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Grades and composition
Seven grades for springs, chosen by temperature, corrosion and whether the part can be aged after coiling.
| Grade | UNS | Service ceiling | Chosen for |
|---|---|---|---|
| Inconel 718 | UNS N07718 | 700 °C | Age-hardenable after coiling; high strength springs |
| Inconel X-750 | UNS N07750 | 815 °C | Relaxation resistance at temperature; the classic high-temperature spring grade |
| Inconel 625 | UNS N06625 | 980 °C | Corrosion plus heat; springs in chemical service |
| A-286 | UNS S66286 | 650 °C | Iron-based alternative to 718; lower cost, lower ceiling |
| Monel K-500 | UNS N05500 | 480 °C | Marine and sour service springs |
| MP35N | UNS R30035 | 400 °C | High strength plus corrosion; medical and marine |
| 3J21 | GB/T 14992 | 400 °C | Precision elastic parts, instrument springs |
Ageing after coiling
718, X-750 and K-500 are age-hardenable: the spring is coiled in the annealed or solution-treated condition and aged afterwards, which is what gives it its final load. That route has to be planned with the wire condition, so tell us whether you age after coiling.
Relaxation
A spring under load at temperature slowly loses length. The grade decides how fast; X-750 and 718 are chosen specifically because they lose it more slowly than the alternatives at the same temperature.