Key takeaways
- Do not issue a new PO for 'CK45' alone. Resolve the legacy term to a current controlling standard or make it a purchaser-approved deviation case.
- C45 and C45E share the same nominal carbon range in ISO 683-1, but C45E has tighter phosphorus and sulfur limits; the suffix is not decorative.
- SAE J403_202402 defines SAE 1045 cast-analysis chemistry. It doesn't supply a single tensile, yield, impact, hardness, size, or delivery-condition requirement for bar.
- Mechanical values travel with condition, ruling section, test location, and product document. A certificate showing a familiar grade name is not enough to approve substitution.
- For a practical RFQ, connect the chosen route to the part, machining sequence, supplied surface, straightness, inspection, and later heat treatment.
What CK45 means on an old drawing
CK45 remains common on older drawings, maintenance lists, distributor catalogs, and multilingual purchase records. The problem is not that the word is unfamiliar; it is that the word alone does not identify a current edition, product scope, delivery condition, chemistry table, mechanical-property table, or inspection route. A supplier can honestly quote several different materials against that label and still leave the buyer without a single conformity basis.
Start by finding the source document. Check the drawing title block and revision history, legacy material specification, equipment manual, prior certificate, approved-vendor record, and whether the component owner intended the former DIN route.
If the design is being refreshed, ask the responsible engineer to select C45 or C45E under ISO 683-1 or another clear current route. Do not let purchasing translate CK45 into SAE 1045 merely because both are medium-carbon steels; translation is an engineering change when it affects chemistry limits, product specification, testing, or customer approval. [1][2]
A safe legacy disposition has three fields: 'drawing designation,' 'controlling order designation,' and 'approval reference.' This preserves traceability without pretending the old label disappeared. Example: drawing says CK45; order requires C45E to ISO 683-1:2016; deviation approval ENG-247 authorizes the conversion for revision B. If no authorized conversion exists, quote the uncertainty openly and obtain a decision before order acceptance.
Chemistry and properties without mixing standards
ISO 683-1:2016 covers specified non-alloy steels in stated product forms and conditions. Its published mechanical requirements are restricted to the sizes in the relevant tables, and special variations can be agreed at enquiry and order. The table below uses the quenched-and-tempered C45/C45E size bands as a concrete example. It doesn't mean every C45 bar is supplied +QT, and it doesn't apply to bright products outside the standard's scope without the applicable product route.
SAE J403_202402 uses heat-analysis ranges and product-analysis variation rules for SAE carbon steel designations. Its 1045 chemistry overlaps C45, but not every limit is identical. J403 also requires reporting of several residual elements when heat analysis is requested, which is useful certificate evidence but still not a product or mechanical-property specification. A buyer wanting hot-wrought or cold-finished bar should identify the applicable ASTM or other product document and then state any property, condition, dimensional, surface, and inspection clauses needed for the actual component.
| Grade and controlling standard | Cast-analysis chemical composition, mass % | Mechanical-property basis | Buyer interpretation |
|---|---|---|---|
| C45 — ISO 683-1:2016 | C 0.42–0.50; Si 0.10–0.40; Mn 0.50–0.80; P ≤0.045; S ≤0.045; Cr ≤0.40; Mo ≤0.10; Ni ≤0.40; Cu ≤0.30; Cr+Mo+Ni ≤0.63. | +QT, round ruling section d ≤16 mm: Rp0.2 ≥490 MPa, Rm 700–850 MPa, A ≥14%, Z ≥35%, KV ≥15 J; d >16–40 mm: Rp0.2 ≥430 MPa, Rm 650–800 MPa, A ≥16%, Z ≥40%, KV ≥15 J; d >40–100 mm: Rp0.2 ≥370 MPa, Rm 630–780 MPa, A ≥17%, Z ≥45%, KV ≥15 J. | Use the row only for the applicable product, +QT condition, ruling section, and sampling basis in ISO 683-1. |
| C45E — ISO 683-1:2016 | C 0.42–0.50; Si 0.10–0.40; Mn 0.50–0.80; P ≤0.025; S ≤0.035; Cr ≤0.40; Mo ≤0.10; Ni ≤0.40; Cu ≤0.30; Cr+Mo+Ni ≤0.63. | The same listed +QT size-banded mechanical requirements as C45 in the applicable ISO table; the distinction is the tighter P and S chemistry limits. | Do not delete the E suffix in quotation or certification. Confirm whether the drawing requires the cleaner chemistry route. |
| SAE 1045 — SAE J403_202402 | C 0.43–0.50; Mn 0.60–0.90; Si 0.15–0.35; P ≤0.030; S ≤0.035; reported residual limits include Cu ≤0.20, Ni ≤0.25, Cr ≤0.20, Mo ≤0.06 for the standard 1045 route. | SAE J403 specifies chemical composition and product-analysis rules; it doesn't specify a single delivered-bar Rm, yield, elongation, impact, or hardness range. | Add the applicable bar/product specification and the required condition, properties, section, sampling, surface, dimensions, and inspection. |
Product form, condition, and ruling section
A chemistry designation answers 'what steel family was melted?' It doesn't answer 'what bar did we buy?' For hot-wrought SAE 1045, a purchaser may select an ASTM product route that invokes general requirements such as ASTM A29/A29M. For cold-finished shafting, ASTM A108 may be the relevant route.
