Santini, L.; Benavidez, E.; Brandaleze, E.
January 2010
Acta Microscopica;2010, Vol. 19 Issue 1, p1
Academic Journal
In continuous casting of steel, mold fluxes are used to prevent surface defect, such as longitudinal cracks. The crystallization of these materials promotes mild cooling of the steel shell. The mold powder selection to be applied in plant depends on operation parameters, physical properties and crystallization grade. To know the crystallization kinetics is necessary to prepare laboratory samples because it is very difficult to extract samples from the process. This study was carried out to analyze the crystallization behavior at different thermal conditions. A commercial mold powder was melted at 1300ºC and then quenched to obtain solid layers. These layers were heat-treated in an electric furnace between 400ºC and 1000ºC, maintaining the samples at different times. Then, specimens were prepared to microstructural study and a particular etching technique was developed to reveal the crystals present in the glassy matrix. Light microscopy and scanning electronic microscopy (SEM) were applied to evaluate the crystallization evolution. The columnar crystals grains developed at the surface of the samples transform from dendritic pattern to polygonal and acicular crystals. Besides, irregular crystals nucleated about 400ºC in the glassy matrix increased in size with time and temperature up to 700ºC. Then these crystals become to dissolve. In particular, at 700ºC was possible to evaluate the increase of the surface crystalline layer and the dissolution rate of the irregular crystals. All this information was useful to understand the crystallization behavior at the mentioned temperature range.


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