P. Burgardt, P. W. Hochanadel, A. N. Duffield, D. D. Kautz, Los Alamos National Laboratory, Los Alamos, NM
Circle deflection and the utilization of defocus are common practices in electron beam welding (EBW). Their advantages include higher confidence in consuming the weld joint and improved resistance to “cold shut”-type anomalies. The current work was undertaken to determine if changes in composition or processing would reduce porosity common to this material.
Electron beam welding was used to weld three heats of 21-6-9 stainless steel using variable focus and circle deflection settings. The welds were subsequently sectioned for examination with light optical microscopy (LOM) to view the weld sections for depth of penetration, microstructural features and presence of weld anomalies, such as porosity and cracking. The porosity was further quantified in terms of average size (area) per cross-sectional view.
Porosity was observed to be an issue in the 21-6-9 stainless steel, especially in low and intermediate circle deflection ranges (between 10 and 700 Hz deflection settings). Welds made with defocus settings were found to be similar in nature to the welds made with circle deflection in terms of aspect ratio.
The weld depth of penetration was found to vary as a function of both defocus settings and circle frequency. In addition, the depth of penetration at low frequency is nearly the same as when welding at sharp focus and no circle deflection. The average porosity density was determined to be strongly dependent upon processing parameters, but not upon material composition.
Summary: This paper describes the weldability of 21-6-9 in terms of porosity generation by electron beam welding with both circle deflection and defocus settings.
