Study On The Bonding Behavior Of Stainless Steel/Carbon Steel During Roll-bonding Process

Stainless steel/carbon steel laminated composites,which have the characteristic of corrosion resistance of the stainless steel as well as the characteristics of the high strength and low cost of the carbon steel,are widely used in the chemical,petroleum,and food industries,as well as water conservancy facilities and other fields.Hot roll-bonding has become the main method to fabricate stainless steel-carbon steel metal laminated strip,while it is of great significance to understand whether this composite can be produced using warm roll-bonding or even cold roll-bonding method,which both performed below recrystallization temperature.In addition,although many hypotheses have been put forward,the research on rolling recombination mechanism is not thorough,which also restricts the development of stainless steel-carbon steel rolling recombination technology.In this study,experiment and multiscale numerical simulations are adopted to investigate the interfacial bonding behavior,contact surface deformation behavior and micro deformation behavior of bonded interface.The influences of temperature,deformation,surface morphology and interface on the composite process were analyzed.Finally,the industrial test is carried out and the technological conditions for realizing the interface bonding of stainless steel/carbon steel during non-hot rolling were put forward.The main work and conclusions are as follows.(1)The hot and cold static pressure experiment were designed to simulate the rolling process of stainless steel/carbon steel,and the effects and rules of the process parameters(temperature,strain rate,reduction rate,time)on the interface bonding were studied.The performance of a bimetallic joint was characterized by two geometric indexes:the thickness of the diffusion layer and the interfacial bonding rate.It was found that the deformation temperature has a beneficial effect on the bonding rate.Owing to the short contact time,only a shallow diffusion of approximately 2-3 ?m can be achieved.A slight decrease in the interfacial bonding rate after heat preservation is correlated to the difference between the thermal expansion coefficients of the two materials,but the thickness of the diffusion layer shows a significant increase.The mechanical properties of AISI stainless steel/Q235A carbon steel were investigated by tensile tests.It was found that the strength of the composites is mostly related to the bonding rate and the strength of the relatively soft material,which can be captured by an explicit equation.(2)The static pressure experiment was designed to simulate the contact deformation law of different surface morphology of the substrate during the roll-bonding process.The results show that the deformation forms of rough peaks of stainless steel and carbon steel are different during the static pressure composite process.The rough peaks of harder stainless steel are embedded in the carbon steel almost without deformation,while the rough peaks of softer carbon steel are obviously flattened.(3)Based on the commercial finite element software,the deformation process of the surface roughness peak during the deformation process was simulated and analyzed.As the roughness of stainless steel increases and the roughness of carbon steel decreases,the relative sliding of the metal on both sides of the interface decreases and the contact pressure per unit area increases because of the pinning of the surface roughness of the stainless steel surface to the surface of the carbon steel,resulting in the improve of interfacial bonding quality.(4)The bonded interface is divided into complete bonded interface and incomplete bonded interface on the micro scale.The molecular dynamics method is used to simulate the micro deformation behavior and law of bimetal from the point of view of mechanical properties and dislocation evolution,and compared with the experimental process to explore the rolling composite deformation mechanism of stainless steel/carbon steel.The results show that complete bonded interface and incomplete bonded interface both hinder dislocation propagation through the interface during roll-bonding process,resulting in significant strengthening effects via plastic deformation.In addition,the alternately change of the dislocation density within the two matrixes during the deformation process leads to the special phenomenon that the deformation of the two matrixes is alternately changed.(5)Industrial experiment are adopted to investigate the interfacial bonding behavior of stainless steel/carbon steel during warm roll-bonding process.According to the actual rolling conditions,the finite element modeling and simulation research are carried out.The results of industrial experiments not only verify the above conclusions,but also get a new understanding of the rolling bonding mechanism.(6)The technological conditions for realizing the interface bonding of stainless steel/carbon steel during non-hot rolling were put forward,including a reduction rate of at least 65%to expose fresh sub-surface metals,a rolling pressure per unit area of at least 0.22GPa to ensure sufficient real contact area between surfaces,a rolling zone temperature of at least about 350? to activate surface atoms of the strip,and enough back tension together with good lubrication between the roller and the strip to ensure the approximate non-sliding surface contact between the surface of strips.