| 摘要 |
PURPOSE:To manufacture a steel for prehardening metal mold for plastic molding having superior machinability and grinding finish characteristic, by incorporating specific percentage of C, Si, Mn, Ni, Al, and Cu to Fe. CONSTITUTION:A steel which has a composition consisting of, by weight 0.08-0.17% C, <=0.60% Si, 0.50-1.20% Mn, 2.50-3.50% Ni, 0.85-1.50% Al, 1.80-2.50% Cu, and the balance Fe with usual impurities and containing, if necessary, <=0.50$ Cr and/or either or both of Mo and W independently or in combination so that 1/2W+Mo=0.10-0.70% is satisfied is prepared. This steel is provided in a prehardened state with a hardness of HRC37 or above and is subjected, in this state, to die sinking and grinding work, and further to high-degree mirror finish and crimping working treatment and used.
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