JIS S48C is a medium-high carbon machine structural steel defined under JIS G4051, with a carbon content of 0.45–0.51%. It sits one step above S45C in the carbon ladder, delivering induction-hardened surface hardness of HRC 56–62 — a meaningful step up for sliding surfaces, sprockets, crankshafts, and cams where S45C hardness margins are too tight. Weldability is severely restricted. Internationally it aligns with AISI 1049 (USA) and is close to DIN C50 (Germany).
- International Equivalent Grades
- Chemical Composition
- Mechanical Properties
- Physical Properties
- Heat Treatment Conditions
- Machinability
- Weldability
- Common Mistakes
- When to Choose S48C
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4051 | S48C | Japan | Reference |
| ASTM / AISI | 1049 | USA | ✅ Nearest Exact |
| ISO 683-1 | C50 | International | ⚠️ Nearest Equivalent |
| DIN | C50 / 1.0540 | Germany | ⚠️ Nearest Equivalent |
| EN | C50E / 1.1206 | Europe | ⚠️ Nearest Equivalent |
2. Chemical Composition
| Element | JIS S48C | AISI 1049 | DIN C50 |
|---|---|---|---|
| C | 0.45–0.51% | 0.46–0.53% | 0.47–0.55% |
| 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 | ≥ 640 MPa | ≥ 92.8 ksi |
| Yield Point | ≥ 380 MPa | ≥ 55.1 ksi |
| Elongation (GL=5d) | ≥ 14% | ≥ 14% |
| Reduction of Area | ≥ 35% | ≥ 35% |
| Hardness | 179–255 HB | 179–255 HB |
Induction hardening (surface, sections ≤ 30 mm / 1.2 in)
| Property | Value |
|---|---|
| Surface hardness | HRC 56–62 |
| Effective case depth | 1.0–3.0 mm (0.039–0.118 in) |
After through-hardening + temper (sections ≤ 25 mm / 1 in)
| Temper Temperature | Tensile Strength | Hardness |
|---|---|---|
| 400°C (752°F) | ~1000–1100 MPa (145–160 ksi) | HRC 36–43 |
| 550°C (1022°F) | ~800–900 MPa (116–130 ksi) | HRC 26–34 |
| 650°C (1202°F) | ~650–750 MPa (94–109 ksi) | HRC 20–28 |
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 | 49 W/(m·K) | 340 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 | ~486 J/(kg·K) | 0.116 BTU/(lb·°F) |
5. Heat Treatment Conditions
| Process | Temperature | Cooling | Purpose |
|---|---|---|---|
| Normalizing | 820–860°C (1508–1580°F) | Air cool | Refine grain, relieve stress |
| Annealing | 800–840°C (1472–1544°F) | Furnace cool | Soften for machining |
| Through-Hardening (quench) | 810–850°C (1490–1562°F) | Water or oil quench | Full-section hardening |
| Tempering | 400–650°C (752–1202°F) | Air cool | Adjust strength / toughness balance |
| Induction Hardening | 860–930°C surface (1580–1706°F) | Water or oil quench | Surface hardening HRC 56–62 |
6. Machinability
- Machinability rating: approximately 50–55% relative to AISI 1212 baseline (100%)
- Anneal or normalize before rough and finish machining
- Carbide tooling required for production runs; high-speed steel acceptable for light finishing only
- Induction-hardened surface finishing requires grinding — no cutting tool approach is viable
7. Weldability
S48C is in the difficult-to-weld category. The elevated carbon content raises HAZ hardening tendency significantly compared to S45C.
- Preheat: 125–175°C (257–347°F) for all sections over 10 mm (0.4 in); mandatory for restrained joints
- Process: Low-hydrogen consumables only — E7018 for SMAW, ER70S-6 for GMAW
- Post-weld: Stress relief at 550–600°C (1022–1112°F) strongly recommended
- Recommendation: Avoid specifying S48C in welded assemblies. If welding is a design requirement, substitute S35C or a structural grade.
8. Common Mistakes
The hardness gap between S45C and S48C after induction hardening is only 1–3 HRC under typical conditions. Before switching grades, verify that the S45C heat treatment process (austenitizing temperature, quench severity, section size) is properly optimized. In many cases, the apparent shortfall in S45C hardness is a process issue, not a material limitation. Switching to S48C adds cost and restricts weldability without solving the root cause.
S48C’s Ceq is high enough that HAZ cold cracking is a serious risk in any restrained joint without rigorous preheat. Engineers who apply S45C welding procedures to S48C without adjustment regularly encounter cracking, especially in cold environments or thick sections. S48C should be treated as a non-weldable grade for practical design purposes.
9. When to Choose S48C
- ✅ Sprockets, cams, and crankshafts requiring induction surface hardness of HRC 56–62
- ✅ Sliding surface components where S45C cannot reliably meet a minimum HRC 58 specification
- ✅ Direct replacement for AISI 1049 in North American-designed parts manufactured in Japan
- ✅ Machining-only applications with no welding in the production or service workflow
- ❌ Welded assemblies of any kind — use S35C or SM490
- ❌ Maximum hardness above HRC 62 — use S55C or a tool steel grade
- ❌ Large cross-sections requiring deep through-hardness — upgrade to SCM445 or SCM450
10. FAQ
Q: What is the practical difference between S48C and S45C?
Surface hardness after induction hardening: S45C reaches HRC 55–62, S48C reaches HRC 56–62. The overlap is large and in most applications the grades are interchangeable. S48C becomes the justified choice when a minimum hardness guarantee of HRC 58 or higher is needed, and the component will not be welded. The weldability trade-off is real — S48C’s higher Ceq requires more demanding preheat and process control.
Q: Can DIN C50 substitute for S48C?
Close, but not identical. DIN C50 allows carbon up to 0.55%, which is higher than S48C’s 0.51% ceiling. At the upper end of the C50 range, as-quenched hardness will be higher and toughness marginally lower. For most applications the difference is inconsequential. When precision heat treatment response is specified, verify the actual mill carbon value from the material certificate before substituting.
Q: Can S48C reliably achieve HRC 60 or above in induction hardening?
Not guaranteed across all heats. S48C’s carbon range of 0.45–0.51% means that heats at the lower end (0.45–0.47% C) may achieve only HRC 56–58 under standard induction hardening conditions. If HRC 60 minimum is a hard requirement across production lots, S55C is the safer specification — its higher carbon floor makes the target more consistent.
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