THE ROLE OF DEFORMATION TWINNING ON MECHANICAL-PROPERTIES OF AN AUSTENITIC FE-30MN-1.2AL-0.3C ALLOY

An austenitic Fe-30Mn-1.2Al-0.3C alloy has been investigated under tensile and total-strain controlled fatigue tests between room temperature and 77 K. The alloy exhibits an elongation peak between room temperature and 77 K. It was found that tensile elongation is not controlled by the total amount of deformation twinning, but rather the rate and temperature sensitivity of deformation twin formation. Total-strain-controlled fatigue tests show that the fatigue resistance of the Fe-30Mn-1.2Al-0.3C alloy at 77 K is superior to that at room temperature in the 10(2)-10(4) cycles fatigue life range, although the monotonic tensile elongation at 77 K is lower than that at room temperature. The enhancement of fatigue resistance at 77 K is due both to an increased fatigue ductility coefficient, because of strain-induced deformation twins, and to increased strength. Increased formation of deformation twins during the fatigue test is responsible for the increased fatigue resistance at 77 K.