Key takeaways
- Do not purchase a finished fastener property class by naming a bar grade. ISO 898-1 governs defined finished bolts, screws, and studs; the bar standard, heat treatment, thread manufacture, and finished-product tests must be connected in the order.
- 35CrMo, 40Cr, 42CrMo, 42CrMo4, and SAE 4140 are standard-specific routes, not a single ladder of interchangeable names. Keep the designation, edition, chemistry, delivery condition, and allowed substitution authority explicit.
- Reference-specimen mechanical values and size-banded +QT values are screening evidence, not blanket guarantees through every ordered diameter or finished thread root. State the heat-treatment section and test location.
- Thread rolling or cutting, decarburization, surface discontinuities, electroplating, hydrogen control, lot traceability, and release testing can change the risk after the bar certificate has been issued. Allocate those controls before quotation.
Translate the finished fastener duty into a bar route
Start with the finished item and its controlling drawing or product standard, not with a familiar alloy name. Record whether the supply becomes a fully threaded stud, headed bolt, tie rod, machined blank, rolled-thread component, or a bar that another party will heat treat. State thread system and size, stressed length, unthreaded shank, head or end geometry, minimum service temperature, preload method, cyclic or impact exposure, corrosion environment, and the consequence of fracture. These details decide which properties and inspections are relevant; a nominal tensile target alone does not describe thread-root fatigue, delayed fracture, stripping, or brittle-impact risk.
Keep three dimensions separate: ordered bar diameter, heat-treatment section, and finished fastener geometry. A bar may be rough turned before quenching, heat treated as a blank, then rolled or cut to its final thread. Cooling distance and property uniformity follow the heat-treatment section, while fatigue and surface acceptance follow the finished thread and transitions. If the supplier receives only the final thread diameter, it may qualify a different section from the one actually processed. The RFQ should identify who owns heat treatment and whether reported results represent the production blank, a prolongation, a separately heat-treated coupon, or the finished fastener.
A grade certificate also does not create a finished property class. ISO 898-1 defines mechanical and physical requirements for specified metric bolts, screws, and studs tested within its scope, and explicitly does not cover every service characteristic such as fatigue, shear, corrosion resistance, or torque-clamp performance. Use it when the finished item is in scope, but supplement it with drawing requirements and application validation where the joint design depends on excluded behavior. If another fastener standard controls, name that standard and edition rather than borrowing an ISO 898-1 class label.
Sources:[4]
Compare standard routes without assuming equivalence
The comparison below keeps each designation inside its controlling route. GB/T 3077 gives chemistry and prescribed reference heat-treatment specimen values for 35CrMo, 40Cr, and 42CrMo. ISO 683-2 gives 42CrMo4 chemistry and quenched-and-tempered properties by ruling-section band. SAE J404 controls the chemical composition of SAE alloy steels such as 4140 but does not create a universal mechanical-property guarantee. Similar-looking chromium-molybdenum names can overlap in chemistry, yet their limits, sampling rules, delivery options, and mechanical-property basis are not identical.
Use the table to screen bids, then verify the licensed standard edition and all order options. A bidder proposing 42CrMo4 against a 42CrMo requirement should submit a clause-by-clause deviation, not only an equivalence statement. Likewise, an SAE 4140 chemistry certificate cannot establish ISO size-banded +QT properties. Approval should cover the exact standard, product form, heat-treatment condition, section band, specimen location, inspection document, and finished-fastener requirements.
