HIGH STRENGTH STEEL SHEET AND METHOD FOR PRODUCING SAME

WIPO Patent Application WO/2019/130713

A1

The present invention addresses the problem of providing: a high strength steel sheet which has a more excellent balance between strength and processability; and a method for producing this high strength steel sheet. A high strength steel sheet according to the present invention has a specific component composition and a steel structure which contains, in area ratios, 40-100% in total of lower bainite, martensite and residual austenite, 15% or less of residual austenite, and 0-60% in total of upper bainite and ferrite. With respect to the steel structure, elongated ferrite phases having an aspect ratio of 3 or more are 1% or less in an area ratio; the average grain size of martensite grains in a region from the steel sheet surface to the depth of 50 μm is 20 μm or less; the density of oxides having a minor axis length of 0.8 μm or less in the region from the steel sheet surface to the depth of 50 μm is 1.0 × 1010 pieces/m2 or more; and the density of coarse oxides having a minor axis length of more than 1 μm in the region from the steel sheet surface to the depth of 50 μm is 1.0 × 108 pieces/m2 or less. The amount of trapped hydrogen within the steel sheet is 0.05 ppm by mass or more.

HASEGAWA HIROSHI (JP)
MINAMI HIDEKAZU (JP)
NAKAGAITO TATSUYA (JP)
SASAKI KANA (JP)
TANAKA SHOJI (JP)

PCT/JP2018/037569

July 04, 2019

October 09, 2018

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JFE STEEL CORP (JP)

C22C38/00; C21D9/46; C22C38/06; C22C38/60

WO2013047760A1	2013-04-04
WO2016129213A1	2016-08-18
WO2016113788A1	2016-07-21
WO2015198582A1	2015-12-30

JP2016128598A	2016-07-14
JP2015193907A	2015-11-05
JP2010126787A	2010-06-10
JP2005068548A	2005-03-17
JP2009275256A	2009-11-26
CN104928579A	2015-09-23

See also references of EP 3715493A4

KUMASAKA Akira et al. (JP)

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