Effect of aluminium content on creep and stress rupture properties of high carbon Fe–Al alloys

Abstract

Abstract Ingots of Fe–Al alloys containing 1.1wt%C each and 8.5, 16 and 20wt%Al, respectively, were prepared by a combination of air induction melting and electroslag remelting (ESR). The ESR ingots exhibited a significant amount of precipitation of Fe3AlC0.5 phase. Creep and stress rupture tests were carried out on cast ESR alloy samples at a temperature of 873 K and a tensile stress of 140 MPa. The Fe–8.5wt%Al–1.1wt%C alloy exhibited a minimum creep rate of 1.62% h−1 and a stress rupture life of six hours. In comparison, a decrease 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 attributed to the absence of a continuous network of Fe3AlC0.5 phase and a relatively fine microstructure observed in this alloy. Such a network leads to the formation of a duplex Fe3Al–Fe3AlC0.5 structure in the other two alloys and 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 alloys are determined by the volume fraction and morphology of Fe3AlC0.5 phase present in the alloy and the Al-content of the matrix plays a relatively minor role.