What is the maximum carbon content in steel that can be absorbed in solution with iron?

• A. 2%
• B. 1%
• C. 3%
• D. 4%

Answer: (A)

The test is about how much carbon can stay dissolved in iron as a solid solution before forming separate carbides. In the high-temperature phase of iron (austenite), carbon can dissolve up to about 2% before reaching the solubility limit. As the alloy cools, that limit drops, so additional carbon tends to precipitate as cementite or graphite rather than remain dissolved in the iron lattice. This is why steels—iron–carbon alloys in which carbon remains in solid solution—generally cap at around 2% carbon. Values higher than that push the material toward other structures, like cast iron. So the maximum carbon content that can be absorbed in solution with iron is about 2%.