| TWIP(Twin-Induced Plasticity)steel has achieved a combination of high strength and high toughness,and has been widely used in the automotive industry.However,due to the high content of alloy elements,its weldability is poor.Compounding TWIP steel with low-cost LC(low carbon)steel with good mechanical properties and weldability to prepare bimetallic composite materials can make up for the deficiencies of a single TWIP steel and expand its scope of application.In this paper,TWIP/LC double-layer and LC/TWIP/LC three-layer composite sheets are prepared by diffusion welding and hot-rolled and warm-rolled method.The diffusion welding temperature is 1000? and 1100? respectively,Fe-Si-B amorphous alloy is added as the intermediate layer,and the samples are heated to 850?,900? and 950? for quenching treatment.When preparing three-layer composite sheets,SPS are used to connect the three plates before rolling them.During rolling,the total height of the three-layer sheet is the same,and the thickness ratio of LC/TWIP/LC is 1:1:1,1:2:1,1:6:1 respectively.And the three-layer composite sheet with Fe-based intermediate layer was prepared by the same process.Metallographic microscope and electronic probe(EPMA)were used to analyze the interface morphology and composition of the composite sheets prepared by the two processes.The hardness of the interface was tested using a microhardness tester.Tensile properties and fracture morphology of the rolled composite sheet were analyzed by using electronic universal testing machine and high-resolution scanning electron microscope.The grains of TWIP/LC double-layer composite prepared by diffusion welding are coarsened,and Si elements are uniformly diffused from the intermediate layer to both sides of the matrix,and the higher the temperature,the more the diffusion amount,the better the interface bonding.In order to improve the mechanical properties of the composite material,the samples after diffusion welding were quenched at different temperatures.After quenching,martensite structure is formed on the side of the LC steel,and the microhardness is improved.The quenching heating temperature is 850?,holding for 10 minutes,the microhardness of the sample after water cooling is higher than that of the sample with the same holding and cooling method of heating temperature 900? and 950?.Interface of the LC/TWIP/LC three-layer composite sheet prepared by the rolling process is tightly bound,and there are no defects such as pores and cracks.The diffusion phenomenon of Mn element at the TWIP/LC interface is obvious.After rolling,the material dislocation density increases,grain refinement,and hardness increase.The average microhardness of TWIP steel and LC steel before rolling were 260 HV and 160 HV respectively,and the average microhardness of TWIP steel and LC steel without intermediate layer sample after rolling were 517 HV and 260 HV respectively(the average microhardness of TWIP steel and LC steel with intermediate layer samples is 540 HV and 295 HV respectively).Tensile test results show that the strength and elongation of the TWIP-cored three-layer steel sheet are proportional to the thickness ratio of the three-layer board,which conforms to the ROM law.During the tensile process,the grains of the steel sheets on both sides coordinately deformed,and the cracks first appeared on the LC side,then the cracks propagated,and finally formed continuous cracks at the TWIP/LC interface.Due to the incomplete melting of Fe based amorphous and the appearance of brittle phase at the interface,the tensile strength and elongation of composite sheets with intermediate layer are lower than those without intermediate layer. |
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