Showing papers by "Tarasankar Debroy published in 1998"

Quantitative modelling of motion, temperature gyrations, and growth of inclusions in weld pool

Abstract: The velocity and temperature fields, the shape and size of the fusion zone, and the motion of the inclusions were calculated by the solution of equations of conservation of mass, momentum, and energy in three dimensions for various welding conditions. The loci and the temperature gyrations experienced by a large number of inclusions were calculated numerically to seek a statistically meaningful residence time distribution of the inclusions and the number of intensities of the temperature cycles experienced by these particles. Finally, both the growth and dissolution of the inclusions were considered to calculate their size distribution. The inclusions experienced considerable recirculatory motion and strong temperature gyrations along their paths in the weld pool. The temperature–time plots for most of the inclusion particles displayed several temperature peaks. However, about one-third of the particles experienced continuous cooling behaviour. The average number of the temperature peaks in the t...

Enhanced dissolution of nitrogen during gas tungsten arc welding of steels

Abstract: Although nitrogen concentrations at levels much higher than Sieverts' Law predictions during the arc welding of iron and steel are well established, there is currently no commonly accepted methodology to determine this concentration quantitatively. The nature and concentrations of various species in the plasma phase above the weld pool surface are therefore investigated in the present work using both theoretical and experimental techniques. A comprehensive thermodynamic analysis of the nitrogen containing plasma phase of a gas tungsten welding arc shows that ionised species dominate close to the electrode, whereas neutral monatomic and diatomic nitrogen are the primary species near the metal surface at plasma temperatures as low as 5000 K. When oxygen is added to a nitrogen containing plasma, the resulting nitrogen concentration in the weld metal is further enhanced. Definitive proof is provided for a mechanism in which nitrogen and oxygen species interact in the plasma phase at temperatures below...

Inclusion formation in low-alloy steel welds

Abstract: This paper summarizes four models for describing inclusion formation in steel welds These methods include simple fixed oxidation sequence model, thermodynamic model, thermodynamic-kinetic model, and thermodynamic-kinetic-fluid flow model Complexities of these models increase with a need to describe details of the inclusion formation The applicability of the models was illustrated with two examples In one of the examples, thermodynamic calculations of phase stability between liquid steel, AlN and Al{sub 2}O{sub 3} explained the inclusion formation in self-shielded flux cored arc weld In the second example, thermodynamic-kinetic calculations illustrated the competing effects of weld metal composition and cooling rate effects on the inclusion formation in electron beam and laser beam welds Limitations of the current inclusion models and recommendations for future work on the inclusion formation were highlighted