The Corrosion Resistance Of Low Carbon Bainitic Weathering Steel In The Coastal Atmosphere And Industrial Atmosphere

With the development of economy and society and the advancement of science and technology, steels with high strength and toughness, excellent impact properties in low temperature, highly weldable and excellent corrosion-resistant are being eagerly needed in the areas of the oil and natural gas, car manufacturing, bridge construction, mechanical and military industry. However, because of the shortage of energy, the cost of the production of steel should be controlled strictly. The low carbon bainitic weathering steel alloy with its unique design, excellent overall performance and low cost is widely applied to all fields.This paper refers to the chemical composition and mechanical properties of steel used in offshore oil platform. Two different low carbon bainitic weathering steels were designed. The one is Cu, P free steel (1#) and another steel contains Cu, P (2#). In the experiment carbon steel Q345and weathering steel09CuPCrNi were used as comparing steel. Simulating ocean atmospheric-, industrial atmospheric-and coastal atmospheric corrosion tests were conducted, to evaluate the corrosion resistance of the new low carbon bainitic weathering steel.In this paper, the weight gain (weight loss) experiment, XRD analysis, morphology observation by SEM and electrochemical experiment were performed to compare the corrosion resistance of four steels. The results show that in the three corrosion experiments, Cu-P composite adding low carbon bainitic steel (2#steel) has the best corrosion resistance, the corrosion resistance of the traditional weathering steel09CuPCrNi has little difference with the low carbon bainitic weathering steel without Cu, P. Q345steel has the worst corrosion resistance. In the corrosion process the corrosion products of four steels are all Fe+3O(OH)、FeO(OH) and Fe3O4. The corrosion products of outer rust layer is mainly Fe+3O(OH), the corrosion products of inner rust layer is mainly Fe3O4. Cl-environment promotes the formation of β-FeOOH which does not have the protective role. With the elongation of corrosion time β-FeOOH transforms to γ-FeOOH and α-FeOOH. The rust layer of Cu-P composite adding low carbon bainitic weathering steel consists of protected corrosion product α-FeOOH, which can inhibit the corrosive ions penetrating into the rust layer apparently. The polarization curve parameters of the four steels’bare samples have less difference, but that of the samples with rust became larger. The Cu-P composite adding low carbon bainitic weathering steel has the smallest corrosion current density, the highest corrosion potential, polarization resistance and rust resistance.