SCM415 is the primary low-carbon carburizing grade in JIS G4105’s chromium-molybdenum steel series. With 0.13–0.18% carbon, it is engineered for case hardening — delivering HRC 58–64 surface hardness over a tough HRC 28–38 core. This page covers equivalent grades (AISI, DIN, EN), chemical composition, mechanical and physical properties, heat treatment, machinability, weldability, and application guidance.
- International Equivalent Grades
- Chemical Composition
- Mechanical Properties
- Physical Properties
- Heat Treatment Conditions
- Machinability
- Weldability
- Common Mistakes
- When to Choose SCM415
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4105 | SCM415 | Japan | Reference |
| ASTM A29/A29M | AISI 4115 | North America | ✅ Nearest Exact (C 0.13–0.18%, Cr 0.80–1.10% slightly lower than JIS) |
| DIN EN 10084 | 16MnCr5 / 1.7131 | Europe (Germany) | ⚠️ Nearest Equivalent (no Mo, higher Mn) |
| EN 10084 | 18CrMo4 / 1.7243 | Europe | ⚠️ Nearest Equivalent (slightly higher C range, similar Cr-Mo) |
2. Chemical Composition
| Element | JIS SCM415 | AISI 4115 | DIN 16MnCr5 |
|---|---|---|---|
| C | 0.13–0.18% | 0.13–0.18% | 0.14–0.19% |
| Si | 0.15–0.35% | 0.15–0.35% | ≤ 0.40% |
| Mn | 0.60–0.90% | 0.75–1.00% | 1.00–1.30% |
| P | ≤ 0.030% | ≤ 0.035% | ≤ 0.035% |
| S | ≤ 0.030% | ≤ 0.040% | ≤ 0.035% |
| Cr | 0.90–1.20% | 0.80–1.10% | 0.80–1.10% |
| Mo | 0.15–0.30% | 0.15–0.25% | — (none) |
Sources: JIS G4105:2015, ASTM A29/A29M, DIN EN 10084
3. Mechanical Properties
3-1. Core Properties After Carburizing + Quench + Low Temper (Section ≤ 25 mm / 1 in)
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Core tensile strength | 785–980 MPa | 114–142 ksi |
| Core yield point | ≥ 590 MPa | ≥ 85.6 ksi |
| Core elongation | ≥ 17% | ≥ 17% |
| Core reduction of area | ≥ 55% | ≥ 55% |
| Core hardness | HRC 28–38 | HRC 28–38 |
3-2. Case Properties After Carburizing + Quench
| Property | Value |
|---|---|
| Surface hardness | HRC 58–64 |
| Effective case depth (550 HV limit) | 0.5–1.5 mm (0.020–0.059 in) |
4. Physical Properties
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Density | 7.85 g/cm³ | 0.284 lb/in³ |
| Young’s modulus | 206 GPa | 29,900 ksi |
| Thermal conductivity | 42 W/(m·K) | 291 BTU·in/(hr·ft²·°F) |
| Thermal expansion (20–100°C / 68–212°F) | 11.2 × 10⁻⁶ /°C | 6.2 × 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 | Grain refinement before machining |
| Annealing | 830–870°C (1526–1598°F) | Furnace cool | Soften for rough machining |
| Carburizing | 900–950°C (1652–1742°F) | Oil quench | Build carbon in surface layer |
| Case hardening (direct) | 820–860°C (1508–1580°F) | Oil quench | Harden case after carburizing |
| Low tempering | 150–200°C (302–392°F) | Air cool | Relieve quench stress, retain HRC 58–64 |
| Core hardening (separate) | 840–880°C (1544–1616°F) | Oil quench | Maximize core toughness |
6. Machinability
- Rating: approximately 70% vs AISI 1212 baseline (100%)
- Easier to machine than S45C due to lower carbon content
- Anneal before rough machining; use carbide tooling for finish passes
- After carburizing and hardening, surface grinding only — no cutting operations
7. Weldability
- Rating: Fair. Carbon equivalent (Ceq) ≈ 0.35–0.48
- Preheat to 100–150°C (212–302°F) for sections greater than 20 mm (0.8 in)
- Post-weld heat treatment recommended to relieve residual stress
- Use low-hydrogen welding consumables
- Important: welding a carburized part is essentially never done in practice — always weld before carburizing
8. Common Mistakes
SCM415 case depth greater than 2.0 mm increases brittleness risk at the case/core interface. For lightly loaded gears, 0.5–0.8 mm effective case depth (to 550 HV) is sufficient. Always match case depth to the contact stress level and tooth module — deeper is not necessarily better.
DIN 16MnCr5 contains no molybdenum, giving it lower hardenability in the core. For small sections less than 20 mm (0.8 in), the difference is minor and the substitution is often acceptable. For sections greater than 30 mm (1.2 in), SCM415’s Mo content provides meaningfully better core hardness after oil quenching. Always verify section size before approving the substitution.
9. When to Choose SCM415
- ✅ Automotive transmission gears requiring HRC 58–62 surface with tough HRC 28–38 core
- ✅ Camshafts, piston pins, and sprockets in carburized condition
- ✅ When AISI 4115 or 4118 sourcing in North American mills is required
- ✅ Small-to-medium section parts (≤ 40 mm / 1.6 in diameter) where Mo adds useful hardenability
- ❌ Through-hardening applications — use SCM440 or SCM445 instead
- ❌ Sections greater than 80 mm (3.1 in) where hardenability is insufficient — upgrade to SNCM420
- ❌ Applications involving welding after carburizing — rethink the design process
10. Frequently Asked Questions
Q: What is the difference between SCM415 and SCM420?
Carbon content is the primary distinction: SCM415 (0.13–0.18%) vs SCM420 (0.18–0.23%). Both are carburizing grades, but SCM420 gives a slightly tougher case and higher core strength after hardening. SCM415 is preferred for fine-pitch gears where lower carbon reduces distortion tendency; SCM420 is used where heavier loading demands higher core strength.
Q: Can SCM415 be through-hardened?
Technically yes, but to limited hardness. With 0.13–0.18% carbon, the maximum as-quenched hardness is approximately HRC 38–45 depending on section size and quench severity. This is insufficient for most wear applications. SCM415 is designed for carburizing, not through-hardening. Specify SCM440 or SCM445 for through-hardened applications.
Q: Is AISI 4115 widely available in North America?
AISI 4115 is less commonly stocked than 4118 or 4120 in North American service centers. AISI 4118 (C 0.18–0.23%, Cr 0.40–0.60%, Mo 0.08–0.15%) is more commonly used for similar carburizing applications and is sometimes substituted. Always verify the actual composition on the mill certificate before specifying, as Cr content differs significantly from SCM415.
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