Study On Stress Corrosion Behavior And The First Principle Of Shielded Stainless Steel H 2

For the stress corrosion behavior and cracking mechanism of duplex stainless steel in H2S environment are not form a unified understanding,this paper selects2205duplex stainless steel as the research object,using slow strain rate test and C-rings test to analysis its corrosion behavior and cracking mechanism in saturated H2S environment,using OM,SEM,EDS,XRD and electrochemical methods to analysis the development of crack,and based on the first principles density functional theory method,we calculate the diffusion coefficient and its transition states of H atom in alpha Fe and gamma Fe,from the electronic level reveals the intrinsic reason of stress corrosion cracking,finally we discuss the main alloy elements such as Cr,Mo,Ni which have an infulence on alpha Fe hydrogen diffusion,accumulating for the theretical development of alloy design data and menthods.In this paper,we have a certain understanding of the stress corrosion behavior and cracking mechanism of duplex stainless steel in H2S environment through theoretical and experimental research,the results are as follows:(1) The stress corrosion cracking(SCC) sensitive rates of2205duplex stainless steel in saturated H2S environment is between10-7and10-6s-1,fracture analysis shows that brittle fracture happened caused by H atom,at the same time companion with the cuctile fracture,we can preliminary indicated that the steel has a good resistance to H2S stress corrosion cracking from stress corrosion sensitivity coefficient;(2) C-rings without break in720hours in H2S environment further illustrates its ability to have a good resistance to H2S stress corrosion cracking,the crack distribution is loose and discontinuous in stress concentrated place,EDS spectrum analysis shows that the dissociation of H2S is conducive to the further development of the crack;(3) Electrochemical test results show that the SCC critical potential of2205duplex stainless steel is higher,the surface passivation film have a good protection effect on substrate materials,but once the passivation film destroyed,H atoms will penetrate into the substrate metal from pitting corrosion pit,then H atoms difuss and affregate in matrix metal,eventually leading to cracks;(4) The relation between diffusion coefficient and temperature about H atoms obtained in alpha Fe cells and gamma Fe cells are calculated by first-principles calculation: m2/s,the diffusion activation energy is about14.8kJ/mol, m2/s,the diffusion activation energy is about100.2kJ/mol,it shows that in the same environment conditions,H atoms are more likely to spread from alpha Fe cells,and when the distance between tow H atoms is greater than3.6A,the two atoms are attractive,so it is easy to form hydrogen molecules in crystal defect place,forming hydrogen pressure,ultimately result in the crack of the material;(5) Hydrogen induced cracking in2205duplex stainless steel in the ferritic phase characterized by transgranular cracking,in the process of transmission,which is hampered by the austenitic phase,made it developments along the two phase interface,it belongs to the mixed cracking way,ferrite phase are more likely to lead to crack;(6) Alloy elements of Mo greatly improve the hydrogen diffusion activation energy,it is good for H2S stress corrosion resistance of duplex stainless steel,so increasing the amount of Mo helps to prevent hydrogen induced cracking of ferrite.