When both are called shaft steel, what really separates the choice?
A heavy-shaft decision between 1.7225 and 1.6582 must connect diameter, load spectrum, fatigue details, core toughness, heat treatment and inspection evidence.
42CrMo4 / 1.7225 and 34CrNiMo6 / 1.6582 are established quenched-and-tempered engineering steels. VCN150 offers nickel-assisted toughness and hardenability potential, while MO40 is an efficient solution for a broad range of shafts; neither name can replace a duty-based decision.
This guide is intended for designers, buyers, heat-treatment teams and workshops supplying parts across Iran. It translates a familiar market enquiry into requirements that can be checked before payment, cutting, machining or furnace work.
Quick decision map
| Question | Why it matters | Required evidence |
|---|---|---|
| Diameter and core location | Large sections amplify through-thickness differences | Effective diameter and required property at the critical radius |
| Load spectrum | Static torque, rotating bending, shock and overload create different needs | Duty cycle, peak load, reversals and service temperature |
| Fatigue details | Keyways, shoulders and surface damage may govern before bulk strength | Radius, finish, decarburisation and inspection plan |
| Heat treatment and evidence | The alloy advantage exists only through a controlled route | Condition-specific MTC, process record and representative tests |
Identity, standard and the real engineering question
The shaft is a system of material, diameter, transitions, keyways, surface condition, residual stress and service load. A grade comparison is meaningful only when both candidates are evaluated in the intended delivery and heat-treated condition.
MO40 is often a strong starting point where section and duty fit its proven Q&T capability. VCN150 becomes attractive for larger sections or high consequence where additional hardenability and toughness potential are technically required and can be verified.
Diameter and core location
Large sections amplify through-thickness differences. Record Effective diameter and required property at the critical radius before commercial comparison begins. If this field remains verbal, purchasing, production and inspection can each interpret the same requirement differently.
Load spectrum
Static torque, rotating bending, shock and overload create different needs. The order should therefore require Duty cycle, peak load, reversals and service temperature. Catalogue data becomes useful only after product form, section and test condition are made comparable.
Section, process and delivered condition
Section size changes cooling rate, property distribution, sampling position and sometimes the applicable property range. Product form also matters: bar, plate and forging may share a grade name but follow different dimensional, testing and delivery requirements.
Equal surface hardness does not mean equal fatigue life or core behaviour. Shaft performance can be dominated by stress concentration, straightness, residual stress, grinding damage, inclusions and the actual load history.
Inspection evidence that closes the decision
Evidence should answer a defined question. An MTC records heat identity and declared results; a process record proves the route used; a supplementary test report proves a result at a stated location. None of them should be treated as a substitute for the other two.
Fatigue details
Keyways, shoulders and surface damage may govern before bulk strength. Define Radius, finish, decarburisation and inspection plan and identify the point where production must stop if the evidence is missing or outside the agreed range.
Heat treatment and evidence
The alloy advantage exists only through a controlled route. Release should be based on Condition-specific MTC, process record and representative tests, attached to the same heat and piece identity. A valid test report has limited conformity value after traceability has been lost.
A defensible purchase specification
Provide the shaft drawing, raw and final diameter, length, critical radii and keyways, load and speed, delivery condition, heat-treatment route, straightness allowance, NDT and core-property acceptance location.
Grade/material number: [complete]; standard and edition: [complete]; form and dimensions: [complete]; delivery condition: [complete]; quantity and cutting tolerance: [complete]; MTC type: [complete]; supplementary test and acceptance rule: [complete]. Topic-specific requirement: Provide the shaft drawing, raw and final diameter, length, critical radii and keyways, load and speed, delivery condition, heat-treatment route, straightness allowance, NDT and core-property acceptance location.
Ordering checklist for Tehran, Tabriz, Isfahan and Yazd
- Write the recognised market term, but place MO40 or VCN150 and the documented designation on the same enquiry.
- Close Diameter and core location with Effective diameter and required property at the critical radius.
- Close Load spectrum with Duty cycle, peak load, reversals and service temperature.
- Define Fatigue details before irreversible processing.
- Keep Heat treatment and evidence traceable through cutting, storage and loading.
- State destination, required dispatch date, packaging, piece count and who authorises release.
Related encyclopaedia pages and guides
- 42crmo4 1 7225
- 34crnimo6 1 6582
- Previous Week-01 technical guide
- Next Week-01 technical guide
- Alloy-steel encyclopaedia
- Evidence and calculation methodology
- Contact Shaygan Steel
Frequently asked questions
Is VCN150 always better for a large shaft?
No. It is justified when section, toughness or consequence need it and the process can demonstrate the required properties.
Does equal hardness mean equal performance?
No. Core properties, toughness, cleanliness, fatigue details and residual stress can differ at the same local hardness.
Which purchasing document matters most?
The traceable MTC is essential, but it must be combined with the drawing, delivery condition, process record and any specified supplementary tests.
Sources and method
This article uses the official references below as technical orientation and translates them into a procurement workflow for the Iranian market. A producer data sheet applies to the product and conditions it states; it does not replace the current purchase standard, drawing or MTC for the delivered heat.
- Ovako Steel Navigator — official technical reference
- Ovako Steel Navigator — official technical reference
- Ovako Material Data Sheets — official technical reference
Conclusion and next step
Start with load, geometry and failure consequence. Choose MO40 when it closes the requirement efficiently; choose VCN150 when the real section and duty need—and the evidence confirms—its additional capability.
For an enquiry, send material number, form, raw and final dimensions, quantity, delivery condition, inspection needs and destination in one message. Shaygan Steel can then review the evidence for current stock before proposing a supply route.
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