Rule of thumb for hold time: one hour at temperature for every inch of the heaviest cross section, counted once the furnace or load thermocouple reaches setpoint. It is conservative for carbon steel in a well-loaded atmosphere furnace and gets adjusted for tool steels, dense loads, vacuum heating and tempering. Many shop recipes start from it before process data takes over.
Six-inch hub, hour per inch, so it sits six hours once the load TC says it's there.
The clock starts when the part is at heat, not when the door closes. Counting from door-close is the classic way to make soft cores.
Also heard as
- an hour an inch
- hour-per-inch rule
Related terms
Soak
To hold parts at a set temperature until they are evenly heated and the intended change is complete.
At heat
Shop phrase meaning a load has reached its setpoint temperature, so its soak time can start counting.
Recipe
Shop word for the stored program of temperatures, times and atmosphere setpoints that runs a furnace cycle.
Tempering
Reheating hardened steel below its lower critical temperature to trade some hardness for toughness.