Exploiting Residual Elements Arising from Scrap Steel in Future Sustainable Steel Alloy Design

More scrap steel is being used as feedstock during steelmaking to reduce CO 2 emissions, which results in increasing residual element content in the steel, such as Cu, Sn, Cr, Mo, and Ni. Significant research has been carried out on detrimental effects (e.g., hot shortness from Cu) and associated mitigation routes (e.g., adding Ni). However, less has been reported on the potential advantages that can arise from the presence of residual elements. This article reports how residual elements can be exploited to provide microstructure control during processing, with particular attention to Cu and Sn and their effect on grain growth, recrystallization, phase transformation, and strengthening. Examples include how the solute drag effect on austenite grain growth and recrystallization is significant for Sn (greater than that of Mo), while Cu only has a minor effect. Sn and Cu provide solid solution strengthening (120 and 38 MPa/wt%, respectively), while Cu also forms precipitates, although at residual content levels, precipitate strengthening is less significant as precipitates preferentially form on cementite. A case study is presented where deliberate Nb microalloying additions can be reduced, while achieving the same strength from austenite grain size control, due to the presence of residual levels of Cu and Sn.