Key takeaways
- A grade cross-reference is a screening tool, not substitution approval. Lead the RFQ with the controlling standard, edition, designation, product form, and condition.
- ISO 683-2 gives size-banded mechanical requirements for 42CrMo4 in specified conditions; SAE J404 and JIS G 4053 are principally chemistry routes and do not create the same universal bar-property contract.
- Legacy EN 10083-3 values may still control an old drawing only when that edition is contractually named; the European replacement route is EN ISO 683-2.
- Compare offers on section-relevant heat-treatment evidence, sampling, surface and dimensional route, certificate identity, and deviation handling—not on the four-digit or regional grade name alone.
Separate designation similarity from contractual equivalence
The four names describe related medium-carbon chromium-molybdenum steels, which is why ERP systems, handbooks, and supplier quotations often place them on one line. That relationship is useful at the market-screening stage: it tells procurement which mills and heat-treatment routes may be relevant. It does not prove that a heat made to one document conforms to another. Each designation remains attached to its own chemistry table, general delivery rules, product-form scope, sampling and testing provisions, and edition history.
For a current ISO/European route, specify 42CrMo4 to ISO 683-2:2016 or the adopted EN ISO 683-2:2018 edition required by the project. EN 10083-3:2006 is withdrawn and replaced in the SIS catalog by EN ISO 683-2:2018. A legacy drawing may still contractually invoke EN 10083-3; in that case, do not silently update it during quotation. Flag the obsolete reference and ask the design or quality authority to approve either continued use or a controlled conversion.
For a North American chemistry route, write SAE 4140 to SAE J404_200901 and add the applicable product specification, such as a purchaser-selected ASTM bar document, because J404 alone does not define the complete supplied bar. For SCM440, write JIS G 4053:2023 and the required product, condition, dimensions, tests, and inspection terms. For 42CrMo, write GB/T 3077-2015. Avoid the composite phrase '42CrMo4/4140/SCM440 equivalent' unless the next sentence states who evaluates and approves the alternative.
Read chemistry and mechanics from the same controlling route
The side-by-side table deliberately keeps chemistry and mechanical-property status in separate columns. Chemistry defines what may be called the grade under the named standard; it does not establish the delivered condition. ISO 683-2 publishes mechanical requirements for 42CrMo4 only within its stated product, heat-treatment, and size scope. SAE J404 and JIS G 4053 do not provide an interchangeable set of quenched-and-tempered bar properties. GB/T 3077 uses a prescribed reference-specimen heat-treatment basis that must not be relabeled as the center property of any ordered diameter.
The overlapping carbon, chromium, and molybdenum ranges explain why substitutions are often technically feasible after review. The non-overlapping limits explain why a certificate can conform to one route and miss another. For example, a compliant SAE 4140 heat near its manganese upper limit is not automatically a compliant SCM440 heat, and an SCM440 heat can use chromium or molybdenum limits outside the SAE row. Procurement should compare the actual heat analysis to every mandatory limit only after the purchaser has agreed that cross-standard qualification is permitted.
| Grade and controlling standard | Cast-analysis chemical composition, mass % | Mechanical-property basis | Buyer interpretation |
|---|---|---|---|
| 42CrMo4 — ISO 683-2:2016 / EN ISO 683-2:2018 | 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. | ISO mechanics are size- and condition-banded. State the ruling section and sampling basis; do not apply a small-section row to a larger bar. |
| 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 chemical composition; it does not state one universal delivered-bar tensile, yield, elongation, impact, or hardness range. | Add the selected bar/product specification, condition, size-based properties, sampling, tests, and certificate terms. '4140 QT' alone is incomplete. |
| 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 alloy-steel material route but does not create one universal quenched-and-tempered mechanical-property range for every supplied section. | State heat treatment, properties and test location through the applicable order and product requirements; preserve JIS identity on the certificate. |
| 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 is not a blanket full-bar value. | Keep the GB/T reference-specimen basis visible and request section-relevant production evidence when the ordered bar or core controls the design. |
This condensed comparison is for RFQ screening. Check the purchaser's licensed editions, product-form clauses, heat/product analysis rules, sizes, conditions, sampling, and test definitions before acceptance. Only accepted order terms define the requirements for a specific supply.
