AISI 5160 spring steel: properties, hardness, equivalents
AISI 5160 is the chromium leaf-spring steel: 0.60 % C and 0.80 % Cr, 1600–1900 MPa tensile at 48–52 HRC. Composition, heat treatment, hardness bands and 55Cr3/SUP9 equivalents.
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What is 5160?
AISI 5160 is the leaf-spring steel of North America and, in its European form 55Cr3, of much of the rest of the world. The recipe is deliberately plain: 0.60 % carbon for hardness, 0.80 % chromium for hardenability, 0.90 % manganese to help both — and nothing else. There is no vanadium, no molybdenum and no excess silicon, which keeps the price near that of a plain carbon steel while giving genuine through-hardness in a 25 mm leaf.
The number that matters when working with it is the as-quenched hardness: 60–63 HRC. At that carbon content 5160 comes out of the oil far harder than any spring needs, so the temper, not the quench, defines the part. A leaf tempered at 425 °C reads 50–53 HRC and 1700–1900 MPa and will take a set or crack under impact; the same leaf tempered at 480–500 °C reads 45–49 HRC and lasts. Nearly every failure attributed to the steel is an under-temper or a decarburised surface.
Outside the spring industry 5160 has a second life as a forging and blade steel. Knife and sword makers choose it precisely because it is not a wear-resistant steel: the low alloy content gives an exceptionally tough blade at 55–58 HRC, it forges easily, it takes a differential or clay-tempered heat treatment well, and a worn edge can be re-hardened by anyone with a forge. Those same properties — tough, cheap, forgiving, not very wear resistant — are why it is also used for agricultural tines, plough points and hand tools.
JIS SUP9A is the same steel; EN 55Cr3 is the same steel with tighter phosphorus, sulphur and decarburisation requirements, which matters for a fatigue-loaded spring and not at all for a knife. 5160H is ordinary 5160 bought against a guaranteed hardenability band rather than against chemistry alone.
5160 chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | 0.56 – 0.64 | |
| Si | 0.15 – 0.35 | |
| Mn | 0.75 – 1 | |
| P | ≤ 0.035 | |
| S | ≤ 0.04 | |
| Cr | 0.7 – 0.9 |
SAE J404 / ASTM A29 grade 5160 (UNS G51600). 5160H is the same analysis ordered to a hardenability band with a slightly widened carbon range (0.55–0.65 %). The European counterpart 55Cr3 (1.7176) in EN 10089 sets C 0.52–0.59, Si 0.25–0.50, Cr 0.60–0.90 and caps phosphorus and sulphur at 0.025 % — a cleaner steel for the same job.
5160 mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| Annealed (delivery for forming) | — | ≈ 720–850 (≈ 104.4–123.3) | ≈ 17 | ≤ 255 HB |
| Hot rolled, as supplied | ≈ 600 (≈ 87.0) | ≈ 1000 (≈ 145.0) | ≈ 12 | 280–320 HB |
| 830–860 °C oil + 425 °C temper | 1500–1650 (217.6–239.3) | 1700–1900 (246.6–275.6) | 5 | 50–53 HRC |
| 830–860 °C oil + 480 °C temper | 1300–1450 (188.5–210.3) | 1500–1700 (217.6–246.6) | 7 | 45–49 HRC |
| 830–860 °C oil + 540 °C temper | 1100–1250 (159.5–181.3) | 1250–1400 (181.3–203.1) | 9 | 38–42 HRC |
| Hardened 840 °C oil, as-quenched | — | — | — | 60–63 HRC |
ASTM A29 is a bar specification: it fixes the analysis, the dimensions and the surface quality, and leaves the mechanical properties to be agreed. There is therefore no standard tensile table for 5160 and the figures above are the normal correlation for a 20 mm section. Note the as-quenched row — at 0.60 % carbon the steel reaches 60+ HRC, well above spring hardness, which is why the temper is what sets the property and why an under-tempered leaf cracks rather than bends.
