Quick Comparison at a Glance
| Parameter | CK75 | C75Cr1 |
|---|---|---|
| Common designation | CK75 / C75S / 1.1248 | C75Cr1 / 75Cr1 / 1.2003 |
| Reference standard | EN 10132-4 (cold-rolled spring steel strip) | DIN 17350 (tool steel); DIN EN ISO 4957 successor framework |
| Carbon (C) | 0.70–0.80% | 0.70–0.80% |
| Chromium (Cr) | ≤ 0.40% max (residual) | 0.30–0.40% (intentional alloy addition) |
| Silicon (Si) | 0.15–0.35% | 0.25–0.50% |
| Manganese (Mn) | 0.60–0.80% | 0.60–0.80% |
| Typical positioning | Non-alloy spring / general-purpose high-carbon strip | Low-alloy tool / saw-blade strip |
| Hardenability emphasis | Moderate; adequate for thin sections and conventional quench | Enhanced by Cr; more consistent response in thicker sections or demanding wear parts |
| Typical hardness (Q+T) | ~35–55 HRC depending on temper (broad range) | ~58–62 HRC after optimized hardening and tempering |
| Signature applications | Shutter springs, stamped parts, hand tools, watch components | TCT/PCD saw blade carriers, industrial knives, cutting tools |
1. Grade Designations and Applicable Standards
CK75 belongs to the EN 10132-4 family of cold-rolled narrow steel strip for heat treatment, specifically the spring steel and general high-carbon strip segment. Its material number is 1.1248, and it is also referenced as C75S or C75E in European delivery documents. The grade is conventionally treated as an unalloyed carbon steel because it contains no deliberate alloying addition beyond carbon and manganese; any chromium present is residual and capped at 0.40% max.
C75Cr1, by contrast, originates from the DIN 17350 tool steel tradition and carries the material number 1.2003. It is classified as a low-alloy tool steel because chromium is an intentional specification item at 0.30–0.40%. The current international framework for this grade family is DIN EN ISO 4957, which supersedes the older DIN 17350 for tool steel delivery conditions.
The standards difference is not cosmetic. EN 10132-4 is structured around cold-rolled strip for heat treatment, with temper designations and mechanical property tables oriented toward strip products. DIN 17350 / ISO 4957 is structured around tool steel condition and hardenability, reflecting a tooling rather than spring-strip delivery logic. This means a CK75 certificate and a C75Cr1 certificate answer different questions: the CK75 certificate emphasizes strip temper, dimensional tolerance, and tensile range, while the C75Cr1 certificate emphasizes tool-steel chemistry and hardening response.
2. Chemical Composition Comparison
The most important compositional fact is that carbon alone does not distinguish these grades. Both sit at 0.70–0.80% C, which places them in the same high-carbon, near-eutectoid territory. The meaningful differentiator lies in chromium and silicon.
CK75 chemistry (EN 10132-4 reference) is approximately:
- C: 0.70–0.80%
- Si: 0.15–0.35%
- Mn: 0.60–0.80%
- P: ≤ 0.025% (tight strip specification) or ≤ 0.035%
- S: ≤ 0.025% or ≤ 0.035%
- Cr: ≤ 0.40% max (residual, not an alloy addition)
This is consistent with the Matthey and Robert data sheets for 1.1248 / CK75.
C75Cr1 chemistry (DIN 17350 / DIN EN ISO 4957 reference) is approximately:
- C: 0.70–0.80%
- Si: 0.25–0.50%
- Mn: 0.60–0.80%
- P: ≤ 0.030%
- S: ≤ 0.030%
- Cr: 0.30–0.40%
These ranges are reported across multiple tool-steel data sources and are stable to the DIN 17350 specification.
3. Hardenability and Heat Treatment Considerations
Hardenability is the decisive technical axis for substitution decisions between these two grades.
CK75 is an unalloyed high-carbon steel. It responds well to conventional quenching and tempering, and in thin strip sections it can achieve high hardness because the short diffusion distance allows martensite formation even without strong alloy hardenability. However, as section thickness increases, the absence of deliberate alloying elements limits the depth of full hardening. Its typical hardened-and-tempered hardness range is often quoted broadly (roughly 35–55 HRC depending on temper and section), with the upper end accessible in thin strip and the lower end associated with higher tempering temperatures for toughness. Annealing is commonly performed in the 650–750 °C range, and austenitizing for oil quenching is typically around 810–840 °C.
C75Cr1 carries a deliberate chromium addition specifically to improve hardenability and wear resistance relative to plain carbon grades like C75 . Chromium raises the ideal critical diameter, slows the pearlite/bainite transformation, and allows more uniform through-hardening in thicker sections or in parts with complex geometry. This is why C75Cr1 is often specified for saw blade carriers and cutting tools where edge hardness and wear resistance must be maintained through the tool body, not just at the surface. Reported hardened hardness for C75Cr1 is commonly 58–62 HRC after appropriate austenitizing and tempering, with austenitizing temperatures in the 830–860 °C range and oil quenching. Annealing is typically performed around 700–720 °C, producing a soft machinable condition of roughly 160–200 HB.
Practical implication: If the application relies on through-hardening of a section thicker than thin strip, or if the part must maintain hardness after tempering at elevated temperatures, C75Cr1’s chromium is a functional advantage. If the part is thin strip and the hardness requirement is moderate, CK75’s leaner chemistry may be sufficient and more economical. The grade name alone does not tell you which condition you are in—the section size, quench severity, and required hardness profile do.
