ÉLÉMENT DE COMPRESSION À CHAUD ET SON PROCÉDÉ DE FABRICATION, ET TÔLE D'ACIER LAMINÉE À FROID POUR COMPRESSION À CHAUD ET SON PROCÉDÉ DE FABRICATION

摘要

Disclosed is a hot-pressed member that can exhibit very high tensile strength after hot pressing as high as TS: 1780 MPa or more, excellent resistance to resistance welding cracking, and excellent delayed fracture resistance after resistance welding by having a specific chemical composition, and a microstructure such that a prior austenite average grain size is 7 µm or less, a volume fraction of martensite is 90 % or more, and at least 5 Nb-based precipitates having a grain size of less than 0.08 µm are present on average per 100 µm²of a cross section parallel to a thickness direction of the member within a range of 100 µm in the thickness direction from a surface of the member, and such that a Ni diffusion region having a thickness of 0.5 µm or more is present in a surface layer of the member.