5160 equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| SUP9 | JIS (Japan) | Identical | JIS G4801 SUP9: C 0.52–0.60, Si 0.15–0.35, Mn 0.65–0.95, Cr 0.65–0.95. SUP9A raises carbon to 0.56–0.64 and chromium to 0.70–1.00, which is the direct 5160 match. |
| 55Cr3 | EN (European) | Near | EN 10089 55Cr3 (1.7176): C 0.52–0.59, Si 0.25–0.50, Mn 0.70–1.00, Cr 0.60–0.90. The same chromium spring steel with slightly less carbon and, more importantly, phosphorus and sulphur capped at 0.025 % against 0.035/0.040 — plus a decarburisation limit that SAE 5160 does not carry. |
| 51CrV4 | EN (European) | Near | 1.8159: less carbon, more chromium, and 0.15 % vanadium. The vanadium pins the grain, so 51CrV4 survives hot forming and overheating far better and is tougher at the same hardness; it is the European default where 5160 is the North American one. |
| 55CrMnA | GB/T (China) | Near | GB/T 1222 55CrMnA: C 0.52–0.60, Mn 0.65–0.95, Cr 0.65–0.95; 60CrMnA with 0.56–0.64 % C is the closer match to 5160. |
| 50KhG | GOST (Russia/CIS) | Near | GOST 14959 50KhGA: C 0.46–0.54, Mn 0.70–1.00, Cr 0.90–1.20 — lower carbon, more chromium. 60S2KhA is the Russian grade closer in strength. |
| 9260 | AISI / SAE | Functional | The silicon spring steel: same carbon, 2 % silicon and no chromium. Higher elastic limit and better resistance to sag, but much shallower hardening — the choice for coil springs where 5160 goes into leaves. |
| 1095 | AISI / SAE | Functional | Plain high-carbon steel: harder edge, no hardenability. A 1095 leaf is hard at the surface and soft in the middle, which is why carbon spring steels are confined to thin strip and 5160 takes the thick sections. |
| 4140 | AISI / SAE | Functional | The general-purpose quenched and tempered engineering steel. Deeper hardening thanks to molybdenum but only 0.40 % carbon, so it tops out well below spring hardness and is used for shafts rather than springs. |
| 60Si7 | IS (India) | Functional | The chromium leaf-spring steel: deeper hardening and less decarburisation-sensitive, with a lower elastic limit at the same hardness. |
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 5160 →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| 527A60 | BS 970 (withdrawn) | The British chromium spring steel of the same class; 527H60 is the hardenability-guaranteed version. |
| EN48 | BS 970:1955 | The pre-1970 British designation of the 0.60 % C chromium spring steel. |
| 55Cr3 | DIN 17221 (withdrawn) | The German grade, carried into EN 10089 unchanged with number 1.7176. |
| 9254 | SAE J404 | Not the same steel — a silicon-chromium grade sometimes substituted in modern coil springs. It is listed here only because stockists occasionally offer it against a 5160 enquiry. |
Product forms and tolerance standards
Product forms: hot-rolled flat bar for leaf springs, round and square bar for coil springs and torsion bars, annealed flat stock for knife and tool making, 5160H hardenability-guaranteed bar.
Dimensional tolerances: hot-rolled spring flats: ASTM A29/A29M and the mill's spring-flat section list; hot-rolled bar: ASTM A29/A29M, or EN 10092-1 where supplied as 55Cr3; hardenability band: 5160H to ASTM A304 (J-distance limits agreed on order).
Key property values
5160 hardness and temper
As-quenched 60–63 HRC, which is above any service condition. The usable bands come from the temper: 50–53 HRC at 425 °C, 45–49 HRC at 480 °C, 38–42 HRC at 540 °C. Automotive leaf springs are finished at 44–48 HRC, agricultural tines and tillage parts at 46–50 HRC, forged blades at 55–58 HRC from a lower temper. Annealed delivery for forming is ≤ 255 HB; as-rolled bar runs 280–320 HB.
Heat treatment
Normalise 860–880 °C. Austenitise 830–860 °C (hold 10–20 min at section temperature), quench in oil; water quenching is possible on thin leaves but cracks thick ones. Temper 400–550 °C for 1–2 h and air cool. Stay out of the 250–400 °C band, which crosses the tempered-martensite embrittlement trough. Soft anneal 650–700 °C. Hot forge 1150–850 °C and always normalise afterwards — do not quench directly from forging heat, because the grain is coarse. Ac1 ≈ 740 °C, Ac3 ≈ 780 °C, Ms ≈ 255 °C.
Hardenability
Chromium and manganese give full hardness through about 25–30 mm in oil — thinner than 51CrV4 but enough for the overwhelming majority of leaf sections. Jominy values run roughly 63 HRC at J1.5, 55 HRC at J6 and 40 HRC at J15. 5160H is the same steel ordered to a hardenability band under ASTM A304 and is what a spring maker buys when the quench is fixed and the hardness must repeat heat to heat. Above 40 mm, move to 51CrV4 or a molybdenum grade.
Why it is tough rather than wear resistant
The alloy content is low and there are no hard alloy carbides — the structure after tempering is a plain tempered martensite with a little chromium carbide. That gives a high fracture toughness and a high fatigue limit at 45–50 HRC, and a low abrasion resistance. For a spring, a plough point or a blade that must survive impact, this is the right trade; for a tool that must hold an edge against abrasive material, a tool steel is the correct choice and 5160 will simply wear.
Surface condition and fatigue
5160 is normally bought hot rolled, which means mill scale and some decarburisation. Both cut the fatigue limit: the decarburised skin has lost its carbon and therefore its strength, at exactly the fibre carrying the highest stress. Practice is to shot peen after forming and grinding — typically 500–900 MPa compressive in the top 0.2 mm and double the fatigue life — and to specify 55Cr3 to EN 10089 instead where the decarburisation limit needs to be contractual rather than assumed.
