Effects of solution treatment on microstructure and fatigue crack propagation behavior of 2205 duplex stainless steel

Effects of solution treatment on microstructure and fatigue crack propagation behavior of 2205 duplex stainless steel (DSS) were studied by means of light microscopy, scanning electron microscopy, EDS and mechanical testing, etc. The results show that compared with the commercial hot-rolled plate, the fatigue crack growth threshold of solution-treated samples all increases obviously and the steady fatigue crack propagation rate all decreases with the samples solution treated in the range of 950 to 1150℃. At 950℃, σ phase is precipitated along the boundary between α phase and γ phase and in α phase, which leads to an obvious decrease of the steady fatigue crack propagation rate. With the further increase of solution temperature, the volume fraction of α phase increases gradually, σ phase dissolves, and the steady fatigue crack propagation rate increases at first and then decreases. When the solution temperature reaches 1150℃, the volume fraction of α phase gets a maximum, duplex crystal particle coarsens, and the steady fatigue crack propagation rate becomes a minimum. Meanwhile, the sample exhibits highest fatigue crack resistance. The phase transformation from γ phase to α phase and the precipitation and dissolution of σ phase both in the α phase and along the duplex boundary together with the crystal particle coarsening might be the reason for the non-monotonic variation of fatigue of DSS2205.