Abstract
The effects of precipitation of intermetallic phases on the microstructure, ferrite content and hardness in 22Cr-5Ni-3Mo-0,15N (wt.%) duplex stainless steel (DSS) have been investigated after ageing heat treatment in the temperature range of 400-800 °C for 30 min, 2, 10, and 100 h. During ageing at 400 and 500 °C, the hardness of the ferrite phase increased. The embrittling reaction, termed "475 °C embrittlement", due to the decomposition of the ferrite phase into a Cr-rich, α', and Fe-rich, α was observed. During ageing in the temperature range of 600-800 °C various intermetallic phases precipitated in DSS (σ, χ, γ₂, R-phase, chromium carbides and nitrides). The hardness increased and ferrite content decreased with an increase of content of intermetallic phases.

Key words
duplex stainless steel, intermetallic phases, 475 °C embrittlement, ferrite content

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