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Dissimilar metal joining of aluminum to steel, which is difficult due to the formation of the brittle intermetallic compound at the interface of the welded joint, by DC pulsed MIG arc brazing in a lap joint with the flux cored Al-Si filler wire has been investigated for the application of the weight saving of automobiles. The major compound formed at the interface between steel and weld metal was determined to be Al 7.4 Fe 2 Si as the Al-Fe-Si ternary compound. The composition control of weld metal can suppress the growth of the intermetallic compound layer less than the thickness of 2.5 mm. In this condition, the transverse tensile strength of the welded joint was about 80 MPa, 70 % of that of Al base metal due to the fracture at HAZ on the aluminum side. The mechanism of the suppressed growth of the intermetallic compound layer during MIG arc brazing has been discussed.

Alkali hydrothermal synthesis of zeolite A using blast furnace (BF) slag was investigated. The preliminary experiment was conducted in use of synthetic slag consisting of SiO 2 , Al 2 O 3 , and CaO powders, and it was made clear that the most optimum slag compositions to synthesize zeolite A were the molar ratio of Si to Al (Si/Al) of 1 and reduction of CaO content down to 15 mass%, and that hydrothermal treating conditions were the temperature range from 328 to 358 K, NaOH solution of 1 M (ϭmol/L) and the ratio of the volume of NaOH solution to total mass of slag (V sol /W slag ) of 15 (mL/g). It was also found that synthetic slag with such a higher content of CaO as 40 % resulted in formation of tobermorite and hydrogarnet. In the experiment using BF slag, zeolite A could be successfully synthesized by optimizing both conditions of the compositions of raw material powders and hydrothermal treatment as noted above, where optimization of the compositions of raw material powders such as Si or Al content were performed by the suitable amount of addition of SiO 2 powder or NaAlO 2 powder as a source of Si and Al. The ball milling type reaction vessel containing numerous small SiC balls which was first adopted in this hydrothermal treating study was confirmed to be very effective for acceleration of synthetic reaction rate, shortening markedly the time period needed for fully synthesis of zeolite A. Temperature dependence of heat capacity of zeolite A powder synthesized in use of BF slag was measured after absorption of vapor at the ambient temperature, showing endothermic behavior with the peak at the temperature of around 473 K.

Decreasing the carbon dioxide emission from steel industries is an important issue. It is considered that due to the high reactivity of carbon iron ore composite, it can control the thermal reserve zone temperature and decrease the consumption of reducing agents in blast furnace. In the present study, a reaction model of the carbon iron ore composite based on a lumped system is proposed to analyze the reduction behavior in the blast furnace. This model is composed of several reaction steps between carbon, iron ore, and gas phase. The carbon solution loss reaction rate of the small particles of reducing agents is determined by the thermogravimetric method. It is found that the gasification of reducing agents is the rate-determining step in the reduction of the carbon iron ore composite. Accordingly, the particle size and reactivity of reducing agents such as coke have an influence on the reduction rate of the carbon iron ore composite. The influence of the gas composition in the atmosphere around the composite on the reduction is analyzed by using the reaction model. Moreover, the reduction behavior of the carbon iron ore composite in the blast furnace is quantitatively examined by comparison of reduction degree and gas composition change in order to investigate the reduction mechanism of reducing agents.KEY WORDS: carbon iron ore composite; mathematical model; carbon gasification; blast furnace; carbon dioxide; ironmaking. 827© 2009 ISIJ of this burden on reducing agents. Hence, this research focuses on the modeling of the carbon iron ore composite for the application to the blast furnace mathematical model and the analysis of the reduction behavior. Various reaction models of the composite have been already proposed on the basis of the concept of a discrete system with its particles exhibiting diffusion phenomena. [6][7][8] Although these models are sufficient for analyzing the reaction behavior of a single particle, they are not suitable simulating blast furnaces since these models are complicated. In the present study, a reaction model of the carbon iron ore composite based on a lumped system is proposed to examine the reduction behavior of the carbon iron ore composite. This model can be easily used for simulating blast furnaces. Moreover, the optimum structure of the carbon iron ore composite and the influence of the atmosphere on the reduction are analyzed by using the proposed model. Reaction Model of Carbon Iron Ore Composite Concept of Reaction ModelSeveral reaction models that take into consideration the gas and heat diffusions inside a composite have been proposed. These models are supposed to be used under constant temperature conditions and rapid heating conditions, e.g., in a rotary hearth furnace. The reaction model of carbon iron ore composite can be used simulating blast furnaces only if the models are simple. The heating rate and the reaction rate in a blast furnace are slower than that of a rotary hearth furnace. Therefore, the temperature distribution in the composite can be considered to be ...