Effect of B, Zr, Ce and Nb addition on structure and mechanical properties of high carbon Fe-10.5 wt% Al alloy

Abstract

Iron aluminides based on Fe3Al offer a combination of attractive properties such as excellent resistance to oxidation and sulfidation with lower density and material cost than austenitic and ferritic steels [1–3]. However poor room temperature ductility, poor toughness, poor machinability and low strength as well as poor creep resistance at temperature above 873 K have limited their acceptance for structural applications. Recent developments have indicated that the room temperature ductility to Fe3Al alloys can be improved by the addition of Cr, Ce and combined addition of Zr and C. [4–7]. The addition of Nb, Mo and W has significantly improved the high temperature strength and creep resistance [8– 10]. Recently, it has also been shown that, carbon may be an important alloying element to Fe–Al alloys containing 8–16 wt% (15–28 at.%) aluminum. The addition of carbon up to 1 wt% leads to improved strength, creep resistance and machinability and resistance to environmental embrittlement [11–14]. The addition of carbon also allowed the use of the low cost raw material such as steel scrap. The purpose of the present paper is to report the effect of B, Zr, Ce and Nb addition on microstructure and mechanical properties of ternary high carbon Fe-10.5 wt% Al-0.7 wt%C base alloy at ambient and high temperature of 873 K. Forty-kilogram melts of five alloys with nominal compositions listed in Table I were prepared in an Inductotherm medium frequency air induction-melting furnace (all compositions are in wt% unless otherwise specified). Induction melting was carried out under protective flux cover (AIMFC) in an alumina-lined crucible using proprietary charging schedule. The melt was top-poured in to 55-mm diameter spilt cast iron molds. Commercial purity aluminum, ferro-cerium, ferro-boron, Nb, zirconium sponge and steel scrap were used as raw materials. The total amount of impurities (Mn, Si, Cu, P etc.) present in melt stock was about 0.7 wt%. The 55-mm diameter AIMFC ingots were