The effect of thermo-mechanical treatment on the high temperature tensile behavior of an alumina-forming austenitic steel

Two different thermo-mechanical treatments (TMT) were performed on an alumina-forming austenitic (AFA) stainless steel, DAFA 29, which was recently developed at Oak Ridge National Laboratory for application in advanced ultra supercritical power plants. The resulting fine-grained TMT materials showed yield stresses more than double the yield stress of the as-received material at room temperature and more than 50% higher at 600 ºC, but lower yield stresses (but greater elongations) at 700 ºC and above. Strain rate jump tests performed at both 600 ºC and 700 ºC showed that the TMT materials have greater strain rate sensitivity and lower activation volumes at both temperatures. The strain rate has a power law relationship with the flow stress with a stress exponent of ~5. The as-received AFA alloy showed serrated stress-strain curves at 600 ºC suggesting the occurrence of dynamic strain aging.