Interaction Between Hydrogen And Normalizing Structure Of Q500 Steel And Hydrogen Embrittlement Sensitivity

Low alloy structural steel will be subjected to hydrogen corrosion due to environmental impact during long-term service,and some hydrogen atoms will enter the steel material matrix and be enriched in dislocations,grain boundaries,non-metallic inclusions and other defects,which will lead to a decrease in the macroscopic plasticity and strength of the metal material,a decrease in mechanical properties,and the occurrence of hydrogen embrittlement,and with the improvement of steel strength,the hydrogen embrittlement sensitivity of steel becomes more and more obvious.Hydrogen embrittlement is an important problem often present in industrial production and applications,as it can cause catastrophic failure of structural materials.In this thesis,the original hot-rolled state and normalized state of Q500thick plate steel are taken as the research objects,through electrochemical hydrogen charging,double electrolytic cell hydrogen permeation,slow strain rate tensile experiments,metallographic microscopy（OM）,electron scanning microscope（SEM）and other detection methods were used to observe the microstructure and fracture morphology,the number of internal hydrogen traps,hydrogen diffusion behavior and hydrogen embrittlement sensitivity of steel before and after hydrogen charging were studied,and the influence of hydrogen charging on internal friction peak was studied by multifunctional internal consumption meter.The main research contents and results are as follows:（1）Fe-HP-12 metal hydrogen permeability tester was used to study the hydrogen diffusion behavior of normalized steel.The results show that the microstructure of the original experimental steel is mainly slatted bainite,and the microstructure after normalizing is granular bainite and degenerate photomass.As the normalizing temperature increases,the grain size gradually increases.Under the same hydrogen charging current,the hydrogen trap density decreases with the increase of normalizing temperature,and the diffusion coefficient increases.The number of hydrogen traps and hydrogen diffusion coefficient of the original steel and the normalized steel at 910°C are similar.（2）The electrolytic hydrogen charging device and MEP-1000 multifunctional internal friction meter were used to study the internal consumption behavior of normalized steel.The results show that the P1 peak appears at low temperature in the original steel,disappears after normalizing and reappears after hydrogen charging,and it is inferred that this peak is a relaxation internal consumption peak caused by the diffusion of interstitial hydrogen atoms according to the peak temperature and activation energy.P2,P3 and P4 peaks appeared in the steel before and after hydrogen charging.According to the peak temperature and activation energy,it is estimated that the P2 peak is the SKK peak produced by the interaction of interstitial hydrogen atoms with dislocations,the P3 peak is the internal consumption peak generated by the diffusion of interstitial carbon atoms,and the P4 peak and P4 peak are the SKK peaks caused by the interstitial carbon hindering the dislocation motion.（3）MFDL100 slow tensile stress corrosion testing machine was used to study the mechanical properties and hydrogen embrittlement sensitivity of normalized steel.The results show that the yield strength and tensile strength of the original experimental steel after normalization decreased,while the elongation increased,and the mechanical properties of Na OH solution after electrolytic hydrogen charging remained almost unchanged,while the mechanical properties of H₂SO₄solution decreased significantly after electrolytic hydrogen charging.When unfilled with hydrogen,the tensile fractures of the original and normalized steel have necking,and the micromorphology of the fracture is tenacity and socket,which is a ductile fracture.Na OH solution occurs under long-term low-current hydrogen charging is ductile fracture,obvious necking;In a short period of time,the high-current H₂SO₄solution is filled with hydrogen,and the material is brittle fractured.Hydrogen charging of H₂SO₄solution will reduce the mechanical properties of the material.