Research On Corrosion Behavior Of TWIP Steel In Oilfield Simulated Environment

TWIP steel has broad application in the field of petroleum-engineering materials and the automotive industry due to its excellent work hardening.Adding alloy elements such as Cr and Mo can improve the toughness and corrosion resistance of TWIP steel.Cr,Mo and other alloy elements not only improve the corrosion resistance of TWIP steel,but also effectively improve its mechanical properties through solid solution.The basic constituent elements of TWIP steel are Fe-Mn-C.Alloy elements such as Cr and Mo can form carbides with C,which has an impact on the comprehensive performance of the material,especially the problem of corrosion and stress corrosion cracking in acid corrosion environments.So further research is needed.In paper,Fe-Mn-C twinning-induced plasticity steel（TWIP）is made by adding Cr and Mo elements.The effects of Cr/Mo carbides on the corrosion and stress corrosion behavior of TWIP steel are studied.In order to obtain carbide precipitates with different contents,three kinds of material are obtained by aging treatment,namely solution,700℃-6h,700℃-24h,respectively.The research shows that the MoC and Cr₃C₂,carbide precipitated phase,appear preferentially at the grain boundaries,and partly appears inside the grains as the aging time increases.Cr/Mo carbides and austenite matrix form a micro galvanic couple with a large potential difference,which will cause galvanic corrosion.As the aging time increases,the carbides increase and the corrosion becomes more serious.Due to the formation of galvanic couples,TWIP steel not only has corrosion behavior,but also has obvious hydrogen embrittlement sensitivity in the acid oil and gas field environment.Therefore,this paper continues to study its hydrogen embrittlement behavior.High-resolution SKPFM technology is used to observe the adsorption of hydrogen on carbides in situ.The results show that carbides have a stronger capacity of hydrogen absorption than metal substrates.As hydrogen traps,carbides effectively reduce concentration of the diffusible hydrogen in the metal substrate,reducing the hydrogen embrittlement sensitivity of TWIP steel.Tensile testing of TWIP steels with different aging treatments before and after electrochemical hydrogen charging demonstrates that the TWIP steel with carbides have a lower sensitivity to hydrogen embrittlement than that solid solution.Fracture analysis of the specimens reveals that a large number of secondary cracks begin to nucleate and propagate almost at the carbides.