Toughness mechanism analysis of submerged arc welding joints of ultra-low carbon bainitic steel

In this paper, the microstructure of ultra-low carbon bainitic steel submerged arc welding joints was analyzed, which shows that there is a certain relationship between toughness and the content of acicular ferrite in weld seam. SEM-EDS(Scanning Electron Microscopy-Electron Dispersed Spectrum)observations and analysis of weld seam was conducted on a field emission scanning electron microscope.Results show that several ferrite laths or plates are nucleated on Al₂O₃ inclusion. EBSD analysis was conducted with a FE-SEM to investigate the crystallographic orientation of weld joint microstructures.Results indicate that the crystallographic orientation of acicular ferrite is not completely random. A certain crystallographic orientation is dominant for acicular ferrite. Acicular ferrite is separated by high angle boundaries. Some acicular ferrite laths or plates which are formed on one inclusion and grow in opposite directions have the same crystallographic orientation, presumably because it has some crystallographic orientation relations with the prior austenite.