In recent years, the reduction of CO2 emissions and the stable supply of raw materials are two major issues for the steel industry. Low reducing agent operation in the blast furnace is required to reduce CO2 emissions in ironmaking. As a mean of realizing low reducing agent operation with using low-grade raw materials, ferro coke characterized by high coke reactivity is considered to be useful. Theoretical and experimental studies were carried out to verify the effect of the ferro coke usage on reaction behavior in blast furnace. Investigation of CO2 reactivity at the simulated blast furnace condition revealed that the initial temperature of CO2 reaction of ferro coke is lower than the temperature of conventional coke. At the temperature of over 1100°C, the deterioration of ferro coke strength after reaction was depressed because the reaction occurred preferentially at the surface of the ferro coke. The coke and ferro coke strength after reaction was estimated based on the experimental results with the two-dimensional mathematical model of the blast furnace. The average coke strength of ferro coke and conventional coke with charging of ferro coke (100 kg/t) was little less than the coke strength without ferro coke charging. It is predicted that the carbon saving with charging of ferro coke (100 kg/t) is about 6% in comparison to without ferro coke charging.
JFE Steel Corporation developed the hydrogen-based gas fuel injection technology for sintering machines to improve sinter quality without increasing coke breeze ratio. With the technology, it is possible to extend the temperature zone between 1200°C and 1400°C by injecting the gaseous fuel from the top surface of the sintering machine as a partial substitute for coke breeze. Theoretical and experimental studies were carried out to verify the effect of the gaseous-fuel injection technology on pore structure in the sinter cake with the X-ray CT scanner and sintering pot test. It is important to hold the temperature between 1200°C and 1400°C in order to produce high strength and high reducibility sinter. The liquid phase ratio can be increased with extending the proper temperature zone by applying the gaseous fuel injection technology. The increase in liquid phase ratio promotes the combination of pores (1–5 mm) and sinter strength is improved. At the same time, the pores over 5 mm growth are promoted and the permeability is improved in the sintering bed. Moreover, the low-temperature sintering process depresses the iron ore self-densification. Micro pores under 1 μm remain in unmelted ores and improve sinter reducibility. As a result, the technology enables to improve the pore structure in the sinter cake and sinter quality. The technology was put into commercial operation at Keihin No. 1 sinter plant in January 2009 and stable operation has continued up to the present. As a result, the energy efficiency in the sintering process is greatly improved, and it has been achieved to reduce CO2 emissions by a maximum of approximately 60000 t/year at Keihin No. 1 sinter plant.
Cold model experiments are carried out to understand the spout eye area in a cylindrical bath agitated by bottom gas injection. Low-density particles are used for slag to investigate the effect of a density ratio of molten slag to molten steel on the spout eye area. The spout eye area increases with a decrease in the density ratio and is governed by the same modified Froude number as that proposed for a silicone oil and mercury system. An empirical equation is proposed for the spout eye area.
Nitrogen solubility and rate of nitrogen absorption and desorption in High Cr Steel under Pressurized Atmosphere were investigated using pressurized directional solidification furnace. In this study, melting experiments were performed under maximum 1.0 MPa gas condition. It was found that nitrogen solubility was deviated from Sieverts'Law over 0.60 mass% nitrogen contents in molten high Cr steel. It was assumed that this phenomenon was not caused by high nitrogen partial pressure but by high nitrogen content in molten high Cr steel. In this study, 1st and 2nd order nitrogen interaction parameters were estimated. And calculated results using estimated parameters were suitable to explain nitrogen solubility of molten high Cr steel. Nitrogen absorption rate was almost same in same nitrogen partial pressure even if total pressure was different. In this study, the apparent mass transfer coefficient in liquid phase of high Cr steel at 1823K was estimated approximately 8.8×10−5 (m·s−1). Nitrogen desorption rate was decreased with increase in total pressure or nitrogen partial pressure. It was indicated that mixed control model of gas phase mass transfer and chemical reaction at gas/liquid interface could be applied to explain nitrogen desorption reaction of molten high Cr steel under pressurized atmosphere.
Oil-in-water (O/W) emulsions are widely used in tandem cold rolling mills as coolants in order to reduce frictional forces and prevent heat scratches. Although the lubricating properties of O/W emulsions are determined by various factors, two particularly important ones are the amount of plate-out oil on the strip surface and the dynamic concentration mechanics of the emulsion at the inlet of roll bite, which has been a subject of much interest since the 1970s. As many studies have focused only on a single phenomenon, it is important to simulate the interaction of the two phenomena as it occurs in actual cold rolling. In this paper, first, a new method of evaluating the relationship between plate-out oil and lubrication characteristics is proposed, which enables control of plate-out oil before rolling. It was found that rolling force decreased when a plate-out oil film was formed before rolling, but the reduction of rolling force was saturated when the amount of plate-out oil exceeded a certain level. The influence of roughness, the roll coolant, and other factors was also examined using the proposed method. In particular, in tandem cold rolling, it is necessary to consider the influence of plate-out oil carried over by the preceding stand on the lubrication characteristics of the following stand. The results of this research suggest that it is possible to clarify the mechanism of emulsion lubrication using the proposed method.