Yindong Yang

Evaluation of B2O3 as replacement for CaF2 in CaO–Al2O3 based mould flux

In order to develop low fluoride or fluoride free CaO–Al2O3 based mould flux for casting high aluminium steel, an investigation was carried out to study the effect of substituting CaF2 with B2O3 on heat transfer and crystallisation behaviour of CaO–Al2O3 based mould flux by employing a heat transfer simulator of mould flux and a single hot thermocouple technique. The results showed that addition of CaF2 promoted heat transfer of CaO–Al2O3 based mould flux, which was opposite to the effect of CaF2 on heat transfer in conventional CaO–SiO2 based mould flux. Addition of CaF2 inhibited crystallisation of CaO–Al2O3 based mould flux by lowering the start crystallisation temperature and prolonging the incubation time of crystallisation. B2O3 showed similar effects to CaF2 on heat transfer and crystallisation of CaO–Al2O3 based mould flux, but its ability to promote heat transfer and suppress crystallisation was stronger than CaF2. Ca3B2O6 (melting temperature 1480°C) was found as the primary crystalline phase in fluoride free CaO–Al2O3 based mould flux compared with the primary crystalline phase Ca2Al3O6F (melting temperature 1507°C) in fluoride bearing (20% CaF2) CaO–Al2O3 based mould flux.

Phosphate and sulphide capacities of CaO-CaCl2-CaF2 slags

AbstractThe phosphate capacity of CaO–CaCl2–CaF2 slags with X CaO = 0.2 and X CaCl2 + X CaF2 = 0.8 was measured in the temperature range of 1175°C to 1350°C. The activity coefficient of PO2.5 was calculated using phosphorus distribution data. The sulphide capacity was calculated from a correlation between phosphate and sulphide capacities.It was observed that the phosphate capacity increased with increasing CaF2 mole fraction and decreasing temperature. At 1200°C the log γPO2.5 decreased from −9.7 in a CaO–CaCl2 binary slag to about −10.4 in a CaO–CaCl2–CaF2 ternary slag. The effect of temperature on log −PO2.5 was observed to be smaller than the experimental error. A linear relationship between phosphate and sulphide capacities and optical basicity was observed at different temperatures.

Dimensionless Analysis and Mathematical Modeling of Electromagnetic Levitation (EML) of Metals

Electromagnetic levitation (EML), a contactless metal melting method, can be used to produce ultra-pure metals and alloys. In the EML process, the levitation force exerted on the droplet is of paramount importance and is affected by many parameters. In this paper, the relationship between levitation force and parameters affecting the levitation process were investigated by dimensionless analysis. The general formula developed by dimensionless analysis was tested and evaluated by numerical modeling. This technique can be employed to design levitation systems for a variety of materials.

Applications of Electromagnetic Levitation and Development of Mathematical Models: A Review of the Last 15 Years (2000 to 2015)

Electromagnetic levitation (EML) is a contact-less, high-temperature technique which has had extensive application with respect to the investigation of both thermophysical and thermochemical properties of liquid alloy systems. The varying magnetic field generates an induced current inside the metal droplet, and interactions are created which produce both the Lorentz force that provides support against gravity and the Joule heating effect that melts the levitated specimen. Since metal droplets are opaque, transport phenomena inside the droplet cannot be visualized. To address this aspect, several numerical modeling techniques have been developed. The present work reviews the applications of EML techniques as well as the contributions that have been made by the use of mathematical modeling to improve understanding of the inherent processes which are characteristic features of the levitation system.

Electromagnetic Levitation of Silicon and Silicon-Iron Alloy Droplets

Abstract In this paper, the design of an electromagnetic levitation system and a technique for non-conductive silicon heating and conductive silicon levitation is described. The aim of the work is to describe the various parameters including coil design, applied power and specimen weight that govern the temperature of levitated silicon and silicon-iron alloy droplets.

Recovery of iron from waste slag of pyrite processing using reduction roasting magnetic separation method

