Stress Relief and Setting for Springs: Why It Matters
Short answer: Stress relief and setting are the two heat-and-load steps that decide whether a spring holds its rated load for 10 cycles or 10 million. Stress relief removes the residual stresses left by coiling and forming, typically at 200–450 °C for 30–60 minutes depending on material. Setting (presetting, or scragging) then overloads the spring past its working range so it takes a permanent set in the factory instead of in your assembly. Together they cut initial load loss from 5–15% to under 2–3%, stabilize free length, and can lift fatigue life by an order of magnitude. Skipping them saves cents per part and costs you field failures.
Springs look simple. A coil of wire, a few bends, done. In practice, a spring is a structure that lives under permanent stress, and the way you treat it after coiling determines almost everything about how it behaves in service. Two processes matter most: stress relief and setting. Buyers who understand them get predictable assemblies. Buyers who don't end up with springs that relax, sag, or crack.
What Is Stress Relief in Spring Manufacturing?
Stress relief is a controlled low-temperature heat treatment applied after coiling, winding, or stamping. Its job is not to change the wire's microstructure the way hardening or tempering does — it is to let the material relax the internal stresses locked in by cold forming.
When wire is coiled into a helix, the inside of the coil is compressed and the outside is stretched. Those opposing stresses stay in the part. They make the spring dimensionally jumpy, they add to the stress the spring already sees in service, and they make fatigue cracks start earlier.
What stress relief actually changes
- Dimensional stability. The spring stops drifting after coiling and holds free length and diameter better.
- Residual stress reduction. Peak locked-in stresses drop, so the working stress has more headroom before yield.
- Fatigue performance. Fewer stress risers mean cracks initiate later. Typical fatigue life improvement is 20–100% for well-executed stress relief, and more when the process is tuned to the material.
- Load consistency. Batch-to-batch load scatter narrows, which matters when you assemble thousands of units.
Typical stress relief parameters
These are indicative ranges for common spring materials. Exact values depend on wire diameter, coil ratio, and required tolerance — always confirm with your supplier's process sheet.
| Material | Typical temperature | Typical time | Notes |
|---|---|---|---|
| Music wire (ASTM A228) | 200–260 °C | 30 min | Low temperature preserves tensile strength |
| Oil-tempered MB / hard-drawn | 200–300 °C | 30–45 min | Avoid over-tempering |
| Stainless 302 / 304 | 250–400 °C | 30–60 min | Higher range helps stabilize austenitic grades |
| 17-7PH (CH900) | 400–480 °C | 60 min | Precipitation hardening interacts with relief |
| Phosphor bronze | 150–200 °C | 30 min | Lower ceiling; easy to over-soften |
| Inconel 718 / X-750 | 400–500 °C | 60–240 min | Material-specific; verify with mill data |
Two mistakes are common. First, running too hot — you lose the cold-work strength that made the wire usable. Second, running too cool or too short — you get the cost of the furnace without the benefit. A spring that was "heat treated" at 150 °C for ten minutes has effectively not been stress relieved at all.
What Is Setting (Presetting or Scragging)?
Setting is a mechanical process, not a thermal one. The spring is compressed (or extended, for extension springs) to a defined overload — usually 1.1 to 1.5 times the maximum working deflection, or up to a stress level near but below yield. It is held there briefly, sometimes cycled several times, then released.
The spring does not come back to its original free length. It comes back shorter. That is the point.
Why a spring "sets" at all
Every spring has a small zone near the yield strength of the wire where the material deforms plastically. When you first load a spring to its working height, the most highly stressed coils — usually the ones nearest the ends, or the ones with the tightest curvature — yield slightly. The spring gets shorter, and because spring rate depends on the number of active coils, the load at a given height changes.
