Potential Influences of Impurities on Properties of Recycled Carbon Steel

Contamination with tramp elements is a major concern in steel recycling. This study aimed to identify the influence of impurity elements on the major properties of carbon steel. The content of impurity elements in recycled steel was determined via elemental analysis of randomly sampled steel bars. Of the 23 impurity elements considered, 15 were found to be mixed in the recycled steel. Industrial standards stipulate that the six major properties of carbon steel are tensile strength, elongation, yield point or proof stress, soundness in the welding area, fracture toughness, and bendability. The influence of the fifteen impurity elements on all of these properties except bendability was investigated by reviewing previous academic reports. Properties related to strength and stress were found to be enhanced by the presence of almost any impurity, while elongation and welding soundness were often compromised. The influence of impurities on the other properties remains largely unknown. The negative effects of impurities on the workability and weldability can be minimized by adjusting the steelmaking, casting, and annealing processes, or rethinking the design of products and manufacturing processes. Further, the incorporation of impurities may be prevented during the recovery of steel scrap from end-of-life products. A useful approach to the prevention of the negative influence of impurities is a new concept termed R-PSPP, which stands for recovery, process, structure, property, and performance.