Abstract
Influence of the surface characteristics of metallic substrate on the formation of initial solidification structure of steel was experimentally studied using AISI 304 stainless steel and the surface treated copper plates. The molten steel was dropped onto the copper substrate with or without surface undulation at the room temperature or heated to 673K, respectively. The other substrates had dimples machined by shot blasting or Rockwell hardness tester. The solidification structure and the dendrite arm spacing were analyzed on each solidified shell, and heat flux across the molten steel and the substrate was evaluated with the measured substrate temperature. It was found that the roughness of the substrate surface in a range of 10-16 μm had little influence on the heat transfer. The dendrite convergent spot (DCS) was evaluated by the direction of the primary dendrite arms near the surface. DCSs were appeared at 0.2-0.5 mm intervals on the flat substrate, and the interval of DSCs was broadened as increasing the substrate temperature. DCSs were appeared on the ridge of the dimples of the substrate, and another DCS was appeared between the pair of dimples when the distance of ridges exceeded 0.5 mm. Mechanism of DCS formation on the flat substrate was discussed. Furthermore, the influence of thermal diffusion during initial rapid solidification on the intervals of DCSs was evaluated.
