| 摘要 |
PURPOSE: To provide a steel material suitable for induction hardened shaft parts, excellent in cold workability before induction hardening and excellent in torsional fatigue strength after induction hardening. CONSTITUTION: This steel material has a composition containing, by weight ratio, 0.35-0.60% C, 0.01-0.15% Si, 1.0-1.8% Mn, 0.05-0.8% Mo, 0.01-0.15% S, 0.015-0.05% Al, 0.005-0.05% Ti, 0.0005-0.005% B, and 0.002-0.01% N and having P, Cu, and O contents limited to specific values, respectively, or further containing either or both of specific amounts of Nb and V, or further containing either or both of Cr and Ni. Moreover, this steel material has a microstructure consisting of ferrite and lamellar pearlite, and further, the fraction of structure of ferrite is <=35% and ferritic crystalline grain size is <=20μm.
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