Effect of post-weld heat treatment on microstructure, mechanical properties, residual stresses and electrochemical behavior of aisi 4140 tig weldments

Welded structures, specifically their fusion and heat-affected zones, are majorly prone to embrittlement and enhanced corrosion due to the induced residual stresses resulting from the complexity of the heating and cooling cycles during welding. In this work, TIG welding of AISI 4140 alloy steel (chromium-molybdenum steel) was done using the filler wire ER80S-B2 (AWS A5.28) followed by post-weld heat treatment. A comparison of base metal, as-welded, and post-weld heat-treated samples is made based on residual stresses, corrosion resistance, and mechanical properties. Due to the presence of stresses and the formation of unstable martensitic structure, the as-welded samples depicted the highest corrosion rate (8.982mpy) as compared to the post-weld heat-treated sample (5.707mpy) which is closer to that of base metal (5.627mpy). Post-weld heat treatment relieves the residual stresses which results in the enhancement of corrosion resistance. The tensile strength for the base metal, as-weld and PWHT samples come out to be 739, 763, and 744MPa, respectively. Ductility, on the other hand, is restored by post-weld heat treatment which was compromised in the as-welded samples.