42CrMo4 / 4140 mechanical property specification for RFQs

Choose one complete material and product route before setting property values

The first RFQ decision is not the tensile number; it is the route that owns that number. 42CrMo4 is covered by ISO 683-2 for specified alloy-steel product forms and conditions. SAE 4140 is a chemical designation in SAE J404. ASTM A434/A434M can be invoked as a quenched-and-tempered alloy-bar product specification with strength classes and size controls, but 'ASTM 4140' does not identify a complete order. If a drawing says EN 10083-3, preserve the exact controlled edition or route an explicit standards-migration proposal to the design authority rather than silently replacing it.

Write the specification hierarchy in the inquiry: accepted purchase order and deviations; drawing and project material schedule; product/material standard and edition; test methods; inspection plan; then supplier procedures. Equivalent-grade tables may support sourcing research, but they cannot authorize substitution. A SAE 4140 offer against 42CrMo4 must state the proposed chemistry route, product specification, QT class or agreed property values, size limits, sampling, surface, inspection, certificate, and every variance.

Define the material state represented by acceptance. A bar may be hot rolled, forged, annealed, normalized, quenched and tempered, peeled, turned, ground, or rough machined. Thermal condition and surface route are separate fields. If the buyer will reforge or re-heat-treat after delivery, the incoming QT certificate does not guarantee the final component. If the supplier owns final QT, its qualification and production evidence must represent the ordered section and lot.

Start from the drawing's load case and failure consequence, but do not ask the bar supplier to infer design values. Procurement should obtain the required property schedule from engineering, then ask suppliers whether that schedule is achievable within the named standard route. Values on a website or historical certificate remain context until incorporated into accepted order language.

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Compare standard chemistry and section-banded mechanics without inventing equivalence

The chemistry ranges explain why 42CrMo4 and SAE 4140 are often reviewed together, but they are not identical. ISO 42CrMo4 permits a different carbon maximum, manganese band, chromium maximum, molybdenum maximum, and phosphorus/sulfur limits from the cited SAE 4140 row. An actual heat can meet one standard and miss another. Dual certification requires verification against both complete standards and product routes, not a seller's family-name statement.

ISO +QT mechanics are explicitly size-sensitive. The smaller round ruling-section row shown below has higher minimum yield and tensile range than the >40–100 mm row. Ruling section is the standard's basis for choosing a mechanical-property band; it is not automatically the final shaft's fatigue-critical diameter. The RFQ should identify the heat-treatment section, purchased size, finished geometry, and which section controls product acceptance.

SAE J404 does not supply one tensile, yield, elongation, impact, or hardness range for all 4140 bars. Pair it with a product specification and property route. ASTM A434/A434M is one possible QT bar route, but its class and applicable size must be named from the purchaser's licensed edition. Do not paste ISO 683-2 values beside SAE J404 chemistry and call the combination ASTM compliance unless engineering intentionally defines and approves that hybrid requirement.

Values are condensed from the named standards for RFQ screening. Verify the purchaser's licensed editions, product forms, heat and product analysis rules, delivery condition, ruling section, specimen geometry/location/orientation, impact temperature and averaging basis, class and size limits, dimensions, surface, sampling, and retest clauses. Only accepted order terms define the requirements for a specific supply.

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Sources:[1][2][3][4][5]

Define the specimen and section represented before accepting a test result

A tensile report is interpretable only when the specimen's identity and representation are known. ISO 6892-1 defines the room-temperature tensile method and the properties that can be determined; the product standard and order must define specimen geometry, location, orientation, preparation, test rate option where relevant, number of tests, acceptance, and retest. Ask whether a result comes from the production bar, a prolongation, a sacrificial bar, or a separately heat-treated coupon. Record the heat and heat-treatment lot it represents.

For a large bar, radial location can matter as much as diameter. Near-surface, mid-radius, and center material experience different cooling histories. If design requires center performance, the drawing or inspection plan must state a section-relevant verification route. A surface hardness check or a small coupon should not be described as proof of full-bar core properties. Conversely, do not demand destructive core testing on every lot without defining why it changes acceptance and how the specimen is to be taken.

Impact requirements need their own complete clause. ISO 148-1 defines the Charpy pendulum impact test method, but the product/order basis must still set specimen size, V-notch configuration, orientation, location, test temperature, number of specimens, minimum/average rule, and retest disposition. The ISO 683-2 values shown in the table must remain attached to their standard impact conditions. Do not compare a room-temperature result, a subsize specimen, and a low-temperature project requirement as if they were the same evidence.

