Investigation Of The Influence Of Stress And Strain On The Hydrogen Diffusion Behavior And Traps In Steels

In order to meet the requirements of light weight and safety in utilization,the requirements for properties of high-strength steel in industrial manufacture are becoming higher.The third generation advanced high-strength steel for automobiles obtains balance of strength and product of strength and plasticity by modifying the content of martensite and retained austenite.The weathering steel for containers is micro-alloyed,which improves the strength and resistance to atmospheric corrosion.However,with the increase in strength and the possibility of introducing more hydrogen in special service environments,the deterioration of mechanical properties(strength and plasticity)caused by hydrogen embrittlement of diffusible atomic hydrogen in steel has greatly limited the application of high-strength steel in industry.There are many factors affecting hydrogen embrittlement in steel:strength level,diffusible hydrogen content,microstructure,stress and strain.From the microscopic perspective,hydrogen embrittlement is closely related to the movement of hydrogen atoms in the steel and the hydrogen traps served by the heterogeneous structure.Therefore,in order to better explore the methods to improve the resistance to hydrogen embrittlement,in-depth research on the behavior of hydrogen atoms in steel and its different phases is necessary.During the utilization,steel inevitably undergoes stress and strain from the environment.Therefore,the influence of stress and strain as an important external factor on the hydrogen diffusion behavior in steel deserves further study.Based on two kinds of steels for automobiles and containers,this paper uses Q&P 980 and BC 550 steels as research objects,and explores the hydrogen diffusion behavior and the change of hydrogen traps under stress and strain.On the one hand,the effect of plastic stage strain on the content of different hydrogen traps and hydrogen desorption behavior in Q&P 980 was investigated by changing the amount of plastic deformation and thermal desorption experiments after electrochemical hydrogenation.On the other hand,a stress-loaded in-situ electrochemical hydrogen permeation experiment method was proposed to study the hydrogen atom diffusion coefficients and the change of hydrogen traps in Q&P 980 and BC 550.Through the above experiments,the main conclusions are as follows:1.In Q&P 980,there exists irreversible hydrogen traps at 700°C,which is related to blocky retained austenite.As the amount of strain increases, the blocky retained austenite decomposes,and then the irreversible hydrogen trap peaks in the steel disappear.There are two kinds of irreversible hydrogen traps in BC 550,the Cu-rich particles with a desorption temperature of 433? and M₇C₃ with a desorption temperature of 536?;2.As the amount of strain increases,the amount of hydrogen desorption from the reversible hydrogen trap in Q&P 980 increases,and the desorption temperature moves to high temperatures.On the one hand, with the increase of the strain,the stress concentration of the material is severer,the dislocation density increases,and more hydrogen can be accommodated;on the other hand,when the martensite phase transformation occurs in the blocky retained austenite,the austenite/martensite interface may be a new reversible hydrogen trap with a higher desorption temperature than dislocations and other point defects.3.Due to the decrease of the activation energy of the hydrogen trap and the increase of the atomic gap under the elastic stress,the apparent hydrogen diffusion coefficients of Q&P 980 and BC 550 increase with the increasing of elastic stress,and the total trap density of Q&P 980and BC 550 decreases.Under the stress of 200 MPa,the density of irreversible hydrogen traps in Q&P 980 has no effect,but the density of irreversible hydrogen traps in BC 550 decreases.