Kobe Steel, Ltd.

Toshiya Nakata

Toshio Murakami

Kenji Saito

Yukihiro Utsumi

Fumio Yuse

Kosuke Shibata

Atsuhiro Shiraki

Takahiro Ozawa

Provided is an ultra-high-strength steel sheet having a component composition that includes specific amounts of each of C, Mn, and Al and a remainder of iron and unavoidable impurities, and in which the amounts of each of P, S, and N among the unavoidable impurities are limited to a specific amount. The ultra-high-strength steel sheet includes 2 area% or more of a region having a structure that includes 90% or more of martensite and 0.5% or more of residual austentite by area ratio relative to the entire structure, the local Mn concentration in said region being at least 1.1 times that of the Mn content of the entire steel sheet. The ultra-high-strength steel sheet has a tensile strength of 1470 MPa or more.

Ultra-high-strength steel sheet having excellent delayed fracture resistance at cut end thereof

Growing community of inventors

Hyogo, Japan

Toshiya Nakata