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During the solidification of steel, phosphorus strongly segregates in the interdendritic liquid phase. In the continuous casting process, even low levels of P may have a detrimental effect on the final product quality. However, phosphorus is partly added up to 0.10 wt pct to improve the mechanical properties of advanced steel grades nowadays, e.g., High-Strength Interstitial-Free (HSIF). To provide new experimental data for the development of thermodynamic databases and solidification models for P alloyed steel grades, phase equilibria in the Fe-P and Fe-C-P key systems were studied up to 1550 °C using differential scanning calorimetry (DSC) and high temperature laser scanning confocal microscopy (HT-LSCM). Special focus was placed on solid/liquid equilibrium temperatures in the Fe-rich part of the binary Fe-P system between 0.025 and 9 wt pct P. In the ternary system, three isoplethal sections with 0.10 mass pct. P, 0.20 mass pct. C and constant mass percent ratio P/C of 2 were investigated. In the latter section, HT-LSCM observations were linked with DSC signals to optically identify present phase stabilities. Particularly at [pct P] < 1, significant differences between performed measurements and calculated phase equilibrium temperatures using thermodynamic assessments from the literature were identified. In all ternary sections, the experiments indicate less influence of P on the hypo-peritectic range compared to the thermodynamic calculations.

Abstract:The formation of nonmetallic inclusions in the solidification process can essentially influence the properties of steels. Computational simulation provides an effective and valuable method to study the process due to the difficulty of online investigation. This paper reviews the modeling work of inclusion formation during the solidification of steel. Microsegregation and inclusion formation thermodynamics and kinetics are first introduced, which are the fundamentals to simulate the phenomenon in the solidification process. Next, the thermodynamic and kinetic models coupled with microsegregation dedicated to inclusion formation are briefly described and summarized before the development and future expectations are discussed.

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Different alloying concepts to trace deoxidation products, mainly aluminium oxides, using rare earth elements (REEs), were tested on the laboratory scale by melting trials with a high-frequency remelting furnace. Lanthanum and Cerium, which belong to the group of light REEs, were used for these experiments. The formed multiphase inclusions were characterized by scanning electron microscopy with energy dispersive spectroscopy. Concerning the higher atomic numbers of REEs, traced non-metallic inclusions (NMIs) seem brighter than the steel matrix compared to deoxidation products. REE-traced aluminium oxides showed a primarily heterogeneous and almost globular morphology. The mean equivalent circle diameter of REE-containing NMIs is for all trials similar and is about 2 µm. The experimental results pointed out that the recovery rates of the various alloying concepts differ only slightly. In contrast, the values mainly depend on the surface-tovolume ratio and the amount of oxygen in the melt.

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.

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The Arvedi ESP process and a variety of produced materials have been continuously developed since the opening of the Arvedi ESP plant in Cremona in 2009 to meet market demands for more sophisticated steel grades. The development of grades for more advanced applications such as advanced high strength steels and multiphase grades is of interest. Dual phase grades such as DP600 are already produced through an ESP line on an industrial scale; additional multi-phase grades such as TRIP are under development. High-strength steels for the automotive industry have especially high demands on material properties. In addition to the mechanical material properties, an excellent surface quality is required. The fundamental basis for such material properties on rolled coils needs to be provided from continuous casting. This paper deals with the classification of different – either Si - or Al-based – alloying concepts for TRIP steels with respect to their prospective behaviour in a thin slab caster.