Microstructure and mechanical property relationship for different heat treatment and hydrogen level in multi-pass welded P91 steel joint

The effect of heat treatment condition and diffusible hydrogen level on microstructure and mechanical properties of multi-pass shielded metal arc welded (SMAW) P91 steel butt joints of 18 mm thickness has been studied. Field-emission scanning electron microscope (FESEM), Mercury diffusible hydrogen measurement, Charpy test, room-temperature tensile testing, hardness measurement and energy dispersive X-ray spectroscopy (EDS) were performed to characterize the multi-pass SMAW joints in as-welded, post-weld heat treatment (PWHT) and normalizing/tempering (N&T) state. The P91 steel butt joints with low level of diffusible hydrogen exhibited higher tensile strength and toughness. Both PWHT and N&T treatment provided similar mechanical properties but a significant microstructure variation was noticed for different zones of P91 welds. N&T treatment produced the homogenize microstructure along the P91 weldments both in terms of microstructure and micro-hardness. (C) 2017 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.