Corrosion Behavior Of Low Alloy Steel Containing RE In Soil

With the development of economy,more and more steel are used in our daily life.Many pipelines for energy transportation and large equipment construction have important connection with steel.The corrosion of steel in soil environment is one of the most important corrosion problems.The corrosion of steel in soil environment is not only considered as an important technical subject in the field of corrosion physics and science,but also an urgent practical problem in the application of underground engineering.Low alloy steel as a kind of structural steel is developed by adding a small amount of Mn,Si and Nb,V,Ti,Al and other alloy elements on the basis of carbon structural steel.However,the price of Nb,V,Ti and other alloy elements is relatively expensive.China has rich rare earth reserves and has a strong price advantage.Adding rare earth into steel can purify steel liquid,refine inclusions,and capture hydrogen to improve the mechanical and corrosion resistance of steel.In this paper,comparing with Q450 weathering steel,the corrosion behavior of low alloy steel with different rare earth content in soil simulation solution was explored,the corrosion kinetics was studied,and the effect of rare earth on corrosion resistance was studied.Then study the influence of different p H on the corrosion resistance of low alloy steel with best corrosion resistance,and explore the corrosion mechanism and corrosion kinetics in soil simulation solution with different p H value.The main conclusions are as follows.Rare earth can improve the corrosion resistance of low alloy steel by denaturing inclusions and promoting the formation of dense corrosion products.When the addition of rare earth in low alloy steel is 0.0047%,the corrosion resistance is the best,the corrosion rate is reduced by65%.Compared with Q450 weathering steel,the corrosion rate is reduced by 22.24%.The corrosion products of low alloy steel containing rare earth are double-layer structure,dense inner layer and loose outer layer.The corrosion products are mainly?-Fe OOH,Fe₃O₄,?-Fe OOH,etc.The reaction of low alloy steel containing rare earth in soil simulation solution is a first-order reaction,and the dissolution of anode is the restricted link of the whole process.In soil simulation solution,the smallest apparent corrosion rate constant k is 2.359×10^-4.The low alloy steel with 0.0047%rare earth content has better corrosion resistance in alkaline soil simulation solution.When the corrosion environment is acidic,the main corrosion products consist of?-Fe OOH.Due to the existence of H⁺,H₂ is formed,which leads to loose corrosion products and serious corrosion.Hydrogen evolution reaction is the restricted link.When the corrosion environment is alkaline,the formation of corrosion active point on the metal surface and the dissolution rate of anode are the restricted links.OH^-can promote the transformation of?-Fe OOH to more dense Fe₃O₄ and?-Fe OOH,forming a more stable corrosion product layer,thus hindering the diffusion of corrosive ions in the solution and protecting the matrix effectively.