Effect of post weld heat treatment soaking time on microstructure and mechanical properties of TIG welded grade 91 steel

Development of new alloy materials is in progress to improve thermal efficiency of supercritical boilers. One of such material is modified 9Cr-1Mo (Grade 91) martensitic alloy steel referred as T/P91. This material is extensively used in high temperature applications such as fabrication of superheater, reheater and economizer sections of a boiler. The present study is made to find the effect of post weld heat treatment (PWHT) soaking time on microstructure and mechanical properties of TIG welded ASTM A213 Grade 91 steel plate. Experiments were conducted for PWHT at 760°C for different soaking time such as 2, 4 and 6 hours to get the desired mechanical properties. The investigated results suggest that PWHT of 2 hours at 760°C is optimal to regain the strength of Grade 91 steel after welding.