Key takeaways
- Begin with the component drawing and the sequence from bar to finished part.
- Specify the heat-treated section, test representation and critical-surface inspections.
- Approve any change in grade or manufacturing route before production.
The component route is critical context
Describe the component and whether the purchased bar becomes a forging, a machined blank, or another intermediate product. Attach the drawing and process revision and identify critical transitions, journals, bores, and other features relevant to the inspection plan. Confirm who approves the material route and validates the finished part.
Section size and condition
List supplied diameter and length, forging or rough-machining dimensions, and the section during each heat-treatment stage. State the required delivery condition and allowance at critical surfaces. The specimen plan should identify which of those states and sections the reported properties represent.
Fatigue, toughness, and inspection
Translate specified toughness, fatigue, or internal-soundness concerns into the required tests and process checks. State tensile and impact sampling, hardness locations, UT method and coverage, inspection stage, and acceptance criteria. Keep final component validation on the drawing and process plan rather than inferring it from a bar certificate.
A study by Lanzutti and co-authors found that surface treatment and the flash region affected fatigue crack initiation in forged 42CrMo4 specimens. For a forged component, carry flash removal and critical-surface inspection into the manufacturing plan. The published specimen results are not a crankshaft or connecting-rod life rating. [5]
Why equivalent-grade wording causes trouble
Name one required grade and standard on the order. Where alternatives such as 42CrMo4 and SAE 4140 or 34CrNiMo6 and SAE 4340 are under review, require a comparison of the applicable product, chemistry, condition, properties, and sampling. Obtain approval before replacing the drawing designation or certificate requirement.
The full component route before the bar RFQ
Crankshafts and connecting rods combine geometry, section transitions, manufacturing history, and cyclic duty. A bar supplier cannot infer those design inputs from the component name. Provide the controlled drawing, supplied and finished envelopes, critical zones, forging or machining route, heat-treatment responsibility, surface operations, NDT stage, and component validation owner. Procurement then specifies only the bar evidence needed at the contractual supply boundary.
ISO 683-2 provides product and condition context for covered alloy steels, but it doesn't qualify a finished crankshaft or connecting rod. Avoid claims that a grade guarantees fatigue resistance, toughness, or service life. Where tensile or impact evidence is justified, link the ordered values to the approved product or project specification and define exactly which production material and process lot the specimen represents.
What the bar inspection can cover
| Decision | RFQ input | Evidence to return | Person accepting the result |
|---|---|---|---|
| Bar identity and state | Grade, product standard, edition, section, condition, surface, and process boundary | Inspection document, actual ordered results, heat and lot map | Material engineering accepts the incoming bar route |
| Mechanical representation | Tensile and impact methods, values, specimen geometry, orientation, location, temperature, frequency, and retest | Reports linked to heat covered, section, and treatment lot | Engineering and quality approve representation and judgment |
| Internal inspection | Applicable UT method, product state, coverage, reference basis, acceptance, end zones, personnel, and report | Approved procedure, personnel records, and identity-linked report | Buyer confirms bar-method applicability and indication disposition |
| Downstream component | Forging or machining, treatment, surface operations, final NDT, geometry, assembly, and validation plan | Records purchased under the downstream scope | Component owner retains finished-part acceptance |
Specimen representation and UT applicability
For tensile and Charpy testing, state specimen geometry, orientation, radial and longitudinal location, section covered, material state, treatment-lot link, frequency, and retest disposition. ISO 6892-1 and ISO 148-1 are test methods; they don't select component values or prove performance. A separately prepared coupon or near-surface specimen should represent production material only when the accepted product route and sampling schedule authorize it.
RFQ example
Item: Alloy-steel bars for [crankshaft or connecting-rod drawing and revision], [size and quantity]
Supply boundary: [bar or prepared blank]; downstream forging, machining, treatment, surface processing, final NDT, and validation by [party]
Material: [grade] to [product standard and edition], [section, condition, and surface]; alternatives quoted separately
Mechanical evidence: Approved tensile and Charpy requirements with methods, specimens, orientations, locations, temperature, lot covered, and retest
UT: Bar examination only to the applicable approved procedure, with state, coverage, reference basis, acceptance, end zones, personnel, and report fields
Documents: Actual results and heat-to-process-lot-to-bar map, deviations, subcontract reports, and inspection index
Approval and release: Written acceptance of alternatives and closure of the named hold point before dispatchQuestions buyers ask
What should a crankshaft steel bar RFQ include?
A crankshaft steel bar RFQ should include part route, controlling grade standard, diameter, length, rough and final sizes, delivery condition, heat-treatment expectation, drawing revision, inspection coverage, certificate requirement, quantity, packing, and destination.
Which steel grades are often reviewed for heavy-duty rotating parts?
Buyers often review alloy steel routes such as 42CrMo4 / 4140, 42CrMo, and 34CrNiMo6 / 4340 depending on section size, toughness, fatigue, heat treatment, and inspection requirements.
Why should drawing and inspection details be sent with the inquiry?
Drawing and inspection details help align rough size, machining allowance, heat-treatment condition, UT or mechanical testing, certificate scope, and shipment documents before the supplier prepares a quotation.
RFQ checklist
- Part route such as crankshaft, connecting rod, eccentric shaft, heavy shaft, or reciprocating component blank
- Controlling grade standard and acceptable equivalent-grade wording if alternatives are allowed
- Diameter, length, rough bar size, final drawing size, machining allowance, and section-size concerns
- Delivery condition, heat-treatment route, hardness target, or mechanical property requirement
- Fatigue, toughness, impact, internal soundness, or load-bearing requirement if specified
- Drawing revision, controlled dimensions, special notes, and document hierarchy
- Inspection coverage such as UT, hardness, mechanical testing, MTC, heat number, and third-party witness
- Packing, marking, traceability, destination, and shipment document requirements
- Component drawing revision, critical sections, duty concern, and supplied boundary
- Grade, product standard, edition, section, delivered condition, and surface route
- Forging, machining, treatment, surface work, NDT, assembly, and validation owners
- Tensile and impact methods, specimens, locations, orientation, temperature, lot, and retest
- UT applicability, state, coverage, reference basis, acceptance, personnel, and reports
- Alternative approval, heat and process-lot traceability, deviations, dossier, and release
References
- ISO 683-2:2016 Alloy steels for quenching and tempering
- ISO 6892-1:2019 Metallic materials — Tensile testing at room temperature
- ISO 148-1:2016 Metallic materials — Charpy pendulum impact test
- BS EN 10308:2002 Ultrasonic testing of steel bars
- Lanzutti et al.: fatigue, forging flash and surface treatment in 42CrMo4
Inquiry support
Working from a part drawing?
Send the drawing or RFQ with the grade, size, condition, processing, inspection, quantity, and destination. We can flag open points before quotation.