Microsegregation of Silicon in Iron-Carbon Alloys

Abstract

Residual microsegregation of silicon in hypoeutectic Fe-C alloys was shown to depend on the ratio of silicon to carbon. Concentration regions where direct and inverse microsegregation of silicon develops were established experimentally in the Fe-C-Si system. The behaviour of the third component changes in a similar manner in other systems, featuring a positive slope in the liquidus isotherms such as Fe-C-AI, Fe-C-Cu, and Fe-C-Ni. The concepts of para- and meta- equilibrium are defined, it being shown how geometric thermodynamic methods were employed to establish the equilibrium of the liquid and solid phases which was chosen as the criteria for describing the absence of silicon microsegregation in an alloy. X-ray spectrum analysis of the micro-segregation zones revealed that rules of dendritic segregation established for ternary alloys are applicable to real multi-component Fe-C alloys containing Si, Al, Cu and Ni within the range which is typical for unalloyed steels and irons. The peculiarities of silicon eutectic segregation, in relation to the valley geometry of double eutectics having stable and metastable phases, were considered. Finally, the microsegregation effect of major components, primarily silicon and manganese, on the formation of both structure and properties of irons and unalloyed steels is discussed.