Which statement about cap steel porosity relative to rimmed steel is true?

• A. Cap steel has less porosity than rimmed steel.
• B. Cap steel has more porosity than rimmed steel.
• C. Cap steel has porosity equal to rimmed steel.
• D. Porosity cannot be compared.

Answer: (A)

Porosity in steel is largely driven by the amount of gas trapped in the metal during melting and solidification. Rimmed steel is produced in a way that leaves more dissolved gases, so as the ingot solidifies these gases form voids that show up as porosity, especially near the surface “cap.” Cap steel, with more thorough deoxidation and different pouring practices, tends to trap fewer gases, resulting in less porosity. That’s why cap steel generally has less porosity than rimmed steel. The other options don’t align with how production methods affect gas retention and porosity in steel.