302 Stainless Spring Wire - Carbon Content and Drawn Strength
302 stainless spring wire
,stainless steel spring wire
,drawn strength spring wire
302 Stainless Spring Wire - Carbon Content and Drawn Strength
Product Introduction
302 and 304 are often treated as the same wire with two names, and for many applications they behave that way. The difference that matters on a spring is carbon: 302 carries up to 0.15% carbon against the 0.08% ceiling of 304.
That extra carbon in solid solution strengthens the austenite, and after cold drawing the gap widens further. At the same diameter and the same reduction, a drawn 302 section reaches a higher tensile than drawn 304, which is why the grade has survived in spring shops long after 304 became the volume grade.
Available from 0.15 mm to 12 mm, drawn to spring temper, bright or soap coated.
Product Specifications
| Parameter | Specification |
|---|---|
| Grade | AISI 302, SUS 302, EN 1.4319 |
| Carbon | ≤ 0.15% |
| Chromium | 17.0–19.0% |
| Nickel | 8.0–10.0% |
| Diameter Range | 0.15–12 mm |
| Diameter Tolerance | ±0.02 mm up to 2.0 mm; ±0.03 mm above 2.0 mm |
| Delivery Condition | Cold drawn spring temper |
| Tensile Strength | 1450–1900 MPa, grade and diameter dependent |
| Surface | Bright or soap coated |
| Cast and Helix | Controlled and stated per order |
| Coil Weight | 100–500 kg |
| Reference Standard | ASTM A313, EN 10270-3, JIS G4314 |
What the Extra Carbon Does
Strength in the Annealed State
Carbon held in solution in the austenitic matrix raises the base strength of the wire before any drawing takes place. The effect is modest at the annealed stage but it is the starting point that the draw builds on.
Strength After Drawing
Cold drawing multiplies the effect. The same reduction that brings a 304 wire to 1700 MPa brings a 302 wire higher, so for a spring designed to a given load the 302 wire can carry it at a slightly smaller section, or run at a lower stress at the same section.
The Trade-Off: Sensitisation
Higher carbon has a cost at temperature. Between roughly 450 and 850 °C, chromium carbides precipitate at grain boundaries and deplete the chromium next to them, which lowers corrosion resistance in the affected zone. For a spring that will never see those temperatures in service or in fabrication, the trade does not arise. For a spring that will be soldered, welded or brazed after coiling, it does.
302 Against 304 and 316
Drawn Strength at the Same Diameter
For spring temper wire, 302 sits above 304 at equal diameter and equal reduction. If the spring design is stress limited rather than corrosion limited, that difference is usable and it is why some coiling plants keep 302 on the rack.
Corrosion Margin
The corrosion behaviour of annealed 302 and 304 in atmospheric service is close. After heavy cold work the difference stays small for dry environments. In chloride-bearing or continuously wet service the lower carbon of 304 gives a better reserve against sensitisation, and 316 adds molybdenum on top of that.
When the Answer Is 316
Where the spring sees salt, marine air, or chemical washdown, the grade decision is made on corrosion before it is made on strength, and 316 is the default. 302 is the choice when the environment is benign and every unit of load per millimetre counts.
Drawing to Spring Temper
Reduction and Diameter
Tensile strength in the spring range comes from total cold reduction. Fine diameters accumulate more reduction per pass and therefore sit at the top of the band; heavy diameters sit lower for the same grade. The band is stated per diameter rather than as one number.
Cast Control
Drawn wire carries a natural curvature from the last pass. Cast is held within a stated limit per coil so the wire feeds a coiler without fighting the straightener before the first turn is formed.
Surface
Drawing produces a bright surface directly. A soap coating is applied for customers running high-speed coilers, and it washes off during degreasing after forming.
Applications
Static and Low-Cycle Springs
Compression, extension and torsion springs in dry interior service, where the higher drawn strength of 302 is used and the corrosion reserve of 304 is not needed.
Clips and Retaining Rings
Formed parts that hold load permanently and benefit from the higher yield of a high-carbon austenitic section.
Wire Forms
Bent and looped components where dimensional stability and a consistent tensile band matter more than peak corrosion performance.
Product Advantages
- Higher carbon than 304 gives a stronger drawn section at the same diameter, so the spring carries more load from the same coil.
- Tensile bands stated per diameter rather than as one number, so spring design calculations use values that match the wire supplied.
- Cast and helix controlled and stated per order, which keeps coiler setup time down across lots.
- Soap coated option for high-speed coiling, washing off in the normal degreasing step after forming.
- Full chemistry including carbon reported on the mill certificate, so the grade can be verified against the order.
Quality Control
Chemical composition by optical emission with carbon reported, tensile strength per diameter band, diameter and ovality at both ends of the coil, surface condition under magnification, and a cast and helix check. A mill test certificate 3.1 is issued with each shipment and retained samples are kept for twelve months.
Selection and Ordering Notes
- State the wire diameter and the tensile band required for the spring design, so the reduction schedule can be set to match.
- Tell us the service environment. Dry interior suits 302; wet, chloride or washdown service needs 304 or 316.
- Confirm whether the part is soldered, welded or brazed after coiling, since that raises the sensitisation question.
- Give cast and helix limits, or the spring index and free length, so the coil feeds your machine directly.
- State coil weight and pay-off direction so the coil matches your feeding equipment.
Send the spring drawing, the load requirement and the service environment, and we will confirm whether 302 earns its place or whether 304 is the better value.
