Mechanical properties deterioration of high strength steels after high temperature exposure

摘要

Presented in this paper are test results on mechanical properties of high strength Q690 steel after being exposed to high temperatures. Yield strength, tensile strength, elastic modulus and ratio of ultimate elongation were obtained based on tension stress-strain relationships of Q690 steel after exposure to temperature ranging from 300 to 1000 degrees C. Two cooling methods, namely air cooling and water cooling, were applied to cool down the heated specimens from high temperature to ambient condition. The mechanical properties comparison on different high strength steels with various thickness are carried out to investigate the effect of thickness on reduction factors of strength and elastic modulus of high strength steels after high temperature exposure. The study shows that the strength deterioration after being exposed to high temperatures is not significant for the temperature up to 600 degrees C, no matter which cooling method is applied. The strength reduction is approximately 25% after being exposed to temperature 700 degrees C. However, when the air cooling is applied, the strength decreases significantly and the ultimate elongation increases noticeably being exposed to temperature 800 degrees C-1000 degrees C but the opposite is found when water cooling is applied. The influence of elevated temperature and cooling method on the elastic modulus is negligible. The deteriorations of the material properties are different for different steels. The strength deterioration of thinner steel plate is more significant than that of thicker steel plate. Equations to predict residual factors of mechanical properties of high strength Q690 steel with 20 mm thickness were proposed to evaluate the post fire capacity of high strength Q690 steel members. (C) 2018 Elsevier Ltd. All rights reserved.