Effect of temperature and strain rate on the mechanical properties of Fe-40Al-0.6C

The microstructure and mechanical properties of an Fe-40Al-0.6C alloy was c haracterized in the extruded and low-temperature annealed condition. The mi crostructure consisted of a B2 FeAl matrix with Fe3AlC0.5 perovskite-type c arbides distributed within the grains and at grain boundaries. These carbid es dissolve completely in the matrix at 950 degrees C. In addition, a small amount of free carbon in the form of graphite was also present, and at tem peratures in excess of 1050 degrees C, a reaction of the type alpha + C dou ble left right arrow alpha + C + L leading to the formation of a grain boun dary liquid film occurs; quenching from above this temperature produces an extremely brittle material. Tensile testing of the extruded and low-tempera ture annealed material revealed a positive temperature dependence of streng th, a brittle to ductile transition at similar to 350 degrees C, and a stra in-rate dependency of ductility in air at room temperature accompanied by f racture transition from an intergranular mode at fast strain rates to subst antially transgranular cleavage at the slowest strain rate. At elevated tem peratures, a strain rate dependency of strength and ductility is noted and explains the observed loss in impact toughness at these temperatures. These observations are discussed on the basis of the observed microstructures an d available theories. (C) 1998 Elsevier Science S.A. All rights reserved.