Sampling frequency should reflect the process lot. Define a lot by heat, furnace charge or continuous-furnace batch, diameter, condition, and relevant process variables. If mixed heats or heat-treatment batches share a certificate, the buyer cannot tell what a failing or passing result represents. Require controlled notification when the supplier changes the qualified section, furnace route, quench medium, processing site, or specimen representation where the accepted order makes that change material.

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Use hardness as a defined control and make the certificate report actual evidence

Hardness may support process consistency, incoming machining control, or a project acceptance requirement, but it is not a universal proxy for tensile strength, toughness, fatigue, or core response. State the method and scale, target or range, surface preparation, indentation location, distance from ends, number and spacing of readings, product state, frequency, and treatment of individual versus averaged values. If a traverse is required, define the section and radial points. Do not rely on an unapproved scale conversion for acceptance.

Coordinate hardness with the process sequence. A reading taken before final tempering, grinding, stress relief, straightening, induction hardening, or coating preparation may not describe the delivered or finished state. Identify which operation establishes acceptance and which later operations can alter or obscure the result. If the buyer performs final heat treatment, incoming hardness should be labeled as an incoming control rather than a finished-part guarantee.

ISO 10474 defines inspection-document types supplied in accordance with the order. It does not decide which tests exist. List the actual certificate contents: grade and standard edition; heat analysis; product form and delivery condition; heat and heat-treatment lot; tensile, impact, and hardness results where ordered; specimen identity and location; dimensions, straightness, surface and marking; NDT report if separately required; deviations; and heat-to-bar or heat-to-bundle traceability.

If purchaser or third-party review is required, distinguish document review from witness and hold points. State notice period, records available before the event, who may waive attendance, who releases a nonconformance, and whether shipment waits for written release. A generic 'TPI accepted' line cannot substitute for an executable inspection plan.

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Convert the property schedule into a quotation-ready RFQ line

Give bidders one mandatory route and a separate place for alternatives. The mandatory line should fix the grade and product standard, edition, purchased and ruling section, length and quantity, delivery and surface condition, applicable property band, added project values, test representation, frequency, certificate, traceability, dimensions, surface, packing, and destination. The alternative schedule should show every chemistry, condition, property, sampling, inspection, price, and lead-time difference and require written approval before manufacture.

The worked example uses bracketed fields where the drawing owner must make a project-specific decision. It does not add a generic hardness range because neither ISO 683-2 nor SAE J404 creates one finished-component target for every 42CrMo4/4140 use. If the buyer chooses ASTM A434/A434M, replace the ISO route with the exact ASTM class, size and test basis from the controlled edition rather than mixing both casually.

At bid review, compare compliance line by line. Check whether each result represents the same state and section, whether excluded tests are visible, and whether deviations are priced rather than buried in notes. Resolve contradictions before PO release and require the supplier acknowledgment to repeat the accepted standard, condition, property route, sampling, certificate, and deviations. Only accepted order terms define the requirements for a specific supply.

Item: 42CrMo4 / 4140 alloy-steel round bars for shaft blanks, drawing [number / revision], [quantity]
Required route: 42CrMo4 to ISO 683-2:2016 [or purchaser-controlled adoption]; SAE 4140 is an alternative only when paired with SAE J404_200901 and an approved product/property specification
Size: Ø[ordered diameter] × [length / tolerance]; ruling section [definition]; heat-treatment blank and finished envelope shown on drawing
Delivery condition: +QT, [hot rolled / peeled / rough machined]; supplier to declare furnace-lot and straightening/stress-relief sequence
Mechanical requirements: [applicable size-band Rp0.2, Rm, A, Z and impact basis plus project additions]; no transfer from another section band or standard
Hardness: [method, scale, range if genuinely required, preparation, surface/radial locations, number of readings, frequency and nonconformance rule]
Sampling: [specimen geometry, axial/radial location, orientation, represented heat-treatment lot, tests per lot, impact temperature/averaging, retest rule]
Inspection: Heat analysis, ordered mechanics/hardness, dimensions, straightness, surface and marking; NDT only to the separately stated method, coverage, calibration and acceptance
Certificate: ISO 10474 type [state type] with actual results, specimen identity, heat, process-lot, bar/bundle traceability, deviations and linked reports
Alternatives: Clause-by-clause schedule with technical, price and lead-time effects; written purchaser approval required before manufacture
Packing / destination: [preservation, supports, bundle mass, port, Incoterm]
Only accepted order terms define the requirements for a specific supply.

Sources:[1][2][3][4][5][6]