Fine Stainless Steel Wire: Where Breakage Comes From in Drawing

Below about 0.5 mm the wire stops behaving like wire and starts behaving like a filament. Surface finish, tension and heat build-up dominate, and a defect that would pass unnoticed on 2 mm becomes a break at the die or a snap at the spool.

This wire is drawn from 0.15 mm to 12 mm, in 304 and 316L, annealed at 550-750 N/mm2 or in spring temper. The fine range is where the process is controlled hardest: pass reduction, lubricant film and spool tension are all set for the diameter, not carried over from the previous size.

Breakage is a symptom rather than a cause. In practice it traces back to one of three things: a worn die that has changed the pass schedule, a lubricant film that failed and let metal touch metal, or an inclusion in the rod that only becomes significant at small cross-sections.

Product Specifications

What Changes Below 0.5 mm

Surface becomes the whole cross-section

At 0.15 mm a surface layer of a few micrometres is a measurable share of the diameter. A die line or an inclusion at the surface is no longer a cosmetic mark; it is a notch across a large fraction of the load-bearing area.

Tension sensitivity

The force needed to pull fine wire is small, so small variations matter. A spool that pays off unevenly, or a capstan that slips, changes tension enough to alter both diameter and elongation along the length.

Heat build-up

Drawing work turns into heat and fine wire has very little mass to absorb it. Without adequate cooling and lubricant flow, the wire can reach temperatures that affect the annealing state locally, which shows up later as inconsistent forming.

The Three Causes of Breakage

Die wear and pass schedule

Each pass reduces area by a set percentage. A worn die changes that percentage and shifts the load to the next pass, so a schedule that was balanced becomes progressively harder on the wire. Die inspection on a fixed interval is cheaper than a spool of breaks.

Lubricant film failure

The film has to stay intact through the die. Contamination, wrong viscosity or insufficient flow breaks the film and metal contacts metal, which scratches the surface and raises the drawing force at the same time.

Rod quality and inclusions

Non-metallic inclusions that are tolerated at 3 mm become the weak point at 0.2 mm. This is why rod source and chemistry control sit at the front of a fine wire process rather than at the back.

How to Specify Fine Wire

Diameter band and ovality

At the fine end the band should be stated in absolute terms, not as a percentage, and ovality should be limited separately. Both affect how the wire sits in a guide or a needle.

Spool weight and pay-off

A smaller spool runs out sooner but pays off more evenly. The spool weight should be chosen against the machine, not against shipping convenience.

Surface and coating

Bright for visible or clean-critical parts, soap-coated where the wire passes through guides and needles. The coating is a process aid, not a corrosion measure.

Applications

Braiding and knitting

Wire from 0.15 mm to 0.5 mm braided around cores or knitted into mesh, where breakage stops the machine and the joint shows in the product.

Filtration and screen cloth

Fine woven cloth where an even diameter is what makes the aperture predictable across the roll.

Precision springs and connectors

Small springs, contact wires and retaining forms, where surface condition affects both forming and fatigue.

Product Advantages

• Pass schedule set per diameter - the reduction sequence is not carried over from a heavier size, which is the most common cause of fine-wire breaks.
• Die inspection on interval - worn dies are replaced before they shift the load onto the next pass.
• Lubricant and cooling controlled - the film stays intact, which protects both surface and drawing force.
• Layer-wound spools - consistent pay-off keeps tension steady, so diameter and elongation hold along the length.
• Diameter and ovality stated separately - both are measured at the fine end rather than averaged into one figure.
• Traceable lots - heat number on every spool label, with diameter and tensile results on the mill test report 3.1.

Quality Control

Rod is verified by chemistry and surface inspection before drawing. Diameter is measured inline by laser gauge and checked at spool ends, ovality on two axes, and tensile and elongation per heat per ISO 6892-1. Spool build and layer alignment are checked before packing, since a crossed layer becomes a break at the machine.

Selection and Ordering Notes

1. State the diameter and whether the band needs to be absolute or percentage.
2. Give the machine type and the spool weight it accepts.
3. Confirm the surface: bright, bright annealed or soap-coated.
4. Mention the downstream process, since braiding and weaving stress the wire differently.
5. Provide sizes and annual volume for a tolerance and packing review.

Send the diameter, grade, spool weight and downstream process for technical confirmation and quotation.