Metallurgical issues related to ferrous scrap: residuals

While scrap metal has become an important raw material for the steel industry, with appropriate conditioning and treatment, its use is not without its problems.

These problems are of two kinds: adaptation to the melting process, and adaptation to the manufactured product, essentially to its properties.

Indeed, by its very nature, scrap has the composition of steel, and this composition varies according to the grade, with the addition of alloying elements, usually in small quantities (high-alloy steels such as stainless steels are, in principle, recycled separately). Coating metals such as zinc and tin are frequently present, as are metalloids such as sulfur and phosphorus, and of course carbon and nitrogen. What's more, despite grinding and magnetic sorting, other metals associated with steel in the equipment, such as copper and aluminum, are entrained and remain until the melting process.

Finally, there is an interaction between the steelmaking process and the final composition of the steel, due to the elimination of certain elements. On the other hand, the melting of scrap in an electric furnace results in a high nitrogen uptake, which characterizes this process. The importance of nitrogen justifies a special paragraph.

In addition, detailed product-by-product properties show that the influence of an element depends not only on its average content, but also on interactions with other elements and with thermomechanical cycles, in particular segregation during casting, heating and cooling, with the added effect of wrought or treated materials.