Which of the following best describes killed steels?

• A. Partially deoxidized; gas evolves; low quality.
• B. Fully deoxidized with no gas evolution; shrinkage at top of ingot removed; highest quality.
• C. Fully deoxidized; gas evolves; medium quality.
• D. Not deoxidized; no gas; unknown quality.

Answer: (B)

Fully deoxidized steel, or killed steel, is produced by adding strong deoxidizers (like aluminum or silicon) that remove essentially all dissolved oxygen from the melt. Because the oxygen is tied up, there’s no gas formed as the metal solidifies, so blowholes and other porosity defects are minimized. This makes the ingot solid and uniform, which is why killed steel is considered the highest quality among common steels. The statement about shrinkage at the top of the ingot being removed aligns with the overall improvement in soundness that comes from eliminating gas porosity during solidification. If the steel isn’t fully deoxidized, gas evolves and porosity can occur, leading to lower quality.