The study of minor elements and shielding gas on penetration in TIG welding of type 304 stainless steel

The effects of minor elements and shielding gas on the penetration of TIG welding in type 304 stainless steel have been studied. The bead-on-plate test was performed, then the depth and width of the weld were measured using an optical projection machine. The arc voltage was measured with an arc data monitor. In addition, the metallurgical characteristics of weld were examined using OM and SEM. The results show that oxygen and sulfur are beneficial in increasing a depth/width ratio because of the increased surface tension/temperature gradient. Elements, such as aluminum, that have a deleterious effect on the depth/width ratio will combine with oxygen and reduce the soluble oxygen content in the weld pool. On the other hand, silicon and phosphorus have a minor effect on the depth/width ratio. Shielding gas using Ar + 1% O₂ or Ar + 5% H₂ can significantly promote the depth/width ratio. The former contains increased soluble oxygen content in the weld pool, and the latter produces an arc that is hotter than that produced by pure argon.