*2.1.2 Gas purity*

Metals differ in their tolerance for foreign components of the shielding gas. Impurities of shielding gases affect weld quality and eventual fitness. Basyigit and Kurt [11] employed five different shielding gases such as, pure argon, 99%Ar + 1% N2, 97%

#### **Figure 1.**

*Effects of welding current on the sigma and carbide phases distribution of 316 stainless steel, achieved by FESEM – EDX (a) current 90A and (b) current 110A.*

**Figure 2.** *Graph of arc current (A) versus mean of tensile strength (MPa) for316 stainless steel welded joint.*

#### **Figure 3.**

*Comparison of number of points versus hardness (HV) of 316 stainless steel welded joint.*

Ar + 3% N2, 94%Ar + 6%N2, and 91%Ar + 9% N2 for welding 2205 DSS using TIG welding. The austenitic structure increased with increasing N2 content in shielding gas (**Figure 4**). Increasing N2 content in argon shielding gas led to improve grain size, UTS and HV of DSS welds (**Figure 5**).

Besides that, Mosa et al. [12] studied the effect of shielding gas and heat input on mechanical properties of ASS 304 L welded by TIG welding. Tensile strength and hardness values decrease with increasing heat input, but the ferrite number, impact toughness, penetration depth and weld bead width increase. Addition of N2 in Ar increases UTS and HV but reduces FN and impact toughness (**Figures 6**–**11**).

**Figure 4.** *The effects shielding gas composition on phases grain size.*

**Figure 5.** *The effects of shielding gas composition on micro-hardness values of base metal and weldments.*

**Figure 6.**

*Comparison between ultimate tensile strength of welding procedures using shielding gas pure Ar and 2%N/98%Ar.*