If you let this happen in the customer's assembly, you get:
- Load loss after the first few cycles
- Free length drift that breaks height tolerances
- Preload that disappears in a bolted joint
- Uneven behavior across a production batch
What setting delivers
Setting forces that plastic deformation to happen under controlled factory conditions. After setting, the spring is dimensionally stable within its working range, and the load-height curve is repeatable.
| Parameter | Without setting | With setting |
|---|---|---|
| Initial load loss (first cycles) | 5–15% typical | Under 2–3% typical |
| Free length drift | Noticeable, batch-dependent | Stabilized |
| Load scatter across batch | Wider | Narrower |
| Fatigue life at same stress | Baseline | Often improved |
| Fit in a preloaded assembly | Risky | Predictable |
Note that setting is not "overload the spring and hope." It is a calculated overload with a defined hold time and a defined number of cycles, followed by measurement. If a supplier cannot tell you the setting load and hold time, they are guessing.
How Stress Relief and Setting Work Together
The two processes are complementary, and the order matters.
1. Coil or form the spring.
2. Stress relieve to remove forming residual stresses and stabilize dimensions.
3. Set / preset to force controlled plastic deformation at the working end of the range.
4. Measure and sort — free length, rate, and load at test height.
5. Optional secondary stress relief for high-cycle or high-temperature applications.
If you set a spring before stress relief, you are pushing a stress-laden part into plastic deformation, and the result is less predictable. If you stress relieve but never set, the spring still loses load in the first cycles of service — just less dramatically.
When you can skip a step
Not every spring needs both. Guidance:
- Light-duty, non-critical springs (a latch return, a display detent) often need only stress relief, or in some cases neither.
- Preloaded assemblies (bolted joints, seals, connectors) almost always need setting, because load loss directly causes failure.
- High-cycle springs (valves, pumps, actuators, shock absorbers) need both, plus attention to shot peening and surface condition.
- High-temperature springs need stress relief tuned to the service temperature; a spring that relaxes at 200 °C in service needs a relief cycle above that.
Does Stress Relief Affect Spring Rate?
Strictly, stress relief does not change the elastic modulus of the wire, so it does not change spring rate in the elastic range. What it changes is the consistency of rate and load across a batch, and the point at which the spring starts to behave non-linearly.
Setting, by contrast, does change the load-height curve — because it removes active coils from the elastic response. A spring that was set will read a different load at the same height than an identical unset spring. This is why drawings should specify whether the spring is supplied set or unset, and at what test height the load is measured.
If your drawing says "rate 12 N/mm, free length 40 mm" with no mention of setting, two suppliers can both meet the drawing and still deliver springs that behave differently in your assembly. This is one of the most common sources of "the springs are out of spec" disputes — and it is a specification problem, not a manufacturing problem.
Material-Specific Considerations
Different wire grades respond differently, and the process window is not interchangeable. A few practical notes:
- Music wire and oil-tempered wire are the workhorses. They stress relieve at low temperature and set predictably. They are also the most sensitive to over-tempering, so temperature control matters.
- Stainless steels (302, 304, 316) have lower modulus and different relaxation behavior. They benefit from higher stress relief temperatures, but too high and you lose the cold-work strength. See our notes on spring material selection and music wire for how grade choice interacts with processing.
- 17-7PH and 17-4PH are precipitation-hardening grades. Stress relief and aging can be combined, but the schedule has to be designed, not copied.
- Nickel alloys (Inconel, Hastelloy) are used where temperature and corrosion rule out everything else. Relief cycles are longer and hotter, and setting loads are chosen with more margin.
Fatigue Life: Where the Payoff Shows Up
Fatigue is the dominant failure mode for springs in motion. A crack starts at a surface defect or a stress concentration, usually on the inside of the coil where tensile stress is highest.
Stress relief helps because residual tensile stress from coiling adds directly to the service tensile stress. Remove it, and the effective alternating stress drops. Setting helps because it pre-loads the wire in compression at the critical surface, which is the same principle behind shot peening.
Typical combined effect: a spring that would fail at 200,000 cycles unrelieved and unset may reach 1–2 million cycles with both processes applied correctly. That is an order of magnitude, and it is usually cheaper than upgrading the material. For more on how cyclic loading interacts with design margins, see spring design for dynamic loads.
