| 摘要 |
PROBLEM TO BE SOLVED: To produce case hardening boron steel excellent in cold workability at the time of cold forging and capable of preventing the generation of coarse grains and the formation of a slack-quenched region formed to a depth of 0.2 to 0.7 mm from the surface at the time of carburizing and to provide its producing method. SOLUTION: This steel a composition containing 0.1 to 0.3% C, 0.01 to 0.15% Si, 0.2 to 0.8% Mn, 0.7 to 1.5% Cr, 0.005 to 0.3% Mo, 0.002 to 0.006% B, 0.015 to 0.05% Al and 0.01 to 0.1% Ti and in which the content of P is limited to <=0.025%, S to <=0.02%, V to <=0.01%, Mg to <=0.03%, N to <=0.005% and 0 to <=0.002%, respectively. In the producing method of the above steel, heating temperature is controlled to >=1,150 deg.C, the finishing temperature in hot rolling is controlled to 840 to 1,000 deg.C, and successively to the hot rolling, slow cooling is performed in the temperature range of 800 to 500 deg.C at a cooling rate of <=1 deg.C/sec.
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