Mechanical properties and marine atmosphere corrosion behavior of E690 ocean platform steel

Compared with E36 ocean platform steel, the microstructures and mechanical properties of three kinds of E690 ocean platform steels were studied as well as their corrosion behavior in simulating marine atmosphere. The corrosion rates during different periods were measured by the weight-loss method, the morphology and microstructure of the surface corrosion products were analyzed by scan electron microscopy and X-ray diffraction, and the grain boundaries were examined through electron backscattered diffraction. E690 platform steels consisting of bainite demonstrate outstanding mechanical properties and their impact values at-40℃ exceed 200 J. The majority of grain boundaries are sub-grain boundaries in a range from 3° to 15° and high angle grain boundaries surpassing 50°. The minimum corrosion rate of E690 ocean platform steels after 16 d is 0. 84 mm·a^-1, which is far below 1. 4 mm·a^-1 of ferrite + pearlite steels. The corrosion rates also tend to stabilize due to a compact rust layer. The rust layer consists of Fe₃O₄, α-FeOOH, β-FeOOH, γ-FeOOH and amorphous substances. It is revealed that the heat treatment and microstructure play an important role in the corrosion behavior during the earlier stage, but the chemical composition and density of the rust layer influence the corrosion behavior greatly in the later stage.