Effect Of Microstructure Characteristics On Hydrogen Diffusion Behavior And Hydrogen Embrittlement Sensitivity Of EH36 Steel

By studying the hydrogen diffusion and hydrogen embrittleness failure behavior of EH36 offshore steel in marine service environment,in order to ensure the safety and reliability of ship plate steel,extend the service life of Marine steel facilities,and promote the vigorous development of domestic Marine industry.Since there are few researches on hydrogen trap and hydrogen diffusion behavior in EH36steel,the research content of this thesis has certain guiding significance to the application of steel.In this thesis,the microstructure of EH36 steel samples at different thicknesses was observed by means of optical microscope and scanning electron microscope,and the microstructure differences at different thicknesses were compared.Then through the experimental steel XRD diffraction,OTS analysis,hydrogen penetration test,internal friction test,slow tensile test and other research methods,and the tensile fracture morphology observation,hydrogen diffusion behavior,hydrogen and the thickness of the experimental steel microstructure interaction,hydrogen on the hydrogen embrittleness sensitivity of the experimental steel content.The conclusion is as follows:（1）The microstructure of the surface and 1/4 thickness of EH36 steel are mainly lath bainite,and the 1/2 thickness of steel is ferrite and pearlite.The total number of inclusions at three kinks of thickness decreases from the surface to the inside,which are 49.3mm^-2,42.8mm^-2,33.0mm^-2.Before hydrogen charged,the dislocation density and micro-deformation were the largest at the surface and the smallest is 1/2 thickness of steel.After hydrogen charged,the dislocation density at the surface and 1/4 thickness of the steel are increased,while the dislocation density at 1/2 thickness of steel is decreased.The hydrogen diffusion coefficient at each thickness increases from the surface to the inside,which are 4.43×10^-6cm²/s,6.75×10^-6cm²/s and 9.31×10^-6cm²/s.The density of reversible hydrogen trap and irreversible hydrogen trap also decreased respectively.（2）There are 6 kinds of internal friction peaks in the test steel,and the activation energy changes as follows:with the extension of hydrogen charging time,the activation energy of P1 peak（H-snoek peak）at the surface is almost unchanged,while the activation energy of 1/4 and 1/2 thickness of the steel are decreased.The activation energy of P2 peak（H-SKK peak）and P3 peak（C-snoek peak）decreased with the extension of hydrogen charging time.The activation energy of P4 peak（C-SKK peak）shows an increasing trend.The internal friction P5 peak（grain boundary peak）only appears in the internal friction curve at the surface,and its activation energy decreases after hydrogen charged.P6 peak（carbide peak）only appeared at the surface and 1/4 thickness of the steel,and the activation energy mainly decreased with the extension of hydrogen charging time.（3）With the increasing of hydrogen charging time or current density,the yield strength,tensile strength and elongation of tensile pattern at different thicknesses are decreased to different degrees.Hydrogen embrittlement sensitivity increases gradually.The yield platform length（YPE）at each thickness decreases with the increase of hydrogen charging time,the upper and lower yield point difference at the surface and 1/4 thickness of the surface are increased first and then decreased,and the 1/2 thickness of steel is decreased.（4）The observation of fracture morphology shows that with the increase of hydrogen charging time or current density,the fracture morphology of sample steel changes from micro-porous aggregation toughness fracture to brittleness fracture,and some hydrogen-induced cracks are observed at the 1/2 thickness of steel.The best anti-hydrogen brittleness is the surface of steel,and the worst is the 1/2thickness of steel.The typical“fish-eye”brittle zone is observed when hydrogen is filled at the 1/2 thickness of steel at 50 m A/cm²-2h and 100 m A/cm²-1h.