A specification hierarchy behind the grade field
An enquiry may list SCM440, 42CrMo4, 42CrMo, and SAE 4140 while checking availability. Before it becomes a purchase order, select the required designation and standard. Their chemistry ranges, product scope, analysis rules, property requirements, and sampling differ. Ask each supplier to identify exactly which specification its offer and certificate will meet.
Write the hierarchy clearly: PO and approved deviations; drawing and project specification; required material standard and edition; applicable product or general-delivery standard; inspection plan; packing and shipment instructions. ISO 404 provides general technical delivery context and states that order or product-standard requirements prevail where they differ. Use that principle to remove conflict, but do not rely on it as a substitute for deciding which document controls each requirement.
A legacy drawing can remain contractually binding even when a newer standard edition exists. Procurement should flag edition mismatches and route them to design or quality approver instead of silently updating the number. Likewise, national or regional adoptions should be named when the project requires them. Lock the accepted edition at PO release and ask the supplier acknowledgment to list every exception; a later certificate cannot repair an ambiguous grade line.
Chemistry and properties under the same standard
Check chemistry and mechanical requirements under the same approved order route. ISO 683-2 specifies 42CrMo4 within its product, condition, and size scope. SAE J404 supplies SAE 4140 chemistry and needs an applicable product specification and agreed mechanical requirements for a bar order. JIS G 4053 identifies the SCM440 low-alloy machine-structural steel route; it does not give every section one common QT property range.
GB/T 3077 gives 42CrMo chemistry and a prescribed heat-treated reference-specimen property route. Those reference values are meaningful under that standard's preparation and test rules; they aren't necessarily the center properties of a large production bar. Preserve the basis on quotations and certificates. If the design needs core performance at a specific ruling section, add section-relevant production evidence and test locations instead of relabeling the reference result.
Even chemistry overlap is incomplete. SAE 4140 permits a different manganese band from SCM440, and their chromium and molybdenum limits are not identical. A heat near an edge can conform to one row and fail another. Dual certification therefore requires comparison of the actual heat and all other mandatory clauses, not a database equivalency statement. Require the supplier to identify whether it offers single-standard conformity, verified dual conformity, or a proposed substitute.
| Designation / controlling standard | Cast-analysis chemical composition, mass % | Mechanical-property basis | Purchase-order control |
|---|---|---|---|
| SCM440 — JIS G 4053:2023 | C 0.38–0.43; Si 0.15–0.35; Mn 0.60–0.90; Cr 0.90–1.20; Mo 0.15–0.30; P ≤0.030; S ≤0.030; Ni ≤0.25; Cu ≤0.30. | JIS G 4053 defines the low-alloy machine-structural material route but not a single quenched-and-tempered mechanical-property range for every supplied section. | State condition, section-based properties, sampling, tests, dimensions, surface, certificate, and any additional product requirements while preserving JIS identity. |
| 42CrMo4 — ISO 683-2:2016 | C 0.38–0.45; Si 0.10–0.40; Mn 0.60–0.90; Cr 0.90–1.20; Mo 0.15–0.30; P ≤0.025; S ≤0.035. | +QT, round ruling section d >16–40 mm: Rp0.2 ≥750 MPa, Rm 1000–1200 MPa, A ≥11%, Z ≥45%, KV ≥35 J; d >40–100 mm: Rp0.2 ≥650 MPa, Rm 900–1100 MPa, A ≥12%, Z ≥50%, KV ≥35 J. | State product form, condition, ruling section and applicable table. Do not extend a smaller-section row or relabel it as another standard's property contract. |
| SAE 4140 — SAE J404_200901 | C 0.38–0.43; Si 0.15–0.35; Mn 0.75–1.00; Cr 0.80–1.10; Mo 0.15–0.25; P ≤0.035; S ≤0.040. | SAE J404 controls alloy-steel chemistry; it doesn't define a complete bar form, QT strength class, impact, hardness, sampling, dimensional, or inspection contract. | Add the selected product specification, condition, size-based values, specimen locations, tests, traceability, and documents. '4140 QT' is incomplete. |
| 42CrMo — GB/T 3077-2015 | C 0.38–0.45; Si 0.17–0.37; Mn 0.50–0.80; Cr 0.90–1.20; Mo 0.15–0.25; P ≤0.030; S ≤0.030; Ni ≤0.30; Cu ≤0.30. | Prescribed reference heat-treated specimen: Rm ≥1080 MPa; yield strength ≥930 MPa; A ≥12%; Z ≥45%; KV2 ≥63 J. This isn't a blanket full-bar value. | Keep the GB/T reference-specimen basis on the PO and request additional section-relevant evidence when production-bar or core performance controls. |
Condition, testing, and deviations before manufacture
State the thermal condition and surface process separately. Identify who performs heat treatment, the section treated, required properties or hardness, impact temperature where specified, specimen orientation and location, sampling frequency, and lot definition. Add straightening and later machining or treatment so the supplier can confirm which delivered state the results represent.
