Effect of strain rate on fracture behaviour of Cr18Ni11Ti stainless steel at high temperatures

The effect of strain rate on the fracture behaviour of Cr18Ni11Ti stainless steel at high temperatures was analysed. The steel was subjected to solid solution treatment at 1050 °C and ageing at 650 °C for 24 h. The high-temperature tensile properties of Cr18Ni11Ti stainless steel were subsequently investigated via high-temperature tensile testing at 650 °C and different strain rates (1.43 × 10^–1, 1.43 × 10^–2, 1.43 × 10^–3, 1.43 × 10^–4, and 1.43 × 10^–5 s⁻¹). The microstructure, precipitated phase, tensile fracture surface, and dislocation of the experimental steel were analysed by scanning electron microscopy, transmission electron microscopy and energy spectrometry. The results show that Cr18Ni11Ti stainless steel is mainly austenite, with a large number of twin crystals, chromium-rich precipitated phase and composite precipitated phases of TiC and AlMgCaO. With decreases in strain rate, the yield strength, ultimate tensile strength, and reduction in area also decrease. When the strain rate is high, obvious necking and ductile fracture occur in the experimental steel. However, when the strain rate is reduced to 1.43 × 10^–5 s⁻¹, the necking phenomenon is not obvious and intergranular brittle fracture appears. Greater segregation of P and S contents at grain boundaries, or dislocation motion creep and grain-boundary sliding creep, leads to brittle fracture of the steel at lower strain rates of 1.43 × 10^–4 to 1.43 × 10^–5 s⁻¹.