What 51CrV4 is
51CrV4 is a chromium-vanadium spring steel standardised in EN 10089 under material number 1.8159. It carries about 0.5 % carbon, 0.90 to 1.20 % chromium and 0.10 to 0.25 % vanadium. The vanadium keeps the grain fine, so the steel holds fatigue strength and impact toughness at hardness levels where plain chromium spring steels turn brittle.
The grade sits between a quenched and tempered structural steel and a tool steel. At 0.5 % carbon it hardens deeply and reliably in oil. Chromium supplies the hardenability and slows softening during tempering.
Vanadium is the element the grade is named for. Fine vanadium carbides pin the austenite grain boundaries during heating, which raises fatigue life and makes 51CrV4 far less sensitive to overheating than a plain chrome-carbon spring steel such as 5160.
Those properties made 51CrV4 the standard choice for leaf springs, torsion bars and heavy hand tools. They also make it awkward to forge. At this carbon level a section cooled too fast off the press will crack, and a billet soaked much above 1150 °C loses the fine grain the vanadium was added to protect.
How we work this grade
Jiangyin Jiangnan Metal Co., Ltd. forges 51CrV4 at its plant in Zhouzhuang Town, Jiangyin, Jiangsu Province. Work on this grade runs to a controlled reheat and a slow cool off the press. Forgings leave as forged, rough machined or finish machined to drawing, in soft annealed (+A), normalised (+N) or quenched and tempered (+QT) condition, with an EN 10204 3.1 certificate.
51CrV4 equivalent grades
The closest international equivalents of 51CrV4 (1.8159) are AISI/SAE 6150 and UNS G61500 in the United States, SUP10 in Japan, 50CrVA in China, 735A50 or EN47 in the United Kingdom, 50CrV4 in the older German DIN system, and 50KhFA in Russia. These are near equivalents, not identical chemistries.
International cross-reference for 51CrV4 (near equivalents, verify against the heat analysis on the mill certificate)
| Region and standard | Designation | Notes |
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| EN 10089, Europe | 51CrV4 · 1.8159 | Reference grade for this page |
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| EN ISO 4957, tool steel | 1.2241 | Same chemistry, supplied to the tool steel standard |
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| DIN 17221, Germany, withdrawn | 50CrV4 | Former name, same material number |
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| ASTM and SAE, USA | AISI 6150 · SAE 6150 · UNS G61500 | Wider carbon band, lower vanadium minimum |
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| JIS G 4801, Japan | SUP10 | Standard Japanese spring grade |
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| GB/T 1222, China | 50CrVA | Direct domestic equivalent |
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| BS 970, United Kingdom | 735A50 · EN47 | EN47 is the legacy designation |
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| AFNOR, France | 50CV4 · 51CrV4 | |
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| UNI, Italy | 50CrV4 | |
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| SS, Sweden | SS 2230 | |
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| GOST, Russia | 50KhFA | Slightly different manganese range |
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| IS, India | 50Cr4V2 | |
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Cross-reference tables map grades by intended use, not by identical limits. Where a specification is safety critical, order to the exact standard called out on the drawing and check the delivered heat analysis.
Chemical composition of 51CrV4
51CrV4 contains 0.47 to 0.55 % carbon, max 0.40 % silicon, 0.70 to 1.10 % manganese, max 0.025 % phosphorus, max 0.025 % sulfur, 0.90 to 1.20 % chromium and 0.10 to 0.25 % vanadium, balance iron. These limits apply in EN 10089, EN 10083-3 and EN 10277-5.
Chemical composition of 51CrV4 / 1.8159, weight % (heat analysis limits to EN 10089:2002 and EN 10277-5)
| C | Si | Mn | P | S | Cr | V |
|---|
| 0.47–0.55 | max 0.40 | 0.70–1.10 |
max 0.025 | max 0.025 | 0.90–1.20 | 0.10–0.25 |
What each element does
- Carbon, 0.47 to 0.55 %. Sets the hardness the steel can reach. Around 0.5 % carbon a fully martensitic structure gets to roughly 58 HRC, high enough for spring duty and still temperable to a tough condition.
- Chromium, 0.90 to 1.20 %. Raises hardenability so heavier sections through-harden in oil, and slows softening during tempering.
- Vanadium, 0.10 to 0.25 %. Forms fine carbides that restrict austenite grain growth. This is what lifts fatigue strength and cuts sensitivity to overheating in the forge.
