Section Size
Deep-seated, subsurface porosity usually was located adjacent to the 90° re-entrant angle or "step," and most often occurred in section thicknesses from 0.875-1.375 in. (2.22 and 3.5 cm). These locations act as localized hot spots, since a small volume of the core is heated from both sides by the solidifying iron. In thinner sections, varying degrees of surface porosity or pockmarking were found.
These defects probably were formed by gaseous decomposition products pushing away the semi-skinned-over casting surface. Since these bubbles are formed late in solidification at the mold-metal interface, there was not enough time for them to dissolve. Consequently, a depression is left in the surface, when final solidification commences. This surface porosity varied between somewhat large, semi-rounded holes extending 0.125 in. (0.3 cm) to small surface pores having no appreciable depth.
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[Binder Ratio] [Binder Level] [Casting Temperature] [Section Size]