Effect of interfacial segregation of magnesium on high carbon (18%Cr) cast steel

Abstract

AbstractThe effect of Mg on the microstructure and properties of a high carbon cast steel (nominal composition, wt-%: 18Cr–2Ni–0·75Mo–Mn–Si–Febal.) is investigated. It is shown that the microaddition of Mg refines the primary carbide (Cr0·51Fe0·49)7C3 and promotes an equiaxial dendritic structure, and the resulting structure refinement improves significantly the impact toughness of the alloy. Using Auger electron spectroscopy and electron probe microanalysis, it is shown that there is an unusually high Mg segregation (~70 at.-%) at the carbide interface region. It is proposed that the Mg enrichment at the carbide interface is primarily a result of the liquid phase separation that occurs in liquid Fe–Mg alloys when the Mg level attains a minimum value (~1–2 at.-%), and that this initial enrichment is a result of a combination of Mg rejection by the carbide and uphill diffusion of Mg to the carbide interface region. A thermodynamic analysis is presented to show the degree of component (Cr, Ni) segregation r...