Abstract:
This investigation was carried out with the aim of studying the effects of post-weld heat treatments (PWHTs) on the microstructure, mechanical and corrosion properties of gas metal arc welding (GMAW) of AISI 304 Stainless Steel (SS). GMAW of AISI 304 SS was performed at an optimum setting of welding parameters, using butt joint configuration. Thereafter, different PWHTs including annealing, normalizing and tempering were carried out on the weldments. The microstructure of the base metal, as-welded joint and post-weld heat treated joints samples were examined, using optical microscopy and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Hardness, tensile and impact properties of the entire weldments were determined, using Vickers micro-hardness tester, Instron universal testing machine, and Charpy impact testing machine, respectively. The electrochemical corrosion resistance of the base metal and the entire welded joints were also examined. The as-welded joint was characterised with sub-granular grain structure and Cr-rich carbide precipitates around the grain boundaries. The precipitate was significantly absent in the joint after post-weld normalising and tempering processes. The as-welded joint was found to be the hardest because of the Cr-rich carbide precipitate and martensite formation during rapid solidifcation of the weld pool. All the post-weld heat treated weldments exhibited higher elongation (better ductility) but only the post-tempered sample demonstrated superior ultimate tensile strength (about 10% higher) than the as-welded sample. Due to high brittleness and hardness of the as-welded sample, all the post-weld heat treated weldments showed higher impact energy than it. The post-annealed sample showed the highest impact energy after the base metal. The hardness and tensile properties of gas metal arc AISI 304 SS weldment can be improved by carrying out post-weld tempering process while post-weld annealing process improved the impact strength of the weldment. All the post weld heat treated sample exhibited higher corrosion resistance compared to the as-welded. This work provides the most appropriate post weld heat treatment required for improving the mechanical and corrosion properties of GMA welded AISI 304 stainless steel.
