Experimental study on fatigue behavior of Q420 high-strength steel at low temperatures

Engineering structures are erected in all kinds of terrain and climate, and structural deformation and vibration may appear in anytime, such as deflection, shrinkage-expansion and vibration response. Fatigue failure of steel structure is a long-term behavior and difficult to estimate, especially in low temperatures. In order to study the fatigue behavior of Q420B steel at low temperatures, this paper conducted a series of experiments. Firstly, Charpy V-notch impact tests and strength tests of Q420B steel under normal and low temperatures were performed, and this type of steel can meet the requirements of Chinese and American standards. Secondly, the test specimens, temperature control system and loading method were designed, after which the fatigue tests of Q420B steel plates were carried out under different stress amplitudes (0.5 fy, 0.7 fy and 0.9 fy) and different temperatures (25 °C, 0 °C, −15 °C and −30 °C, i.e. 298 K, 273 K, 258 K and 243 K), respectively. At the stress amplitude 0.5 fy, all the cyclic loading number of the specimens exceeded 2.0 million times, and no fatigue fracture or obvious deformation appeared under above temperatures. However, the fatigue fracture occurred at the fatigue stress amplitude 0.7 fy and 0.9 fy, and the fatigue life obviously increased with the decrease of temperature. Therefore, it can be concluded that the low temperature can improve the fatigue performance of Q420B steel in some degree. What's more, the tested fatigue life was larger than the theoretical values of the current specifications. Lastly, the S-N curves of Q420B steel under different temperatures were provided.