HIGH-STRENGTH STEEL SHEET AND METHOD FOR PRODUCING SAME

摘要

Provided are: a high-strength steel sheet which is suitable as a material for an automotive part, has yield strength (YS) of 780 MPa or more and tensile strength (TS) of 1180 MPa or more, and also has excellent spot weldability, ductility and bending workability; and a method for producing the high-strength steel sheet. The high-strength steel sheet has a C content of 0.15% or less and contains ferrite at an area ratio of 8 to 45% and martensite at an area ratio of 55 to 85%, wherein the ratio of martensite adjacent only to ferrite to the whole structure is 15% or less, the average crystal particle diameter of each of ferrite and martensite is 10 μm or less, and the ratio of the area of ferrite having a crystal particle diameter of 10 μm or more relative to the area of ferrite existing in a region lying between the depth of 20 μm from the surface of the steel sheet and the depth of 100 μm from the surface of the steel sheet is less than 5%.