Abstract: This steel sheet includes, in mass % C: 0.15% to 0.50%, Si: 0.01% to 1.00%, Mn: 1.00% to 3.00%, P: 0% to 0.0200%, S: 0.0001% to 0.0200%, Al: 0.001% to 0.100%, and N: 0% to 0.0200%, with the remainder being Fe and impurities, in which a metallorgraphic structure has an area fraction of 0% to 10.0% of retained austenite and 0% to 5.0% of pearlite, ferrite, and bainite in total, with the remaining structure being martensite and tempered martensite, a maximum diameter of MnS predicted by extreme value statistics is 30 ?m or less, a surface roughness Ra is 5 ?m or less, and a surface layer has a Vickers hardness of greater than or equal to a tensile strength TS (MPa) of the steel sheet×0.25.

Abstract: This steel sheet has a predetermined chemical composition, a tensile strength is 780 MPa or greater, a total of the area ratio of ferrite and an area ratio of bainite is 10% or greater and 90% or less, a total of an area ratio of martensite and an area ratio of tempered martensite is 10% or greater and 90% or less, and a total of an area ratio of pearlite and an area ratio of residual austenite is 0% or greater and 10% or less, a number proportion of crystal grains of ferrite and bainite having an area of 6 ?m2 or less is 40% or greater to a total number of crystal grains of the ferrite and the bainite, and a number proportion of crystal grains of ferrite and bainite having an area of 50 ?m2 or greater is 5% or less to the total number of crystal grains of the ferrite and the bainite, and a maximum Mn content in a region up to 0.