C75 vs C55: Both unalloyed spring steels — C75 much harder but more brittle
C75 vs C55
Side-by-side chemical composition and mechanical property comparison.
Overview
C75
1.0605
High-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.
C55
1.0535
Medium-high carbon unalloyed steel. Higher strength than C45 with reduced weldability. Used for rail wheels, agricultural equipment, springs, hand tools, and wear-resistant parts. Often used for induction-hardened components.
| C75 | C55 | |
|---|---|---|
| Material Number | 1.0605 | 1.0535 |
| Category | Carbon Steel | Carbon Steel |
| Standard | EN 10132-4 | EN 10083-2 |
Chemical composition (wt%)
| Element | C75 | C55 | Overlap |
|---|---|---|---|
| C | 0.7–0.8% | 0.52–0.6% | No overlap |
| Si | 0.15–0.35% | 0–0.4% | OK |
| Mn | 0.6–0.9% | 0.6–0.9% | OK |
| P | 0–0.025% | 0–0.03% | OK |
Mechanical properties
| Property | C75 | C55 | Unit |
|---|---|---|---|
| tensile_strength | 850–1100 | 800–950 | MPa |
| yield_strength | 500–700 | ≥ 420 | MPa |
| elongation | 8–12 | ≥ 13 | % |
Compatibility Assessment
C75 achieves 58-62 HRC (vs ~50-55 for C55) but is more brittle and harder to machine. C55 has better toughness and wider applications beyond springs. Choose C75 for maximum hardness springs/saw blades; C55 for general engineering with spring properties.
Frequently Asked Questions
Is C75 the same as C55?
C75 and C55 have a 70% composition overlap. Both unalloyed spring steels — C75 much harder but more brittle
Can I replace C75 with C55?
In many cases, yes. The compositions overlap significantly (70%). However, always verify mechanical property requirements and heat treatment compatibility for your specific application.
What is the difference between C75 and C55?
The main differences are in the following elements: C. C75 is a Carbon Steel grade, while C55 is a Carbon Steel grade.
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Data provided for reference only. Always verify against the applicable specification for critical applications.
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