EN 47 (51CrV4) is a high-strength chromium-vanadium spring steel supplied in the quenched-and-tempered condition to EN 10089. The vanadium addition refines grain size and improves fatigue resistance and temper stability, giving excellent elasticity and load-bearing capacity. It is the standard choice for highly stressed springs and components that must flex repeatedly without taking a permanent set.
Composition limits per EN 10089:2002 (weight %). Balance iron.
| Element | Min % | Max % |
|---|---|---|
| Carbon (C) | 0.47 | 0.55 |
| Silicon (Si) | — | 0.40 |
| Manganese (Mn) | 0.70 | 1.10 |
| Phosphorus (P) | — | 0.025 |
| Sulphur (S) | — | 0.025 |
| Chromium (Cr) | 0.90 | 1.20 |
| Vanadium (V) | 0.10 | 0.25 |
Typical property levels by delivery condition.
| Condition | Yield Rp0.2 (MPa) | Tensile Rm (MPa) | Elong. A5 (%) | Red. of area Z (%) | Hardness | Impact (ISO-V) |
|---|---|---|---|---|---|---|
| Quenched & tempered (+QT) | 1200 min | 1350–1650 | 6 min | 30 min | — | 8 J at 20 °C |
| Soft annealed (+A) | — | — | — | — | max. 248 HB | — |
| Spheroidize annealed (+AC) | — | — | — | — | max. 230 HB | — |
| As sheared (+S) | — | — | — | — | max. 280 HB | — |
| Transformation point | Temperature (°C) |
|---|---|
| Ms | 273 |
| Ac1 | 738 |
| Ac3 | 778 |
| Treatment | Temperature cycle | Cooling / quenching |
|---|---|---|
| Hot forging | 800–1100 °C | In still air |
| Normalizing | 840–880 °C | In still air |
| Soft annealing | 730–750 °C for 2 h | 20 °C/h to 650 °C, then still air |
| Stress relieving | 550–650 °C | In still air |
| Hardening | 830–860 °C | Quench in oil |
| Tempering | 380–680 °C for 1 h | In air |
Indicative curves from published band data (EN 10083-3), for a reference oil quench of 850 °C. Actual results depend on section size, austenitising temperature and quench severity.
Typical values at ambient temperature unless stated.
| Property | Typical value |
|---|---|
| Young’s modulus | 210 GPa |
| Poisson’s ratio | 0.30 |
| Shear modulus | 80 GPa |
| Density | 7,800 kg/m³ |
| Thermal expansion (20–300 °C) | 12 µm/m·K |
| Specific heat (50–100 °C) | 460–480 J/kg·K |
| Thermal conductivity | 40–45 W/m·K |
| Electrical resistivity | 0.20–0.25 µΩ·m |
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