Study On The Intergranular Corrosion Behavior Of 904L Stainless Steel By Surface Modification

904L austenitic stainless steel is a super austenitic stainless steel containing low carbon,high chromium and nickel.Although it shows excellent corrosion resistance in acidic environments,904L stainless steel still has intergranular corrosion.At present,the mechanism of intergranular corrosion of 904L stainless steel is not clear.The most commonly used explanation for the intergranular corrosion of austenitic stainless steel is that austenitic stainless steel after sensitization treatment,the formation of carbides(M₂₃C₆)leads to the appearance of chromium-depleted zone at the grain boundaries.As for 904L austenitic stainless steel as a low-carbon stainless steel,whether there will be the formation of such carbides needs further study.Therefore,this paper takes 904L austenitic stainless steel as the researc h object,aiming at the problem of intergranular corrosion of 904L stainless steel in acidic environment,using electrochemical,SKPFM,EPMA,TEM and other testing methods to study the mechanism of intergranular corrosion of 904L stainless steel in depth.At the same time,ultrasonic rolling technology was used to modify the surface of sensitized 904L stainless steel.The results obtained are as follows:(1)Compared with the original sample,the passivation film formed in acidic solution is less dense and has more point defects after ageing treatment of 904L stainless steel.Ageing treatment is easier to reduce the sensitivity of 904L stainless steel to intergranular corrosion after solid solution.In the same concentration of hydrochloric acid and hydrofluoric acid,the corrosion rate of 904L after ageing treatment in hydrofluoric acid is greater than that in hydrochloric acid.(2)As the sensitization time increases,the electrochemical corrosion behavior of 904L stainless steel becomes lower.After a long time of sensitization treatment for904L stainless steel,a new phase(?phase)will be precipitated at the grain boundary.The?phase exists in the form of intermetallic compounds,and its Volta potential difference is higher than that of the?phase and its size is 500 nm.The formation of?phase will affect the contents of Cr and N i around the grain boundary at 3 um,making the 3 um region a sensitive area for intergranular corrosion.(3)The sensitized 904L stainless steel undergoes ultrasonic rolling surface modification,and its electrochemical corrosion behavior will be improved to a certain extent.The surface of the sample still maintains good roughness after rolling,and the residual compressive stress on the surface is improved.The?phase will be reduced in quantity at the grain boundary of the sample after ultrasonic rolling,so that the width of the element depleted zone becomes narrower and the degree of intergranular corrosion decreases.