Effect of sigma phase precipitation on the mechanical and wear properties of Z3CN20.09M cast duplex stainless steel

The effect of sigma phase on the mechanical and wear properties of a Z3CN20.09M cast duplex stainless steel (CDSS) used in primary coolant pipe of nuclear power plants has been investigated. The experimental results showed that the sigma phase precipitated from ferrite at a temperature range of 600–900 °C. The tensile and yield strengths of the specimens aged at 700 °C decreased first and then increased with the increase of aging time. With increasing aging time, the impact energy of specimens decreased slightly before 4 h and then dropped drastically when aged a longer time more than 10 h. Fracture surface analysis showed that the hard and brittle sigma phase degraded the toughness of the aged steel. The hardness and wear resistance of the specimens aged for 1–4 h were lower than those of un-aged ones. However, the higher values of hardness and wear resistance were got in the specimens aged more than 10 h.

► The σ phase in the steel precipitated at a temperature range of 600–900 °C.
► The decomposition of α-ferrite into γ2 and σ phase in aged specimens is suggested.
► The tensile and yield strengths decreased first and then increased with aging time.
► The impact energy decreased slightly first but then drastically with aging time.
► The hardness and wear rates are not sensitive parameters to aged specimens.