It is well known that a material subjected to progressive creep eventually fractures at a time determined by the applied stress and temperature. However, the processes which exhaust the metal ductility in creep are very poorly understood. Until these processes are clearly defined it is not possible to arrive at a satisfactory fracture theory for creep nor is it possible to predict intelligently the effects of creep history on the rupture life.

In this investigation the progressive metal deterioration occurring during creep at 1000 F is measured by the retained 1100 F stress-rupture properties. This “creep damage” is shown to be both strain and time-sensitive. The creep conditions producing large damages are defined and a mechanism for the damage suggested. It is also shown that reheat treatment is able to heal the most severe damages produced in this investigation.

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