Key takeaways
- Hardness is not the same as hardenability: one is a stated local measurement, while the other describes response through depth as cooling conditions change.
- An actual end-quench result, an agreed hardenability band, an agreed calculated curve, and finished-section verification answer different questions and must not be treated as interchangeable evidence.
- Section size, geometry, heat-treatment route, and process uncertainty belong in the evidence decision because distance from the quenched end is not literal depth in every finished component.
- The RFQ should name the standard and edition, evidence route, heat or lot identity, acceptance basis, reporting route, and supplier-purchaser approval of any alternative.
Hardness is not hardenability
Hardness is a result produced with a named test scale, surface preparation, material condition, and measurement location. It describes the condition at that location. Hardenability describes how steel responds through depth when cooling conditions change. Hardness is not the same as hardenability, and neither term by itself establishes strength, toughness, fatigue resistance, wear life, or suitability for a component.
That distinction matters before a buyer compares grades. Two heats within a permitted composition range can produce different hardenability evidence, and a finished section can experience cooling that differs from a standardized test specimen. A grade designation therefore starts the technical review; it does not close the evidence question.
For an RFQ, first state the finished or rough section, delivery condition, intended heat-treatment route, and the property question that must be controlled. Then select evidence that answers that question. Asking only for a hardness value can miss depth response, while asking only for a Jominy result can miss the processed section and the location where the finished requirement applies.
ISO 642:2024, ASTM A255-20a, and SAE J406_202402 provide method context for hardenability determination. Their scopes do not convert a standardized test into a finished-part design rule. The purchaser remains responsible for connecting material evidence to the governing drawing, application analysis, heat-treatment procedure, and acceptance specification.
What the end-quench method measures
The end-quench method creates a controlled cooling gradient in a standardized specimen. Conceptually, the specimen is austenitized, one end is water quenched, prepared flats are produced, and hardness positions are evaluated along it. The licensed standard controls the procedure and reporting details.
An actual end-quench result is measured evidence from an identified specimen or heat under the named method and edition. ISO 642:2024 also permits an accepted calculation model by agreement for a defined application. ASTM A255-20a describes end-quench and chemical-composition calculation methods, requires supplier-user agreement on the selected method, and requires the certified material test report (CMTR) to state it.
SAE J406_202402 says actual Jominy tests remain important despite prediction methods. Estimates can support review when inputs and limits are clear, but they remain estimates. Final correlation on actual parts is necessary when the decision concerns the processed component.
How distance from the quenched end is interpreted
Distance from the quenched end is the controlled position axis of the end-quench test. The quenched end experiences the most direct cooling, and positions farther away represent a changing cooling response within that standardized arrangement. The measured sequence describes the hardenability response of the identified test material under the stated method.
That distance must not be read as literal depth in every finished part. A round bar, stepped shaft, forged blank, bored component, or heat-treated assembly has its own geometry, thermal path, surface condition, loading significance, and process controls. Mapping a test position directly to a component location without a validated model or finished-section evidence overstates what the test establishes.
A plotted record needs an identity: actual measured result, contract-defined band, or calculated curve; governing standard and edition; relevant heat, specimen, inputs, or specification; and reporting convention. The RFQ must not invent distances, hardness values, or band limits from a public illustration.
Why section size changes the buyer decision
Section size matters because a processed bar or component does not cool uniformly merely because its grade name is familiar. Relevant geometry may include diameter, wall thickness, local transitions, machining stock, bores, shoulders, and the location where a requirement applies. The heat-treatment equipment, loading arrangement, austenitizing route, quench route, tempering route, and process variation also affect the engineering context.
SAE J413_202412 treats section size as material to composition selection for heat-treated wrought steels. Its charts are contextual rather than universal acceptance data, and exact information may require testing an individual heat. Section size is therefore an input to the decision, not a standalone predictor of properties and not proof that a named composition will meet a finished location.
SAE J406_202402 likewise keeps prediction in perspective: estimates can be useful but imprecise, while actual Jominy testing remains important and final correlation on actual parts may be necessary. Application consequence, unusual geometry, an unfamiliar heat-treatment route, or uncertain transfer can justify stronger evidence, but there is no universal threshold.
Choose actual, band, calculated, or finished-section evidence
The four routes are separate contractual choices. An actual result is measured under the selected method. An agreed band supplies controlling limits from a named specification. An agreed calculated curve is an estimate from stated inputs under a permitted model. Finished-section verification measures the processed outcome at agreed locations and condition.
