51CrV4
6150 · EN 10089 · 1.8159
51CrV4 (6150) is a spring steel (Chromium-Vanadium family) to EN 10089 (1.8159). It has a specified 0.2 % proof stress of 1200 MPa and a typical tensile strength of about 1450 MPa, with a uniform elongation of 6 %. Nominal carbon content is around 0.51 %. For nonlinear FEA, a bilinear model uses E = 210 GPa up to yield and a tangent modulus of 4781 MPa above it. Its high elastic limit and fatigue resistance suit it to springs and resilient components.
Bilinear material model — nonlinear FEA
Uniform elongation εu = 6.0% · conservative analysis limit ½εu = 3.0%
Bilinear (BISO) approximation. Elastic modulus E up to the 0.2% proof stress R_p0.2, then a single tangent slope Eₜ to the ultimate tensile strength: Eₜ = (Rₘ − R_p0.2) / (εu − R_p0.2/E − 0.002), where εu is the uniform elongation and Rₘ is a typical (nominal) UTS within the specified band. The half-εu figure is a conservative strain limit for the analysis. Treat these as guidance for first-pass models; for critical work use a measured true stress–strain curve for the actual product and condition.
Ratings — engineering judgement
Weldabilitypoor
Not normally welded — medium-high carbon plus alloying gives a strong crack risk, and welding ruins the spring temper. Join mechanically.
Formabilitymoderate
Formed (coiled, bent) in the soft/annealed condition, then hardened and tempered to the spring temper.
Machinabilitymoderate
Machinable when annealed; hard and abrasive once heat treated.
Corrosion resistancepoor
None inherent — springs are usually shot-peened and coated/oiled; corrosion pits are fatigue initiators.
Hardenabilityexcellent
Good depth of hardening from Cr; vanadium refines grain and adds temper resistance, so it holds strength in larger sections and at mildly elevated temperature.
Toughnessmoderate
Tempered to a high hardness for elastic performance rather than impact toughness; surface quality dominates fatigue life.
Expert notes
51CrV4 (EN47 / 6150) is a premium spring steel — the chromium gives depth of hardening and the vanadium refines the grain and resists softening, so it keeps its strength in thicker sections and at mildly elevated temperatures where a plain-carbon spring steel would sag.
It is used at a high tempered hardness (~42–48 HRC) for the elastic performance, not for toughness. That means surface integrity is everything: decarburisation, seams, scale pits and rough finishes are all fatigue-crack starters. Springs in this steel are almost always shot-peened, and often ground or shot-blasted, precisely to fight that.
Form it soft, then harden and temper — never try to bend it to shape in the hardened state. And don’t weld it: welding both cracks it and destroys the temper. Fix and locate springs mechanically.
For the elastic design itself, remember springs work in shear — size them on the shear modulus (~81 GPa) and the allowable shear stress, not the tensile numbers.
Mechanical properties
| Condition | Section | Yield (MPa) |
|---|---|---|
| 51CrV4 · hardened & tempered (spring temper) | typical | 1200 |
UTS 1350–1650 MPa · Impact not specified (spring temper) · Hardness 42–48 HRC (tempered)
Physical properties
| Density | 7850 | kg/m³ |
| Elastic modulus | 210 | GPa |
| Shear modulus | 81 | GPa |
| Poisson's ratio | 0.30 | |
| Thermal expansion | 12.0 | ×10⁻⁶/°C |
| Thermal conductivity | 46 | W/(m·K) |
| Specific heat | 460 | J/(kg·K) |
Chemical composition (wt %)
Available forms
Equivalent grades
| Standard | Grade | Note |
|---|---|---|
| AISI/SAE | 6150 | |
| EN 10089 | 51CrV4 / 1.8159 | |
| JIS | SUP10 | |
| BS 970 | 735A50 | Near UK equivalent (EN47 family). |
Historical designations
| Standard | Grade | Note |
|---|---|---|
| BS 970 | EN47 | The old British designation for the Cr-V spring steel. |
| Werkstoff Nr. | 1.8159 | German material number. |
Common applications
- Vehicle leaf and coil suspension springs
- Torsion bars and stabiliser bars
- Heavy-duty valve and clutch springs
- Agricultural tines and resilient tools
- Hand tools and chisels
History
Chromium-vanadium spring steels were developed in the early 20th century (vanadium famously championed by Henry Ford for tougher chassis parts) and remain the premium choice for demanding springs.
- 1905Chromium-vanadium steels adopted for automotive springs and chassis parts
- 1942EN47 defined in BS 970
- 1991EN 10089 harmonises 51CrV4 (1.8159) for spring steels