2
Ferrous Materials
Before turning to the specific wires
for the mig welding of ferrous materials, there are basic similarities that
every ferrous wire shares in the alloying
elements added to iron. For mig welding carbon steels, the primary
function of the alloying additions is
to control the deoxidation of the weld puddle and to help determine the
weld mechanical properties. Deoxidation
is the combination of an element with oxygen from the weld puddle
resulting in a slag or glass formation
on the surface. Removing oxygen from the puddle eliminates it as a
cause of weld metal porosity.
Silicon (Si) –
Silicon is the most commonly employed deoxidizing element in wires used for mig
welding. Generally,
wires contain 0.40% to 1.00% Si, depending on their intended use. In this percentage
range, silicon
exhibits very good deoxidizing ability. Increasing amounts of Si will increase
the strength of the weld with
only a small decrease in the ductility and toughness. However, above 1-1.2% Si,
the weld metal may become
crack sensitive. Manganese
(Mn) – Manganese is also a commonly
used deoxidizer and strengthener. Manganese constitutes
1.00% to 2.00% of mild steel wires. Increasing amounts of Mn increases the weld
metal strength to
a greater degree from Si. Manganese will also reduce the hot crack sensitivity
of the weld metal. Aluminum
(Al), Titanium (Ti) and Zirconium (Zr) –
These elements are very strong deoxidizers. Very small
additions of these elements are sometimes made, usually not more than 0.20% combined.
In this range,
some increase in strength is also achieved. Carbon
(C) – Carbon influences the structural
and mechanical properties more profoundly than any other
element. For the purpose of mig welding
steels, the carbon content of wires is usually held between 0.05%
to 0.12%. This level is sufficient
to provide necessary weld metal strength without appreciably affecting
ductility, toughness, and porosity.
Increasing carbon content in both wire and plate has an effect on porosity,
particularly when welding with CO2
shielding gas. When the carbon content of the wire electrode and/or the
workpiece exceeds 0.12% the weld metal
will lose carbon in the form of CO. This can cause porosity, but
additional deoxidizers help to overcome
this. Continued
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