Inspection requests need methods and acceptance rules. For ultrasonic testing, name the relevant product standard or attached procedure, scan coverage, calibration/reference basis, sensitivity, acceptance level, examination stage, personnel qualification, and required report. For hardness, state scale, surface preparation, locations, number of readings, and permitted spread. For tensile or impact testing, state specimen geometry, orientation, location, temperature, frequency, and retest rule. A line saying 'standard inspection' cannot add comparable quotations.
Use a deviation register. Each proposed alternative should show requested and offered designation, standards and editions, chemistry differences, offered heat analysis if available, product form, manufacturing route, condition, properties and sampling, NDT, certificate, marking, lead-time effect, price effect, and reason. Procurement checks completeness, engineering judges functionality, quality accepts evidence, and the customer or drawing owner approves where required. The supplier must not start the alternative route until the named authority records acceptance.
Certificate wording that mirrors the PO
ISO 10474 classifies inspection documents for steel products supplied to an order. Select the type the project needs, then list the data to be returned. The document name does not add a missing impact test, UT method, hardness map, heat-treatment chart, or purchaser witness. A long attachment list without acceptance criteria only creates more paperwork.
The certificate header and result pages should identify supplier and manufacturer roles where required, purchaser, and PO item. State designation, controlling standard and edition, product form, size, quantity, delivery condition, heat, and lot. Include test specimens, actual results and units, conformity statement, authorized validation, and linked attachments. If the seller is not the mill, retain traceability to the original mill. Also define how later heat treatment, machining, testing, or recertification is recorded.
At receiving inspection, reconcile the order, supplier acknowledgment, approved deviations, packing list, marking, bundle or piece identity, certificate, heat analysis, properties, NDT report, dimensions, and quantity. Quarantine discrepancies before material is cut, mixed, or issued. A certificate that lists 'SCM440/4140 equivalent' when the PO required 42CrMo4 is a conformity question, even if the heat looks chemically close; route it through the deviation approver instead of rewriting receiving records.
Review JOTAIN's redacted inspection document examples as document-format examples, not results for the heat you plan to order. Agree the issuing mill, actual tests, specimen basis and heat-to-shipment link in the quotation. Keep upstream mill records distinct from any subsequent JOTAIN heat-treatment, cutting or machining records; third-party inspection and the document type must be confirmed for the order.
One required purchase line, one deviation channel
The example names 42CrMo4 as the required material. A supplier offering SAE 4140, SCM440, or 42CrMo must return the proposed standard and the differences for review before manufacture. Where another designation is required by the drawing, rewrite the order around that specification and its accepted property and sampling requirements. Do not carry over ISO values without engineering approval.
Require quotation and acknowledgment to repeat the accepted standard edition and delivery condition. Ask for a clause response when the order is critical or cross-standard: comply, deviation, or not applicable, with a referenced note for each exception. Commercial qualifications should be separated from technical deviations so a lead-time or minimum-order issue cannot be mistaken for material approval. Expire unaccepted alternatives when the PO is released.
Before manufacture, make sure the PO, drawing, specification hierarchy, approved deviation, inspection plan, and certificate instructions tell one consistent story. Before shipment, review a draft certificate layout when a customer format or third-party endorsement is required. At receiving, close discrepancies using the same approval list.
For a JOTAIN quotation, use the 4140 / 42CrMo4 QT round bar supply scope to check the offered form and processing stage. JOTAIN supplies QT bars and machined blanks, with downstream heat treatment, cutting and machining. Send one controlling grade and standard, diameter, length, quantity, properties, surface condition and destination. Confirm the size/property combination in the quotation and identify any SCM440 or 42CrMo alternative separately.
