Effects of solution treatment and continuous cooling on σ-phase precipitation in a 2205 duplex stainless steel

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2001-07, Vol.311 (1), p.28-41
• Main Authors: Chen, T.H, Yang, J.R
• Format: Article
• Language: English
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Duplex stainless steel; Element partitioning; Exact sciences and technology; Heat treatment; Materials science; Metals. Metallurgy; Orientation relationship; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Precipitation; Production techniques; Sigma-phase; Solid-phase precipitation; Solution treatment; Thermochemical treatment and diffusion treatment
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/S0921-5093(01)00911-X

A commercial 2205 duplex stainless steel with three different solution treatments (at 1020, 1080 and 1200°C for 3 min) followed by continuous cooling at four respective cooling rates (1, 0.5, 0.25 and 0.1°C s −1) has been investigated by means of optical metallography, transmission electron microscopy, electron probe microanalysis, X-ray diffraction and differential thermal analysis. It is found that the lower solution treatment temperature with the lower cooling rate significantly enhanced the σ phase transformation. The σ precipitate could be detected when the specimens were solution-treated at 1020 and 1080°C and cooled at the rate of 0.25°C s −1; substantial amounts of σ phase formed when the specimens were cooled at 0.1°C s −1. The precipitation of σ phase was considerably retarded as the solution temperature increased from 1080 to 1200°C. The precipitation behaviors of σ phase and M 23C 6 carbide were characterized by transmission electron microscopy. The results indicated that the Cr- and Mo-rich σ phase preferentially nucleated at the pre-formed M 23C 6 carbide particles, which were located at δ/ γ interface or within δ ferrite grain. The selected area diffraction patterns displayed the complicated crystallography of σ phase, and revealed the orientation relationships between the interfacial σ precipitate and adjacent matrix phases.