| 摘要 |
PROBLEM TO BE SOLVED: To provide a new prehardened-type steel for metal mold for plastic molding, extremely excellent in mirror finish characteristics and machinability and also having superior toughness. SOLUTION: This steel has a composition which consists of, by weight, 0.07-0.16% C, <=60% Si, 0.60-1.50% Mn, 2.50-3.50% Ni, 0.30-1.40% Al, 1.80-2.50% Cu, and the balance Fe with impurities and in which the amounts of S, O, and N as impurities are regulated to <=0.004%, <=0.0015%, and <=0.0030%, respectively, or further, <=0.60% Cr and Mo and W, independently or in combination, in the amounts satisfying 1/2W+Mo = 0.10 to 0.70% are properly added to the steel for metal mold.
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