Preliminary observations of bursting of molten steel thick films in a steel plate irradiated by a high energy laser

This talk presents preliminary observations of the bursting of films of molten steel following illumination of a thin vertical steel plate by a 1075-nm continuous-wave 1000W Ytterbium fiber laser. Molten steel formed in the illuminated region persists as a molten disk for several seconds before a hole forms. Gravity is responsible for the formation of a dimple in the upper part of the molten disk and a bulge in the lower part. After several seconds, a hole appears at the dimple. Hole enlargement is quite sudden, like a soap film popping. Following this, a molten drop forms and falls under the influence of gravity below the laser beam, leaving behind a hole in the plate. Images of the initial hole captured by a high speed digital camera show that the hole forms first in the top portion of the molten disk, not in the center.

The molten steel is modeled as liquid contained within a hoop with size of the final hole. 3D images produced by Surface Evolver, an interactive program for modelling liquid surfaces, indicate the presence of a dimple within the molten region near the location of first appearance of the hole, and a bulge in the molten region near the lower portion for a liquid with density and surface tension taking on values near the melting point of iron.