الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The effect of nitrogen addition, heat input and filler metals on weld metal microstructure and mechanical properties of alloy 316 ASS are studied. Autogenous gas tungsten arc welding (GTAW) is employed by adding up to 2vol. % N2 in Ar. These variables affect a number of welding aspects, including arc characteristics and microstructure. The influence of shielding gas mixtures on microstructure and mechanical properties of GTAW of austenitic 316 stainless steel is studied. Mechanical properties of welds are determined through uniaxial tension, hardness measurements, impact and bending tests. Weld defects, as porosity and inclusions are examined using radiographic testing. Weld specimens are free of porosity, inclusions and hydrogen cracking. Mechanical properties and cooling rate are lower at higher heat input, but the cooling time, nugget area and solidification time are higher. Addition of N2 to Ar shielding gas leads to higher values of the ultimate tensile strength ‘UTS’, yield stress ‘YS’ and elongation percent. UTS, YS and elongation of welds depend on heat input, filler metal and N2 content of shielding gas. UTS and hardness values decrease with increasing heat input. Best results are obtained under ERNiCrMo-3 with Ar-2%N2. Hardness values of heat affected zone and base metal under pure Ar, 98%Ar-2%N2 are higher than those of the weld zone. Best results are obtained under ERNiCrMo-3 with Ar-2%N2. Impact values of all weld joints increase with increasing heat input, but decrease with increasing N2 content in shielding gas. Grain size of weld metal increases with increasing heat input and N2 content of shielding gas. Weld dendritic structure is refined by increasing N2 content in Ar. A mathematical model is built depending upon the welding current, filler metals and shielding gases. Finally, applying the bending test up to 180o no cracks, tearing or surface defects could be observed.