AISI 9260 spring steel: properties, hardness, equivalents
AISI 9260 is the 2 % silicon spring steel: the highest elastic limit of the plain spring grades and strong resistance to set, 50–54 HRC. Composition, decarburisation risk and SUP7/60Si2Mn equivalents.
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What is 9260?
AISI 9260 is the silicon spring steel — 0.60 % carbon, 2 % silicon, and no chromium, molybdenum or vanadium at all. Everything that distinguishes it comes from that silicon, and the mechanism is worth stating plainly: silicon dissolves in the ferrite and raises the yield strength much more than it raises the tensile strength. At a 450 °C temper the yield-to-tensile ratio is about 0.89 against roughly 0.86 for 5160 at the same hardness, which means a larger share of the steel's strength is available before anything takes a permanent set.
For a spring that is the whole point. A coil or leaf that sags has failed just as surely as one that breaks, and sag is a yield phenomenon. Silicon also slows the diffusion that drives tempering, so the steel holds its strength further up the temper curve and relaxes less at warm running temperatures. This is why the silicon family — 9260, 9254, 54SiCr6, 61SiCr7 — dominates modern automotive coil springs, and why 9260 at 52–55 HRC is a favourite of sword makers who need a long blade to flex and return straight.
The price is paid in two places. Hardenability is poor: with no chromium there is nothing to hold the transformation back, so full hardness reaches only 15–20 mm in oil, about half the depth of 5160. And silicon promotes decarburisation — it accelerates carbon loss from the surface during hot forming and hardening, in a component whose highest stress is at that surface. ASTM A29 sets no decarburisation limit, so on a fatigue-critical spring the European grade 56Si7 to EN 10089, which does, is the safer purchase.
JIS SUP7, GB 60Si2MnA, GOST 60S2A and IS 60Si7 are the same steel. The sister grades differ only in carbon and, in 9262, in a chromium addition that buys back some of the missing depth.
9260 chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | 0.56 – 0.64 | |
| Si | 1.8 – 2.2 | |
| Mn | 0.75 – 1 | |
| P | ≤ 0.035 | |
| S | ≤ 0.04 |
SAE J404 / ASTM A29 grade 9260 (UNS G92600). The sister grades differ only in carbon: 9254 at 0.51–0.59 % and 9255 at 0.51–0.59 % with the same silicon, 9262 at 0.55–0.65 % with 0.25–0.40 % chromium added. There is **no chromium, molybdenum or vanadium** in 9260 — the silicon does all the work, and that single fact explains both its strengths and its limits.
9260 mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| Annealed (delivery for forming) | — | ≈ 780–900 (≈ 113.1–130.5) | ≈ 15 | ≤ 269 HB |
| Hot rolled, as supplied | ≈ 650 (≈ 94.3) | ≈ 1050 (≈ 152.3) | ≈ 11 | 290–340 HB |
| 830–860 °C oil + 400 °C temper | 1650–1800 (239.3–261.1) | 1850–2000 (268.3–290.1) | 4 | 52–55 HRC |
| 830–860 °C oil + 450 °C temper | 1500–1650 (217.6–239.3) | 1700–1850 (246.6–268.3) | 6 | 48–52 HRC |
| 830–860 °C oil + 500 °C temper | 1300–1450 (188.5–210.3) | 1450–1600 (210.3–232.1) | 7 | 43–47 HRC |
| Hardened 850 °C oil, as-quenched | — | — | — | 61–64 HRC |
ASTM A29 fixes the analysis and the bar quality, not the mechanical properties, so there is no standard tensile table for 9260 and the rows above are typical for a 20 mm section. The figure worth comparing against other spring steels is the **ratio of yield to tensile**: at 450 °C temper it is about 0.89, against roughly 0.86 for 5160 at the same hardness. That elastic margin — not strength — is what silicon buys.
