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ispartof: ISIJ INTERNATIONAL vol:62 issue:8 pages:1573-1585 status: published

ispartof: ISIJ INTERNATIONAL vol:61 issue:9 pages:2400-2409 status: published

ispartof: ISIJ INTERNATIONAL vol:61 issue:5 pages:1357-1362 status: published

Surface active elements in liquid steel may affect the morphology of non-metallic particles during deoxidation. The effect of Te on the morphology of alumina particles was therefore studied by adding Te to molten iron before Al deoxidation at 1873 K. Dendritic, spherical, faceted, plate-like and clustered particles were identified in all samples. Te, however, considerably changes the rela-tive frequencies of the morphologies, decreasing the amount of dendritic and spherical particles whereas increasing the amount of faceted and plate-like particles. This effect is closely related with the supersaturation degree, stirring, and Te content. The way Te influences the morphology of the alumina particles and the factors influencing Te effectiveness are discussed. ispartof: ISIJ INTERNATIONAL vol:59 issue:9 pages:1529-1536 status: published

Traditional techniques of inclusion size determination are time consuming and cannot be implemented for on-line quality control. With the development of pulse discrimination analysis – optical emission spectroscopy (PDA-OES), the on-line determination of inclusions has become possible. However, PDA-OES measures only the number of inclusions present in the steel irrespective of size. In the present paper, the potential of PDA to determine the inclusion size is evaluated by employing two methodologies: (i) obtaining the average inclusion size by dividing the difference of total and soluble aluminium concentration by the number of Al based inclusions for 200 industrial ULC heats and (ii) measuring the Al concentration for individual peak intensity for specific heats, giving the inclusion size distribution. The methodologies of inclusion size measurement by PDA-OES as well as the possible causes of the discrepancies obtained after comparison with the inclusion extraction technique are explained in detail.

The phenomena taking place at the early stage of Al deoxidation were investigated with specific attention on the formation of Al2O3 inclusions. In a quartz tube, Al was exposed to liquid Fe containing different amounts of dissolved oxygen ((O) under bar) for 1, 5, 30 and 60s. In this paper, quenched microstructures of the diffusion couple were examined to identify the interactions and the nature of the phases at the experimental temperature. They revealed that the reaction zone was composed of successive layers of Fe-Al intermetallic compounds, as predicted by the phase diagram of the system, i.e. alpha Fe(Al), FeAl, FeAl2, Fe2Al5 and FeAl3. Based on the microstructure, the concentration profiles, diffusion processes in solid and liquid phases, and the behavior of Al2O3 inclusions in the reaction zone, it was demonstrated that the reaction zone was completely liquid and that the solid Fe shell melted for the samples with holding time of 30 and 60 s.

The process of Al deoxidation and Ti alloying during RH degassing treatment was studied under an Ar atmosphere at secondary steelmaking temperature (1600—1650°C) in an induction furnace equipped with an oxygen probe and a steel sampler. The formation of inclusions during partial Al deoxidation and Ti addition, and the reduction of Ti–Al–O inclusions by second Al addition are discussed using thermodynamic calculations. Specific attention is given to inclusion size and the compositional relation between the inclusions and the steel. The combination of experimental and calculated results shows that, in order to prevent Ti oxidation in liquid steel, it is essential to control [Al] in liquid steel to a level of approximately 200 ppm prior to Ti addition to achieve around 500 ppm [Ti] with minimal Ti loss during the alloying process.

The Mn and Cr equilibria between a Mn rich stainless steelmaking slag (CaO–SiO2–MgOsat.–MnO–CrO1.5) and Fe–Cr–Mn stainless steel were investigated in a temperature range from 1823 to 1873 K under Ar atmosphere. The partition ratios LMn and LCr between liquid slag and steel were determined as a function of slag composition and temperature. By combining the experimental results with thermodynamic calculations, it was found that, as basicity increases, LMn decreases, while LCr increases. The elevated basicity leads to a high MnO activity coefficient. On the other hand, the CrO1.5 activity coefficient decreases with higher slag basicities. The influence of MnO and CrO1.5 contents on the activity coefficients was also considered. It is concluded that in order to maximize Mn recovery during high Mn stainless steel production, a basic slag with a high MnO activity coefficient must be employed whereas high temperatures should be avoided.