2021 Tawara Award, Sawamura Award and Distinguished Article Award

In order to achieve carbon neutrality by 2050, it is necessary to significant reduce coke consumption, which is a reducing agent for blast furnaces. On the other hand, coke, which does not deform even at high temperatures, is necessary for keeping the permeability of the cohesive ore layer, and it is necessary to formulate the permeability of the cohesive layer in order to reduce coke.

In this paper, novel experiments, such as an apparatus that enables the extraction of cohesive ore layers by rapid cooling and visualization of three-dimensional gas flow paths using CT are conducted. In addition, a new permeability equation of the inhomogeneous cohesive layer was proposed by extending the permeability equation of the fluid in the circular pipe.

This research result not only contributes to blast furnace process technology, but is also excellent academically, and is considered to be a suitable paper for Sawamura Paper Award.

The microstructure of multiphase cold rolled steel sheet, such as dual Phase（DP） steel sheet and low carbon TRIP steel sheet used for automobile is mainly controlled by the transformation during the cooling process after the intercritical annealing. Although para-equilibrium theory and local equilibrium theory were proposed for explaining the transformation behavior of Fe-C-X (X: substitutional element), the analysis considering the partitioning of solute elements during intercritical annealing had never been considered.

In this paper, the authors succeeded in the two-dimensional visualization of ferrite formation from austenite in Mn, Si partitioned two-phase region by observing the distribution of solute elements including carbon. A new FE-EPMA technique enabled for highly accurate C distribution measurement. In addition, they succeeded in reasonably explaining the ferrite transformation behavior of this alloy based on the local equilibrium theory. It highly evaluated that the ferrite transformation behavior of Fe-C-Mn-Si alloy, which is basics of steel materials, was clarified theoretically.

This research clarified the importance of partitioning of solute element in ferrite transformation of low carbon steel after intercritical annealing. Furthermore, findings of this research are expected to contribute new steel material design. Accordingly, this paper is highly valuable in both academic and technical aspects and is worth of the Sawamura award.

In the ironmaking and steelmaking processes, ionic melts at high temperatures, such as slag and mold flux, have complex structures on the basis of the polarity of ionic species and electrostatic interactions, which greatly affect various physical properties of the melts. In the view of process design and its control, physical properties such as viscosity are very important, and the understanding of its mechanism is very essential from the viewpoint of accurate prediction of physical properties and new slag design.

In the case of silicate melts which are most important in ironmaking and steelmaking, some researches have reported that the substitution of oxide ions to both nitride and fluoride ions increases the viscosity, while others reported the increase by nitride ions and the decrease by fluoride ions. The effect of anion species on the viscosity has not yet been clarified. The authors selected a simple Na₂O-SiO₂ melt and precisely measured the change in viscosity by the change in the anion composition (O/N/F ratio) with the fixed cation composition (Na/Si ratio). Further, the relationship between anion composition and melt structure was clarified through MAS-NMR measurements of 29Si and 19F.

Through these studies, they concluded that the substitution of oxide ions to nitride or fluoride ions has opposite influences on the viscosity and explained its mechanism using a structural model. The results of this research will lead to a better understanding of the properties and structure of complex anion-based melts, such as mold fluxes, and will greatly contribute to the advancement of steel processing.

The accurate quantification method of the constituent phases of iron sintered ores is supposed to be developed because the important characteristics of sinters such as strength and reducibility are relevant to the microstructures. So far, the mass fractions of the phases of sinters have been calculated from the area ratios obtained by the cross-sectional observations using optical or scanning electron microscopes. However, some multi-component calcium ferrites (SFCA and SFCA-I) are difficult to distinguish using the images because the chemical compositions and densities are similar.

In this paper, the X-ray diffraction (XRD) Rietveld method has been applied to the quantification of the constituent phases of sinters. The authors have developed a correction method which enables us to calculate the mass fractions of the phases accurately even on the samples having different particle sizes and similar crystalline structures. The proposed correction method was successfully applied to the synthesized iron sintered ores composed of α-Fe₂O₃, SFCA and SFCA-I. It has been found that the mass fractions of the constituent phases can be obtained with an accuracy of ±3 mass% even when Cu Kαradiation is used as X-ray source.

