Abstract: A steel having such a good machinability that it can be directly cut without being annealed and a good induction hardenability. The steel consists essentially of C: 0.37-0.45%, Si: up to 0.35%, Mn: more than 1.0% - up to 1.5%, B: 0.0005-0.0035%, Ti: 0.01-0.05%, Al: 0.01-0.06% and the balance of Fe, the content of N being up to 0.022 and has a fine structure of ferrite crystal grain size number 6 or more as defined by JIS-G0552. In addition to the above basic composition, the alloy may further contain some optional alloying elements.The material is suitable for manufacturing machine structural parts such as drive shafts of automobiles.

Abstract: A steel composition for gears, consisting of: 0.10-0.30% by weight of C; less than 0.15% by weight of Si; no more than 1.5% by weight of Mn; no more than 0.015% by weight of P; no more than 0.005% by weight of S; 0.50-1.50% by weight of Cr; 0.005-0.06% by weight of Pb; and the balance being Fe and inevitably included impurities.

Abstract: A high strength bolt made of a steel having a specifically defined chemical composition, i.e., by weight C: 0.30-0.50%; Si: not more than 0.15%; Mn: not more than 0.40%; Cr: 0.30-1.50%; Mo: 0.10-0.70%; and V: 0.15-0.40%, the balance being Fe and inevitable impurities such as P, S, etc. in trace amount. The manufacturing method therefor is featured in a strictly controlled heat treatment in respect to the temperature range such as: hardening by quenching from 940.degree..+-.10.degree. C. and tempering 575.degree..+-.25.degree. C.

Abstract: A high strength bolt made of a steel having a specifically defined chemical composition, i.e., by weight C: 0.30-0.50%; Si: not more than 0.15%; Mn: not more than 0.40%; Cr: 0.30-1.50%; Mo: 0.10-0.70%; and V: 0.15-0.40%, the balance being Fe and inevitable impurities such as P, S, etc. in trace amount. The manufacturing method therefor is featured in a strictly controlled heat treatment in respect to the temperature range such as: hardening by quenching from 940.degree..+-.10.degree. C. and tempering 575.degree..+-.25.degree. C.

Abstract: A bolting bar material consists in weight ratio of 0.05.about.0.2% of C, 0.05.about.0.8% of Si, 0.8.about.2% of Mn, not more than 0.035% of P, not more than 0.030% of S, 0.005.about.0.05% of Nb, 0.01.about.0.05% of Al, 0.005.about.0.025% of N, 0.05.about.0.35% in total of at least one element selected from not more than 0.25% of V, not more than 0.25% of Ti and not more than 0.25% of Zr, and if necessary, 0.05.about.1.5% in total of at least one element selected from 0.05.about.0.5% of Ni, 0.05.about.0.5% of Cr and 0.05.about.0.5% of Mo, and the balance of Fe. In the production of the bolting bar material, the steel having the above composition is heated to 1000.degree..about.1100.degree. C., rolled at a finish rolling temperature of 750.degree..about.950.degree. C. and cooled at a rate of 5.degree..about.50.degree. C./sec on average.