Effects Of Welding Procedure On The Microstructure And Properties Of Welded Joint Of Cryogenic Steel SA516Gr.60

Different welding procedures were adopted to weld cryogenic steel SA516Gr.6 for the purpose of investigation on the relationship between welding parameters and the microstructure and properties of welded joints. The analytic methods include tensile test, low temperature impact test, metallographic examination, microhardness test, Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), Transmission Electron Microscope (TEM) and so on.The effect of different amount of alloy element in weld metal composition on the microstructure and properties of weld metal are studied, the result indicate that weld metal can achieve good toughness when the composition is 0.06⁰.08%C, 1.0¹.2%Mn, 0.25⁰.35% Si. Quality and cost are considered together, the recommended electrode for Shielded Metal Arc Welding (SMAW) is J507DR and the recommended welding materials for Submerged-Arc Welding (SAW) are H09MnDR welding wires and matched SJ208DR agglomerated flux.The effect of weld heat input on the microstructure and properties of welded joint are discussed in a systematic way, the conclusion is that the tensile strength and low temperature toughness of weld metal increase first and then decrease with the increase of weld heat input. The recommended parameters are 14kJ/cm when use SMAW and 21kJ/cm when use SAW.The effect of interpass temperature on the microstructure and properties of welded joint are analyzed, the result is that the low temperature toughness of weld metal increase first and then decrease with the increase of interpass temperature, so interpass temperature should be controlled at 150℃.The recommended welding procedure is adopted to do fieldwork, conduct a series of charpy V-notch impact test and discover that the ductile-brittle transition temperature (FATT₅₀ )of base metal, weld metal and heat-affected zone are respectively -60℃,-57℃ and -52℃,and all are lower than -45 ℃, it is safe that such kind of equipment service at -45 ℃ and it is also proved that the appropriate procedure is adopted.The welded joint has good low temperature toughness because the weld metal has a considerable volume of acicular ferrite (AF). By means of EDS analysis and diffraction design demarcate of inclusions in the weld metal, the Transformation Kinetics of AF are discussed. The demarcated composition are MnOAl₂O₃, MnS and CaO·2Al₂O₃. The point is that the inclusions in proper size can supply nucleus to promote the forming of AF and improve the toughness of weld metal.