What is a potential consequence of using a pencil to mark high-temperature alloy parts?

• A. Intergranular stress
• B. Improved readability
• C. Increased strength
• D. Reduced fatigue life

Answer: (A)

Introducing graphite from a pencil onto high-temperature alloy parts provides carbon that can diffuse into the metal when heated. This carbon tends to segregate at grain boundaries and form carbides, which weakens the cohesion between grains. The result is intergranular stresses along those boundaries, making the material more susceptible to cracking under stress or fatigue. So the main concern is the development of intergranular stress due to carburization at the grain boundaries. The marks don’t improve readability and don’t increase strength; while embrittlement can lower fatigue life, the direct, notable consequence here is the creation of intergranular stresses from carbide precipitation at the grain boundaries.