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.