| Grade / standard route | Chemical composition range (mass %) | Mechanical-property basis for screening | Buyer interpretation |
|---|---|---|---|
| 35CrMo — GB/T 3077-2015 | C 0.32–0.40; Si 0.17–0.37; Mn 0.40–0.70; Cr 0.80–1.10; Mo 0.15–0.25; P ≤0.030; S ≤0.030; Ni ≤0.30; Cu ≤0.30. | Prescribed reference heat-treated specimen: Rm ≥985 MPa; yield ≥835 MPa; A ≥12%; Z ≥45%; KV2 ≥63 J. | A GB route often reviewed for high-strength threaded parts. Confirm specimen basis, ordered section, heat treatment, and finished-fastener tests; do not apply the reference values automatically through the bar. |
| 40Cr — GB/T 3077-2015 | C 0.37–0.44; Si 0.17–0.37; Mn 0.50–0.80; Cr 0.80–1.10; P ≤0.030; S ≤0.030; Ni ≤0.30; Cu ≤0.30. | Prescribed reference heat-treated specimen: Rm ≥980 MPa; yield ≥785 MPa; A ≥9%; Z ≥45%; KV2 ≥47 J. | A chromium-alloy route for suitably engineered duties; its reference elongation and impact line differ from the Cr-Mo routes and still need an order-specific section basis. |
| 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 ≥930 MPa; A ≥12%; Z ≥45%; KV2 ≥63 J. | A GB Cr-Mo route with higher listed reference strength than 35CrMo, but not proof of finished-thread fatigue, core response, or compliance with an ISO/SAE designation. |
| 42CrMo4 +QT — ISO 683-2:2016, d >16–40 mm | 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. | Round ruling section: Rp0.2 ≥750 MPa; Rm 1000–1200 MPa; A ≥11%; Z ≥45%; KV ≥35 J. | Use only when the product form, +QT condition, ruling section, sampling, and impact basis match the order. The row cannot qualify a larger heat-treatment section. |
| 42CrMo4 +QT — ISO 683-2:2016, d >40–100 mm | Same ISO 683-2 42CrMo4 chemistry range as the preceding row. | Round ruling section: Rp0.2 ≥650 MPa; Rm 900–1100 MPa; A ≥12%; Z ≥50%; KV ≥35 J. | The lower size-banded strength illustrates why buyers must state the actual ruling section instead of copying the smaller-diameter line into an RFQ. |
| 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. | J404 is a chemical-composition route; no universal mechanical-property range is created by the designation alone. | State the separate bar/product specification, delivery condition, heat-treatment section, required properties, sampling, and finished-fastener test standard. |
Values are condensed from the named standards for buyer-side RFQ comparison. Confirm licensed editions, analysis type and permissible deviations, product form, delivery condition, ruling section, specimen position/orientation, impact test basis, and all order options. Reference-specimen or size-banded values are not universal finished-bar or finished-fastener guarantees. Only accepted order terms define the requirements for a specific supply.
Qualify hardenability, heat treatment, and thread manufacture together
Hardenability describes depth response during quenching; it is not a specified surface hardness or guaranteed core property. ISO 642 standardizes the Jominy end-quench test and also provides for an agreed calculated curve within its stated field. Jominy information can help compare heats or control a band, but it does not reproduce the bar diameter, blank geometry, furnace load, transfer time, quenchant, agitation, temper, or straightening used in production. For a critical or large-section fastener, agree how production-section properties will be demonstrated and whether a process qualification, sacrificial blank, prolongation, or lot test is required.
Choose the thread stage deliberately. Rolling after appropriate heat treatment can create a different surface and residual-stress condition from cutting; rolling before final heat treatment exposes the thread to scale, decarburization, distortion, and later finishing. Cutting removes material and can expose internal discontinuities or machining damage. Procurement should not claim one route is always superior. It should state the permitted sequence, starting diameter and allowance, thread standard and tolerance, end geometry, surface-discontinuity acceptance, decarburization control, and which dimensions and properties are checked after the final thermal and mechanical operations.
Ask who owns the heat-treatment recipe, lot definition, furnace and quench controls, tempering, straightening, reheat or repair restrictions, and retest disposition. The supplier can protect proprietary process details while still declaring the variables that would constitute a process change. If bars are supplied annealed for the buyer's later treatment, the bar supplier should not be asked to guarantee final fastener properties it does not control; instead, order the material and hardenability evidence needed by the downstream validated route.
Control evidence after the bar certificate
Build the inspection plan around the point at which each characteristic becomes final. The bar certificate can report heat chemistry, material condition, dimensions, and agreed bar tests. Heat treatment creates the final strength and toughness route; threading creates roots, flanks, runouts, and dimensional characteristics; coating changes dimensions and may introduce hydrogen risk. A single mill test certificate issued before those operations cannot release the finished fastener. Define heat and processing-lot traceability so later tensile, proof-load, hardness, impact, decarburization, surface, dimensional, coating, and other specified results can be linked to delivered pieces.
