JIS S30C is a medium-carbon machine structural steel defined under JIS G4051, with a carbon content of 0.27–0.33%. It is the first grade in the G4051 series where the manganese range steps up to 0.60–0.90%, meaningfully improving hardenability over S25C. Through-hardening to HRC 50–55 on small sections is practical, and induction hardening is a common surface treatment. Internationally it matches AISI 1030 (USA) and aligns closely with DIN C30 (Germany).
- International Equivalent Grades
- Chemical Composition
- Mechanical Properties
- Physical Properties
- Heat Treatment Conditions
- Machinability
- Weldability
- Common Mistakes
- When to Choose S30C
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4051 | S30C | Japan | Reference |
| ASTM / AISI | 1030 | USA | ✅ Exact Match |
| ISO 683-1 | C30 | International | ⚠️ Nearest Equivalent |
| DIN | C30 / 1.0528 | Germany | ⚠️ Nearest Equivalent |
| EN | C30E / 1.1178 | Europe | ⚠️ Nearest Equivalent |
2. Chemical Composition
| Element | JIS S30C | AISI 1030 | DIN C30 |
|---|---|---|---|
| C | 0.27–0.33% | 0.28–0.34% | 0.27–0.34% |
| Si | 0.15–0.35% | 0.10–0.35% | ≤ 0.40% |
| Mn | 0.60–0.90% | 0.60–0.90% | 0.50–0.80% |
| P | ≤ 0.030% | ≤ 0.040% | ≤ 0.045% |
| S | ≤ 0.035% | ≤ 0.050% | ≤ 0.045% |
Sources: JIS G4051:2016, ASTM A29/A29M, DIN EN 10083-2
3. Mechanical Properties
As-normalized
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Tensile Strength | ≥ 470 MPa | ≥ 68.2 ksi |
| Yield Point | ≥ 295 MPa | ≥ 42.8 ksi |
| Elongation (GL=5d) | ≥ 21% | ≥ 21% |
| Reduction of Area | ≥ 50% | ≥ 50% |
| Hardness | 137–197 HB | 137–197 HB |
After through-hardening + temper (sections ≤ 30 mm / 1.2 in)
| Property | Water Quench | Oil Quench |
|---|---|---|
| Surface Hardness (as-quenched) | HRC 50–55 | HRC 42–50 |
| Hardness after temper at 550–650°C (1022–1202°F) | HRC 25–35 | HRC 22–32 |
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 | 50 W/(m·K) | 347 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 | ~486 J/(kg·K) | 0.116 BTU/(lb·°F) |
5. Heat Treatment Conditions
| Process | Temperature | Cooling | Purpose |
|---|---|---|---|
| Normalizing | 860–900°C (1580–1652°F) | Air cool | Refine grain, relieve stress |
| Annealing | 830–870°C (1526–1598°F) | Furnace cool | Soften for machining |
| Through-Hardening (quench) | 840–880°C (1544–1616°F) | Water or oil quench | Full-section hardening |
| Tempering (post through-harden) | 550–650°C (1022–1202°F) | Air cool | Restore toughness |
| Induction Hardening | 870–920°C surface (1598–1688°F) | Water or oil quench | Surface hardening to HRC 50–55 |
6. Machinability
S30C machines comparably to AISI 1030. The higher manganese content (vs. S25C) contributes marginally to chip formation and slightly improves surface finish relative to lower-Mn grades at the same carbon level.
- Machinability rating: approximately 60–65% relative to AISI 1212 baseline (100%)
- Normalized condition recommended for rough and semi-finish machining
- Finish grinding required after induction hardening or through-hardening
- Positive-rake tooling reduces cutting forces in the soft condition
7. Weldability
S30C marks the start of the range where preheat becomes a practical consideration. Its carbon equivalent (Ceq) of approximately 0.37–0.44 places it in the “conditionally weldable” zone.
- Preheat: 75–100°C (167–212°F) recommended for sections over 25 mm (1 in); not mandatory for thin sections in low-restraint joints
- Process: SMAW, GMAW, GTAW compatible; low-hydrogen consumables preferred
- Filler: ER70S-6 for GMAW; E7018 for SMAW
- Post-weld heat treatment: Stress relief at 550–600°C (1022–1112°F) recommended for high-restraint joints
8. Common Mistakes
The 0.05% carbon difference is secondary — the real change at S30C is the Mn range jumping from 0.60% max to 0.90% max. This makes S30C meaningfully more hardenable. Engineers who treat the two grades as interchangeable risk under- or over-hardening parts in through-hardening applications.
S30C is occasionally specified for carburized parts when the designer wants a “slightly tougher core.” In practice, the elevated carbon content makes the core harder but more brittle, which is the opposite of what carburizing aims to achieve. Use S20C or S15C for carburizing applications.
S30C’s Ceq sits in the range where hydrogen-induced cracking becomes possible without preheat, especially on sections over 25 mm (1 in) or in cold environments. Engineers accustomed to S20C and S25C (which rarely need preheat) may carry those assumptions into S30C work and encounter cold cracking.
9. When to Choose S30C
- ✅ Small-to-medium through-hardened shafts, pins, and keys where HRC 50–55 surface is sufficient
- ✅ Induction-hardened components requiring moderate surface hardness over a tough core
- ✅ Applications where S25C lacks sufficient hardenability and S35C/S45C is over-specified
- ✅ Cold-formed parts (bolts, studs) requiring moderate strength without alloy steel cost
- ❌ Carburizing applications — use S20C or S15C
- ❌ Large cross-sections (> 30 mm / 1.2 in) requiring consistent through-hardness — upgrade to SCM420/SCM440
- ❌ Structures requiring easy field weldability — use S25C or structural grades (SS400, SM400)
10. FAQ
Q: Is S30C exactly the same as AISI 1030?
Very close. The carbon ranges overlap almost completely (JIS: 0.27–0.33%, ASTM: 0.28–0.34%). The manganese ranges are identical. JIS G4051 sets tighter P and S limits, making S30C marginally cleaner. For most mechanical applications, S30C and 1030 are fully interchangeable.
Q: What makes S30C different from S25C despite only 0.05% more carbon?
The carbon increase is secondary. The key change is the manganese range — S30C jumps to 0.60–0.90% Mn from S25C’s 0.30–0.60%. Higher Mn improves hardenability independently of carbon, so S30C through-hardens noticeably deeper and to higher hardness than S25C in the same section size.
Q: What surface hardness does induction hardening achieve on S30C?
Typically HRC 50–55 on the surface for sections in the 25–50 mm (1–2 in) range. This is lower than the HRC 55–62 achievable with S45C or S50C. For wear-critical applications requiring maximum surface hardness, specify a higher-carbon grade or a Cr-Mo alloy steel.
Q: How does S30C compare to S35C for through-hardening?
S35C (0.32–0.38% C, Mn 0.60–0.90%) sits just above S30C and achieves HRC 53–58 surface hardness under similar quenching conditions — meaningfully harder than S30C’s HRC 50–55. If the application requires hardness at the upper end of the carbon-steel range, S35C is the more appropriate choice.
Q: Can DIN C30 be used as a direct substitute for S30C?
In most cases, yes. The primary difference is DIN C30’s lower Mn minimum (0.50% vs. JIS 0.60%), which could produce slightly less consistent hardenability at the low end of the Mn range. For non-critical applications this is inconsequential; for precision heat-treatment work, verify the actual Mn content from the mill certificate.
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