Optimization Of Grain Boundary Characteristic Distribution Of 304 Stainless Steel And Its Effect On Hydrogen Embrittlement Resistance

304 stainless steel is an excellent corrosion resistant material.Compared with low alloy steel and carbon steel,304 stainless steel is more difficult to produce hydrogen embrittlement corrosion.Therefore,304 stainless steel is widely used in ocean,petroleum,aerospace,hydrogen energy,nuclear industry and other fields.However,when hydrogen concentration or hydrogen pressure is too high,hydrogen embrittlement will inevitably occur in 304 stainless steel,leading to workpiece failure,which poses a higher challenge to the hydrogen embrittlement resistance of stainless steel.At present,the design and control of grain boundaries is an effective method to improve the comprehensive properties of polycrystalline materials.Hydrogen embrittlement of 304 stainless steel is closely related to grain boundary.Therefore,optimizing grain boundary characteristic distribution of 304 stainless steel by grain boundary engineering is an effective means to improve its hydrogen embrittlement resistance.In this paper,the effects of deformation,annealing temperature and annealing time on grain boundary characteristic distribution of stainless steel were studied.The optimum process parameters for grain boundary optimization were determined.The effect of grain boundary characteristic distribution on hydrogen embrittlement resistance of stainless steel was further investigated.The main conclusions are as follows:(1)According to the results of grain boundary characteristic distribution control,the optimum process parameters for grain boundary optimization of 304 austenitic stainless steel were determined as follows:annealing at 1075?for 7 min after 7%cold rolling deformation,special grain boundary ratio increased to 75%and the connectivity of random grain boundary was effectively interrupted.(2)With the increase of low?CSL grain boundary ratio,the elongation and section shrinkage of 304 austenitic stainless steel increased continuously,too.The hydrogen-induced elongation loss rate and hydrogen-induced section shrinkage loss rate of base metal with low?CSL grain boundary ratio of 54%were 13.6%and 7.2%,respectively.The hydrogen-induced elongation loss rate and hydrogen-induced section shrinkage loss rate were only 5.1%and 1.6%respectively when the low?CSL grain boundary ratio was 75%,the plastic loss decreases greatly and the hydrogen embrittlement resistance increased greatly.(3)With the increase of low?CSL grain boundary ratio,the optimization of grain boundary characteristic distribution resulted in the decrease of hydrogen charge.The hydrogen volume and hydrogen content of the base metal with a low?CSL grain boundary ratio of 54%were 2.3cm~3 and 38.26wppm,respectively.When the low?CSL grain boundary ratio was increased to 75%,the hydrogen volume and hydrogen content were 0.8cm~3 and13.31wppm respectively.The hydrogen embrittlement resistance of the material was improved significantly.(4)Hydrogen-induced cracks mainly initiate and propagate along large-angle random grain boundaries,because random grain boundaries have high energy and are easy to capture hydrogen atoms as"hydrogen traps".The optimization of grain boundary characteristic distribution hinders hydrogen-induced crack growth mainly in two forms:(a)low?CSL grain boundaries hinder crack growth;(b)annealing twins hinder crack growth.