Characterization of Creep Crack Growth Rate at the Early Stage and Estimation of Creep Crack Initiation Life for High Cr Steels and Their Weldments
Ryuji SUGIURA, Toshimitsu YOKOBORI, Kazuto SATO, Masaaki TABUCHI, Kenichi KOBAYASHI, Masataka YATOMI and Kamran NIKBIN
Abstract:Most boiler component structures are mainly fabricated by welding which are likely to be regions of crack initiation and propagation. In such weldment, it is known that the multi-axial stress fields appear due to the plastic constraint induced by the differences in material micro-structure between the weld metal, heat affected zone and base metal. Additionally, the technique of predicting the life of creep crack initiation and growth have not been clearly developed for weldments of high Cr steels due to many factors such as the variation in micro-structure and the residual stresses caused by welding and thermal cycles. The present paper indicates that in order to predict the total fracture life for weldment of high Cr steels, it is important to clarify the incubation process and path on a structural mechanical basis in order correctly determine the incubation time of creep crack growth. It may be useful to look at the role of Q* as correlating parameters to identify how best to rationalize the correlating parameter that can be used to predict both creep crack initiation and growth in weldments. Key Words:High Cr steel, Weldment, Creep crack growth, Creep crack initiation, Incubation time, C*,dƒÂ/dt, Q*, Stress multi-axiality