Substance Flow and Stock of Chromium Associated with Cyclic Use of Steel in Japan

Previous studies have pointed out that some quantity of ferritic stainless steel scrap is mixed with carbon steel scrap, thus resulting in the accumulation of chromium in carbon steel products. Chromium substance flow accounts for 97% of its consumption in Japan. This paper describes the analysis chromium substance flow in stainless steel, other alloy steels, and carbon steel in Japan. The analysis was carried out using dynamic modeling. To classify the different kinds of alloys, stainless steel is subdivided into 13Cr, 18Cr, Cr-Ni, and Cr-Ni-Mo. Heat-resistant steel, structural alloy steel, bearing steel, and spring steel are also considered as steel alloys that include chromium. Carbon steel is classified into BOF (basic oxygen furnace) carbon steel and EAF (electric arc furnace) carbon steel to reflect differences in the raw materials from which they are composed. It was found that in-use stocks of chromium in the forms of stainless steel and other alloy steel in 2005 were 3.4 and 0.7 Tg, respectively. Other chromium stock as an alloying element in carbon steel was estimated as being 0.7 Tg in 2005, and it is dissipated in the carbon steel cycle. From the results of the dynamic model, the rates of ferritic stainless steel and other alloy steel recovered as carbon steel were approximately 40 and 80%, respectively, in 2005. Chromium accumulation in EAF carbon steel was dynamically analyzed from 1990 to 2030. On the basis of the assumption that future steel demand will be the same as the current demand, it is predicted that the mean chromium content in EAF carbon steel will gradually increase and reach 0.24% in 2030.