JIS S58C is the highest-carbon grade in the JIS G4051 machine structural steel series, with a carbon content of 0.55–0.61%. After water quenching, surface hardness reaches HRC 62–65 — approaching the lower range of tool steels. It is used for wear blades, agricultural implements, high-load wear shoes, and applications where maximum hardness from a carbon steel is required without the cost of alloy tool steel. Internationally it aligns with AISI 1060 (USA) and DIN C60 (Germany).
- International Equivalent Grades
- Chemical Composition
- Mechanical Properties
- Physical Properties
- Heat Treatment Conditions
- Machinability
- Weldability
- Common Mistakes
- When to Choose S58C
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4051 | S58C | Japan | Reference |
| ASTM / AISI | 1060 | USA | ⚠️ Nearest Equivalent |
| ISO 683-1 | C60 | International | ⚠️ Nearest Equivalent |
| DIN | C60 / 1.0601 | Germany | ⚠️ Nearest Equivalent |
| EN | C60E / 1.1221 | Europe | ⚠️ Nearest Equivalent |
2. Chemical Composition
| Element | JIS S58C | AISI 1060 | DIN C60 |
|---|---|---|---|
| C | 0.55–0.61% | 0.55–0.65% | 0.57–0.65% |
| Si | 0.15–0.35% | 0.10–0.35% | ≤ 0.40% |
| Mn | 0.60–0.90% | 0.60–0.90% | 0.60–0.90% |
| 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 | ≥ 690 MPa | ≥ 100.1 ksi |
| Yield Point | ≥ 400 MPa | ≥ 58.0 ksi |
| Elongation (GL=5d) | ≥ 11% | ≥ 11% |
| Reduction of Area | ≥ 30% | ≥ 30% |
| Hardness | 197–269 HB | 197–269 HB |
After quench + temper (sections ≤ 20 mm / 0.8 in)
| Temper Temperature | Hardness (HRC) | Typical Application |
|---|---|---|
| As-quenched (water) | HRC 62–65 | Maximum hardness (brittle — temper required) |
| 300–400°C (572–752°F) | HRC 52–60 | Wear blades, cutting edges |
| 400–500°C (752–932°F) | HRC 44–52 | Agricultural blades, wear shoes |
| 550–650°C (1022–1202°F) | HRC 28–38 | Impact-resistant wear parts |
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) | 11.1 × 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 |
| Spheroidizing Anneal | 740–770°C (1364–1418°F) | Furnace cool | Soften for machining / cold working |
| Through-Hardening (quench) | 790–830°C (1454–1526°F) | Water or oil quench | Maximum hardness HRC 62–65 |
| Wear Temper | 300–500°C (572–932°F) | Air cool | HRC 44–60 for wear applications |
| Toughening Temper | 550–650°C (1022–1202°F) | Air cool | HRC 28–38 for impact resistance |
6. Machinability
S58C is difficult to machine in normalized condition due to its high carbon content and resulting hardness (up to 269 HB normalized). Spheroidizing anneal is strongly recommended before any precision machining.
- Machinability rating: approximately 40–50% relative to AISI 1212 baseline (100%)
- Spheroidizing anneal reduces hardness to 170–210 HB — manageable for carbide tooling
- HSS tooling is not recommended for production runs in normalized condition
- All finishing after hardening must be done by grinding
7. Weldability
S58C is considered non-weldable for practical engineering purposes. Its carbon equivalent (Ceq ≈ 0.62–0.70) places it beyond the reliable welding range for standard processes.
- Risk: Extremely high susceptibility to hydrogen cracking and brittle HAZ formation
- Recommendation: Design S58C parts to require no welding. If joining is necessary, use mechanical fastening or bonding
- Emergency only: If welding is unavoidable, preheat to 300–400°C (572–752°F), use low-hydrogen electrodes, and perform post-weld stress relief immediately
8. Common Mistakes
S58C’s high hardness comes with trade-offs: poor toughness, poor weldability, and high quench cracking sensitivity. Before specifying S58C, confirm that S45C or S55C cannot meet the hardness requirement — in many cases they can, with far better processability.
As-quenched S58C is extremely brittle and under high residual stress. Parts left in the as-quenched state — even briefly — are prone to spontaneous cracking. Temper within minutes of quenching, before the part fully cools.
S58C reaches tool steel hardness levels but lacks the alloying elements (Cr, Mo, V, W) that give tool steels their wear resistance, red hardness, and dimensional stability. For dies, punches, and cutting tools that see repeated heating or abrasive wear, upgrade to SKD11, SKH51, or an equivalent tool steel.
9. When to Choose S58C
- ✅ Agricultural blades, tillage tools, and wear shoes requiring high hardness at low cost
- ✅ Wear-resistant liners and plates on small sections (≤ 20 mm / 0.8 in)
- ✅ High-hardness pins and rollers in non-impact wear applications
- ✅ When S55C’s maximum hardness is insufficient but full tool steel cost is unjustified
- ❌ Impact-loaded parts — brittleness at high hardness levels makes S58C prone to fracture under shock loading
- ❌ Welded assemblies — non-weldable at practical preheat levels
- ❌ Large sections — hardenability is limited to approximately 20 mm (0.8 in) for consistent through-hardening
- ❌ Precision dies and cutting tools — use SKD11, SK85, or dedicated tool steels
10. FAQ
Q: Is S58C equivalent to AISI 1060?
Nearest equivalent. S58C (C: 0.55–0.61%) and AISI 1060 (C: 0.55–0.65%) overlap in the lower carbon range, but 1060 allows up to 0.65% C, creating a wider spread. For most wear and hardening applications the grades behave similarly. Verify actual carbon content from the mill certificate when tight hardness control is critical.
Q: How does S58C compare to SK85 (carbon tool steel)?
SK85 (C: 0.80–0.90%) is a dedicated carbon tool steel with higher carbon, providing greater as-quenched hardness (up to HRC 65–67) and better wear resistance than S58C. SK85 is defined under JIS G4401 and has tighter cleanliness requirements. S58C is the structural steel option for applications that need high hardness without the cost premium of a tool steel specification.
Q: What tempering temperature gives the best balance of hardness and toughness in S58C?
For most wear applications, 400–450°C (752–842°F) provides a practical balance — HRC 48–55 with sufficient toughness to resist light impact. For applications with significant impact loading, temper at 550–600°C (1022–1112°F) to reach HRC 30–38, accepting the lower hardness in exchange for improved toughness.
Q: Why is S58C’s section limit for through-hardening smaller than S55C’s?
Both grades have similar hardenability because their Mn content is the same. The slightly higher carbon in S58C gives a marginally higher as-quenched hardness but does not significantly increase hardenability depth. For large sections requiring consistent through-hardness, add alloying elements (Cr, Mo) — use SCM440 or similar alloy steels.
Q: Can S58C be used for knife blades?
Yes, at the budget end of knife steel selection. It achieves the hardness range (HRC 55–60 after temper) used in commercial knives. However, dedicated stainless grades (SUS420J2, SUS440C) offer better corrosion resistance, and dedicated tool steels (SK95, SK85) offer better edge retention. S58C knives require diligent maintenance to prevent rust.
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