The effect of beam oscillations on the microstructure and mechanical properties of electron beam welded steel joints

Abstract

The influence of beam oscillations on the microstructure and mechanical properties of low-carbon steels, subjected to electron beam welding, was investigated. Beam oscillations created a dynamic distribution of power around the stationary position of the beam resulting in the enhanced flow of heat inside the keyhole and yielded wider fusion and heat-affected zones. A reduction in the undercutting at the weld root was also achieved through beam oscillation. The weld microstructure consisted of large columnar grains in the fusion zone and equiaxed grains of varying sizes in the heat-affected zone. The variation in grain size across the weld joint was attributed to the steep temperature gradients produced during electron beam welding. High hardness was seen in the fusion and heat-affected zones due to the occurrence of martensite. Weld samples fabricated using beam oscillations showed lower microhardness compared with joints produced by stationary beam welding. This decrease in hardness arose from enhanced grain growth and additional diffusion of carbon out of the austenite lattice due to beam oscillations. Beam oscillations did not introduce any significant morphological changes to the weld microstructure, but resulted in enhanced tensile strength and lower microhardness in the weld joints.