Experimental investigation on the low temperature fracture performance of Q690 steel for application to long-span high-speed railway bridges in Tibet harsh environment

Charpy impact test and three-point bending test on 32 mm and 50 mm thick Q690 high-strength steel were carried out according to the environmental features of plateau low temperature to assess the fracture toughness of long-span high-speed railway bridge steel in Tibet difficult environment. The results show that that the effect of temperature (T) on Charpy impact energy (AKV) and CTOD (δ) follows the Boltzmann function law. The ductile-brittle transition temperature of Q690 high-strength steel is determined using the Boltzmann function, and the mechanism of brittle fracture of high-strength steel caused by low temperature is revealed using a metallographic phase and microstructure of the target material. The nonlinear relationship between Charpy impact energy and CTOD is established based on the Roos-Kussmaul nonlinear empirical equation with the same thickness, which is basically consistent with the test data. As a result, the complex CTOD test, which is costly, can be determined by a simple low-cost Charpy impact test, providing guidance for the widespread application of Q690 high-strength steel in low temperature environments at high altitude or high latitude.