Copper in Steels: From Residual Contamination to a Functional Alloying Element

Steel recycling is fundamental for advancing a circular economy and green steel mission, as producing steel from scrap substantially reduces energy consumption and CO 2 emissions compared with ore‐based steelmaking. However, the uncontrolled retention of residual Cu in recycled steels poses a significant challenge known as copper contamination. During hot working, Cu enrichment at surfaces and near‐surface grain boundaries can lead to the formation of low‐melting Cu‐rich liquid films, which result in hot shortness and surface cracking. Moreover, depending on Cu content, precipitate size, and processing conditions, Cu segregation and precipitation of Cu‐rich phases during cooling or aging may cause embrittlement and reduced toughness. In contrast, when Cu incorporation is carefully controlled and combined with appropriate alloy design and processing parameters, it can enhance mechanical properties through nanoscale precipitate strengthening, improve corrosion resistance via the formation of protective patina layers, and impart antibacterial functionality in specific steel grades and environments. This work reviews the dual role of Cu as both a detrimental residual element and a beneficial alloying addition in steels and provides important considerations for the design of high‐performance, sustainable, and multifunctional Cu‐bearing steels with potential applications in automotive, construction, marine, pipeline, medical, food, and sanitary sectors.