Takayoshi Kasugai

SH-CCT diagrams for welding and continuous cooling transformation behaviour for ductile cast iron

The purpose of this study is to clarify the continuous cooling transformation behaviour of the HAZ (Heat-Affected Zone) of a ductile cast iron according to JIS FCD700. For this purpose, two SH-CCT diagrams (Continuous Cooling Transformation Diagrams for simulated HAZ) for welding were prepared at a maximum temperature of 1223 K corresponding to a region of the HAZ near the base metal, and of 1323 K corresponding to a region of the HAZ near the fusion line. Ferrite and pearlite transformation regions in the SH-CCT diagram at 1323 K occurred after a longer time than those at 1223 K. A Bainite transformation region existed only in the SH-CCT diagram of 1223 K. Martensite transformation temperature is about 530 K for both of the simulated HAZs. These effects will be because of non-homogeneous carbon distribution in austenite near the graphite caused by the dissolution and growth of graphite during the heating and cooling in a welding thermal cycle.The range of cooling times when the hardness drops rapidly was...