Fig. 12.Measured and calculated l 2 -spacings over half the slab thickness and segregation coefficient for Mn.

The clogging of the submerged entry nozzle (SEN) during the continuous casting of steel can be divided into two stages: the “early stage,” when the initial layer of the clog covers the SEN refractory surface owing to chemical reactions, and the “late stage,” when the clog layer continues to grow because of the deposition of non-metallic inclusions (NMIs). In this paper, a mathematical formulation is proposed for the build-up of the initial oxide. The chemical reaction mechanism is based on the work of Lee and Kang (Lee et al. in ISIJ Int 58:1257–1266, 2018): a reaction among SEN refractory constituents produces CO gas, which can re-oxidize the steel melt and consequently form an oxide layer on the SEN surface. The proposed formulation was further incorporated as a sub-model in a transient clogging model, which was previously developed by the current authors to track the late stage of clogging. The thermodynamics and kinetics of CO production, depending on the local pressure and temperature, must be considered for the sub-model of early-stage clogging. Test simulations based on a section of an actual industrial SEN were conducted, and it was verified that the clogging phenomenon is related to the SEN refractory, the chemical reaction with the steel melt, the local temperature and pressure, and the transport of NMIs by the turbulent melt flow in the SEN. The model was qualitatively validated through laboratory experiments. The uncertainty of some parameters that govern the reaction kinetics and permeability of the oxide layer is discussed.

The hot ductility and malleability of a vanadium-microalloyed steel is investigated by means of tensile and compression tests at temperatures ranging from 700 to 8508C and strain rates of 3 Â 10 À4 to 0.3 s À1 . The deformation tests are performed after austenitization and cooling to test temperature. The so-called second ductility minimum is located around 7508C for all strain rates except for the highest one, where no ductility trough is observed. Ductility steadily increases with strain rate at a given temperature, and the fracture mode progressively changes from intergranular to transgranular. In the region of minimum ductility, intergranular cracking occurs at low strain rates by void nucleation, growth and coalescence within thin layers of deformation induced ferrite covering the austenite grain boundaries. Cracking is favoured by V(C,N) precipitation associated with the g/a phase transformation. Ductility remains low above the temperature of minimum ductility, where no apparent ferrite formation is observed (790 8C). Void formation takes place as a result of grain boundary sliding in combination with matrix and grain boundary precipitation. These voids are able to grow and link up forming intergranular cracks. Ductility increases with strain rate mainly due to the short time available for precipitation as well as for intergranular void growth and coalescence.

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Analytical liquidus equations were evaluated using differential scanning calorimetry (DSC) and differential thermal analysis (DTA). Results of 180 measurements in the Fe-C-Si-Mn-Al-P subsystems were considered, where the experimental methodology was demonstrated for four alloys in the Fe-Si-Mn-Al system. Excellent agreement between the DSC/DTA dataset and the most recently published equation was found (error 2.1 ± 1.6 °C). For this equation, suggested modifications of phosphorus parameters will help to improve calculations for P-alloyed steels.