SCr430 is JIS G4105’s medium-carbon chromium alloy steel delivering 750–1100 MPa tensile strength after quench and temper. It occupies the strength tier between plain carbon S45C and the higher-carbon SCr440, offering better toughness and easier machining than SCr440 while exceeding plain carbon grades in hardenability. This guide covers international equivalents, composition, mechanical and physical properties, heat treatment, and selection guidance for manufacturing engineers.
- International Equivalent Grades
- Chemical Composition
- Mechanical Properties
- Physical Properties
- Heat Treatment Conditions
- Machinability
- Weldability
- Common Mistakes
- When to Choose SCr430
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4105 | SCr430 | Japan | Reference |
| ASTM A29/A29M | AISI 5130 | USA | ✅ Nearest Exact |
| DIN EN 10083-1 | 28Cr4 / 1.7030 | Germany / Europe | ⚠️ Nearest Equivalent |
| EN 10083-1 | 28Cr4 / 1.7030 | Europe | ⚠️ Nearest Equivalent |
AISI 5130 is the closest match: C 0.28–0.33% and Cr 0.80–1.10% vs SCr430’s Cr 0.90–1.20%. The slightly lower Cr in 5130 is negligible for sections ≤ 25 mm (1 in). DIN 28Cr4 has a lower C minimum (0.25% vs 0.28%), which is noted in the Common Mistakes section.
2. Chemical Composition
| Element | JIS SCr430 | AISI 5130 | DIN 28Cr4 |
|---|---|---|---|
| C | 0.28–0.33% | 0.28–0.33% | 0.25–0.32% |
| 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% | 0.80–1.10% | 0.90–1.20% |
Sources: JIS G4105:2015, ASTM A29/A29M, DIN EN 10083-1
3. Mechanical Properties
3-1. Normalized Condition
| Property | Metric | Imperial |
|---|---|---|
| Tensile strength | ≥ 620 MPa | ≥ 90 ksi |
| Yield strength (0.2%) | ≥ 390 MPa | ≥ 56.6 ksi |
| Elongation | ≥ 22% | ≥ 22% |
| Hardness | 156–217 HB | 156–217 HB |
3-2. Quench and Temper (Oil Quench + Temper)
| Temper Temp | Tensile | Hardness |
|---|---|---|
| 400°C (752°F) | ~1000–1100 MPa (145–160 ksi) | HRC 33–40 |
| 550°C (1022°F) | ~780–880 MPa (113–128 ksi) | HRC 25–33 |
| 650°C (1202°F) | ~640–730 MPa (93–106 ksi) | HRC 20–27 |
3-3. Induction Hardening (Surface, Section ≤ 25 mm / 1 in)
| Condition | Surface Hardness |
|---|---|
| Induction hardened | HRC 50–56 |
4. Physical Properties
| Property | Metric | 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) | 11.5 × 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 | 850–890°C (1562–1634°F) | Air cool | Grain refinement, stress relief |
| Annealing | 830–870°C (1526–1598°F) | Furnace cool | Softening for machining |
| Hardening (oil quench) | 840–880°C (1544–1616°F) | Oil | Achieve full martensite |
| Tempering | 400–650°C (752–1202°F) | Air cool | Toughness / final strength |
| Induction hardening | 870–930°C (1598–1706°F) surface | Water or oil quench | Surface wear resistance HRC 50–56 |
6. Machinability
- Machinability approximately 65–70% relative to AISI 1212 free-machining steel in the annealed or normalized condition.
- Cutting speeds 10–15% higher than SCr440 in equivalent conditions due to lower carbon content.
- Carbide tooling (P20–P30 grade) recommended for production turning; HSS acceptable for small batches.
- Chip formation is consistent in the normalized condition. Gummy behavior may occur if hardness drops below 150 HB — normalize before machining.
- Finish machine before final Q+T to minimize distortion from heat treatment.
7. Weldability
- Carbon equivalent: Ceq ≈ 0.46–0.58 (IIW formula). Preheat is mandatory for sections above 20 mm (0.79 in).
