Hot-rolled steel sheet for tailored rolled blank and tailored rolled blank

Patent metadata

Field	Value
Publication number	US-10590506-B2
Application number	US-201916398310-A
Country	US
Kind code	B2
Filing date	Apr 30, 2019
Priority date	Apr 23, 2014
Publication date	Mar 17, 2020
Grant date	Mar 17, 2020

Abstract

A hot-rolled steel sheet for a tailored rolled blank is provided that has high tensile strength and is excellent in cold formability. The hot-rolled steel sheet has: a chemical composition that contains, in mass %, C, Si, Mn, P, S, Al, N and Ti, with the balance being Fe and impurities, and that satisfies Formula (1); and a microstructure containing, in terms of area ratio, 20% or more of bainite, wherein 50% or more in terms of area ratio of the balance is ferrite. In the interior of the hot-rolled steel sheet an average value of pole densities of an orientation group {100}<011> to {223}<110> is 4 or less, and a pole density of a {332}<113> crystal orientation is 4.8 or less. In an outer layer of the hot-rolled steel sheet, a pole density of a {110}<001> crystal orientation is 2.5 or more. Furthermore, among Ti carbo-nitrides in the hot-rolled steel sheet, the number density of fine Ti carbo-nitrides having a particle diameter of 10 nm or less is 1.0×10 17 per cm 3 or less, and a bake hardening amount is 15 MPa or more,

[Ti]−48/14×[N]−48/32×[S]≥0  (1).

First claim

The invention claimed is:

1. A tailored rolled blank in which a sheet thickness changes in a tapered shape in a rolling direction, comprising:
a thick-wall portion, and
a thin-wall portion that is thinner than the thick-wall portion;
wherein:
in the tailored rolled blank, a ratio of an average hardness H t max of a thickest wall portion at which the sheet thickness is thickest to an average hardness H t min of a thinnest wall portion at which the sheet thickness is thinnest is in a range of more than 1.0 to 1.5,
an average dislocation density of the thinnest wall portion is 1×10 14 m −2 or less, and
a number density of fine Ti carbo-nitrides having a particle diameter of 10 nm or less is more than 2×10 17 per cm 3 .

2. The tailored rolled blank according to claim 1 ,
further comprising a galvanized layer on a surface thereof.

3. The tailored rolled blank according to claim 1 , wherein the tailored rolled blank is produced using a hot-rolled steel sheet comprising:
a chemical composition consisting of, in mass %,
C: 0.03 to 0.1%,
Si: 1.5% or less,
Mn: 1.0 to 2.5%,
P: 0.1% or less,
S: 0.02% or less,
Al: 0.01 to 1.2%,
N: 0.01% or less,
Ti: 0.015 to 0.15%,
Nb: 0 to 0.1%,
Cu: 0 to 1%,
Ni: 0 to 1%,
Mo: 0 to 0.2%,
V: 0 to 0.2%,
Cr: 0 to 1%,
W: 0 to 0.5%,
Mg: 0 to 0.005%,
Ca: 0 to 0.005%,
rare earth metal: 0 to 0.1%,
B: 0 to 0.005%, and
one or more types of element selected from a group consisting of Zr, Sn, Co and Zn in a total amount of 0 to 0.05%, with the balance being Fe and impurities, and satisfying Formula (1); and
a microstructure containing, in terms of area ratio, 20% or more of bainite, with 50% or more in terms of area ratio of the balance being ferrite;
wherein:
at a depth position that is equivalent to one-half of a sheet thickness from a surface of the hot-rolled steel sheet, an average value of pole densities of an orientation group {100}<011> to {223}<110> comprising crystal orientations {100}<011>, {116}<110>, {114}<110>, {113}<110>, {112}<110>, {335}<110> and {223}<110> is four or less and a pole density of a {332}<113> crystal orientation is 4.8 or less;
at a depth position that is equivalent to one-eighth of the sheet thickness from the surface of the hot-rolled steel sheet, a pole density of a {110}<001> crystal orientation is 2.5 or more;
a number density of fine Ti carbo-nitrides having a particle diameter of 10 nm or less among Ti carbo-nitrides in the hot-rolled steel sheet is 1.0×10 17 per cm 3 or less; and
a bake hardening amount is 15 MPa or more;
[Ti]−48/14×[N]−48/32×[S]≥0  (1),

where a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1).

4. The tailored rolled blank according to claim 3 , further comprising a galvanized layer on a surface thereof.

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Yokoi Tatsuo
• Sakurada Eisaku
• Sugiura Natsuko
• Fukui Kiyoyuki

Classifications

• C22C38/008

  containing tin · CPC title

• C21D2211/002

  Bainite · CPC title

• C21D8/0278

  involving a particular surface treatment  (C21D8/0294 takes precedence) · CPC title

• C22C38/00

  Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00) · CPC title

• C21D8/0226

  Hot rolling · CPC title