CK45 seamless precision steel tubes are cold drawn seamless tubes in medium carbon steel - European grade C45E, material number 1.1191, the same steel as AISI 1045 and JIS S45C. They carry 0.42–0.50% carbon, so unlike the low-carbon E235/E355 precision grades they can be quenched and tempered or induction-hardened for wear parts. The one number that decides your wall thickness is the yield you design to: 380 MPa normalized (+N) or 420 MPa stress-relieved (+SR) - not a single fixed value.
CK45 seamless precision steel tubes are built for machinery components that are machined, then often heat-treated after delivery - shafts, bushings, pistons, guide bars and cylinder barrels. The name CK45 fixes only the chemistry; the mill then chooses a CK45 delivery condition (+C +LC +SR +A +N) that moves the yield by about 40 MPa and the elongation by double digits, which is why the same tube can arrive at very different strengths.
We supply CK45 (C45E, 1.1191) to EN 10305-1 as cold drawn seamless tube in outside diameters from 4 mm to 380 mm (0.16–14.96 in) and wall thicknesses from 0.5 mm to 25 mm (0.02–0.98 in), with EN 10204 3.1 material certificates and third-party inspection on request. Send your OD × wall, delivery condition and quantity for a quotation.
Technical Specifications
| Parameter | Capability |
|---|---|
| Grade / material number | CK45 / C45E / 1.1191 (AISI 1045, JIS S45C, GB 45#) |
| Standards | EN 10305-1:2016; DIN 2391 Ck45; ASTM A519 1045; JIS G3445 (STKM13C); GB/T 3639 (45#); EN 10297-1 C45E above 380 mm OD |
| Outside diameter | 4–380 mm (0.16–14.96 in) |
| Wall thickness | 0.5–25 mm (0.02–0.98 in) |
| Length | Up to 12 m (39 ft); longer by agreement |
| OD tolerance | ISO 7606 grade 7 / 8 / 9 (per order) |
| Wall tolerance | ±10% or ±0.1 mm (whichever is tighter) |
| Straightness | ≤ 0.0015 × length (≤ 1.5 mm/m) |
| Surface (as-drawn) | Bright, Ra ≤ 1.6 µm |
| Delivery condition | +C, +LC, +SR, +A, +N |
| Ends & preservation | Plain, bevelled or capped; rust-proof oil, plastic caps |
| Certification | EN 10204 3.1; third-party inspection available |
Chemical Composition
CK45 chemical composition (cast analysis, % by mass) follows EN 10305-1:2016 Table 5 for grade C45E. Carbon at 0.42–0.50% is what makes CK45 a heat-treatable steel - and what forces preheat when the tube is welded.
| Element | C45E (1.1191) min | C45E (1.1191) max |
|---|---|---|
| Carbon (C) | 0.42 | 0.50 |
| Silicon (Si) | 0.15 | 0.40 |
| Manganese (Mn) | 0.50 | 0.80 |
| Phosphorus (P) | - | 0.025 |
| Sulfur (S) | 0.020 | 0.040 |
| Chromium (Cr) | - | 0.40 |
| Molybdenum (Mo) | - | 0.10 |
| Nickel (Ni) | - | 0.40 |
| Cr + Mo + Ni | - | 0.63 |
Note: some older references (DIN 17200 lineage, EN 10083-2 non-E, GB 45#) quote carbon up to 0.55%; EN 10305-1:2016 caps it at 0.50%. Confirm the edition named on the order. Phosphorus and sulfur are tightened in the E-grade for batch consistency.
