Influence of alloying elements on as-cast microstructure and strength of gray iron

Casting experiments were carried out to produce gray cast irons with compositions in the range (wt.%): Fe–3.2C– w Cu–xMo–yMn–zSi, where w = 0.78–1.79, x = 0.11–1.17, y = 0.68–2.34 and z = 1.41–2.32. These key elements were varied systematically during sand casting into 30-mm diameter bars to assess their influence on the development of microstructure and mechanical properties. It was found that microstructures ranging from fully pearlitic to an intimate mixture of retained austenite and bainitic ferrite, termed ausferrite, were produced and a reasonable linear correlation was observed between ausferrite volume fraction and strength. The optimum combination of mechanical properties was achieved in an alloy of approximate composition Fe–3.2C–1.0Cu–0.7Mo–0.55Mn–2.0Si, which generated 100% ausferrite without alloy carbides. This alloy has a microstructure and mechanical properties comparable to austempered gray iron without many of the problems associated with austempering.