Patent ID: 9695488
Date: 2017-07-04
CPC Classifications: C21D,C22C,C23C,F16B

Claim:
1. A bolt, comprising: a steel comprising C in a mass percentage of 0.30% or more and less than 0.45%; Si in a mass percentage of 1.0% to 2.5%; Mn in a mass percentage of 0.1% to 1.5%; P in a mass percentage of greater than 0% to 0.015%; S in a mass percentage of greater than 0% to 0.015%; Cr in a mass percentage of 0.15% to 2.4%; Al in a mass percentage of 0.010% to 0.10%; N in a mass percentage of 0.001% to 0.10%; Cu in a mass percentage of 0.1% to 0.50%, and Ni in a mass percentage of 0.1% to 1.0%, so that [Ni]/[Cu]≧0.5 is met, where [Ni] and [Cu] denote the mass percentage of Ni and Cu in the steel, respectively; and Ti in a mass percentage of 0.05% to 0.2%, and V in a mass percentage of 0% to 0.2%, so that [Ti]+[V] is 0.085% to 0.30%, where [Ti] and [V] denote the mass percentage of Ti and V in the steel respectively; and iron, wherein the bolt has an austenitic grain size number of 9.0 or more in a shank thereof; the bolt has a G-value meeting a condition as specified by Expression (1) as follows: where: the G-value indicates a percentage of carbide particles formed at austenite grain boundaries in the shank, L denotes a total length of carbide particles formed at the austenite grain boundaries and having a thickness of 50 nm or more; and L0 denotes a length of the austenite grain boundaries.