Toughness Improvement of Resistance-Butt Welded Joints in Steel
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The development of welding technologies with high productivity is very important in the field of welding. One shot welding methods, such as upset/flash welding, are essentially very fast can meet this requirement. However, their fracture toughness has generally been unacceptable, which has been considered to be an essential week point. In this report, to improve the toughness of upset/flash welds are examined. The factors affecting flash weld toughness are summarized, and the improvement methods are discussed. Based on the results of several studies, ways to improve toughness are considered to the cleaning of the weld interface by way of oxide extrusion on upsetting and grain refining of the microstructures in the heat-affected zone (HAZ). One solution is the use of pulsed high current to concentrate resistance heat on the contact area and minimize total heat input. Homopolar pulse welding (HPW), which can supply very high current through the homopolar generator, has been examined for this purpose. The weld toughness of high tensile strength steel and high Chromium martensitic stainless steel was examined. Homopolar welds showed acceptable toughness and the values of high Chromium stainless steel were comparable with those of the base metal. The HAZs were narrow with fine-grained microstructures, and no discernible localized softened regions were observed. The fine-grained microstructure of HPW welds results from the combination of its rapid thermal excursion and deformation while upsetting. Sufficient plastic deformation also makes it possible to obtain defect free welds without localized softened regions. From these results, this pulsed high current welding methods has been found to play a role in the improvement of fracture toughness.