日本における鉄鋼材の循環利用に伴うクロムの物質フロー

抄録

Previous studies pointed out that some ferritic stainless steel scrap is mixed in carbon steel scrap and chromium is accumulated in carbon steel product. This paper analyzed Japanese substance flows of chromium involved in stainless steel, other alloy steel and carbon steel by using a dynamic modeling. Those substance flows covered 97% of chromium consumption in Japan. To classify different kind 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 taken into account as steel alloys including chromium. Carbon steel is classified into BOF (basic oxygen furnace) carbon steel and EAF (electric arc furnace) carbon steel due to difference of raw materials. It was found that in-use stock of chromium as stainless steel and other alloy steel were 3.4 Tg and 0.7 Tg in 2005, respectively. Other chromium stock as an alloying element in carbon steel was estimated as 0.7 Tg in 2005, which is dissipated into the carbon steel cycle. From the results of the dynamic model, rates of ferritic stainless steel and other alloy steel recovered as carbon steel were approximately 40% and 80% in 2005, respectively. Chromium accumulation in EAF carbon steel was dynamically analyzed from 1990 to 2030. Based on an assumption that future steel demand is same to the current demand, it was predicted that the average chromium content in EAF carbon steel would gradually increase and reach to 0.24% in the year 2030.