302 Spring Wire - Delivery Condition Terms Explained

Soft annealed, bright annealed, light drawn, spring temper and EPQ appear on quotes as if they were interchangeable quality levels. They are not. Each one describes a different combination of strength, ductility and surface, and each one suits a different forming operation. Choosing the wrong condition produces a part that either cracks at the bend or will not hold its shape, even though the grade and the diameter are correct. This page sets out what each term means, what it changes in the metal, and how to write the condition on the purchase order so that the next delivery behaves like the last one.

Product Specifications

What Each Delivery Condition Actually Means

Soft Annealed

Soft annealed wire has been heated to 1050-1120 °C and cooled so that the cold work from drawing is fully removed. The structure is single phase austenite with a grain size set by the furnace, the strength sits at the low end of the grade range, and elongation is at its highest. This is the condition to choose when the metal will be moved a long way: cold heading, deep forming, tight bends, or any operation where the wire has to flow rather than spring back.

Bright Annealed

Bright annealing is the same thermal treatment carried out in a protective atmosphere, so the surface stays free of oxide scale instead of requiring pickling afterwards. The name describes the surface, not the strength: a bright annealed coil and a soft annealed coil of the same diameter commonly carry the same mechanical properties. The difference matters downstream, because a scale free surface can be plated, welded or polished without an extra removal step, and a pickled surface carries a slightly different texture that shows through thin coatings.

Light Drawn and Skin Passed

Light drawn wire is annealed first and then given a small final reduction, typically in the region of 5-15% of area. The purpose is dimensional and cosmetic rather than structural: the final pass tightens the diameter tolerance, improves straightness and cast, and produces a brighter surface while keeping most of the ductility. It is the usual choice for automatic feeding where the wire must be straight and consistent but must still form easily.

Spring Temper

Spring temper is the opposite route. The wire is drawn to final size with no final anneal, so the accumulated cold work delivers the highest strength the grade can reach at that diameter. Spring temper wire is strong in the direction of the wire axis and holds a wound shape without a heat treatment, which is why it is the standard for compression, extension and torsion springs. It is also the least forgiving: bend radii below about three times the wire diameter become unreliable, and every further forming step spends ductility that will not come back.

EPQ and Polished Qualities

EPQ stands for extra polish quality, a designation used mainly for fine wire intended for weaving, knitting and medical parts. The wire is produced with a controlled surface finish that reduces the density of drawing lines and surface inclusions, so the woven mesh has a more uniform appearance and fewer initiation sites for corrosion or fatigue. EPQ is a surface specification; it does not by itself define strength, so the temper has to be stated alongside it.

How to Match the Condition to the Process

The Forming Operation Decides First

Start from the deformation, not from the strength. A part that is cold headed, coined or bent below three times the wire diameter needs a soft or light drawn condition regardless of the load it will eventually carry. A part that is coiled and used as a spring needs spring temper, because a soft wire would simply deform in service. Between these two extremes, light drawn covers most wire forms, clips and retainers where some stiffness is wanted but the bend radius is still moderate.

The Surface Requirement Decides Second

Once the temper is fixed, the surface question is about what happens next. Welding, plating and passivation all prefer a bright, residue free surface. Cold heading prefers a bonded lubricant carrier such as soap or oxalate. Weaving and knitting prefer the smoother, more uniform EPQ finish. A wire that satisfies the mechanical requirement and not the surface requirement still fails, just later in the process.

Applications

Compression, Extension and Torsion Springs

Spring temper wire at 1400-1800 MPa is the standard input for coil springs. Diameters from 0.15 mm to 8 mm cover most production, with soap coating retained as a coiling lubricant where the winder needs it.

Wire Forms, Clips and Retainers

Light drawn wire gives the combination these parts need: enough stiffness to hold a shape, enough ductility to survive a bend, and the straightness that automatic feeding requires. Where the form includes a sharp corner, soft annealed is the safer choice and the stiffness is obtained from the geometry instead.

Cold Headed Fasteners and Rivets

Heading is a bulk deformation and needs the lowest strength and the highest reduction of area available, so soft annealed wire with a suitable coating is the normal specification. Spring temper wire is not used for heading, whatever the required fastener strength, because the upset will crack before the head is formed.

Product Advantages

• All five delivery conditions produced from the same grade, so a change of condition does not force a change of material approval.
• Strength range stated for each condition at the ordered diameter, since spring temper strength varies with size.
• Bright annealing under protective atmosphere, giving a scale free surface that welds and plates without pickling.
• Diameter tolerance of ±0.01 mm on fine sizes, held through the final pass on light drawn and spring temper wire.
• Surface finishes including bright, soap coated and EPQ, matched to the next process rather than to a default.

Quality Control

Each lot is tested for tensile strength, elongation and diameter, and the delivery condition is recorded against the heat number so that a later query can be traced to a specific annealing charge and drawing route. Surface is inspected over the full coil length. Where a customer process depends on a particular surface, the finish is checked against a reference sample rather than described in words alone.

Selection and Ordering Notes

1. Name the condition and the strength range together: soft annealed at 600-750 MPa, or spring temper at 1700-1850 MPa for the actual diameter.
2. Do not use bright as a synonym for soft. Bright describes the surface; the temper has to be specified separately.
3. State the forming operation so the condition can be checked against the deformation rather than against a catalogue heading.
4. Add the surface requirement for the next process: soap coated for heading, bright for welding or plating, EPQ for weaving.
5. Keep the condition on the drawing and on the order, because a supplier who changes from light drawn to spring temper to meet a tensile figure can change the forming behaviour at the same time.

Delivery condition is the link between the mill and the machine, and it is the line most often left vague on a purchase order. Send the forming operation, the required strength and the next process step, and the condition can be specified as a set of numbers instead of an adjective.