The Effects of Hold Period on the Fatigue Crack Growth Rate of 2 1/4 Cr-1Mo Steel at Elevated Temperatures

Abstract

The effects of various loading wave forms on the fatigue crack growth rate of 2 1/4 Cr-1Mo steel at 482 and 538°C tested in air have been determined. Scanning electron fractography was used to measure the fatigue striation spacing on the fracture surface of strain controlled push-pull fatigue tests. The fatigue striation spacing was then used as a monitor of the fatigue crack growth rate in these specimens once a fatigue crack had been initiated. Constant strain hold periods were introduced during each cycle at various points of the hysteresis loop. Both increasing temperature and strain range increased the fatigue crack growth rate for continuously cycled tests as expected. However, when a hold period was introduced, the crack growth rate was dominated by the time that preceded each strain reversal; temperature and strain range effects became secondary to hold time. The effect of hold periods for the conditions examined is primarily crack tip oxidation rather than creep crack growth during the hold period.