The conditions of deposition of alumina and metal on ZrO2-CaO-C refractory have been investigated in comparison with Al2O3-C refractory by laboratory scale test. The results are summarized as follows: (1) When aluminum content is low, or amount of alumina inclusions are little, ZCG refractory is more hardly to be deposited than AG, as is reported before. On the contrary, ZrO2-CaO-C refractory was more easily deposited than AG in the case of some level of aluminum content and non-metallic inclusions. (2) The deposition may be composed of two steps. The first is the formation of a fine oxide layer (the network alumina) in the hot face during the very short time after immersion. The second is the deposition of non-metallic inclusions on the fine oxide layer. (3) The generation mechanism of the fine oxide layer is due to the reaction between aluminum in the molten steel and the next substances. (1): SiO2 in the refractory, (2): SiO cand CO gases generated by the reaction between SiO2 and graphite in the refractory, (3): ZrO2 in the refractory. Concerning to ZrO and CO gases generated by the reaction between ZrO2 and graphite in the refractory, more detail study is necessary to clarify the contribution to the reaction.
Equilibrium between CaO-Al2O3-TiOx or BaO-Al2O3-TiOx slags and a liquid Fe-20 mass%Cr alloy with respect to oxygen and nitrogen was studied at 1873 K as a function of Ti (or Al) content in alloys, using an Al2O3 crucible. The Al-O and Ti-Al relations in liquid alloy were studied, and nitride capacity defined by CN=(mass%N)·PO23/4/PN21/2 was obtained from nitrogen distribution ratios, coupled with the analyzed oxygen content in liquid alloy or the PO2 determined by Ti/TiO2 equilibrium. Based on these results, activity of Al2O3 and activity coefficients of TiO2, TiO1.5 and CrO1.5 were evaluated.
Sheet and coated steel have been demanded to meet quality requirements of ever increasing severity in recent years. Reduction in nonmetallic inclusions is an important challenge in this respect. Protection on the molten steel in the tundish against contamination is of special importance in not only improving steel product quality, but also avoiding immersion nozzle clogging and increasing the number of sequence-cast heats. To supply molten steel with high cleaniliness in a stable manner, the cleaning behavior of the molten steel in the tundish was investigated and mechanism whereby the molten steel is kept clean in the tundish was quantified. Based on the results achieved, technology was studied for keeping the molten steel clean in the tundish.
The sulphide capacity as originally defined by Fincham and Richardson is a strong function of composition in pseudobinary oxide melts of interest in extractive metallurgy. From an analysis of data available in the literature, it is shown that sulphide capacity is directly proportional to the activity of the basic oxide in the melt, within the uncertainty of experimental data. A single parameter is sufficient to describe the sulphide capacity of a binary slag system under isothermal and isobaric conditions. The correlation indicates that the activity coefficient of the sulphide ion or the neutral base metal sulphide dissolved in the melt is independent of composition in pseudobinary melts within experimental uncertainty. Structural variations in the melt with composition do not seem to affect the activity coefficient of the sulphide. A modified sulphide capacity function is defined which makes the treatment more elegant and greatly simplifies data storage and retrieval. The modified function is not based on any model for the melt.
A water model is used to investigate the effect of imparting a swirl flow in the entrance region of a nozzle. The study is aimed at the injection region of continuous casting process. The purpose is to make the injection velocity more uniform and so reduce the disturbance of the free surface. It was shown using the water model that a uniform outlet flow could be obtained by imposing a swirling flow pattern in the entrance region of a divergent nozzle. This suggests that the outlet flow pattern in a continuous caster may be controlled by introducing swirl flow in the molten metal using an externally imposed magnetic field.
A numerical model is used to study the flow pattern in an immersion nozzle of a continuous casting mold with swirl flow imposed in the pouring tube. Comparison is made between the numerical results and those measured in a water model described in the preceding paper. The good comparison gives confidence in the model so that it can be extended to a more realistic steel system. The maximum velocity at the outlet of the nozzle with swirl is reduced significantly in comparison with that without swirl. In addition, the mechanism for obtaining the uniform velocity profile at the nozzle outlet was correlated with the flow pattern of the nozzle and the strength of the swirl. This is also done for a system in which swirl is generated by a rotating magnetic field imposed on the pouring tube. The model shows how the flow of steel form the nozzle may be modified using such a system. Such a swirling flow can provide a uniform, low velocity at the nozzle exit, which may be highly desirable for continuous casting purposes.
Morphology, size and distribution of II-type manganese-sulfide are investigated taking steel-dendrite structures into account. Quantitative relationships between solidification conditions and steel-dendrite morphology are discussed first, based on steady state uni-directional solidification experiments. A new idea is proposed as Solidification-Unit-Cell, which is applied to a numerical treatment of relationship between dendritic structure of manganese-sulfide inclusions and solidification conditions. Diameter of dendritic II-type manganese-sulfide rods is correlated to a solidification parameter: R-mG-n which originally is related to steel-dendrite arm spacings, whereas stretches of the inclusions are related to the size and shape of residual melt pool, and amounts of constituent elements supplied thereinto.
The red scale, which is one of the major defects on hot-rolled Si added steel sheets, is reproduced experimentally. On the basis of detailed observation of the scale properties, we propose the mechanism of formation of the red scale. Imcomplete descaling of FeO prior to hot rolling causes red scale formation even in Si-free steels, since the reaction from FeO to Fe3O4 and red Fe2O3 is largely accelerated by the breakage of the FeO scale. In Si-added steels, descaling is quite difficult to perform, because the eutectic compound of FeO/Fe2SiO4 is formed at the scale/steel interface and penetrates irregularly into both upper FeO and lower steel sides. Quite high strength of the eutectic compound, even just below the solidus temperature of 1173°C, can also make it difficult to descale.
Damping capacity in an Fe-27Mn-3.5Si alloy has been greatly improved with significant anisotropy by cold-rolling. The alloy, consisting of stacking faults and thermal ε martensite before rolling, shows poor damping capacity at low strain amplitude and strong amplitude dependence. The increase and anisotropy in the damping capacity are attributed to ε martensite induced by cold-rolling. The alloy is found to adjust itself to the deformation by forming ε martensite which has a preferred orientation of (1013)ε ε. The mechanism of formation of the preferred orientation can be explained by the shear model in γ→ε transformation. With the result of microstructure and preferred orientation, a damping mechanism by ε martensite and its anisotropy is discussed.
The tempreature of no-recrystallization, Tnr, was measured by means of laboratory torsion rests for three low carbon steels. The Tnrvalues for these steels were also established from rolling mill log data obtained from the Algoma plate mill; these were found to be virtually identical to those from torsion tests. The mill log calculations were carried out by organizing the Sims roll force equations into a spreadsheet software for desktop personal computers. The results of both the torsion testing and mill log calculations compare well with previously developed correlations between Tnrand the chemical composition, and between Ar3 and the composition. It was also found that the overall levels of the mean flow stresses calculated from the mill logs are close to those determined from torsion testing. This excellent agreement confirms that laboratory torsion testing can provide a convenient and very effective simulation of industrial hot rolling operations.