Grain refinement is effective for improving strength and toughness. Phase transformation from ferrite (α) to austenite (γ) is often used to refine the γ grain size in the steel production process. However, the degree of grain refinement depends on various factors and the mechanism of this phenomenon has not been well explained.

In this paper, the authors focused on the grain refinement due to reverse transformation and tried to clarify the mechanism of γ memory and grain refining behavior. Microstructure evolution during the reverse transformation of low alloy steel consisting of lath martensite and chromium carbide was examined using in situ electron backscatter diffraction (EBSD) technique at high temperatures. Austenite grains nucleated during the reverse transformation can be categorized into the two types. In type A, austenite grains nucleated along the lath boundaries with almost the same crystal orientation as the prior austenite. And in type B, austenite grains nucleated at the prior austenite grain boundaries or inside the prior austenite grains with a different crystal orientation. Based on those results, the relationships among the nucleation and growth of γ grains and the γ memory were discussed. And the mechanisms of austenite memory phenomenon and grain refinement due to reverse transformation to γ were summarized.

From the above reasons, the academic and engineering contributions of the present paper are outstanding and this paper is worthy of the Sawamura award.

There is a growing demand to use low grade iron ores, i.e., iron ores with high content ratio of gangue (SiO₂, Al2O₃) or fine ores, etc., as burden of BF from the viewpoints of lack of high grade iron ores or expensive cost. To maintain the stable operation and high productivity of BF in the future, the strength and reducibility of iron ores should be kept by preparing the above mentioned low grade iron ores precisely before charging them into BF. Among the preparation of iron ores, granulation is especially an important process because this process has an influence on the structure and strength of burden. Generally the size of granule grows large by adding water, CaO, coke in the granulation process, but the phenomenon of the intra-particle water migration has been not entirely clear at the time.

In this paper, the intra-particle water migration dynamics was analyzed and simulated in order to clarify the mechanism of iron ore granulation process. To investigate the influence of porous structure on the migration, the authors proposed a new water migration model considered both the pore size distribution and closed pore. It could be explained that the capillary force was larger in iron ores having finer pores and consequently the water migration ratio into closed pores was higher by both theoretical and experimental analysis.

Considering the above achievements, this paper has an academic and a technical significance, and especially promises the ripple effect in the field of iron-making. Thus it is worth of the Sawamura Award.

In steelmaking processes, there are incentives to reduce slag volume and CaO consumption. The key to meet these requirements is the better understanding of CaO dissolution mechanism into molten slag, which relies on the knowledge of the thermochemical properties of slags and fluxes used for dephosphorization. Attention was focused on the 3-phase assemblage of CaO +Ca₂SiO₄–Ca₃P₂O₈ solid solution +liquid slag in the quaternary system CaO–SiO₂–P₂O₅–FexO. The liquidus compositions of this 3-phase region were determined at 1 573 K. It is clarified that the contents of SiO₂ and P2O5 were very low in these quaternary liquid slags. The FexO activities were also measured at temperatures between 1542 K and 1604 K by using an electrochemical technique involving stabilized zirconia electrolyte, and the results support the reaction mechanism between solid CaO and molten slag. Moreover, it is technically valuable to have estimated the phosphorus distribution ratios from present experimental data.

That is, the phase equilibria and the activity of FexO, which are necessary to estimate phosphorus behavior in utilizing 2CaO・SiO₂ solid solution as an absorbent of phosphorus, were measured and clarified precisely. It has much academic value from the viewpoints of advanced experimental technique, understanding of phase equilibria, and prospect of phosphorus distribution ratio and its concept of derivation. The paper apparently has an absolute value with an academic and a technical significance, and thus it is worth well the Sawamura Award.

TMCP technology has been widely utilized for plate rolling, which contributes to obtaining high performance in material properties along with reducing alloying cost. For this purpose, precise control technology with respect to temperature and reduction during rolling is necessary.

In this paper, authors have developed a new draft schedule setup system for the plate rolling. The difficulty in the setup calculation for plate rolling is that the number of pass is not a priori fixed and hence the degree of freedom of the schedule is much higher than other hot rolling processes, which leads to high computing cost. The developed system realizes a highly precise calculation by employing a new temperature model, a material flow stress model considering an evolution of dislocation density, static recovery and static recrystallization, as well as an original rolling function model and so on. Besides the calculation time can be reduced to an enough acceptable range for online usage by applying parallel computing with GPGPU.

The technology described in this paper is the integrated one in which the advanced software technologies are well coordinated into the up-to-date hardware system, and is expected to bring industrially useful results.

Therefore, this paper is considered to be valuable with respect to not only academic but also industrial point of view, and hence worthy of the Sawamura Award.