Effect Mechanism of α-Ferrite Sustained Precipitation on High-Temperature Properties in Continuous Casting for Peritectic Steel

Exploring the mechanism of the alpha-ferrite precipitation process on high-temperature properties plays an important guiding role in avoiding slab cracks and effectively regulating quality. In this work, in situ observation of the alpha-ferrite sustained precipitation behavior for peritectic steel during the austenitic phase transition process has been investigated using high-temperature confocal scanning laser microscopy. Meanwhile, the high-temperature evolution of the phase fractions during the phase transition process was quantitatively analyzed based on the high-temperature expansion experiment using the peak separation method. Furthermore, the high-temperature properties variations of the casting slab during the alpha-ferrite sustained precipitation process were investigated with the Gleeble thermomechanical simulator. The results show that the film-like ferrite precipitated along the austenite grain boundaries at the initial stage of phase transition, then needle-like ferrite initiates rapid precipitation on film-like ferrite when the average thickness reaches 15 similar to 20 mu m. Hot ductility reached a minimum at the ferrite phase fraction f(alpha) = 10 similar to 15%, while high-temperature properties returned to a higher level after f(alpha) > 40 similar to 45%. The appearance of a considerable amount of needle-like ferrite and grain refinement effectively improves the high-temperature properties with the alpha-ferrite precipitation process advances.