Mechanical Properties
CK45 mechanical properties by delivery condition follow EN 10305-1:2016 Table 6. Yield for the cold-worked conditions is a ratio of tensile strength, so the actual value tracks the measured Rm.
| Delivery condition | Tensile Rm (MPa) | Yield ReH (MPa) | Elongation A (%) |
|---|---|---|---|
| +C (cold drawn hard) | ≥ 640 | ≥ 0.8 × Rm | - |
| +LC (lightly stress-relieved) | ≥ 580 | ≥ 0.7 × Rm | - |
| +SR (stress-relieved) | ≥ 560 | ≥ 420 | ≥ 11 |
| +A (annealed) | ≥ 470 | ≥ 0.5 × Rm | ≥ 16 |
| +N (normalized) | 580–760 | ≥ 380 | ≥ 12 |
DIN 2391 (the older German system, using BK/BKW/BKS/GBK/NBK) lists somewhat higher cold-drawn guarantees (BK around 700 MPa). If you need the DIN values, name the standard on the order - the steel is the same, only the guaranteed floor differs.
Grade Comparison - CK45 vs E355 vs 42CrMo4
| Property | CK45 (C45E) | E355 (1.0580) | 42CrMo4 (1.7225) |
|---|---|---|---|
| Carbon class | Medium (0.42–0.50%) | Low (≤ 0.22%) | Medium + alloy |
| +N yield (MPa) | 380 | 235 | ~ 550 |
| Heat-treatable? | Yes (Q+T, induction) | No | Yes (deep harden) |
| Weldable without preheat? | No (preheat 150–250 °C) | Yes | No (strict preheat) |
| Typical use | Machined + hardened parts | Structural, welded frames | High-stress, through-hardened |
C45E and Ck45 Are the Same Steel
If a drawing says "Ck45" and the certificate says "C45E", they are asking for the same 1.1191 steel - the names belong to different standard generations (the older DIN 2391 Ck45 vs the current EN 10305-1), not to different steels. CK45 equivalent AISI 1045 is equally direct: AISI 1045 is the US grade, supplied as tube to ASTM A519 1045. Quote the legacy name when matching an old print, and write C45E / 1.1191 on new orders so the certificate lines up with the current standard. The same 1.1191 steel also appears as JIS S45C and GB 45#.
Applications
CK45 is chosen wherever a precision tube must be machined and then carry load or resist wear at room temperature. The main applications:
Hydraulic and Pneumatic Cylinder Barrels
Honned or skived-and-roller-burnished CK45 tube is a default barrel material when the bore needs wear resistance and the rod side needs a hardened surface; the mother tube in this page is the same steel before finishing. See our CK45 Honed Tube for Hydraulic Cylinder page for the finished part.
Machined Shafts and Pistons
Cold drawn CK45 gives a straight, concentric blank that machines to tight size with little stock removal, then quenches for strength where the section allows.
Bushings, Sleeves and Guide Bars
The uniform wall and good surface of the cold drawn tube make it a direct-turn bushing stock without a second straightening pass.
Gears and Transmission Parts
Small- to medium-load gears and couplings are cut from CK45 and through-hardened when the section is within the approximately 60 mm through-hardening limit.
General Engineering and Tooling
Jigs, fixtures and structural machine members use CK45 for its strength-to-cost balance versus alloy steels such as 42CrMo4.
Choosing the Delivery Condition
| If the part will be… | Choose | Why |
|---|---|---|
| Machined, then quenched-tempered | +N or +A | Soft, uniform base for heat treatment |
| Honed or lightly cold-formed | +SR | Lower residual stress, 420 MPa yield |
| Ground only, never bent or welded | +C / +LC | Highest as-drawn strength, cheapest |
| Heavily machined to thin sections | +A | Best chip control, lowest hardness |
Quality Control and Testing
| Check | It proves |
|---|---|
| OD / wall / length gauge | The tube matches the ordered tolerance grade |
| Tensile / yield / elongation | The delivery condition meets EN 10305-1 Table 6 |
| Surface and visual | No seams, laps or drawing marks |
| Heat-number traceability | Certificate ties to the stamped tube |
| Third-party inspection (on request) | Independent verification for project QA |
Impact and hardness are not standard EN 10305-1 requirements for CK45; they are project or purchaser supplements and must be requested explicitly.
