High-Temperature Spring Materials: The Ladder from 120°C to 550°C
Heat kills springs quietly: not by breaking them, but by relaxing them until the mechanism stops working. Material choice sets the ceiling.
The temperature ladder
| Material | Practical ceiling | Notes |
|---|---|---|
| Music wire | ~120°C | Relaxation accelerates beyond |
| Hard-drawn / SWO | ~120–150°C | Similar behavior |
| Chrome silicon | ~245°C | The affordable heat upgrade |
| Stainless 302/304 | ~260°C | Plus corrosion resistance |
| 17-7PH | ~340°C | Strength + heat |
| A286 | ~450°C | Between stainless and Inconel |
| Inconel X-750 | ~550°C | The standard superalloy answer |
Ceilings assume sustained service with moderate stress; short excursions above are survivable with a relaxation penalty.
What "relaxation" means for your design
Load a spring at temperature and hold it: force decays over hours-to-months, fastest at first. A music-wire spring held at 150°C can lose 10–15% of its force in the first days. The relaxation triples roughly every 30–50°C. Design responses:
- Derate stress: operating at 30% of tensile instead of 45% cuts relaxation dramatically
- Pre-relax at the factory: heat-set springs stabilize before shipment — specify "hot pressing"/heat setting for critical force retention
- Overshoot the force slightly and let early relaxation settle into your window
Specification checklist
State continuous temperature, peak temperature and duration, force loss budget (e.g., "≤5% over 10 years"), and atmosphere (oxidizing, steam, chemical). These four lines determine the material more precisely than any catalog. Our RFQ review prices two adjacent rungs when the answer is borderline.
Frequently Asked Questions
My spring works at 200°C. Music wire or chrome silicon?
Chrome silicon, clearly — music wire relaxes badly past 120°C. At 200°C Cr-Si with moderate stress runs reliably; 304 stainless is the alternative when corrosion coexists.
What is heat setting and do I need it?
The factory compresses the spring at elevated temperature, pre-consuming the fastest part of relaxation. Specify it when force must stay in a tight window over life at temperature.
Do springs also get weaker instantly when hot?
Yes, modulus drops ~2–3% per 100°C, so the spring is slightly softer while hot — separate from permanent relaxation. Precision designs account for both.