Spring steel grades
1 spring steel grades from 1 designation systems, each with a full data sheet. Sorted by system; the yield and tensile values are the first line of each grade's mechanical table.
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AISI / SAE
| Grade | No. | Type | C % | Yield MPa | Tensile MPa | Equivalents |
|---|---|---|---|---|---|---|
| 1095 | G10950 | High-carbon steel (spring / knife / blade steel) | 0.9 – 1.03 | ≈ 380 | ≈ 650 | C100S, C90S / C98S, SK95 (SK4) |
Elastic limit, not ultimate strength
A spring steel is chosen for how far it can be deflected and return, which means a high ratio of yield to tensile strength and high fatigue resistance. Silicon does most of the work — 55Si7 and 60SiCr7 carry 1.5 to 2 % silicon precisely to raise the elastic limit.
Ultimate tensile strength is almost irrelevant here. A steel that is very strong but yields early makes a poor spring; one that returns cleanly from high strain makes a good one even at lower ultimate strength.
Surface decides the fatigue life
Spring failures are fatigue failures and they start at the surface, almost always at a defect: a decarburised skin, a seam, a scratch from handling or a tool mark. That is why spring steel is supplied with tight surface requirements and why shot peening is standard practice — it puts the surface into compression so that a crack cannot open.
Decarburisation is the specific enemy. A surface that has lost carbon during hot rolling or heat treatment is softer and weaker exactly where the stress is highest, and it will halve the fatigue life of an otherwise correct spring.
faq.h
What steel are leaf springs made from?
Silicon-manganese grades such as 55Si7, 60SiCr7 or SAE 9260, hardened and tempered to a high elastic limit. Coil springs use similar chemistry, often with chromium and vanadium for larger sections.
Why is silicon added to spring steel?
Silicon raises the elastic limit — the stress at which the steel stops returning to shape — and improves resistance to relaxation under sustained load. That is exactly the property a spring is bought for.
What is shot peening and why do springs need it?
Bombarding the surface with small shot to put the outer layer into compressive stress. Fatigue cracks start at the surface and cannot open against compression, so peening can multiply spring fatigue life several times over.
What is decarburisation and why does it matter?
Loss of carbon from the surface during hot rolling or heat treatment, leaving a softer skin. Since a spring's stress is highest at the surface, a decarburised layer dramatically shortens fatigue life and is limited tightly in spring steel standards.