SCr440 is JIS G4105’s primary through-hardening chromium steel, offering a cost-effective alternative to SCM440 (Cr-Mo) when molybdenum’s hardenability benefit is not required. With 0.38–0.43% carbon and 0.90–1.20% Cr, it through-hardens reliably in sections up to 40 mm (1.6 in) and achieves HRC 52–58 after induction hardening. DIN 41Cr4 and AISI 5140 are the closest international equivalents. 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 SCr440
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4105 | SCr440 | Japan | Reference |
| ASTM A29/A29M | AISI 5140 | North America | ✅ Nearest Exact (C 0.38–0.43%, Cr 0.70–0.90% — slightly lower Cr ceiling) |
| DIN EN 10083-1 | 41Cr4 / 1.7035 | Europe (Germany) | ✅ Nearest Exact (C 0.38–0.45%, Cr 0.90–1.20% — essentially identical range) |
| EN 10083-1 | 41Cr4 / 1.7035 | Europe | ✅ Nearest Exact |
2. Chemical Composition
| Element | JIS SCr440 | AISI 5140 | DIN 41Cr4 |
|---|---|---|---|
| C | 0.38–0.43% | 0.38–0.43% | 0.38–0.45% |
| Si | 0.15–0.35% | 0.15–0.35% | ≤ 0.40% |
| Mn | 0.60–0.85% | 0.70–0.90% | 0.60–0.90% |
| P | ≤ 0.030% | ≤ 0.035% | ≤ 0.025% |
| S | ≤ 0.030% | ≤ 0.040% | ≤ 0.035% |
| Cr | 0.90–1.20% | 0.70–0.90% | 0.90–1.20% |
| Mo | — (none) | — (none) | — (none) |
Sources: JIS G4105:2015, ASTM A29/A29M, DIN EN 10083-1
3. Mechanical Properties
3-1. After Q+T — Multiple Temper Temperatures (Section ≤ 25 mm / 1 in)
| Temper Temperature | Tensile Strength | Hardness |
|---|---|---|
| 400°C (752°F) | ~1100–1200 MPa (160–174 ksi) | HRC 36–43 |
| 550°C (1022°F) | ~850–950 MPa (123–138 ksi) | HRC 26–34 |
| 650°C (1202°F) | ~700–800 MPa (102–116 ksi) | HRC 22–30 |
3-2. Normalized Condition
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Tensile strength | ≥ 690 MPa | ≥ 100 ksi |
| Yield strength | ≥ 440 MPa | ≥ 63.8 ksi |
| Elongation | ≥ 20% | ≥ 20% |
| Hardness | HB 163–241 | HB 163–241 |
3-3. Induction Hardened Surface (Section ≤ 25 mm / 1 in)
| Property | Value |
|---|---|
| Surface hardness | HRC 52–58 |
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) | 11.5 × 10⁻⁶ /°C | 6.4 × 10⁻⁶ /°F |
| Specific heat | ~477 J/(kg·K) | 0.114 BTU/(lb·°F) |
5. Heat Treatment Conditions
| Process | Temperature | Cooling | Purpose |
|---|---|---|---|
| Normalizing | 840–880°C (1544–1616°F) | Air cool | Refine grain before machining |
| Annealing | 820–860°C (1508–1580°F) | Furnace cool | Soften for machining |
| Through-hardening quench | 830–870°C (1526–1598°F) | Oil quench | Full-section hardening |
| Tempering | 400–650°C (752–1202°F) | Air cool | Adjust strength/toughness balance |
| Induction hardening | 860–920°C (1580–1688°F) surface | Water or oil quench | Surface hardness HRC 52–58 |
6. Machinability
- Rating: approximately 60% vs AISI 1212 baseline (100%)
- Similar to S45C but Cr addition marginally improves chip formation
- Anneal before heavy rough machining to reduce tool wear and improve surface finish
- Carbide tooling recommended for production runs
- After induction hardening, grinding only for finishing
7. Weldability
- Rating: Restricted. Carbon equivalent (Ceq) ≈ 0.55–0.67
- Preheat to 150–200°C (302–392°F) required for all section sizes
- Low-hydrogen welding consumables essential
- Post-weld stress relief at 550–600°C (1022–1112°F) strongly recommended
- SCr440 should not be specified for welded assemblies — select S35C or SM490 instead
SCr440 vs SCM440: SCr440 contains no molybdenum, giving it lower hardenability than SCM440 for large sections. For sections up to 30 mm (1.2 in), SCr440 is sufficient and more economical. For sections greater than 50 mm (2 in), SCM440 provides significantly better through-hardness due to Mo’s hardenability contribution.
8. Common Mistakes
Without molybdenum, hardenability drops sharply for diameters greater than 50 mm (2 in). Core hardness after oil quench may fall below HRC 25, which is insufficient for most structural and wear applications at that section size. For large sections, upgrade to SCM440 (with Mo) or SCM445. Always check the Jominy end-quench curve for your required section before specifying SCr440.
Both grades contain approximately 0.40% carbon and are through-hardenable. The key difference is SCr440’s 0.90–1.20% Cr addition, which boosts hardenability and delivers 10–15 HRC deeper hardness at the same section size compared to S45C. SCr440 costs more — justify the upgrade based on your actual section size and required core hardness, not by habit.
9. When to Choose SCr440
- ✅ Medium shafts, axles, and bolts with section ≤ 40 mm (1.6 in) where Cr hardenability is sufficient
- ✅ Induction-hardened parts requiring HRC 52–58 surface hardness
- ✅ Applications where DIN 41Cr4 or AISI 5140 is the design standard in European or North American supply chains
- ✅ Cost-sensitive designs where SCM440’s Mo premium is not justified by section size or load requirements
- ❌ Sections greater than 50 mm (2 in) requiring deep through-hardness — use SCM440
- ❌ Welded assemblies — use S35C or SM490
- ❌ Applications requiring surface hardness greater than HRC 58 — use S48C or S55C with induction hardening
10. Frequently Asked Questions
Q: What is the difference between SCr440 and SCM440?
SCM440 adds Mo (0.15–0.30%) to the Cr base, significantly increasing hardenability for large sections. For sections up to 30 mm (1.2 in), both grades achieve similar hardness after oil quench. For sections greater than 50 mm (2 in), SCM440 core hardness is typically 5–10 HRC higher due to Mo’s hardenability contribution. Choose SCr440 for smaller parts to avoid Mo cost; specify SCM440 for larger structural components where consistent through-hardness is required.
Q: Is DIN 41Cr4 interchangeable with SCr440?
Yes, for most practical purposes. DIN 41Cr4 (C 0.38–0.45%, Cr 0.90–1.20%) overlaps almost completely with SCr440. The DIN grade has a slightly wider carbon range with an upper end of 0.45% vs SCr440’s 0.43%, which can produce marginally higher hardness at the upper composition bound. Verify mill certificates when tight hardness tolerances apply — otherwise the grades are functionally interchangeable.
Q: Can SCr440 achieve HRC 55 after induction hardening?
Yes, reliably for sections up to 25 mm (1 in). The surface carbon content at 0.38–0.43% C is sufficient to achieve HRC 52–58 with proper induction heating parameters. For larger sections or lower-frequency induction heating, HRC 52–55 is more typical. If HRC 58 or greater is required, switch to a higher-carbon grade such as S48C or S50C.
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