Formation of Fine Microstructure in Weld Metal Containing Mn-Ti based Oxides

The formation of fine acicular ferrite microstructure and toughness improvement have been observed in a welding metal in which inclusion particles containing Mn-Ti based oxide are dispersed. The inclusion particles are composed of MnTi2O4 , TiO2 , amorphous and MnS phases, while the acicular ferrite has been nucleated from the MnTi2O4 phase. The Baker-Nutting crystal orientation relationship has been found between MnTi2O4 phase and acicular ferrite, whereas the Kurdjumov-Sachs orientation relationship has been found between the prior austenite phase and acicular ferrite. It has been discovered that the favorable lattice matching at the interface between the prior austenite phase and acicular ferrite may possibly have promoted the nucleation and growth of acicular ferrite, as well as the lattice matching at the MnTi2O4 / acicular ferrite interface.