PURPOSE: To prevent the structure decomposition of a ferrous member by the heat at cast-in time and to improve the combining power of the both by forming a porous heat insulating material layer between the both in case of cast-in the ferrous member subjected to an austempering treatment for a base metal.

CONSTITUTION: The bearing metal (ferrous member) 5, 6 of the crank shaft of a cylinder block (casting member) 1, for instance, is subjected to cast-in in the block base metal 7, 8 of an Al alloy. The bearing metals 5, 6 are subjected to austempering treatment to set to the coefft. of thermal expansion with the base metal 7, 8 and to increase the fatigue strength as well. In the metal 6, for instance, the surface of its internal chilled part is subjected to shot blasting after its cleaning and degreasing and the mixed powder of Ni, Cr and Al is plasma thermal sprayed on the surface thereof as an undercoating. A heat insulating layer 14 is then formed by thermal-spraying the mixed powder of ZrO2 and Y2O3 on this surface similarly, this metal 6 is held on a die 12, an Al molten metal is poured into a cavity 13 and the base metal 8 subjecting the metal 6 to cast in is formed via the heat insulating layer 14.