Abstract A considerable amount of waste slag from the pyrite roasting process is produced every year. Recovery of iron from the waste slag is of great interest for maximum use of mineral resource, reduction of environment impact and improvement of economical benefits to the related companies. The objectives of the present work are focused on: compare various options for recovery of iron from the waste slag and select the most advantageous option for industrial trial which is roasting of the waste slag under reducing condition followed by magnetic separation; investigate the optimum conditions for maximum recovery of iron from the waste slag. The experimental results show that under the treatment condition in this work about 70% of the iron was recovered from the waste slag, where the iron content in the concentrate is 57%. After the further treatment with chlorinated segregation–magnetic separation, the iron content in the recovered slag can reach 83%. After the treatment, sulphur content in the concentrate was reduced significantly and gangue materials, such as SiO2, Al2O3 and TiO2, were reduced effectively. This paper is mainly focused on the results of reduction roasting–magnetic separation. À chaque année, on produit une quantité importante de déchets de scorie provenant du procédé de grillage de la pyrite. La récupération du fer des déchets de scorie est d’un grand intérêt pour l’utilisation maximale de la ressource minérale, pour la réduction de l’impact sur l’environnement et pour l’amélioration des bénéfices économiques des compagnies associées. Les objectifs de ce travail sont centrés sur: la comparaison des diverses options de récupération du fer à partir des déchets de scorie et la sélection de l’option la plus avantageuse pour un essai industriel incluant le grillage des déchets de scorie avec réduction, suivi par la séparation magnétique; l’examen des conditions optimales d’une récupération maximale du fer à partir des déchets de scorie. Les résultats expérimentaux montrent qu’avec les conditions du traitement au cours de ce travail, on a récupéré environ 70% du fer à partir des déchets de scorie, où la teneur en fer dans le concentré était de 57%. Après un traitement additionnel par ségrégation chlorée–séparation magnétique, la teneur en fer dans la scorie de recouvrement pouvait atteindre 83%. Après le traitement, la teneur en souffre dans le concentré était réduite significativement et les matériaux de la gangue, comme le SiO2, l’Al2O3 et le TiO2, étaient effectivement réduits. Cet article se concentre principalement sur les résultats du grillage réducteur et séparation magnétique.

Distribution of macro-inclusions in low carbon aluminium-killed steel slabs

ABSTRACT Macro-inclusions in low carbon, aluminium-killed steel slabs were characterised by step-machining within a 10 mm zone from the slab surface using an ASPEX automatic inclusion analyzer. Dendritic structures within the cross-section of slabs were examined. The results show that alumina clusters and alumina associated with bubbles are the dominant macro-inclusions. Along the slab width direction, macro-inclusions were mostly found at the slab centre because of the deeper hooks and freezing meniscus surrounding the submerged entry nozzle. In terms of slab thickness, inclusions were mainly concentrated within the zone 3.5–6 mm from the top of the slab surface, where the columnar dendrites showed a relatively small inclination angle, indicating small cross-flow velocities at the solidification front. The number density of macro-inclusions were strongly dependent on the washing effect produced by the flow velocity. High speed casting promotes this behaviour and improves the surface quality of the slabs.

Formation and evolution of macro inclusions in IF steels during continuous casting

The evolution of macro inclusions during continuous casting was investigated by large-area inclusion characterization using ASPEX and analysis of nozzle blockage deposits. Six kinds of inclusions over 5 μm were observed in samples taken from the tundish and the slabs: single alumina particles, alumina dendrites, refractory-related alumina, alumina associated with bubbles, alumina clusters and Al–Ti complex oxides. By examining the morphology of the nozzle blockage deposit, it was concluded that the refractory-related alumina in the slabs came from the decarburization layer washed away by the steel stream. Some of the alumina clusters that came from the nozzle blockage deposit dislodged by the steel flow, were formed by the agglomeration and sintering of 5–20 μm inclusions that were carried over from the tundish. Two kinds of Al–Ti oxides were found in the tundish, and their evolution mechanisms during the casting process were proposed.

Flow pattern control in continuous slab casting moulds: physical modelling and plant trials

Full-scale water modelling studies combined with nail-dipping industrial trials at Shougang Jingtang (SGJT) Works were carried out in order to investigate the parameters that influence flow patterns in the continuous slab casting mould. The effects of casting speed/mould width combinations, argon bubbling flow rates, submerged entry nozzle (SEN) immersion depths and SEN geometries (port angle and bottom shape) on the flow patterns were examined. A CMI factor defined as casting speed/mould width ratio index is put forward to describe the combined effect of these parameters on the fluid flow patterns in the mould. The results show that the CMI and argon injection rates are the dominant factors that determine the flow pattern. On the basis of the results from this study, critical argon flow rates for different casting combinations have been evaluated. These findings provide operating guidelines for generating optimal flow patterns based on double roll flow with appropriate surface velocities in continuous slab casting moulds. On the basis of these considerations, slab quality at SGJT Works was substantially improved and the percentage of flow pattern-related sliver defects in cold rolled products was decreased from 4.5 to 2.3%.

Inclusion characteristics and microstructure properties under different cooling conditions in steel with nanoparticles addition

ABSTRACT In the present study, the experimental steel containing nanoparticles was manufactured and then cooled to room temperature under different cooling rates. The differences on the inclusion characteristics and microstructure morphologies between the original steel and experimental steel were compared. The results revealed that the majority of reaction products in the experimental steel were Al2O3–MgO-bearing hybrid inclusions. These inclusions under brine quenching, and water quenching had large potential for inducing intra-granular acicular ferrites (IAF). Hence the microstructure in the experimental steel mainly consisted of fine IAF. For the original steel, SiO2–MnO–MnS-based inclusions could hardly induce IAF, and the microstructure consisted of relatively larger intra-granular banded ferrites, and intra-granular polygonal ferrites. The differences on microstructure morphologies between the two steels had a correlation with the inclusion composition, and size. These were the primary factors to determine whether a particular type of inclusion could induce IAF effectively or not.