MECHANICAL-BEHAVIOR OF AN FE-40AL-0.6C ALLOY

The mechanical properties of Fe-40 at.% Al containing 0.6 at.% C have been evaluated in the extruded and low-temperature annealed condition as a function of temperature and strain rate. In the as-extruded condi tion, the yield strength at room temperature is similar to 510 MPa wit h an associated plastic tensile elongation of 2.3%. With increasing te st temperature, the strength decreases steadily to similar to 350 MPa at 600 degrees C; a brittle-to-ductile transition is recognized in the 300-400 degrees C regime. Upon subjecting the extruded material to a two-step low-temperature anneal, the room temperature strength decreas es to similar to 310 MPa and ductility increases to 4.4%. When the str ength of this material was measured as a function of temperature, a po sitive temperature dependence of strength was observed in the 400-600 degrees C range while the brittle-to-ductile transition temperature ra nge decreased by similar to 75 degrees C. At a fairly constant yield s tress, ductility steadily decreased with decreasing strain rate at roo m temperature in air from similar to 12% at 4 x 10(-1)/s to 1.7% at 4 x 10(-7)/s. At -30 degrees C, the ductility for comparable strain rate s, was significantly higher than that at room temperature. These obser vations, when compared to data in the literature, verify that while fr acture occurs by environmental embrittlement, it is delayed in this ca rbide-containing alloy. The carbides are thought to act as hydrogen tr aps and delay the arrival of critical amounts of hydrogen to the crack lip thereby delaying embrittlement. The role of carbide size and dist ribution on tensile properties was examined by developing isochronal a nd isothermal aging curves for this alloy. (C) 1998 Acta Metallurgica Inc.