- Manganese, 0.70 to 1.10 %. Deoxidises, ties up sulfur and adds further hardenability.
- Phosphorus and sulfur, both max 0.025 %. Held low to avoid temper embrittlement and to keep transverse ductility, which matters in a cyclically loaded spring.
Mechanical properties of 51CrV4
In the quenched and tempered (+QT) condition 51CrV4 reaches 1100 to 1300 MPa tensile strength and 900 MPa minimum 0.2 % proof strength up to 16 mm diameter. At 160 to 250 mm this falls to 800 to 950 MPa tensile and 600 MPa proof strength. Soft annealed (+A) material is supplied at max 248 HBW.
Tensile strength, quenched and tempered
Tensile strength Rm by nominal diameter (EN 10277-5, +QT condition)
| Nominal diameter | to 16 mm | 16–40 mm | 40–100 mm | 100–160 mm | 160–250 mm |
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| Rm, tensile strength (MPa) | 1100–1300 | 1000–1200 | 900–1100 | 800–1000 | 800–950 |
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Proof strength, quenched and tempered
Upper yield strength Re or 0.2 % proof strength Rp0.2, minimum values (EN 10277-5, +QT. For flat products read thickness bands to 8, 8–20, 20–60, 60–100, 100–160 mm)
| Nominal diameter | to 16 mm | 16–40 mm | 40–100 mm | 100–160 mm | 160–250 mm |
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| Rp0.2, min. proof strength (MPa) | 900 | 800 | 700 | 650 | 600 |
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Ductility
Minimum elongation and reduction of area (EN 10277-5, +QT, round products, Lo = 5.65 √So)
| Nominal diameter | to 16 mm | 16–40 mm | 40–100 mm | 100–160 mm | 160–250 mm |
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| A, min. elongation (%) | 9 | 10 | 12 | 13 | 13 |
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| Z, min. reduction of area (%) | 40 | 45 | 50 | 50 | 50 |
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Minimum elongation at fracture in the transverse direction, +QT condition: 9 %.
Annealed strip, 0.3 to 3 mm thickness
Properties in the soft annealed condition (EN 10277-5, nominal thickness 0.3 to 3 mm)
| Property | Value |
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| Rm, tensile strength (MPa) | 700 |
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| Rp0.2, 0.2 % proof strength (MPa) | 550 |
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| A, min. elongation, Lo = 80 mm (%) | 13 |
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Hardness
Hardness of 51CrV4 by delivery condition (EN 10277-5)
| Delivery condition | Brinell HBW | Vickers HV |
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| +A, soft annealed | max 248 | max 220 |
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| +S, treated for cold shearability | max 280 | |
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| +AC, spheroidise annealed | max 230 | |
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| +QT, quenched and tempered | | 370–550 |
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Approximate hardness after hardening from 850 °C in oil: 55 to 58 HRC as quenched, 44 to 48 HRC after tempering at 400 to 450 °C for spring service, 28 to 40 HRC after tempering at 540 to 680 °C for structural quench and temper. Figures are indicative and depend on section size and quench severity.
Physical properties of 51CrV4
51CrV4 has a density of 7.85 g/cm³, a modulus of elasticity of about 206 GPa and a shear modulus of about 78.5 GPa at 20 °C. Thermal conductivity is around 44 W/(m·K) and the coefficient of thermal expansion between 20 and 300 °C is around 12.5 × 10⁻⁶ /K.
Typical physical properties at 20 °C (indicative values for low-alloy spring steel, not guaranteed limits)
| Property | Value | Unit |
|---|
| Density | 7.85 | g/cm³ (7850 kg/m³) |
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| Modulus of elasticity E | 206 | GPa |
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| Shear modulus G, spring design | 78.5 | GPa |
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| Thermal conductivity | 44 | W/(m·K) |
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| Specific heat capacity | 460 | J/(kg·K) |
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| Coefficient of thermal expansion, 20 to 300 °C | 12.5 | 10⁻⁶ /K |
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| Electrical resistivity | 0.21 | Ω·mm²/m |
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| Ac1 and Ac3 transformation points | 750 / 810 | °C, approximate |
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| Martensite start Ms | 270 | °C, approximate |
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| Maximum continuous service temperature | 300 | °C, spring duty |
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Forging and heat treatment of 51CrV4
51CrV4 is forged between 1050 °C and 850 °C and cooled slowly in still air. It is soft annealed at 680 to 720 °C with furnace cooling to max 248 HBW, normalised at 870 to 900 °C in air, hardened from 820 to 880 °C in oil, and tempered at 400 to 450 °C for spring properties or 540 to 680 °C for quenched and tempered structural properties.
