الفهرس 
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Abstract
The aim of this work is to study the effect of the welding current and oxygen content in back purging gas on size and microstructure of fusion zone then, on mechanical and corrosion properties of GTA welded joints made using 6.4 mm thick 316L austenitic stainless steel and 254 SMO super austentic stainless steel plates.
In this regard, several GTA welding trials (both autogeneous and butt welded joints) have been made using different welding currents (100A, 125A, 150A) and different oxygen contents (0.05, 0.5%) in purging gas.
Evaluation of welded joints has been carried out using both non-destructive and destructive tests. In other words, welded joints were subjected to visual, dye penetrant and radiography tests before sectioning it for different destructive tests including metallurgical, mechanical and corrosion tests.
The results showed that the higher the welding current, the coarser is the dendritic structure due to decreasing cooling rate. grain growth was observed in HAZ where its width is slightly increased with increasing welding current due to higher heat input. However, a reasonable HAZ width was observed in all cases.
Also the higher the oxygen content in purging gas, the coarser is the dendritic structure, due to decreasing cooling rate as a result of higher heat input. The corrosion rate is increased by increasing either welding current or oxygen content in purging gas, as a result of higher heat input in this case.