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[Display omitted] • The deep cryogenic treatment was first applied to TC4/4J36 diffusion welding joint. • The effects of soaking time and cycles on mechanical properties of joint were studied. • The deep cryogenic treatment improves the quality of dissimilar joint between titanium alloy and steel. • The influence mechanism of deep cryogenic treatment on joint was studied. The diffusion welded joints of 4J36/TC4 with Ni/Cu/V metal interlayer were subjected to deep cryogenic treatment. The results showed that the extension of soaking time could improve the mechanical properties of the joint. The sample soaked for 8 h had the best performance, and it possessed ultimate tensile strength of 357.9 MPa and elongation of 24.9%. All samples failed at Cu/Ni interface with a ductile fracture manner, indicating that the joint still had good performance at low temperature. [ABSTRACT FROM AUTHOR]

• The V/Cu/Ni interlayer was first applied to weld TC4 titanium alloy and 4J36 invar alloy. • The use of V/Cu/Ni interlayer produces solid solutions at all interfaces. • The use of V/Cu/Ni interlayer improves the quality of dissimilar joint between titanium alloy and steel. • The formation mechanism of 4J36/Ni/Cu/V/TC4 bonded joints was studied. Diffusion bonding of 4J36 invar alloy and TC4 titanium alloy was carried out by inserting Ni/Cu/V multi-layer metal interlayer. The results showed that temperature had a significant effect on microstructure and mechanical properties of welded joints. At 890 °C, the joint tensile strength reached maximum value of 249.3 MPa. Fe-Ni solid solution ((Fe,Ni)ss), Cu-Ni solid solution ((Cu,Ni)ss), V-Cu solid solution ((V,Cu)ss) and Ti-V solid solution ((Ti,V)ss) were produced at interfaces of 4J36/Ni, Ni/Cu, Cu/V and V/TC4, respectively, and fracture surfaces of all joints showed dimples of different sizes, which showed that the application of Ni/Cu/V interlayer was an effective method. [ABSTRACT FROM AUTHOR]