For finished products within its scope, ISO 898-1 provides property-class requirements and test methods, but the purchase order must still state the product standard, dimensions, property class, lot and sampling basis, and any drawing additions. Do not substitute bar tensile results for proof load or finished-product testing without written engineering approval. If fatigue is design-critical, establish the applicable component or joint validation rather than inferring fatigue life from Rm. Likewise, specify UT only when the drawing, product risk, customer requirement, or approved inspection plan calls for it, with a named method, coverage, reference basis, acceptance criteria, stage, and report.
If electroplating is planned, allocate hydrogen-embrittlement prevention and verification before the material is chosen and quoted. ISO 4042 covers electroplated coating systems for fasteners and measures intended to minimize hydrogen-embrittlement risk; its scope is not a promise that plating is harmless. State coating system and thickness, thread allowance and gauging stage, cleaning restrictions, baking or relief requirements required by the approved route, lot traceability, testing, and approval of alternative finishes. High hardness, sustained tensile stress, acidic cleaning, and delayed loading warrant a coordinated fastener-manufacturer and plater review.
Issue an RFQ that separates requirements from alternatives
The worked line below is an example of how to expose the decisions that materially affect quotation. It does not select a property class or acceptance plan for a real joint. Replace the bracketed fields with drawing-approved values and name the controlling editions. If the order is for bar only, say that downstream heat treatment and finished-fastener compliance remain with the purchaser; if the supplier owns the finished route, include all final tests and release evidence.
Ask each bidder to return a compliance matrix showing material source and standard, chemistry route, delivery condition, heat-treatment blank and responsibility, thread sequence, coating subcontractor or route, sample/test location, inspection document, deviations, minimum production quantity, destructive-test allowance, lead time, and packing. Compare deviations before price. A quote that silently converts 42CrMo to 42CrMo4, reports a small reference specimen for a large blank, or excludes final coating tests is not commercially comparable with a fully scoped bid.
At order acceptance, freeze the drawing revision, standards and editions, approved grade and alternatives, bar and blank sizes, heat treatment, thread route, mechanical and inspection requirements, lot definition, traceability, coating, hold or witness points, certificate content, deviation authority, preservation, marking, and destination. Resolve any change in the supplier acknowledgment before material is released. Only accepted order terms define the requirements for a specific supply.
Item: Alloy steel bar for rolled-thread stud production
Material route: 35CrMo to GB/T 3077-2015; 42CrMo alternative only by separate deviation and written purchaser approval
Finished fastener: M36 × 3 fully threaded stud to drawing FS-214 rev C; finished property standard/class [state approved requirement]
Bar size: Ø[approved blank diameter] × [length], [quantity]; supplier to identify heat-treatment section and machining allowance
Heat treatment: Quench and temper as production blanks; process owner, lot definition, test-piece relationship and property locations to be stated
Thread route: Roll after heat treatment; thread tolerance, runout, decarburization and surface-discontinuity requirements per drawing/specification
Inspection: Actual heat chemistry, agreed mechanical tests, hardness, dimensions, surface, thread gauges, heat/process-lot traceability and final release report
Coating: [system and thickness] to ISO 4042:2022 plus Amendment 1:2026 where contractually adopted; hydrogen-control plan and final gauging to be confirmed
Certificate: [required inspection document] with actual results and report references
Alternatives/deviations: No substitution without written purchaser approval
Packing/marking/destination: Preserve heat and lot identity; [packing method]; [city, country and delivery term]Fastener bar material selection before RFQ buyer questions
Which steel grades are commonly reviewed for fastener bars?
Buyers often screen 35CrMo, 40Cr, 42CrMo, 42CrMo4, and SAE 4140 routes, but should not rank them by name alone. Compare the controlling standard and edition, heat-treatment section, required finished-fastener property standard, thread and coating sequence, section-relevant evidence, inspection plan, and approval history.
What should buyers send before selecting fastener bar material?
Send the fastener drawing and product standard, joint/service notes, required material standard and alternatives, ordered and heat-treatment sizes, thread route, heat-treatment responsibility, finished property requirement, test locations, coating and hydrogen controls, inspection document, traceability, quantity, packing, and destination.
