Announcement of Sawamura Award - winning Papers (30/10/2013)

Following four papers are awarded the 2013 Sawamura Award.

· Feasibility of solid-state steelmaking from cast iron -Decarburization of rapidly solidified cast iron-【The reason for an award】
—ISIJ International, Vol.52 (2012), No.1, pp. 26-34
Ji-Ook Park, Tran Van Long, Yasushi Sasaki(POSTECH)
Formation of inclusions is inevitable in the current steelmaking process and considerable efforts have been made for their removal. In this paper, a new steelmaking process “Solid State Steelmaking (or S³) process”, which does not need a BOF process or liquid state oxidation process was proposed and its feasibility was discussed based on the laboratory scale experiments. The outline of the new process is: 1) High carbon liquid iron is directly solidified by using twin roll strip caster to produce thin high carbon sheets and 2) produced iron sheet is continuously decarburized to produce low carbon steel sheets. It is possible to be an inherently inclusion-free and low energy consumption steelmaking process since liquid state oxidation process (BOF) is not required. Understanding of the decarburization of high carbon Fe-C equilibrated with Fe₃C sheets is essential to realize the new process. Laboratory scale experiments showed that the decarburization process was controlled by the carbon diffusion through austenite phase but not the decomposition of cementite.
Along with the industrial contribution through a new steelmaking proposal, the present paper also shows that the corresponding research field of high carbon iron is not restricted for cast iron but for other interesting and meaningful subjects, which are remained in the future iron/steelmaking technology. Considering the above points, the present paper is highly valuable and worthy of Sawamura award.

· Enhanced lattice defect formation associated with hydrogen and hydrogen embrittlement under elastic stress of a tempered martensitic steel【The reason for an award】
—ISIJ International, Vol. 52 (2012), No.2, pp. 198-207
Tomoki Doshida, Hiroshi Suzuki, Kenichi Takai(Sophia University), Nagayasu Oshima (AIST), Tetsuya Hirade(JAEA)
The mechanism of hydrogen embrittlement of steels has not yet attained a general agreement, the crucial reason being experimental difficulties on detecting hydrogen behaviors. In this paper, ingenious experiments have been conducted to reveal the formation of lattice defects and their role in the delayed fracture of high strength steels.
Firstly, the evolution of lattice defects during sustained-loading delayed fracture tests was detected utilizing hydrogen as a probe of defects, and then a positron lifetime measurement using a positron probe microanalyzer was successfully applied for the first time to identify vacancies and their preferential formation and clustering in areas close to the fracture surface. Unloading and hydrogen-degassing coupled with annealing during delayed fracture tests demonstrated the decisive role of vacancy clusters, rather than hydrogen itself or dislocations, in the delayed fracture. Further, involvement of plasticity in delayed fracture even under an apparently elastic stress range was revealed by means of fractographic observations and the measurement of the stress dependence of the vacancy creation.
This paper gives clear and strong supports for the hydrogen-enhanced stress-induced vacancy mechanism to operate in the delayed fracture of high strength steels. This paper is worthy of Sawamura Award not only by its academic contributions to the understanding the mechanism of hydrogen embrittlement but also by industrial suggestions for developing high strength steels resistant to hydrogen degradation.

· Effects of ferrite growth rate on interphase boundary precipitation in V microalloyed steels【The reason for an award】
—ISIJ International, Vol. 52 (2012), No.4, pp. 616-625
Toshio Murakami, Hitoshi Hatano(Kobe Steel LTD), Goro Miyamoto, Tadashi Furuhara(Tohoku University)
To use of interphase boundary precipitation of alloy carbide is known to be effective for strengthening steels, such as the improvement of strength-elongation balance and machinability. The nano-sized alloy carbides are dispersed on sheets regularly spaced in ferrite densely, so high precipitation hardening can be obtained. To control the mechanical properties by interphase boundary precipitates, it is necessary to clarify the mechanism of precipitation and to propose the model for interphase boundary precipitation. Previous studies have indicated some precipitation models, although the relationship between ferrite growth rate and intersheet spacing has not been fully confirmed yet.
In the article, the change of intersheet spacing of interphase boundary precipitation of vanadium carbide during isothermal ferrite transformation was examined and as a result to explain the observed behaviors new model was developed. In numerical simulation of vanadium carbide precipitation, the influence of the vanadium concentration on the precipitation behavior at the austenite/ferrite interface during isothermal transformation was examined based on a time-dependent solute drag model incorporated with a parabolic growth rate. It was found that the change of the intersheet spacing during ferrite growth can be simulated by the newly proposed model for interphase boundary precipitation of alloy carbide. This article has not only scientific importance for the precipitation mechanism but has also engineering significance for microstructural control.

· Effect of agitation on crystallization behavior of CaO–SiO₂–R₂O (R = Li, Na, or K) system characterized by electrical capacitance measurement【The reason for an award】
—ISIJ International, Vol.52 (2012), No.12, pp. 2123-2129
Noritaka Saito, Kakeru Kusada, Sohei Sukenaga(Kyushu University), Yoshio Ohta(Fukuoka Institute of Technology), Kunihiko Nakashima(Kyusyu University)
This research paper describes pioneering results on crystallization behavior of molten oxides at undercooled and agitation state such as molten flux in continuous casting process. This paper provides the following two important results from academic and industrial points of view: Firstly, the authors proposed very simple method to detect crystallization behavior of molten oxides by measuring the difference of capacitance between liquid and solid states. CaO-SiO₂ based molten oxides indicate the drastic decrease of capacitance when they start crystallization under cooling. This technique is much simpler than the previous procedures such as observation of crystals in quenched samples by SEM and X-ray diffraction or hot-thermocouple method. Therefore, this new method can be applied to design many kinds of new continuous casting fluxes which have various crystallization behaviors. Secondly, the authors elucidated the effect of agitation on the crystallization behavior of undercooled molten oxides by using rotational cylindrical electrodes for the first time in the world. They observed that the crystallization of CaO-SiO₂ based molten oxides is accelerated by the agitation, of which behavior cannot be detected by the above any other methods. Since continuous casting fluxes are not used in static state, the above results are significantly valuable to understand the dynamic crystallization behavior of continuous casting fluxes and to design a new industrial flux. As describes above, this paper contributes a lot to academic and industrial metallurgical fields.