Research Of Corrosion Behavior Of A572Gr65 With RE Element

China is a Marine big county and has expanded its utilization of the ocean from traditional transportation to production,communication,power transmission,storage and so on.However,the corrosion environment of the ocean is complex.There is a large amount of cl~-in the seawater,which has a large permeability and can increase the conductivity of the solution and accelerate the corrosion rate of the metal.Therefore,the corrosion and protection of the steel in the ocean has always been a hot topic in the research field at home and abroad.A572 Gr65 is high strength and low alloy niobium vanadium structural steel.It is equivalent to the national standard Q450.The steel has some characteristics:low carbon,low silicon,high strength and high toughness.It has good comprehensive performance.With the development of low alloy high structural steels,they will be more and more widely used in the large marine facilities and large steel structure.China is rich in rare earth reserves and is superior in lowcost.Rare earth can improve the mechanical properties and corrosion resistance of steel by purifying liquid steel,changing the composition and morphology of inclusions,controlling grain size and microalloying.In this paper,the samples are the A572 Gr65 with different RE content.The immersion experiment and electrochemical corrosion experiment are used to study the corrosion behavior of the A572 Gr65 with different RE content in the simulated seawater.The water-soluble imidazoline is also selected as the corrosion inhibitor and the corrosion inhibitor is studied.The corrosion process and products are analyzed by SEM,XRD and OM.The experimental results show that rare earth can effectively improve the corrosion resistance of samples.The corrosion rate is reduced,the corrosion potential moves right and corrosion current decreases.When the rare earth content is 47ppm,the corrosion resistance of the test steel is the best.After adding rare earth,the inclusions in the steel become the oxygen sulfide of rare earth and the size of inclusions decreases.It leads to reduce the active area of corrosion and the pitting area.Through the analysis of the corrosion morphology and the corrosion products can be found that the rare earth ions can have obvious effect of inhibiting corrosion.The content ofγ-Fe OOH in the corrosion products reduces and the density and adhesive ability of rust layer become better,so the corrosion product film becomes more stable.This leads the charge transfer resistance increase and plays an important role in preventing the invasion of the corrosive Cl~-,so the corrosion resistance of samples increases.In the process of corrosion,the pitting gradually changes into uniform corrosion and the formation of the active point is the restricted link in the whole corrosion process.Water-soluble imidazoline as a green corrosion inhibitor,has good corrosion inhibition for steel.The experiments show that there exists the competing adsorption phenomena between imidazoline molecules and water on the surface of samples.The imidazoline molecules adsorpted on the surface of the samples can form the adsorption film on the surface of samples.The odsorption film can effectively hinder the transfer of electric charge and suppress corrosion.When the inhibitor concentration is 80 mg/L,the inhibition rate can reach 95.73%.