Influence of pre and post weld heating on weldability of modified 9Cr-1MoVNb steel plates under SMA and GTA welding processes

Abstract

Welding of modified 9Cr-1 Mo(V-Nb) steel plates has been carried out by shielded metal arc (SMA) and gas tungsten arc (GTA) welding processes. The welding has been carried out using different preheating temperatures followed by employing post weld heat treatment (PWHT) at different temperatures. The microstructures of the weld and heat affected zone (HAZ) of the weld joints have been studied under optical microscope and correlated with the temperatures of the pre and post weld heating. The property of the weld joint has been primarily characterised by studying variation in hardness across the weld joint. Average hardness of the weld and different regions of HAZ are evaluated and also correlated with the temperatures of the pre and post weld heating. The tensile and Cy-impact toughness properties of the weld joints are also studied and correlated to the preheating and PWHT temperatures. At a given preheating the tensile and impact toughness properties of the SMA and GTA weld joints observed under different PWHT are compared and correlated to their microstructures. The increase of preheating and PWHT coarsened the microstructures of weld and HAZ and significantly influenced the properties of the weld joints. The moderate preheating and PWHT at about 523 K and 1 023 K respectively gave optimum tensile properties of the SMA welds. The toughness of weld deposit of 9Cr-1 Mo grade alloy was improved by PWHT at high temperature in presence of its modification by addition of V and Nb.