Announcement of Sawamura Award - winning Papers (22/10/2014)

Following four papers are awarded the 2014 Sawamura Award.

· Influence of Unstable Non-equilibrium Liquid Iron Oxide on Clustering of Alumina Particles in Steel【The reason for an award】
—ISIJ International, Vol.53 (2013), No.4, pp. 639-647
Toshiaki Mizoguchi, Yoshiyuki Ueshima, Masaaki Sugiyama, Kazumi Mizukami(Nippon Steel & Sumitomo Metal Corporation)
To control alumina cluster formation has been one of the important issues to avoid casting defects attributed to inclusions in the motel steel. It has been accepted that clustering was proceeded by sintering of agglomerated alumina particles. On the other hand, there were still ambiguities in understanding the formation by sintering. In this study, SEM and TEM observations were extensively performed for alumina clusters produced in the molten steel after the degassing process and in the CC slab. The significant finding is contribution of liquid FeO on alumina particles to rapid formation of rigid alumina clusters. The paper thermodynamically proves that liquid FeO can be formed in some conditions. A new mechanism of alumina clustering due to the capillary effect of liquid FeO between alumina particles is proposed. The study clearly shows the physics behind the alumina cluster formation and eliminates the ambiguities. In addition, applicable guides to avoid the alumina cluster formation are also pointed out. This study will surely develop fundamentals of steel solidification and improve the casting processes.
The mechanism of alumina cluster formation and the guides to avoid clustering are significant achievements in the field of steel making. From viewpoints of both scientific and industrial contributions, this paper is highly appreciated and deserves Sawamura award.

· Factors Affecting Static Strain Aging under Stress at Room Temperature in a Fe-Mn-C Twinning-induced Plasticity Steel【The reason for an award】
—ISIJ International, Vol. 53 (2013), No.6, pp. 1089-1096
Motomichi Koyama, Eiji Akiyama(National Institute for Materials Science), Kaneaki Tsuzaki(National Institute for Materials Science, Tsukuba University)

· Effect of Grain Size on Thermal and Mechanical Stability of Austenite in Metastable Austenitic Stainless Steel【The reason for an award】
—ISIJ International, Vol. 53 (2013), No.7, pp. 1224-1230
Yoshikazu Matsuoka, Tatsuya Iwasaki, Nobuo Nakada, Toshihiro Tsuchiyama, Setsuo Takaki(Kyushu University)
It is well-known that the thermal stability of austenite is increased by grain refinement. In this paper, the effect of grain size on the thermal and the deformation stabilities of austenite was described in the metastable austenitic stainless steel (Fe-16%Cr-10%Ni) with the grain size of 1 ~ 80 μm.
The martensitic transformation on cooling (athermal martensitic transformation) was suppressed by grain refinement (< 20 μm) of austenite. The thermal stability of austenite depends on the grain size. On the other hand, no effect of grain size was seen on the deformation-induced martensitic transformation during tensile deformation, which indicates that the mechanical stability of austenite is independent of the grain size. In the crystallographic analysis by means of EBSD (electron backscattering diffraction), it was found that some special martensite variants tend to be selected in an austenite grain on the deformation-induced martensitic transformation (near single-variant transformation) and this results in the formation of texture along tensile direction. This indicates that the most advantageous variants are selected in the deformation-induced martensitic transformation to release tensile strain and leads to the grain size independence of the mechanical stability of austenite.
This paper is worthy of Sawamura Award not only by its academic contributions to the understanding the effect of grain size on the thermal and the mechanical stability of austenite but also by industrial suggestions for developing high strength steels, such as TRIP-assisted low-alloy steels.

· "Continuous Cooling Transformation (CCT)" Concept for Iron Ore Sintering Using In Situ Quick X-ray Diffraction and Confocal Laser Microscope【The reason for an award】
—ISIJ International, Vol.53 (2013), No.12, pp. 2047-2055
Masao Kimura, Reiko Murao(Nippon Steel & Sumitomo Metal Corporation)
Most of current studies focused on the phase stability of various types of calcium ferrites and SFCAs that are included in specimens prepared in equilibrium and isothermal conditions or in the obtained sinters. However, sintering in a real process progresses in short periods between 1-2×10² s in the temperature range T=1473-1873 K, and the sintering reaction progresses under a non-equilibrium and non-isothermal condition. Thus the final microstructure and type of coexisting phases of the sinter are highly susceptible to the heating conditions, especially the heating and cooling rates and gas atmosphere such as the oxygen partial pressure Po₂.
This research describes pioneering investigation on in situ and real-time observation of the formation of calcium ferrites using a newly developed system, i.e. "quick X-ray diffraction (Q-XRD)" and an in situ laser microscope. In situ observation both of crystal structure and microstructure successfully reveals the effect of heating and cooling rates on the sintering reaction in the CaO-Fe₂O₃ system with attention to overheating and overcooling phenomena. The first continuous transformation (CCT) concept for iron ore sintering is proposed to understand overcooling phenomena when the molten oxide cooled down to room temperature and magnetite, hematite, and various types of calcium ferrite are formed. The CCT diagram for sintering provides crucial and fundamental information on the sintering accompanying solidification, precipitation, and formation of calcium ferrites from the molten oxides, and can be used as a guideline for controlling sintering processes.
This paper contributes a lot to academic and industrial metallurgical fields.