304 Stainless Spring Wire: Tensile, Cast and Coil Consistency

Spring wire is not judged on tensile strength alone. Two numbers decide whether a coiling line runs: the tensile band and the elastic limit, which is the stress the wire carries without taking a permanent set. A coil that meets the tensile figure but sits at the top of its band will coil to a different diameter than one at the bottom of the same band.

This 304 spring wire is cold drawn to spring temper, typically 1400-1900 N/mm2 with the band set by diameter, and supplied from 0.15 mm to 12 mm. Bright annealed temper is available where the part is formed first and springs afterwards.

Cast and straightness matter as much as tensile on automated equipment: a coil with heavy cast fights the feed rolls, changes pitch, and shows up as rejected parts rather than as a material complaint.

Product Specifications

What to Agree Before Ordering

Tensile band, not tensile figure

A single minimum value allows a wide spread between coils. Fixing an upper and lower limit is what keeps coiling diameter and spring rate repeatable across a production run.

Cast and feed behaviour

Cast is the natural curvature the wire holds off the coil. On a CNC coiler it sets how the wire enters the feed rolls; excessive cast causes pitch drift and tool wear rather than a clean break.

Stress relief after coiling

Coiling leaves residual stress in the bends. A low-temperature stress relief after forming stabilises dimensions and reduces relaxation under load, and the temperature depends on the temper supplied.

Applications

Compression and extension springs

General-purpose springs in 0.2-6 mm, where 304 gives adequate corrosion resistance and predictable spring rate.

Retaining rings and clips

Parts that are opened once at assembly and must hold their shape afterwards, formed from 0.5-3 mm wire.

Torsion springs and spring wire forms

Wire forms where the spring action comes from the wire itself, usually 0.3-4 mm, with the bend radius kept above the cracking limit.

Product Advantages

• Tensile band agreed per order - a stated upper and lower limit, so coiling diameter does not drift between coils.
• Cast controlled at rewinding - cleaner feeding on automated coilers, less pitch drift and fewer rejects.
• Surface inspected as a fatigue variable - die lines and scratches are crack initiation sites on a cycled spring, so they are checked, not assumed.
• Two tempers from one source - spring temper for direct coiling, annealed where the part is formed before it springs.
• Full diameter range - 0.15-12 mm, so fine springs and heavy retaining parts share one specification.
• Grade scope stated plainly - 304 for general service; 316 where chlorides or washdown apply, quoted separately.

Quality Control

Rod grade is verified before drawing. Diameter is measured inline and at coil ends, tensile is tested per heat, and a torsion test per ASTM A313 can be supplied on request. Surface is inspected for die lines and scratches before packing, since these become fatigue origins in service.

Selection and Ordering Notes

1. Give the spring index, wire diameter and required rate, so the tensile band can be fixed around them.
2. State whether the part is coiled directly from the wire or formed before springing.
3. Confirm whether a stress relief step follows coiling, and at what temperature.
4. Mention any torsional or cyclic duty, so surface and torsion testing are planned.
5. Provide sizes and annual volume for a tolerance and packing review.

Send the diameter, spring type, rate and coiling process for technical confirmation and quotation.