Impact of Electron Beam Welding on the Microstructure of PM2000 ODS Steel

This work investigated the impact of electron beam (EB) welding, using various traverse speeds of the electron beam (1200-2200 mm/min), on the microstructure of PM2000 ODS steel which was characterized using analytical electron microscopy and microhardness. The different heat inputs during welding explored in this study (72-39 J/mm), related to the traverse speed used, correlated with small differences in the widths of the fusion zone. Only minor differences in local microstructures and hardness of the fusion zones were detected amongst the four butt welds produced. The fusion zone is characterized by large columnar grains in the ferritic matrix, together with a coarsened Y-Al-O particle distribution and a reduction in its particle number density as compared to the base material. There is also a sharp border between the fusion zone and base material, with the joint showing little evidence of a heat-affected zone. These changes in microstructure during welding led to a hardness reduction of approx. 30% in the fusion zone of the welds with respect to the base material.