SCr415 is the low-carbon carburizing grade in JIS G4105’s chromium steel series. With no molybdenum addition, it has lower hardenability than SCM415, making it the cost-optimized choice for small-to-medium section carburized parts — pins, bushings, small gears, and sprockets where section size is below 25 mm (1 in). AISI 5115 is the nearest North American equivalent; DIN 15Cr3 is the closest European grade. This page covers equivalent grades, composition, mechanical and physical properties, heat treatment, machinability, weldability, and application selection guidance.
- International Equivalent Grades
- Chemical Composition
- Mechanical Properties
- Physical Properties
- Heat Treatment Conditions
- Machinability
- Weldability
- Common Mistakes
- When to Choose SCr415
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4105 | SCr415 | Japan | Reference |
| ASTM A29/A29M | AISI 5115 | North America | ✅ Nearest Exact (C 0.13–0.18%, Cr 0.70–0.90% — slightly lower Cr) |
| DIN EN 10084 | 15Cr3 / 1.7015 | Europe (Germany) | ⚠️ Nearest Equivalent (C 0.12–0.18%, Cr 0.60–1.00% — lower Cr range) |
| EN 10084 | 15Cr3 / 1.7015 | Europe | ⚠️ Nearest Equivalent |
2. Chemical Composition
| Element | JIS SCr415 | AISI 5115 | DIN 15Cr3 |
|---|---|---|---|
| C | 0.13–0.18% | 0.13–0.18% | 0.12–0.18% |
| Si | 0.15–0.35% | 0.15–0.35% | ≤ 0.40% |
| Mn | 0.60–0.85% | 0.70–0.90% | 0.30–0.60% |
| P | ≤ 0.030% | ≤ 0.035% | ≤ 0.035% |
| S | ≤ 0.030% | ≤ 0.040% | ≤ 0.035% |
| Cr | 0.90–1.20% | 0.70–0.90% | 0.60–1.00% |
| Mo | — (none) | — (none) | — (none) |
Sources: JIS G4105:2015, ASTM A29/A29M, DIN EN 10084
3. Mechanical Properties
3-1. Core Properties After Carburizing + Quench + Low Temper (Section ≤ 20 mm / 0.8 in)
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Core tensile strength | 690–880 MPa | 100–128 ksi |
| Core yield point | ≥ 490 MPa | ≥ 71 ksi |
| Core elongation | ≥ 18% | ≥ 18% |
| Core reduction of area | ≥ 60% | ≥ 60% |
| Core hardness | HRC 25–35 | HRC 25–35 |
3-2. Case Properties After Carburizing + Quench
| Property | Value |
|---|---|
| Surface hardness | HRC 56–62 |
| Effective case depth (550 HV limit) | 0.3–1.2 mm (0.012–0.047 in) |
SCr415 vs SCM415: SCr415 lacks molybdenum, giving it lower hardenability. For sections up to 20 mm (0.8 in), both grades achieve similar case and core results. For sections greater than 30 mm (1.2 in), SCM415 maintains significantly better core hardness. SCr415 is the cost-optimized choice for small parts where Mo’s hardenability contribution is not needed.
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 | 43 W/(m·K) | 298 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 | 860–900°C (1580–1652°F) | Air cool | Grain refinement before machining |
| Carburizing | 900–940°C (1652–1724°F) | Oil quench | Surface carbon enrichment |
| Case hardening | 820–860°C (1508–1580°F) | Oil quench | Harden case |
| Low tempering | 150–200°C (302–392°F) | Air cool | Retain HRC 56–62, relieve quench stress |
6. Machinability
- Rating: approximately 72% vs AISI 1212 baseline (100%) — best machinability in the SCr/SCM carburizing series
- Low carbon content makes pre-hardening machining straightforward
- Standard HSS tooling acceptable for roughing; carbide tooling recommended for production finishing passes
- After case hardening, grinding only — no cutting operations on the hardened surface
7. Weldability
- Rating: Fair. Carbon equivalent (Ceq) ≈ 0.30–0.42 — better weldability than SCM415 due to absence of Mo
- Preheat to 75–125°C (167–257°F) for sections greater than 20 mm (0.8 in)
- Low-hydrogen welding consumables recommended
- Always weld before carburizing — welding a carburized surface is not acceptable practice
8. Common Mistakes
Without molybdenum, hardenability drops rapidly with increasing section size. Core hardness after oil quench falls below HRC 25 for sections greater than 30 mm (1.2 in), which may be insufficient for medium-to-heavy duty gear core requirements. Upgrade to SCM415 for larger sections — the Mo addition provides meaningful core hardness improvement above this threshold.
DIN 15Cr3 has significantly lower manganese (0.30–0.60%) compared to SCr415 (0.60–0.85%). Manganese contributes to hardenability, so parts made from 15Cr3 will show lower core hardness than SCr415 at the same section size. If sourcing from European mills using 15Cr3, verify actual core hardness requirements against 15Cr3 hardenability data rather than assuming full interchangeability.
9. When to Choose SCr415
- ✅ Small gears, pins, bushings, and sprockets with section ≤ 25 mm (1 in)
- ✅ High-volume automotive components where Mo cost is not justified by section size
- ✅ When AISI 5115 sourcing is needed in North American supply chains
- ✅ Applications requiring maximum machinability in the pre-hardened state
- ❌ Sections greater than 30 mm (1.2 in) where hardenability is insufficient — use SCM415
- ❌ Applications requiring core tensile strength greater than 900 MPa (130 ksi) — use SCM420 or SNCM420
- ❌ Heavy-duty transmission gears — use SCM415 or SCM420
10. Frequently Asked Questions
Q: What is the difference between SCr415 and SCM415?
SCM415 adds Mo (0.15–0.30%) to the chromium base. Molybdenum dramatically improves hardenability for larger sections and provides better retained core hardness after tempering. For parts up to 20 mm (0.8 in), SCr415 and SCM415 perform comparably in both case and core properties. Above 30 mm (1.2 in), SCM415 core hardness is typically 5–8 HRC higher after oil quench. Specify SCr415 for small parts where Mo’s benefit is minimal and cost matters; upgrade to SCM415 when section size increases.
Q: Is AISI 5115 widely available in North America?
AISI 5115 is less commonly stocked than AISI 8620 or 4118 in North American service centers. AISI 8620 (with Ni addition, C 0.18–0.23%) is the most widely available carburizing grade in North America and is often used as a substitute where SCr415 or 5115 is not readily available. Note that 8620 has higher carbon (0.18–0.23% vs 0.13–0.18%), which affects distortion tendency and core strength — verify suitability before substituting.
Q: Can SCr415 be induction hardened instead of carburized?
Possible but not recommended. With C 0.13–0.18%, induction hardening produces only HRC 40–48 maximum surface hardness — significantly lower than the HRC 56–62 achievable via carburizing. The low carbon content limits the martensite hardness achievable by induction heating. If induction hardening is required for the application, specify a medium-carbon grade such as SCr440 or S45C instead.
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