9260 equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| 60Si2MnA | GB/T (China) | Identical | GB/T 1222 60Si2MnA: C 0.56–0.64, Si 1.60–2.00, Mn 0.60–0.90. One of the most widely produced spring steels in China; the A suffix marks the higher-cleanliness version. |
| 60S2A | GOST (Russia/CIS) | Identical | GOST 14959 60S2A: C 0.57–0.65, Si 1.60–2.00, Mn 0.60–0.90. 60S2KhA adds chromium for deeper hardening. |
| 60Si7 | IS (India) | Identical | IS 3431 60Si7: C 0.55–0.65, Si 1.50–2.00, Mn 0.60–0.90. The Indian silicon spring steel and the dominant leaf-spring grade on the subcontinent; functionally the same steel as 9260. |
| SUP7 | JIS (Japan) | Identical | JIS G4801 SUP7: C 0.56–0.64, Si 1.80–2.20, Mn 0.70–1.00. The same steel, same windows. SUP6 is the lower-silicon version. |
| 5160 | AISI / SAE | Near | The chromium leaf-spring steel at the same carbon level. 5160 hardens roughly twice as deep; 9260 has the higher elastic limit and resists sag better. The split in practice is 5160 for thick leaves, 9260 and its relatives for coils and thinner sections. |
| 56Si7 | EN (European) | Near | EN 10089 56Si7 (1.5026): C 0.52–0.60, Si 1.60–2.00, Mn 0.60–0.90. Slightly less carbon and silicon than 9260, and — the real difference — phosphorus and sulphur capped at 0.025 % with a contractual decarburisation limit. 61SiCr7 (1.7108) is the higher-strength European silicon grade with chromium added. |
| 1095 | AISI / SAE | Functional | Plain 0.95 % carbon steel. Harder at the surface and much cheaper, but it has essentially no hardenability and no silicon, so it takes a permanent set where 9260 springs back. |
| 51CrV4 | EN (European) | Functional | 1.8159: chromium-vanadium, deeper hardening and far more tolerant of hot forming because the vanadium pins the grain. Chosen where section size or process robustness governs rather than elastic limit. |
Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for 9260 →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| 250A58 / 250A53 | BS 970 (withdrawn) | The British silicon-manganese spring steels of the same class. |
| EN45 / EN45A | BS 970:1955 | The pre-1970 British designation; EN45A is the higher-carbon version and the closer match to 9260. |
| 56Si7 | DIN 17221 (withdrawn) | Carried into EN 10089 unchanged (1.5026); the European 2 % silicon grade. |
| 9255 / 9254 | SAE J404 | Lower-carbon members of the same silicon family; 9254 is the one used in modern automotive coil springs. |
Product forms and tolerance standards
Product forms: hot-rolled flat bar for leaf springs, round bar for hot-coiled compression springs, annealed flat stock for blade and tool making, 9260H hardenability-guaranteed bar.
Dimensional tolerances: hot-rolled bar and spring flats: ASTM A29/A29M; hardenability band: 9260H to ASTM A304; surface quality: ASTM A29 requires freedom from injurious imperfections but sets no decarburisation depth — specify it separately or buy to EN 10089 instead.
Key property values
9260 hardness and elastic limit
As-quenched 61–64 HRC; usable hardness comes from the temper: 52–55 HRC at 400 °C, 48–52 HRC at 450 °C, 43–47 HRC at 500 °C. Tensile strength reaches 1850–2000 MPa at the 400 °C temper, among the highest of any plain spring steel. The number that matters more is the yield: 1650–1800 MPa in the same condition, close to 90 % of the tensile. Annealed delivery for forming is ≤ 269 HB.
What the 2 % silicon actually does
Three things. It strengthens the ferrite in solid solution, raising the yield disproportionately — the elastic limit, not the breaking strength, is what a spring is designed against. It retards tempering by slowing carbon diffusion, so hardness falls more slowly with tempering temperature and relaxation at service temperature is lower. And it raises the austenitising temperature slightly and widens the useful temper window. The cost is decarburisation sensitivity and graphitisation risk on long anneals.
Hardenability — the limiting property
With no chromium, manganese alone carries the hardenability: full hardness through about 15–20 mm in oil, roughly half the depth of 5160 and less than half that of 51CrV4. Jominy falls off quickly — around 63 HRC at J1.5 but below 45 HRC by J9. Consequences: thick leaves will be soft in the middle, and either the section is kept thin, or a chromium-bearing silicon grade (9262, 61SiCr7, 60S2KhA) is used. 9260H ordered to ASTM A304 is how a spring maker makes the result repeatable despite the steep curve.
Decarburisation and graphitisation
Silicon accelerates carbon loss from the surface at forming and austenitising temperatures. Because a spring carries its highest stress at the outer fibre, a decarburised skin cuts the fatigue limit directly — and ASTM A29 imposes no depth limit, unlike EN 10089. Practice: protect the surface with a controlled atmosphere, salt bath or coating; minimise time at temperature; grind or shot peen the surface afterwards. A separate risk on prolonged soft annealing is graphitisation, the precipitation of free graphite, which is why the anneal is kept short and below 700 °C.
Heat treatment
Soft anneal 680–700 °C, kept short. Normalise 870–890 °C. Austenitise 840–870 °C — slightly above a plain carbon steel because silicon raises the transformation temperatures — hold 10–20 min, quench in oil. Temper 380–520 °C for 1–2 h and air cool; avoid the 250–380 °C embrittlement trough. Hot form 1150–850 °C and normalise afterwards. Ac1 ≈ 765 °C, Ac3 ≈ 810 °C, Ms ≈ 250 °C.
Physical properties
Density 7.80 g/cm³ — a little lower than plain steel because of the silicon. E = 200 GPa, shear modulus G = 78 GPa, both marginally below a carbon steel and the reason a silicon spring of the same geometry is slightly softer in rate. Thermal conductivity ≈ 38 W/m·K, expansion 11.9 × 10⁻⁶/K (20–200 °C). Useful service temperature to roughly 250 °C, better than the carbon grades.
