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 does not supply one universal 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.
Resolve CK45 before asking mills to quote
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 explicit 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.
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.
Compare chemistry and mechanical values 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 does not mean every C45 bar is supplied +QT, and it does not 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 does not specify one universal 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. |
The figures are condensed RFQ aids, not substitute standards. Verify the purchaser's licensed edition, product scope, heat/product analysis rules, delivery condition, ruling section, and test clauses. Only accepted order terms define the requirements for a specific supply.
Specify product form, condition, and ruling section separately
A chemistry designation answers 'what steel family was melted?' It does not 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.
Approve substitutions against the finished-part route
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. A practical matrix contains requested and proposed standard editions, designation, product form, heat and product analysis limits, grain-size or special-quality requirements if used, delivery condition, ruling section, mechanical values, sampling and retest, dimensions and tolerances, surface quality, NDT, certificate, traceability, marking, and downstream heat-treatment responsibility. Unresolved cells stay open; they do not become 'equivalent' through silence.
For repeat purchases, save the approval reference and exact accepted route in the material master. Preserve the old drawing term in a note only when traceability requires it, and prevent the supplier from mixing heats made to different standards under one line item unless the order explicitly allows that lot structure. Incoming inspection should verify the standard and designation printed on the certificate, not only the buyer's internal alias.
Use RFQ wording that closes the legacy-name gap
The example below converts a maintenance request containing CK45 into a current C45E order route while preserving the approval trail. It is not a universal 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 scope.
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. Only accepted order terms define the requirements for a specific supply.
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]CK45, C45, and SAE 1045: compare the standard before the grade name buyer questions
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 does not establish a complete hot-wrought or cold-finished bar order, nor one universal 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.
CK45, C45, and SAE 1045: compare the standard before the grade name 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, approval authority, and explicit no-substitution-before-approval wording
- Packing, preservation, bundle weight, destination, delivery term, and shipping documents
References
- ISO 683-1:2016 Non-alloy steels for quenching and tempering
Supports: Confirms the current ISO product scope, size-restricted mechanical requirements, and enquiry-and-order agreement route for C45 and C45E.
Limitation: The public abstract does not replace the licensed chemistry, mechanical, sampling, dimensional, surface, or optional-requirement tables.
- SAE J403_202402 Chemical Compositions of SAE Carbon Steels
Supports: Defines the current stabilized SAE carbon-steel chemistry route, heat-analysis tables, product-analysis variation framework, and reporting context for SAE 1045.
Limitation: SAE J403 is not a complete bar product, mechanical-property, dimensional, surface, inspection, or certification specification.
- ASTM A29/A29M-20 General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought
Supports: Shows why a hot-wrought SAE chemistry designation is joined to an applicable bar product or general-requirements route and purchaser order clauses.
Limitation: A29/A29M applies when invoked by the applicable ASTM specification or order; it does not convert SAE 1045 into C45/C45E or set universal final-part properties.
- SS-EN 10083-2:2006 Technical delivery conditions for non-alloy steels
Supports: Confirms that EN 10083-2:2006 is withdrawn and replaced in the SIS catalog by EN ISO 683-1:2018.
Limitation: The catalog status does not itself authorize a drawing change; the purchaser must approve any migration from legacy CK45 or EN wording.
Revision note: Expanded on 18 July 2026 with current ISO and SAE chemistry/property boundaries, legacy CK45 disposition, product-route controls, substitution workflow, and worked RFQ wording.
Inquiry support
Send the required grade standard, allowed alternatives, size, and condition.
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