Minimum Bend Radius on Annealed Stainless Wire: A Practical Guide

When a drawing specifies a bend, the question behind it is usually whether the wire will crack at that radius. The answer depends on three things: wire diameter, the tensile band of the coil, and where surface defects sit relative to the outside of the bend.

As practical guidance for annealed 304 and 316L, an inner radius of one wire diameter (R = 1d) is achievable on a 180 degree bend. Tighter radii are possible on a 90 degree bend, or by agreeing a softer tensile band in the 550-620 N/mm2 range. Below that, the correct move is usually a smaller wire diameter rather than a softer coil.

This wire is supplied annealed from 0.15 mm to 12 mm, bright or soap-coated, with the tensile band fixed at order stage so the radius that worked in the sample run also works in production.

Product Specifications

The Three Variables

Diameter sets the floor

Bend severity is the radius expressed in multiples of the wire diameter. A 1 mm wire bent to a 1 mm inner radius and a 5 mm wire bent to a 5 mm inner radius are the same job for the material, even though the tooling is entirely different.

Tensile band sets the margin

Two coils in the annealed range can still differ by 200 N/mm2. A part sitting close to the radius limit on 750 N/mm2 will form cleanly on 580 N/mm2, which is why the band should be written into the order rather than left to the mill average.

Surface sets the failure point

The outside of the bend is under tension. A die line or scratch on that face becomes the crack initiation site, so surface quality matters more on bent parts than on straight ones.

Applications

Hooks, handles and pulls

180 degree returns and closed loops on wire handles where the radius is fixed by appearance and by hand clearance.

Clips and retaining springs

Parts that are formed once and then flexed in service, where a soft band keeps the bend zone from work-hardening to fracture.

Frames and corner bends

Rack and guard frames in 3-8 mm where the corner radius is visible and cracking cannot be polished out.

Product Advantages

• Radius rule stated up front - R = 1d for a 180 degree bend gives a starting point instead of a trial-and-error loop.
• Soft band on request - 550-620 N/mm2 for parts that sit at the radius limit.
• One tensile band per order - the radius proven on the sample coil holds through the production run.
• Surface controlled at the bend - die lines and scratches inspected before packing, since that face carries the tension.
• Full size range - 0.15-12 mm, so the diameter can be reduced when the radius is the real constraint.
• Grade scope stated plainly - 304 for general service; 316L where chlorides or washdown apply, with different springback expected.

Quality Control

Rod grade is verified before drawing. Diameter is measured inline and at coil ends, tensile and elongation are tested per heat per ISO 6892-1, and surface is inspected for die lines and scratches. A bend sample at the agreed radius can be supplied with the lot on request.

Selection and Ordering Notes

1. Give the inner radius and the bend angle from the drawing, not only the finished shape.
2. State whether the part is bent once or flexed repeatedly in service.
3. Confirm the tensile band, particularly if the radius is close to the limit for the diameter.
4. Say which face of the wire is visible, so surface inspection can focus there.
5. Provide sizes and annual volume for a tolerance and packing review.

Send the diameter, bend radius, bend angle and forming method for technical confirmation and quotation.