What should buyers include when sourcing fastener bar material?
Include the exact fastener and material standards with editions, grade, dimensions, quantity, heat-treatment section and condition, thread stage, property and sampling basis, surface/coating route, inspection and lot traceability, deviation approval, packing, and destination. Separate mandatory requirements from alternatives the supplier may propose.
Fastener bar material selection before RFQ RFQ checklist
- Finished fastener type, drawing revision, product standard, property class or approved requirement, and joint duty
- Required bar designation, controlling material standard and edition, and separately approved alternatives
- Ordered bar diameter/length, heat-treatment blank or ruling section, final thread geometry, quantity, and allowance
- Product form, delivery condition, heat-treatment owner, lot definition, and permitted process changes
- Thread rolling or cutting sequence, starting size, tolerance, runout, end details, and final gauging stage
- Required yield/tensile, elongation, reduction, impact, hardness, proof-load, or other finished tests with scope
- Specimen relationship, location, orientation, frequency, retest rules, and nonconforming-lot disposition
- Hardenability or production-section qualification requirement when section response is acceptance-critical
- Surface discontinuity, decarburization, dimensional, marking, and preservation requirements
- Coating system, thickness, thread allowance, hydrogen-control route, testing, and alternative-finish approval
- Inspection document, actual results, heat/process-lot traceability, report references, and record retention
- Purchaser or third-party hold/witness points, deviation authority, release status, packing, destination, and delivery term
References
- GB/T 3077-2015 Alloy structure steels
Supports: Official catalog status, publication and implementation dates for the GB/T 3077 alloy structural steel route used for 35CrMo, 40Cr, and 42CrMo screening.
Limitation: The public catalog page does not reproduce the licensed chemistry, specimen, heat-treatment, sampling, or mechanical-property tables; purchasers must verify the controlled standard text and order clauses.
- ISO 683-2:2016 Heat-treatable steels, alloy steels and free-cutting steels — Part 2: Alloy steels for quenching and tempering
Supports: Official scope for alloy steel semi-finished products, bars, wire rod, hot-rolled strip, forgings, and size-restricted quenched-and-tempered mechanical-property routes.
Limitation: The catalog is not the licensed table set and the standard excludes some product forms, including bright and cold-heading bars; applicability, order options, section and sampling basis must be checked.
- SAE J404_200901 Chemical Compositions of SAE Alloy Steels
Supports: Official SAE catalog route for chemical-composition limits of SAE alloy steels, including the 4140 designation used in the comparison table.
Limitation: J404 is a chemistry standard and does not by itself specify bar delivery condition, section-based mechanical properties, heat-treatment capability, or finished-fastener performance.
- ISO 898-1:2013 Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1
Supports: Official scope and property-class route for specified metric bolts, screws, and studs made of carbon and alloy steel, including stated test-temperature and dimensional limits.
Limitation: The scope does not cover every service property, including weldability, corrosion resistance, shear resistance, torque-clamp behavior, or fatigue resistance; the catalog does not replace the licensed test clauses.
- ISO 642:2024 Steel — Hardenability test by end quenching (Jominy test)
Supports: Official current route for determining steel hardenability by the Jominy end-quench method and, within its field, an agreed calculated hardenability curve.
Limitation: A Jominy curve characterizes hardenability under a standardized route; it does not guarantee hardness, microstructure, toughness, or mechanical properties throughout a production-size fastener blank.
- ISO 4042:2022 Fasteners — Electroplated coating systems
Supports: Official scope for electroplated coating systems on fasteners, dimensional considerations, and measures intended to minimize hydrogen-embrittlement risk.
Limitation: The catalog and standard route do not prove that a selected fastener is immune to hydrogen damage; material hardness, cleaning, plating, baking, loading, testing, and joint approval remain order-specific.
Revision note: Expanded on 2026-07-19 with standard-specific chemistry and mechanical-property bases, finished-fastener and hardenability boundaries, thread/coating risk controls, a worked RFQ line, and source limitations.
Inquiry support
Send part route, grade, condition, inspection needs, and destination.
JOTAIN can review the stated grade, size, delivery condition, processing route, inspection requirements, and export details against the project requirement.