Temperatures in the keyhole
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I.
INTRODUCTION
CALCULATIONS of the thermal profiles in high-energy density welding, whether the calculation is strictly conduction or includes the convection of the molten pool, are based on a heat source that is a modification o f the heat source used in arc-welding calculations. The heat source for arc welding has resulted in calculations that are a good approximation of the experimental data. Similarly, for highenergy density welding, the modified arc-welding heat source has served as a good approximation, and the calculations of thermal profiles are representative of the experimental data. However, the physics of the processes is completely different. In arc welding, a small volume of the metal is melted, the temperature of which is only slightly above the melting temperature of the alloy. In high-energy density welding, a keyhole or vapor column is formed as a result of vaporization of the alloy. The temperatures in this vapor column can be greater than the vaporization temperatures of the elements in the alloy, m The movement of this vapor column along the joint created by the two plates to be welded, results in a weld that has a high depth-to-width ratio, which is a characteristic of high-energy density welding. Klemenst2~ has provided us with remarkable insight into the balance of forces that must exist between a moving vapor column and the opposing forces of the molten pool that tend to collapse the keyhole. Basically, the vapor pressure of the keyhole is balanced by a hydrostatic pressure term and the surface tension divided by the radius. Unfortunately, as has been discussed in a previous publication, [~ this leads to an inconsistency in the temperature. Kristensen and Hansson[3] have developed a simple numerical model for the electron beam interaction, in which equilibrium conditions between the vapor pressure and the surface-free energy, vapor pressure, and temperature and between the temperature, heat input, and amount of heat dissipated are used to determine the temperatures during
E.A. METZBOWER, Branch Head, is with the Physical Metallurgy Branch, United States Naval Research Laboratory, Washington, DC 20375-5343. Manuscript submitted September 23, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS B
welding. The model assumes a cavity wall temperature of 2500 ~ well below the vaporization temperature of the alloy. DebRoy and co-workers [4-7] have used the vaporization and depletion of manganese in AISI 201 stainless steel during laser beam conduction welding to determine the temperature of the surface of the molten pool. This comprehensive modeltn predicts laser-induced metal vaporization rates and the resulting weld pool composition changes. The velocity distribution functions of the gas molecules at various locations above the weld pool surface and the heat transfer and fluid flow phenomena in the pool have been coupled to model the rates of the vaporization of various alloying elements during laser beam welding of stainless steels. Essentially, they found vaporization rates that are approximat
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