- Reason for the award -

The softening and melting of sinter in the cohesive zone alter the packed-bed structure and thereby strongly affect gas permeability in a blast furnace. Conventional models often treat sinter particles as homogeneous bodies and thus cannot adequately capture the effects of irregular geometry, internal pores, and spatial variations in reduction.

This paper presents a unified convergence-simulation framework incorporating the actual three-dimensional particle geometry and internal pore structure obtained by X-ray computed tomography. Using these data as boundary conditions, the authors calculated spatially resolved reduction and core–shell distributions with a three-dimensional reaction–diffusion model. The distinct deformation and flow characteristics of the FeO-rich core and reduced-iron shell were then represented by combining a Bingham fluid model with an elastic force based on the shape-matching method. Integrating actual structure, reaction, and mechanics within a single dynamic framework is highly original.

The model’s validity was confirmed through comparison with high-temperature, load-softening experiments on individual sinter particles at different temperatures and overall reduction degrees. It was further extended to a coke–sinter packed bed to analyze shell deformation and breakage, core outflow, and changes in bed height and void-fraction distribution. The model also distinguishes particle translation and rotation from actual local deformation.

By bridging particle-scale behavior and packed-bed structural evolution, this study provides a valuable analytical basis for understanding cohesive-zone phenomena and supporting future blast-furnace operation design. It is therefore of substantial academic and engineering significance and fully deserving of the Sawamura Award.

- Reason for the award -

To improve the fatigue strength of Ti alloys, understanding the relationship between the material microstructure and the fatigue process is essential. To date, approaches for detecting the fatigue process in Ti alloys by acoustic emission (AE) methods have been proposed; however, there are few reports regarding dwell-fatigue analysis, and quantitative evaluation of the fatigue process has been difficult because there are still challenges in handling and interpreting AE data.

In this paper, fatigue tests and AE measurements were conducted on three types of Ti-6Al-4V alloys whose microstructures were altered by heat treatment, and it was shown that the strain accumulation behavior in dwell fatigue differs depending on the microstructure. In addition, AE data analysis methods based on Bayesian statistics were developed, which successfully detected stage transitions in dwell fatigue and proposed strain accumulation models for each stage using multiple AE parameters such as amplitude and average frequency as variables. Furthermore, it was clarified that the average frequency of AE is an important parameter in predicting the strain rate in the primary stage of dwell fatigue.

This paper is highly significant as it paves the way for the development of nondestructive monitoring techniques for the fatigue process of Ti alloys by applying Bayesian statistical analysis to AE data, and is recognized as worthy of the Sawamura Award.

- Reason for the award -

Nitrogen addition is known to improve the elevated-temperature strength of austenitic stainless steels, but the intrinsic contribution of solute nitrogen has remained unclear because of the concurrent effects of nitride precipitation; this study therefore aimed to clarify its strengthening action and governing deformation mechanism.

Using Fe–18%Cr–8%Ni–N alloys, the authors systematically combined tensile testing, creep testing, stress-change testing, and detailed characterization of dislocation structures at 1173 K, where nitride precipitation was suppressed. They demonstrated that the 0.2% proof stress and tensile strength increase with solute nitrogen content. Up to 0.1 mass% nitrogen, the strength scales with the square root of nitrogen concentration; at 0.2 mass%, however, it deviates markedly from this relationship and rises more steeply. The microstructural and mechanical evidence further revealed a transition in the governing deformation mechanism. The 0.1% nitrogen steel exhibits recovery-controlled deformation, characterized by distinct subgrain formation and deformation governed by edge-dislocation climb. In contrast, the 0.2% nitrogen steel exhibits suppressed subgrain formation and glide-controlled deformation caused by solute-drag resistance associated with nitrogen and Cr–N atmospheres. By consistently linking the nonlinear strength increase to this mechanistic transition, the study provides an original and compelling explanation of nitrogen strengthening at high temperature. Its rigorous separation of solid-solution and precipitation effects substantially advances the scientific understanding of high-temperature deformation and offers a valuable design principle for developing heat-resistant austenitic steels. The paper is therefore highly significant both academically and industrially and is fully deserving of the Sawamura Award.

