Interface characteristics between TiN and matrix and their effect on solidification structure

Heterogeneous nucleation is an effective way to promote the dispersion and precipitation of second-phase particles in steel and refine the grain size of the solidification structure.Not only refining as-cast structure grain size,but TiN in ferritic stainless steel can also pin grain boundaries and restrain the overgrowth of grains during rolling.The interface characteristics between TiN and heterogeneous phases(high-melting inclusions and ferrite phase)were studied based on the wetting angles between molten steel with different compositions and TiN substrate,and on the matching degree between TiN and ferrite lattice.It was found that,for the molten steel with the same composition,the wetting angle with the TiN substrate was significantly smaller than the contact angles with the other three substrates,while the wetting angle between ferrite phase and TiN was the smallest.The lattice matching was compared among MgAl_(2)O_(4),TiN andδmatrix by means of a high-resolution transmission electron microscope,which revealed that a coherent or semi-coherent interface was formed between the crystal plane(400)of MgAl_(2)O_(4)and the crystal plane(200)of TiN,as well as between the crystal plane(200)of TiN and the crystal plane(110)ofδmatrix,with a lattice misfit of 5.1%and 3.4%,respectively.Finally,these two characteristics between TiN and ferrite phase were both explained from the perspective of interfacial energy.The microstructure refinement mechanism from high temperature to room temperature can be better reflected by the proposed wetting–lattice misfit theory.