Effect Of High-pressure Hydrogen On Fatigue Cracks And Microscopic Mechanical Behavior Of X80 Pipleline Steel

Hydrogen energy is a kind of efficient,clean,sustainable "carbon-free" energy.The big technical problem of the hydrogen energy application is how to implement the safe and efficient hydrogen storage,transportation and charging.In this paper,we assess the X80 pipeline of hydrogen compatibility and research on its mechanical property in hydrogen environment.In this research,an observation of the X80 pipeline steel microstructure was carried;Fatigue tests in nitrogen and hydrogen environment were done,observing the fatigue fracture morphology and the initiation fatigue micro crack and summarizing the crack initiation law of the fatigue tests in both ambience;Continuous Stiffness Measurement,Basic Hardness/Modulus test,Creep test and Strain-rate Sensitivity test were carried to the hydrogen charged and uncharged X80 pipeline by using the nanoindenter.The main conclusions are shown as follows:Microstructure of X80 constitutes irregular acicular ferrite,polygonal ferrite,bainite and white martensite/austenite island structure.Hydrogen influences the law of fatigue crack initiation,hydrogen could reduce the maximum fatigue stress of the fatigue crack initiation progress;hydrogen could reduce the fatigue cycles of the fatigue crack initiation progress.Hydrogen reduces the X80 pipeline steel ductility,toughness and increases brittleness;The slip band produced in hydrogen environment fatigue test with further quantity,more dense and glide step much deeper;Fatigue microcracks initiation along the slip lines or in the inclusions,microvoids;There are much more cracks initiation in the inclusions,microvoids in the hydrogen environment fatigue test than the nitrogen environment fatigue test's;The crack growth zone of the hydrogen environment fatigue fracture is flatter,and the quasi-cleavage facets are found in this zone;Its core section dimple area compared to the nitrogen atmosphere fracture center portion,which dimple depth shallow,smaller size,but also a small number.The indentation tests' results show that when the indentation depth is more than 500 nm,the hydrogen charged sample's elasticity modulus decreases;When the indentation depth is less than 1200 nm,the hydrogen charged X80 pipelines' hardness increases.Hydrogen decreases the displacement mutation critical load of X80 pipeline steel;The displacement mutation critical load is0.15 m N without hydrogen charged,the load decrease to 0.1m N with hydrogen charged;This indicates that hydrogen can reduce the stress proliferation of large-scale dislocations external required for plastic deformation occurs,which also reflects the hydrogen can promote the proliferation of dislocations.The hydrogen increases the creep displacement and decreases the stress exponent n;These results indicate that hydrogen has increased the sensitivity of X80 pipeline steel creep.The strain rate sensitivity factor m measured from the hydrogen charged sample is greater than the value of m measured from the sample without hydrogen charged;The hydrogen uncharged sample's m value is equal to 0.024,and the hydrogen charged sample's m value is equal to 0.031;This result indicates that hydrogen increases of X80 pipeline steel hydrogen strain rate sensitivity.