Strategic Optimization of Post Weld Heat Treatment for Dissimilar TIG Weldment of P22 and P91 Steels

The Gas Tungsten Arc Welding (GTAW) between P22 (2.25Cr-1Mo) and P91 (9Cr-1Mo) steels are quite common in heavy vehicle structures like; railway locomotives and war (or combat) vehicles. After welding, high hardness values of the Heat-Affected Zones (HAZs) of these dissimilar weld joints are possibly obtained. The uneven hardness in HAZ comes from the austenite transformation to Martensite, because of highly uncontrolled cooling rates. The considerable difference in hardness among various zones leads to prior cracking and is bound to failure during high-temperature operations. Therefore, there is a dire need to establish an appropriate Post Weld Heat Treatment (PWHT) to temper the dissimilar weld joints for required durability. The study investigates the microstructure and mechanical properties of various erupted zones of steel, before and after the application of PWHT. Before and after PWHT, weld zone and HAZ in P22 and P91 are mechanically tested and metallurgically examined. Further PWHT is tried to be optimised strategically and statistically, for the least variation in hardness among different zones. So that any failure due to thermal stresses or strains, during normal running conditions can be avoided.