Make size, condition, and test location part of the grade
A usable offer reads like '42CrMo4, ISO 683-2:2016, +QT, 85 mm ruling section' rather than '4140 equivalent.' ISO explicitly restricts its mechanical-property requirements to the sizes in the relevant table. As ruling section grows, the stated minimum yield and tensile bands change. The supplier therefore needs both purchased diameter and the geometry represented by the property requirement. For forged or stepped parts, the purchaser should define whether the ruling section is based on the heat-treatment blank, final component, or a separately agreed qualification geometry.
Delivery condition also changes what the buyer is purchasing. Annealed or normalized bar may be intended for machining or forging followed by customer heat treatment; its incoming hardness is a processing control, not final component strength. Quenched-and-tempered bar transfers more thermal responsibility to the supplier, but the order still needs a property range, test location, frequency, and traceability. Bright, peeled, turned, or ground describes a surface route and dimensional state; it does not replace the metallurgical condition.
Ask what the mechanical test represents. A test cut from a prolongation, a separately cast coupon, a sacrificial bar, or a small machined specimen can each answer a different question. Record orientation, radial location, distance from the end, heat-treatment relationship, and whether results are heat-level or lot-level. If the component is fatigue-sensitive, surface integrity, decarburization, straightening history, and machining damage may matter more than a small difference between nominal chemistry ranges.
Evaluate a substitution as a controlled technical deviation
Give suppliers a structured alternative-offer form. It should show the requested designation and edition, proposed designation and edition, every chemistry limit that differs, offered heat analysis if known, product standard, manufacturing route, delivery condition, available size, proposed property and sampling basis, surface and tolerance route, inspection plan, certificate type, lead-time effect, and price effect. A statement that the grades are 'international equivalents' is not a completed deviation.
The approval sequence should be explicit. Procurement can verify completeness and commercial comparison; materials or design engineering decides whether the chemistry and performance route is acceptable; quality confirms inspection, certificate, and traceability controls; the purchaser records approval before the PO changes. If the customer owns the drawing, customer approval may also be required. This separation prevents a salesperson's cross-reference or an ERP material alias from becoming an unauthorized engineering change.
Inspection should close the risks introduced by the chosen route. At minimum, reconcile heat analysis, designation, standard, size, quantity, condition, and heat number across the order, marking, and certificate. Add mechanical tests, hardness mapping, hardenability evidence, UT, macrostructure, cleanliness, grain size, surface testing, or third-party witnessing only with a defined method and acceptance rule. For UT, specify the relevant product standard or written procedure, scan coverage, calibration/reference basis, acceptance criteria, test stage, personnel qualification, and report fields rather than asking for 'standard UT.'
Build the purchase line around one controlling standard
The worked line below uses the current ISO route for a quenched-and-tempered round bar. It allows alternatives to be proposed but never pre-approves them. If the project instead requires SAE, JIS, GB/T, or a legacy EN edition, replace the controlling line and rebuild the property, product, and test clauses around that document. Do not retain ISO size-banded values beside a different grade standard unless engineering has intentionally created a dual-conformance requirement and verified every clause.
Require the quotation to identify exceptions. A supplier that cannot meet the exact diameter, property band, impact sampling, or certificate term may still have a viable proposal, but the difference must be visible before price comparison. Ask for a compliance matrix when the order is high consequence or cross-standard: 'comply,' 'deviation,' or 'not applicable' for every clause, with a referenced attachment. This is faster to review than searching a quotation for buried assumptions.
At PO release, freeze the accepted standard edition and alternative status. Avoid changing only the grade field while leaving conflicting notes elsewhere on the drawing, purchase line, inspection plan, or certificate instructions. The PO, referenced drawing, specification hierarchy, approved deviation, and supplier acknowledgment should tell one consistent story. Only accepted order terms define the requirements for a specific supply.
Item: Quenched-and-tempered alloy steel round bar for transmission shaft blanks
Required grade: 42CrMo4
Standard and edition: ISO 683-2:2016 (or project-required EN ISO adoption stated by purchaser)
Size and quantity: Ø85 mm × 6,200 mm, 24 bars; ruling section 85 mm unless drawing review establishes otherwise
Delivery condition: +QT, peeled; ordered diameter tolerance and straightness per attached specification
Mechanical requirements: Applicable ISO size band plus project impact requirement at the stated orientation and sampling location
Inspection: Heat analysis, tensile and impact results, hardness, dimensions, surface, marking; UT only per attached method and acceptance criteria
Certificate: EN 10204 type 3.1, actual results, heat number and bar/lot traceability
Alternatives: SAE 4140, SCM440, or 42CrMo may be submitted only in a clause-by-clause deviation matrix; written purchaser approval required before supply
Packing/marking: Grade, controlling standard, heat, size, PO item and bundle identity
Destination: [city, country and Incoterm]42CrMo4 vs 4140 vs SCM440 for round bar RFQs buyer questions
Are 42CrMo4, 4140, SCM440, and 42CrMo the same in an RFQ?
