Announcement of the winners of the paper awards to be presented in 2025.

There are a variety of measures to evaluate strength of materials. Strain rate sensitivity of materials produced by severe plastic deformation is depending on types of materials. Therefore, it was difficult to evaluate the basic stress bearing capability for long-term use because conventional tensile test shows the strength, which is thermal and time-dependent. In this paper, “permanent strength”, which is athermal and time-independent was proposed by using stress-relaxation test and clarified that steel has a high advantage as a structural material.

The effects of grain refinement and low temperature annealing on the permanent strength were investigated in IF steels produced by severe plastic deformation. The fraction of the permanent strength to the 0.2% proof stress obtained from conventional strain rate (10^-2/s) was about 65% and improved to 90% by low temperature annealing. It was concluded that the grain refinement by severe plastic deformation contributes to the increase in the permanent strength in IF steel in contrast to aluminum and copper.

This study proposed “permanent strength” for long-term use of materials and clarified high effectiveness of grain refinement in the steel compared with other materials. This can be a new measure for material development. Therefore, the paper is worth well to the Sawamura Award.

Controlling the hardness of martensite in steels is important for increasing the strength and performance of steels. However, although it is understood that solute C, dislocations, grain size, and precipitates influence the hardness of martensite, the degree of each contribution has not been clearly explained.

In this paper, the authors take on the challenge of clarifying the strength origin of martensite. For as-quenched or tempered martensite with various C contents, solute C, dislocation density, grain boundaries, precipitates and retained austenite in martensite, which are the influence factors of martensite strength, are accurately quantified and the effect of those factors on martensite hardness are evaluated. As a result, it is clarified that solute C almost controls the martensite hardness. Although the measurement methods of those factors are already known, those analyses are applied to martensite with various C contents and hardness, and the effects of those factors are well separated. These results and knowledge are very useful for the development of advanced high strength steels. Many researchers can understand this paper easily because the logic is simple. It is very good for improving the understanding of martensite strength in the world.

As described above, this paper clarifies quantitively the effect of various strength factor, which is solute C, dislocation density, grain boundary, precipitates and retained austenite, on martensite hardness. It is highly evaluated both academically and industrially, and is therefore appropriate for the Sawamura Award.

A non-uniform deformation band (Lüders band) occurs and propagates during discontinuous yielding of steel. Although various studies have been conducted on the discontinuous yielding of steel, the mechanism that is independent of the steel type and strength has been still under the discussion.

The authors of this paper focused on the discontinuous yielding mechanism and the influential factors and investigated the deformation mechanism and plastic stability at the Lüders front during tensile tests for ferritic steel and TRIP steel with various yield strengths through high-precise experimental techniques. Tensile tests with advanced measurement techniques such as DIC observation, SEM-μDIC, and EBSD observation have clarified the relationship between Lüders strain and yield stress. Besides, it is also found that the Lüders front is composed of hierarchical microscopic shear-like structure. Furthermore, systematic and detailed investigations using steel materials with different dislocation densities have revealed fundamental findings such as influential factors on discontinuous yielding and Lüders strain and have deepened the deformation mechanisms and the complex plastic stability at the fronts of Lüders bands. In addition, these findings are also useful to control discontinuous yielding and elongation, which are often problems in press forming of high-strength TRIP steels.

As described above, this paper is recognized as one of the most valuable papers in terms of both industrial and academic point of view, and therefore is appropriate the Sawamura Award.

Although non-metallic inclusions have negative impacts on steel quality, it has been suggested that secondary inclusions can act as nucleation sites to improve mechanical properties of steels. Therefore, it is important to control the size, number, composition, and distribution of secondary inclusions to produce high-quality steels. It has been possible to obtain comprehensive information on inclusions with SEM-EDX automatic inclusion analysis developed recently.

In this study, the formation of secondary inclusions in Fe-36mass%Ni invar alloy was investigated at various cooling rates especially under slow cooling conditions assuming large ingots. The relationship between micro-segregation and secondary inclusion formation was clarified by using a novel technique combining SEM-EDX automatic inclusion analysis and EPMA element mapping analysis. The experimental results confirmed that high-Al₂O₃ inclusions formed at the early stage of cooling and then the content of Al₂O₃ in inclusions decreased during solidification. These findings were consistent with the thermodynamic calculation analysis.

