51CrMoV4
1.7701CrMoV alloyed spring steel — THE European automotive suspension spring material. CrMo gives deep hardenability for large coil springs, V adds grain refinement and secondary hardening for fatigue resistance. UTS 1350-1600 MPa QT. Used for hot-formed coil springs (cars, trucks), leaf springs, torsion bars, and stabilizer bars. Excellent sag resistance to 200°C.
International equivalents
| Flag | Standard | Country | Grade | Number | Match |
|---|---|---|---|---|---|
| 🇺🇸 | AISI | USA | AISI 6150 (approximate) | — | REF |
| 🇪🇺 | EN | Europe | 51CrMoV4 / 1.7701 | 1.7701 | 100% |
Sources: ASTM A29, EN 10089
Chemical composition comparison (wt%)
Side-by-side: 51CrMoV4 (EN) (EN 10089) vs 51CrMoV4 / 1.7701 (EN) (EN 10089)
| Element | 51CrMoV4 (EN) | 51CrMoV4 / 1.7701 (EN) | Overlap |
|---|---|---|---|
| C | 0.47–0.55% | 0.47–0.55% | OK |
| Si | 0–0.4% | 0–0.4% | OK |
| Mn | 0.7–1% | 0.7–1% | OK |
| Cr | 0.9–1.2% | 0.9–1.2% | OK |
| Mo | 0.15–0.25% | 0.15–0.25% | OK |
| V | 0.1–0.2% | 0.1–0.2% | OK |
Mechanical properties
QT
| Property | Value | Unit |
|---|---|---|
| Tensile Strength | 1350–1600 | MPa |
| Yield Strength | 1200–1400 | MPa |
| Elongation | 6–9 | % |
| Elastic Modulus | ≥ 210 | GPa |
| Density | ≥ 7.85 | g/cm3 |
Heat treatment
| Process | Temperature | Medium | Holding Time | Notes |
|---|---|---|---|---|
| hardening | 840–870 °C | oil | — | Oil quench |
| tempering | 400–480 °C | air | 1-2h | Target HRC 45-50 |
Compatibility verdict
51CrMoV4 and 51CrMoV4 / 1.7701: 100% composition match
Close equivalents but NOT identical.
Related materials
50CrV4
1.8160Chromium-vanadium spring/tool steel — identical alloy system to 51CrV4 (1.8159) but recognized as a separate grade in some standards. Dual use: heavy-duty springs (EN 10089) AND cold work tools (knives, shear blades). V improves temper resistance and grain refinement. UTS 1200-1500 QT. Used for heavy leaf springs, stabilizer bars, torsion bars, and cold work cutting tools.
20MnCr5
1.7147Manganese-chromium case-hardening steel with higher core strength than 16MnCr5. Used for heavily loaded gears, shafts, camshafts, and transmission components requiring high surface hardness with tough core. Popular in automotive and heavy machinery.
25CrMo4
1.7218Medium-carbon chromium-molybdenum steel with good toughness and weldability. Used for seamless tubes, pressure vessels, aircraft structural parts, and automotive components. Better weldability than 42CrMo4 due to lower carbon.
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