Research On Interface Microstructure Regulation And Toughening Mechanism Of Stainless Steel Clad Plate

Stainless steel clad plates,combining the excellent corrosion resistance of stainless steel and the good mechanical properties of carbon steel,have been widely used in marine engineering,petrochemical,nuclear power and other fields.Due to the excessive diffusion of alloying elements,the diffusion zones of carbon,Cr and Ni are formed,which affects the corrosion performance and interfacial bonding strength of clad plates,and is prone to intergranular corrosion cracks and delamination fracture.In this paper,a series of stainless steel clad plates were designed and fabricated under different conditions including rolling reduction ratio,vacuum degree and intermediate layer.The variation of interface microstructure,alloying element diffusion behavior,coordinated deformation behavior and fracture morphology were systematically studied.The interface bonding process and interface toughening mechanism of stainless steel clad plates were clarified.The results are showed as follows:（1）With the increase of rolling reduction ratio,the thicknesses of carburized layer,decarburized layer and martensite layer at the clad interface of stainless steel clad plate were reduced.Meanwhile,the interficial oxide proportion and the diffusion distances of interface alloying elements were gradually decreased.The shear strength,yield strength and tensile strength of the clad plate were improved continuously with the increase of rolling reduction ratio.The shear fracture zone transmitted from clad interface to decarburization layer,and the interfacial delamination crack gradually disappeared.However,the tensile elongation shows a trend of increasing first and then decreasing,which is attributed to the competition among the work hardening,interface strengthening and grain refining.（2）As the vacuum degree was gradually increased,the interfacial oxides of stainless steel clad plate were obviously reduced.Herein,the oxide morphology varied from cluster to block,linear and granular shape,and the oxide component were gradually changed from Mn,Si,Cr to Mn-Si-O or Si O₂ due to the interface selectivity oxidation under different oxygen partial pressures.Nevertheless,The decrease of interfacial oxides can promote the diffusion of alloying elements,resulting into the increasing thicknesses of carburized layer,decarburized layer and martensite layer.The bonding strength and the deformation coordination ability of the clad plate were elevated,which leads to a monotonous rise for tensile elongation.However,the yield strength and tensile strength were gradually decreased with the increase of the vacuum degree,which is attributed to the thickening of the carburized layer and the decarburized layer.（3）The effects of adding different intermediate layers on the microstructure and properties of the stainless steel clad plate are as follows:the addition of Fe foil had little effect on the interface element diffusion and the thickness of the carburized layer and the decarburized layer.The addition of Ni foil and Nb foil effectively inhibited the diffusion behavior of interface carbon element.Herein,the decarburization layer disappeared,and the thickness of the carburized layer was obviously reduced,which significantly relieved the hardness peaks and valleys of the carburized layer and the decarburized layer without any intermediate foil.However,the highest hardness value,between the Nb intermediate layer and the carbon steel layer,is 351 HV,due to that the Nb C carbides belonged to a high hardness phase.The addition of Ni foil and Nb foil can improve the interfacial bonding strength,tensile strength and elongation of the clad plate,and can achieve the purpose of strengthening and toughening the interface.