SNC815 (JIS G4102) is Japan’s high-nickel carburizing steel, engineered for large-section heavy-duty gears and shafts where lighter Ni-Cr grades fall short. With Ni at 3.00–3.50%, it delivers deep hardenability up to 80 mm (3.1 in) sections and core Charpy impact exceeding 127 J — without molybdenum.
- International Equivalent Grades
- Chemical Composition
- Mechanical Properties
- Physical Properties
- Heat Treatment Conditions
- Machinability
- Weldability
- Common Mistakes
- When to Choose SNC815
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4102 | SNC815 | Japan | Reference |
| ASTM A29/A29M | AISI 3310 | USA | ⚠️ Nearest Equivalent — different Cr range (1.40–1.75% vs SNC815’s 0.60–1.00%) |
| DIN EN 10084 | 14NiCr14 / 1.5762 | Germany / EU | ✅ Nearest Exact |
| EN 10084 | 14NiCr14 / 1.5762 | Europe | ✅ Nearest Exact |
2. Chemical Composition
| Element | JIS SNC815 | AISI 3310 | DIN 14NiCr14 |
|---|---|---|---|
| C | 0.12–0.18% | 0.08–0.13% | 0.10–0.17% |
| Si | 0.15–0.35% | 0.15–0.35% | ≤ 0.40% |
| Mn | 0.35–0.65% | 0.45–0.60% | 0.40–0.70% |
| P | ≤ 0.030% | ≤ 0.035% | ≤ 0.025% |
| S | ≤ 0.030% | ≤ 0.040% | ≤ 0.035% |
| Ni | 3.00–3.50% | 3.25–3.75% | 3.00–3.50% |
| Cr | 0.60–1.00% | 1.40–1.75% | 0.70–1.00% |
Sources: JIS G4102:2016, ASTM A29/A29M, DIN EN 10084
3. Mechanical Properties
Core Properties — After Carburizing + Quench + Low Temper (Section ≤ 50 mm / 2.0 in)
| Property | Metric | Imperial |
|---|---|---|
| Core tensile strength | 980–1180 MPa | 142–171 ksi |
| Core yield strength | ≥ 785 MPa | ≥ 113.8 ksi |
| Core elongation | ≥ 13% | ≥ 13% |
| Core Charpy impact | ≥ 127 J | ≥ 94 ft·lbf |
| Core hardness | HRC 32–42 | HRC 32–42 |
Case Properties
| Property | Value |
|---|---|
| Surface hardness | HRC 58–64 |
| Effective case depth | 0.8–3.0 mm (0.031–0.118 in) |
4. Physical Properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.85 g/cm³ | 0.284 lb/in³ |
| Young’s modulus | 205 GPa | 29,700 ksi |
| Thermal conductivity | 37 W/(m·K) | 257 BTU·in/(hr·ft²·°F) |
| Thermal expansion (20–100°C) | 11.4 × 10⁻⁶ /°C | 6.3 × 10⁻⁶ /°F |
| Specific heat | ~477 J/(kg·K) | 0.114 BTU/(lb·°F) |
5. Heat Treatment Conditions
| Process | Temperature | Cooling | Purpose |
|---|---|---|---|
| Normalizing | 850–900°C (1562–1652°F) | Air cool | Refine grain; prepare for carburizing |
| Carburizing | 900–950°C (1652–1742°F) | Oil quench | Carbon enrichment of case to 0.7–0.9% C |
| Case hardening quench | 800–830°C (1472–1526°F) | Oil quench | Austenitize and harden case; preserve core toughness |
| Low tempering | 150–180°C (302–356°F) | Air cool | Relieve quench stress; maintain HRC 58–64 at surface |
6. Machinability
- Machinability approximately 55% relative to AISI 1212 — lower than SNC415 due to higher Ni content.
- Very high Ni increases work hardening rate; dull tools will worsen surface quality rapidly.
- Sharp tooling and moderate cutting speeds (60–90 m/min / 200–295 ft/min) with coated carbide inserts required.
- Anneal before rough machining (at 820–850°C / 1508–1562°F, furnace cool) to reduce hardness to HB 170–210 for best machinability.
