Fatigue Life Assessment of High Temperature Cr-Mo-V Rotors Using X-Ray Diffraction

In order to predict the crack initiation life at periphery grooves for high-temperature rotors in a fossil power plant, a study using X-ray diffraction was conducted. As a conclusion of the study, a diagram for estimating the fatigue life fraction was presented based on the following findings: (1) The half-value breadth of X-ray diffraction line generally decreased with an increase in fatigue damage for Cr-Mo-V material at service temperature of about 500°C. (2) For the constant strain cycling, it was possible to express the relation between the change in half-value breadth and the logarithm of cyclic number by a straight line except in the early part of life. The slope of the line seemed to take a constant value regardless, the strain range. On the other hand, the relation between the half-value breadth and the number of cycles to crack initiation was abe to be expressed using a straight line on the semi-log plotting. (3) Based on the result of (2), it is possible to propose a method for estimating the fatigue life fraction for constant strain cycling. (4) It was recognized that the method is also valid for estimating the fatigue life fraction for two-step multiple strain cycling and strain cycling with hold time.