2020 Tawara Award, Sawamura Award and Distinguished Article Award

Non-directional electromagnetic steel sheets are widely used as the iron core material for motors, and have achieved high permeability and low core loss by controlling the texture through recrystallization and grain growth. Although there have been many studies on the formation of texture in abnormal grain growth, studies on normal grain growth, regardless of its importance, are scarce. In this paper, the effect of micro-alloying of Sn on the normal grain growth after recrystallization was focused on, and the effect of 0.1% Sn addition on the ferrite grain size and texture development was investigated in Fe-3%Si alloys after cold rolling and annealing at various temperatures. This paper clearly shows that grain growth is suppressed by the addition of Sn, and that the texture just after recrystallization is the same regardless of the addition of Sn, while the texture after grain growth changes from {111}<112> to {411}<148> with the addition of Sn. Furthermore, Monte Carlo simulation method was applied with anisotropic effect of Sn on grain boundary mobility and successfully reproduced the effects of Sn on texture evolution, which is a novel approach and of high academic value.

This paper clarifies the effect of adding trace elements, which is the main issue of electromagnetic steel sheets, on the formation of texture in grain growth, from both the experimental and theoretical perspectives, and is therefore worthy of the Sawamura Paper Award.

The authors achieved time-resolved and in-situ observations of the massive-like transformation of Fe-C alloys by using synchrotron radiation X-rays in the previous work. In this article, this developed novel technique was successfully applied to observe the δ/γ phase transformation of Fe-18 mass%Cr-Ni alloys with Ni contents of 8, 11, 14, 20 mass%. According to the phase diagram, δ phase is a primary phase in 8 and 11 mass% Ni cases. In these alloys, δ phase was always nucleated and consequently fine γ grains were formed by the massive-like transformation. In the 14 and 20 mass% Ni cases, δ phase was preferably selected as metastable phase at lower undercooling （<50 K） even though γ phases was a primary phase in the phase diagram. Then, the massive-like transformation occurred and could trigger solidification of γ phase. It was also found that the moving velocity of δ/γ interface during the massive-like transformation was 0.1 mm/s and did not depend on the degree of the undercooling for 8 mass% Ni and from 0.1 mm/s to several 100 mm/s or more for 11 mass % Ni, respectively. The reason of the difference of the moving velocity was also discussed. Moreover, it is suggested that the massive-like transformation will be commonly observed in Fe-based alloys.

This paper reported the excellent observations of the phase transformation at high temperatures by using a novel technique. The impacts and contributions of this paper for both academic and technical aspects are outstanding, and hence this paper is worthy for the Sawamura award.

There are many difficult problems to reduce CO2 emissions from iron and steel industry. We are currently making various efforts in order to achieve 30% reduction of CO2 by 2050 and to realize zero-carbon steel by 2100. It will play an important role to introduce H2 into a blast furnace to realize those goals.

It is known that the reduction with an H₂-CO mixture is very complicated because three kinds of gasification reactions of coke; C + CO₂ = 2CO, C + H₂O = CO + H₂, C + 2H₂O = 2H₂ +CO₂, and water -gas shift reaction; H₂ + CO₂ = CO + H₂O, simultaneously occur with both of CO and H₂ reduction. For this reason, it becomes very difficult to know the effect of water-gas shift reaction precisely under the coexistence of iron ore and coke at high temperature.

In this article, the reaction rate of the water-gas shift reaction is determined by the original method of gas analysis. When three kinds of gasification reactions of coke simultaneously occur, the progress ratio of each reaction is clarified. From these results, we can evaluate the progress of three kinds of gasification reactions of coke and water-gas shift reaction separately. These results can be applied to the analysis of a more complex reaction system of an H₂ and CO mixture, which will become an essential knowledge to the maximization of the hydrogen utilization in blast furnace.

In this article, the water-gas shift reaction in a blast furnace is precisely examined by both of basic experiments and thermodynamic calculations, and it highly evaluated in the aspect of academic usefulness, in particular. Accordingly, it can be judged that the paper is suitable for the Sawamura award.

While various studies on hydrogen embrittlement have been conducted, the essential mechanism of hydrogen embrittlement behavior of practical materials has not been clarified yet. In this study, the relationship between fracture behavior and crystal orientation was investigated by precise EBSD analysis with hydrogen charged tensile test of SUS 304 steel using precisely designed ultra-micro test specimen. In particular, a detailed analysis of the fracture behavior caused by twin boundary, called hydrogen-induced twin boundary separation, was conducted and the mechanism was discussed. As a result, the linear steps formed on the fracture surface of the twin boundary correspond to the （111） slip plane of austenite, and the martensite with the variant parallel to （111） A is formed in the layer in the cross section. Therefore, the authors proposed a fracture mechanism that cracks are initiated in the twin boundary by the formation of deformation-induced martensite which is caused by hydrogen enhanced slip deformation of austenite. Furthermore, a hypothesis that excess hydrogen released by the martensitic transformation promotes slip deformation of austenite and enhances crack propagation was proposed.

