Inclusions or Structural Anomalies
Metallic Inclusions. Metallic or intermetallic inclusions of various sizes which are distinctly different in structure and color from the base material, and most especially different in properties. These defects most often appear after machining.
Possible Causes
Combinations formed as intermetallics between the melt and metallic impurities (foreign impurities);
Charge materials or alloy additions which have not completely dissolved in the melt;
Exposed core wires or rods;
During solidification, insoluble intermetallic compounds form and segregate, concentrating in the residual liquid.
Remedies
Assure that charge materials are clean; eliminate foreign metals;
Use small pieces of alloying material and master alloys in making up the charge;
Be sure that the bath is hot enough when making the additions;
Do not make addition too near to the time of pouring;
For nonferrous alloys, protect cast iron crucibles with a suitable wash coating.