Nippon Steel Corporation

Yoshiro Koyasu

Tatsuro Ochi

Hiromasa Takada

Motohide Mori

Yukio Noguchi

Masami Suzuki

Nobukazu Suzuki

Yutaka Tsuchida

Microalloyed steel for hot forging free of subsequent quenching and

Steel product for induction-hardened shaft component and shaft component

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.

Process for producing steel bar wire rod for cold working

Improved toughness of forging is obtained without quenching and tempering by controlling the steel composition to: 0.05% to less than 0.15% C.; 0.10-1.00% Si; 0.50-3.00% Mn; 1.60-4.20% Mn+Cr; 0.010-0.030% Ti; 0.005-0.0030% B; 0.01-0.05% Al; and 0.0060% or less of N.

Non-heat refined steel bar having improved toughness

Growing community of inventors

Muroran, Japan

Yoshiro Koyasu