No. They are related chromium-molybdenum designations used for initial screening, but each belongs to a different standard route. The RFQ must identify the controlling designation, standard and edition, product form, condition, size, properties, sampling, inspection, and the approval process for any alternative.
Are 42CrMo4, 4140, and SCM440 always interchangeable?
No. Their chemistry ranges overlap but do not coincide, and their standards do not establish the same mechanical-property contract. Interchangeability is an engineering and quality decision for the specific part, section, heat treatment, test evidence, regulation, and customer approval—not a property of the names themselves.
How should buyers write equivalent grades in an RFQ?
Write one required grade and standard first. Then say either 'no alternatives' or 'alternatives may be proposed by deviation.' Require the proposed standard/edition, chemistry comparison, product and condition, properties and sampling, inspection, certificate, commercial effect, and written purchaser approval before substitution.
Does SAE J404 give the mechanical properties of 4140 QT bar?
No. SAE J404 defines chemical compositions for SAE alloy-steel designations. A complete 4140 bar order needs an applicable product specification and accepted clauses for delivery condition, size-based mechanical values, test locations and frequency, surface, dimensions, inspection, traceability, and documentation.
42CrMo4 vs 4140 vs SCM440 for round bar RFQs RFQ checklist
- Required designation, controlling standard, national adoption if relevant, and exact edition
- Legacy EN reference disposition and who can approve migration to EN ISO 683-2
- Product form, purchased size, ruling section, length, quantity, tolerance, and straightness
- Annealed, normalized, +QT, forged, hot-rolled, peeled, turned, ground, or rough-machined condition
- Required property band, impact temperature, hardness, test orientation, location, frequency, and retest rule
- Heat-treatment responsibility, qualification route, straightening sequence, and section-relevant evidence
- Surface quality, decarburization, machining allowance, defect-removal, and downstream processing
- UT or other NDT method, coverage, calibration/reference, acceptance, stage, personnel, and report
- Certificate type, actual heat and test results, heat-to-bar or lot traceability, and marking
- Alternative-offer matrix, purchaser/customer approval authority, and no-substitution wording
- Packing, preservation, bundle mass, destination, delivery term, and required shipment documents
References
- ISO 683-2:2016 Alloy steels for quenching and tempering
Supports: Confirms the current ISO alloy-steel product scope, size-bounded mechanical requirements, and the possibility of enquiry-and-order agreements.
Limitation: The catalog abstract does not replace the licensed chemistry, mechanical, sampling, dimensional, or optional-requirement tables used for an order.
- SS-EN 10083-3:2006 Technical delivery conditions for alloy steels
Supports: Confirms that EN 10083-3:2006 is withdrawn and replaced in the SIS catalog by EN ISO 683-2:2018.
Limitation: A withdrawal notice does not automatically amend a legacy drawing or contract; purchaser approval is still needed to change the controlling edition.
- SAE J404_200901 Chemical Compositions of SAE Alloy Steels
Supports: Provides the SAE alloy-steel chemistry route for SAE 4140 and identifies composition rather than a universal mechanical-property contract.
Limitation: The SAE chemistry designation does not by itself define bar form, condition, dimensions, mechanical values, sampling, inspection, or certification.
- JIS G 4053:2023 Low-alloyed steels for machine structural use
Supports: Confirms the current JIS G 4053 edition and SCM440 chemistry route used in the cross-standard comparison.
Limitation: The public preview is not a substitute for the purchased standard and does not create purchaser-specific heat-treatment or mechanical requirements.
- GB/T 3077-2015 Alloy structure steels
Supports: Confirms the active Chinese standard identity used for the 42CrMo composition and reference-specimen mechanical-property route.
Limitation: The public record does not replace the licensed clauses governing specimen heat treatment, sampling, permissible variation, retest, and delivery acceptance.
Revision note: Expanded on 18 July 2026 with four-standard chemistry, size-banded mechanical evidence, legacy EN status, controlled-substitution workflow, and worked purchase wording.
Inquiry support
Send the required grade standard, allowed alternatives, size, and condition.
JOTAIN can review the stated grade, size, delivery condition, processing route, inspection requirements, and export details against the project requirement.