- Reason for the award -

Reducing CO₂ emissions from the steel industry requires the development of low-carbon blast furnace technologies in which carbon-based reductants are partially replaced by hydrogen-based reductant gases. This study numerically analyzes coke oven gas (COG) and hydrogen gas injection trials conducted in the COURSE50 experimental blast furnace using a three-dimensional mathematical blast furnace model. The model successfully reproduces the experimental results for hydrogen concentration in the furnace, fractions of reduction reactions, and carbon consumption. After validating the model against the experimental results, the analysis is extended to hydrogen-based reductant gas injection conditions beyond those examined in the experimental trials. It is particularly noteworthy that valuable operational data obtained from the experimental blast furnace are combined with numerical analysis to investigate a wide range of operating conditions.

The results demonstrate that increasing hydrogen input decreases direct reduction by carbon and increases indirect reduction by hydrogen, while achieving a carbon reduction rate exceeding 20% is difficult with hydrogen-based reductant gases injected at room temperature alone. Furthermore, analyses of both reduction reactions and the heat balance reveal that further carbon reduction requires additional heat input, such as increasing the hot blast temperature or preheating the reductant gas. These findings provide important guidelines for operating conditions and process design of hydrogen-based low-carbon blast furnaces and are of significant industrial and technological value. Therefore, this paper is considered worthy of the Sawamura Award.

- Reason for the award -

This paper presents an advanced cellular automaton (CA) model for quantitatively predicting dendrite morphology and microsegregation during alloy solidification. Although the CA method has the advantage of relatively low computational cost, accurate calculation of solid–liquid interface curvature has been difficult, resulting in limitations in the reproducibility of dendrite morphology. In this study, a new curvature calculation method based on the height function (HF) method was introduced, enabling highly accurate calculation of the interface shape. In addition, correction of mass-balance errors and solid–liquid interface movements caused by solidification and melting were incorporated, and the originality of this work lies in the integrated treatment of several issues inherent in conventional CA models. In simulations of single-dendrite growth, the development of secondary dendrite arms, which had been difficult to reproduce using conventional methods, was successfully reproduced, demonstrating that improved accuracy in interface curvature calculation enhances the reproducibility of dendrite morphology. Furthermore, simulations of multi-dendrite growth and microsegregation under continuous cooling produced theoretically consistent results, including appropriate solute partitioning, demonstrating the quantitative predictive capability of the model. While maintaining the relatively low computational cost of the CA method, the proposed approach enables highly accurate prediction of solidification microstructures and microsegregation. Further applications to multicomponent alloys, practical steels, and more complex solidification phenomena are expected. This work has high academic and engineering significance as a fundamental analytical method and makes an important contribution to the advancement of numerical analysis in this field.

- Reason for the award -

Accurate thermo-physical properties of mould slags are essential for mathematical modeling of steel continuous casting processes. Previously, there have been no model covering all key properties and estimating the value with reasonable accuracy. The paper, led by the late Professor K.C.Mills, developed routines to provide reliable values for the mould slags from their chemical compositions and temperature. In particular, under the basis that the structure of slags is evaluated by chemical composition, NBO/T and polymerization, (1) estimation of thermal conductivity of liquid and solid slags, (2) estimation of viscosity under the basis of polymerization with consideration of CaF2 and (3) estimation of surface tension, in which slag components are divided into surfactants and bulk components, and the temperature dependencies of each components and surface tension drop due to surfactants are evaluated, are highlighted. It is highly evaluated that these models enable the estimation of thermo-physical properties with reliable accuracy.

As a result, the proposed models have not only been utilized as models for estimating the key physical properties of slags but also as the ones for development of mould powder in the subsequent papers. Therefore, the proposed models are becoming standard tools in the field. Moreover, it is noteworthy that this paper has been referred to the fields of ceramics, mining, reaction engineering and geophysics as well as ironmaking and steelmaking. For these reasons, this paper is regarded as one of the most influential and impactful contributions in the past decade and is deemed fully deserving of the Distinguished Article Award.