Annealing Control: Why Two Soft Coils Can Feel Different

Two coils can both be labelled annealed, both sit inside 550-750 N/mm2, and still behave differently at the press. The reason is that "soft" is a range, and where a coil sits inside that range is decided by the annealing practice rather than by the grade.

Four parameters set the result: soak temperature, holding time, atmosphere, and cooling rate. For 304 the softening anneal runs in the 1010-1120 C range, followed by a cooling rate fast enough to pass through the 450-850 C sensitisation window without dwelling in it. Bright annealing uses a reducing atmosphere, where dew point control decides whether the surface comes out bright or dull grey.

This wire is supplied annealed and bright, from 0.15 mm to 12 mm, with tensile and elongation measured per heat rather than per coil, so the band the order was placed against is the band the certificate shows.

Product Specifications

The Four Variables

Soak temperature and time

Under-annealing leaves part of the drawing work-hardening in the wire, which shows up as a stiffer feel and more springback. Over-annealing grows the grain, and a coarse grain structure is weaker in fatigue and rougher after bending.

Atmosphere and dew point

A reducing atmosphere removes oxide as it forms. If the dew point drifts, the surface turns grey or takes a light tint, which is a cosmetic failure on visible parts and a warning sign on the process.

Cooling through the sensitisation window

Slow cooling lets chromium carbides precipitate at the grain boundaries in the 450-850 C band, reducing corrosion resistance at the boundary. Fast cooling skips the dwell, and low-carbon grades reduce the risk further.

Residual stress

Annealing relieves the stress left by drawing. The more completely it is relieved, the lower the springback at the press and the more predictable the finished angle.

Applications

Parts where hand-feel consistency matters

Formed hardware produced on the same tool across months, where a shift in the tensile band changes the setting the operator already found.

Visible bright parts

Baskets, hooks and frames that are sold without polishing, where the anneal atmosphere is what the customer sees.

Repeated bending and winding

Mesh warp, coiled parts and springs formed from soft wire, where grain structure and elongation decide how many bends the wire survives.

Product Advantages

• Process-controlled softness - temperature, time and cooling are held through the run, so the band is a process output rather than a claim.
• Bright surface from reducing atmosphere - no oxide scale, so visible parts do not need pickling or buffing downstream.
• Fast cool through the sensitisation window - less chromium carbide precipitation, which protects corrosion resistance at the grain boundary.
• Tested per heat, not per coil - the certificate traces back to the furnace lot, which is what a process audit asks for.
• Full size range - 0.15-12 mm on one annealing basis, so sizes in one order behave alike.
• Grade scope stated plainly - 304 for general service, 316L where chlorides apply; the annealing practice is the same, the corrosion limit is not.

Quality Control

Rod grade is verified before drawing. Furnace temperature and atmosphere are logged through the run, diameter is measured inline and at coil ends, and tensile and elongation are tested per heat per ISO 6892-1. Surface is inspected for scale, tint and die lines before packing.

Selection and Ordering Notes

1. State the tensile band your tooling was set against, not just "annealed".
2. Say whether the part is visible, which decides whether bright anneal is required.
3. Confirm whether the wire is bent once or cycled in service, since grain structure matters more in the second case.
4. Ask for tensile and elongation results with the shipment if your process audit requires them.
5. Provide sizes and annual volume for a tolerance and packing review.

Send the grade, diameter, tensile band and surface requirement for technical confirmation and quotation.