UMEDA Takateru Sahaviriya Steel Industries

Cracking Behavior during Solidification of Steel and Aluminum Alloy

Solidification microstructure greatly influences product properties. Formation and control of solidification microstructure have been intensively studied, in particular, primary phase and structure selections and solidification cracking (hot tear) are of vital importance. The first happens at early stage of solidification, which takes place usually under comparatively rapid cooling, and the latter happens at last stage of solidification. This paper mentioned, due to page limitation, solidification cracking of steels and aluminum alloys considering practical importance. Tensile testing during solidification was carried out: mechanical properties were measured; zero strength temperature above which no strength does not show is found to be around fraction solid of 0.6 and zero ductility temperature above which no ductility shows is around complete solidification stage for Fe-C-Mn system. Mechanical properties at mushy zone of commercial aluminum alloys were also measured, from which hot tearing in DC casting was predicted based on the concept that hot tear happens when applied stress (strain) is bigger than the measured fracture stress (fracture strain). The prediction well fit real DC castings. Non-metallic compounds formation during last stage solidification is found to affect the crack-susceptibility. In this paper effects of iron content on high-strength Al-Mg-Si alloys and high tin content on machinability improved 2xxx aluminum alloys with manganese and chromium addition were discussed related between some characteristic compounds formation and cracking..