| 摘要 |
PROBLEM TO BE SOLVED: To provide steel having excellent cold workability, excellent austenite grain size characteristics and excellent heat treatment strain characteristics and fatigue strength characteristics by optimizing heat treatment conditions. SOLUTION: Steel containing, by mass, 0.10 to 0.35% C, 0.03 to 0.35% Si, 0.20 to 2.0% Mn, 0.003 to 0.30% S, 0.010 to 0.05% Al and 0.010 to 0.025% N, and the balance Fe with inevitable impurities is heated at 840 to 930 deg.C. The steel is cooled with the temperature range of 730 to 650 deg.C as a slow cooling temperature region at a cooling rate of 15 to 50 deg.C/h to produce the case- hardening steel having a dual structure of ferrite and pearlite and having excellent cold workability and grain size characteristics.
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