A chromium-vanadium spring steel (AISI 6150) that combines good hardenability with vanadium-refined fatigue strength. It is the North-American workhorse for valve springs, torsion bars and suspension parts that see high cyclic stress.
What Is 6150 Spring Steel?
6150 is an AISI chromium-vanadium spring steel. The chromium gives it oil-hardenability through moderate sections, and the vanadium refines the grain for better fatigue life — the same role as European 50CrV4 / 51CrV4, with slightly lower carbon.
It is widely used for valve springs, torsion bars and high-stress suspension. It is not stainless and, like other spring steels, must be protected against corrosion in service.
Supply Forms and Sizes
Every form is available soft-annealed (for further forming and machining) or heat-treated to your hardness window.
| Form | Condition | Size Range | Typical Use |
|---|---|---|---|
| Cold-drawn wire | Annealed / oil-tempered | 0.2 – 12 mm | Valve springs, coil springs |
| Hardened & tempered strip | Q&T, edge dressed | 0.2 – 6 mm | Clutch springs, washers |
| Hot-rolled bar | Hot rolled / normalized | 8 – 100 mm | Torsion bars, forgings |
| Flat spring steel | Q&T | 3 – 40 mm | Suspension leaves, brackets |
Chemical Composition (AISI 6150)
| C | Si | Mn | Cr | V min | P max | S max |
|---|---|---|---|---|---|---|
| 0.48 – 0.53 | 0.15 – 0.35 | 0.70 – 0.90 | 0.80 – 1.10 | 0.15 | 0.035 | 0.040 |
Heat analysis is reported on the mill certificate for every lot. If your drawing calls for tighter limits than the standard, flag it at enquiry — ladle-refined heats usually meet it without a surcharge.
Physical Properties
| Property | Value |
|---|---|
| Density | 7.85 g/cm³ |
| Elastic modulus (E) | ~200 GPa |
| Shear modulus (G) | ~79 GPa |
| Thermal conductivity | ~40 W/m·K at room temperature |
| Coefficient of thermal expansion | ~12 ×10⁻₆ /K (20 – 200 °C) |
Mechanical Properties
Typical values for 6150 after oil quenching and tempering near 440 °C. The mill certificate is the binding document.
| Condition | Tensile Strength | Yield Strength | Elongation | Hardness |
|---|---|---|---|---|
| Annealed | ≥ 850 MPa | ≥ 690 MPa | ≥ 12 % | ≤ 269 HB |
| Q&T | 1250 – 1500 MPa | ≥ 1050 MPa | ≥ 9 % | 40 – 48 HRC |
| Oil-tempered wire | 1600 – 2000 MPa | — | — | per size class |
Equivalent Grades
| Standard | Designation |
|---|---|
| USA AISI / SAE | 6150 |
| Europe EN | 51CrV4 (similar) |
| Japan JIS G4801 | SUP10 (similar) |
| China GB/T 1222 | 50CrVA (similar) |
Heat Treatment and Processing
Preheat slowly, then raise to the grade forging range. Work above the lower limit and cool slowly after forging to avoid cracks.
680 – 720 °C, soak, furnace cool. Soft condition for forming and coiling.
840 – 880 °C, oil. Full through-harden in moderate sections.
400 – 550 °C by required hardness; ~440 °C gives the usual 44 – 48 HRC spring window.
After machining or forming, 200 – 350 °C for 1 – 2 hours, air cool, to stabilise dimensions and relieve residual stress.
Heat-treated bars and plates are supplied with the hardness and test certificate you specify. For critical parts we can control decarburisation depth and supply a spheroidized or soft-annealed structure on request.
Applications of 6150 Spring Steel
High-cycle life from the V-refined grain.
Suspension torsion bars that store large elastic energy.
Fatigue resistance under continuous load.
Passenger and light-commercial vehicle springs.
Hardened-and-tempered strip at 44 – 48 HRC.
Where relaxation could fail the assembly.
6150 Spring Steel vs Alternative Grades
| Grade | vs 6150 Spring Steel | Choose It When |
|---|---|---|
| 6150 | — | High-cycle valve/torsion springs needing Cr-V toughness. |
| 65Mn | Cheaper, lower alloy | Light, low-cost strip and wire springs |
| 50CrV4 | Slightly higher C and more V | Most demanding fatigue or warm springs |
| 9260 (Si-Mn) | Higher Si, cheaper | Large leaf springs at lower cost |
Quality Control and Mill Certificates
Every shipment ships with an EN 10204 3.1 mill certificate covering heat chemical analysis, hardness and the mechanical test on record. On request we add: ultrasonic test on heavy bar and plate, magnetic particle inspection on machined surfaces, and third-party inspection (SGS / BV) before loading. Dimensional tolerances follow the relevant EN / ASTM / JIS standard or your drawing.
Frequently Asked Questions
What is 6150 equivalent to?
Closely AISI 6150; similar to European 51CrV4, Japanese SUP10 and China 50CrVA. Confirm against the certificate for critical parts.
Is 6150 good for valve springs?
Yes — its chromium-vanadium chemistry gives the fatigue strength and hardenability valve springs require.
What hardness does 6150 reach?
Typically 40 – 48 HRC in the quenched-and-tempered spring condition.
6150 vs 50CrV4?
Very close; 50CrV4 runs slightly higher carbon and vanadium, so a touch more fatigue and temper resistance for the same hardness.
What is the minimum order quantity?
Mill lots typically start at 500 kg per item; trial wire and bar are often from stock.
Related Products
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