Research On Mechanism Of Inhibition Of Sodium Molybdate On Hydrogen Permeation Of 2205 Duplex Stainless Steel

2205 duplex stainless steel is composed of two phases of austenitic and ferrite,which has better corrosion resistance and mechanical properties than single austenitic stainless steel and ferritic stainless steel,so it is widely used in harsh environments.However,2205 duplex stainless steel is widely used in petroleum engineering,pipeline transportation,and marine equipment,which is very susceptible to the corrosion of the environment in the hydrogen environment.Hydrogen damage is a kind of hydrogen corrosion phenomenon that is ubiquitous in structural materials in the fields of petrochemical,aerospace,marine engineering,hydrogen storage materials,nuclear energy development,etc.It often leads to material mechanical properties failure or sudden brittle fracture.With the current development of marine resources and the continuous improvement of marine military requirements for material strength and corrosion resistance,the problem of high hydrogen embrittlement sensitivity of high-strength materials has become a key factor restricting the wide application of marine steel and its welded components.Therefore,it is of great significance to find a practical,efficient and green method to inhibit hydrogen damage and reduce the susceptibility of high-strength components to hydrogen embrittlement.In this study,sodium molybdate(Na₂MoO₄)was selected as the hydrogen inhibitor to investigate the inhibitory effect of sodium molybdate with different concentrations(0.005 M,0.05 M,0.2M)in the hydrogen charging solution on the hydrogen permeation inhibition of 2205 duplex stainless steel.Through a series of characterization methods such as hydrogen permeation current test,macro-electrochemical test,micro-area electrochemical test,etc.,the additive concentration with the most excellent hydrogen blocking efficiency is selected,and the possible mechanism of sodium molybdate blocking hydrogen is proposed.The results show:Under the action of sodium molybdate,the diffusion behavior of hydrogen into the2205 duplex stainless steel is significantly inhibited.The order of the hydrogen blocking effect of sodium molybdate is low concentration>high concentration>medium concentration.At the same time,low,medium and high concentrations of sodium molybdate all have different hydrogen blocking mechanisms: at low concentrations,sodium molybdate has a certain catalytic effect on hydrogen evolution,which greatly increases the hydrogen evolution potential,and a large amount of hydrogen ions are It is reduced to hydrogen and precipitates,which reduces the probability of permeating into the sample.This is achieved by promoting the Tafel reaction and promoting the electrochemical desorption of adsorbed hydrogen atoms;at medium concentrations,sodium molybdate acts as an active reducing agent.It seizes the opportunity of hydrogen ions to be reduced,and consumes a large amount of hydrogen ions in the reduction reaction;at high concentrations,in addition to the effect of consuming hydrogen ions,the reduction product formed on the surface of the sample precipitates a barrier(the composition is not determined),which makes HER It mainly occurs on the precipitation layer rather than the surface of the sample,so that the penetration of hydrogen ions into the sample is blocked,which can temporarily block the penetration of hydrogen ions.Finally,the corrosion resistance and mechanical properties of the pre-charged samples with different concentrations of hydrogen inhibitor added to the hydrogen charging solution were tested.The corrosion resistance and mechanical properties of the pre-charged samples were reduced compared to the same period of hydrogen charging but without the addition of sodium molybdate.Do not get a significant reduction,and the corrosion resistance and mechanical properties of the group added with sodium molybdate are more stable,which shows that sodium molybdate as an tentative hydrogen inhibitor is of practical significance.