Tempering martensite involves reheating to a temperature

Tempering martensite involves reheating to a temperature

• A. In the austenite/ferrite region
• B. In the fully austenitic region
• C. Below the transformation temperature of 723 C
• D. Above the transformation temperature of 723 C

Answer: (C)

Tempering martensite is about letting carbon atoms diffuse enough to relieve internal stresses and form carbides, without dissolving the structure back into austenite. This requires heating to a temperature below the temperature where austenite forms in the iron–carbon system. For plain carbon steel, that transformation temperature (Ac1) is around 723 C, so tempering is done below that point. Heating into the austenite region would revert or reconstitute the martensite, undoing the tempering effect. Therefore, the correct approach is to heat to a temperature below 723 C.

Tempering martensite is about letting carbon atoms diffuse enough to relieve internal stresses and form carbides, without dissolving the structure back into austenite. This requires heating to a temperature below the temperature where austenite forms in the iron–carbon system. For plain carbon steel, that transformation temperature (Ac1) is around 723 C, so tempering is done below that point. Heating into the austenite region would revert or reconstitute the martensite, undoing the tempering effect. Therefore, the correct approach is to heat to a temperature below 723 C.