EFFECT OF DAMNIFICATION IN RUST LAYER ON CORROSION BEHAVIORS OF LOWCARBON BAINITIC STEEL IN THE ENVIRONMENT CONTAINING Cl−

The weatherability of weathering steel depends on the protection of the compact rust layers on its surface. However, the compact rust layers might be damaged when they were subject to external actions, for example, collision and scrape etc., which will influence the protective effect on steel base. It is deserved to put attention on further corrosion behavior of the samples with damaged rust layer, which will determine the long term corrosion property. In the present study, electrochemical measurement, metallographic observation and energy disperse spectrum analysis were employed to investigate the further corrosion behaviors of a low carbon bainitic steel in the environment containing Cl⁻, after its original rust layers had been damaged on different degrees. It was found that the damnification of rust layers on both the low carbon bainitic steel and low carbon steel as a contrast could be rapidly self–repaired in the further corrosion process. When damnification degree and further corrosion time are the same, the resistance and the repair ratio of damaged rust layers on the low carbon bainitic steel are higher than those of the low carbon steel. The fracture toughness of the steel base/rust layer interface of the low carbon bainitic steel is higher than that of the rust layers, so the rust layers would not be abscised thoroughly from the interface and some residual rust would be remained when the steel is subjected to applied actions. The formation of new rust at the damaged sites can be significantly promoted by the residual rust. The contents of Cu and Cr in the original rust layers are close to those in the newly formed rust layers, and both of them are equivalent to those in the steel base. These results indicate that low carbon bainitic steel with excellent mechanical properties and weld ability is a potential candidate for novel weathering steels with higher strength.