Effect Of Specimen Notch On Hydrogen Exbrittlement Of 18CrNiMo7-6 And 300M Steels

Hydrogen embrittlement is a major hidden danger in the use of metal materials.In this paper,the effect of the notch of the specimen on the hydrogen embrittlement behavior of the 18CrNiMo7-6 and 300M steels was studied.The focus is on the 18CrNiMo7-6 gear steel with 300M as the reference.18CrNiMo7-6 gear steel is used in wind power gear because of its excellent performance.However,the presence of surface inclusions will affect the use of 18CrNiMo7-6 gear steel,such as becoming a hydrogen trap and inducing hydrogen embrittlement.When the 18CrNiMo7-6 gear steel is tested in a non-destructive way,once any inclusion is found,it will be judged that the material is unqualified,and it needs to be refurbished in the furnace.Such a situation will cause a waste of resources and time.In the daily business processing of our laboratory,we have encountered many cases of hydrogen embrittlement failure of 18CrNiMo7-6 gear steel.The common point of these cases is that there are large inclusions on the surface.In practical applications,not all inclusions will affect the hydrogen embrittlement of 18CrNiMo7-6 gear steel.From the actual failure case,only the inclusion close to the surface or the inclusion with a certain size can affect the hydrogen embrittlement of the 18CrNiMo7-6 gear steel.However,the relevant factors involved in the surface inclusions are too complex,so it is difficult to carry out the prefabrication simulation,and it is difficult to realize the research on the relationship between the size of inclusions and hydrogen embrittlement.For this reason,this article seeks the second place,trying to provide a static load environment through the stress ring in the case of wire-cutting prefabricated notches on the surface,to explore the relationship between the notch depth and the hydrogen embrittlement fracture time,and to provide ideas for exploring the minimum size of safety defects.In this paper,two materials,300M steel and 18CrNiMo7-6 gear steel,were selected for the experiment.300M steel was used as the first material to explore the experimental conditions and experimental schemes.In the experiment,the hydrogen embrittlement sensitive structures of the two materials were obtained by quenching tempering heat treatment.Then prepared V-notch specimens and smooth surface standard specimens(used to make surface wire-cut notch specimens)with reference to ASTM F519-2017,and then subjected the specimens to mechanical tests.After completion,the acid pickling hydrogen charging and electrochemical hydrogen charging were selected to carry out the hydrogen charging experiment on the specimen.With reference to the part of ASTM F519-2017 standard,taking 75%of the tensile load of the specimen as the static load value of the stress ring on the specimen,the fracture time is used to characterize the difficulty of hydrogen embrittlement,and 200 h is set as the lower limit time without hydrogen embrittlement.Finally,the fracture is judged to be hydrogen embrittlement by fracture and metallographic test.The experimental results showed that in the method of this experiment,the hydrogen charging time and the fracture time had an exponential relationship;the surface notch depth and the fracture time had an exponential relationship;through these two exponential relationships,the maximum charging without hydrogen embrittlement under this experimental condition could be calculated Hydrogen time and maximum surface wire cutting notch depth;18CrNiMo7-6 without surface notch was not prone to hydrogen embrittlement in hydrogen charging experiment;18CrNiMo7-6 V-type specimen was not prone to hydrogen embrittlement during pickling,but in electrochemical experiment in the experiment,hydrogen embrittlement would occur,which was calculated by the fitting formula.Under the electrochemical hydrogen charging condition of this experiment,the 18CrNiMo7-6 V-type specimen would not undergo hydrogen embrittlement.The maximum hydrogen charging time was 0.41 min;In this paper,the maximum notch depth without hydrogen embrittlement was 0.09 mm under acid pickling experiment conditions,and the maximum notch depth was 0.075 mm under electrochemical experiment conditions.