The Effect of Nitrogen Addition on the Stainless Steel TIG-Flux Weldments
The purpose of this research was to study the effect of specific oxide fluxes and nitrogen additions to the shielding gas on the surface appearance, weld morphology, retained delta ferrite content, angular distortion, and mechanical properties of TIG process applied to the welding of 5 mm thick austenitic stainless steel plates. Autogenous gas tungsten arc welding process through a thin layer of activating flux was applied on stainless steels to produce a bead on plate welded joint. A CCD camera was used to record the real time shape of plasma arc during welding. The MnO2 and ZnO fluxes used are packed in powdered form. The experimental results indicated that TIG welding with the oxide fluxes or Ar-N2 mixed gas can effectively enhance the penetration, better mechanical properties, and lower welding distortion in austenitic stainless steel. It was found that electrode erosion in excessive spatter and arc instability. A few nitrogen gases added to the argon shielding gas, a rapid reduction in measured ferrite number was obtained. Additionally, increase in nitrogen content, the retained delta ferrite content in Type 304 stainless steel welds can be reduced to near zero. The increase in arc voltage, retraction of the plasma arc, and contraction of the molten weld pool are the primary factors that effectively enhance the weld penetration.
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