CO₂ Ultimate Reduction System for Cool Earth 50 (COURSE50) successfully carried out operational trials with an experimental blast furnace in which the effect of the reaction-control by COG (Coke Oven Gas) injection, top gas recycling, and use of high reducibility sinter on the carbon rate were determined. The conditions of the operational trials were designed by applying the mathematical blast furnace model that was developed. The results obtained in the operational trials indicate that the proportion of carbon direct reduction can be decreased while maintaining that of CO reduction, by the reaction-control by COG injection, top gas recycling, and use of high reducibility sinter. A reduction in the carbon rate of approximately 10% was achieved as predicted by the mathematical blast furnace model.

A new and efficient process for hot metal pretreatment using convertor was developed in which the whole amount of dephosphorization slag at the preceding charge was left in the convertor and hot-recycled to the following charge, incorporating intermediate deslagging after desiliconization period. In this process, it is necessary to avoid rephosphorization from phosphorus-containing slag. In this study, a series of plant trial was carried out and the change in phosphorus content of hot metal was investigated. During the desiliconization period, rephosphorization or dephosphorization was observed depending on the slag basicity. Rephosphorization occurred under the condition such that the slag composition corresponds to the coexistence of CaO·SiO₂ (CS) and liquid slag (L), provided that the slag is almost considered as [CaO-SiO₂-FeO] ternary system. On the other hand, dephosphorization proceeded under the condition such that the slag is saturated with 3CaO·2SiO₂ (C₃S₂) amd/or 2CaO·SiO₂ (C₂S) based on the ternary diagram. According to the available data, phosphorus distribution ratio in 3-phase coexistence of CS+C₃S₂+L and C₃S₂+C₂S+L are in the order of 10³–10⁴, while it decreases lower than 10² in CS+L region. The range of slag basicity for such a high phosphorus distribution ratio is strongly affected by FeO content in the slag. Taking into account of kinetic advantages as well as equilibrium aspects, an optimum FeO content is discussed and proposed to be around 15 mass%, for preventing rephosphorization from the recycled slag and also for proceeding phosphorus removal sufficiently in the commercial operation.

Cold tool steels contain relatively larger amount of C and Cr to utilize carbide for increase of hardness and wear-resistance. However, in the large-scale ingots, coarsening of carbides caused by microsegregation would degrade steel properties. Also, micro-porosity generated during ingot casting affects the risk of cracking and the occurrence of unclosed defects in the subsequent forging process. Therefore, it is important to predict and control its occurrence. In order to investigate the effect of solidification conditions on the formation of carbides and micro-porosity of 8Cr type tool steel (Fe-1C-8Cr-2mass%Mo), unidirectional solidification experiment with different solidification conditions were conducted. As a result, primary carbides in the interdendritic zone were formed and estimated to be M₇C₃ and M₆C. The distribution coefficients were analyzed using random sampling method. The solid fraction, at which dendrite growth terminated and carbides began to crystallize, changed to higher solid phase fraction as the pull-down speed decreased. G/√R was calculated using the temperature gradient G and cooling rate R, and the relationship between the micro-porosity area fraction was investigated. The results showed that porosity occurrence was minimal in the range of 1.6 to 7.0 (K-s)^1/2/mm. In the larger range of G/√R, the porosity formation is considered to be caused by insufficient supply of liquid phase due to higher solid phase ratio and lower permeability to the final solidification zone when the eutectic phases start to crystallize.

Functionally graded materials (FGMs) have been actively researched owing to their potential applications in aerospace, biomedical engineering, sensing, and energy. FGMs exhibit locally different properties because they are manufactured from multiple materials. Recently, mechanical processing has been utilized to produce FGMs, during which the plastic strain induced by burnishing causes hardening of the surface and increases the compressive residual stress. In our previous study, we reported that the component of shot peening media diffused to the shot-peened surface during hot-shot peening. Hot-shot peening can be used to control the local material composition, while shot peening, which induces plastic deformation, can be used to improve the mechanical properties of the material. The two effects of hot-shot peening can be combined to produce FGMs. The results of this study showed grain refinement and work hardening at 0.25 mm in the hot-shot-peened surface. A tensile residual stress was observed on the bare surface, whereas a high compressive residual stress was observed on the hot-shot-peened surface. A media component diffused layer was not observed on the bare surface, although it was observed on the high-injection air pressure hot-shot-peened surface. Furthermore, a diffusion layer with a larger media component was observed on the hot-shot-peened surface in which the grain boundaries had increased. This was due to the dynamic recrystallization induced by the hot-shot peening process. Thus, the media component diffused layer observed on the hot-shot-peened surface can be grow thicker by increasing the number of grain boundaries.