An Explanation for the Effects of Hold Periods on the Elevated Temperature Fatigue Behavior of 2 1/4 Cr-1 Mo Steel

Abstract

An analysis of previously reported elevated-temperature fatigue with hold time data supplemented by a metallographic examination of the 2 1/4 Cr-1Mo alloy steel specimens is reported. The tests were conducted in air over the temperature range of 427 to 593° C. Hold periods were introduced at various points of the hysteresis loop during each cycle. An explanation for the previously reported effects of these hold periods on the fatigue life is presented. The explanation attributes the reduction in fatigue life to the combination of reduced interaction solid solution hardening and accelerated fatigue crack initiation due to oxide cracking. The effect of hold periods is primarily due to an environmental interaction (rather than to a creep interaction) with the fatigue damage processes.