Multiscale Research On The Mechanical Properties Of Hydrogen Resistant Steel In Hydrogen Environment

Hydrogen-resistant steel for hydrogen storage pressure vessels is usually austenitic stainless steel.Although it has better resistance to hydrogen than ferrite or martensite steels,hydrogen still has non-neglectful effect on the mechanical properties.Therefore,it is of great theoretical and engineering significance to study the mechanism and the regular pattern of this influence and apply the acquired knowledge to structural design and safety assessment.With HR-2 hydrogen resistant stainless steel as the research object,some key macro-and micro-scale information needed for establishing multi-scale model was measured nondestructively by using the newly developed experimental technology.Based on these key information,numerical simulation and application research were carried out.The mechanism and law of the influence of hydrogen on the mechanical properties of stainless steel were studied.Specifically,three kinds of stress distribution data,macro-stress,micro-stress and intergranular stress,are obtained accurately by neutron diffraction stress measurement,and the effect of internal stress on the microstructure of materials is studied.The size,content and specific surface area of nano-scale microstructures in materials are obtained by small angle neutron scattering.The neutron diffraction online observation confirms that no obvious phase transformation occurs during the fracture process of HR-2 steel.The observation of the specimen after fracture confirms that the HR-2 steel still has only the diffraction peaks of FCC crystalline phase in the fracture zone(in the range of centimeters).According to the results of small angle neutron scattering test,the micro-void defect did not change significantly during the fracture process of HR-2 steel sample,and was not the dominant factor of fracture.A micro-meso-macro model system describing the effect of hydrogen atom on HR-2 hydrogen-resistant stainless steel was established by using MD-PD correlation multi-scale model framework.The change of macro-mechanical properties parameters of HR-2 steel with hydrogen concentration in the system was simulated,and the mechanism of hydrogen embrittlement was studied and analyzed.The model system can be used to calculate the elastic model,yield strength and section shrinkage of HR-2 steel under different internal hydrogen concentrations.The qualitative relationship obtained by simulation is consistent with the experiment,and the difference is no more than 10%.The calculated section shrinkage rate is higher than that of the experiment,and the difference between the calculated and the experimental values is no more than 10%when the mass concentration of hydrogen is greater than 0.0004.By observing the output of a large number of fine-scale simulation tasks generated automatically in the simulations,the hydrogen embrittlement of HR-2 steel is understood as follows:when the characteristic distance between twin boundaries is about 100nm and the inclination angle is 43.31,dislocations can form and aggregate near the twin boundaries under tensile stress,and the crystals can be broken off from the twin boundaries to form micro cracks.The important mechanism on the resistance to hydrogen embrittlement of HR-2 steel is that the spatial locations of H atoms at gaps in FCC phase are relatively stable.In the model established here,hydrogen atoms will not obviously move to the grain boundary and micro-cracks if the initial spatial location randomly designated at the very beginning is not less than 5 nm away from the twin boundary.The simulation results show that the hydrogen embrittlement of HR-2 steel at macro scale is dominated by the descending of surface energy cause and the lattice embrittlement caused by hydrogen adsorption.