High temperature ageing behaviour of a duplex stainless steel

The present study concerns the influence of ageing parameters on the microstructure and mechanical properties of a duplex stainless steel. Microstructural evolution is extremely sensitive to chi and sigma phase precipitation during ageing treatment. The precipitation of chi phase increases with the increase of ageing time from 15 min to 120 min at 900 °C. The precipitation rate of secondary phases in 900 °C is faster than that at 700 °C. High hardness is directly related to the abundant chi and sigma phase precipitation in the microstructure. Sigma phase was completely dissolved by heat treatment at 1000 °C; the mechanical properties were then influenced by the sigma-free equivalent volume fractions of ferrite and austenite.