Cold Drawn Stainless Steel Wire - Stable Strength Control
Cold Drawn Stainless Steel Wire
,Stainless Steel Straight Wire
,Stable Strength Control Wire
Cold Drawn Stainless Steel Wire - Stable Strength Control
Cold drawn stainless steel wire acquires its dimensional accuracy and mechanical strength from a sequence of drawing passes, not from a single operation. Each pass reduces the cross-sectional area by a defined amount, and the accumulated deformation determines tensile strength, elongation and the residual stress that later appears during bending or heading. This page explains how draft schedules are arranged for wire from 0.15 mm to 12 mm, how the resulting properties can be read from a mill test certificate, and what to specify when a forming process is sensitive to strength scatter.
Product Specifications
| Item | Specification |
|---|---|
| Product Name | Cold Drawn Stainless Steel Wire |
| Material Grades | 201, 302, 304, 304L, 316, 316L, 430 |
| Diameter Range | 0.15-12 mm |
| Diameter Tolerance | ±0.01 mm (fine wire), ±0.02 mm (0.5-3 mm), ±0.03 mm (above 3 mm) |
| Delivery Condition | Bright annealed, soft annealed, light drawn, spring temper |
| Tensile Strength | 480-1800 MPa, depending on grade and temper |
| Elongation | ≥ 40% in soft annealed condition (gauge length 100 mm) |
| Surface | Bright, soap coated, matte, or as specified |
| Grain Size | ASTM E112 No. 6-9, typical for forming grades |
| Coil or Straight Length | Coil 1-500 kg; straight cut 2-6 m |
| Applicable Standards | ASTM A580, EN 10270-1, GB/T 4240 |
How a Draft Schedule Is Arranged
Total Reduction Determines the Strength Band
Strength in cold drawn wire is a function of accumulated true strain. A rod of 5.5 mm drawn down to 1.0 mm passes through an area reduction of roughly 96.7%, and that much deformation cannot be carried in one step. The schedule is therefore split into passes, with a full anneal inserted whenever the work hardening exceeds what the next die can accept. Two suppliers can deliver the same final diameter with very different properties: one may reach it in a single hard drawn sequence, the other may anneal at an intermediate size and finish with a light final pass. The diameter on the purchase order does not describe the strength; the temper and the reduction history do.
Pass Reduction Limits and Intermediate Annealing
For austenitic grades, a single pass is commonly held between 15% and 30% area reduction. Above that range, drawing force rises quickly, die wear accelerates and the risk of internal defects increases. Fine wire below 0.5 mm usually runs at 10-20% per pass, because the tensile strength of the wire itself approaches the strength of the die assembly. Intermediate bright annealing at 1050-1120 °C in a protective atmosphere restores ductility and dissolves carbides; the cooling rate after annealing matters for 304L and 316L, where slow cooling through 850-450 °C can leave a sensitised structure that later fails in a corrosive environment.
Die Angle, Bearing Length and Surface Result
The die geometry controls how much of the deformation becomes useful work and how much becomes friction. A typical approach half-angle sits between 4° and 8°, with a bearing length of 30-50% of the wire diameter. Too short a bearing gives poor dimensional control and an oval cross section; too long a bearing raises drawing force and heat. The lubrication carrier has to match both the die and the subsequent process: calcium or sodium stearate for dry drawing, drawing oil for wet drawing. A soap film left on the wire lubricates a cold heading die, while the same film left before a bright annealing furnace becomes a residue that has to be removed.
Verifying Strength Consistency Before Production
Reading the Mill Test Certificate
A useful MTC for cold drawn wire reports tensile strength, elongation, diameter and, for spring tempers, the coil set. What matters is not a single value but the spread. A lot certified at 1750 MPa with individual tests between 1680 and 1820 MPa behaves predictably; a lot with a nominal 1750 MPa and results from 1550 to 1950 MPa will show scattered spring-back and inconsistent formed length. Ask for the individual test results, not only the stated range.
Incoming Checks That Take Minutes
Three checks catch most problems before the wire reaches a machine: diameter at three points along the coil with a micrometer, a wrap test around a mandrel equal to the final bend diameter, and a tensile or hardness check against the certificate. If the wrap test cracks at the radius the part will actually use, the temper is too hard for the application regardless of what the certificate states.
Applications
Precision Forming and Bending
Wire for formed parts such as hooks, clips, retainers and wire forms benefits from a controlled soft or light drawn temper, where spring-back is predictable and bend radii stay consistent from coil to coil. Diameters from 0.3 mm to 6 mm cover most of these parts, with 304 and 316L chosen where the part sees moisture or cleaning agents.
Fastener and Screw Blanks
Cold heading demands a low yield strength relative to tensile strength, together with a clean and well lubricated surface. 302, 304 and 201 in the soft annealed condition are common, with a soap carrier that survives the heading die. Wire with surface seams or an excessively work hardened skin will crack at the head fillet, so the drawing schedule and the surface inspection matter as much as the grade.
Woven Mesh, Filters and Screens
Weaving requires uniform diameter and consistent elongation so that warp and weft tension stays balanced across the loom. Diameters from 0.15 mm to 2 mm are typical, in 304, 316L or 430 depending on the corrosion duty. Diameter variation within a coil appears directly as aperture variation in the finished mesh.
Product Advantages
- Draft schedules defined per grade and final diameter, so tensile strength arrives within a stated band instead of a nominal figure only.
- Diameter tolerance held to ±0.01 mm on fine wire, supporting automatic feeding and close tolerance forming.
- Bright annealing under protective atmosphere, giving a residue free surface suitable for later plating or welding.
- Grain size controlled to ASTM E112 No. 6-9 for forming grades, keeping bendability consistent between production lots.
- Full traceability from heat number to coil, with mill test certificates reporting individual test results.
Quality Control
Each production lot is checked for diameter, tensile strength and elongation before dispatch. Surface is inspected for seams, scratches and die marks over the full coil length. Straight lengths are checked for straightness and cut end condition. Where a customer process is sensitive to a specific property, the test method and the acceptance limit are agreed in writing before the order is released, and the same method is applied to every lot in the contract.
Selection and Ordering Notes
- State the grade, the finished diameter and the temper, not only the diameter. 304 at 1.2 mm light drawn and 304 at 1.2 mm soft annealed are different products with different forming behaviour.
- Give the smallest bend radius or the heading ratio the part will use, so the temper can be checked against the actual deformation rather than against a general recommendation.
- Specify the surface condition required by the next process: soap coated for heading, bright for plating or welding, matte where a mechanical key is needed.
- For woven or automatic feeding applications, add a maximum diameter variation within the coil on top of the nominal tolerance.
- Confirm the test method for elongation, including gauge length, and the reporting format of the mill test certificate, since values from different gauge lengths are not comparable.
A wire specification is a combination of grade, temper, tolerance and surface, and the drawing history links them together. Send the part drawing, the forming operation and the corrosion duty, and the wire specification can be matched to the process rather than to the catalogue.
