The dissolution of amorphous SiO 2 particles in CaO-Al 2 O 3 -SiO 2 slags was investigated at 1450°C by high-temperature confocal scanning laser microscopy (HT-CSLM) and thermodynamic/kinetic analyses. The SiO 2 particles used in this experimental study had a spherical form so that any rotation of the particle did not cause errors in the determination of the particle size during the dissolution. Moreover, a wide composition range of the slag could be chosen without forming any solid reaction layer which could distort the evaluation of the dissolution mechanism. The evolution of the diameter of the spherical SiO 2 particle was measured by image analysis of pictures obtained from the HT-CSLM. It was found that the dissolution curve of the SiO 2 particle (size as a function of time) exhibited either a parabolic-like curve or an S-shaped curve depending on the slag composition. The patterns were compared with a well-known shrinking core model (SCM), and it was shown that the SCM could not represent the dissolution behavior of the SiO 2 particle observed in this study. It was experimentally found that the shape of the dissolution curves varies as a function of the slag composition. The curve exhibited a parabolic-like shape for low SiO 2 -containing slags and changed to an S-type shape with increasing SiO 2 concentration in the slag. To elucidate the dissolution mechanism, a model based on approximations for the diffusion near the particle was proposed by modifying the previously available model [M. J. Whelan, Met. Sci. J., 3, 95-97 (1969)]. From the experimental data and the model calculations, the viscosity of the slag was shown to be the major factor affecting both dissolution rate and mechanism. Effective binary diffusion coefficients were estimated using the model and experimental data. Those were shown to be in the range of literature data.
Acicular ferrite is a microstructure nucleating intergranularly on non-metallic inclusions and forming an arrangement of fine, interlocking grains. This structure is known to improve steel properties, especially steel toughness, essentially. The formation of acicular ferrite is mainly affected by steel composition, cooling rate, inclusion landscape and austenite grain size. In recent decades, extensive research has been conducted to investigate these factors. The present paper provides an overview of the impact of published results and the state of knowledge regarding acicular ferrite formation. Special attention is paid to the effect of carbon, manganese and titanium addition to steel, as well as the optimum size, number and composition of non-metallic inclusions. In addition, the reactions during the nucleation and growth of acicular ferrite needles are briefly addressed. Further, characteristics of acicular ferrite and bainite are summarized, which should help to distinguish these similar structures.
High temperature confocal scanning laser microscopy (HT‐CSLM) is used to study the dissolution behavior of Al2O3 inclusions in various slag compositions in the system CaO‐Al2O3‐SiO2‐MgO. This method enables the in situ observation of the dissolution at steelmaking temperatures. The change of the diameter of the spherical inclusion is measured by image analysis of pictures obtained from the HT‐CSLM. Subsequently, dissolution rates and normalized dissolution curves are determined, and the governing dissolution mechanism is identified by the use of a modified approach of the diffusion equation introduced by Feichtinger et al. and compared with the dissolution of SiO2 previously reported by the same authors. Finally, effective binary diffusion coefficients are calculated. Slag viscosity is shown to essentially affect the dissolution behavior, changing the normalized dissolution pattern from rather S‐shaped (high slag viscosity) to a parabolic form (low slag viscosity).
A comprehensive model was developed to simulate manganese sulfide formation during the solidification of steel. This model coupled the formation kinetics of manganese sulfide with a microsegregation model linked to thermodynamic databases. Classical nucleation theory and a diffusion-controlled growth model were applied to describe the formation process. Particle size distribution (PSD) and particle-size-grouping (PSG) methods were used to model the size evolution. An adjustable parameter was introduced to consider collisions and was calibrated using the experimental results. With the determined parameters, the influences of the sulfur content and cooling rate on manganese sulfide formation were well predicted and in line with the experimental results. Combining the calculated and experimental results, it was found that with a decreasing cooling rate, the size distribution shifted entirely to larger values and the total inclusion number clearly decreased; however, with increasing sulfur content, the inclusion size increased, while the total inclusion number remained relatively constant.
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