Which steel type is defined by adding small amounts of deoxidizers to molten steel to remove impurities?

Which steel type is defined by adding small amounts of deoxidizers to molten steel to remove impurities?

• A. Killed steels
• B. Capped steels
• C. Rimmed steels
• D. Semi-killed steels

Answer: (D)

Partial deoxidation is the idea here: you add only small amounts of deoxidizers to molten steel to remove impurities like oxygen, but you don’t remove all of it. This leaves the steel in a state between fully deoxidized (killed) and minimally deoxidized (rimmed). The result is semi-killed steel, which has reduced gas porosity compared to rimmed steel but isn’t as dense and uniform as killed steel. This creates a useful balance of properties—better dimensional stability and machinability than rimmed types, without the higher cost and steelmaking effort of fully killed steel. In practice, deoxidizers such as silicon or aluminum are used in these small amounts to achieve that partial deoxidation.

Partial deoxidation is the idea here: you add only small amounts of deoxidizers to molten steel to remove impurities like oxygen, but you don’t remove all of it. This leaves the steel in a state between fully deoxidized (killed) and minimally deoxidized (rimmed). The result is semi-killed steel, which has reduced gas porosity compared to rimmed steel but isn’t as dense and uniform as killed steel. This creates a useful balance of properties—better dimensional stability and machinability than rimmed types, without the higher cost and steelmaking effort of fully killed steel. In practice, deoxidizers such as silicon or aluminum are used in these small amounts to achieve that partial deoxidation.