Stress Relief Cracking Studies of 2 1/4Cr1Mo Steel

摘要

The stress relief cracking susceptibility of coarse grained heat affected zone microstructures of 2 1/4 Cr 1Mo steel has been assessed using a recently developed constant displacement stress relief cracking test procedure. Two types of test are described: the relaxation test which simulates conditions of stress, strain and temperature during the post weld heat treatment cycle, and the load shedding test which characterizes crack growth behavior in terms of the stress intensity parameter at constant temperatures in the stress relief thermal cycle. Particular attention has been directed at characterizing the micromechanisms of cracking and the role of residual impurities. Two distinct types of stress relief cracking were identified: failure at high temperatures, 875K, was characterized by intergranular ductile microvoid coalescence, whereas at lower temperatures, 725K-875K, a low ductility intergranular failure was produced with the cracking promoted by solute segregation to the grain boundaries and the crack tip region. An increase in the heating rate during the post weld heat treatment was shown to be beneficial to cracking resistance. The application of the laboratory test data to the prediction of stress relief cracking of actual weldments is considered, using two alternative methods.