Design And Preparation Of Stress Ring And Its Application In Hydrogen-induced Fracture Of 18CrNiMo7-6 Steel

18CrNiMo7-6 carburized gear steel was chosed as the experimental material.The hydrogen embrittlement sensitivity of the V-notch of 18CrNiMo7-6 steel was studied by designing and preparing stress rings,and the hydrogen-induced fracture mechanism was discussed.The aim was to use stress rings instead of a durability testing machine to measure the hydrogen embrittlement sensitivity of notched specimens.In order to improve work efficiency and save costs,the stress rings will be applied to practical projects.The subject conducted the design and preparation of stress rings.In order to avoid the problem of stress rings in the H2S stress corrosion test,this paper designed stress rings and three sets of fixtures that were used in conjunction with the stress ring in accordance with ASTM F519-08.The functions of the three sets of fixtures were the connection of the stress ring and the tester,the connection of the stress ring and the digital dial gauge,the connection of the stress ring and the V-notch specimen.Completely solved the problem of overload,error due to measurement position deviation during the experiment.Simplified the stress ring into a circle.Through theoretical calculations and ANSYS finite element software simulation of the stress ring loading process,it was found that the tensile stress on the longitudinal tensile end of the stress ring is approximately the same as the stress on the lateral contraction.It was verified that the deformation and load of the stress ring when compressed or stretched obey Hooke's law,and then the characteristic curve of each stress ring was measured by the principle of least squares method.The subject also conducted the preparation of 18CrNiMo7-6 steel V-notch specimens,and calculated the deformation of each stress ring by measuring the average test load of the specimen.The stress rings were used to load the specimen,and no breakage of the samples were found within the specified time.In order to investigate the hydrogen embrittlement sensitivity of the 18CrNiMo7-6 steel in the actual use environment,the specimens were subjected to hydrogen treatment.After loading,it was found that three specimens broke within a specified time,indicating that the 18CrNiMo7-6 specimen had more strong hydrogen embrittlement sensitivity after been subjected to hydrogen treatment.The microstructure and inclusions of the material were analyzed.The fracture morphology of several specimens was observed.The fracture morphology of the specimen after hydrogen treatment also was analyzed.According to the microstructure,fracture morphology and mechanical properties of the 18CrNiMo7-6 steel,hydrogen-induced fracture mechanism of V-notch specimens was described after the stress ring loading.The use of a stress ring instead of a durability testing machine for the determination of the hydrogen embrittlement susceptibility of 18CrNiMo7-6 steel was simple and straightforward.With only one tensile tester,multiple test specimens could be tested at the same time.The test process was easy to control and the stability was good.The stress ring improved the work efficiency.