The Creep-Rupture Properties of 80 Ni-20 Cr Alloys

The creep-rupture properties and the creep behavior of a series of 80 Ni-20 Cr alloys were investigated over the 1200 to 1800-F range. In the group were two vacuum-melted and three air-melted alloys. Among these five heats there were small but important differences in minor constituents such as silicon, manganese, sulfur, and possible tramp elements, primarily as a result of the melting practice in each case. Of particular interest in this study was the variation in ductility which the various alloys exhibited in creep-rupture tests which lasted from a few minutes to more than 1000 hr. A close examination of ductility behavior was undertaken by breaking down the creep curve into primary, secondary, and third-stage creep as a function of stress and temperature. It is shown that the stress-rupture properties are not affected over a wide temperature and stress range by a change in minor constituents, whereas the ductility behavior can vary considerably.