The Role of MX Carbonitrides for the Particle-Stimulated Nucleation of Ferrite in Microalloyed Steel

The role of titanium and vanadium carbonitrides (Ti,V)(C,N) of the MX series on the austenite-to-ferrite transformation in microalloyed steels and their potential of acting as pre-nuclei for intragranular ferrite nucleation is examined experimentally and by computational simulation. Thermal treatments and single-hit compression tests are performed on a dilatometer and a Gleeble® 3800 thermomechanical simulator to investigate the phase transition and precipitation sequences within microalloyed steel. The analysis of the microstructure and examination of formed precipitates is carried out by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In situ observations are realized via high-temperature laser scanning confocal microscopy (HT-LSCM). The experimental results are compared to kinetic precipitation simulations for MX precipitates’ particle-stimulated intragranular ferrite formation using an on-particle nucleation model for ferrite on the surface of the MX carbonitrides. A particular focus is the comparison of precipitation trends between non-deformed and deformed samples. The physically appropriate modeling of MX precipitation kinetics in combination with intragranular ferrite formation serves as a basis for future industrial process optimizations without extensive experimental work.