Study On Microstructure And Hydrogen Diffuion Characteristics Of 304/Q235B Clad Plate

304/Q235B hot-rolled clad plate is a kind of stainless steel plate commonly used in the industry.This kind clad plate is formed by compounding the base layer(Q235B carbon steel)and cladding layer(304 stainless steel),so that it both has the performance advantages of the base layer and the coating.So it is widely used.However,due to the continuous deterioration of the environment in recent years,the clad plate is prone to hydrogen-induced damage under the action of acid rain and some corrosive gases,which could cause the interface bonding strength of the clad plate to decrease severely.In order to study the mechanism of hydrogen diffusion in the clad plate,we investigated the current status of the development of stainless steel clad plates and the diffusion characteristics of hydrogen in metals.In this paper,we used XRD,metallographic microscope,scanning electron microscope,transmission electron microscope,electrochemical hydrogen permeation and other devices to research the microstructure of each part of 304/Q235B hot-rolled clad plate and its hydrogen permeability characteristics,the experimental results are as follows:The microstructure of 304/Q235B hot-rolled clad plate can be clearly divided into 4parts,that were austenite structure of 304 stainless steel matrix,5?m thick transition layer,and decarburization layer of Q235B steel near the transition layer(thickness of 50?m ferrite structure)and ferrite+pearlite structure of Q235B steel matrix.The structure in the transition layer was mainly lath martensite,and there were a large number of needle-like M₃C type carbides(about 100 nm in length and about 10 nm in diameter)and other types of inclusions in the martensite lath.Diffusion zones of alloy elements such as Cr,Ni,and C existed at the interface of the clad plate,and an obvious element distribution curve was formed.Because of the diffusion of elements at the interface,the organization structure at the interface of the clad plate became extremely complicated,which had a great impact on the hydrogen diffusion.Hydrogen diffusion experiments showed that the effective hydrogen diffusion coefficients of each layer in the clad plate increased with increasing temperatures(25,45,and 65?).At the same temperature,the effective hydrogen diffusion coefficient of each layer in the clad plate had great difference.The effective hydrogen diffusion coefficient of the transition layer and the 304 steel matrix was much lower than that of the decarburized layer and the Q235B steel matrix.The activating energy for hydrogen diffusion of each layer was counted,that was 58.496 k J/mol of the transition zone,55.704 k J/mol of the 304steel matrix layer,28.505 k J/mol of the Q235B steel matrix layer,22.950 k J/mol of the decarburized layer.The hydrogen trap binding energy of each layer was also counted,that was-55.712 k J/mol of the transition zone,-53.800 k J/mol of the 304 steel matrix layer,-26.946 k J/mol of the Q235B steel matrix layer,and-21.325 k J/mol of the decarburized layer.The activating energy of hydrogen diffusion and the binding energy of hydrogen traps respectively represent the energy barrier to be overcome by hydrogen diffusion and the hydrogen trapping ability of hydrogen traps.The larger the two values are,the stronger the hindrance of hydrogen diffusion is.From the experimental results,we found that the more complicated the structure of the layer in the clad plate,the more defects that can be used as hydrogen traps,and the greater the hindrance to hydrogen diffusion.Because the transition layer contains a large number of dislocations,inclusions,and precipitated carbides,these structures seriously affect the diffusion behavior of hydrogen in the clad plate,and will cause a large amount of hydrogen to be clustered in the transition layer,which leads to hydrogen embrittlement.