Spring steel C75S (1.1248) datasheet
C75S is an unalloyed spring steel with about 0.75 % carbon, supplied as strip either hardened and tempered (+QT) or annealed. Hardened it springs; annealed it can be formed and hardened afterwards. Below are the values to EN 10132, with their sources.
Standard: EN 10132 · Sources checked on October 21, 2026
Designations
| EN name | C75S |
|---|---|
| Material number | 1.1248 |
| Former DIN name | Ck75 |
| AISI | 1075 (comparable) |
| UNS | G10750 (comparable) |
Comparable means similar in composition and use, but made to another standard with its own limits. Before substituting one for the other, check both standards.
Chemical composition
Ladle analysis in % by mass.
| Element | min. | max. |
|---|---|---|
| C | 0.7 | 0.8 |
| Si | 0.15 | 0.35 |
| Mn | 0.6 | 0.9 |
| P | – | 0.025 |
| S | – | 0.025 |
| Cr | – | 0.4 |
| Ni | – | 0.4 |
| Mo | – | 0.1 |
Mechanical properties
EN 10132:2021 replaced EN 10132-4. For +QT the range is 1200 to 1900 MPa; within it, a band 150 MPa or 50 HV wide is ordered. The inspection certificate states which band was delivered.
| Condition | Thickness (mm) | Rp0.2 (MPa) | Rm (MPa) | A80 (%) | Hardness (HV) |
|---|---|---|---|---|---|
| Annealed (+A, +LC) | – | ≤ 510 | ≤ 640 | ≥ 15 | ≤ 200 |
| Hardened and tempered (+QT) | 0.3–3 | – | 1200–1900 | – | 370–580 |
None of the sources gives an elongation for +QT; Wälzholz puts the ratio of yield to tensile strength above 90 %. EN 10132 covers +QT for thicknesses from 0.30 to 3.00 mm. Thinner strip such as 0.2 mm lies outside the standard; for it, the maker's own figures apply.
Physical properties
| Density | 7.9 g/cm³ |
|---|---|
| Elastic modulus | 210 GPa (at 20 °C) |
| Thermal expansion | 11 × 10⁻⁶/K (at 20–100 °C) |
| Specific heat capacity | 460 J/(kg·K) (at 50–100 °C) |
| Magnetic | Magnetic |
Guidance values from the datasheets of two strip makers; EN 10132 sets no physical properties. Thermal conductivity is left out because the two sources are too far apart (35 to 52 W/(m·K)).
Processing
Laser cutting
Parts laser cut from hardened strip (+QT) need no heat treatment afterwards. None of the sources quantifies how much the heat changes the hardness at the cut edge; for unhardened strip, h+s describes a harder, less tough cut zone and recommends waterjet cutting for critical parts.[7][6]
Forming and bending
Annealed (+LC), C75S still forms easily and is hardened afterwards. Hardened strip cracks easily at tight radii; it suits parts that are barely formed.[7]
Heat treatment
Matthey gives hardening at 790 to 820 °C with quenching in oil or water, and tempering at 350 to 700 °C. Strip in the +QT condition is already hardened and tempered.[5]
Welding
Not suitable for welding, because of its carbon content of about 0.75 %.[6]
Surface
Hardened strip comes oxide grey to blue, bright hardened, polished, or polished and coloured blue or yellow by tempering.[2]
Corrosion
Not corrosion resistant. The strip arrives lightly oiled and needs corrosion protection in service, such as paint.[6]
High Carbon Steel C75S +QT (1.1248) at Dynamic Parts
We cut parts from 0.2 mm, 0.3 mm, 0.5 mm, 0.8 mm, and 1 mm, up to 550 × 1150 mm, from a single piece. The material page lists prices for every thickness, and the configurator prices a part of your own straight away.
See pricesSources
- SIJ Acroni: Technical Data Sheet SIQUAL 1248 (C75S, 1.1248), 07-2023. Accessed on October 21, 2026.
- Metalle Schmidt: Bandstahl mit hohem C-Gehalt: martensitgehärtet (+QT). Accessed on October 21, 2026.
- C.D. Wälzholz: Hardened and tempered steel strip, metric data sheet, 11/2025. Accessed on October 21, 2026.
- ÚNMS SR: STN EN 10132, Cold rolled narrow steel strip for heat treatment (EN 10132:2021), preview, January 2022. Accessed on October 21, 2026.
- Lamineries Matthey: Steel Ck75 (1.1248), data sheet, v22E. Accessed on October 21, 2026.
- h+s Präzisionsfolien: Material data sheet 1.1248 (C75S), July 2023. Accessed on October 21, 2026.
- Gutekunst Formfedern: Eigenschaften Federbandstahl C75S und 1.4310, 10.09.2021. Accessed on October 21, 2026.
The values come from the sources named and are given for guidance. What binds is the standard in its current edition and the inspection certificate for the batch delivered. Where sources differ, the value says so.