Why Source CK45 Precision Tubes from GNEE
Stock and rolling of C45E (1.1191) cold drawn seamless tube across the 4–380 mm OD range, with +N / +SR / +A conditions.
EN 10204 3.1 certificates with heat-number traceability; third-party inspection (SGS/BV) available.
Technical quotation within 24 hours and support linking the mother tube to the finished CK45 honed cylinder tube.
Test and inspection
Packaging and shipping
Send your OD × wall, delivery condition and quantity - our technical team will confirm the specification and return a quotation with lead time within 24 hours.
Request a CK45 Precision Tube Quote
FAQ
What is CK45 steel equivalent to?
CK45 is the German DIN designation for a medium-carbon steel whose European grade is C45E (material number 1.1191). Its direct equivalents are AISI/SAE 1045 (USA), JIS S45C (Japan), GB 45# (China) and BS 080M46. In tube form it is supplied to EN 10305-1 as C45E, to ASTM A519 as Grade 1045, and to JIS G3445 as STKM13C.
Is CK45 the same as C45E?
Yes. CK45 and C45E are the same steel under material number 1.1191. CK45 is the older DIN 17200 name; C45E is the current EN name and the form used in EN 10305-1 for precision tubes. Use C45E / 1.1191 on new orders so the certificate matches the current standard, and quote CK45 only when matching an old drawing.
Why does CK45 show two yield values?
Because the yield is set by the delivery condition, not the grade. The name CK45 fixes only the chemistry; the mill then supplies it cold drawn (+C), lightly stress-relieved (+LC), stress-relieved (+SR), annealed (+A) or normalized (+N). Normalized tube gives a minimum yield of 380 MPa; stress-relieved tube gives 420 MPa - a 40 MPa gap from processing alone. Design to the value of the condition you actually order.
Can CK45 be hardened?
Yes. Unlike the low-carbon E235/E355 precision grades, CK45 is a quenching-and-tempering steel. Quenched (820–855 °C) and tempered (550–660 °C) it reaches 620–850 MPa tensile with good toughness, and the surface can be induction-hardened to 54–58 HRC. It through-hardens up to about 60 mm section; larger sections harden mainly at the surface. Carburizing is not required - that is a low-carbon steel process.
Is CK45 weldable without preheat?
No, not safely. At 0.42–0.50% carbon its carbon equivalent (CEIIW) runs about 0.60–0.65%, so cold cracking risk is far higher than for low-carbon E355. Preheat to roughly 150–250 °C depending on wall thickness and restraint, use low-hydrogen electrodes, and apply post-weld stress relief. If your assembly is welded and never heat-treated afterward, an E355 or E420 tube may be the cheaper, lower-risk choice.
What delivery condition should I choose for CK45 precision tubes?
Pick by what the part must do. Choose +N (normalized, yield 380 MPa) for general machined parts and good uniformity at lowest cost. Choose +SR (stress-relieved, yield 420 MPa) when you need the extra 40 MPa of yield or tighter residual-stress control for honing or light cold forming. Choose +A (annealed) for heavy machining, +C/+LC (cold drawn hard) only when the tube is finished by grinding and never bent or welded.
What size range does EN 10305-1 C45E cover?
EN 10305-1 covers cold drawn seamless tubes from 4 mm to 380 mm outside diameter and 0.5 mm to 25 mm wall thickness. Above 380 mm OD the same C45E steel is supplied under EN 10297-1 as a mechanical (hot finished or cold finished) tube, where the yield is quoted on the hot-finished basis and the certificate references a different standard. Confirm the route before specifying large cylinders.
Is CK45 suitable for low-temperature service?
No. CK45 is a medium-carbon structural steel with no specified impact toughness at low temperature, so it must not be substituted for low-temperature carbon or fine-grain steels (for example A333 Grade 6 or EN 10216-4 P265NL). Use it for room-temperature machinery, hydraulic and pneumatic cylinders, and general engineering where impact at sub-zero temperature is not a design case.
