Impact of second phase precipitation and solute drag effects on austenite grain growth

In steelmaking processes like continuous casting, controlling austenite grain size is critical to achieving high manufacturing quality standards. Therefore, proper grain growth adjustment reduces the risk of strand embrittlement and surface cracks while significantly influencing the properties of austenite decomposition products such as ferrite, martensite, and bainite.

This PhD thesis investigates key phenomena that govern austenite grain growth at elevated temperatures. A major focus is on impurity-induced solute drag effects, where solutes at grain boundaries impede grain movement. The interaction of different species of solutes at the grain boundaries can show competitive or co-segregation behavior and change the structure and ultimately the grain growth rate. Additionally, second-phase precipitates play a vital role by pinning grain boundaries, with their population and size distribution being critical factors.

The study employs in situ high-temperature laser scanning confocal microscopy (HT-LSCM) and is combined with thermo-kinetic numerical simulations and mean-field modeling. This powerful combination of experimental and computational methods provides insights for optimizing continuous casting processes, particularly in adjusting the chemical compositions and cooling rates to enhance steel quality.