Which statement about carbon content in ferritic iron is true?

Which statement about carbon content in ferritic iron is true?

• A. It can exceed 1%
• B. It is exactly 0.5%
• C. It is limited to a very small fraction, such as about 0.0025%
• D. It is not soluble at all

Answer: (C)

Carbon can dissolve in ferritic iron, but only in tiny amounts because the body-centered cubic ferrite lattice has very little interstitial space for carbon without distorting the structure. That limit is measured in a few thousandths of a percent by weight, typically around 0.0025%, though it can rise only modestly with temperature. Because the solubility is so small, most carbon in steels with higher carbon content ends up in carbide phases (like cementite) or in other microstructures (pearlite, bainite) rather than remaining dissolved in ferrite. So the statement that ferritic iron’s carbon content is limited to a very small fraction, such as about 0.0025%, accurately reflects its solubility behavior.

Carbon can dissolve in ferritic iron, but only in tiny amounts because the body-centered cubic ferrite lattice has very little interstitial space for carbon without distorting the structure. That limit is measured in a few thousandths of a percent by weight, typically around 0.0025%, though it can rise only modestly with temperature. Because the solubility is so small, most carbon in steels with higher carbon content ends up in carbide phases (like cementite) or in other microstructures (pearlite, bainite) rather than remaining dissolved in ferrite. So the statement that ferritic iron’s carbon content is limited to a very small fraction, such as about 0.0025%, accurately reflects its solubility behavior.