Estimate a preliminary furnace soaking duration from section thickness, steel type and the selected heat-treatment process.
Soaking time is the period during which a steel component is held at a selected heat-treatment temperature after the controlling section has reached that temperature and sufficiently equalized.
The purpose is to allow the required thermal and metallurgical changes to occur throughout the component. The required duration depends on material, section thickness, geometry, furnace conditions and the particular heat-treatment process.
The furnace temperature and the actual temperature at the centre of a steel component are not necessarily the same. Thick sections take longer to heat through than thin sections.
For this reason, simple soaking-time estimates commonly use a section-thickness basis. This calculator scales the selected minutes-per-25-mm value against the controlling section thickness.
The basic calculation used by this tool is:
A minimum hold time is then applied so that very small sections do not produce unrealistically short planning durations.
The furnace-condition adjustment is intended only as a preliminary planning factor. It does not model actual furnace heat-transfer behaviour.
| Planning Basis | Typical Use | Effect on Estimated Hold |
|---|---|---|
| 30 min / 25 mm | Faster, well-controlled heating conditions | Shorter preliminary hold |
| 45 min / 25 mm | General preliminary planning | Moderate hold |
| 60 min / 25 mm | Heavy sections or conservative planning | Longer preliminary hold |
Annealing often involves heating the steel into an appropriate transformation range followed by soaking and slow controlled cooling. The required soak depends on grade, section size and the specific annealing process.
Full annealing, process annealing and spheroidizing can require different thermal cycles, so a generic soaking rule should not be treated as a universal production specification.
During hardening, soaking is used after the component reaches the required austenitizing temperature. The required time depends on the steel grade, section thickness, furnace atmosphere and desired microstructure.
Excessive soaking can be harmful for some grades because it can increase grain growth, oxidation or decarburization. Grade-specific heat-treatment data should therefore take priority.
Tempering follows hardening and is performed at a lower temperature. The component must reach a reasonably uniform temperature before the specified tempering hold begins.
The actual tempering procedure should be based on the steel grade and required hardness or mechanical properties rather than thickness alone.
Stress relieving is commonly performed to reduce residual stresses introduced by welding, machining, forming, casting or other manufacturing operations.
Section thickness can influence the required hold, but the applicable procedure may also depend on material grade, component geometry, welding code and required dimensional stability.
This calculator provides a preliminary furnace holding-time estimate. It does not determine the actual thermal profile inside a furnace or component.
What is the difference between heating time and soaking time?
Heating time is the period required to bring the component to temperature. Soaking time is the subsequent holding period after the controlling section has reached the required temperature.
Does thicker steel need more soaking time?
Generally yes. Larger sections take longer to heat uniformly, so section thickness is an important factor in preliminary hold-time planning.
When does the soak timer start?
The meaningful holding period normally begins after the relevant controlling section has reached the specified temperature, rather than simply when the empty furnace reaches temperature.
Can the same soaking time be used for every steel grade?
No. Grade, heat-treatment process, section geometry and furnace conditions can all affect the appropriate soaking procedure.
Can excessive soaking damage steel?
Yes. Excessive exposure at elevated temperature can contribute to grain growth, oxidation, decarburization or unwanted microstructural changes depending on the steel and process.
Is this calculator suitable for production heat treatment?
It is intended for preliminary engineering estimation only. A validated material- and process-specific procedure should control production.