The correct choice depends on whether the material is hot rolled, turned, cold drawn, ground, polished, heat treated, or supplied for later forging and heat treatment. Do not cite multiple product standards as decoration; identify which one controls each requirement and resolve conflicts in the document hierarchy.
Condition changes both machinability and the meaning of test results. Annealed or normalized bar may be purchased to machine efficiently and heat treat later. Quenched-and-tempered bar should carry an accepted mechanical range and a test basis tied to the production section. Cold drawing can change surface condition, residual stress, straightness, and measured properties without giving the same microstructure as quench and temper. A generic hardness range copied from a supplier datasheet may therefore select the wrong process route.
Section size is especially important for medium-carbon non-alloy steel because core response falls as the heat-treatment section becomes more demanding. If the drawing needs through-section strength or a hardened surface over a tough core, define the actual heat-treatment geometry and verification. Surface induction hardening, for example, needs case depth, hardness method and locations, transition-zone control, core condition, and crack inspection; buying C45 or 1045 chemistry alone answers none of those questions.
Substitution review for the finished part
A substitution review should first identify which requirements are design inputs and which are manufacturing controls. Chemistry limits may affect hardenability, machinability, weld procedure, heat-treatment response, and customer material lists. Mechanical requirements may be section- and condition-specific. Surface route affects fatigue initiation, plating preparation, stock allowance, and dimensional capability. Regulations or customer approvals may prohibit a change even when laboratory properties look similar.
Require the supplier to compare actual clauses, not just nominal ranges. List requested and proposed standard editions, designation, product form, and heat and product analysis limits. Include grain-size or special-quality requirements if used. Compare delivery condition, ruling section, mechanical values, sampling and retest, dimensions and tolerances, surface quality, and NDT. Identify the certificate, traceability, marking, and downstream heat-treatment responsibility. Unresolved cells stay open; silence is not approval of equivalence.
For repeat purchases, save the approval reference and exact accepted route in the material master. Keep the old drawing term in a note only when traceability requires it. Do not allow heats made to different standards under one line item unless the order clearly permits that lot structure. Incoming inspection should verify the standard and designation on the certificate, as well as the buyer's internal alias.
When the material is for a piston rod, take the approved designation and condition into the hydraulic cylinder rod application route , where load case, unsupported length, end geometry, straightness, surface route, and inspection can be reviewed together.
RFQ wording for a legacy designation
The example below converts a maintenance request containing CK45 into a current C45E order route while preserving the approval trail. It isn't a blanket recommendation to use C45E. If the equipment owner instead approves SAE 1045, replace both the designation and the complete product/property framework; do not retain ISO mechanical rows beside a J403-only chemistry requirement.
Ask bidders to separate compliance from alternatives. The main quote should match the required standard and condition. Any proposed SAE 1045, C45, or other route should appear as a deviation offer with chemistry comparison, product standard, condition, property and sampling proposal, certificate, commercial effect, and approval dependency. This keeps a lower price from hiding a thinner technical requirements.