It is expected that a combination of SEM-EDX analysis and EPMA mapping analysis suggested in this study will provide a more detailed understanding of formation mechanism of secondary inclusions during solidification, which has academic and technological significance. Therefore, this paper is worth well to the Sawamura Award.

Conventionally, it was known that the yield of the upper layer of the sinter packed bed was extremely low due to heat loss by thermal conduction and a large amount of unburned carbon. REMO-tec was developed as a countermeasure. REMO-tec is a sintering technology that reignites the surface layer of the sinter packed bed at regular intervals. This method has the effect of improving the sintering yield while maintaining high sintering reducibility. This effect reduces the amount of coke fines, which is a source of CO₂ emissions.

In this paper, a basic study was conducted on the technology to reignite the surface layer of the sinter packed bed at appropriate intervals. The originality of this research is that, in order to optimize the heat amount in the entire sinter packed bed, the heat consumption amount considering the coke fines combustion rate was quantified for each layer based on the heat balance of sinter packed bed and gas, and the correspondence with the yield was organized. Through this quantification, it was newly discovered that the reignition method is a highly efficient heat utilization method and can reduce coke fines by four times the amount of reignition heat. Additionally, this paper established a structural analysis of the entire sintered cake using high-energy X-ray CT analysis, and was able to quantitatively evaluate the improvement in strength of the upper layer due to re-ignition, confirming the same phenomenon as in the experiment, which can be said to be an extremely outstanding point. The 6% reduction in coke powder blending, as achieved by actual equipment, is of great industrial utility.

Therefore, this paper is technically and academically of a high level and can be judged to be worthy of the Sawamura Award.

The formation behavior of calcium ferrite (SFCA, SFCA-I) in sintered ores significantly influences the quality of these ores. Consequently, understanding the compositional range for formation and phase equilibrium relationships is essential. In recent years, iron ores have become degraded and the content of Al₂O₃ in iron ores has increased. Therefore, phase diagram for the CaO- SiO₂- Fe₂O₃- Al₂O₃ system, which is the main component of sintered ores, was required to be obtained in the temperature range of around 1250℃.

This study employed original experimental and analytical methods to define the compositional range of SFCA and SFCA-I phases within the CaO- SiO₂- Fe₂O₃- Al₂O₃ system and their phase equilibrium relationship with the liquid phase. The influence of Al₂O₃ on the composition range of SFCA has been investigated, and useful findings have been obtained. The study revealed that an increase in Al₂O₃ concentration expands the SFCA single-phase region, that an SFCA-I single-phase region appears, and that the liquidus shifts to the low Fe₂O₃ side. The increase in Al₂O₃ concentration in iron ore decreases the amount of slag that binds iron ore particles in the sintered ore, increases the amount of SFCA formed from the slag, and promotes the formation of SFCA-I. This knowledge of the effect of Al₂O₃ on the phase equilibrium of the CaO- SiO₂- Fe₂O₃ system contributes to microstructural control for the production of sintered ores from low-grade iron ores, and this paper is judged to be worthy of the Sawamura Award.

One method for increasing the strength of steels is to disperse fine precipitates. However, in interphase precipitated steels that can precipitate nano-sized alloy carbides, the effects of these carbides on strength and ductility are not yet clear. Therefore, it was necessary to understand the mechanical properties and deformation mechanisms in order to establish manufacturing technology for steels with nano-sized precipitates.

In this paper, the interphase precipitation behavior of alloy carbides that form at the austenite/ferrite interface during the ferrite transformation of low-alloy and low-carbon steels and their effects on the mechanical properties were investigated. It was shown that the addition of Ti and Mo can produce finer alloy carbides, and that dispersion of smaller-sized alloy carbides is more effective to obtain higher strength with sufficient ductility. This paper showed that fine alloy carbides contribute to precipitation hardening due to the Ashby-Orowan mechanism rather than the conventional Orowan mechanism, and also proposed a deformation mechanism based on the relationship between fine alloy carbides and dislocation structures to exhibit good work hardening and ductility. It can be said that this paper is highly original in that it academically explained the industrial advantages of the steels with nano-sized precipitates. The results shown in this paper have been cited frequently overseas, particularly in a paper reprinted in ISIJ International, and continue to be cited frequently even now, 10 years later. Accordingly, this paper is deemed worthy of the Distinguished Paper Award.