Importance

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Abstract

This steel member has a predetermined chemical composition, in which, when a ¼ position of a thickness in a thickness direction from a surface is defined as a ¼ depth position, a metallographic structure at the ¼ depth position includes 90% or more of martensite by volume fraction, in the metallographic structure at the ¼ depth position, L49-56°/L4-12°, which is a ratio of a length L49-56° of grain boundaries having an angle of rotation of 49° to 56° to a length L4-12° of grain boundaries having an angle of rotation of 4° to 12° about a <011> direction as a rotation axis, among grain boundaries of grains having a body-centered structure, is 1.10 or more, and a tensile strength of the steel member is more than 1.500 MPa.

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First Claim