Optimization of advanced thermo-mechanical process design for a modern HSLA steel

C. Ledermueller, E. Kozeschnik, R. Webster, S. Primig
Metallurgical & Materials Transactions 50A (2019) 5800-5815.

The results presented here have been achieved in a collaboration between researchers in our team and Prof Ernst Kozeschnik (TU Vienna, Austria), the lead developer of the thermo-kinetic modelling software MatCalc. We propose an optimized advanced thermo-mechanical process route for an industrial grade Ti-Mo-Nb HSLA steel. We thoroughly characterize these microstructures using LOM, SEM/ECCI, EBSD, and TEM.

We find two populations of precipitates in our hierarchical microstructure, FeMnC-rich cementite particles decorating grain boundaries and smaller TiNbC-rich precipitates on dislocations and subgrain boundaries. Our new thermo-kinetic modelling underpins our experimental results concerning the detailed evolution of crystallite size, precipitate morphology and composition, enabling a through-process description of the microstructural evolution. TEM reveals a change in the nanoscale morphology of TiNbC precipitates. It is shown that these particles transform into a core-shell structure when subjected to 60 min direct aging after deformation.