Large subsurface slag inclusions were found in a grey iron casting after machining that contained a mix of reactive gassy slag and sand. Higher magnification views of the defect area showed the slag inclusions combined with embedded sand grains that appeared bright and crystalline in structure under polarized light.

1. CASTING DEFECTS
WHICH FILTRATION CAN
INFLUENCE
SLAG INCLUSIONS IN
GREY IRON CASTING

2. Slag inclusions in a grey iron casting
Large sub-surface inclusions
only visible after machining

3. Macro of the defect area (left),
with a more highly magnified
view below. Showing a mix of
reactive gassy slag in
combination with sand
Slag inclusions in a grey iron casting

4. Slag inclusions in a grey iron casting
The same defect more highly
magnified, viewed under normal
light (left) and polarised light
below. The sand grains are more
clearly visible as bright and
crystalline in structure