A hot-pressed member, a cold-rolled steel sheet for a hot-pressed member, and their manufacturing method

摘要

An object of the present invention is to provide a hot-pressed member having a tensile strength of 1780 MPa or more and having improved delayed fracture resistance, a method for producing the same, and a cold-rolled steel sheet for a hot-pressed member and a method for producing the same. It has a predetermined component composition, and the microstructure of the steel sheet has a prior austenite average grain size of 8 µm or less, and within 30 µm from the surface, the volume fraction of martensite is 95% or more, and Ni in the surface layer A diffusion region has a thickness of 0.5 µm or more, and the standard deviation of Vickers hardness is 35 or less, Mndif (mass%) ≤ 0.20, Mndif (mass%) in the plate thickness direction: Mn segregation degree, tensile strength of 1780 MPa or more absence of press.