ELECTRON BEAM WELDING of steel sheets treated by nitrooxidation

摘要

The paper describes the nitrooxidation process in a fluid environment applied to low-carbon steel sheets. The influence of this process on structural changes, weldability, mechanical properties and formability is also presented. Specimens welded by electron beam welding were examined by visual inspection, microstructure analysis and microhardness analysis. Visual inspection showed irregularities in weld bead formation, significant porosity and excessive spatter. In order to improve the appearance of the weld bead, it was necessary to use a triple welding pass and electron beam oscillation. The structural microanalysis of electron beam-welded specimens revealed a polygonal ferrite structure with the presence of upper bainite. The heat-affected zone was approximately three times wider in comparison to laser beam welding. No grain coarsing was observed in the high temperature heat-affected zone. In comparing electron beam welding and laser beam welding of nitrooxidation-treated materials, it can be claimed that electron beam welding is not a suitable welding method for this type of material.