Patent ID: 8876451

Claim:
A high-strength bolt having a tensile strength of 1.2 GPa or more and comprising a threaded portion and a cylindrical neck portion, wherein the bolt has K of 0.8 or more and satisfies Ho<Hs, Ho and Hs being hardness obtained after a rolling process for forming the threaded portion and a heading process for forming a head portion, K being defined by the following equation (1): ( Ao×Ho )/( As×Hs )=K (1) wherein Ao is an effective cross-sectional area of the cylindrical neck portion, Ho is a Vickers hardness of a portion at which Ao is measured, the Vickers hardness being measured in accordance with a testing method prescribed in JIS-Z-2244, As is an effective cross-sectional area of the threaded portion, and Hs is a Vickers hardness of a portion at which As is measured, the Vickers hardness being measured in accordance with a testing method prescribed in JIS-Z-2244, the Vickers hardness being measured on a cross section of a sample obtained by cutting the bolt along an axis thereof and buffing the cross section to mirror finish.