Microalloyed steels strengthened by precipitates nucleated during the austenite (γ) to ferrite (α) phase transformation can provide steel producers with a new type of High Strength Low Alloy (HSLA) steel suitable for increasing demands for their properties. To better understand the conditions at the migrating α/γ interface, which can lead to said precipitation, the kinetics of the phase transformations are investigated.
Three different microalloyed steels with the same amount of manganese and varying amounts of carbon and vanadium are analysed on four different annealing temperatures. Experimental data on the phase transformation kinetics is obtained through dilatometry. A quantitative solute drag model is developed and tested on the quaternary alloys to obtain data on energy dissipation due to segregation of the substitutional elements. A theory is postulated to relate the experimental data and related obtained interface velocities to the modelling results.
Experimental results vary greatly, but at medium (650°C) to high (750°C) annealing temperatures an increase of vanadium and carbon content leads to a slower transformation compared to the alloy with lower concentrations of said elements.
Modelling results indicate that energy dissipation due to vanadium is minimal, especially relative to that of manganese. This means that observed changes in transformation dynamics for the alloys with changing vanadium and carbon content have to be understood in terms of vanadium-carbide precipitation behaviour and related elemental consumption, and not in energy dissipation due to vanadium segregation.