Physical properties
Density 7.85 g/cm³, E = 205 GPa, shear modulus G = 80 GPa. Thermal conductivity ≈ 46 W/m·K, expansion 12.3 × 10⁻⁶/K (20–200 °C). Service temperature up to about 200 °C before relaxation becomes measurable; coil springs running warm move to a silicon-chromium grade.
Weldability
Weldable only before heat treatment, and that is how spring eyes, brackets and clips are attached. On already-hardened material the carbon equivalent of roughly 0.85 means 300–400 °C preheat, hydrogen-controlled filler, high interpass temperature, slow cooling and an immediate 500 °C temper — and the heat-affected zone will still be softer and coarser than the parent spring. Welding a finished leaf spring is not an accepted repair. Forge welding, by contrast, works well on this steel and is used in blade making.
Machining, forming and heat treatment
Annealed at ≤ 255 HB machinability is about 60–65 % relative to 1 % C free-cutting steel, routine with carbide. As-rolled at 300 HB it is noticeably tougher and drilling is slow — anneal first if much metal is to come off. After tempering to 48 HRC, grinding only. Hot forging is easy and forgiving between 1150 and 850 °C, which is why the grade is popular with blacksmiths and blade makers; always normalise after forging to recover the grain. Cold shearing and punching are done annealed. Grind and peen after all forming, never before.
Typical applications
- Automotive and truck leaf springs, parabolic springs, spring clips
- Heavy coil springs and torsion bars
- Agricultural tines, plough points, cultivator shanks, harrow discs
- Forged hand tools, pry bars, picks and chisels
- Knife, machete and sword blades (forged, 55–58 HRC)
- Grader and scraper blades, wear strips where impact dominates
- Clutch and retaining springs, snap rings
Frequently asked questions
What is the European equivalent of 5160?
55Cr3, material number 1.7176, in EN 10089. It carries slightly less carbon (0.52–0.59 % against 0.56–0.64 %) and the same chromium, but it is a cleaner steel: phosphorus and sulphur capped at 0.025 % against 0.035 and 0.040, plus a contractual limit on surface decarburisation. For a fatigue-loaded spring those delivery requirements matter more than the small carbon difference; for a forged blade they are irrelevant.
What hardness does 5160 reach?
60–63 HRC as-quenched from oil — higher than any spring needs — so the hardness in service is set by the temper: 50–53 HRC at 425 °C, 45–49 HRC at 480 °C, 38–42 HRC at 540 °C. Leaf springs are normally finished at 44–48 HRC and forged blades at 55–58 HRC.
What is 5160H?
The same steel ordered to a guaranteed hardenability band instead of to chemistry alone, under ASTM A304. The carbon range is widened slightly to 0.55–0.65 % and the mill instead guarantees the Jominy curve between agreed limits. A spring maker with a fixed quench buys 5160H so that hardness repeats from heat to heat.
5160 or 51CrV4 — which is better for a spring?
51CrV4 is the better steel and costs more. Its vanadium pins the grain, so it tolerates hot forming and an overheated furnace, it is tougher at the same hardness, and it hardens through 40 mm against 25–30 mm for 5160. 5160 is chosen where the section is moderate and cost matters, which covers most leaf springs ever made.
Is 5160 a good knife steel?
For a large chopping blade, yes — it is one of the classic forging steels. The low alloy content gives exceptional toughness at 55–58 HRC, it forges and normalises easily, it takes a differential or clay temper, and it can be re-hardened with simple equipment. It is not stainless and it has low abrasion resistance, so the edge needs more frequent sharpening than a high-alloy blade steel. For a small slicing knife, a higher-carbon steel holds its edge longer.
How thick a section will 5160 harden through?
About 25–30 mm in oil. Beyond that the core drops below spring hardness and the choices are 51CrV4 (through to roughly 40 mm) or a molybdenum-bearing grade such as 52CrMoV4 for heavier bars.
Why do 5160 springs break?
Three causes account for almost all of it. An insufficient temper leaves the leaf above 53 HRC, where it cracks instead of flexing. A decarburised or scaled surface removes the strength from the fibre carrying the highest stress. And a weld or a drilled hole in the sprung length creates a notch in a component with no tolerance for one. Shot peening addresses the second; the other two are avoided by process, not by material.
Can 5160 be used for coil springs?
Yes, and it is, particularly in heavier hot-coiled sizes. For cold-coiled and high-duty coil springs the silicon grades — 9260, 54SiCr6, 61SiCr7 — are usually preferred, because silicon raises the elastic limit and resists sag, which matters more in a coil than in a leaf. 5160 keeps the leaf-spring market because it hardens deeper than the silicon grades.
Related grades
Verified against ASTM A29/A29M-23, SAE J404; ASTM A29/A29M-23 (grade 5160 analysis); SAE J404 alloy steel compositions; EN 10089:2002 (55Cr3 comparison); JIS G4801:2011 (SUP9/SUP9A comparison). Last checked: October 2026.