Steel Sheet And Method For Producing Same

Abstract: This steel sheet has a prescribed chemical composition and a tensile strength of at least 780 MPa and exhibits a ferrite area ratio of at least 5%, a ferrite + bainite total area ratio of 10-90%, a martensite + tempered martensite total area ratio of 10-90%, and a pearlite + retained austenite total area ratio of 0-10%. With reference to the total number of the ferrite and bainite crystal grains, the percentage for the number of ferrite and bainite crystal grains having an area of not more than 6 µm2 is at least 40% for this steel sheet and the percentage for the number of ferrite and bainite crystal grains having an area of at least 50 µm2 is not more than 5%. The maximum Mn content in the region from the boundary between the ferrite and martensite or tempered martensite to 0.5 µm toward the inside of the ferrite grain in the direction perpendicular to this boundary is at least 0.30 mass% less than the average Mn content in the steel sheet.

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