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

Which steel type is defined by the addition of 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 of molten steel, using small amounts of deoxidizers, creates semi-killed steel. By only partly removing oxygen, this approach reduces impurities and controls gas evolution enough to lower porosity and surface defects, while not requiring the full, intensive deoxidation that kills all gas. The result is a balance: better weldability and predictable properties for larger or heavier sections, with more uniformity than rimmed steel but not as extreme a refinement as killed steel. Deoxidizers like silicon or aluminum bind with dissolved oxygen to form oxides that rise out of the melt, lowering the overall oxygen content without completely eliminating gas pockets.

Partial deoxidation of molten steel, using small amounts of deoxidizers, creates semi-killed steel. By only partly removing oxygen, this approach reduces impurities and controls gas evolution enough to lower porosity and surface defects, while not requiring the full, intensive deoxidation that kills all gas. The result is a balance: better weldability and predictable properties for larger or heavier sections, with more uniformity than rimmed steel but not as extreme a refinement as killed steel. Deoxidizers like silicon or aluminum bind with dissolved oxygen to form oxides that rise out of the melt, lowering the overall oxygen content without completely eliminating gas pockets.