Interfacial Structure And Regulation Of Microstructure And Properties In Ti/Steel Clad Plate

Ti/steel clad plate has wide application prospect and scientific research value.The interfacial structure and microstructure of the clad plate has great influence on its properties.It is one of the hot issues of research to control the interfacial structure and microstructure of clad plate to regulate its mechanical properties.In this paper,commercial pure Ti and ordinary carbon steel were selected as raw materials.Research was carried out according to the hot roll bonding manufacture process of Ti/steel clad plate.The interfacial structure and microstructure of Ti/steel clad plate were characterized by SEM(Scanning Electron Microscopy),EDS(Energy-dispersive Spectroscopy),EBSD(Electron Backscattered Diffraction)and XRD(X-ray Diffraction).The mechanical properties of Ti/steel clad plate were tested by tensile test,tensile shear test,peeling test and hardness test.The changes of interfacial structure and microstructure of Ti/steel clad plate during pre-heating,roll bonding and annealing are described in detail.The method of controlling the interfacial structure of Ti/steel is put forward,and the corresponding relationship between the microstructure and properties of Ti/steel clad plate is improved.(1)During the pre-heating process,the thickness of TiC layer is controlled by the grain orientation of the Ti layer.The TiC layer is thinner when the basal plane of the Ti crystal cell is parallel to the Ti/steel interface,and the TiC layer is thicker when the basal plane of the Ti crystal cell is vertical to the Ti/steel interface.This is due to the anisotropic diffusion behavior of interstitial carbon atoms in the α Ti.When the diffusion temperature is 750 and 800 °C,TiC is the only compound formed at the Ti/steel interface.The coexistence of TiC and Ti-Fe compounds was observed at the Ti/steel interface when the diffusion temperature increased to 850 °C.(2)By using the wedge-shaped Ti/steel specimen during roll bonding,the critical rolling reduction corresponding to the formation of Ti/steel interface is determined.When the rolling reduction is less than 60%,the well bonded Ti/steel interface is not form.At the same time,the peeling strength of the Ti/steel interface is lower.When the rolling reduction reaches 60% or more,the well bonded Ti/steel interface is form,and the peeling strength of the Ti/steel interface increases.When the rolling reduction reaches 60% or more,the cooperative deformation of the Ti layer and the steel layer causes shear deformation in the matrix structure,which results in the difference of the microstructure and texture of the Ti layer and the steel layer along the thickness.In the meanwhile,during the hot roll bonding process,dynamic recrystallization starts in the Ti layer and the steel layer,resulting in the softening of the materials.(3)The interfacial structure and mechanical properties of Ti/steel clad plate are controlled by the material and structure of the interlayer.In the Ti/steel clad plate with single IF(Interstitial Free)steel interlayer,TiC and Ti-Fe phases were detected at the Ti/IF steel interface.The bonding strength of this clad plate was the lowest.Continuous distribution of vanadium carbides was detected at the V/steel interface in the Ti/steel clad plate with single V interlayer.The brittle vanadium carbides also reduce the bonding strength of the clad plate.In the Ti/steel clad plate with IF steel + V interlayer,discontinuous σ phase was observed at V/IF steel interface.The formation of carbides was inhibited by the interlayer structure,so the bonding strength of the clad plate was the highest.In Ti/steel clad plates with IF steel + V interlayer,the size of the σ phase increases with the increase of rolling temperature,and the distribution of the phase is more continuous.At the same time,the higher rolling temperature promotes the recrystallization of Ti,V,IF steel and carbon steel.Therefore,the bonding strength and tensile strength of the clad plate decrease with the increase of rolling temperature.(4)The annealing process can soften the Ti/steel clad plate with IF steel + V interlayer.At the same time,the annealing process promotes the precipitation of vanadium carbides along the V/IF steel interface.When the annealing temperature is 450 °C,recover is occurred in the materials.When the annealing temperature is 550 °C and 650 °C,the materials undergo recrystallization.The degree of recovery and recrystallization increases with the increase of annealing temperature and holding time.During annealing,the vanadium carbides first precipitate in the σ phase and then grows along the V/IF steel interface.At the same time,the annealing process causes the interface to form microscopic holes.The softening of materials during recovery and recrystallization is the main reason why the bonding strength and tensile strength of the clad plate decrease with the increase of annealing temperature and holding time.Meanwhile,the co-existence of the σ phase and vanadium carbides and the diffusion introduced microscopic holes also reduce the strength of the clad plate.