Study of analysis method to predict creep life of 2.25Cr-1Mo steel from welding conditions

The creep rupture life of weld joints decreases to values from half to one-tenth of that of the base metal in Cr-Mo heat-resistant steels. It is industrially very important to understand the creep performance of weld joints and to minimize the reduction in the creep performance of weld joints relative to the base metal. In this study, a consistent prediction computational workflow was developed for practical three-layer cladding welds that connect two modules. These are the weld heat transfer analysis module, which predicts the heat-affected zone (HAZ) shape from welding conditions, and the creep damage analysis module, which calculates the creep rupture life from the predicted shape of the HAZ. Using this workflow, we examined the effects of welding conditions on creep rupture life of 2.25Cr-1Mo steel. Welding conditions were selected on the basis of the design of experiment method, and the correlation between each factor and creep rupture life was evaluated by factorial effect analysis. The results clarify that the creep rupture life changed significantly depending on the control of welding heat input under conditions that simulate practical welding. This suggests that there is an appropriate welding heat input to bring the creep rupture life of weld joints close to that of the base metal. Although previous studies of creep rupture life with relatively simple HAZ geometries have indicated the correlation with the width and angle of HAZ, it was newly discovered that these indices cannot simply explain the creep rupture life of the weld joints with complex HAZ geometries that appear in practical welding. The effect of HAZ shape on creep rupture life is more complicated than previously reported, suggesting that more appropriate HAZ shape factors should be considered.