Effect of Ti, Al, and Mg addition on microstructure evolution in weld metal of stainless steel solidified with F and FA modes and the tensile property

This study investigated the effect of equiaxed primary ferrite nucleation on the weld microstructure and tensile properties of two types of stainless steel solidified with primary ferrite. One was the F mode with only δ–ferrite during solidification, and the other was the FA mode with austenite formed at the end of solidification. MgAl 2 O 4 , formed after alloying of Ti, Al, and Mg and accelerated TiN formation due to the low lattice misfit of 4.88 % under their fully paralleled orientation. Primary ferrite nucleation with equiaxed solidification was achieved in both the F and FA modes. In the F mode, austenite transformed from δ–ferrite grain boundary in solid state and exhibited dependent formation with δ–ferrite morphology. Therefore, the equiaxed δ–ferrite grain promoted the refinement of austenite. Conversely, in the FA mode, austenite formed independently to δ–ferrite during solidification and grew epitaxially from the austenite phase in the base metal. As a result, austenite could not be refined by equiaxed δ–ferrite nucleation. The grain refinement could improve the tensile property. However, the brittle TiN caused the fracture initiation during tensile deformation, degrading the tensile property in both F and FA modes. This comprehensive influence of TiN and the microstructural evolution of δ–ferrite and austenite highlights the tendency of tensile properties to improve in the F mode, whereas diminished in the FA mode.