Corrosion Behavior And Mechanism Of New Type High-Strength 3Ni Steel In The South China Sea Atmosphere Environment

3Ni steel has good corrosion resistance in the marine atmosphere environment.However,the corrosion mechanism in the harsh marine atmosphere environment,such as the South China Sea,is not fully understood,which is a vital issue to retard the improvement of its comprehensive performance and restrict the application in the engineering field.In this work,the microstructure characterization,indoor drywet cyclic corrosion test,and slow strain rate tensile(SSRT)test are used to research the contribution of Mn and Cu to the general corrosion and stress corrosion cracking(SCC)of 3Ni steel in South China Sea atmosphere environment.In addition,the corrosion dynamic mechanism of 3Ni steel under different applied stress are studied by corrosion big data technology combined with the machine learning method.The main findings show:The addition of Mn addition can increase the corrosion resistance.However,only general corrosion is determined from 3Ni steel with different amounts of Mn in the South China Sea atmosphere environment.The higher Mn content can promote the delamination of the rust layer and reduce the ?/?*ratio;hence,more defects are generated in the rust layer,resulting in lower 3Ni corrosion resistance as the rust layer has less resistance to corrosion ions.The addition of Cu improves the corrosion resistance of 3Ni steel in the South China Sea atmosphere environment.The CuO in the rust layer reduces corrosion resistance by inhibiting the anodic reaction transfer from localized corrosion to general corrosion.The type of Cu in 3Ni steel affect corrosion resistance.The Cu precipitation offers higher corrosion resistance than that Cu exsits in solid solution state in 3Ni steel.Cu precipitation increases the proportion of CuO in the early corrosion rust layer and promotes Cu enrichment at the matrix/rust layer interface.The sensitivity of SCC for high-strength 3Ni steel in the South China Sea atmosphere environment is low,but the sensitivity increases under hydrogen evolution conditions.The higher Mn content and Cu precipitation have beneficial effect on resisting hydrogen induced cracking.The increased Mn effectively reduces the diffusible hydrogen content,which promotes acicular ferrite formation and reduces the residual austenite,resulting in lower sensitivity to hydrogen induced cracking.The appearance of Cu nano-precipitate inhibits dislocation proliferation and hydrogen atom movement by pinning dislocations,which makes it difficult for SCC sensitive site to reach critical hydrogen concentration and reduce the SCC sensitivity.The microstructure has a significant effect on SCC to high-strength 3Ni steel in hydrogen evolution conditions.3Ni steel with lath bainite has the highest SCC sensitivity,followed by tempered martensite 3Ni steel,and then 3Ni steel with lath martensite microstructure.Differences in phase,hydrogen trap density,grain boundary type,and dislocation density influence the interactions between materials and hydrogen atoms,resulting in different microstructures having various SCC sensitivity.The corrosion dynamic mehanism of high-strength 3Ni steel in the South China Sea atmosphere environment can be effectively explored by corrosion sensor and machine learning method.The corrosion big data clock diagram method and corrosion cumulative electrical quantity method are used to analyse the multidimensional and massive corrosion data,which are collected by the corrosion sensor.The dynamic corrosion rate and rust layer evolution in the whole working period of high-strength 3Ni steel in the South China Sea atmosphere environment are obtained.Furthermore,the corrosion mechanism difference of high-strength 3Ni steel with different applied stress is identified.In addition,the difference contribution of the environment,materials' factor(composition and microstructure)to the dynamic corrosion rate is predicted from the machine learning method.