The welding time, the rate of advance is not as rapid as that assumed when filling
with molten metal, so that, an area expanding and an area contracting as showing
in picture A and picture B in the parent metal. In the picture A showing the condition
when welding speed relatively slow speed. In this case, the expanding zone (which
is marked greencolor) is small in compression to the width of the contraction zone
(which is marked gray color). Therefore the contraction area is the predominating
factor, because the plates to close-up ahead of the arc. The distortion of the plates
being in the same direction as indicates by the line (which is shown in red dotted
The picture B showing the condition when welding is relatively high-speeds. In this
case the expanding area (which is marked greencolor) relatively large and wide.
It is the predominating factor and causes the plates to open up ahead of the arc.
The distortion being in the direction indicated by the line (which is shown in red
In the above cases, after welding has been completed and the plate has cooled to
room temperature, the filler weld metal and parent metal in the yellow zone (which
is shown in picture) which is subjected to plastic flow and its trying to contraction.
But it is restricted by the base metal outside the plastic flow zone. The residual
stress is happened during the arc welding. This residual stress can be measure by
the strain gauge.
The weld filler metal and the base metal within the plastic flow zone (which is shown
with yellow color) is in tension longitudinally, and the just outside of the base
metal the plastic flow area is in compression stress longitudinally.