Study On Cracks And Microstructure Of Weld Zone Of TA15/Cr18-Ni8Steel Joints By Filler Wire GTAW

Titanium alloy has lower density, higher intensity, good heat conducting property, high temperature resistance, high corrosion resistance and other advantages. It is already widely applied in aerospace, nuclear energy, petrochemical industry, medical devices and other industrial sectors. Connecting titanium alloy and stainless steel can not only solve the problem of the single structure of titanium alloy is expensive, and give full play to the performance advantage of the two metals. It has an excellent development potential in the future.TA15titanium alloy and Cr18-Ni8stainless steel was welded by means of argon tungsten arc welding in this paper, using Cr25-Ni13stainless steel, CuZn alloy and Cu as filler metals. The microstructure and chemical composition of weld joints were analyzed. The cause of precipitated phase and welding cracks as well as their effect on property of welding joints were studied, and preventive measures of cracks were given.Complete joints without cracks can not be obtained by joining TA15titanium alloy to Cr18-Ni8stainless steel using Cr25-Ni13alloy and CuZn alloy. It is easy to produce cold crack in welded joint. A good joint can be got by using Cu as filler metal under the suitable welding heat input, but cold cracks was found in the area near the root welding and titanium alloy side fusion area. Too high welding residual stress is the reason of crack. In order to prevent cold cracks, the welding wire that has high mutual solubility with the two base metals and lower melting temperature than the base metal should be chosen, dehydrogenation should be carried out on the wire and the base metal, and use the higher temperature of the heat preservation after welding to reduce the cooling speed of joint.Using Cu as filler metal can get good joint, the microstructure of weld of the joint from the inside out as:isometric crystals, dendrites, solid solution with precipitated phase. The isometric crystals and dendrites are composed of intermetallic compound of Fe-Ti and Cu-Ti, and the microhardness is 700～813HVsog. The major component of solid solution is Cu, the precipitated phase is CU3P, and the microhardness is steady at around140HV50g. The matrix structure of fusion zone on the side of titanium alloy is solid solution composed of TiFe and Ti2Cu, and there are a large number of block and acicular precipitated phase in it. The block precipitated phase is composed of Ti3P, TiFe, TiFe2and Ti2Cu, and the acicular precipitated phase is composed of TiFe and TiFe2. The microhardness of fusion zone on the side of titanium alloy is500-700HV50g. The fusion zone on the side of stainless steel is given priority to the branch crystal and columnar crystal, it is composed of Fe2P and Cr2P3and a few NiP2, and the microhardness is steady at around550HV50g. The fusion zone on the side of titanium alloy has bigger inhomogeneity of component, and it is the key part affects the performance of whole joint.