Jfe Steel Corporation

Muneka Iwasawa

Yoshiyasu Kawasaki

Yuki Toji

Yoshimasa Funakawa

Kentaro Sato

Takayuki Futatsuka

A high strength steel sheet has a yield-point elongation of 1.0% or greater and a tensile strength of 980 MPa or greater. The high strength steel sheet has a specific chemical composition and microstructure. The ferrite has an average grain size of 5.0 μm or less, the retained austenite has an average grain size of 2.0 μm or less, a value obtained by dividing a Mn content of the retained austenite by a Mn content of steel is 1.50 or greater, 15% or more of all retained austenite grains in the retained austenite have an aspect ratio of 3.0 or greater, and 15% or more of all the retained austenite grains in the retained austenite have an aspect ratio of less than 2.0.

High strength steel sheet, impact absorbing member, and method for manufacturing high strength steel sheet

A high strength steel sheet has a yield-point elongation of 1% or greater and a tensile strength of 980 MPa or greater. The high strength steel sheet has a specific chemical composition and microstructure. A ratio of retained austenite grains adjoining a retained austenite grain having a different crystal orientation to total retained austenite grains is 0.60 or greater, the ferrite has an average grain size of 5.0 μm or less, and the retained austenite has an average grain size of 2.0 μm or less. A value obtained by dividing a volume fraction Vγa by a volume fraction Vγb is 0.40 or greater, where the volume fraction Vγa is a volume fraction of retained austenite in a fractured portion of a tensile test specimen after a warm tensile test at 150° C., and the volume fraction Vγb is a volume fraction of retained austenite before the warm tensile test at 150° C.

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Tokyo, Japan

Muneka Iwasawa