TIG welding is a very clean welding, and produces high-quality welds. But usually it’s performed manually, so that the quality of weld depends on the skill of the operator, and there’s not so much theoretical information about what’s happening while, and just after the welding, and how it affects the properties of the welded sample. Extensive literature is available for weldability of conventional materials such as aluminum, titanium or magnesium materials. TIG welding of powder metallurgy steels has not been attempted by many researchers. The aim of this project is to investigate the possibility of welding powder metallurgy alloy steel by TIG welding process. Mo-alloyed low alloy steel with 0.3% carbon has been synthesized from elemental powders of iron, graphite and molybdenum, through the powder metallurgy processing route. Elemental powder were mixed in suitable proportions, compacted and sintered at 1120 ºC for 20 minutes. The sintered compacts were immediately hot forged between a pair of flat dies and drawn out into flat specimens of size 75mm x 12 mm x 3mm, with a density of about 97% of theoretical density. Manual TIG welding was performed on the flat specimen both transverse and longitudinally. Argon gas was used as shielding gas. After the welding, the welded samples were subjected to tensile test, hardness measurement and microstructural investigation. SEM of the fractured samples was also undertaken. Some of the important conclusions arrived at from the results are: low alloy p/m steel can be successfully welded by manual TIG welding, without the usual weld defects such as lack of fusion, under bead cracks etc. Further, metallurgically sound welds could be produced on porous low alloy steel without porosity affecting the weld metal. The welded samples exhibited higher tensile strength and hardness compared to the base metal, which is an indication of sound weld joint. However, in a few samples, blow holes were observed within the weldment, which have been the prominent factor in reducing the strength of the welded joint. The microstructural analysis of the welded joints indicated basic ferritic structure in weld metal zone and feritic-pearlitic structure in base metal. There is no pronounced heat affected zone, which could be microstructurally distinct in all cases of the welded samples. The SEM fractographs of the failed specimen indicated predominantly mixed mode of fracture by the presence of both dimples and cleavage factes. Additionally, the unclosed pores have also contributed to the fracture origin during the tensile loading, as noticed in the fractographs. The welded samples with blow holes invariably failed in the weld zone, especially fracture originated in the blow hole areas, during tensile test.

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