Hydrogen Diffusion Behavior In An Ultra-fine Bainite Steel

Ultra-fine bainitic steel(or low temperature bainitic steel,super bainitic steel,nanostructured bainitic steel)is one of the advanced high strength steels with ultra-high strength,high plasticity and good toughness.Due to the great difference of hydrogen solubility and diffusion coefficient between retained austenite and bainitic ferrite,the hydrogen trapping behaviors at the two-phase interface,and the shielding and distortion effect of retained austenite on hydrogen diffusion,hydrogen diffusion and trapping behavior in such ultra-fine bainitic steels with BCC / FCC components is very complicated.In this paper,the diffusion behavior of hydrogen in an ultra-fine bainitic steel is analyzed by means of hydrogen electrochemical permeation experiment,numerical simulation and first principles calculation.The main research contents are as follows: firstly,the influencing factors of hydrogen permeation behavior in samples with reversible and irreversible hydrogen traps are simulated and analyzed,and the application prerequisites of classical empirical formula for hydrogen effective diffusivity analysis are discussed.A method to distinguish reversible and irreversible hydrogen traps by means of hydrogen electrochemical permeation experiments is proposed.Then,the results of hydrogen permeation experiment of two kinds of ultra-fine bainitic steel samples with retained austenite in different volume fraction and morphology were compared and analyzed.Based on the mathematical model of retained austenite embedded in ferrite matrix,the effects of retained austenite on hydrogen diffusion behaviors in ultra-fine bainitic steel were discussed,and the effective diffusion path theory was verified.Finally,the influence of alloying elements commonly utilized in ultra-fine bainitic steels on the hydrogen diffusion activation energy is analyzed by using the first principle calculation method.