The influence of carbon content on the mechanical properties of high yield strength bridge steel has been investigated.The results show that the excellent mechanical properties and corrosion resistance are obtained for the steel with carbon content of 0.03%-0.05%(mass percent).According to the results,a new weathering bridge steel plate with carbon content of 0.045%(mass percent) has been developed.The appropriate controlled cooling process should be taken due to the results of CCT(continuous cooling transformation) and TTT(time-temperature-transformation) to ensure both microstructure and mechanical properties.CCT curve of the newly developed steel shows that when accelerated cooling speed is higher than 5 ℃/s,the intermediate transformation products can be formed.The TTT curve displays that the intermediate transformation temperature ranges from 600 to 530 ℃.Yield strength of the newly developed steels reaches 500 MPa,and their elongation and toughness are excellent.
