Effect of test temperature on the cracking resistance of a vessel steel with various impurity content

1. The results show that at temperatures of 293 and 623 °K the fatigue crack growth rate in the 15Kh2MFAA and 15Kh2MFA steels coincides in the middle section of the KDFF. At the same time, the threshold stress intensity factor Kth for 15Kh2MFAA steel is higher than for 15Kh2MFA steel. The increase of the stress ratio from 0.1 to 0.7 reduces the fatigue crack growth rate in both steels. 2. The fracture toughness characteristics Kfc1, Kfck, KIc (KQ5%) of the 15Kh2MFAA and 15Kh2MFA steels increase with increase in test temperature and in the temperature range 250–623°K they reach the upper plateau. In the low-temperature range (>123°K) the characteristics Kfc1, Kfck, KIc converge but the distinctive lower plateau does not form. 3. In the low-temperature range (123–200°K) the cyclic nature of loading reduces the fracture toughness characteristics Kfc1, Kfck, and σfc1, σfck in comparison with the values of KIc and σcmax in static loading. 4. At temperatures below 150°K the fracture resistance in static loading of 15Kh2MFAA steel is lower than that of 15Kh2MFA steel, and in the temperature range 150–623°K it is higher than that of 15Kh2MFA steel. Below 243°K the fracture resistance in cyclic loading 15Kh2MFAA steel is higher than that of 15Kh2MFA steel, and in the temperature range 243–623°K it is lower than that of 15Kh2MFA steel.