Microstructure modeling of high-temperature microcrack initiation and evolution in a welded 9Cr martensitic steel

Welded joints in tempered 9Cr-1Mo operating at elevated temperatures are well known to be prone to premature failure due to cracking in the heat-affected zone. This paper describes a crystal plasticity model to predict the microcrack initiation and evolution in the inter-critical heat-affected zone of 9Cr-1Mo welded steel at elevated temperature. A crystal plasticity finite element model indicates that the micro-cracks of 9Cr-1Mo steel mostly nucleate at prior austenite grain boundaries and boundary clustered regions. Inter-granular and trans-granular microcracking are shown to be the key predicted microdamage mechanisms from the current crystal plasticity model. A small amount of ferrite in the inter-critical heat-affected zone is shown to not only influence the microcrack initiation and evolution, but also significantly accentuate material degradation for a given applied load leading to premature failure at high temperature.This publication has emanated from research conducted with the financial support of Science Foundation Ireland under Grant No. 14/IA/2604 and the College of Engineering and Informatics at NUI Galway. The authors are grateful to the Irish Center for High-End Computing (ICHEC) for supporting the computational work (uleng040b). Helpful discussions with the Mechannics team (NUI Galway and UL). The assistance of Mr Edward Meade of the Bernal Institute at UL is also gratefully acknowledged. The 9Cr-1Mo welded material was provided by Mr. Stephen Scully of Electricity Supply Board (ESB International). Mr. Scully also provided helpful insight into the operation of conventional power plant and the metallurgy of martensitic steelspeer-reviewe