Title:
HIGH-STRENGTH STEEL SHEET AND METHOD FOR PRODUCING SAME
Document Type and Number:
WIPO Patent Application WO/2021/161679
Kind Code:
A1
Abstract:
The purpose of the present invention is to provide: a high-strength steel sheet which has a tensile strength of 1,180 MPa or more and good bending workability, while being insusceptible to the occurrence of liquid metal embrittlement during welding; and a method for producing this high-strength steel sheet. A high-strength steel sheet which has a tensile strength of 1,180 MPa or more, while having a predetermined component composition and a steel structure wherein: the area ratio of ferrite is 5% or less; the area ratio of martensite is from 2% to 10%; the area ratio of bainite is from 5% to 37%; the area ratio of tempered martensite is from 42% to 65%; the volume ratio of residual austenite is from 3% to 15%; the average grain size of ferrite and bainite is 3 μm or less; in a region at a depth of 50 μm from the steel sheet surface in the sheet thickness direction, the average grain size of prior austenite grains is 10 μm or less, the average grain size of prior austenite grains in the sheet thickness direction is 0.9 or less of the average grain size thereof in the rolling direction, and 80% or less of the grain boundary of prior austenite grains is a large-angle grain boundary having an orientation difference of 15° or more; and in a region at a depth of 200 μm from the steel sheet surface in the sheet thickness direction, the average grain size of precipitates is 1.0 μm or less, the average grain size of prior austenite grains is 15 μm or less, and the average grain size of prior austenite grains in the sheet thickness direction is 0.9 or less of the average grain size thereof in the rolling direction.
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Inventors:
OJIMA MAYUMI (JP)
FUNAKAWA YOSHIMASA (JP)
YOKOTA TAKESHI (JP)
FUNAKAWA YOSHIMASA (JP)
YOKOTA TAKESHI (JP)
Application Number:
PCT/JP2020/048798
Publication Date:
August 19, 2021
Filing Date:
December 25, 2020
Export Citation:
Assignee:
JFE STEEL CORP (JP)
International Classes:
C21D9/46; C22C18/00; C22C38/00; C22C38/14; C22C38/38; C23C2/02; C23C2/06
Foreign References:
| JP2018197380A | 2018-12-13 | |||
| JP2016028172A | 2016-02-25 | |||
| JP2016008310A | 2016-01-18 | |||
| JP5671391B2 | 2015-02-18 | |||
| JP5958669B1 | 2016-08-02 | |||
| JP5780171B2 | 2015-09-16 | |||
| JP2017510702W |
Other References:
See also references of EP 4074847A4
Attorney, Agent or Firm:
KUMASAKA Akira et al. (JP)
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