Killed steels are described as which of the following?

• A. Gas evolution occurs during solidification.
• B. Partial deoxidation with high porosity.
• C. Lowest quality.
• D. Fully deoxidized and no gas evolution occurs.

Answer: (D)

Killing the steel is all about removing dissolved oxygen before it solidifies. When the melt is thoroughly deoxidized, usually with elements like aluminum or silicon, the oxygen is tied up as stable oxides and no gas bubbles form as the metal cools. That means the solidification proceeds without gas evolution, producing a dense, defect-free structure. This is the defining trait of killed steels: they are fully deoxidized and show no gas evolution during solidification, which is why they are considered high quality.

In contrast, steels that aren’t fully deoxidized can let gases form during solidification, creating porosity or blowholes—these are more typical of rimmed or semi-killed steels, not killed steels. So the description “fully deoxidized and no gas evolution occurs” captures the essential behavior of killed steels and explains why they’re preferred for cleaner, more uniform castings.