| In order to meet the industrial requirements of corrosion resistance and long life cycle of concrete structures,it is urgent to develop a kind of particular building material with excellent corrosion,weather resistance and marine environment suitability.The composite material composed of stainless-steel and carbon-steel（SS-CS）not only satisfies the critic requirement of corrosion environment,but also reduces the economical cost.It also has the excellent properties with the high strength,good plasticity as well as toughness,etc.In this paper,the coordinated deformation and micro-structure evolution behavior are researched at the high-temperature near the interface of composite material.The thermal compression tests were carried out at the temperatures varied from 950°C to 1150°C and strain rates varied from 0.01 s-1to 1 s-1on the Gleeble 3800 thermal-mechanical simulation machine.The constitutive model of SS-CS was developed based on Arrhenius hyperbolic sine equation by means of the kinetic analysis,which is a coupling mathematical model by the strain rate,plastic strain and deformation temperature.Furthermore,the reasonable processing scopes of SS-CS were also obtained preliminarily from the established the thermal processing maps.In order to further study micro-structure evolution near the interface and solidify the hot processing scopes,the micro-structures near the interface were investigated under the various deformation conditions.The main contents include the micro-structure evolution rules of the sides of SS-CS as well as near the interface,the transition-layer and the evolution of holes,the distribution of interface elements and the effect of process parameters on diffusion behavior of Fe,Cr,and Ni elements.The results show that on a certain of strain rate,the diffuse phenomenon of carbon atoms from the side of carton-steel forwards to the side of stainless-steel is obvious and the width of the decarburization layer increases with the increasing deformation temperature.It can be found that the size of ferrite grains in the decarburized layer is larger than that in the carbon-steel matrix.The deformed grains on the side of stainless-steel are gradually replaced by those recrystallized grains,and the precipitated carbides are also reduced in the grain boundaries,resulting in the smaller size of grains and the high uniformity.However,when the deformation temperature rises to 1150°C,a part of recrystallized grains excessively grow and the distribution is uneven.On the certain of the strain rate,the rubbing force would cause the indentation tearing between the interface of bi-metal at the lower deformation temperatures（950°C,1000°C,1050°C）,resulting in the discontinuous pores,micro-cracks,and impurity particles at the interface.However,at the higher deformation temperatures（1100°C,1150°C）,the severe plastic deformation would force the impurity particles to be broken and dispersed,and the interface holes disappear.The thermal motion of atoms becomes stronger with the increasing deformation temperature,which is favorable for the hole closure and dynamic recrystallization of grains in the interfacial transition zone.Meanwhile,the diffusion distance of interface atoms also increases.In particular,at 1100℃and 1 s-1,the curve of element diffusion is smooth,and there is no aggregation of Cr and C atoms.There is nearly no defect of impurities but a small number of fine carbide particles at the interface.Combining with the analysis of the deformation behavior at the high-temperature and the micro-structure evolution of interface,based on the electron backscatter diffraction（EBSD）technique,the effect of deformation parameters on the micro-structure evolution and deformation coordination near the interface was studied and the processing parameters were also optimized by mean of the analyse approaches including IPF+grain boundary analysis,misorientation distribution of grain boundary,recrystallized grain distribution,misorientation distribution of grain,local misorientation distribution and Schmid factor distribution.The results show that the grains occur dynamic recrystallization on the side of carbon-steel near the interface and the average size increases with the increasing deformation temperature.And the intragranular dislocations and substructures on the side of stainless-steel near the interface are gradually consumed with the appearance and growth of austenite grains,which causes the dislocation density to decrease and the grain boundaries with low-angle are turned into the high-angle ones.At 1100℃and 1 s-1,the average sizes of grains on the side of stainless-steel and carbon-steel near the interface are 11.38μm and 13.54μm,respectively.The volume fractions of recrystallized grains are 31.2%and 39.3%,respectively,indicating a proportion coordination of dynamic recrystallized grains.The GOS range on both sides of the interface is 0～2.5°,and the strain gradient of grains decreases obviously.The average value of local misorientation difference is small and the ratio is close.Also,the average Smith factor is greater than 0.4 and the ratio is close.The above analysis results show that the composite interface has a high deformation coordination. |
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