2024/06/04

Nippon Steel Co., Ltd.

Nippon Steel Co., Ltd. (hereafter, Nippon Steel) received the “Invention Award” for “inventing chromium resource recycling/environmentally friendly stainless steel processes” at the Reiwa 6 National Invention Awards by the Inventions Association. The National Invention Award is a traditional and prestigious award held for the purpose of encouraging and fostering inventions and contributing to the improvement of science and technology and industrial development in Japan. Also, the award ceremony will be held at Hotel Okura Tokyo on Thursday, July 11th this year. An overview of the winning inventions is as follows.
＜Award contents＞
(1) Award name: Invention Award
(2) Award title: Invention of chromium resource recycling and environmentally friendly stainless steel processes
(3) Winners
Asahara Norifumi, Electric Furnace Laboratory Research Section Chief, Steelmaking Research Division, Process Research Institute, Technology Development Division, Nippon Steel Corporation
Katsuhiko Kato, former Steel Engineering Group Manager, Steel Division, Yawata Steel Works, Nippon Steel Co., Ltd.
Ogawa Yuji Former Chief Researcher, Steel Research and Development Department, Environmental and Process Research and Development Center, Nippon Steel Co., Ltd.
Hirashima Naoki Former Director of Stainless Steel Planning Office, Stainless Steel Division, Yawata Steel Works, Nippon Steel Co., Ltd.
Mikio Futaka Former Steel Engineering Group Manager, Steel Division, Yawata Steel Works, Nippon Steel Co., Ltd.
(4) Overview
The present invention is a technology that enhances chromium reduction and recovery capacity in stainless steel processes, makes effective use of chromium resources, and reduces the environmental impact of slag, which is a by-product.
Chromium resources are unevenly distributed in some countries, and in Japan, it is an important mineral subject to national reserves from an economic security perspective. Most chromium is consumed in stainless steel, but global stainless steel production is increasing year by year, and saving chromium resources in stainless steel is an urgent issue. In the stainless steel manufacturing process, iron source and chromium source are dissolved, and carbon as an impurity is removed by oxidative refining, but during this process, part of the chromium becomes an oxide and is lost from the molten iron side to the slag side. In the conventional method, reduction refining is carried out in the same furnace after oxidation refining, and chromium reduction recovery capacity was insufficient.
In the present invention, we have developed a technology to control molten iron components and slag components in electric furnaces that perform reduction refining after completely separating oxidation refining and reduction refining. Specifically, by increasing the carbon concentration in molten iron during reduction, the reducing power was greatly increased due to thermodynamic interaction, and chromium oxidation loss was thoroughly reduced. Also, during reduction refining, both solubility (action that makes the oxide melt easier) and reactivity (action that makes the chromium reduction reaction from the oxide easier to proceed) are required, but by controlling it to an optimal slag component using alumina or lime without environmental impact, we achieved both solubility and reactivity without using fluorite, which has an environmental impact when using slag. As a result, we have established a fast and highly efficient chromium reduction recovery process at a level that was previously difficult on an industrial scale.

Return to the list of press releases