4. Typical Application Differences
CK75 is most frequently associated with spring-type and general-purpose high-carbon strip duties:
- Rolling shutter springs and spring elements
- Stamped parts with high mechanical requirements
- Hand tools, construction tools, and general metal parts
- Watch components, dials, and precision stamping in thin strip form
- Saw blades and cutting tools in non-severe, thin-section contexts
These applications leverage CK75’s good formability in the annealed condition, its ability to be hardened and tempered to a useful strength range, and its cost-effectiveness in thin cold-rolled strip.
C75Cr1 is more strongly positioned in tooling and cutting-edge duties:
- TCT (tungsten carbide-tipped) and PCD (polycrystalline diamond) saw blade carriers
- Industrial knives, band saw blades, and circular saw blade bodies
- Cold-work tools such as punches and small dies
- Wear parts requiring a combination of high hardness and abrasion resistance
- Components where edge retention and dimensional stability under cutting loads are critical
These applications value the chromium-bearing grade’s higher hardenability, its ability to reach 58–62 HRC, and its wear resistance in abrasive or high-load contact conditions.
There is overlap: both grades appear in spring and strip product lists, and both can be supplied annealed, cold-rolled, or quenched and tempered. But the center of gravity differs. CK75 leans toward elastic elements and general stamping; C75Cr1 leans toward cutting edges and wear-resistant tool bodies. This difference should guide preliminary grade selection, while final selection should be based on the specific mechanical property and heat-treatment requirements of the part.
5. How to Confirm Substitution Compatibility
Do not treat CK75 and C75Cr1 as interchangeable on the basis of the “75” carbon designation. A defensible substitution assessment should proceed through the following verification sequence.
Step 1 — Compare the actual certified chemistry, not the grade name. Request the mill certificate or heat analysis for the specific lot. Confirm Cr, Si, Mn, P, and S values against the governing standard. A CK75 lot near the upper residual Cr limit may behave more like a lean C75Cr1; a CK75 lot with very low Cr will not. Conversely, a C75Cr1 lot at the bottom of its Cr window may provide less hardenability margin than expected. The certificate is the only reliable basis for this comparison.
Step 2 — Define the required hardenability from the part, not from the grade. Specify the required surface hardness, case depth (if applicable), core hardness, and the maximum section thickness that must harden. Then compare the two candidate heats using hardenability data or, preferably, a Jominy end-quench test or a representative quench trial. A grade substitution that ignores section size and quench severity is a chemistry exercise, not an engineering validation.
Step 3 — Re-validate the heat-treatment cycle. CK75 and C75Cr1 do not share identical austenitizing or tempering windows. C75Cr1 generally requires a higher austenitizing temperature (830–860 °C) than CK75 (810–840 °C), and its tempering response will differ because of the chromium content. A substitution that retains the original CK75 cycle for a C75Cr1 lot may under- or over-austenitize, producing retained austenite, excessive grain growth, or insufficient hardness. Heat treatment must be re-established for the substitute grade.
Step 4 — Check the downstream process compatibility. C75Cr1’s higher alloy content and hardness potential can affect machinability, formability in the annealed state, weldability, and dimensional distortion during quenching. If the part is stamped, bent, or welded before hardening, confirm that the substitute grade’s annealed condition and forming response are acceptable. C75Cr1 is generally considered to have moderate machinability in the annealed condition but poor weldability due to its high carbon and chromium content.
Step 5 — Issue a limited qualification run before full production release. Produce a small batch of finished parts from the candidate substitute, subject them to the full production heat treatment, and test the properties that matter: hardness profile, microstructure, dimensional conformance, and any application-specific performance criterion (fatigue life, edge retention, wear rate). Only after this qualification should the substitution be released for routine production.
Frequently Asked Questions
Is C75Cr1 a direct replacement for CK75?
No. They share a nominal carbon range but differ in chromium intent and hardenability. C75Cr1 is a low-alloy tool steel with deliberate Cr; CK75 is an unalloyed carbon steel with residual Cr. Substitution requires chemistry verification and heat-treatment re-qualification.
Can CK75 achieve the same hardness as C75Cr1?
In thin strip sections, CK75 can reach high hardness after quenching and tempering, but its hardenability is lower because it lacks deliberate alloying. C75Cr1 is specifically formulated for more consistent through-hardening and wear resistance, with reported hardened hardness in the 58–62 HRC range.
Which grade is better for springs?
CK75 is more commonly associated with spring elements, shutter springs, and general elastic parts. C75Cr1 can be used in spring-type applications, but its primary positioning is tooling and cutting edges.
Which grade is better for saw blades?
C75Cr1 is the more typical choice for TCT/PCD saw blade carriers, band saw blades, and industrial knives because its chromium content supports hardenability and wear resistance at the cutting edge.
What is the single most important check before substituting?
The certified chromium value and the demonstrated hardenability for the actual section size. The grade name alone does not guarantee interchangeable performance.
Do CK75 and C75Cr1 use the same heat-treatment temperature?
No. CK75 is typically austenitized around 810–840 °C for oil quenching, while C75Cr1 is commonly austenitized at 830–860 °C. Tempering windows also differ. A substitution must include a re-established heat-treatment cycle.
