or more and 0.05% or less,
- Ti:
- 0.001% or more and 0.050% or less,
- B:
- 0.0002% or more and 0.0050% or less,
- Ca:
- 0.005% or less,
- V:
- 0.05% or less,
- Sb:
- 0.001% or more and 0.020% or less,
- Ni:
- 0.50% or less, and
- Sn:
- 0.50% or less,
- with a balance consisting of Fe and inevitable impurities;
- and
- a microstructure in which a volume fraction of granular carbide of 0.1 μm or more in grain size is 1.0% or more and 25% or less.
Dependencies are inferred from the claim text.