Creep rupture properties of HAZs of a high Cr ferritic steel simulated by a weld simulator

摘要

In this work, creep rupture properties of the heat affected zones (HAZs) of P122 steel, simulated by employing a weld simulator are studied and the results are compared with those of HAZs simulated by heat treatment. Microstructures corresponding to intercritical HAZ, fine-grained HAZ and coarse-grained HAZ (CGHAZ) were produced using a weld simulator in the middle of specimens. These specimens were then subjected to heat treatment equivalent to post weld heat treatment and the creep specimens machined from them were tested at 923 K at three stress levels. Results showed that, irrespective of the peak temperature of simulation, fracture always occurred in that part of the specimens heated to the temperature close to Ac_3 during simulation, which was found to have a fine grain structure and minimum creep strength. However, in specimens with temperatures of simulation above Ac_3, creep cavities were observed and for those with a 1473 K simulation temperature, fracture occurred with very low ductility as observed in actual weld joints. Stress and strain distributions within the specimen during creep deformation were analyzed using the finite element method. The results indicate that creep deformation and fracture are influenced by the multiaxial stress state produced in the specimen due to the existence of different microstructures varying significantly in their creep properties. Results also suggest that the creep tests using specimens with CGHAZ microstructures simulated at the centre can successfully produce a creep fracture similar to the Type IV fracture that is observed in ferritic steel weld joints.