Effects of microstructure changes on the superplasticity of 2205 duplex stainless steel

The high temperature deformation behavior of 2205 duplex stainless steel under different conditions had been studied by tensile tests. The whole tensile test was conducted at a constant temperature 950 °C with an initial strain rate 1.5 × 10−3/s. Some tests were interrupted purposely and then the samples were quenched using water. Elongations of the fractured specimens were calculated. Microstructure changes just before and during the deformation were observed. Phase ratio of σ precipitate was analyzed. The results showed that the superplasticity of 2205 duplex stainless steel was directly affected by the microstructure before the deformation. The recrystallization phenomenon was distinct along with the homogenizing time and the grains became equiaxed and stable. Meanwhile, the quantity of σ phase increased when prolonged the homogenizing time. After homogenized for 7 min before the tensile test, the σ phase ratio was about 4.8% and the grain size was about 998 nm, the maximum elongation value 1260% was obtained. During the deformation progress, dynamic recrystallization was observed and quantity of σ phase increased with the increasing of deformation strain. The σ phase restricted the grain growth and kept the equiaxed duplex structure stable with a grain size of about 1 μm.