Experimental Researches On The Interfacial Strength Of 304L/533B Clad Steel Fabricated By Different Techniques

The advantages of clad plate and base plate are exploited in composite plates,which increase the application widely.They play irreplaceable roles in the fields of transportation,chemical anticorrosion,energy and daily life.Different bonding quality laminate plates are obtained with various manufacture methods.The stress in laminate plate is different from uniform metal for the existing of bonding interface and mismatching of clad plate and base plate.Therefore,masses of research focusing on interfacial microstructure,mechanical properties,formability are carried out.In this thesis,304L/533B laminate plates manufactured with cold rolling composite and explosive welding were taken as the research object.Nanoindentation and in situ tensile unit combining SEM were used to study on material mechanical properties,mechanical behaviors and failure mechanism.Finite element analysis and theoretical modeling were used to discuss the influence factors on composite plates tensile property.The main research contents and conclusions are listed as following:Observable microstructure and properties difference exist between two composite steel plates obtained with two methods.Micro structure and micro defects in interface of composite plates were observed with optical microscope and scan electron microscope.Phase transformation and component analysis were confirmed by transmission electron microscope and energy disperse spectroscopy.Nanoindentation was used to analyze mechanical properties distribution cross bonding interface.Combining above studies,the relationship between microstructure and properties were analyzed and discussed for the two typical bonding methods.Results reveal that flat interface was observed and only local texture structure formed in a range of 500 ?m interfacial clad plate in cold rolling composite steel plate.Nano-hardness increase in this deformation area.Wave shape interface was observed in explosive welding composite steel plate.Recrystallization and phase transformation in interfacial materials confirmed and carbide precipitations were formed in interfacial clad plate.All these microstructures change lead to properties variation and the maximum and minimum nano-hardness appear at bonding interface and decarburized layer in base plate.Compare this two composite steel plates,cold rolling composite process only lead to small scale interfacial deformation and properties change,complicated microstructure variation and properties transition were resulted for severe deformation in explosive welding process.Interface is a main factor of composite steel plate failure.In situ tensile unit was used to measure bonding strength under different external load.Combining with SEM,materials deformation and interfacial defects evolution in interface were observed in time.Local deformation was measured with digital image correlation(DIC)method.Abaqus finite element software was used to analyzed to tensile behavior and failure mechanism.Results reveal:bonding strength of 304L/Ni interface is weaker than that of 533B/Ni interface in cold rolling composite steel plate.Microcrack generated in this interface first then propagate along direction vertical to external fore.Explosive welding composite steel plate's weakness is decarburization layer specimens fracture here both under normal stress and shear stress.Moreover,the bonding strength of cold rolling composite plate is higher than that of explosive welding composite plate.Observation of defects evolution in this two type composite steel plates show that shape change and dimension enlarge resulted from plastic deformation and concentrate of stress/strain accelerated defects evolution.But deformation and extension of defects had no effect on materials reliability.Tensile test of specimens with different geometry size and different base plate volume ratio were carried out by in-situ tensile unit,then mechanical behavior was analyzed combining with composite stress-strain relationship.Finite element was used to analyze the influence of geometry size and mechanical properties on tensile behavior of composite plate.Results reveal that tensile curves obtained by in situ unit could match with standard specimen tensile curve by correction,and the correction coefficient related to the specimen geometry size.Base plate volume ratio influenced its tensile strength and ultimate strain directly,tensile strength decreasing and ultimate strain increasing with base plate volume ratio decreases.Simulation results indicate that the maximum interfacial stress appeared when the load direction parallel to the interface.Interfacial stress was influenced by composite plate thickness,wave amplitude and wavelength,elastic modulus and yield strength of clad plate.As we all known,the higher interfacial stress the lower reliability under the same external load.Thus,the optimal geometric parameters and clad plate properties may obtain to guide composite process.