Suggest a thorough reading of relevant sections of any Physical Metallurgy book.

Still a few points before that:

1. Steelmaking is a process of oxidation while iron-making is a process of reduction. So, presence of oxygen in steel is inevitable.

2. Killed steel has negligible oxygen content, while oxygen is hardly removed in rimming steel. Semi-killed falls between these two.

3. Production of killed steel, therefore, involves secondary steel-making, ladle treatment, etc while semi-killed may not have all of these.

4. Killed steel is most expensive.

5. Inclusion content is least in killed steel.

6. Piping loss during ingot solidification is negligible in killed steel while it is considerable in semi-killed.

Read more about ladle metallurgy, why Silicon is used, what does it remove and then why do we use Aluminium?

DHURJATI SEN

Silicon is the major deoxidizer in both killed and semi killed steel. Aluminum is used to produce fine grain steels in silicon deoxidized 'killed" steels or produce deep drawing characteristics in fully aluminum killed steels. Semi killed steels are used to provide greater ingot to final product yields where mechanical properties especially toughness properties are not of great concern in the steels final use.

Dhurjati Sen
Thank you... I suppose having killed steel is less inclusion than semi killed

weldstan ...thank you ..So Aluminum is rarely used as oxidizer compared to Si....Any reason for this?

When I was in steel making (Open hearth and BOF) 50 years ago, it was primarily cost.