Micro-macro simulation of type III and type IV creep damage in 21/4Cr-1Mo steel welds

A simulation method of the creep damage progress combining the random fracture resistance model and FEM elastic-creep analysis was proposed and was applied to the evaluation of Type III and Type IV creep damage respectively in the coarse and fine grain heat affected zone (HAZ) in welded joints of 2 1/4Cr-1Mo steel. Firstly following the previous work on the fine grain HAZ, parameters for the coarse grain HAZ were identified for simulating the increase of number density of small defects on the basis of the random fracture resistance modeling. Secondly the simultaneous damage simulation for both fine and coarse grain HAZ was applied to both the welded joint model test and the burst test of elbow. A possibility of predicting the final failure time of welded joint was also discussed on the basis of the effective stress against the final failure surface. The proposed simulation successfully reproduced the increase of the number density of small defects in the fine and the coarse grain HAZ, and could predict the failure time of welded joints.