Revealing the influence of niobium addition on interphase precipitation in titanium microalloyed high-strength low alloy steel

High-strength low-alloy (HSLA) steel is widely utilized in structural applications due to its excellent mechanical properties and formability. In this work, the influence of niobium on the precipitation behavior of HSLA steel is studied, and two distinct precipitation modes—dispersed and interphase precipitation—are identified within the ferritic matrix. A comparative analysis of their composition, morphology, and crystallographic orientation is conducted using advanced techniques, including scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), high-resolution transmission electron microscopy (HRTEM), and atom probe tomography (APT). The results show that interphase precipitates primarily consist of (Ti,Nb)C, whereas dispersed precipitates are identified as TiC. Nb is observed to significantly retard phase boundary migration and resulting in refined precipitate size. Despite differences in their precipitation mechanisms, both precipitation modes maintain a consistent crystallographic orientation relationship with the ferrite matrix. These findings enhance the fundamental understanding of Nb-driven precipitation in HSLA steels and offer insights for tailoring microstructure through alloying strategies.