TIG Welding Carbon SteelTIG welding may be used for welding carbon steel but because deposition rates are low, it is usually restricted to sheet and thin sections for high quality applications, small components and root passes of multipass butt joints in plate and pipe. Standard DC TIG equipment is normally suitable and DCEN polarity is usually chosen to provide good workpiece heating. Tungsten electrodes with additions of thorium oxide, cerium oxide, or lanthanum oxide are used for welding steel and they give good arc stability. Only inert or reducing gases should be used for TIG welding and pure argon is normally recommended as the shielding gas for steel. Filler rods are usually selected to match the chemical composition and the mechanical properties of the parent plate. The weldability of the steel may impose restrictions on the choice of filler rod. Steels with carbon contents above about 0.3% are hardenable, and fast cooling will produce a hard HAZ and this is liable to result in hydrogen cracking. This form of cracking can be prevented by use of preheat and suitable welding procedures. TIG welding these materials may present possible electrical and radiation hazards, and thoriated tungstens are mildly radioactive. Welding fume generation is normally very low.
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