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Abstract

A high strength steel sheet has tensile strength of at least 1470 MPa and (tensile strength ×total elongation) of at least 29000 MPa·% with a composition including, by mass %, C.: 0.30% to 0.73%, Si: 3.0% or less, Al: 3.0% or less, Si+Al: at least 0.7%, Cr: 0.2% to 8.0%, Mn: 10.0% or less, Cr+Mn: at least 1.0%, P: 0.1% or less, S: 0.07% or less, N: 0.010% or less, and remainder as Fe and incidental impurities; and processing the steel sheet such that microstructure satisfies area ratio of martensite with respect to the microstructure of 15% to 90%; content of retained austenite of 10% to 50%; at least 50% of the martensite is constituted of tempered martensite and area ratio of the tempered martensite with respect to the microstructure is at least 10%; and area ratio of polygonal ferrite with respect to the microstructure is 10% or less.

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First Claim