| 摘要 |
PURPOSE:To manufacture the titled press die combining high strength with high toughness and having superior durability at the pressing surface, by casting a ductile cast iron with a specific composition in a mold having the same shape as that of the pressing surface of a casting to be subjected to casting finish and by subjecting the above to heating and then to rapid cooling under specific conditions. CONSTITUTION:The ductile cast iron consisting of, by weight, 3.0-4.0% C, 2.0-3.0% Si, 0.1-0.6% Mn, <=0.3% Mo, <=2.0% Cu, <=2.0% Ni, 0.02-0.08% Mg, and the balance Fe with inevitable impurities is used. This cast iron is cast in a mold having the same shape as that of the pressing surface of the casting to be subjected to casting finish so as to be formed into a press die which can be used in the as-cast state. This press die is heated to 820-900 deg.C and held for 0.5-0.5hr to undergo austenitizing, which is cooled rapidly down to 240-400 deg.C without delay and then held for >=0.5hr at the above temp. to undergo isothermal transformation treatment. Owing to the above treatments, the part >=about 2mm deep from the surface is formed into bainite structure, so that trimming press due for casting finish reduced in deformation due to heat treatment can be obtained.
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