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

A high strength steel sheet, the high strength steel sheet having a yield-point elongation (YP-EL) of 1% or greater and a tensile strength (TS) of 980 MPa or greater and 1020 MPa or less,

• the high strength steel sheet having a chemical composition containing, in mass %,
• C:
• 0.030% or greater and 0.250% or less,
• Si:
• 0.01% or greater and 2.00% or less,
• Mn:
• 3.10% or greater and 6.00% or less,
• P:
• 0.001% or greater and 0.100% or less,
• S:
• 0.0001% or greater and 0.0200% or less,
• N:
• 0.0005% or greater and 0.0100% or less, and
• Al:
• 0.001% or greater and 1.200% or less, with a balance of Fe and incidental impurities, and
• the high strength steel sheet having the microstructure in which ferrite is present in an area fraction of 30.0% or greater and less than 80.0%, martensite is present in an area fraction of 3.0% or greater and 30.0% or less, bainite is present in an area fraction of 0% or greater and 3.0% or less, retained austenite is present in a volume fraction of 12.0% or greater and 19.9% or less, a ratio of the number of retained austenite grains adjoining a retained austenite grain having a different crystal orientation to the total number of retained austenite grains is 0.60 or greater, 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, and a value obtained by dividing a Mn content (mass %) of the retained austenite by a Mn content (mass %) of the high strength steel sheet is 1.50 or greater,
• wherein the 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.