Annealing
Choosing and specifying annealing by alloy, starting condition, metallurgical objective, thermal history, atmosphere, and verified output condition.
Tags: processes, heat-treatment, annealing
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An example anneal requires 90 continuous minutes with all designated load thermocouples in band. The controller reaches setpoint at 08:00, sensor A enters the band at 08:15, and the last sensor enters at 08:40. The hold ends no earlier than 10:10. Ending at 09:30 gives the last location only 50 minutes. Use the qualified load-sensor locations, temperature band and cooling requirements.
Specify the material, incoming condition, intended change and acceptance. An anneal for ductility, carbides or residual stress can require different heating and cooling.
This page concerns metals. Glass and polymer annealing require their own material-specific treatment definitions.
Choose the mechanism before the cycle
Bodycote describes annealing as a generic term encompassing subcritical, intermediate, and full treatments. Its recrystallisation guidance distinguishes new-grain formation in cold-worked metal without phase change from recovery, where internal strains relax before recrystallisation. Heating rate and soaking conditions depend on composition and prior cold work. Thus, stress reduction alone does not demonstrate a fully recrystallised structure. Bodycote annealing overview · Recrystallisation
| Treatment description | Intended change | What must be resolved |
|---|---|---|
| Full annealing of steel | Transformation followed by controlled cooling to obtain the specified softened structure | Grade-specific critical temperatures, starting structure, cooling path, and final condition |
| Process or intermediate annealing | Restore workability during a manufacturing sequence | Whether recovery, partial/full recrystallisation, or another change is required |
| Recrystallisation annealing | Replace deformed grains with newly formed grains | Prior deformation, degree of recrystallisation, and acceptable grain structure |
| Stress-relief treatment | Reduce manufacturing residual stresses | Allowed property changes and compatibility with the existing temper |
| Spheroidising | Develop rounded carbides in a ferritic steel matrix | Required carbide morphology, uniformity, and subsequent forming or machining needs |
| Solution annealing/treatment | Dissolve specified phases and obtain the required solution-treated condition | Alloy-specific temperature, cooling rate, and any later aging operation |
ASM's 2013 chapter Annealing of Steel separates subcritical, intercritical, supercritical/full, and process annealing, and identifies spheroidising as a treatment for cold formability. These names describe different routes rather than interchangeable purchase conditions. Its public abstract does not supply a complete cycle for a particular part. ASM Handbook, volume 4A, 2013
TWI distinguishes annealing from solution treatment, tempering, aging, and stress relief. In its steel-oriented explanation, annealing commonly involves recrystallisation and/or transformation with slow cooling, whereas solution treatment retains constituents in solution by rapid cooling. The word “annealing” must therefore be read in its alloy context; furnace cooling is not a universal requirement. TWI heat-treatment methods
Starting condition changes the result
A grade designation alone is insufficient. Record whether the input is cast, hot worked, cold worked, welded, hardened/tempered, solution treated, or aged. Identify reductions, forming operations, or previous heat treatments that establish the current condition. The required treatment may remove strengthening that the drawing otherwise relies on.
Kupferverband explains that copper recrystallisation depends on initial grain size, prior deformation, temperature, and time; insufficient deformation can lead to coarse grains. Its stress-relief discussion instead selects conditions below the recrystallisation threshold to limit loss of strength. These are distinct objectives. The association also warns that atmosphere selection depends on the copper material and flags hydrogen-related damage for susceptible oxygen-bearing copper in reducing environments. “Protective gas” is therefore not synonymous with “compatible with every copper alloy.” The web guidance has no verified issue date here. Kupferverband: heat treating copper materials
For aluminum, the supplier's temper designation is part of the material identity. Aerometals Alliance distinguishes partial annealing after strain hardening, such as H24, from solution heat treatment followed by natural or artificial aging in applicable alloys. Its data sheet is explicitly updated 13 November 2018. Do not substitute a softening operation for a required solution-and-age route or assume that every annealed product has identical properties. Aluminum temper designations
Bounded producer example: tool steel
Uddeholm's Calmax, Edition 9, May 2021, gives separate instructions for soft annealing and stress relieving. Its soft-annealing guidance specifies heating through to 860 °C, holding two hours, then furnace cooling at 20 °C/h to 770 °C, followed by 10 °C/h to 650 °C and free air cooling. In contrast, its rough-machining stress-relief instruction uses 650 °C with a different cooling sequence. These are recommendations for the named producer steel, not a general tool-steel cycle. The document's approximate soft-annealed delivery hardness is not an acceptance guarantee for every re-annealed component. The edition is printed inside the PDF; the upload path's 2024 date is not the publication edition. Uddeholm Calmax, pages 2, 4–5
Bodycote's soft-annealing guidance describes spheroidisation of pearlitic cementite and use of protective gas or vacuum against oxidation/decarburisation. It also cautions that making low-carbon steel very soft can impair cutting behavior. “Softer” is consequently not a sufficient machinability specification, and the steel transformation temperature terminology on that page must not be transferred to copper or brass. Bodycote soft annealing
Cooling, atmosphere, and dimensions
Outokumpu's stainless guidance describes solution annealing after cold work and warns that incorrect temperature/time/cooling combinations can impair toughness and corrosion resistance. Grade-dependent rapid cooling may be necessary to avoid detrimental phases. Annealing in air can create scale requiring subsequent surface restoration; variations in section thickness can also generate new residual stresses during rapid cooling. Stress relief is not automatically a harmless alternative, especially where a grade is susceptible to unwanted precipitation. The technical web page is undated. Outokumpu post-fabrication heat treatment
Specify the acceptable surface state and subsequent cleaning or material removal. Include scale, decarburisation where applicable, and dimensional allowance in the manufacturing plan. Evaluate fixture support, asymmetric geometry, and machining sequence with the processor. Annealing intended to improve later stability does not mean the current part will retain its exact dimensions.
Original example: hold time at the load
Compare the controller and load readings for the hypothetical 90-minute hold. Assume both load sensors stay in band after entry.
| Timing basis | Hold start | Earliest end |
|---|---|---|
| Furnace controller alone | 08:00 | 09:30 |
| Required load evidence | 08:40 | 10:10 |
The controller-based end is 40 minutes early under this instruction. Establish transformation and cooling from separate evidence.
Acceptance and useful handoff
Release the treatment against agreed outputs as well as the recorded cycle. Depending on the material and purpose, these can include hardness with method/location, grain structure or carbide morphology, tensile properties, corrosion-related tests, surface condition, and dimensional inspection. A hardness result alone cannot demonstrate residual-stress removal or acceptable grain structure. Choose the checks required by the product specification and application rather than applying every possible test.
A useful order contains four groups of information:
- Material and history: alloy/producer designation, product form, section sizes, starting temper, prior work, welds, and previous thermal exposure.
- Treatment objective: required output condition, governing document and edition, approved route, and prohibited property changes.
- Process controls: heating/holding/cooling requirements, atmosphere, load arrangement, temperature evidence, cleaning, and machining allowance.
- Acceptance and records: test methods/locations, sampling, limits, dimensional checks, load traceability, and approved disposition of deviations.