In tempering, what is the primary fate of carbon trapped in martensite?

In tempering, what is the primary fate of carbon trapped in martensite?

• A. The carbon is released
• B. The carbon remains trapped
• C. The carbon forms carbide clusters
• D. The carbon evaporates

Answer: (A)

In tempering, carbon that is trapped in martensite becomes mobile and diffuses out of the supersaturated solid solution. It tends to combine with iron to form carbide particles, such as cementite (Fe3C), and these carbides precipitate at defects, dislocations, and grain boundaries within the matrix. This precipitation relieves internal stresses and reduces lattice distortion, which lowers hardness slightly and improves toughness. Evaporation does not occur at tempering temperatures, and the carbon does not simply stay locked in solution indefinitely; it moves and becomes part of carbide clusters.

In tempering, carbon that is trapped in martensite becomes mobile and diffuses out of the supersaturated solid solution. It tends to combine with iron to form carbide particles, such as cementite (Fe3C), and these carbides precipitate at defects, dislocations, and grain boundaries within the matrix. This precipitation relieves internal stresses and reduces lattice distortion, which lowers hardness slightly and improves toughness. Evaporation does not occur at tempering temperatures, and the carbon does not simply stay locked in solution indefinitely; it moves and becomes part of carbide clusters.