SCr435 is JIS G4105’s mid-range chromium alloy steel, bridging the gap between SCr430 (0.28–0.33% C) and SCr440 (0.38–0.43% C). It delivers 820–1150 MPa tensile strength after quench and temper — making it the right choice when SCr430 is under-specified but SCr440 would over-harden the component. This guide provides complete international equivalent grades, composition, mechanical and physical properties, heat treatment parameters, and selection criteria for manufacturing engineers.
- International Equivalent Grades
- Chemical Composition
- Mechanical Properties
- Physical Properties
- Heat Treatment Conditions
- Machinability
- Weldability
- Common Mistakes
- When to Choose SCr435
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4105 | SCr435 | Japan | Reference |
| ASTM A29/A29M | AISI 5135 | USA | ✅ Nearest Exact |
| DIN EN 10083-1 | 34Cr4 / 1.7033 | Germany / Europe | ⚠️ Nearest Equivalent |
| EN 10083-1 | 34Cr4 / 1.7033 | Europe | ⚠️ Nearest Equivalent |
AISI 5135 is the closest match with identical C range (0.33–0.38%) and overlapping Cr (0.80–1.05% vs SCr435’s 0.90–1.20%). DIN 34Cr4 is a near equivalent — note the lower C minimum (0.30% vs 0.33%) discussed in Common Mistakes. AISI 5135 is less commonly stocked in North America than 5140; confirm availability before specifying.
2. Chemical Composition
| Element | JIS SCr435 | AISI 5135 | DIN 34Cr4 |
|---|---|---|---|
| C | 0.33–0.38% | 0.33–0.38% | 0.30–0.37% |
| Si | 0.15–0.35% | 0.15–0.35% | ≤ 0.40% |
| Mn | 0.60–0.85% | 0.60–0.80% | 0.60–0.90% |
| P | ≤ 0.030% | ≤ 0.035% | ≤ 0.025% |
| S | ≤ 0.030% | ≤ 0.040% | ≤ 0.035% |
| Cr | 0.90–1.20% | 0.80–1.05% | 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 | ≥ 660 MPa | ≥ 95.7 ksi |
| Yield strength (0.2%) | ≥ 420 MPa | ≥ 60.9 ksi |
| Elongation | ≥ 20% | ≥ 20% |
| Hardness | 167–229 HB | 167–229 HB |
3-2. Quench and Temper (Oil Quench + Temper)
| Temper Temp | Tensile | Hardness |
|---|---|---|
| 400°C (752°F) | ~1050–1150 MPa (152–167 ksi) | HRC 34–42 |
| 550°C (1022°F) | ~820–920 MPa (119–133 ksi) | HRC 26–34 |
| 650°C (1202°F) | ~660–760 MPa (96–110 ksi) | HRC 20–28 |
3-3. Induction Hardening (Surface, Section ≤ 25 mm / 1 in)
| Condition | Surface Hardness |
|---|---|
| Induction hardened | HRC 52–58 |
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 | 840–880°C (1544–1616°F) | Air cool | Grain refinement, stress relief |
| Annealing | 820–860°C (1508–1580°F) | Furnace cool | Softening for machining |
| Hardening (oil quench) | 830–870°C (1526–1598°F) | Oil | Full martensite transformation |
| Tempering | 400–650°C (752–1202°F) | Air cool | Final strength and toughness |
| Induction hardening | 860–920°C (1580–1688°F) surface | Water or oil quench | Surface wear resistance HRC 52–58 |
6. Machinability
- Machinability approximately 60–65% relative to AISI 1212 free-machining steel in normalized condition.
- Higher carbon content than SCr430 makes SCr435 marginally more difficult to machine; cutting speeds should be reduced by 5–8% compared to SCr430 parameters.
- Carbide tooling (P20–P30 grade) recommended for production turning and milling.
- Machine in the annealed or normalized condition before final Q+T whenever section geometry allows.
- Work hardening tendency is moderate; maintain consistent chip load to prevent rubbing.