Thermal processing for 51CrV4 / 1.8159
| Operation | Temperature | Cooling | Result |
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| Hot forming and forging | 1050–850 °C | Still air, slow | Wrought structure, no quench cracks |
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| Normalising | 870–900 °C | Air | Refined, uniform grain |
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| Soft annealing | 680–720 °C | Furnace | Max 248 HBW, machinable |
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| Hardening | 820–880 °C | Oil or polymer quench | 55 to 58 HRC as quenched |
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| Tempering for spring duty | 400–450 °C | Air | 44 to 48 HRC, high elastic limit |
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| Tempering for +QT | 540–680 °C | Air | 800 to 1300 MPa per section size |
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| Stress relieving | 550–650 °C | Furnace to 500 °C, then air | Removes machining stresses |
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The reference heat treatment quoted in EN 10089:2002 is a quench from 850 °C followed by tempering at 450 °C.
Forging notes
- Do not overheat the billet. Much above 1150 °C the vanadium carbides dissolve, the austenite grain coarsens, and the fatigue strength the grade was chosen for is gone for good.
- Do not finish forging below 850 °C. At 0.5 % carbon the steel work-hardens sharply as it cools and will tear.
- Never air-blast a heavy forging straight off the press. Cool slowly, or move it directly into an annealing furnace. Heavy sections of 51CrV4 crack on an uncontrolled cool.
51CrV4 forged products we manufacture
Jiangyin Jiangnan Metal Co., Ltd. produces 51CrV4 / 1.8159 open-die forgings to customer drawing: forged round, square, flat and hexagonal bar; hollow bar, sleeves, bushings and cylinders; seamless rolled rings and slewing bearing rings; discs, blocks and plates; gear shafts, pinion shafts and spindles.
- Forged barsRound, square, rectangular, flat and hex bar, black or rough turned
- Hollow bars and sleevesBushings, cylinders, barrels, casings, shells, hubs, housings
- Seamless rolled ringsRing rolled from a pierced forged blank for continuous grain flow
- Slewing bearing ringsRaceway rings for bearings and turntables
- Discs, blocks and platesUpset discs and rectangular blocks for machined components
- Gear and pinion shaftsStepped shafts, spindles, gear blanks
- Forged flangesFlanges and flanged hubs machined to drawing
- Custom profilesMade to your drawing, sample or specification
Supply options for 51CrV4 forgings
| Item | Options |
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| Dimensions | Quoted per drawing. Send the part print, or the diameter, length and quantity. |
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| Delivery condition | +A soft annealed, +N normalised, +QT quenched and tempered |
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| Surface | As forged (black), shot blasted, rough machined, finish machined |
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| Machining allowance | To DIN 7527 or per drawing |
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| Certification | EN 10204 3.1 mill test certificate |
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| Marking | Heat number stamped or tagged on every piece |
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| Packing | Seaworthy wooden case, steel pallet, or as specified |
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Applications of 51CrV4
51CrV4 is used for leaf springs, coil springs, torsion bars and spring plates in vehicles and rail rolling stock, for camshafts, racks, pinions and high-strength fasteners in machinery, and for chisels, wrenches, agricultural blades, plough shares and knives where hardness has to be combined with shock resistance.
By industry
- Automotive and commercial vehicle. Leaf and parabolic springs, torsion bars, stabiliser bars, valve springs, spring plates.
- Rail. Bogie suspension springs, spring plates, clamping components.
- Machinery and gear building. Camshafts, racks and pinions, gear blanks, high-strength shafts, safety valve springs.
- Hand tools and cutting. Chisels, wrenches, shears, punches, industrial knives.
- Agriculture and earthmoving. Plough shares, tine and blade components, wear plates under impact.
When to choose a different grade
Specify 51CrV4 when the part is loaded cyclically within its elastic range and has to resist fatigue and impact. Use 42CrMo4 (1.7225) for large shafts and pressure components, where through-hardening in heavy sections and temper resistance count for more than spring behaviour. Use 34CrNiMo6 (1.6582) where very heavy sections need higher toughness at high strength. Do not select 51CrV4 for welded assemblies.
