Every forming operation leaves the metal harder than it found it. Bend a strip of steel back and forth and the bend stiffens, then cracks - that is work hardening in the hand. Annealing is the reset: heat the part, hold it, cool it, and the crystal structure recovers so the metal can be formed again.
What is annealing?
Annealing is a controlled heat treatment: the metal is heated to a temperature where its internal structure recrystallises, held long enough for that to complete, then cooled. The result is lower yield strength, higher elongation and softer metal, with the internal stresses from cold working largely removed. In metal forming it is used as an intermediate step - a deep drawn cup that would tear on the second or third stage is annealed between stages so that it can be drawn further. Typical temperatures are around 650–700 °C for low-carbon deep drawing steels, 400–600 °C for copper and brass depending on temper, and over 1,000 °C for a full anneal of austenitic stainless steel, with a lower 350–450 °C stress relief used instead where only residual stress needs to be removed.
Why forming needs it
- Work hardening - drawing stretches the wall and raises its yield strength. After enough strain the metal has no ductility left and the next operation tears it.
- Draw depth - the depth a cup can reach in one stage is limited by the material's strain-hardening behaviour. Annealing between stages is what makes a tall part possible at all.
- Springback - an annealed, softer material springs back less, so a part with tight form tolerances is often annealed before the final forming stage rather than after it.
- Formability of the next operation - a part that must be drawn and then flanged, or drawn and then expanded, usually needs the anneal between the two.
The four anneals that show up in a quotation
| Treatment | What it does | Where it is used |
|---|---|---|
| Full anneal | Complete recrystallisation; softest condition | Before a heavy first draw, or to restore a material after rolling |
| Process (intermediate) anneal | Restores ductility between forming stages | Multi-stage deep drawn cups, housings and shells |
| Stress relief | Removes residual stress without softening much | Machined parts that must stay flat, welded assemblies |
| Bright anneal | Annealing in a controlled atmosphere so no scale forms | Stainless parts where a clean surface is required after treatment |
Typical temperatures
| Material | Typical annealing temperature | Note |
|---|---|---|
| Low-carbon steel (DC01–DC04) | 650–700 °C | Batch anneal; scale forms unless atmosphere controlled |
| Copper C11000 | 400–600 °C | Softer tempers at the higher end |
| Brass (CuZn) | 400–600 °C | Higher zinc brasses need care to avoid dezincification |
| Austenitic stainless 304 | 1,040–1,120 °C then quench | Full anneal; 350–450 °C if only stress relief is needed |
| Ferritic stainless 430 | 750–850 °C | Annealing also affects magnetic behaviour |
| Aluminum alloys | 300–420 °C | Alloy dependent; some grades are age hardened instead |
Temperatures are typical published ranges for the families, not a recipe. The correct cycle depends on the alloy, the amount of cold work and the required final properties, and it belongs on the heat treatment specification rather than being left to the furnace operator.
What it adds to a programme
- An extra operation - every anneal is a movement, a furnace cycle and a return to the press, and it appears in the quotation as such.
- Batch heat treatment is outsourced - for Balford, bulk heat treatment is a subcontracted process, and we disclose it rather than implying the furnace is in our own plant.
- Scale and cleaning - a non-atmosphere anneal leaves scale that has to be removed, which is a second operation on top of the first.
- Distortion - thin drawn parts can distort in the furnace, so the fixture or the packing method becomes part of the process design.
- Hardness after treatment - the drawing may call for a final hardness or temper; that is a second heat treatment, not the same one.
Key point
If a part tears on the second or third draw, annealing between stages is usually the answer - it costs an operation and buys the depth. Specify the alloy, the amount of cold work and the properties you need afterwards, and let the cycle be set from those rather than from a temperature copied out of a table.
Frequently asked questions
What does annealing do to metal?
It softens it. Heating to the recrystallisation temperature and cooling removes the effects of cold work, lowering yield strength, raising elongation and relieving internal stress so the part can be formed further.
Why do deep drawn parts need annealing?
Because each drawing stage work-hardens the wall. Once the material has no ductility left it tears, so an intermediate anneal is used to restore ductility before the next stage.
Is annealing the same as normalizing?
No. Normalizing also heats the steel above its critical temperature but cools it in air, producing a finer, stronger structure than a full anneal, which cools slowly in the furnace.
Does annealing change the magnetic properties?
It can. Annealing relieves stress and can change the magnetic behaviour of ferritic and silicon steels, which is why it appears in magnetic shielding and soft magnetic part routes, and why we treat magnetic annealing as its own specification.