7. Weldability
- Carbon equivalent: Ceq ≈ 0.50–0.63 (IIW formula). Preheat is mandatory for all sections above 20 mm (0.79 in).
- Preheat temperature: 125–175°C (257–347°F); maintain interpass temperature at minimum preheat level.
- Recommended process: SMAW with low-hydrogen electrodes (E7018 class), GMAW with ER70S-2. Avoid cellulosic electrodes.
- Post-weld: Stress relief at 600–650°C (1112–1202°F) is strongly recommended to reduce HAZ hardness and cold cracking risk.
- Design guidance: SCr435 is practically non-weldable in fabricated assemblies. If welding is required in the design, substitute a lower-carbon structural alloy steel.
8. Common Mistakes
Designers frequently jump directly from SCr430 to SCr440, missing SCr435 as an intermediate option. When the required tensile strength is 900–1100 MPa — below the peak achievable with SCr440 but above SCr430’s practical ceiling — SCr435 may deliver the optimal balance of strength, toughness, and cost. This is particularly relevant for heavy structural bolts and agricultural axle pins where SCr440 properties are unnecessarily high and add procurement cost.
AISI 5135 is less common than AISI 5140 (the closer analog to SCr440) in North American service centers. Specifying 5135 on a drawing without confirming stock availability can cause lead-time surprises. In many cases, procurement will substitute 5140 without engineering notification. If the intermediate carbon range of SCr435/5135 is deliberately specified, call it out explicitly in procurement documentation and pre-qualify the substitution rule.
9. When to Choose SCr435
- ✅ Heavy structural bolts (M24–M48 range) requiring 900–1100 MPa tensile after Q+T
- ✅ Agricultural machinery axles and PTO pins where SCr440 would over-specify hardness
- ✅ Induction-hardened shafts where HRC 52–58 surface is the target
- ✅ Applications where AISI 5135 is the design-specified standard grade
- ✅ Medium-duty gear blanks where intermediate carbon provides toughness advantage over SCr440
- ❌ High-hardness applications requiring surface > HRC 58 — use SCr440 or S48C
- ❌ Large sections > 50 mm (2 in) — add Mo by specifying SCM435 or SCM440
- ❌ Welded fabricated assemblies
- ❌ Carburizing applications — carbon too high; use SCr415 or SNCM220
10. FAQ
Q: How does SCr435 compare to SCr440?
The primary difference is carbon content: SCr435 (0.33–0.38% C) vs SCr440 (0.38–0.43% C). In equivalent Q+T conditions, SCr440 achieves approximately 50–100 MPa higher tensile strength and 2–3 HRC higher hardness. SCr435 offers marginally better core toughness. For most production applications, SCr440 is preferred due to wider stock availability in global markets. SCr435 is specified when the tighter AISI 5135 composition range is deliberately required for the design or when the intermediate strength tier is intentional.
Q: Is DIN 34Cr4 interchangeable with SCr435?
Largely yes, with one important caution. DIN 34Cr4 allows C as low as 0.30% vs SCr435’s minimum of 0.33%. At the lower C bound, 34Cr4 heats will produce slightly less hardness after quenching — approximately 2–3 HRC lower in worst-case comparison. For non-critical applications this difference is negligible. For precision-controlled heat treatment batches or when hardness bands are tight, verify the mill certificate C value before treating the grades as fully equivalent.
Q: What applications commonly use SCr435?
SCr435 finds use in heavy truck axle shafts, agricultural PTO shafts and yokes, structural fasteners in the M24–M48 bolt range, and gear blanks for medium-duty applications where the intermediate strength-toughness balance is deliberately specified. It is less common in production databases than SCr430 or SCr440 but is explicitly called out in designs that originated from AISI 5135 specifications in North American or European engineering environments.
Q: Can SCr435 replace SCr430 without design review?
Not recommended without review. While SCr435 is the next step up in carbon content, substituting it for SCr430 raises the as-tempered hardness and reduces toughness slightly. In components where ductility or fatigue resistance at a specific strength level were the design basis, the substitution may move properties outside the design envelope. Always perform a formal material substitution review and update heat treatment parameters.
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