- All critical dimensions and features should be completed before carburizing; post-case grinding is the only practical finishing method.
7. Weldability
- Rating: Very restricted — not suitable for welded assemblies.
- High Ni + Cr combination creates severe HAZ cracking risk during cooling after welding.
- Carbon equivalent (Ceq) exceeds 0.60, making preheat alone insufficient to prevent delayed cracking.
- In practice, SNC815 components are not designed for welded joints. If a repair weld is unavoidable, consult a metallurgist for procedure qualification.
- Welding is absolutely prohibited after carburizing — the hardened case will crack under thermal stress.
8. Common Mistakes
For sections below 25 mm (1.0 in), SNC415 or SNCM220 achieves the same case hardness (HRC 58–64) and adequate core properties at meaningfully lower material cost. SNC815’s hardenability advantage — its justification for existence — only becomes relevant at sections above 40 mm (1.6 in). Using SNC815 for module 3–5 gears in light industrial machinery is an unnecessary cost premium. Evaluate section size first, then select the minimum-cost grade that meets the hardenability requirement.
AISI 3310 has significantly higher Cr (1.40–1.75%) versus SNC815 (0.60–1.00%). Higher Cr raises the Ac1 and Ac3 transformation temperatures, requiring different austenitizing conditions for equivalent case hardness. Engineers who directly substitute 3310 for SNC815 and use SNC815’s nominal 800–830°C (1472–1526°F) case hardening temperature may achieve incomplete austenitizing and softer case than expected. Always verify the quench temperature with the heat treater when changing grade specifications.
9. When to Choose SNC815
✅ Choose SNC815 when:
- ✅ Large-module gears (module ≥ 8) in mining, steel mill, and marine applications
- ✅ Heavy pinions and ring gears where section exceeds 50 mm (2.0 in)
- ✅ Applications requiring core Charpy impact above 120 J for shock and impact resistance
- ✅ When DIN 14NiCr14 (1.5762) is the specified European equivalent for import substitution
- ✅ Propulsion shafts and large planet gears in marine and wind turbine gearboxes
❌ Avoid SNC815 when:
- ❌ Small or medium gears with section below 40 mm (1.6 in) — use SNC415 or SNCM220 at lower cost
- ❌ Through-hardening applications — use SNCM625 or SNCM447
- ❌ Welded assemblies — high Ni + Cr makes welding impractical
10. FAQ
Q: What is the practical difference between SNC815 and SNCM415?
Both are high-Ni carburizing steels used for large-section gears, but they achieve hardenability by different mechanisms. SNC815 relies on high Ni (3.00–3.50%) without Mo; SNCM415 uses lower Ni (1.60–2.00%) combined with Mo (0.15–0.30%). For sections ≤ 50 mm (2.0 in), SNCM415 often performs comparably with better cost control, as Mo is very efficient at suppressing bainite during quench. For sections above 60 mm (2.4 in), SNC815’s higher Ni can provide better deep hardenability in oil quench. In practice, SNCM415 is more commonly specified for its balanced cost-to-hardenability ratio.
Q: Is DIN 14NiCr14 widely available?
Yes. 14NiCr14 (material number 1.5762) is a standard EN carburizing grade documented in DIN EN 10084 and available from European specialty steel mills in Germany, Sweden, and the UK. It is widely specified for heavy industrial gearing in the automotive supply chain and for mining and cement plant applications. Stock availability in bar form (25–200 mm diameter) is generally good from distributors serving these markets.
Q: How does SNC815 compare to SNCM625 for very large sections?
SNCM625 adds Mo (0.25–0.40%) to a Ni-Cr base, giving it superior hardenability for sections exceeding 100 mm (3.9 in). SNC815 is suitable for sections up to approximately 80 mm (3.1 in) with oil quench and achieves consistent core hardness in that range. For the largest sections — such as bull gears and large mill pinions above 100 mm (3.9 in) — SNCM625 with its Mo content is preferred because the oil quench rate at the core of very large sections is too slow for SNC815’s hardenability. If in doubt, calculate the ideal critical diameter (DI) and compare to the actual quenched section.
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