Research On The Interface Behavior And Technological Basis Of The Titanium/Steel Composite Thin Plate Formed By Cold-Hot Rolling

Titanium/steel composite plate has both the excellent corrosion resistance of titanium and the high strength and low cost of steel.It is widely used in petrochemical,nuclear power,ship and marine engineering and other fields.At present,the methods used to produce titanium/steel composite plate mainly include explosive welding method and hot rolling composite method.If the titanium layer or steel layer is thin,the titanium layer is easy to be burst through during explosion.Multi-pass hot rolling is required for hot rolling composite method,but multi-pass hot rolling of thin titanium layer and steel layer will lead to continuous reduction of interfacial bonding strength.Traditional methods are difficult to produce high-quality titanium/steel composite thin plate,which can not meet the demand for lining materials of marine engineering.Therefore,the research of high-performance titanium/steel composite thin plate and its short process and efficient forming method become important development direction.In this context,the cold-hot rolling method was proposed to prepare titanium/steel composite thin plate.The key scientific problems such as the mechanism of the bonding interface of cold-rolling titanium/steel composite plate,the reaction behavior of the hot-rolling interface and its influence on the interface bonding strength have been systematically studied with the help of metallographic microscope,scanning electron microscope,X-ray diffractometer,spherical aberration correction transmission electron microscope,universal testing machine and digital image correlation method and other equipment and methods.The main results of this paper are as follows:The influence mechanism of mechanical grinding methods and grinding stripe direction on the composite behavior of cold rolling titanium/steel interface was investigated.Realize the control of the cold rolling titanium/steel interface structure and improve the interface bonding strength.It was found that the grinding of steel wire brushes and flap disc will form a hardened layer of about 8 μm thick on the surface of titanium.The hardened layer of titanium cracked during cold rolling,and the steel was squeezed into the cracks.It was easy to form a tooth-like interface containing gaps,cracks and amorphous defects,which damaged the interface bonding strength.Transverse mechanical grinding stripes could promote the interface to expose more fresh metal,which was conducive to interface bonding.On this basis,this paper proposed the method of brazed diamond grinding disc transverse grinding to reduce the work hardening of the titanium surface while increasing the surface roughness of the plates,forming a metallurgical bond and defect-free titanium/steel cold roll bonding interface.The problem of titanium/steel cold roll bonding was successfully solved,so that the cold roll bonding critical reduction of titanium/steel billets was reduced to 42%,and the interface bonding strength was 40%-50%higher than that of wire brush grinding and flap disc grinding.The interfacial reaction behavior of the hot rolling titanium/steel and its influence mechanism on the bonding strength of the interface were explored.The hot rolling temperature was the main factor affecting the reaction behavior of the titanium/steel interface.When the hot rolling temperature was less than or equal to 850℃,the titanium/steel composite thin plate would form a 600 nm thick TiC layer andα-Ti/α-Fe interface alternately distributed mixed interface.The interface was tightly bonded,and the interface bonding strength increases with the increase of hot rolling temperature.When the hot rolling temperature was greater than or equal to 900℃,the titanium/steel composite thin plate formed a 2 μm thick FeTi,Fe2Ti and TiC mixed interface layer and a 55 nm thick FeTi/Fe2Ti interface alternately distributed mixed interface,and micron-level pores were easily formed at the alternate interface,which would seriously damage the bonding strength of the interface and cause brittle fracture at the interface of the titanium/steel composite thin plate during tensile shear test.Within the experimental range of this paper,the reasonable hot rolling process parameters of titanium/steel composite thin plate should be hot rolling temperature～850℃,holding time 20-40 min,hot rolling reduction 35%-40%,the interface bonding strength of the titanium/steel composite thin plate prepared in this hot rolling process could exceed 220 MPa.A two-stage heating method for regulating the interfacial reaction behavior of titanium/steel was proposed,which improved the interface bonding strength of the titanium/steel composite thin plate.A TiC layer was pre-fabricated on the titanium/steel interface through the first stage of low temperature heating at 850℃,and the coarse-grained area of the TiC layer was used to hinder the diffusion of Fe and Ti elements at the interface during the second stage of high temperature heating at 900℃,which could realize high temperature hot rolling at 900℃ and avoid the formation of Fe-Ti phase at the interface.When the second heating temperature was 900℃ and the hot rolling reduction was 25%,the interfacial bonding strength of titanium/steel composite thin plate could reach 240 MPa.However,when the heating temperature of the second stage reached 950℃,the pre-fabricated TiC layer would decompose and lead to the formation of Fe-Ti phase at the interface,which would reduce the bonding strength of the interface.The deep processing properties of titanium/steel composite thin plate were improved by heat treatment,and the interfacial delamination mechanism of titanium/steel composite thin plate in tensile and bending deformation was revealed.The results showed that high temperature short-time heat treatment can improve the deep processing properties of titanium/steel composite thin plate and ensure high interfacial bonding strength.The interfacial bonding strength,yield strength and elongation after fracture of titanium/steel composite thin plate heat treated at 900℃for 10 minutes were 198 MPa,163 MPa and 52%respectively.The main reason for the interface delamination in the plastic deformation of the titanium/steel composite thin plate was that the difference in the plastic deformation capacity or the degree of deformation of the two metal layers leads to the first necking of a certain metal layer.The research results were transformed into an enterprise and pilot production was realized,and a pilot production line for cold-hot roll bonding of titanium/steel composite thin plate was formed,and high-quality titanium/steel composite thin plate was produced in stable batches.