Fracture toughness and mechanism of 20 steel under different conditions of low temperature and stress states

In this paper, the influence of low temperature and stress state on the fracture behaviour of 20 steel was investigated from both macroscopic and microscopic points of view. At the temperature of 20°C, -60°C, -100°C, -140°C and -180°C, the macroform fracture toughness of critical void growth ratio VGC was determined by use of the smooth and notched tensile specimens, and the microform ones RC/RO were quantitatively measured under the Scanning Electron Microscope (SEM). The variations of VGC, RC/RO and the effective fracture strain εf, with the temperature or stress state, were illustrated. According to the analysis from the measurement data, the suitability of the fracture theory of void growth ratio for the steel under different temperatures was discussed.