Lower purchase price or lower lifetime risk?
Choose CK45 or MO40 by load, section, fatigue, surface treatment, manufacturing route and failure cost—not by raw-material price or hardness alone.
C45E / 1.1191 and 42CrMo4 / 1.7225 can both appear in shaft, pin and machine-part enquiries, but their alloy design and through-section response are different. The economical choice is the grade-process combination that meets duty with controlled manufacturing and acceptable failure consequence.
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 |
|---|---|---|
| Load and failure mode | Separates simple static duty from fatigue, impact or overload | Load spectrum, stress raisers, service environment and consequence |
| Section and core requirement | A larger effective section increases the value of hardenability | Critical diameter, core property and test position |
| Surface and heat treatment | Induction hardening, Q&T and local treatment create different cases and cores | Qualified route, case requirement and tempering condition |
| Total manufacturing cost | Raw-price savings can be lost in scrap, testing or downtime | Material, machining, treatment, inspection and failure cost |
Identity, standard and the real engineering question
CK45 is a medium-carbon steel used widely for general machine components and surface-hardening routes. MO40 adds chromium and molybdenum and is normally considered when hardenability, section strength or demanding fatigue duty justifies the additional material and process control.
CK45 may be fully adequate when section, load and required properties are moderate and a suitable surface treatment protects the working zone. MO40 is not an automatic upgrade; its benefit appears when the part and heat-treatment route actually use its greater hardenability.
Load and failure mode
Separates simple static duty from fatigue, impact or overload. Record Load spectrum, stress raisers, service environment and consequence before commercial comparison begins. If this field remains verbal, purchasing, production and inspection can each interpret the same requirement differently.
Section and core requirement
A larger effective section increases the value of hardenability. The order should therefore require Critical diameter, core property and test position. 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.
Machinability depends strongly on delivered hardness and microstructure. Welding either grade requires procedure control, but the higher hardenability of MO40 increases sensitivity to hydrogen cracking and hard heat-affected zones unless preheat, consumable and cooling are controlled.
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.
Surface and heat treatment
Induction hardening, Q&T and local treatment create different cases and cores. Define Qualified route, case requirement and tempering condition and identify the point where production must stop if the evidence is missing or outside the agreed range.
Total manufacturing cost
Raw-price savings can be lost in scrap, testing or downtime. Release should be based on Material, machining, treatment, inspection and failure cost, 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
Send component duty, drawing, raw and final section, delivery condition, planned heat treatment, critical surface/core property, inspection method and acceptable failure risk before comparing CK45 and MO40 quotations.
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: Send component duty, drawing, raw and final section, delivery condition, planned heat treatment, critical surface/core property, inspection method and acceptable failure risk before comparing CK45 and MO40 quotations.
Ordering checklist for Tehran, Tabriz, Isfahan and Yazd
- Write the recognised market term, but place CK45 or MO40 and the documented designation on the same enquiry.
- Close Load and failure mode with Load spectrum, stress raisers, service environment and consequence.
- Close Section and core requirement with Critical diameter, core property and test position.
- Define Surface and heat treatment before irreversible processing.
- Keep Total manufacturing cost traceable through cutting, storage and loading.
- State destination, required dispatch date, packaging, piece count and who authorises release.
Related encyclopaedia pages and guides
- c45e 1 1191
- 42crmo4 1 7225
- Previous Week-01 technical guide
- Next Week-01 technical guide
- Alloy-steel encyclopaedia
- Evidence and calculation methodology
- Contact Shaygan Steel
Frequently asked questions
Which is better for a shaft, CK45 or MO40?
It depends on diameter, load spectrum, fatigue details, heat treatment, required core properties and failure consequence.
Can CK45 be heat treated?
Yes. It can be quenched and tempered or surface hardened, but its through-section response differs from alloyed MO40.
Does MO40 always repay its higher price?
No. It creates value only when the design and controlled process need its hardenability or strength-toughness capability.
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 Heat Treatment Guide — official technical reference
Conclusion and next step
Compare total risk-adjusted manufacturing cost. CK45 can be the correct economical steel for moderate duty; MO40 is justified when section response and service demand need the alloy 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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