In Situ Observation of High‐Temperature Microstructure of Cu‐Bearing 2205 Stainless Steel

The repeated recycling of scrap steel introduces and progressively enriches residual Cu in recycled stainless steels. To investigate the influence of Cu on the high‐temperature phase stability and microstructural evolution of 2205 duplex stainless steel, in situ high‐temperature observations were conducted using laser scanning confocal microscopy. The results reveal that increasing Cu content leads to a stable increase in the γ:α ratio. Meanwhile, the temperatures at which austenite transforms to ferrite initially decrease and subsequently rise with further Cu addition. This dual behavior arises because Cu enhances the thermodynamic activity of Cr, thereby promoting δ‐ferrite formation; simultaneously, Cu acts as an austenite stabilizer, and its influence on expanding the γ‐phase region becomes increasingly dominant at higher Cu concentrations. Cu addition (≤1.9 wt%) exerts a negligible influence on the liquidus temperature, which remains consistently above 1450 °C. No evidence of Cu segregation, intergranular liquation, or localized melting was observed, which indicates that Cu would not induce hot cracking susceptibility under typical processing conditions.