Studying the Effect of PWHT on Microstructural Evolution and Mechanical Properties of Welded A517 Quenched and Tempered Steel

Abstract

Sometimes post-weld heat treatment (PWHT) is required for stress relieving both the weld metal and heat-affected zone in A517 Quenched and Tempered (QT) steels. This process unavoidably results in further tempering which adversely affects the mechanical properties of the welded joints. Investigations on A517 QT steel are presented in as-welded condition and after PWHT at 560 and 630 °C. Microstructural variation upon applying PWHT and its influence on impact absorbed energy, fatigue behavior, tensile and hardness properties of the material in as-welded condition and after PWHT are studied. The decrease in hardness is very remarkable after PWHT at 630 °C. Increasing heat treatment temperature from 560 to 630 °C results in reduction of YS and UTS. Void coalescence and coarsening of carbides after PWHT makes the fracture easier and results in reduction of absorbed impact energy. Elimination of acicular ferrite after PWHT at 630 °C increases crack growth rate, and fatigue endurance limit is reduced.