CONDITIONS OF STRUCTURAL TRANSFORMATION OF GRAPHITE IN Fe-C-Si ALLOY UNDER UNIDIRECTIONAL SOLIDIFICATION

An investigation was made of the influence of modifying element Ce and of solidification rate on the structural transformation of graphite in the Fe-C-Si alloy. It is proposed that during the transformation between spheroidal and overcooled graphite or between vermicular and flake ones, the modifying element Ce added may be the main effective factor, and the critical wt-% of Ce addition for each transformation may be expressed as Ce_((S-D))=-0.0296 1g R+0.162 and Ce_((V-A))=-0.0353 1g R+0.147 respectively. The solidification rate seems to be predominant while the transformation between spheroidal and vermicular graphite, and the critical rate in μm/s to complete the spheroidal or vermicular graphite transformation may be R_s=55×10~(-2.5Ce) or R_v=32.4×10~(-2.3Ce) respectively. It is confirmed that the structural transformation between vermicular and flake graphite may be carried out continuously during the growth of graphite crystals. The graphite of vermicular structure is a special one which is growing up under certain conditions of modifying element Ce and solidification rate with no need to decay the nodularization or to break the graphite nodules prior to its growth.