Effect of Ti carbonitride on hot ductility of Ti microalloy steel during continuous casting

High temperature tensile were performed by using a thermo-mechanical GW1600 to simulate the deformation of Ti microalloy steels at high temperatures and low deformation rates similar to those during continuous casting. An equivalent austenite diameter was proposed, taking into account the weakening effects of proeutectoid ferrite films and Ti carbonitride precipitation. Based on this, a hot ductility prediction model for the slab was established to investigated hot ductility. The results show that as Ti content increases, the hot ductility of Ti microalloy steel initially increases and then decreases. At low Ti content, the pinning effect of Ti carbonitrides increases with the increase in Ti content, which inhibits grain coarsening for improving hot ductility. As Ti content increases, the size of carbonitrides grows, weakening the pinning effect and leading to austenite grain coarsening. Simultaneously, the formation of Ti carbonitrides inhibits proeutectoid ferrite film formation, leading to a reduction in its thickness. These combined factors reduce the hot ductility of the continuous casting steel. According to the hot ductility prediction model, in order of severity, the factors affecting hot ductility are: proeutectoid ferrite film, chain-like nanoscale Ti carbonitrides, austenite grain size, and dispersed nanoscale Ti carbonitrides. An accuracy error of less than 10% is shown by the model.