Computational modeling of stationary gastungsten-arc weld pools and comparison to stainless steel 304 experimental resul
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INTRODUCTION
W E L D I N G is an extremely important industrial process, and it is widely recognized that temperature distribution and weld puddle shapes are keys to quality weldments. Welding as a fabrication process poses a number of difficult problems to the design, development, and manufacturing community. The use of fusion welding for fabrication results in the joint area being subjected to localized heating (above the melting temperature) and cooling, with the thermal cycle that is experienced varying over a wide range depending on the specimen size and geometry, and the welding proc e s s . [1'2] In recent years, there has been growing recognition of the fact that convection in the weld pool can significantly influence the properties of the weldment. [3-19] For example, fluid flow in the weld pool can influence the weld pool shape due to enhanced convective heat transfer in the direction of the flow. [3-71 The flow may affect the profile of the finished weld, it may affect the uniformity of composition in the weld, and finally, it may influence the weld solidification structure by controlling the weld solidification rates. Furthermore, the thermal cycle experienced by the heat-affected zone during a welding operation can influence and control solidstate transformations, thereby influencing the microstructure. [1,2,2~ Therefore, it would be extremely
T. ZACHARIA, Research Staff Member, S.A. DAVID, Group Leader, and J.M. VITEK, Research Staff Member, are with Oak Ridge National Laboratory, Oak Ridge, TN 37831. H.G. KRAUS, Research Staff Member, is with Idaho National Engineering Laboratory, EG&G Idaho, Inc., Idaho Falls, ID 83415. Manuscript submitted August 1, 1990. METALLURGICAL TRANSACTIONS B
useful to obtain relevant information about the thermal cycle experienced by the weld metal, the size and shape of the puddle, and the local solidification rates. Convection is an essential and important part of the mechanism that controls the development of the weld pool. In order to understand the convective behavior in a weld pool, it is insmactive to examine the driving forces for fluid flow. The heat flux from the welding arc generates spatial and temporal density gradients in the molten metal which cause thermally driven flows in the weld pool. The welding current and the self-induced magnetic field can influence fluid flow in the weld pool by way of electromagnetic forces. For a symmetric field, the tendency is to produce an inward torroidal flow. tl~ However, in actual welding operations, the asymmetric magnetic field may produce a rotational flow within the weld pool. Finally, convection in the weld pool due to the spatial variation of surface tension in the weld pool (Marangoni convection) has been shown to have a controlling effect on the weld fusion zone. 13-7,15[ The concentration of surface-active elements in the base metal (particularly sulfur and oxygen) can dramatically alter the weld penetration shape and size by controlling the surface tension gradient-driven flow in the weld pool. A simple surfac
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