Effect Of Interlayers And Heat Treatments On Interfacial Microstructure And Bonding Properties Of Hot Rolled Titanium-steel Clad Plate

Because of the combination of titanium with the good characteristics of corrosion resistance,small density,high specific strength and steel with high strength,hot-rolled titanium steel clad plates have broad application prospects in the fields of ocean engineering and petrochemical industry.The current researches on hot-rolled titanium steel clad plates are mostly focused on the effect of rolling process parameters upon the microstructure and mechanical properties of the materials.Some scholars have studied the effect of Cu and Ni interlayers,while the discussion about Nb interlayer and Nb+Ni double interlayers are less.In this paper,the experiment was carried out using vacuum hot-rolled Q235-TA2 plates.The OM and SEM were used to observe the interfacial microstructure,and the diffusion of interfacial elements was detected by SEM-EDS.The interfacial bonding properties were characterized by compression shear tests,and the phase analysis was performed by XRD.The main contents of this paper are as follows:First of all,the influence of interlayers to interfacial microstructure and bonding properties has been investigated.Results show that when the rolling temperature is 875 ℃,the compressive strength of the Nb interlayers is the highest(280 MPa),followed by Nb+Ni double interlayers samples(239 MPa),and the compressive strength of samples without interlayers is the lowest(231 MPa).As for samples of Nb interlayers,there are some Fe2Nb existing at the Q235-Nb interfaces,and the fracture occurs at the Q235-Nb interface in the compression shear test.As for samples of Nb+Ni double interlayers,the existence of Ni3Nb at the interface of Nb-Ni and the micropores distributing along the interface are the main reasons for the fracture at the Nb-Ni interface.As for samples without interlayers,there are some TiC existing at the Q235-Ti interfaces,and the fracture occurs at the Q235-Ti interface in the compression shear test.When the rolling temperature is 925 ℃,the compressive shear strength of Nb interlayers specimens is still higher than that of Nb+Ni double interlayers specimens.Compared with samples at 875 ℃,the compressive shear strength of Nb and Nb+Ni double interlayer specimens decreases at 925 ℃.The brittleness Fe2Nb increases with the increase of temperature and new phase FeNb produces at the interface of the Nb interlayer samples.The pore size becomes larger and the thickness of Ni3Nb layer increase at the interface of the Nb+Ni double interlayers.Second,the influence of heat treatments on the interface without interlayers has been discussed after hot rolling.The compressive shear strength of the high temperature tempering samples at 650 ℃ are 138 MPa and that of the normalized samples at 900 ℃are 143 MPa.The thin film TiC layer is formed near the Q235 side of the Q235-Ti interface,and the thickness of TiC increases significantly compared with the rolling state.Moreover,the increase of TiC caused by high temperature diffusion is the main reason for the decrease of interfacial bonding strength.Finally,the effect of heat treatments on the interface with Nb interlayer has been further discussed.Because of the pores of at Q235-Nb interface,the compression shear strength of the high temperature tempered samples(162 MPa)is slightly lower than that of the normalized samples(171 MPa).There are some Fe-Nb intermetallic compounds existing at the Q235-Nb interface of the high temperature tempered Nb interlayer specimens.After normalizing,the Fe2Nb phase is formed at the Q235-Nb interface,and the needle like structure is observed at the Nb-Ti interface.In the process of compression shear tests,all the specimens are fractured at the Q235-Nb interfaces,and the bonding strength of Q235-Nb interface is weaker than that of Nb-Ti interface.