Relation between Inclusion Surface and Acicular Ferrite in Low Carbon Low Alloy Steel Weld

The inclusion of low carbon submerged arc weld metals of a Ti-B system with different aluminum contents has been studied. The inclusions contributing to acicular ferrite nucleation were multi-phase consisting of MnS, MnAl2O4 and amorphous phases. In the energy dispersive X-ray spectroscopy mapping analysis, inclusions were surrounded by a titanium-rich layer. This layer was analysed as Ti-O by energy disperse X-ray spectroscopy spectrum from the interface between inclusion and ferrite. The selected area diffraction pattern of inclusion surface was characterized as TiO. The acicular ferrite had Baker-Nutting orientation relationship with this TiO layer on the inclusions surface, and the lattice misfit was 3.0%. Therefore, it was supposed that the narrow TiO on the inclusion surface promotes acicular ferrite nucleation supplying low interface energy.