الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Shielding gases are of considerable significance in the protection of molten metal from atmospheric contamination during welding processes. These gases play an important role in a number of aspects of welding, including arc characteristics and the microstructure of weldments. The influence of different shielding gas mixtures of nitrogen, hydrogen, and argon on the microstructural evolution and the mechanical properties of gas tungsten arc welds (GTAW) of austenitic 316 stainless steel are studied in the current work. The influence of different nitrogen and hydrogen additions with (5%N2, 10%N2, 2.5%H2, 5%H2, or 10%H2) to argon shielding gas on the mechanical properties of austenitic stainless steel welds ,the mechanical properties of the welds are evaluated through uniaxial testing, hardness measurements, and bending testing. The weld defects, such as porosity and inclusions are examined using radiographic testing. The defect incurred is porosity and it is observed in specimens welded under 95%Ar-5%N2 and 90%Ar-10%N2. On the other hand, specimens welded under 100%Ar, 97.5%Ar-2.5%H2, 95%Ar-5%H2 or 90%Ar-10%H2, the radiographic test results show that all welding specimens are free from defects such as porosity and hydrogen cracking. The results indicate that the higher nitrogen and hydrogen contents in the shielding gas mixture, the lower are the mechanical properties. The tensile strength of welds is strongly dependent upon nitrogen and hydrogen contents in the shielding gas. The ultimate tensile strength decreases with increasing nitrogen and hydrogen contents. The best results are obtained under Ar-2.5%H2. On the other hand, the base metal has the lowest ultimate tensile strength. The hardness values of the weld zone (WZ) under pure argon, 95%Ar-5%N2, or 90%Ar-10%N2 is higher than the heat affected zone xv (HAZ) and base metal (BM). On the other hand ,the hardness values of the weld zone under 97.5%Ar-2.5%H2, 95%Ar-5%H2, or 90%Ar-10%H2 is lower than that of the HAZ and the base metal. The grain size in the weld metal increases with increasing nitrogen and hydrogen contents of shielding gas. Additionally, weld metal penetration depth and its width increase with increasing nitrogen and hydrogen contents. Furthermore, cracks, tearing and surface defection after bending test are not observed on the samples welded under all shielding media.