Comparison of GMAW and SAW for NGW of 50 mm Q&T Steel Plate

A one-pass-per-layer technique was used for narrow gap welding (NGW) of 50 mm thick plate of quenched and tempered steel with 690 MPa minimum yield strength. GMAW and SAW were investigated for pulsed and non-pulsed welding using the same 1.2 mm strength-matching welding consumable and the same nominal heat inputs for each of the pulsed and non-pulsed welds. The welds were defect-free and the hardness, tensile strength and Charpy impact energies were generally consistent with high weldment integrity. Pulsing of the welding current had the effect of slightly increasing side-wall fusion, flattening the weld bead and decreasing its volume. The most significant differences between the welds produced by GMAW and SAW were that SAW resulted in a lower peak HAZ hardness and higher HAZ Charpy values. These differences arise because different thermal cycles are associated with the two welding processes. Although the nominal heat inputs were the same, the effective heat inputs differed because of the different shielding methods and weld bead profiles. The HAZ hardness and CVN values are consistent with lower cooling rates for the SAW welds. Key words: Narrow gap welding, GMAW, SAW, 50 mm Q&T plate, Mechanical properties