Compositional Variability in Recycled Steel Destined for Thermal Processing: A Supply Chain Approach

Unintentional compositional variability in steel can lead to several downstream thermal processing concerns. Compositional variability can arrive in the form of residual elements (e.g., Cu, Sn, N, Nb, Ti, V, B and several others) that cannot be removed from the steel once present, or it can take the form of intentional alloy additions that are meant to provide mechanical or other desirable properties. One factor that affects compositional variability in steel is the recycled steel added to the electric arc or basic oxygen furnaces during steel making. Recycled steel is often screened and sorted, but the methods employed by different facilities do not necessarily employ the same level of rigor and it is possible for steel makers to select alloy element substitutions for a single grade based on the available recycled steel. The research presented here focuses on the many sources of recycled steel, the methods for sorting recycled steel, and the regional variability in recycled steel composition in order to shed light on the bigger picture concern of controlling steel composition. Sources of information include repositories of data from US government sources (e.g., USGS), independent non-profit organizations (e.g., ISRI, AIST, SMDI) and self-reported data by companies. The research takes a supply chain approach, using Material Flow Analysis and Neural Network Analysis methods to map the movement of recycled steel in the United States. The results of this pilot study provide a regional comparison of recycled steel compositional variability and predictions for final product variability when additional screening methods are not employed.