INVESTIGATION ON WELDABILITY OF 9Cr-1-MoUb STEEL PLATES WITH - MMA AND TIG . WELDING PROCESSES

Abstract

Modified 90r-lMo weldments were prepared using 5mm thick plates, using shielded metal arc welding (SMAW) and tungsten inert gas (TIG) welding processes. In case of SMAW process PHILIPS KV7 electrode was used while in case of TIG, filler wire was taken from the base material itself. During welding,,preheating was varied in the range of 423°K to 523°K and post weld heat treatment temperature was varied in the range of 923°K to 1123°K, keeping the heat input constant. The effect of preheating temperatures and postweld heating temperatures on the weldments mechanical properties such as hardness, tensile strength, impact toughness and on microstructure of weld deposit and HAZ have been studied. Microstructure of weld deposit was found to contain primarily martensite and ferrite mixture. The increase in PWHT temperature and preheat temperature has been found to increase the grain coarsening in the weld and HAZ. Hardness of weld centre and HAZ has been found to be reduced with the increase in PWHT temperature. Tensile strength of the joint has been found ' to be very sensitive to the PWHT temperature Higher PWHT temperatures have reduced the joint strength. At lower post weld heat treatment temperature, the toughness values of SMAW and TIG welds are comparable. Where as at higher PWHT temperature, the weldments prepared using TIG process, have shown much superior toughness values as compared to the shielded metal arc welded weldments.