Research On The Experiments Of C-276/304 Dissimilar Welding Based On Laser Energy Offsets

The end sealing of AP1000 nuclear reactor coolant pump can was welded with the method of arc welding traditionally. But the arc welding process was unstable, weld defects appeared easily, which have remarkable effects on the performance of welding joint in the end. According to the existing problems in the process of welding nuclear reactor coolant pump can and end cover by the arc welding, based on the physical and chemical characteristics of C-276 alloy and 304 stainless steel, the methlod of welding the dissimilar metal by pulsed laser was proposed and investigated. In order to optimize welding process parameters and get a good dissimilar welding appearance, the characteristics of macro morphology of C-276/304 dissimilar weld were observed by optical microscope, revealing the forming mechanism of C-276/304 laser dissimilar weld. Under the condition of good weld appearance, microstructure and element distribution of dissimilar weld joint under the condition of different laser energy offsets were studied, analyzing the influence of laser energy offsets on element distribution and building the corresponding fitting formula. The corrosion resistance and mechanical properties of the dissimilar weld joint were studied with the methods of electrochemical corrosion and tensile test, analyzing the effects of laser energy offsets on corrosion resistance and mechanical properties, optimizing laser energy distribution proportion acting on C-276 alloy and 304 stainless steel. The main contents are as follows:(1) Research on macro-morphology of weld joint. Effects of laser welding process parameters on welding appearance were studied with the methods of single factor experiment. The parameters of laser welding process were optimized, which made the width of dissimilar weld joint narrower. On this basis, in order to research on the influence of laser energy offsets on weld macro morphology, the welding experiments on the condition of laser energy offsets were did.(2) Research on microstructure of weld joint. The microstructure characteristics of C-276/304 dissimilar weld joints were observed by optical microscope, revealing the distribution characteristics of microstructure in the dissimilar weld joint. The chemical element distribution was studied by the methods of electron probe (point and line analysis), researching on the influence of laser energy offsets on Fe, Ni, Cr, Mo and W elements composition. In order to predict the weld chemical element composition accurately, the mathematical model between laser energy offsets and chemical distribution was set up.(3) Research on mechanical properties of weld joint. On the basis of good weld appearance, tensile test and hardness test were done respectively combined with the microstructure characteristic of the base material and dissimilar weld. In order to further study fracture mechanism of the base metal and dissimilar weld joint, micro-analysis on fracture appearance was did with the methods of scanning electron microscope (SEM).Results indicated that:with the laser energy moving to C-276, tensile strength and micro-hardness of dissimilar weld joint could be improved effectively.(4) Research on the electrochemical corrosion performance. Corrosion resistance of base metal and dissimilar weld joint in acid solution was analyzed with the methods of polarization curve and corrosion current density/time, the corrosion differences between base metal and dissimilar weld were analyzed. Corrosion mechanism was revealed on the basis of element distribution in every dissimilar weld joint. With the laser energy moving to C-276, corrosion resistance of dissimilar weld joint increased gradually.