If the carbon was lapped at room temperature it can go out of flat at temperature extremes. The hard face Thermal cracking is common in some ceramics. Heat check is a problem with plated or coated hard faces. It is caused by dissimilar materials expanding at different rates . The hard coating or plating lifts off if the sealing fluid attacks the base material.
Coating are porous.
High face heat will accelerate the process. The hard face can go out of flat due to differential expansion of the various cross sections. The metal parts Critical dimensions and surface finishes can change. A metal bellows can lose strength as the metal approaches its annealing temperature. Heat accelerates any corrosion problems caused by the product or any chemical used to clean the system.