Effects of high-temperature cooling and ultralow cyclic loading on mechanical behavior of Q450 weathering steel

The emphasis of this research is to investigate the mechanical behavior of Q450 weathering steel after high-temperature cooling and cyclic loading. A total of 174 steel specimens were tested in this study. The experiment consisted of three parts: heating and cooling tests, pre-cyclic loading tests (hysteretic tests) and tensile tests. These tensile specimens were first heated to nine target temperatures, and then cooled down to ambient temperature with water and firefighting foam. The effects of high temperatures and artificial cooling methods on the mechanical behavior of Q450 weathering steel were studied. According to the experimental results, the exposure temperature that caused a significant change in the mechanical behavior of Q450 weathering steel can be found. Meanwhile, the hysteretic behavior of Q450 weathering steel after being cooled from six target temperatures using water and firefighting foam was tested. Based on the post-fire mechanical behavior and hysteretic behavior of Q450 weathering steel, the damage degree of cyclic loading can be determined at each exposure temperature. Finally, the residual mechanical behavior of Q450 weathering steel after high-temperature cooling and cyclic loading was tested. According to the test results, hysteretic curves, skeleton curves and stress-strain curves were obtained. The mechanical properties such as elastic modulus, yield strength, ultimate strength and ductility were analyzed and discussed. To better understand the influence of high-temperature cooling and cyclic loading on the mechanical behavior, the macroscopic characteristics of Q450 weathering steel were observed. Moreover, polynomial equations and corresponding three-dimensional surfaces were proposed to predict the residual mechanical properties of Q450 weathering steel after high-temperature cooling and cyclic loading.