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Inomoto T.,Nippon Steel & Sumitomo Metal Corporation | Matsuo M.,Japan Research and Development Center for Metals | Yano M.,Nippon Steel & Sumitomo Metal Corporation
ISIJ International | Year: 2015

For the mass production of ultra-low-carbon steel, application of the chemical vacuum method was examined in depth. In the present study, based on the results of 600-kg-scale experiments and theoretical analysis of them, the possibility of innovative creation producing ultra-low-carbon products without using a vacuum degasser was obtained. To confirm the effect, a 60-t-scale AOD plant test was carried out. As a result, by using the chemical vacuum effect, the carbon content is reduced to 9 ppm in normal steel because of its much higher CO partial pressure than that of stainless steel. The results of the examination show that, theoretically, the reaction rate can be further enhanced. However, it is necessary to construct a dispersion condition in a large-scale metal vessel with small argon bubbles because applying the current technique of small bubble production cannot produce a sufficiently high argon injection flow rate. For the construction of an innovative secondary refining process in the future steelmaking process, the gas dispersion technique is strongly preferred. © 2015 ISIJ.

Yamashita K.,Kyushu University | Sukenaga S.,Tohoku University | Matsuo M.,Japan Research and Development Center for Metals | Saito N.,Kyushu University | Nakashima K.,Kyushu University
ISIJ International | Year: 2014

The slags and fluxes found in modern steelmaking convertors all contain finely dispersed gas phases, which are generated by the refining reaction used to decarburize the molten iron. The frothing effect that is often generated as a result of these gasses can often prove to be a fatal obstacle in the efficient operation of the converter. In the present study, a simulated slag foam was produced by dispersing N2bubbles in silicone oil. The effect of varying the volume fraction and bubble size of the dispersed gas phase, the shear rate, and the viscosity of the liquid phase, was then systematically investigated by measuring the viscosity of the N2bubble dispersed silicone oil with a rotating viscometer. This found that the relative viscosity is increased as the volume fraction of the gas phase is increased, ultimately transitioning from a Newtonian to pseudo-plastic fluid at higher gas phase rates. In addition, an empirical model for the viscosity of the slag foam was developed by modifying the Einstein-Roscoe equation, with this model capable of reproducing the variation in relative viscosity with various gas phase rates, shear rates, and bubble sizes. © 2014 ISIJ.

Nakagawa Y.,Jfe Holdings | Tada M.,Jfe Holdings | Kojima K.,Jfe Holdings | Nakamaru H.,Japan Research and Development Center for Metals
ISIJ International | Year: 2016

Soft-tempered, fine-grained ferritic steel is preferred for film-laminated steel for drawn cans from the viewpoints of surface quality and high formability. Generally, ultra-low carbon steel (ULC) is soft but has coarse ferrite grains. On the other hand, low carbon steel (LC) has a fine ferrite grain size but is hard and has inferior formability, and thus is not suitable for drawing. In order to solve this problem, the contents of carbon and niobium in ULC steel were varied in order to control the size of niobium carbide precipitates. This study suggested that the newly-developed steel has the potential to have an excellent balance of ferrite grain size and formability. © 2016 ISIJ.

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