Overview
JIS SUP10 is a chromium-vanadium alloy spring steel standardized under JIS G4801, designed for applications demanding superior fatigue life, toughness, and impact resistance. The addition of vanadium (≥0.15%) refines the austenite grain structure during heat treatment, resulting in finer martensite and significantly better fatigue performance compared to Si-Mn grades. Its nearest international equivalents are SAE/AISI 6150 and EN 51CrV4 (material number 1.8159).
SUP10 is the choice when both high fatigue strength and impact resistance must coexist — for example, in valve springs, precision instrument springs, and aerospace applications where Si-Mn grades (SUP6, SUP7) are insufficient.
Quick Comparison: SUP10 vs. Global Equivalents
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4801 | SUP10 | Japan | Reference |
| SAE/AISI | 6150 | USA | Nearest Equivalent |
| EN 10089 | 51CrV4 (1.8159) | Europe | Nearest Equivalent |
| DIN | 50CrV4 | Germany | Nearest Equivalent |
| ISO 683-14 | 51CrV4 | International | Nearest Equivalent |
SAE 6150 and EN 51CrV4 are nearest equivalents to SUP10, but vanadium minimum content and carbon ranges differ between standards. Always verify the vanadium content (SUP10 requires ≥0.15% V) from the mill certificate, as some heats of SAE 6150 sit at the lower V limit.
Chemical Composition
| Element | SUP10 % (JIS G4801) | SAE 6150 % | EN 51CrV4 % |
|---|---|---|---|
| C | 0.47–0.55 | 0.48–0.53 | 0.47–0.55 |
| Si | 0.15–0.35 | 0.15–0.35 | 0.10–0.40 |
| Mn | 0.65–0.95 | 0.70–0.90 | 0.70–1.10 |
| Cr | 0.80–1.10 | 0.80–1.10 | 0.90–1.20 |
| V | ≥0.15 | ≥0.15 | 0.10–0.25 |
| P | ≤0.035 | ≤0.035 | ≤0.025 |
| S | ≤0.035 | ≤0.040 | ≤0.025 |
Source: JIS G4801, SAE J404, EN 10089
Role of Vanadium: V combines with C to form fine VC carbides that pin austenite grain boundaries during austenitizing. The resulting finer martensite after quenching improves both fatigue strength and impact toughness — the key advantage of SUP10 over Si-Mn grades.
Mechanical Properties
| Property | Value | Imperial |
|---|---|---|
| Tensile Strength | ≥1,860 MPa | ≥270 ksi |
| Yield Strength (0.2%) | ≥1,620 MPa | ≥235 ksi |
| Elongation (GL=50mm) | ≥10% | ≥10% |
| Reduction of Area | ≥40% | ≥40% |
| Hardness (after HT) | 54–60 HRC (typical) | — |
| Charpy Impact (20°C) | ≥49 J (typical, Q&T) | ≥36 ft·lbf |
Notable: SUP10 has better elongation (≥10%) and reduction of area (≥40%) than Si-Mn grades (≥8% / ≥35%), reflecting the toughness benefit of the V addition.
Physical Properties
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Density | 7.85 g/cm³ | 0.284 lb/in³ |
| Thermal Conductivity | ~42 W/(m·K) | ~292 BTU·in/(hr·ft²·°F) |
| Thermal Expansion (20–200°C) | ~11.5 × 10⁻⁶ /°C | ~6.4 × 10⁻⁶ /°F |
| Young’s Modulus | ~206 GPa | ~29,900 ksi |
Heat Treatment Conditions
| Process | Temperature | Cooling |
|---|---|---|
| Austenitizing (Quench) | 830–870°C (1526–1598°F) | Oil quench |
| Tempering | 400–480°C (752–896°F) | Air cool |
| Annealing | 780–820°C (1436–1508°F) | Furnace cool ≤20°C/hr |
VC carbides in SUP10 dissolve fully at approximately 850°C (1562°F). Austenitizing below 830°C (1526°F) risks incomplete carbide dissolution, reducing hardness and uniformity. Hold time should be sufficient for the section size — typically 20–40 minutes for sections up to 30 mm (1.18 in).
Practical Advice
Machinability
SUP10 in annealed condition machines at approximately 65–70% of AISI 1212 free-machining steel. The Cr-V combination provides better machinability than high-Si grades (SUP6, SUP7), with less tendency for built-up edge. Carbide tooling recommended; HSS tooling acceptable for low-volume work at reduced speeds.
Heat Treatment Guide
Oil quench from 830–870°C (1526–1598°F). Tempering at 400°C (752°F) yields maximum hardness (~58–60 HRC) with adequate toughness. For applications requiring higher impact resistance (valve springs, aerospace), temper at 450–480°C (842–896°F) to achieve 54–57 HRC. The Cr-V combination gives SUP10 excellent temper resistance — properties change slowly with tempering temperature, giving a wider processing window than plain carbon or Si-Mn grades.
Welding
SUP10 has high hardenability and a carbon equivalent well above 0.5. Welding of finished spring components is not recommended. If raw stock welding is unavoidable, preheat to 300–350°C (572–662°F), use low-hydrogen electrodes, and perform post-weld stress relief at 600–650°C (1112–1202°F).
Common Mistakes
Some mill heats of SAE 6150 meet only the minimum V requirement (0.15%) while SUP10 applications may expect higher V for grain refinement. Request the actual vanadium content from the mill certificate, especially for precision instrument or aerospace springs.
VC carbides require adequate time to dissolve. Insufficient hold at austenitizing temperature leaves undissolved carbides, resulting in non-uniform hardness and reduced fatigue performance. Use the rule of 1 minute per mm of cross-section as a minimum hold guideline.
When to Choose SUP10
- Valve springs requiring combined high fatigue life and impact resistance
- Precision instrument springs (watches, gauges, medical devices)
- Aerospace spring applications with shock loading
- When Si-Mn grades (SUP6, SUP7) show inadequate toughness in service
- Applications at moderately elevated temperatures (up to ~200°C / 392°F)
FAQ
Q: Is SUP10 the same as SAE 6150?
A: They are nearest equivalents with nearly identical composition ranges. The main practical difference is in vanadium content verification — SUP10 and SAE 6150 both require ≥0.15% V, but actual heat compositions vary. For critical applications, confirm the actual V percentage from the mill certificate.
Q: How does SUP10 compare to SUP7 in fatigue life?
A: SUP10 generally delivers superior fatigue life due to vanadium-induced grain refinement. In valve spring applications, Cr-V grades typically show 20–40% longer fatigue life than Si-Mn grades at equivalent stress levels, with better consistency between heats.
Q: Is SUP10 suitable for elevated temperature use?
A: Yes, more so than Si-Mn grades. The Cr content improves oxidation resistance and the V addition improves temper resistance. SUP10 retains adequate spring properties up to approximately 200°C (392°F); above this, specialized high-temperature spring steels (e.g., SUH grades) should be considered.
Q: What is the difference between SUP10 and SUP9?
A: SUP9 is a Cr-Mn spring steel (SAE 5160 nearest equivalent) without vanadium. SUP10 adds V for grain refinement and improved toughness. For the same cross-section, SUP10 typically provides better impact resistance and more consistent fatigue life, but at higher material cost.
Summary
- JIS SUP10 = Cr-V alloy spring steel, JIS G4801
- Nearest equivalents: SAE 6150, EN 51CrV4 (1.8159)
- Tensile strength ≥1,860 MPa (≥270 ksi), elongation ≥10% after Q&T
- Heat treat: quench 830–870°C oil / temper 400–480°C
- Best for: valve springs, precision instruments, aerospace, and impact-loaded springs
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