If the carbon content increases while keeping the cooling rate the same, what happens to martensite hardness?

If the carbon content increases while keeping the cooling rate the same, what happens to martensite hardness?

• A. It increases
• B. It decreases
• C. It stays the same
• D. It becomes unpredictable

Answer: (A)

When the cooling rate is kept the same, increasing carbon content makes martensite harder. This happens because martensite forms when austenite is quenched, and the carbon atoms that end up in the martensitic lattice create solid-solution strengthening and lattice distortion. The more carbon locked in, the more dislocation movement is hindered, which raises hardness and usually strength. So, with a fixed quench, higher carbon steels yield harder martensite than lower carbon steels.

When the cooling rate is kept the same, increasing carbon content makes martensite harder. This happens because martensite forms when austenite is quenched, and the carbon atoms that end up in the martensitic lattice create solid-solution strengthening and lattice distortion. The more carbon locked in, the more dislocation movement is hindered, which raises hardness and usually strength. So, with a fixed quench, higher carbon steels yield harder martensite than lower carbon steels.