Abstract: This invention aims at providing a carburizing bearing steel which can provide excellent rolling fatigue characteristics by providing a long life carburizing bearing steel comprising, in terms of percent by weight, 0.1 to 0.35% of C, 0.3 to 2.0% of Mn, 0.001 to 0.03% of S, 0.4 to 1.5% of Cr, 0.01 to 0.07% of Al, 0.003 to 0.015% of N, 0.0005 to 0.03% of T.Mg, "0.35 to 1.70% of Si" or "0.05 to 1.70% of Si and 0.30 to 1.20% of Mo", a specific amount of at least one member consisting of Ni and V, and not more than 0.025% of P, and not more than 0.0050% of Ti and not more than 0.0020% of T.O, wherein a number ratio of Mg type oxides contained in the steel is at least 0.8.

Abstract: A process for producing a hot forged steel of ferrite+bainite structure type which is characterized by: applying hot forging to a steel product of a composition by weight ofC: 0.10-0.35%,Si: 0.15-2.00%,Mn: 0.40-2.00%,S: 0.03-0.10%,Al: 0.0005-0.050%,Ti: 0.003-0.050%,N: 0.0020-0.0070%,V: 0.30-0.70%, andfurther containing one or more of Cr, Mo, Nb, Pb and Ca in a specified amount; cooling thereafter so that 80% or more of the metallographic structure after finishing of the transformation is ferrite+bainite structure; and further applying aging treatment at a temperature of 200.degree.-700.degree. C. According to the present invention, it is possible to produce a hot forged steel which has satisfactory fatigue strength, machinability and yield strength; its industrial advantages are enormous.

Abstract: The present invention provides a steel product, for all induction-hardened shaft component, which can prevent quench crack and has an excellent torsional strength of not less than 160 kgf/mm.sup.2, and a shaft component using the steel product.The subject matter of the present invention resides in a steel product for an induction-hardened shaft component comprising C: 0.35 to 0.70%, Si: more than 0.15 to 2.5%, Mn: 0.2 to 1.5%, Cr: 0.20 to 1.5%, Mo: 0.05 to 0.5%, Al: 0.015 to 0.05%, N: 0.002 to 0.02% and other ingredients, reduced amounts of P, Cu and O, further comprising particular amounts of Ti, B and the like, and an induction-hardened shaft component using the steel product, which shaft component has an average in-section hardness HVa of not less than 560, a grain size number of prior-austenite in an induction-hardened layer of not less than 9 and a surface residual stress of not more than -80 kgf/mm.sup.2.

Abstract: A steel comprising 0.1 to 1.5% of C and 0.25 to 2.0% of Mn is heated to 900.degree. to 1250.degree. C., and the heated steel is hot-rolled at a temperature in the range of from Ar.sub.3 to (Ar.sub.3 +200).degree. C. or Arcm to (Arcm+200).degree. C. with a total reduction of area of 30% or more. The hot-rolled material is cooled to complete a ferrite/pearlite transformation or a pro-eutectoid cementite/pearlite transformation. The transformed material is subjected to finish hot rolling at a temperature in the range of from (Ac.sub.1 -400) to Ac.sub.1 .degree. C. with a total reduction ratio of 10 to 70%. If necessary, the material after the finish hot rolling is cooled to 300.degree. C. at an average cooling rate of 1.degree. C./sec or less. A spheroidization annealing of the steel bar wire rod produced according to the process of the present invention enables a good spheroidized texture to be formed.