Mechanical Behavior of Alloy 800 at 838 K

Abstract

Three commercial heats of Alloy 800 have been tested at 838 K in simple tension and in fatigue at constant plastic strain ranges from 0.2 pct. to 1.4 pct. Although all three heats met the ASTM specifications for Alloy 800, the heats exhibited significant differences in elevated temperature mechanical properties. These differences were functions not only of heat-to-heat chemistry variations, but also of the final annealing treatment given during their manufacture. The microstructures of several samples cycled to failure in the above tests were examined by transmission electron microscopy and compared with the microstructures of the as-received heats. It was found that significant additional precipitation occurred during the fatigue testing of two of the heats, and this was correlated with secondary hardening behavior found during the mechanical tests. The observed precipitation behavior could be explained using suggested isothermal transformation curves and solvus curves taken from the literature.