Coherent precipitation of copper in Super304H austenite steel

The precipitation behavior of copper-rich phase in an austenitic stainless steel and the interface structure between the precipitates and the matrix have been investigated combining transmission electron microscopy and coarsening analysis. The fine dispersed Cu precipitates were spherical and highly stable in the austenite matrix, with the size being only 32 nm in diameter even after a long time 10,000 h aging at 650 °C. The average size of Cu precipitate was increasing with aging time, as predicted by the Lifshitz–Slyozov–Wagner theory. The coherent relationship between the precipitates and the matrix was preserved during the whole aging process, even at the later stage. The interfacial energy of Cu in the austenitic matrix has been independently derived from the data on coarsening experiment based on two kinds of approximations: γ-Fe and Fe–18Cr–9Ni–3Cu matrix were considered separately instead of complex austenite in this study. It was 0.086 J/m2 for Cu/γ-Fe and 0.017 J/m2 for Cu/Fe–18Cr–9Ni–3Cu. Both values are satisfied with the range of coherent interfacial energy. The coherent interfacial structure and highly stable microstructure play a key role on strengthening materials.