Effect of alloying additions on structure and mechanical properties of high carbon Fe-16 wt.% Al alloy

Abstract

Effect of quaternary alloying elements Mn, Cr, Ni and Ti on structure and properties of Fe 3Al-based alloy containing about l wt.% carbon have been investigated. Four different alloys were prepared. The composition of the quaternary alloying element was proposed to be ≈4 wt.% and was substituted for iron. Processing of Fe-16Al-4.1Mn-1.0C, Fe-16.5Al-3.5Cr-0.94C, Fe-16Al-4.0Ni-0.9C and Fe-15.6Al-2.8Ti-1.0C alloys through a combination of air induction melting with flux cover (AIM) and electroslag remelting (ESR) yields a sound ingot free from macro and microporosity with very low sulphur, oxygen and nitrogen. This process route also exhibited excellent recovery of alloying elements. As-cast alloys were examined using optical microscopy, X-ray diffraction, electron probe microanalyses (EPMA) and scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray analysis to understand the microstructure of these alloys. The as-cast ESR ingots of alloys containing Mn, Cr and Ni exhibited a two-phase structure of Fe 3AlC 0.5 precipitate in the Fe 3Al-based matrix. Both phases exhibited considerable amount of solid solubility for Mn, Cr and Ni, whereas the alloy containing Ti exhibited a three-phase microstructure of TiC particles and Fe 3AlC precipitates in the Fe 3Al-based matrix. This alloy has also exhibited very low solubility of Ti in the Fe 3Al-based matrix and no solubility in the Fe 3AlC precipitates. Several microcracks were observed in the as-cast ESR ingots of the high carbon Fe 3Al alloy containing Ni and tensile tests could not be carried out for this composition. Tensile and creep tests were performed on the high carbon Fe 3Al alloys containing Mn, Cr and Ti in the as-cast condition. No improvement in room temperature tensile strength and inferior high temperature strength and creep properties was observed by the addition of quaternary alloying elements.