Research On Corrosion Resistance Of Marine Steel And Electroless Plating Coating

Q235 steel is a kind of carbon-steel which was widely applied in the ocean. But Q235 steel will be corroded in ocean environment. If to a certain degree, marine accidents and economic losses will be triggered. It is particularly important to know about the corrosion resistant properties of Q235 steel in the seawater, and some anticorrosive measures should be taken.Corrosion resistant and corrosion mechanism of Q235 steel in simulated seawater immersion zone were analyzed by static coupon test method. The results show that, when the corrosion rate is uniform in that condition, corrosion rate is around 0.041 mm/a, belong to the corrosion level 4-5. The corrosion begin with pitting, with the corrosion time of increase,the pits increase and gradually linking, pits disappear and finally form a uniform corrosion layer. The corrosion layer is divided into two layers. The outer rust layer is γ-FeOOH, and the inner rust layer are the mixture of Fe3O4、α-FeOOH 、γ-FeOOH、β-FeOOH. Oxygen diffusion leads to the form of corrosion products.In order to improve the corrosion resistance of Q235 steel, electroless plating method was adopted to plating Ni-P coating on Q235 steel surface. The complex agent and temperature, in the process parameters of Ni-P chemical plating, are the main factors. Process recipe of electroless Ni-P was Preliminary explored and optimized by orthogonal test. The best process were obtained. Complex agent A is 8g/L, complex agent B is10g/L and the temperature is 85℃. The temperature is the biggest influence on the deposition rate and corrosion rate.The corrosion resistance of Ni-P coating and Q235 steel was compared and analyzed. The corrosion potential of Q235 was-0.54 v, the polarization resistance was 704 ohm The corrosion potential of Ni-P coating was-0.49 v, the polarization resistance was 1501 ohm.The results show that the seawater corrosion resistance of Ni-P coating is better than Q235 steel.