An actual result does not establish every finished location, and there is no universal band. A calculated route is usable only when the material chemistry and product are within the selected standard or model scope and its declared ranges. A calculated curve must identify its inputs, model, edition, application, and calculated status; it is neither tested evidence nor proof of a finished condition.
Finished-section verification is separately defined when consequence, geometry, process uncertainty, or design control makes other evidence insufficient. It is not automatically required by the Jominy method; its locations, preparation, condition, acceptance basis, traceability, and disposition must be agreed.
| Question answered | Minimum input or agreement | Evidence returned | Principal limitation | Condition that triggers stronger verification |
|---|---|---|---|---|
| Actual end-quench result | Named standard and edition, identified heat or specimen, test route, reporting convention, and acceptance basis | Measured position-by-position end-quench evidence from the identified test record | Method-specific evidence; not a direct measurement of the finished section | Finished geometry, process transfer, consequence, or location-specific requirements remain unresolved |
| Agreed hardenability band | Controlling specification, approved band source, applicable grade or heat identity, method, and disposition rule | Comparison with the agreed upper and lower limits for the controlling hardenability requirement | No universal band; the governing limits and method must come from the contract | The band does not resolve finished-section response or an unusual process route |
| Agreed calculated curve | Permitted standard route, accepted model, stated composition and inputs, governing edition, application, and reporting label | A calculated estimate generated from the agreed inputs and identified model | Calculated is not tested, and model applicability does not establish a finished-part result | Input uncertainty, model limits, application consequence, or process correlation requires measured evidence |
| Finished-section verification | Processed condition, measurement locations, preparation, method, acceptance basis, traceability, and disposition ownership | Measurements from the processed finished section or representative controlled section at the agreed locations | Location-specific evidence; it does not turn one result into a universal material guarantee | The drawing, design review, or process-validation plan requires direct confirmation of the delivered outcome |
The matrix selects evidence qualitatively. It does not create a named-grade curve, band limits, acceptance values, specimen dimensions, or a universal escalation rule.
State the limits of grade names and generic curves
A designation such as 4140 or 42CrMo4 identifies a specification route, not one universal hardenability curve. Composition ranges, product standard, heat identity, test method, material condition, and reporting basis still matter. Related product pages can help buyers organize grade-route questions, but they do not supply interchangeable curves or establish equivalence for a particular order.
No generic numerical Jominy curve for 4140, 42CrMo4, or another named grade is approved for this article. The reviewed public evidence does not provide a reusable dataset with verified steel identity, composition, heat treatment, specimen preparation, hardness scale, measurement positions, and test-method metadata.
The NIST paper Impact properties of slack-quenched alloy steels is historical research by M. R. Meyerson and S. J. Rosenberg. In that study, experimental curves did not generally coincide with computed curves. This supports caution about treating calculation as measurement, but it establishes no general error direction and supplies no generic modern grade curve, current band, or finished-section prediction.
The SAE paper Use of Hardenability Tests for Selection and Specification of Automotive Steels is historical method context only. It does not support modern dimensions, acceptance values, current grade performance, or supplier capability, and it does not enlarge the scope of current method records.
Write the RFQ wording and verification checklist
A workable RFQ statement begins with the question to be controlled: standardized hardenability evidence, conformance to an agreed band, a permitted calculated estimate, or the processed condition at defined finished-section locations. It then names the governing standard and edition, product and grade specification, section and geometry, delivery condition, heat-treatment route, heat or lot identity, reporting route, and acceptance source.
Suggested structure: Hardenability evidence shall follow the named standard and edition. Supplier and purchaser shall agree whether the order uses an actual end-quench result, the controlling hardenability band, or an accepted calculated curve. The CMTR or agreed report shall identify the determination method and traceability. Any finished-section verification shall be separately defined by condition, location, method, acceptance basis, and disposition.
When a band controls, attach or reference the licensed specification and identify which limits apply; do not paste an unattributed curve into the inquiry. When calculation is permitted, state the accepted model, inputs, governing edition, field of application, declared chemistry range, report label, and approval route. Do not permit a calculated record to be relabeled as tested evidence.
When the finished outcome controls, coordinate the requirement with the drawing owner, heat-treatment plan, and quality documentation. Material-certificate identity belongs in the MTC guide. Internal-soundness inspection belongs in the UT guide and is not a substitute for hardenability or finished-section hardness verification.
Jominy hardenability and section-size evidence for steel bar RFQs buyer questions
What is the difference between hardness and hardenability?
