201 Stainless Spring Wire for Coils That Hold Their Load After Stress Relief

Product Introduction

A spring that is coiled and shipped without stress relief is a spring that will change shape on the customer's bench. Coiling leaves residual stress locked into every turn, and that stress relaxes over the first weeks of service whether or not anyone planned for it.

Stress relief is a low temperature anneal applied after coiling. It does not change the grade or soften the wire; it lets the locked-in stress redistribute so the spring holds the load it was designed for.

This 201 spring wire is drawn to a stable tensile range and supplied with a documented stress relief window, so the oven setting on your line has a starting point rather than a guess.

Available from 0.15 mm to 12 mm, bright or soap coated.

Product Specifications

Why a Coiled Spring Needs a Stress Relief

Where the Residual Stress Comes From

Coiling bends the wire past yield. The outer fibres of each turn are left in tension and the inner fibres in compression, and the two are in balance only as long as nothing moves. Add service load, and the balance shifts.

What the Oven Actually Does

A low temperature hold gives the dislocations enough mobility to rearrange without recrystallising the structure. Stress redistributes, the spring takes a more stable set, and the load at a given deflection stops drifting.

What It Does Not Do

Stress relief does not raise tensile strength, does not improve corrosion resistance, and does not fix a spring that was coiled outside its index range. It stabilises a sound spring; it cannot rescue a badly formed one.

Setting the Temperature and Time

The Lower Bound

Below roughly 200 °C the hold is too short in effect to move dislocations at any useful rate, and the spring behaves as if it had not been treated. Many shop ovens that appear to do nothing are simply running below this line.

Why Overheating Is Worse Than Underheating

Above about 450 °C the structure starts to recover and hardness falls. A spring that loses hardness loses load, and the loss is not recoverable. An under-treated spring can be run through the oven again; an over-treated one is scrap.

Time and Section Size

Fine wire reaches temperature quickly, so twenty minutes at the set point is often enough. Heavier sections need a longer hold to bring the core up to temperature, and the hold should be counted from the moment the load is at temperature rather than from the door closing.

Colour as an Indicator Only

Straw to light brown is what a clean 200–300 °C surface looks like. Colour tells you the surface saw temperature; it does not tell you the core did, and it says nothing about how long the hold lasted.

What Changes in the Spring

Dimensions

Free length and coil diameter relax slightly. On a compression spring this is normally a few tenths of a millimetre, and it should be allowed for in the coiling setup rather than corrected afterwards.

Load at Deflection

Load drops slightly as a direct result of the relief, and stabilises. The important number is the load measured after relief and again after a settling cycle, because that is what the spring will deliver in service.

Fatigue Behaviour

A relieved spring carries a more even stress distribution along the wire section. Under cyclic load this delays the point at which a crack starts on the tensile side of the coil.

How 201 Compares With 301 and 304 Here

Recovery at the Same Temperature

201 is austenitic like 304 but leaner in nickel, and it reaches the same relief at a comparable temperature. The observable difference is that 201 coils carry a slightly higher residual stress from forming, so the relief step is less optional on this grade than it is on a 301.

When a Different Base Grade Is the Better Answer

For high cycle springs, or where the service temperature itself is elevated, 301 or 302 gives more margin. For dry interior springs at moderate duty, 201 with a proper relief step is the economical route, and the relief step is what makes it work.

Applications

Compression Springs

Interior springs for latches, dispensers and mechanisms, where the load has to stay within a band over the life of the product.

Torsion and Clip Springs

Formed springs where the legs carry bending load and residual stress from forming would otherwise show up as a change of angle in service.

Formed Wire Parts

Bent and looped components where dimensional stability matters more than the peak load, and a settling step is part of the acceptance test.

Product Advantages

• Stable drawn tensile range, so the relief window behaves the same from coil to coil instead of needing a new setting each time.
• Documented relief window of 250–400 °C for 20–60 minutes, giving the oven a defensible starting point.
• Controlled cast and helix, so the coil feeds a coiler without fighting the wire before the first turn is formed.
• Diameter tolerance of ±0.02 mm up to 2.0 mm, which is what holds spring index and load repeatability.
• Bright or soap coated finish, matched to the coiling method and to whether parts are cleaned after forming.

Quality Control

Chemical composition by optical emission, tensile strength, 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 the tensile range is stated per lot.

Selection and Ordering Notes

1. State the spring type, wire diameter and the load the spring must hold at its working deflection.
2. Tell us your relief temperature and hold time if you already run one, so we can confirm the wire tensile suits it.
3. Give the cast and helix limits your coiler needs, or the coil size and free length of the finished part.
4. State whether the parts are cleaned or passivated after forming, since that changes the surface requirement on the wire.
5. For springs in cyclic service, mention the cycle count so we can advise whether 201 or a higher nickel grade is the better base.

Send the spring drawing, the working load and your relief schedule, and we will match the wire tensile and surface to it.