Effect of niobium and carbon on microstructure and compressive yield strength of as cast ESR Fe–8·5Al alloy

Abstract

The effect of niobium (1·5 and 3·5 wt-%) addition on the microstructure and mechanical properties of as cast ESR Fe–8·5Al–0·1C alloy has been studied. Alloys were prepared by a combination of air induction melting with flux cover (AIMFC) and electroslag remelting (ESR). As cast ESR alloys were characterised using an optical microscope, a scanning electron microscope (SEM) and an electron probe microanalyser (EPMA). Compression tests were carried out on as cast ESR alloy samples at temperatures up to 800°C. Addition of 1·5 wt-% Nb to Fe–8·5Al–0·1C alloy resulted in a marginal improvement in the compressive yield strength at test temperatures up to 1073 K, whereas addition of 3·5 wt-% Nb significantly improved the strength. This significant improvement in the room and high temperature compressive strength may be attributed to solid solution strengthening as well as precipitation hardening by the presence of fine and higher volume fractions of niobium and niobium carbide precipitates, in contrast to the relatively soft Fe₃AlC_0·5 precipitates present in the Fe–8·5Al–0·1C alloy.