High temperature strength property evaluation of heat affected zone in boiler weldment parts of 2.5Cr-1Mo steel
Ogata Takashi; Yaguchi Masatugu
Abstract:In view of the situation that aging of boiler components proceeds and some 'Type IV' cracking incidents are reported recently, the development of an accurate remaining life evaluation method for boiler weldment parts is an important subject for the utilities. In this study, simulated materials with coarse and fine grain microstructures in a weldment heat affected zone were produced, and their high temperature strength properties were evaluated. The strength property of the weld joint was also discussed based on the experimental and analytical results. It was found that the creep rupture strength of the fine grain material was as low as one half of the base metal and as 1/5 of the coarse grain material, and the weld joint ruptured at the fine grain region in a shorter period than the base metal as the applied stress level decreased. Many grain boundary creep cavities were also observed in the fine grain region. A creep deformation analysis by FEM indicated that the creep strain accumulation at the fine grain region in the weld joint preceded against other regions, suggesting that the rupture of weld joint occurred at the fine grain region in the experiment. Key Words:aging boiler, weldment part, heat affected zone, 2.25Cr-1Mo steel, creep, fatigue, microstructure