PROBLEM TO BE SOLVED: To obtain a casting having excellent toughness and bending characteristics on the surface layer part and high strength spheroidal graphite cast iron structure in the inner part and provided with spot facing parts and holes without applying a turning work with a machine by using a member having different matrix structures on the surface layer part and in the inner part and arranging a flat surface and the holes by pressing. ;SOLUTION: The molten spheroidal graphite cast iron is poured into a mold using a sand mold and crude material for bracket 1 is cast and shaken off after cooling, and the molding sand stuck to the casting surface is removed after removing feeder heads and runners to obtain the as-cast shape. After charging this casting into a heat treatment furnace at 900°C in-furnace temp., this casting is held for 5 min and, successively, after furnace-cooling to 740°C and holding for 10 min, the casting is slowly cooled in the furnace to 650°C. Then, the plate 4 of the bracket 1 having ferritic layer on the surface layer part and pearlitic layer in the inner part, is obtd. Coining 8 is applied by using a hydraulic press to the desired four positions. Further, a punch applied with quenching heat treatment is abutted on the center of the surface to which the coining is executed, and the punching-out is applied with the hydraulic press to open the holes 9.;COPYRIGHT: (C)1999,JPO
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