What to Put on Your Spring Drawing
If you want these processes applied, specify them. Suppliers build to the drawing, not to your intent.
| Drawing item | Why it matters |
|---|---|
| Material grade and wire diameter tolerance | Determines the process window |
| Stress relief: temperature range and time | Prevents "we did something" heat treatment |
| Setting: load or deflection, hold time, cycles | Makes setting repeatable |
| Test height for load measurement | Removes ambiguity about set vs. unset |
| Rate tolerance and load tolerance | Two different things; specify both |
| Surface finish / shot peening requirement | Interacts with fatigue life |
| Service temperature | Sets the minimum relief temperature |
A drawing that specifies "stress relieve per good commercial practice" is not a specification. It is a hope.
Quality Control and Verification
At a minimum, a competent spring supplier should be able to show:
- Furnace records with actual temperature and time per batch
- Setting equipment with recorded load and deflection
- Load testing at the specified test height, with sampling per lot
- Free length and squareness measurement
- Fatigue or relaxation testing for critical programs
BQUQ runs four production lines in one Dongguan factory under ISO9001, covering CNC machining to ±0.005 mm, metal stamping, custom springs, and heat sinks. Spring production includes controlled stress relief and setting, with load testing recorded per lot. Quotes come back in 12 working hours, and MOQ is flexible — including prototype and short-run quantities, which is often where setting behavior first gets validated. If you are planning a program, our guide to spring lead time planning covers how heat treatment and setting fit into the schedule.
Frequently Asked Questions
Q: Is stress relief the same as tempering?
A: No. Tempering is a higher-temperature treatment applied after hardening to adjust the microstructure and toughness of the steel. Stress relief is a lower-temperature treatment applied after cold forming to reduce residual stresses without significantly changing microstructure or hardness. For music wire and oil-tempered wire, stress relief happens well below the tempering range, so it does not undo the wire's existing heat treatment.
Q: How much load loss should I expect from an unset spring?
A: For a typical unset compression spring loaded to its working height, initial load loss is commonly 5–15% in the first few cycles, depending on material, stress level, and coil ratio. A properly set spring typically holds within 2–3%. The gap widens at higher stress levels and with stainless grades, which relax more readily than carbon steel wire.
Q: Can setting be done at the customer's assembly instead of at the factory?
A: It can, but it is rarely a good idea. Setting in the assembly means the first load cycle deforms the spring unpredictably, and any preload or height tolerance you designed around shifts. It also means the plastic deformation happens without measurement or control. Factory setting is repeatable, verified, and documented, which is why preloaded assemblies should always specify it.
Q: Does stress relief change the spring's color or surface?
A: Low-temperature stress relief in air can produce a light oxide tint on carbon steel, ranging from straw to blue depending on temperature. This is cosmetic and does not affect function. If appearance matters, specify a post-treatment such as passivation for stainless or a light oil finish for carbon steel. Stress relief does not remove plating or coating, so coated springs are usually relieved before coating.
Q: What happens if a spring is stress relieved at too high a temperature?
A: You lose cold-work strength. Music wire and hard-drawn wire gain much of their strength from drawing, not from alloy content. Overheating relaxes that, lowering yield strength and reducing the load the spring can carry. The spring may pass a load test cold and then sag in service. This is why temperature control and batch records matter more than the nominal furnace setting.
Related Resources
- Learn how BQUQ approaches precision manufacturing: /about/
- Browse compression springs, extension springs, and torsion springs: /compression-springs/, /extension-custom-springs/, /torsion-springs/
- Industry trends affecting lead times and material availability: /industry-dynamics/
- More technical articles on springs, stamping, and CNC: /bquq-blog/
- Common sourcing and specification questions: /faq/
- Program examples and process capability: /case/
- Send a drawing for a 12-hour quote: /contact/
Authored by the BQUQ Engineering Team. BQUQ (Dongguan) runs CNC machining (±0.005 mm), metal stamping, custom springs, and heat sink production in one ISO9001 factory. Source-direct from Dongguan, China — quote in 12 hours: sc@bquq.com | WhatsApp +86 13713157787 | www.bquq.com
