Secondary Materials in Steel Production and Recycling

Abstract

With regard to the utilisation of the by-products of the steelmaking process (slag, dust, sludge, mill scale) the German steel industry has been in a leading position for many years. Slags, especially those from the blast furnace process, are utilised as materials for the construction industry (road building, cement production, fertilisers). Dusts, sludges and mill scale are either re-used directly in the steelmaking process or treated in special equipment to recover valuable metals (iron, zinc). Steel is undoubtedly one indispensable material of our modern technologydriven society. At present, steel encompasses a class of over 2500 different steel grades, hence there is a wide variety of properties leading to an even wider range of uses. There are countless possibilities of combinations with regard to micro and macro structures, alloying elements, heat and mechanical treatment procedures. Steels represent materials with a high potential for innovation, although they have been known to mankind for several thousand years. Another peculiarity of steels is their high rate of recycling, some aspects of which will be discussed in this paper. There exist two different technological routes for steel production. One is based primarily on the reduction and smelting of iron ore, this is the so called blast furnace – oxygen converter route (BF-BOF). The other one is based on steel scrap smelting and employs electric arc furnaces (EAF). Steel scrap is used as a source of iron in both processes but the scrap proportions in the charge are quite different. While in electric steelmaking the iron-bearing charge consists only of scrap, the oxygen converter uses up to 25% scrap, the rest being hot metal from the blast furnace. It is evident that electric steelmaking plays a more important role in the recycling of steel than the BF-BOF process. That is why this paper concentrates on the material cycle steel-scrap-steel and discusses the complex relationships between