The authors have theoretically and experimentally studied that the combination of XRD Rietveld analysis with the proposed correction method is applicable to the quantification of the constituent phases on vaious industrial materials with complicated crystalline phases such as sinters. The academic and industrial contribution of this paper is significant, and thus, the paper is definitely worthy of the Sawamura Award.

Microstructure and property of precipitation-strengthened Ni-based superalloys vary significantly depending on hot working temperature. It is thus necessary to accumulate the flow stress data obtained with high accuracy in relation to microstructural evolution, to predict the microstructure and property of hot-worked materials. In this paper, advanced hot compression technique that can uniformly compress workpiece under isothermal condition was developed by homogenizing the temperature distribution within workpiece and reducing the friction between ceramic tools and workpiece, and the reliability of flow stress obtained was verified. First, isothermal condition was achieved as follows. High heat-resistant alloys were placed between ceramic tools and workpiece to prevent heat from escaping to the ceramic tools. The specifications of induction heating for uniform heating of workpiece were optimized by FEM calculations coupled with deformation-temperature electromagnetic fields. Second, the friction between ceramic tools and workpiece was found to be considerably reduced by using a glass sheet as a lubricant. As a result, uniform hot compression was achieved under isothermal condition up to a high strain, and flow stress was successfully measured with a very high reliability using inverse analysis method. Furthermore, valuable finding is that flow stress can be compensated for by the inverse analysis that takes into account the increase in friction coefficient in a high strain when mica is used as a lubricant. The developed hot compression test and the obtained findings can be expected to be applied not only to Ni-based superalloys but also to various materials. Therefore, this paper is worthy for the Sawamura award.

Microstructural control of second-phase austenite is a key technology to improve the strength–ductility balance of advanced-high strength steels. In this paper, the effects of interrupted quenching (IQ) process, which is the quenching after austenitization to a temperature between Ms and Mf, on microstructural evolution during the subsequent intercritical annealing and tensile properties were investigated in medium Mn steel with 5.0Mn–1.2Si–0.1C in mass%. Microstructural characterizations proved that the interphase boundary between austenite and martensite formed via IQ process migrates in accompany with long-range Mn diffusion, and consequently, acicular austenite grains consisted of a core region with lower Mn concentration and a shell region with higher Mn concentration form during the intertrial annealing. The distributions of Mn and C predicted by a simulation for diffusion-controlled transformation under local equilibrium could explain that the core region transform into fresh martensite, while the shell one retained austenite at ambient temperature due to the austenite stability. Since the fresh martensite and the retained austenite contribute to the improvements of strength and ductility, respectively, it was concluded that the strength–ductility balance of the medium Mn steel can be optimized by IQ temperature.

From the view point of that the diffusivity of substitutional solute Mn is significantly lower than that of interstitial solute C in medium Mn steel, authors indicated the possibility of a novel microstructural control for advanced-high strength steel with second-phase austenite. From this point of view, this paper is worthy for the Sawamura award.

A novel model experiment was established to clarify the mechanism of entrapment of inclusions and bubbles by the solidifying steel shell during continuous casting of steel. The velocity of the molten steel was estimated by using a numerical simulation which well-considered the solidification condition. It was quantitatively estimated that the entrapment of inclusions is greatly reduced by the existence of a flow of molten steel at the solid-liquid interface with 0.05 m/s. The mechanism of the entrapment of the inclusions and bubbles were governed by a suction force which depends on the gradient of interfacial energy in front of the solidifying steel shell. Furthermore, the distribution of the bubbles and inclusions in the actual steel slab was compared with the calculated one under the existence of DC magnetic field. Then, the effect of the electromagnetic brake on the flow velocity of the molten steel was quantitatively related to the distribution of the bubbles and inclusions. From these investigations, guideline was proposed to evaluate the entrapment of the bubbles and inclusions in the actual operation in the continuous casting of the steel. In this paper, the devised experiments and exquisite numerical simulation were combined very well, and it was clarified that the mechanism of entrapment of the bubbles and inclusions during initial solidification of the steel. This paper is considered as pioneering work in this field and has influenced the following research for decade. Therefore, it deserves the Distinguished Article Award.