THE EFFECTS OF SQUAREWAVE POLARITY PARAMETERS ON MICROALLOYED STEEL CHARPY V-NOTCH RESULTS

摘要

The welding processes used to produce microalloyed steel pipe can result in mechanical property changes in the heat affected zone (HAZ) regions of seam and double joint (circumferential) welds. HAZ properties are controlled primarily by the microstructures resulting from the thermal history during welding. While multi-pass welds have successfully achieved CVN values greater than 66.4 ft-lbs (90 J) at the fusion line, this work explores the use of single-OD welds to achieve similar toughness values. Thus, single OD-pass submerged arc welding (SAW) test specimens were produced to examine the effect of electrode polarity on the HAZ Charpy V-notch (CVN) toughness. CVN results indicate that a DC+ lead, AC 50% trail tandem arc setting produces moderately improved CVN test HAZ results at -20°C compared with an AC 75% lead, AC 25% trail tandem arc setting. The difference is believed to be related to differences in effective heat input, though further investigation is required. The CVN specimens notched furthest from the fusion line gave the largest toughness result scatter. The elevated values are believed to be the result of greater lengths of the notch passing through unaffected base metal. Lower values (average CVN from 37 to 59 ft lbs (51 to 80 J)) were produced by notches located at the fusion line, which would pass through significant amounts of coarse grain heat affected zone (CGHAZ). The weld and base metal CVN results for both sets of welding conditions were comparable. Further optimization of welding parameters is required for a single pass weld procedure to achieve HAZ CVN values exceeding 66.4 ft-lbs (90 J) at the fusion line.