Crystal Orientation Relationships between Acicular Ferrite, Oxide, and the Austenite Matrix

Abstract

Crystal orientation relationships between acicular ferrite (AF), oxide and the austenite matrix have been investigated in low carbon steel weld by the submerged arc welding process. In particular, this study focused on the formation mechanism of the crystal orientation relationships. The AF microstructure was observed in weld metal containing titanium. Oxide particles were composed of MnTi₂O₄, amorphous phase and TiO₂. The AF nucleated on MnTi₂O₄ having the Baker-Nutting (B-N) orientation relationship with the MnTi₂O₄ and Kurdjumov-Sachs (K-S) orientation relationship with the austenite matrix. This result implies that the MnTi₂O₄ had a rational orientation relationship with the austenite matrix. The orientation relationship is considered to be (001)_MnTi2O4//(111)_γ, [100]_MnTi2O4//[211]_γ from the viewpoint of the lattice coherency. It is supposed that the MnTi₂O₄ can be formed within oxide particles having this orientation relationship with the austenite matrix at high temperature during welding process. This mechanism allows the coexistence of both B-N and K-S orientation relationships, which lowers the AF/MnTi₂O₄ and AF/austenite interfacial energies. This results in the decrease of the activation energy for AF nucleation.