Cryogenic temperatures are very cold temperatures.
In the seal business we are concerned about elastomer temperature limits, so we get concerned any time the temperature falls bellow -40°F or -40°C.(at this temperature Centigrade and Fahrenheit are the same)
Most grades of carbon/graphite will not perform at cryogenic temperatures because the graphite will not release from the carbon/ graphite mixture and provide the lubrication we need between the lapped faces.
Moisture must be present for this releasing to take place.
Cryogenic fluids can be dangerous, so dual sealing is always recommended
See “cryogenic sealing“