Weldability
Not weldable in the sprung section. The 2 % silicon makes the weld metal and the heat-affected zone more crack-sensitive than in a plain spring steel, on top of a carbon equivalent near 0.9. Where attachment is unavoidable, weld before heat treatment, with 300–400 °C preheat, hydrogen-controlled consumables and an immediate 500 °C temper. Forge welding is practical and is used in blade making. A weld across a finished spring is a fracture waiting for its first cycle.
Machining, forming and heat treatment
Annealed at ≤ 269 HB machinability is roughly 55–60 % relative to 1 % C free-cutting steel — slightly harder cutting than 5160 at the same hardness because silicon stiffens the ferrite and the chip is abrasive. Carbide tooling, moderate speeds, sharp edges. As-rolled at 300–340 HB, drilling is slow and annealing first is usually worth the time. After tempering to 50 HRC, grinding only — and grind wet, because this steel is easy to burn and a burnt surface is a tempered, weakened surface. Hot forging is straightforward between 1150 and 850 °C; normalise afterwards and keep the furnace time short to limit decarburisation.
Typical applications
- Hot-coiled compression springs for rail, mining and heavy vehicles
- Automotive coil springs (more often the lower-carbon 9254)
- Leaf springs in thinner sections, spring clips and spring washers
- Flat and spiral springs, clutch springs
- Sword and large knife blades needing flex and return (52–55 HRC)
- Spring-loaded machine parts, detents and latch springs
- Agricultural spring tines and seed-drill springs
Frequently asked questions
What is the European equivalent of 9260?
56Si7, material number 1.5026, in EN 10089 — C 0.52–0.60, Si 1.60–2.00, Mn 0.60–0.90. It is marginally leaner in carbon and silicon but, more importantly, it is bought against tighter phosphorus and sulphur limits and a contractual decarburisation limit, which 9260 to ASTM A29 does not have. Where chromium is wanted as well, the European grade is 61SiCr7.
What hardness does 9260 reach?
61–64 HRC as-quenched, and in service 52–55 HRC from a 400 °C temper, 48–52 HRC from 450 °C or 43–47 HRC from 500 °C. Tensile strength at the 400 °C temper is 1850–2000 MPa, with yield around 90 % of that — the high elastic ratio is the point of the grade.
9260 or 5160 — which should I use?
Section size usually decides it. 5160 hardens through 25–30 mm against 15–20 mm for 9260, so thick leaves go to 5160. Where the section is thin enough for either, 9260 has the higher elastic limit and resists sag and relaxation better, which is why coil springs favour the silicon grades. 9260 is also the more decarburisation-sensitive of the two.
Why is 9260 popular for swords?
Because a long blade has to bend a long way and come back straight, which is an elastic-limit problem rather than a hardness problem — exactly what 2 % silicon improves. At 52–55 HRC a 9260 blade takes a large deflection without setting, and it is tough because there are no hard alloy carbides. The trade-off is modest edge retention and no corrosion resistance.
How thick a section will 9260 harden through?
About 15–20 mm in oil. With no chromium there is little to slow the transformation, so the Jominy curve falls away quickly — below 45 HRC by J9. For thicker parts use 9262 (which adds chromium), 61SiCr7, 5160 or 51CrV4.
Is 9260 prone to decarburisation?
Yes, noticeably more so than the chromium grades, because silicon accelerates surface carbon loss at forming and austenitising temperatures. On a spring that matters a great deal, since the highest stress sits at the surface the decarburisation has weakened. Protect the surface during heat treatment, keep furnace times short, and shot peen or grind afterwards. ASTM A29 sets no depth limit — specify one, or buy 56Si7 to EN 10089 where the limit is part of the standard.
What is the difference between 9260, 9254 and 9262?
Carbon and chromium. 9254 and 9255 carry 0.51–0.59 % carbon with the same 2 % silicon and are the usual automotive coil-spring steels. 9260 raises carbon to 0.56–0.64 % for more hardness. 9262 keeps the higher carbon and adds 0.25–0.40 % chromium, which buys back part of the hardenability that 9260 lacks.
Can 9260 be annealed soft for machining?
Yes, at 680–700 °C, down to 269 HB or below. Keep the cycle short and the temperature under about 700 °C: at 2 % silicon a prolonged high anneal risks graphitisation, the precipitation of free graphite, which permanently damages the steel. Machine annealed, then harden and temper.
Related grades
Verified against ASTM A29/A29M-23, SAE J404; ASTM A29/A29M-23 (grade 9260 analysis); SAE J404 alloy steel compositions; EN 10089:2002 (56Si7 comparison); JIS G4801:2011 (SUP7 comparison); GB/T 1222-2016 (60Si2MnA comparison). Last checked: October 2026.