Analysis Of Fluid Flow Behavior During Pulsed Laser Welding Of Hastelloy C-276Alloy

As the global warming and the depletion of fossil energy, new energy has become a topic and been paid attention to by the people all over the world. The technologies of nuclear energy, wind energy, solar energy and tidal energy have become the main research field by most of the countries in order to strengthen the economic power. With the characteristics of non-independence of natural conditions and consuming fewer resources, the nuclear energy has got more and more national attention increasingly. Especially, AP1000as the most advanced and third-generation nuclear power plant, which uses the canned pump with high reliability and low maintenance requirements. The can as the most import part of the canned pump, which has a characteristic of larger ratio of length to diameter (the diameter of the forming components is565mm, the length of the can is no less than3000mm), the ultra thickness (with the thickness of which is0.5mm) and so on. Moreover the requirements of the accuracy is really high (diameter error of which is±0.076mm) and the working life is long (60years).Therefore during the welding process not only the mechanical properties, corrosion resistance but also the the welding morphology must be controlled. The material of the work piece melt during the welding process, and then the convection occurs due to the variation of the surface tension. The convection in the welding pool will redistribute the energy in the welding pool, which will have a significant influence on the welding morphology. The fluid field during the welding process shall be analyzed to control the weld shape more precision. But analysis of the weld pool flow by experimental methods is very difficult. Using numerical simulation method to analyze the flow of the weld pool is always an important direction in the field of welding.In this paper, based on the characteristics of the canned pump of the nuclear power plant and the pulsed laser welding process, the following aspects are studied:(1) Using the CFD software FLUENT based on the theories of fluid dynamics and heat transfer and the basic assumptions, the3-D transient model of fluid flow and heat transfer is established. The Gauss surface heat resource is selected as the welding heat resource, at the same time the method of dealing with the boundary conditions and source term is given. Then the model is verified by the experiment;(2) The0.5mm Hastelloy C-276alloy is welded by using the JK701H type Nd:YAG pulsed laser and proper welding parameters. The effective peak power density of pulsed laser welding, the number of Marangoni Ma and the Pelect number Pe is induced to analyze the effect of welding parameters on the temperature field, fluid field, the characteristic of fluid flow and heat transfer;(3) The proper parameters of pulsed laser welding of0.5mm Hastelloy C-276alloy are founded based on lots of experiments;(4) On the basis of existing experimental conditions in the laboratory, the effects of external conditions (lateral blowing in laser welding, coaxial blowing, the surface coated with active agents) on the characteristics of fluid flow in the welding pool is studied. Furthermore, the influences of active elements on the characteristics of fluid flow and heat transfer in the molten pool is pointed out, and then based on the theory of Marangoni convection it is found that the heat redistribution caused by Marangoni convection is the main reason for changing the weld morphology.