MANUFACTURE OF AUSTEMPERED DUCTILE CAST IRON AND AUSTEMPERED DUCTILE CAST IRON OBTAINED FROM THE SAME

摘要

PURPOSE: To obtain a ductile cast iron having toughness together with hardness by applying isothermal transformation treatment while holding continuous temp. gradient in the inner part of the cast iron material at the time of obtaining the ductile cast iron by applying austemper treatment to a spheroidal graphite cast iron material. ;CONSTITUTION: A high temp. and a low temp. salt bath furnaces 1, 2 surrounding the circumferences with e.g. refractory bricks 4 and rock wools 5 are connected, and a partitioned plate 3 is provided so as to restrict the movement of the fused salts between the furnaces. At this time, heat capacity in each slat bath furnace is sufficiently large to the heat moving amount between the furnaces. Successively, the salt baths in the furnaces 1, 2 are heated while stirring so as to uniformize the temps. in the furnaces, and the temps. are detected with thermocouples 6, 7 and the desired temp. in each furnace is held. Then, after quickly fixing the austenized spheroidal graphite cast iron flat plate having the dimension and the shape with role of the partitioned plate to the partitioning part, the partitioned plate 3 is removed and the front and the rear surfaces of the flat plate are heat-treated at different temps., respectively. By applying the isothermal transformation treatment in such a manner, the desired austempered ductile cast iron available as an alternate material for a forged steel, is obtd.;COPYRIGHT: (C)1993,JPO&Japio