Effect of post-weld heat treatment (PWHT) time and multiple PWHT on mechanical properties of multi-pass TIG weld joints of modified 9Cr-1Mo steel

Abstract

The effect of post-weld heat treatment (PWHT) time and multiple PWHT on mechanical properties of modified 9Cr-1Mo steel weld joints has been studied using multi-pass tungsten inert gas (TIG) weld joints fabricated from 12.5-mm-thick plates using matching composition ER90S-B9 filler wire. Radiographically qualified weld joints were subjected to single PWHT at 760 °C for different hold times, viz. 1, 3, 4, 8 and 12 h, as also to multiple PWHT cycles of (1 h + 3 h) and (4 h + 4 h) for comparing with single PWHT of 4 h and 8 h, respectively. Transverse-weld tensile strength of the weld joints (as also the base material) decreases marginally with increasing heat treatment duration. In all heat-treated conditions, the Charpy V-notch impact toughness of more than 200 J is obtained for the weld and base materials. Multiple PWHT is found to have no adverse effect on the tensile properties and impact toughness of the weld joint, which has been corroborated by microstructural examination and hardness measurements.