Hardness is a named-scale result at a stated location, preparation, and condition. Hardenability describes response through depth as cooling conditions change. It does not by itself establish strength, toughness, wear life, or finished-part suitability.
Does a Jominy curve predict finished-part hardness?
No. An end-quench record describes standardized test evidence. Finished response also depends on section geometry, heat-treatment route, process variation, and measurement location. Direct finished-section verification must be separately specified when that outcome controls.
Can a calculated curve replace an actual end-quench result?
Only when the governing method permits calculation and the parties agree it for the defined application. The record must state its model, inputs, edition, and calculated status. It remains an estimate, not tested evidence.
When should an RFQ require finished-section verification?
Consider it when geometry, process transfer, application consequence, or location-specific requirements make standardized or calculated evidence insufficient. The drawing or validation plan should define condition, locations, method, acceptance basis, traceability, and disposition.
Jominy hardenability and section-size evidence for steel bar RFQs RFQ checklist
- Controlling steel grade, product standard, and edition, with any equivalent designation treated only as a purchaser-approved alternative
- Product form, ordered section, relevant finished geometry, machining stock, and location where the property requirement applies
- Delivery condition and intended heat-treatment route using unambiguous condition terminology
- Named hardenability standard and edition, including any purchaser-specific adoption or supplementary requirement
- Selected evidence route: actual end-quench result, agreed hardenability band, agreed calculated curve, or finished-section verification
- Heat, lot, specimen, or processed-section identity needed to connect the evidence to the order
- For an actual test, the required report identity, hardness scale, position convention, and agreed acceptance comparison
- For a band, the controlling licensed specification, applicable limits, method, and discrepancy disposition
- For a calculated curve, the accepted model, required composition and other inputs, governing edition, permitted application, and calculated label
- For finished-section verification, the processed condition, measurement locations, preparation, method, acceptance basis, and disposition owner
- CMTR wording that states the hardenability determination method and preserves heat or lot traceability
- Any required heat-treatment records, mechanical-property evidence, hardness records, or certificate submission timing
- Separate UT requirement when internal soundness is relevant, without treating UT as hardenability evidence
- Purchaser approval route for method changes, alternative evidence, deviations, and order-specific calculations
- Quotation-stage confirmation of unresolved assumptions without a supplier capability, stock, delivery, or finished-performance claim
References
- ISO 642:2024 - Steel - Hardenability test by end quenching (Jominy test)
Supports: Supports steel hardenability determination by end quenching and, by agreement for a defined application, replacement by an accepted calculation model.
Limitation: The public page supports scope only; it does not license reproduction of procedure details, dimensions, acceptance content, or a named-grade curve.
- ASTM A255-20a - Standard Test Methods for Determining Hardenability of Steel
Supports: Supports end-quench and chemical-composition calculation methods; the supplier and user agree which method applies, and the certified material test report (CMTR) states the method of determination.
Limitation: A permitted calculation remains calculated evidence, not an actual test and not a finished-part guarantee; calculation applies only within the standard's specified composition ranges, and contract details require the licensed edition.
- SAE J406_202402 - Methods of Determining Hardenability of Steels
Supports: Supports method and prediction context: actual Jominy tests remain important despite prediction methods, and the selected determination route must remain identifiable.
Limitation: Prediction estimates can be useful but imprecise, and final correlation on actual parts is necessary; the method scope covers shallow- and medium-hardening steels and excludes deep-hardening steels that normally air harden.
- SAE J413_202412 - Mechanical Properties of Heat Treated Wrought Steels
Supports: Supports that section size is material to composition selection when reviewing heat-treated wrought-steel property context.
Limitation: Its charts are contextual, and exact information may require individual-heat testing; it does not replace application design, process validation, or finished-section evidence.
- Impact properties of slack-quenched alloy steels
Supports: Historical slack-quenched alloy-steel research by M. R. Meyerson and S. J. Rosenberg in which experimental curves did not generally coincide with computed curves.
Limitation: This is not a generic modern grade curve, error direction, current acceptance band, or finished-section prediction; its historical steels and methods bound its use.
- Use of Hardenability Tests for Selection and Specification of Automotive Steels
Supports: Provides historical context for the development and use of hardenability tests in steel selection and specification.
Limitation: Historical method context only; it does not support modern dimensions, acceptance requirements, grade performance, finished-section claims, or supplier capability.
Revision note: Published 2026-07-14 after source-scope review of ISO 642:2024, active ASTM A255-20a, SAE J406_202402, SAE J413_202412, and the bounded historical NIST and SAE records. Revalidate editions and contractual wording before reuse.
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