Random smooth depressions or shallow pits in the casting
Indicates that oxygen reacted with the chrome in metal
This reaction is more prevalent with certain metals
400 stainless series and pH stainless metals may be more prone to this defect
Causes of this defect are evident in the other portion of the process; to cure, R&R recommends taking the following actions:
Oxygen reaction with metal.
Eliminate/reduce oxygen presence after pouring.
Chromium (Cr) oxides form when oxygen is present during solidification.
Avoid contact with oxygen during solidification. Implement canning practice once shells are poured.
CO gas forms through reaction between C in steel with the refractories of the mold.
Use carbon stucco, put molds in sand and use alternative refractories.