Graphitization of carbon steels begins to occur when metal temperatures exceed:

Graphitization of carbon steels begins to occur when metal temperatures exceed:

• A. 600°F.
• B. 900°F.
• C. 800°F.
• D. 1000°F.

Answer: (C)

Graphitization is a slow, long-term degradation process in carbon steels where carbon atoms migrate and form graphite along grain boundaries, transforming the microstructure from pearlite/ferrite toward graphite. This weakens the metal, reducing strength and toughness over time when the steel is kept at elevated temperatures. For typical carbon steels used in piping, the onset of this transformation happens with prolonged exposure around 800°F (about 427°C). At temperatures lower than this, the rearrangement of carbon is too slow to matter within normal service life. At higher temperatures, graphitization occurs more quickly, but the baseline point at which it can begin during extended service is around 800°F. That’s why 800°F is identified as the threshold.

Graphitization is a slow, long-term degradation process in carbon steels where carbon atoms migrate and form graphite along grain boundaries, transforming the microstructure from pearlite/ferrite toward graphite. This weakens the metal, reducing strength and toughness over time when the steel is kept at elevated temperatures.

For typical carbon steels used in piping, the onset of this transformation happens with prolonged exposure around 800°F (about 427°C). At temperatures lower than this, the rearrangement of carbon is too slow to matter within normal service life. At higher temperatures, graphitization occurs more quickly, but the baseline point at which it can begin during extended service is around 800°F. That’s why 800°F is identified as the threshold.