**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. The 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. Finally, a mathematical model is built depending upon the welding current, filler metals, and shielding gases.

**Keywords:** TIG welding, filler metals, nugget area, cooling rate, welding variables
