The Experimental And Numerical Research On Hydrogen Induced Brittle Fracture Of 45 Steel And 310s Stainless Steel

The hydrogen embrittlement of metal materials has been a significant problem in the energy,transportation and construction industries for decades.The entry of hydrogen into the metal structure would lead to a dramatic decrease in the reliability and durability of the metal structure,and hydrogen embrittlement is prone to occur without warning.In this paper,an investigation was performed on the hydrogen embrittlement with a combination of experiments and numerical simulation.310 s austenitic stainless steel has not only a high resistance to hydrogen embrittlement,but also high strength and toughness,and it is widely used in hydrogen energy related equipment;while 45 steel is relatively sensitive to hydrogen.Therefore,the hydrogen embrittlement experiment was performed on 310 s austenitic stainless steel and 45 steel,respectively.In an attempt to explore various factors affecting the hydrogen embrittlement,the solid and smooth round bar and different U-notch solid round bar specimens of 45 steel were subjected to the tensile experiments with different hydrogen charging degrees.The failure mode difference of 45 steel caused by different hydrogen charging degrees was numerically simulated and analyzed.The finite element method was first employed to simulate the hydrogen diffusion process of 45 steel specimens,and subsequently a modified GTN model was employed to numerically analyze the process of tensile hydrogen embrittlement in specimens with different hydrogen charging times.The main research results are presented as follows:(1)As per the tensile experiment of 310 s stainless steel solid round bar specimens,hollow round tube specimens and plate specimens with different thicknesses after hydrogen charging,it was found that only the hollow round tube samples charged with hydrogen on the outer surface and the one side hydrogen charging of 2mm plate specimen displayed a decrease in ductility,which indicated that 310 s stainless steel had a strong resistance to hydrogen embrittlement.Combined with the existing related research,it can be concluded that the hydrogen diffusivity of 310 s stainless steel was small and hydrogen was only enriched on the subsurface of the specimen,which induced hydrogen embrittlement on the subsurface.(2)The tensile experiment was performed on 45 steel solid round bar specimens after hydrogen charging with different times,based on which the hydrogen embrittlement of 45 steel under different concentrations of hydrogen was subject to an investigation.The experimental results showed that with the increase in the hydrogen charging time,the elongation and average fracture strain of the specimen decreased,the number of fracture dimples decreased,and the quasi-cleavage fracture area increased;However,the change gradually slowed down and tended to be stable with the prolonged hydrogen charging time.(3)In order to explore the effect of notches on the hydrogen embrittlement of 45 steel,tensile experiments were performed on U-notch solid round bar specimens with and without hydrogen charging.By comparing the stress-displacement curves,fracture strains and fracture microscopic morphology of the two,it was found that hydrogen would affect the hydrogen-induced failure of notched specimens,and the smaller the notch,the greater the effect of promoting the destruction.(4)The finite element simulation analysis was performed on the hydrogen diffusion process in the 45 steel solid round bar specimen and different U-notch specimens during hydrogen charging and tensile experiments.The simulation results showed that the hydrogen in specimens would have further diffusion under the action of the concentration gradient and stress gradient during the tensile experiment,and the distribution of hydrogen concentration in specimens before the tensile fracture increased first and then decreased along the direction of reduced radius.(5)As per the experimental observations,the HEDE mechanism and the evolutionary mechanism of material microvoids affected by hydrogen were introduced into the GTN constitutive model.The model hypothesis that the volume fraction of microvoid nucleation would increase with the increase in the concentration of hydrogen and the initiation of nucleation and polymerization would be advanced was proposed.This model was employed for the finite element numerical simulation of the tensile fracture of 45 steel solid round bars with different hydrogen charging and U-notch solid round bars with hydrogen charging.The simulation results showed that both the elongation and fracture shrinkage of specimens decreased under the influence of hydrogen,and the position of the crack initiation point changed with the change of hydrogen concentration distribution.These simulation results can reasonably explain and reproduce the process and phenomena observed in the experiment.