C75
1.0605High-carbon unalloyed spring steel. Near-eutectoid composition (0.70-0.80% C). Excellent elastic properties after hardening and tempering. Limited hardenability — effective oil quench diameter ≤12mm. Cost-effective for small/medium springs. Used for spring wire, clock springs, saw blades, retaining rings, and precision strip springs. ≈ AISI 1075.
International equivalents
| Flag | Standard | Country | Grade | Number | Match |
|---|---|---|---|---|---|
| 🇺🇸 | AISI | USA | AISI 1075 | — | REF |
| 🇪🇺 | EN | Europe | C75 / C75S | 1.0605 / 1.1248 | 100% |
| 🇯🇵 | JIS | Japan | S75C | — | 95% |
Sources: ASTM A29, EN 10132-4, JIS G4801
Chemical composition comparison (wt%)
Side-by-side: C75 (EN) (EN 10132-4) vs S75C (JIS)
| Element | C75 (EN) | S75C (JIS) | Overlap |
|---|---|---|---|
| C | 0.7–0.8% | — | — |
| Si | 0.15–0.35% | — | — |
| Mn | 0.6–0.9% | — | — |
| P | 0–0.025% | — | — |
| S | 0–0.025% | — | — |
| Cr | 0–0.4% | — | — |
Mechanical properties
QT
| Property | Value | Unit |
|---|---|---|
| Tensile Strength | 850–1100 | MPa |
| Yield Strength | 500–700 | MPa |
| Elongation | 8–12 | % |
| Elastic Modulus | ≥ 210 | GPa |
| Density | ≥ 7.85 | g/cm3 |
Annealed
| Property | Value | Unit |
|---|---|---|
| Tensile Strength | ≤ 650 | MPa |
| Hardness HB | ≤ 248 | HB |
Heat treatment
| Process | Temperature | Medium | Holding Time | Notes |
|---|---|---|---|---|
| hardening | 780–820 °C | oil or water | — | Water for max hardness, oil for less distortion. Effective ≤12mm |
| tempering | 350–500 °C | air | — | Spring temper 380-420°C for ~45 HRC |
Compatibility verdict
C75 and S75C: 95% composition match
Close equivalents but NOT identical.
Related materials
S355JR
1.0045High-strength low-alloy structural steel with minimum yield strength of 355 MPa. Standard grade for bridges, buildings, cranes, and general structural applications. Impact tested at +20°C (JR).
S690QL
1.8928High-strength quenched and tempered fine-grain structural steel with minimum yield strength of 690 MPa. Used for heavily loaded structures like mobile cranes, mining equipment, bridges, and pressure vessels.
S275JR
1.0044Medium-strength structural steel with minimum yield strength of 275 MPa. Bridges the gap between S235JR and S355JR. Used for general structural applications, lattice towers, masts, and light crane components. Impact tested at +20°C (JR).
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