| Stainless steel clad plate which has the advantages of high strength,good corrosion resistance and low cost is widely used in petrochemical,power generation,shipbuilding industry.Constrained by technical level and equipment capacity,only small specifications of clad plate can be produced at home using hot rolled method,holding the problems of unstable performance,poor quality and low production efficiency.Therefore,it is important to develop large size clad plate and improve the existing clad process and will bring significant social and economic benefits.The clad plate is composed with Q345 R carbon steel and 310S/316 L stainless steel,using optical microscope(OM)and scanning electron microscope(SEM),energy dispersive spectroscopy(EDS),mechanical property test etc.,establishing the model of the relationship between process parameters and properties of the clad plate,through the study of surface treatment,vacuum and rolling process parameters of the interface structure and properties of clad plate.The proposed method is suitable for hot rolling process of clad plate,providing a theoretical foundation for the development of wide thick clad plate.The effect of interface elements on the clad plate was obtained from the interface elements of the heating rolling process of clad plate diffusion mechanism,microstructure characteristics near the interface of clad plate,element distribution and hardness distribution on both sides of the interface.The interface properties were improved by the composite interface adding Ni intermediate layer,which can effectively prevent the diffusion of alloying agent and the formation of interfacial alloy oxide alloy.The interface element diffusion and interface bonding strength of the nickel layer on the clad plate under different deformation conditions were also studied,which can effectively eliminate the decarburization and interface the chromium layer and improve the interfacial bonding strength and resistance to intergranular corrosion.The true stress-strain curves and the relation curve between flow stress,strain rate and deformation temperature of stainless steel and carbon steel during high temperature compression deformation were presented.Through numerical processing,activation energy and stress exponent of deformation were obtained under the condition of thermal deformation,and then get the solution conditions of the thermal deformation equation.By studying the deformation behavior of clad plate and thermal deformation mechanism,a reasonable hot working process was developed,providing the theoretical foundation for performance optimization and organization.According to carbon steel CCT curve,effects of different cooling rates were analyzed on the starting point and phase transition and the changes of the microstructure.Based on the cooling curve of low carbon steel and the sensitization curve of austenitic stainless steel,the heat treatment specification of clad plate were obtained,composite rolling in high temperature region,the final rolling temperature is near 1000℃,the total amount of pressure is about 75%(dynamic recrystallization during rolling),and then with the speed below 7℃/s,the clad plate is cooled to 450℃,then air cooling to room temperature.The microstructure of Q345 R after rapid cooling are mainly composed of bainite and ferrite,the yield strength is more than 400 MPa,the tensile strength is more than 590 MPa,the impact energy is more than 50 J,the bonding strength is up to 400 MPa.Based on the previous research,industrial and heavy-gauge specifications(3500×100mm)clad plate was produced using symmetric group method.The influence of different straightening parameters and different treatments on the microstructure,mechanical properties and corrosion resistance of the clad plate were studied.Mechanical properties of the clad plate test show that the shear strength is greater than 350 MPa,tensile strength is up to 550 MPa,yield strength is 360 MPa,no crack at the interface and basic/cladding layer surface after inner/outer/lateral bending,impact energy of the carbon steel layer is much larger than 34 J at 0℃,and the interface has no defects which is well combined after nondestructive testing.All the performance index of the trial-produced heavy-gauge specifications clad plate were all up to the requirements of the 863 Program,which can be used as an alternative to the imported products. |
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