Effect of aluminium content on creep and stress rupture properties of highcarbon Fe-Al alloys

Ingots of Fe-Al alloys containing 1.1wt%C each and 8.5, 16 and 20wt%Al, res pectively, were prepared by a combination of air induction melting and elec troslag remelting (ESR). The ESR ingots exhibited a significant amount of p recipitation of Fe3AlC0.5 phase. Creep and stress rupture tests were carrie d out on cast ESR alloy samples at a temperature of 873 K and a tensile str ess of 140 MPa. The Fe-8.5wt%Al-1.1wt%C alloy exhibited a minimum creep rat e of 1.62% h(-1) and a stress rupture life of six hours. In comparison, a d ecrease in minimum creep rate and an increase in stress rupture life of up to two orders of magnitude was observed for the other two alloys. The poor creep and stress rupture properties of Fe-8.5wt%Al-1.1wt%C alloy are attrib uted to the absence of a continuous network of Fe3AlC0.5 phase and a relati vely fine microstructure observed in this alloy. Such a network leads to th e formation of a duplex Fe3Al-Fe3AlC0.5 structure in the other two alloys a nd results in improved creep and stress rupture properties observed. It is argued that unlike the case with carbon free alloys where Al-content of the alloy may be important, the creep rate and stress rupture life in these al loys are determined by the volume fraction and morphology of Fe3AlC0.5 phas e present in the alloy and the Al-content of the matrix plays a relatively minor role. (C) 1999 Elsevier Science S.A. All rights reserved.