Centerline Cracking in Electron-Beam Cap-to-Header Welds in Type 304L Stainless Steel

摘要

Two sets of cap-to-header EB welds in Type 304L exhibited a significant difference in hot cracking susceptibility which could be associated with the heat-to-heat variations in chemical composition and the resultant change in solidification behavior of the fusion zone. In one case, solidification of the entire fusion zone occurred with delta ferrite as the primary phase of solidification and resulted in crack-free weldments. In the other case, a localized shift from solidification as delta ferrite to solidification as austenite along the weld centerline was accompanied by hot cracking in the austenitic region. Segregation of nitrogen, a powerful austenite former, to the weld centerline promoted the transition to solidification as austenite. Microprobe and Auger surface analyses of the crack-susceptible microstructures revealed that enhanced sulfur segregation accompanied the shift in solidification behavior and was integral in the mechanism of crack formation. (ERA citation 07:059746)