White exposure
As chill is called a casting defects in cast iron ( cast iron with lamellar graphite). The fracture structure shows a white radiation, which gradually or abruptly merges into gray.
The cause is the excessive cooling rate of the white solidified area. The wall thickness of the cast pieces is too small or the chemical composition of the melt to be cast is not adapted to the smallest wall thickness of the cast part. A low silicon or carbon content or too high a proportion of hardening alloy components ( manganese , chromium , etc.) are particularly noticeable. Other causes are unsuitable raw materials or severely overheated iron . If there is no gradual transition of the structure from white to gray, the ratio of sulfur to manganese is too high.