Superplastic Welding Of1.6%C-UHCS/40Cr With Interlayer

Ultra-high carbon steel (UHCS) is a kind of new highly performed steels;however, large number of carbide contained in steel results bad weldability and hasrestricted its engineering application. Based on the fact that steel with big volume ofcarbide has super plasticity and sandwich material is in favor of solid weldingof different materials, conduct the superplastic welding research of UHCS withinterlayer thus provide a convenient and high-quality welding method for suchdifficult-welding materials.Take1.6%C-UHCS after ball annealing and40Cr after overall salt bath cyclingquenching as the research object, optimize the interlayer design and conductthe superplastic welding of1.6%C-UHCS/40r with interlayer. Discuss the influence ofinterlayer, welding technology parameters and electricity on its joint welding.Analyze and detect the micro structure of the joint. Discuss the effect of interlayer andelectricity during the superplastic welding. Put forward a superplastic weldingmodel with interlayer.The results show that when the welding temperature is750℃, welding time is10min, the joint strength is35%higher when with industrial pure iron as interlayerthan without, which is the same with the40Cr base material. Adding appropriateelectric field and interlayer can improve the joint superplasticity, it is beneficial for thewelding of interlayer with base materials and diffusion as well as joint microstructure,strength. when the electricity is+3kV/cm, temperiture is750℃, after10minuteswelding, the strength can reach728MPa, which is higher than without electricity. Thejoint can be divided into "sandwich area","interface area","transitional zone" and"mother material area", Conduct weldings at UHCS and40Cr’s best superplastictemperatures respectively, there is difference in the joint plastic deformation anddiffusion mechanism, joint organizations characteristics and fracture mechanisms arenot the same. When welding at750℃, form uniform sandwich district micrstucture, while non-uniform organization when780℃The mass ferrite in the sandwichdistrict near40Cr is the weak area of the whole joint. The joint fracture can be dividedinto the following three features area: analogous original interface area, transitionalzone and metallurgical bond area. The main defects are mechanical combined area,interfacial microscopic gaps, non-metallic inclusion, and intergranular crack and so on.Using Industrial pure iron as an interlayer can control the interfacial reaction, decreasethe density of the Second Phase, increase interface diffusion, welding rate, and it willalso reduce the joint stress, avoid harmful organization generation, improve thewelding quality.