The effects of temperature (1373-1673 K) and oxygen potential on removal of sulfur from hot metal desulfurization slag were investigated in laboratory-scale experiments. Both CaS and CaSO4 exist as sulfur compounds in hot metal desulfurization slag. CaS can be removed under the condition of higher oxygen potential, whereas CaSO4 can be removed at a lower oxygen potential. Thus, in order to remove both CaS and CaSO4 from desulfurization slag, it is important to control the temperature and oxygen potential to the optimum values. In this study, a higher sulfur removal ratio exceeding 90% was obtained under the conditions of a temperature range of 1473-1673 K and oxygen potential range of 10–3-10–8 atm. These results were in good agreement with thermodynamic calculations.
In order to confirm the possibility of reusing desulfurization slag as flux after sulfur removal, hot metal desulfurization experiments were carried out with a 70 kg-scale laboratory furnace. At the same CaO amount in the desulfurization flux, [S] content at 900 seconds after flux addition was approximately equal to that when using virgin flux. The effect of SiO2 contamination due to slag recycling on the desulfurization rate constant K was also estimated.
From these experimental results, it may be suggested that removal of sulfur from desulfurization slag is an effective approach for constructing a slag recycling system.
In the continuous casting of steel, the state of the mold flux plays a significant role in the quality of the steel as well as the casting operation. In this study, the state of the mold flux was estimated by measuring the friction force of mold oscillation and establishing a lubrication model. The friction force was measured with a slab caster equipped with hydraulic oscillators, and the relationship between the friction force and continuous casting factors such as the mold oscillation conditions, mold flux properties and casting speed was investigated. The main results are summarized as follows.
(1) The friction force was proportional to the relative velocity of the slab to the mold. The lubrication condition became fluid lubrication when the value of the casting speed was higher than 1.4 m/min.
(2) The temperature dependence of viscosity was measured with a rotation viscometer. Employing the measured values, a new fluid lubrication model, which considers the temperature dependence of viscosity, was established. Using the model, the lubrication layer thickness was estimated as being approximately 50 μm.
(3) The heat transfer of the mold flux was also evaluated by using the developed lubrication model. The thermal resistance of the air gap and the solidified flux layer was successfully estimated by applying the model. As a result, the resistance of crystallized flux was larger than that of glassy flux.
Although the closure of defects at the center of round billets on rolling such billets is an important subject, a method of quantity evaluation for such closure has not yet been clarified. Therefore, to explain the effect of rolling conditions including grooved shape, we carried out the experiments with round billet which has an artificial defect and finite element analysis, especially with respect to the integration of the hydrostatic stress Gm. The results showed that grooved shape affected the closure of center defect, and Gm could express the relationship between closure and rolling conditions without the consideration of the difference in the ratio of defect size and roll size. However we found that original Gm could not express the influence of the grooved shape, at the same time.
This paper presents a study of the gas wiping process, which is used in coating processes to control the final coating weight applied on a substrate. The wiping process is one of the factors which limit the maximum line speed of continuous galvanizing lines (CGL). A multi-slot type wiping nozzle was proposed for improving coating weight controllability, and was investigated by numerical simulation in recent years. Here, the impinging jet characteristics of a 3-slot nozzle are investigated by experimental and numerical analysis, focusing on the jets mixing process and the impinging pressure distribution. The gas wiping capability is tested in wiping model experiments with a molten paraffin coating. It is confirmed that the impinging pressure distribution of a 3-slot nozzle with a lower auxiliary jet velocity is sharper than that of a single-slot nozzle, and this leads to a coating weight decrease. When the jet velocity of the auxiliary slots approaches that of the main slot jet, the width of the impinging pressure distribution spreads and the coating weight increases. The turbulent kinetic energy of flow field is changed by auxiliary jets velocity, and the energy distribution decide the width of mixed jet flow.
The influence of the Mn content of Si-added steel sheets on the Fe-Zn galvannealing reaction was investigated. Three steel sheets, 1.5 mass%Si-1.4, 1.9 and 2.7 mass%Mn, were annealed in a 10vol%H2-90vol%N2 atmosphere. Si and Mn oxides were analyzed by reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive X-ray spectrometry. SiO2 and Mn2SiO4 formed as selective oxides at the steel surface after recrystallization annealing. The ratio of the oxide species changed depending on the Mn content in the steel. When the Mn content was lower, formation of SiO2 was promoted and that of Mn2SiO4 was suppressed. In the selective oxide layer which formed on the surface of the 1.5 mass%Si-1.4 mass%Mn steel sheets, Mn2SiO4 formed at the outer side, and SiO2 formed at the inner side. This can be explained by consideration of the thermodynamic oxygen potential gradient. Furthermore, areas where SiO2 mainly formed and those where Mn2SiO4 mainly formed were distributed on the surface of the 1.5 mass%Si-1.4 mass%Mn steel sheets. In this case, the Fe-Zn intermetallic compound (IMC) formed preferentially on the Mn2SiO4 between the zinc coating and the substrate steel after galvanizing, and the Fe-Zn galvannealing reaction was suppressed on the SiO2 layer. It is considered that a dense and continuous protective SiO2 layer acted as a barrier to the Fe-Zn galvannealing reaction.
Work hardening of ferritic steels containing fine carbides varied from 3 nm to 15 nm was investigated and compared to Ashby’s model, which is well known as a work hardening theory of metals containing hard particles. A specific work hardening behavior was observed in the steels strengthened by the nanometer-sized carbides; work hardening proceeded in two stages within a few plastic strains. In the former step, the matrix deformed without the geometrically necessary dislocation since a misfit strain between the carbides and matrix is close to the Burgers vector. So the Ashby’s model cannot explain this phenomenon. Yet in the later stage, the amount of work hardening was close to predicted value based on the Ashby’s model. The plastic strain at which the later stage started decreased with the increase in the diameter of carbides since the geometrically necessary dislocation is easier to be generated by the larger carbides. A new model which can be applied to steels containing the nanometer-sized carbides by focusing generating dislocation into the matrix around carbides was established.
Industrial pure iron specimens with the thickness varied from 0.2 to 2.0 mm were investigated in tensile test to examine the influences of specimen thickness on elongation and deformation energy.
Conventionally, the total elongation of tensile specimen can be converted by JIS 0202-1987 formula, which is related to the tensile test specimen thickness. However, in this experiment, it was noticed that there were number of factors which led to the inaccuracy in the result. The total elongation was influenced by the stress triaxiality. According to the FEM (Finite Element Method) analysis, it showed that the stress triaxiality increased significantly with the thinner specimen, this was due to the void growth behavior, observed by SEM (Scanning Electron Microscope) under low voltage. These results revealed that voids nucleation and growth behavior influenced by the stress triaxiality were the main cause for the formula incompatibility.
After the tensile test, stress-strain curve can be obtained and categorized into the uniform and local deformation. The uniform deformation energy was not depended on the specimen thickness in contrast to duplex stainless steel of previous study. On the other hand, the local deformation energy lowered with the decrease in specimen thickness as with duplex stainless steel. These results indicated that the void nucleation and growth behavior had a significant impact on the total elongation.