Testing and certification
51CrV4 forgings from Jiangyin Jiangnan Metal are supplied with an EN 10204 3.1 mill test certificate reporting the heat analysis, heat treatment condition and mechanical test results. Ultrasonic inspection, magnetic particle inspection, hardness mapping and grain size determination are available on request.
- Chemical analysis. Ladle and product analysis against EN 10089 limits, reported per heat number.
- Mechanical testing. Tensile, proof strength, elongation, reduction of area and hardness, on test pieces in the delivered condition.
- Impact testing. Charpy at ambient or reduced temperature where specified.
- Ultrasonic inspection. To SEP 1921, EN 10228-3 or a customer nominated acceptance class.
- Surface inspection. Magnetic particle inspection to EN 10228-1.
- Metallurgical. Grain size, inclusion rating and microstructure examination on request.
- Traceability. Heat number stamped or tagged on every piece.
Third party inspection by SGS, BV, TUV or a customer representative can be arranged before shipment.
51CrV4 questions and answers
What is 51CrV4 steel?
51CrV4 is a chromium-vanadium spring steel standardised in EN 10089 under material number 1.8159. It carries about 0.5 % carbon, 0.90 to 1.20 % chromium and 0.10 to 0.25 % vanadium. The vanadium keeps the grain fine, which holds fatigue strength and impact toughness at high hardness. Jiangyin Jiangnan Metal Co., Ltd. open-die forges 51CrV4 into bars, rings, discs and shafts at its plant in Jiangyin, Jiangsu Province, China.
Is 51CrV4 the same as AISI 6150?
51CrV4 and AISI/SAE 6150 (UNS G61500) are the closest international equivalents and are used interchangeably in most applications. They are not identical. AISI 6150 allows a slightly wider carbon band and a lower minimum vanadium content than EN 10089 51CrV4. For safety critical springs, order to the EN grade and check the actual heat analysis on the EN 10204 3.1 certificate.
What is the difference between 51CrV4 and 50CrV4?
They are the same steel under two designations. 50CrV4 is the older DIN 17221 name and 51CrV4 is the current European designation in EN 10089. Both carry material number 1.8159. The same grade appears as 1.2241 when supplied to the tool steel standard EN ISO 4957.
What is the forging temperature of 51CrV4?
51CrV4 is forged between 1050 °C and 850 °C. Heat uniformly to 1050 to 1100 °C, finish all deformation above 850 °C, and cool slowly in still air. Going much above 1150 °C coarsens the grain and permanently reduces toughness. Finishing below 850 °C risks forging cracks.
What hardness can 51CrV4 reach?
As quenched from 850 °C in oil, 51CrV4 reaches roughly 55 to 58 HRC. Tempered at 400 to 450 °C for spring service it holds about 44 to 48 HRC. Tempered at 540 to 680 °C for structural quench and temper it falls to about 28 to 40 HRC, which matches the 370 to 550 HV range quoted for the +QT condition. Soft annealed material is supplied at max 248 HBW.
Can 51CrV4 be welded?
Welding 51CrV4 is not recommended. At 0.5 % carbon the carbon equivalent is high and the heat affected zone hardens and cracks readily. Where welding cannot be avoided, preheat to 300 to 400 °C, use low hydrogen consumables, and stress relieve immediately after welding.
What is the difference between 51CrV4 and 42CrMo4?
51CrV4 carries higher carbon, about 0.5 % against 0.42 %, plus vanadium. It reaches higher hardness and performs far better under cyclic elastic loading, which is why it is the spring grade. 42CrMo4 contains molybdenum, giving better temper resistance and more even through-hardening in heavy sections, so it suits large shafts, gears and pressure parts.
What is the maximum service temperature of 51CrV4?
51CrV4 springs are normally held to about 300 °C in continuous service. Above that the tempered martensite softens and the spring relaxes, losing load. For higher temperatures specify a Cr-Mo-V or stainless spring grade.
What is the density of 51CrV4?
The density of 51CrV4 is 7.85 g/cm³, or 7850 kg/m³, at 20 °C. Modulus of elasticity is about 206 GPa and shear modulus, used in coil spring design, is about 78.5 GPa.
Who supplies 51CrV4 open-die forgings?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China that manufactures 51CrV4 / 1.8159 forgings to customer drawings. Products include forged round and flat bar, hollow bar and sleeves, seamless rolled rings, slewing bearing rings, discs, blocks and gear shafts, supplied in +A, +N or +QT condition with EN 10204 3.1 certification. Contact sales@steelforgepieces.com or +86-189-2135-9659.