Before release, reconcile the PO line with the drawing, conversion approval, inspection plan, and certificate instruction. State which document wins if they conflict. Make the supplier acknowledgment repeat the controlling designation and edition.
After the controlling designation and substitution rule are resolved, use the CK45 / 1045 round bar product route to align product form, condition, machining allowance, inspection, certificate, quantity, and destination before quotation.
Item: Medium-carbon steel round bar for replacement guide shafts
Drawing designation: CK45 (legacy wording; drawing revision C)
Required grade: C45E
Standard and edition: ISO 683-1:2016
Approval reference: Engineering material conversion ENG-247 attached
Size and quantity: Ø65 mm × 4,050 mm, 32 bars; finished geometry per drawing
Delivery condition: +QT, peeled; applicable ISO ruling-section property band plus drawing requirements
Mechanical requirements: Actual tensile and impact results from the agreed orientation and sampling location; hardness range per drawing
Inspection: Heat analysis, dimensions, straightness, surface condition, marking and traceability
Certificate: EN 10204 type 3.1 with actual heat and mechanical results
Alternatives: SAE 1045 or C45 may be quoted only as a separate deviation; written purchaser approval required before supply
Packing/marking: Standard, grade, heat, size, PO item and bundle identity
Destination: [city, country and delivery term]Questions buyers ask
Are CK45, C45, C45E, and SAE 1045 the same purchase specification?
No. CK45 is legacy or informal wording, C45/C45E belong to the ISO 683-1 route, and SAE 1045 belongs to SAE J403 chemistry. A complete order also needs product form, condition, ruling section, properties and sampling, dimensions, surface, inspection, certificate, and substitution approval.
What does SAE J403 establish for SAE 1045 buying decisions?
SAE J403 establishes heat-analysis chemistry, product-analysis variation rules, and reporting provisions for SAE carbon-steel designations. It cannot confirm a complete hot-wrought or cold-finished bar order, nor a single mechanical-property range for SAE 1045.
How should a buyer handle CK45 in a new RFQ?
Trace CK45 to its drawing or legacy specification, then obtain an authorized conversion to a named current designation and edition. Keep the legacy term and approval reference visible for traceability. If no conversion is approved, stop the ambiguity before PO release rather than choosing C45 or 1045 by habit.
Does C45E mean the same thing as C45?
No. Under ISO 683-1, C45E retains the C45 carbon range but uses tighter phosphorus and sulfur limits. The suffix is part of the designation and should remain on the RFQ, order, marking, and certificate when that route is required.
When should buyers review CK45, C45, or SAE 1045 round bar?
These medium-carbon routes are often reviewed for shafts, cylinder rods, gears, bolts, pins, and general machined parts. Choose the route from the drawing and part duty, then state the controlling standard, bar form, delivery condition, size, surface and machining sequence, inspection, certificate, and any allowed alternative.
RFQ checklist
- Legacy drawing term, source document, revision, current required designation, and conversion approval reference
- Controlling ISO, SAE, ASTM, DIN/EN adoption, or other product standard and exact edition
- C45 versus C45E suffix requirement or SAE 1045 chemistry route—never an unlabeled family name
- Hot-wrought, cold-finished, annealed, normalized, +QT, peeled, ground, or customer-heat-treated condition
- Purchased diameter, heat-treatment ruling section, finished geometry, length, quantity, tolerance, and straightness
- Mechanical values, hardness, impact temperature, sampling orientation/location, test frequency, and retest rule
- Surface quality, decarburization, allowance, cold-work state, and downstream machining or induction-hardening route
- Applicable bar specification, dimensional inspection, any NDT, and acceptance criteria
- Certificate type, actual heat/test results, heat-to-lot traceability, marking, and document language
- Clause-by-clause alternative matrix, approver, and clear no-substitution-before-approval wording
- Packing, preservation, bundle weight, destination, delivery term, and shipping documents
References
Inquiry support
Comparing two material routes?
Send the drawing or RFQ with the grade, size, condition, processing, inspection, quantity, and destination. We can flag open points before quotation.