| 摘要 |
PURPOSE:To reduce the cost of primary heat treatment by forming a spheroidal graphite cast iron casting contg. a specified number of graphite grains, annealing the casting to convert the matrix into ferrite and carrying out mechanical working and austempering. CONSTITUTION:A spheroidal graphite cast iron casting contg. >=250 graphite grains per 1mm<2> is formed by a pouring or in-mold method. The casting is annealed by holding at about 700-750 deg.C for about 0.5-8hr to covert the matrix into ferrite. After the casting is mechanically worked, it is worked, it is austenitized by holding at 800-950 deg.C for <=about 4hr and subjected to isothermal transformation by holding at 250-42o deg.C for >=about 15min to carry out austempering. Thus, it is not necessary to carry out chill decomposition during the primary heat treatment before the mechanical working and he cost of the heat treatment is considerably reduced.
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