Study Of Hydrogen Embrittlement Susceptibility And Hydrogen Permeation Behavior Of DP600 Steel

Advanced high strength dual-phase?DP?steels are important materials to reduce automotive weight because of the good combination of strength and plasticity.Hydrogen atom can permeate into steel in the process of smelting,pickling,electroplating,welding and service,has led to the risk of HE of dual phase steels,especially HE susceptibility increases with the increase of strength,which has become a important factor to hinder the development of the high-strength steel of automotive.This paper took DP600 steel as the research object,tested the HE susceptibility and hydrogen permeation behavior based on electrochemical hydrogen charging,SSRT and hydrogen permeability test,characterized the corresponding microstructure combining with OM?SEM?TEM and EBSD test,discussed the influence of hydrogen concentration,the strain rate,pre-strain,annealing temperature and overaging temperature on HE susceptibility and hydrogen permeation behavior.The results showed that:?1?With the increase of pre-charging time,absorpted diffusible hydrogen concentration increases first and then tends to be saturated in tested steel,HE susceptibility increases and then gradually stable.Within a certain pre-charging time?30min?t?180min?,C_H has a linear relationship with?.The HE susceptibility increases significantly with the decrease of the dynamic strain rate.?2?With the pre-strain range from 0%to 20%,the HE susceptibility of tested steel increases with increase of pre-strain when the level of pre-strain is below 15%,and then tends to be stable when the pre-strain exceeds 15%.The pre-strain increases dislocation density and the amount of effective hydrogen in steel,but decreases the effective diffusivity of hydrogen,so that the HE susceptibility increases.However,when the pre-strain increases to more than 15%,the HE susceptibility gradually becomes stable due to the decrease of hydrogen diffusion and accumulation caused by tangle dislocation.?3?With the annealing temperature increases from 780?to 840?,the content and size of martensite island increases and pearlite and bainite generates;hydrogen diffusion coefficient D_eff presents a increasing trend with the increase of annealing temperature,the HE susceptibility first increases and then decreases.?4?With the overaging temperature increases from 270?to 350?,dislocation density decreases,martensite island decomposes into carbide precipitation and the content of low angle grain boundary reduces but high angle grain boundary increases in tested steel.The density of hydrogen traps increases but the hydrogen diffusion coefficient and HE susceptibility decreases.The decrease of dislocation and low angle grain boundary,increase of carbide precipitation and high angle grain boundary are the important reasons for the reduced HE susceptibility of tested steel.