The Comparison of Fatigue Crack Growth Behaviors for Long Term Used and Heat Treated 1Cr-0.5Mo Steel Under Various Load Frequencies and Temperature

Abstract

As the operating time of a power plant approaches its design life, the characteristics of crack initiation and growth in thick-section boiler components becomes major concerns. But few data have been reported for long term served materials because it is very difficult to acquire that. In this study, the characteristics of the crack growth behavior of used 1Cr - 0.5Mo steel which was served for a boiler header for 30 years and heat-treated 1Cr - 0.5Mo steel were studied experimentally by performing fatigue crack growth tests at 538°C and room temperature under triangular and trapezoidal wave-shapes. In order to evaluate hold time effect at elevated temperature, the results of fatigue test with 10 seconds hold time (0.083 Hz) were compared with the results of fatigue test with triangular wave-shapes (0.5Hz). As frequency decreased, the fatigue-crack growth rate showed a significant increase at high temperature. In the case of fatigue test with hold time, the rates of fatigue crack propagation were faster than those in the results of fatigue test without hold time. Finally, fatigue crack growth rates of reheat-treated material were slower than those of long term served material. And the behavior could be characterized by stress intensity factor range.