Weldability and Post Weld Heat Treatment of T23 Boiler Grade Steel

T23 is a low alloy ferritic steel used for boiler super heater and re-heater tubes and water panels in complex fuelled power plants as they exhibit superior high temperature strength and creep behaviour compared to other low alloy ferritic steels. T23 steel is in bainitic structure which holds greater toughness than tempered martensite and also they possess increased resistance to thermal fatigue. With the help of T23 steel, the weight and piping component of the boiler can be reduced. The microstructure of the weldment without proper Post Weld Heat Treatment (PWHT) was not in equilibrium state which led to the secondary hardening during subsequent exposure at high temperature. So there occurred a significant increase in hardness due to non-tempered weld joints and decrease in toughness. Therefore, Post Weld Heat Treatment for T23 steel is necessary. Using Tungsten Inert Gas (TIG) process, the T23 steel was welded under suitable welding parameters (welding current, voltage and shielding gases). A study was done to know the effect of Post Weld Heat Treatment on T23 steel and also the influence of welding parameters. Hardness of T23 steel was measured. The heat treated specimen is examined through Optical microscope and Scanning Electron Microscope. Finally it was noticed that the Post Weld Heat Treatment has enhanced the mechanical properties as well as the metallurgical arrangement of the T23 steel.