By the application of external transverse magnetic field, the arc may be deflected either forward towards the direction of welding or backward. Forward deflection can be used to advantage for welding thin sections. With forward deflection of the arc the weld width increases and penetration is decreased, weld metal spreads because of arc deflection.

This effect can also be used to advantage in the welding of plates at higher welding currents and higher welding speeds. Normally higher welding speeds and higher currents cause undercuts to develop on the weld deposits. Because of arc deflection forward direction weld metal spreads and fills up the undercuts formed. Jackson C. E. has used this effect in the welding of aluminium and welding speeds upto 2 times the normal welding speeds could be reached with no undercuts. The strength of the welds was not only unaffected but was a little on the improvement side.

Forward deflection of the arc has also been used to advantage by the author in the hard facing by arc welding. Forward deflection caused sallow penetration, the dilution of the weld deposit with the base plate was reduced and a weld deposit rich in alloy content and improved overall properties was obtained.

Arc deflection by the proximity of multiple arcs can also be used to advantage. A two-or three-wire submerged arc utilises the magnetic fields of neighbouring arcs to obtain higher travel speeds without undercuts.

Backward deflection causes heavy undercutting and extensive reinforcement. This has little use in practical welding.

Alternating (transverse fields, however, cause the arc to oscillate back and forth across the weld axis with a frequency equal to that of the applied field. This effect is used to advan­tage in the gas tungsten arc welding GTAW process using hot wire. Higher welding speeds with good penetration and absence of undercuts were the advantages associated with this type of field.

The weld deposit microstructure showed fine grains. Weld strength was also improved.

Axial magnetic field rotates the arc. This field has been used by the author in improving the weld deposit characteristics of underwater welds. Constant external axial field causes arc rotation. The metal drops do not fall straight but they also rotate in a circular path before depositing on the plate. Rotation of the drop in circular path causes centrifugal forces to act on it. The drops fall on the plate in a large area causing weld width to increase. Higher welding speed and higher currents could be used with the absence of undercuts. The mechanical properties of the welds are not changed. Welding production rate can thus be doubled without affecting the weld deposit properties.

With axial field and consequent rotation of arc the penetration is reduced under similar welding conditions. This can also be used for welding thin plates and for hard facing of metals.

Alternating axial magnetic field has been found (by the author) to be of good value. Alternating axial field causes the arc to oscillate in a circular path. The arc twists rightward and leftward. This effect causes stirring of weld pool which causes the formation of finer grains and consequent improvement of mechanical properties. The author has found improvement in mechanical properties upto 30% of that obtained without field, in underwater welding.