Which structure is formed directly as a result of quenching steel?

Which structure is formed directly as a result of quenching steel?

• A. Martensite
• B. Ferrite
• C. Pearlite
• D. Cementite

Answer: (A)

Quenching steel triggers a diffusionless transformation from austenite into martensite. When steel is cooled rapidly from the high-temperature austenite stage, there isn’t enough time for carbon to diffuse and form the layered structures that come from slower cooling. Instead, the crystal lattice distorts quickly into a body-centered tetragonal arrangement, trapping carbon in solid solution. This martensitic structure is extremely hard and strong but also quite brittle.

If cooling were slower, you'd see ferrite and cementite forming through diffusion, or a layered pearlite structure resulting from the eutectoid transformation. Tempering afterward can relieve some brittleness by allowing controlled changes in carbon distribution, but the direct product of rapid quenching is martensite.