Tensile strength: have more than 900 MPa, and provides a steel sheet and a manufacturing method thereof has good weldability.
Area and specific chemical composition, 30% or less of ferrite area ratio (including 0%), where 70% or more in area ratio of martensite tempered (including 100%), except ferrite and tempered martensite as the remaining structure a total rate of 10% or less include (including 0%), the average particle size of the martensite tempering 5μm or less, an average particle size of the iron-based carbide precipitated on grain boundaries of martensite tempering 100nm or less, shrink the total of Si and Mn on the grain boundary of martensite the return anda steel structure is 5 atomic% or more in atomic concentration, tensile strength and thin steel sheet, characterized in that at least 900 MPa.