Effect of ageing on precipitation and impact energy of 2101 economical duplex stainless steel

The impact energy and microstructure of a thermally aged 2101 duplex stainless steel with composition of Fe–21.4Cr–1.2Ni–5.7Mn–0.23 N–0.31Mo were studied. The results showed that the room temperature impact energy of specimens decreased gradually with ageing temperature up to 700 °C and then increased with aging over 700 °C. The minimum value of impact energy was 37 J after 700 °C aging, which was only 34% of that for as-annealed specimens. For specimens aged at 700 °C, the room temperature impact energy decreased significantly after 3 min and was halved after 10 min. Fractographs showed that, with increasing aging time, the fracture morphology changed from fibrous fracture to transgranular and intragranular fracture. Scanning electron micrographs revealed that many precipitates were distributed along α/γ and α/α interfaces. The precipitates were extracted and confirmed by X-ray diffraction to be Cr₂N. Therefore, it can be concluded that precipitation of Cr₂N is the main reason for the decrease of impact energy in aged 2101 duplex stainless steel.