This paper clarifies the mechanism of hydrogen cracking caused in twin boundary by an innovative test approach and precise crystallographic analysis, and it should be a very valuable research from a technical and scientific point of view. And, a lot of possibilities in the hydrogen embrittlement research is expected by applying this method to various materials. Therefore, this paper is worth for the Sawamura Award.

Precipitation of iron carbides is one of the most important phenomena for microstructure control in steels. This paper aimed to clarify the effect of Si addition on the carbon concentration and stability of εcarbide. The authors examined εcarbide and cementite formed by tempering of martensite using first-principle calculation, field emission transmission electron microscopy （TEM）, and three-dimensional atom probe （3DAP）analysis. TEM analysis confirmed that in Fe-0.6C-1Mn steel （mass%） εcarbide forms by tempering at 100 and 200 °C and cementite becomes to form at 400 °C, while only εcarbide precipitates at tempering temperatures up to 400 °C in Fe-0.6C-1Mn-2Si steel. The first-principle calculation revealed that partitioning enthalpy of Si in εcarbide is positive: it is 0.62 eV at 20 at.% carbon and increases twice at 25 at.% carbon. This result indicates that the εcarbide with a lower carbon concentration tends to form by addition of Si. This tendency has been experimentally supported by 3DAP analysis performed on the Fe-0.6C-1Mn and Fe-0.6C-1Mn-2Si steels tempered at 200 °C.

Beside the above results, this paper showed many valuable findings about precipitation of iron carbides in tempered martensite, and its contribution to steel science and engineering is significant. Therefore, this paper is worthy of the Sawamura Award.

It can be said that the hot metal temperature control is a very important control item for stable operation of blast furnace. The hot metal temperature should be properly controlled because of the slag drainage problem from the tap hole when the heat level becomes too low, and enormous fuel consumption and CO₂ emission occurs when the heat level becomes excessively high.

The authors newly created a one-dimensional unsteady physical model for hot metal temperature prediction for the purpose of automatic stabilization control of blast furnace hot metal temperature. In order to improve the accuracy of the model, the error of the model was investigated using principal component analysis and list diagram. This discussion's result indicated that the error can be explained mainly by the fluctuations of the reducing agent ratio and the reduction efficiency. By sequentially correcting the parameters related to this variable factor retroactively, The authors appropriately reflected the influence of disturbance in the model calculation. This method achieved the model was made highly accurate, and it was possible to make predictions 8 hours ahead in real time.

The well-developed method solved the practical problems as follows; it was difficult to predict the long-term future with existing statistical models; it made the deterioration of accuracy due to disturbances such as material fluctuations with general physical models. The content of this report is versatile enough to practically use, and further technological development can be expected. The theory is highly evaluated, and the contribution as an academic paper is very high, and hence is worthy of Sawamura Award.

This paper well investigates thermodynamic behavior of possible boron removal from molten silicon into highly basic slag under a reducing atmosphere which removal was considered difficult in zone melting process in viewpoint of partition ratio between solid and liquid, and succeeded in indicating the possibility of application of basic slag to the refinement of non-ferrous and reactive metals, which well extends the applicability of ferrous metallurgy technology. Authors devised the addition of Na₂O and CaF₂ in CaO-SiO₂ as compositional trial for further removal of boron and kept the atmosphere reducing enough to avoid oxidation of molten silicon with low oxygen partial pressure to ensure the slag-metal reaction. Further thermodynamic discussion has been successfully made on borate capacity which can systematically evaluate boron absorbing ability of the slags, and comparison of which with sulfide capacity would verify the assumed function of oxide ion in the slag. This paper finds the way to correspond the diversity of impurities and variation in matrix metals in the field of refinement by appropriate thermodynamic evaluation of impurity absorbing abilities of slags in the conception of slag capacity for highly basic oxide melts and fluxes. Accordingly, this paper would influence many possible refining processes perpetually and deserves distinguished paper award of the journal, ISIJ International.

Various kinds of studies have been reported in the developments of high strength steels to meet the needs for weight savings and to cope with environmental regulations in the automotive industry. In the studies about high strength steels, the austenitic steel containing 15–25 mass% manganese （Mn） so called twinning induced plasticity （TWIP） aided steels have been focused on. The 15–25% Mn TWIP steels show excellent mechanical properties of high tensile strength （≥1200 MPa） and large elongation （~70%）. This paper investigated hydrogen delayed fracture of the TWIP steel for the first time in the world.

The authors conducted the slow strain rate test and thermal desorption analysis for the Fe-18Mn-1.5Al-0.6C TWIP steel. As a result, most hydrogen became non-diffusible after the slow strain rate test. It was also found that the major trapping sites of hydrogen were dislocations, grain boundaries and twins. Furthermore, the activation energies for detrapping of hydrogen for dislocations, grain boundaries and twins were estimated quantitatively. Those findings have thus largely contributed to the developments of hydrogen embrittlement in austenitic steels including TWIP steels.

Therefore, the present paper is considered as a pioneering work in the field of the analyses of hydrogen embrittlement in the TWIP steels and it is worthy of the Distinguished Article Award.