Item: Quenched-and-tempered alloy steel round bar for gearbox output shafts
Required grade: 42CrMo4
Standard and edition: ISO 683-2:2016; purchaser project specification PS-MAT-17 revision D also applies
Product and size: Hot-rolled round bar, Ø90 mm × 6,100 mm, 30 bars; ruling section 90 mm unless approved drawing review states otherwise
Delivery condition: +QT, peeled; diameter tolerance, straightness, machining allowance, marking and surface acceptance per PS-MAT-17
Mechanical requirements: Applicable accepted size band plus [project impact requirement], with specimens at [orientation, radial and longitudinal location] and frequency [per heat/lot]
Inspection: Heat analysis, tensile, impact, hardness, dimensions, surface and marking; UT to attached procedure, coverage and acceptance criteria
Certificate: ISO 10474 document type [state type], actual results, heat-treatment condition, heat and lot traceability, test locations, and linked NDT report
Deviations: SCM440 to JIS G 4053:2023, SAE 4140 to SAE J404_200901 with a named product specification, or 42CrMo to GB/T 3077-2015 may be proposed only in a clause-by-clause deviation matrix; written purchaser approval required before manufacture
Destination and packing: [city, country, Incoterm, preservation, bundle and document requirements]Questions buyers ask
Are SCM440, 42CrMo4, 42CrMo, and 4140 the same in a purchase order?
No. They are related Cr-Mo designations used for sourcing review, but their chemistry limits and the evidence required by each standard differ. The PO should name one required designation, standard and edition, product form, condition, section, properties, tests, documents, and traceability. Any other route should be approved as a documented deviation.
What is the safest way to write equivalent-grade RFQ language?
Write the required grade and standard first, then state either 'no alternatives' or 'alternatives may be proposed by deviation.' Require a clause comparison covering chemistry, product route, condition, ruling section, properties, specimen locations, inspection, certificate, marking, traceability, schedule, price, and written purchaser approval before manufacture.
Why does certificate wording matter for SCM440 / 42CrMo4 / 42CrMo orders?
The certificate is how receiving and downstream users connect the physical supply to the accepted material route. It should repeat the controlling designation and edition, condition, heat and lot, specimen basis, actual ordered results, conformity statement, and traceability. A slash-separated equivalent list can conceal a deviation rather than prove conformity.
RFQ checklist
- One required designation, controlling standard, national adoption if relevant, and exact edition
- PO, drawing, project specification, product standard, inspection-plan, and deviation hierarchy
- Whether SCM440, 42CrMo4, 42CrMo, SAE 4140, or any other route may be proposed
- Product form, diameter, ruling section, length, quantity, tolerance, straightness, and machining allowance
- Hot-rolled, forged, annealed, normalized, +QT, peeled, turned, ground, or rough-machined condition
- Heat-treatment responsibility, lot definition, process qualification, straightening sequence, and rework rule
- Property range, impact temperature, hardness, specimen orientation, radial/longitudinal location, and frequency
- Heat and product analysis, permissible variation, residuals, actual heat comparison, and dual-compliance basis
- UT or other NDT method, coverage, calibration/reference, sensitivity, acceptance, stage, personnel, and report
- Surface quality, decarburization, dimensions, marking, sampling, retest, and third-party witness requirements
- ISO 10474 inspection-document type and exact actual results and attachments to be returned
- Heat-to-bar or lot traceability, seller/manufacturer identity, marking, certificate validation, and record retention
- Deviation matrix, engineering and quality approver, customer approval, reason, lead-time effect, and price effect
- Supplier acknowledgment, pre-shipment document review, receiving reconciliation, discrepancy quarantine, and closure
- Packing, preservation, bundle mass, destination, Incoterm, shipment documents, and language requirements
References
- JIS G 4053:2023 Low-alloyed steels for machine structural use
- ISO 683-2:2016 Alloy steels for quenching and tempering
- SAE J404_200901 Chemical Compositions of SAE Alloy Steels
- GB/T 3077-2015 Alloy structure steels
- ISO 404:2013 Steel and steel products — General technical delivery requirements
- ISO 10474:2013 Steel and steel products — Inspection documents
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