TWI Industrial Member Report Summary 273/1985
By M H Rodwell
Background
Two 1.2mm diameter Type 347 stainless steel MIG wires have been tested under spray transfer conditions and found to exhibit different welding characteristics with regard to both arc stability and weld bead profile. These differences were attributable directly to the composition and surface condition of each wire, rather than to any variation in the performance of the welding equipment. One wire displayed frequent, often violent arc instabilities and deposited an extremely peaky weld bead with poor wetting characteristics. The surface condition of this wire was partly responsible for the severity of the arc disturbances, probably by reducing the efficiency and consistency of current pick-up, however it was the presence of surface slag islands in the weld pool which was found to cause a ragged arc appearance and initiate major arc disturbances through its interaction with the arc column. The relatively high surface tension of the molten weld pool was apparently responsible for the persistently peaky weld profile with this wire, arising from the low concentrations present of the surface active elements sulphur and oxygen, in conjunction with an abnormally high aluminium content.