- Preheat temperature: 100–150°C (212–302°F) for t > 20 mm; maintain interpass temperature.
- Recommended process: SMAW with low-hydrogen electrodes (E7018 or equivalent), GMAW with ER70S-2, or GTAW for precision welds.
- Post-weld: Stress relief at 600–650°C (1112–1202°F) recommended. Avoid air quenching the weld zone.
- Design guidance: SCr430 is generally not recommended for welded assemblies in structural applications. Use low-alloy structural steels (e.g., SM490) where welding is the primary joining method.
8. Common Mistakes
SCr430 (0.28–0.33% C) has a maximum Q+T tensile of approximately 1100 MPa (160 ksi) — about 100 MPa lower than SCr440’s ceiling. For components designed to ≥ 1100 MPa tensile or surface hardness > HRC 56, SCr430 is under-specified. Specify SCr440 for higher-strength gears, or add Mo by switching to SCM430 where large section hardenability is also a concern.
DIN 28Cr4 allows carbon as low as 0.25% vs SCr430’s minimum of 0.28%. Heats supplied at the lower C bound of the DIN specification will produce 2–4 HRC less hardness after quenching compared to SCr430 heats at the lower C bound. For critical parts or precision applications, verify the mill certificate carbon value before accepting DIN 28Cr4 as a drop-in substitute.
9. When to Choose SCr430
- ✅ Medium-duty shafts and axles with section ≤ 40 mm (1.6 in) requiring 750–1000 MPa tensile after Q+T
- ✅ When AISI 5130 is the design-specified grade and JIS procurement is required
- ✅ Connecting rods and steering components in light automotive and agricultural machinery
- ✅ Applications where SCr440 would over-specify hardness and reduce toughness unnecessarily
- ✅ Induction-hardened shafts needing surface HRC 50–56 with a tough core
- ❌ High-hardness applications requiring tensile > 1100 MPa — use SCr440 or SCM440
- ❌ Large sections > 50 mm (2 in) — insufficient hardenability; use SCM430 (adds Mo)
- ❌ Welded structural assemblies — use a weldable structural grade instead
- ❌ Carburizing applications — carbon too high for effective case-to-core gradient; use SCr415
10. FAQ
Q: What is the difference between SCr430 and SCr440?
Carbon content is the key differentiator: SCr430 (0.28–0.33% C) vs SCr440 (0.38–0.43% C). After equivalent Q+T, SCr440 achieves approximately 100–150 MPa higher tensile strength and 5–8 HRC higher surface hardness. SCr430 offers better toughness and easier machining. Choose SCr430 for medium-strength shafts and axles (750–1000 MPa range); choose SCr440 for higher-strength gears and axles needing 1000 MPa or above.
Q: Is AISI 5130 a direct substitute for SCr430?
Very close. AISI 5130 specifies Cr 0.80–1.10% vs SCr430’s 0.90–1.20% — a slightly narrower Cr window. For sections ≤ 25 mm (1 in), the difference is negligible and the grades are interchangeable for engineering purposes. For larger sections (25–40 mm), the SCr430 Cr advantage can improve core hardness by approximately 2–3 HRC in oil quench conditions. Confirm composition from mill certificates for critical applications.
Q: Can SCr430 be carburized?
Not practical. With 0.28–0.33% C, the core carbon is too high to establish the sharp case-to-core carbon gradient needed for effective carburizing. The resulting case depth and core toughness will be inferior to purpose-made carburizing grades. SCr430 is a through-hardening grade. For surface-hardened gears requiring a carburized case, specify SCr415 (0.13–0.18% C) or SCM415 for sections requiring deeper hardenability.
Q: What industries most commonly use SCr430?
SCr430 sees primary use in light to medium automotive components (steering knuckles, connecting rods), agricultural machinery (pivot pins, axle shafts), and medium-duty fasteners (bolts M16–M36 in strength grade 10.9 range). It is common in Japanese supply chains and is directly sourced via AISI 5130 in North American manufacturing.
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