Issue 36

F. Z. Liu et alii, Frattura ed Integrità Strutturale, 36 (2016) 139-150; DOI: 10.3221/IGF-ESIS.36.14 141 when the material was tempered at 400 °C, elongation decreased under the effect of temper embrittlement. Figure 1 : Vibration tendency of the mechanical performance of the experimental materials along with tempering temperature. The delay fracture resistance of experimental materials Fig. 2 and 3 show the curves for applied stress – time of failure (S-T) in notched tensile experiment. It can be seen that, time of failure increased with the decrease of applied stress. Compared to samples in quenching state, the S-T curve of samples at different tempering temperatures moved towards upper right first and then left lower when the tempering temperature rose to 400 °C. It indicated that, tempering processing improve the delay fracture resistance of the experimental materials; and samples processed at tempering temperature of 200 °C had the highest critical fracture stress and the longest fracture lifespan (Fig. 3). Figure 2 : Curves for stress – time of failure of the experimental materials in quenching state in notched tensile experiment. Results of notched tensile experiment carried out on the experimental materials are shown in Tab. 2. Fig. 4 and 5 show the vibrations of critical fracture stress and delay fracture strength ratio of the experimental materials along with the changes of strength and tempering temperature. It can be seen that, critical fracture stress and delay fracture strength ratio of the experimental materials except for samples processed at a tempering temperature of 400 °C gradually increased with