Rtech Tig200, Operating Instructions Manual

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3.3 Alloyed Steel
TIG welding may be used for welding alloy
steels but because deposition rates are low,
it is usually only used for welding 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 welding
alloy 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.
Alloy steels with high carbon equivalents 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.