| 12Cr2Mo1R?H?anti-hydrogen steel is mainly used to make hot well hydrogenation reactor.Hydrogenation reactor works in harsh service condition of high pressure and hydrogen environment for a long time.The hydrogen embrittlement?HE?tends to happen during its service.As a result,micro-cracks are easy to generate in the collected stress section,which causes a sudden break up and safety incident.In order to study the HE of the12Cr2Mo1R?H?anti-hydrogen steel,internal hydrogen experiment and environment hydrogen experiment were used to investigate its HE characteristic and mechanism in this paper.Before tensile test,in order to determine the important parameters such as hydrogen-charging time and current density,firstly,time-lag method was used to estimate the diffusion coefficient of hydrogen in steel and the value is about 3.40×10-66 cm2/s.It can be sure that the sample gets saturated after charging in a 0.5 mol/L H2SO4 solution added with 2g/L ammonium thiocyanate for 4 h.Then,by studying the impact of charging current density and time on hydrogen blisters of sample surface,the result showed that no hydrogen damage occurred on the sample surface when charging density is less than critical current density of about 25 mA/cm2.When charging with a current density of 50 m A/cm2,many hydrogen blisters occurred on the sample surface and some of them are cracked.Some hydrogen induced cracks?HIC?were found in the specimen interior.Transgranular is the predominant fracture mode observed from the IQ map around the HIC.The HE of anti-hydrogen steel at different strain rates after pre-charging hydrogen for4h was investigated in the internal hydrogen experiment.The results showed that the embrittlement index?EI?increase with the decrease of strain rates,and reach a stable value of about 20%after the strain rate of 5×10-4 s-1,Which belong to mild hydrogen damage.SEM images depicted small and deep flakes at high stretch rates,which are induced by inclusions of steel,and flakes grew larger at slow strain rates.Besides,transgranular is the predominant fracture mode of the hydrogen-induced cracks.High strain field surrounds the crack tips,which makes the crack tips of two close and parallel cracks deflect toward each another and even form crack coalescence.The HE of anti-hydrogen steel under in-situ hydrogen charging at different strain rate was studied in environment hydrogen experiment.The result pointed out that hydrogen significantly reduced the material's ductility.With the decrease of strain rates,the UTS of the charged samples progressively decreased.The embrittlement index reaches 78.05%at the lowest strain rate of 5×10-6 s-1.The interaction of hydrogen atoms and dislocations in the stage of plastic flow resulted in the formation of“Cottrell atmosphere”,which pinned the moving dislocations and caused the solid solution strengthening effect.SEM images of the fracture surface of hydrogen charged samples showed that the Intergranular?IG?is the main fracture mode,and the area of intergranular?IG?increased with the decrease of strain rates.In order to study the hydrogen induced cracks of the sample.Electron backscatter diffraction?EBSD?technique was used to investigate the effects of grain boundaries,KAM maps,recrystallization fraction,Taylor factor and coincidence site lattice?CSL?boundaries on the HIC propagation.High densities of dislocations and deformation were found at crack extension area,especially around the crack tips,where grains are highly prone to HIC cracking.The grain boundaries identified between two grains with a mismatch in Taylor factor were more susceptible to intergranular fracture while transgranular fracture occurred in fragmented grains with low Taylor factor.The results of the study indicate that the anti-hydrogen steel have good resistance of HE in the pre-charging condition.However,hydrogen damage would even happen after long-time service in hydrogen environment.When plasticity flow occurs in hydrogen environment,the hydrogen would accelerate the deterioration of its performance.The corresponding conclusion would also give reference for smelting process and service condition,including reducing the number of inclusions of steel in smelting process to decrease the risk of hydrogen damage,and avoiding the plastic deformation in service. |
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