In this work the welding behavior of alloy 21Cr-6Ni-9Mn has been characterized for fiber laser beam welding. Bead morphology, porosity formation, alloying element loss and microhardness of bead-on-plate welds were analyzed for a wide range of processing parameters.
At high travel speeds the depth-to-width ratio reached an asymptotic limit for a given laser power. Bead shapes similar to electron beam welding were observed at high travel speeds, at lower travel speeds typical hourglass bead shapes were observed. Active zone porosity, gas porosity, and cold shut defects were all observed. An increase in porosity was observed as travel speed increased. The change in porosity formation is likely related to changes in keyhole stability. The porosity size and shape was different than that typically observed in electron beam welding. Nitrogen loss was approximately 10-20% of the initial base metal nitrogen content, similar to the nitrogen loss observed in electron beam welding. Nitrogen loss decreased as travel speed decreased in the upper portion of the weld metal. No change in microhardness was found between base metal and weld metal. Considering the loss of nitrogen which provides solid solution strengthening, the similar hardness in weld metal and base metal may indicate strengthening though microstructural refinement.