Segregation: It is the difference in composition of steel within the ingot than some average composition. Segregation is due to

a) Difference in solubility of solute elements in liquid and solid steel i.e. partition coefficient of element in     steel. Partition coefficient of solute (K) is defined as

The value of K  The solute elements whose K = 1 do not segregate. All elements whose tend to segregate.

b) Rate of solidification: faster rate of solidification avoids the elements to segregate. The initial chill layer     of ingot has practically the same composition as that of liquid steel. Decrease in rate of solidification     causes elements to segregate.

c) Larger size ingots are prone to segregation than smaller size ones. Larger size ingots require more     time for solidification.

Remedy: soaking of ingots at high temperature can minimize segregation.

Non metallic inclusions:

Non metallic inclusions are inorganic oxides, sulphides and nitrides formed by reaction between metal like  with non metallic elements like oxygen, nitrogen, sulphur etc.. An inclusion is a mismatch with the steel matrix. See lectures 27-30 for details about inclusions.

Fine size inclusions when distributed uniformly are not harmful. Non deformable inclusions like  are undesirable.

Inclusion modification is the remedy to alleviate the harmful effect of inclusions on properties of steel