2015 Sawamura Award (29/09/2015)

Following four papers are awarded the 2015 Sawamura Award. · Finite Element Analysis of Three-Dimensional Hot Bending and Direct Quench Process Considering Phase Transformation and Temperature Distribution by Induction Heating【The reason for an award】 —ISIJ International, Vol.54 (2014), No.8, pp. 1856-1865 Hiroaki Kubota, Atsushi Tomizawa, Kenji Yamamoto, Nobuhiro Okada (Nippon Steel & Sumitomo Metal Corporation), Takayuki Hama, Hirohiko Takuda (Kyoto University)  This paper discusses the thermal, mechanical and metallurgical behaviour during three-dimensional hot bending and direct quench (3DQ) process in steel products. The 3DQ technique combines heating, 3D hot forming and quenching altogether and hence it allows to produce high strength steels with high cost efficiency. A thermo-mechanical-metallurgical finite element numerical simulation employed in the paper reveals the thickness distribution and the camber evolution behaviour caused by the 3D bending and the inhomogeneous cooling rate. Temperature history was carefully reproduced by the electromagnetic analyses followed by the heat conduction simulations that are the basis of phase transformation and stress/strain calculations. The most striking improvement made in this attempt is that it considers the phase transformation effect with a judicious choice of appropriate models. Indeed, the flow stress changes significantly during phase transformation and the effect results in an eventual residual stress and shape change. Accordingly, the transformation model is imperative in this kind of simulation. The remarkable agreement between numerical and experimental results makes the paper outstanding as well, confirming the validity of the numerical framework of this paper. The paper apparently has an absolute value with an academic and an industrial significance, and thus it is worth well the Sawamura Award. · A Novel Measurement Method for Coal Thermoplasticity: Permeation Distance【The reason for an award】 —ISIJ International, Vol. 54 (2014), No.11, pp. 2484-2492 Yusuke Dohi, Kiyoshi Fukada, Tetsuya Yamamoto, Takashi Matsui, Hiroyuki Sumi, Izumi Shimoyama (JFE Steel Corporation)  Coke strength is strongly depends on void structure in coke cake. This study has achieved that a novel measurement for accurate evaluation of coal thermoplasticity is established.  In this paper,first, the technical problem is clarified that by use of conventional methods of Gieseler plastometer or piston displacement of dilatometeras it is difficult to evaluate coal thermoplasticity exactly, especially, for high fluidity coal, which causes decrease of coke strength. For solving it, a small and simple experimental apparatus has been contrived for simulating fluidity phenomenon at coking. Then a new index “Maximum permeation distance” is proposed as expressing coal fluidity. As an ingenious analysis utilizing the apparatus, by comparison of profiles between permeation distance and conventional Gieseler plastometer, it is clarified that permeation phenomenon does not depend on only viscosity. Furthermore, the index of permeation distance is generalized as formula based on parameters of Kozeny-Carman, pressure drop of coal packed bed, liquid viscosity and time. The new index has been justified by showing strong correlation between maximum permeation distance and coke strength index and by observing void structure of coke cake.  Trough operational result at a commercial plant, it is confirmed maximum permeation distance can express coke strength variation though ordinary indices (MF,Ro) is constant  As well as scientific value, the paper has significant value as utilization the theory for higher operational performance.    1) Selecting coal resource strategy through controlling coke strength by designing coal blending condition.    2) Contributing higher productivity and lower reduction rate at BF operation through production with higher coke strength  From viewpoints of both scientific and industrial contributions, this paper is highly appreciated and deserves Sawamura award. · Direct Measurement of Agglomeration Force Exerted between Alumina Particles in Molten Steel【The reason for an award】 —ISIJ International, Vol. 54 (2014), No.12, pp. 2780-2789 Katsuhiro Sasai (Nippon Steel & Sumitomo Metal Corporation)  It is extremely important for improvement of steel quality to avoid agglomeration of inclusion particles in molten steel. Although several efforts for explanation on behavior of agglomeration have been made from surface chemical interaction among particles, a mechanism of agglomeration of inclusions in molten steel has not yet been adequately clarified because it has been difficult in steel melt to measure forces acted on inclusions.  In this study, however, the authors succeeded for the first time the direct measurement of the agglomeration force acted among alumina inclusions without suffering affection of melt flow by constructing a fully worked-out original apparatus for the experiment. Besides above, they discussed theoretically the agglomeration force acted among alumina inclusions from interfacial properties between steel melt and alumina, to propose newly that the force acted among particles was not Van der Waals force but cavity bridge force caused due to alumina particles, which is unlikely to be wet with molten steel. Moreover, they explained reasonably that this cavity bridge force is large compared with the buoyant force and the drag force exerted on alumina inclusion and that the agglomerated alumina inclusions could easily maintain their state without separating each other even under a flow of molten steel.  This paper is pioneering at the point that the agglomeration force among inclusions in steel melt is clarified from both original experiments and detailed theory. Furthermore, a calculation model of the cavity bridge force proposed in this study is considered to have scientifically a significant value. · Effect of Ti on Evolution of Microstructure and Hardness of Martensitic Fe-C-Mn Steel during Tempering【The reason for an award】 —ISIJ International, Vol.54 (2014), No.12, pp. 2890-2899 Carin Emmy Ingrid Christersdotter Öhlund (Delft University of Technology), Jonathan Weidow, Mattias Thuvander(Chalmers University of Technology), Sven Erik Offerman (Delft University of Technology)  Demands for using martensitic steels for further strengthening of various structural components are increasing recently. Tempering of martensite is usually used to obtain superior strength-toughness balance. To maintain required strength, alloy addition is made to retard softening or obtain secondary hardening by fine precipitation of alloy carbide. However, microstructure change during tempering is complex due to hierarchical substructure of martensite and transition of carbide phase and thus, physically based modeling of tempered microstructure and corresponding mechanical properties is still not sufficient.  This paper has performed quantitative characterization of carbide precipitation and microstructure change in the martensite matrix and hardness change in multi-scale during tempering of microalloyed steels utilizing various experimental methods. Also advanced modeling of carbide precipitation has been proposed. It represents the high standard in characterization of martensite tempering, and simulation made by a model taking various effects into account systematically is in good agreement with the experimental observations. This paper has made important contributions in both of the academic and industrial aspects and is worthy of the Sawamura Award.