When reviewing steel standards for stainless or engineering steel CNC parts from Vietnam, specify the exact grade, product standard, delivery condition and required evidence. A familiar cross-reference can help a supplier understand the material family, but it cannot replace an engineering review or authorize a substitution.
The Vietnamese word “inox” means stainless steel. It does not identify a particular grade. Likewise, “steel” or “alloy steel” alone is insufficient for a controlled machining order.
Steel standards: define the family and complete requirement
Keep stainless steel, carbon steel and alloy engineering steel separate in the RFQ. Identify the specified bar, plate or other product form and the condition in which it must be supplied. If heat treatment is required after machining, define the final requirement and inspection stage as well.
Requirements may include chemistry, mechanical properties, hardness, heat treatment, surface condition, traceability and testing. Not every project needs every test, but the required scope should be agreed before material is purchased.
Stainless steel: US, EN and JIS comparison references
The following rows are selected similar-composition references from the worldstainless comparison based on ISO 15510:2010. That document is a historical comparison aid, not a current purchasing standard or a declaration of interchangeability. Other variants exist within some of these groups.
| US type reference | UNS reference | Selected EN reference | Selected JIS reference |
|---|---|---|---|
| 303 | S30300 | 1.4305 | SUS303 |
| 304 | S30400 | 1.4301 | SUS304 |
| 304L | S30403 | 1.4307 or 1.4306, subject to the required specification | SUS304L |
| 316 | S31600 | 1.4401 | SUS316 |
| 316L | S31603 | 1.4404; other EN variants also exist | SUS316L |
The presence of more than one EN reference is a reason to ask for the exact grade, not permission to select any entry in the group. Compare the specified composition and properties under the applicable product standard. The grade name and a supplier’s “equivalent” label do not settle that comparison.
Why might a drawing specify one stainless grade rather than another?
Begin with the design requirement and the service conditions. For orientation, 303 is associated with free-machining applications; Outokumpu’s 303/4305 guidance describes its resulfurized machining grade. That is not a reason to substitute it for 304 or 316 without approval.
304/304L are general austenitic stainless references, while 316/316L belong to the molybdenum-alloyed group. Alleima’s 316/316L material information explains the corrosion-performance context of its product. This does not make every 316 component suitable for every chemical or chloride environment.
The low-carbon L designation is also part of the requirement, not an optional label to omit. Give the supplier any welding, cleaning, corrosion, finish and testing requirements that affect the selection. Material selection remains with the responsible design authority; a machine shop should flag a proposed change rather than choose a different grade solely for easier machining.
Carbon and alloy engineering steel: compare families carefully
Two groups frequently appear in cross-standard sourcing discussions:
| US / SAE reference | EN grade commonly compared | JIS grade commonly compared | Required review |
|---|---|---|---|
| 1045 | C45 | S45C | Check exact chemistry, product form, delivery condition and required properties. |
| 4140 | 42CrMo4 | SCM440 | Check the complete specification, heat-treatment condition, section-dependent properties and any hardenability requirement. |
These are comparison families rather than guaranteed substitutes. The steel producer Aktif Çelik’s grade comparison groups these references. The historical China Steel Corporation product manual also shows separate JIS and SAE specifications and broader comparison families. Use such literature to identify what to investigate, then check the actual contractual standards and mill evidence.
Do not replace C45 with C45E merely because the names look similar, or drop an “H” or another suffix from a specification. Additional letters or delivery symbols can carry requirements that matter to the application. Keep the complete original callout visible in the technical review.
The delivery condition is part of the material
A grade name does not establish whether stock is supplied annealed, cold drawn, normalized or quenched and tempered. Nor does it establish the final hardness or properties of the machined part. For example, Ovako’s 42CrMo4 information discusses the grade in the context of quenching and tempering and its own product variants. A different mill’s stock needs its own applicable evidence.
Where the order specifies hardness, record the method, range and measurement stage. If the requirement applies after heat treatment or a surface process, the plan should reflect that sequence. Ask how distortion, finish allowance and final dimensional verification will be handled.
State whether the required material condition is an input to machining or a final delivered condition. This avoids a quotation that assumes easy-to-machine stock while the buyer expects a finished part with different properties.
A material change needs a documented decision
Illustrative case: a buyer specifies a 4140 bar in a defined condition, and the supplier offers SCM440. The shared comparison family is not enough to release the change.
- Retain the original grade, product standard, edition and condition from the drawing or contract.
- Identify the exact proposed grade, product, condition and source.
- Compare chemistry limits, required properties, hardness, testing and any additional requirements.
- Review the manufacturing sequence and whether the change affects machining, heat treatment, finishing or inspection.
- Record unresolved differences and obtain approval from the authorized buyer or design authority before purchase.
If only a generic comparison chart is available, the review is incomplete. Ask for the applicable specification and suitable material evidence rather than treating the chart as a certificate.
Define material records and verification at RFQ stage
Ask what document can be supplied for the actual stock. Agree whether you need a mill test record, a particular inspection document or another form of evidence. A distributor’s sales description should not be presented as the original mill record.
When traceability is required, establish how the heat or lot identification connects the certificate, stock, cut blanks and finished production lot. Where additional material testing is needed, agree the method and acceptance criteria. Do not assume that one identification test verifies every chemical element, mechanical property or heat-treatment condition.
A material record and a finished-part inspection report answer different questions. Use the quality documentation guide to define the delivery pack and the quality-control guide to plan acceptance.
Keep service conditions and availability visible
If the component will be welded, exposed to chemicals, used in a corrosive environment or subjected to a specified cleaning or surface process, provide those requirements to the responsible material/design specialist. “Stainless” is not a sufficient service-performance specification. Do not change a grade solely because it is easier to machine.
For supply in Vietnam, confirm grade, stock form, size, condition, available evidence and lead time for the actual order. Local purchase does not establish local mill origin. The Vietnam material sourcing guide covers that distinction; the aluminum standards guide applies the same complete-specification approach to aluminum.
US, German and Canadian buyers should state their governing requirements explicitly rather than expect the supplier to infer them from the destination. List permitted alternatives in the quotation or order only after approval.
Frequently asked questions
Is SUS304 the same as 1.4301 for purchasing purposes?
They appear as similar-composition references, but approval still requires the actual product standard, condition, properties and evidence to satisfy the order. Do not treat the name alone as a complete specification.
Can SCM440 be supplied against a 4140 drawing?
Only after the buyer’s permitted-alternative rules or a documented technical approval establish that the proposed product meets the requirement. A cross-reference table alone is insufficient.
Why does heat-treatment condition affect the quotation?
It changes the route the supplier must plan, including stock selection, machining sequence, outside processing, inspection and possible finishing allowance. The quotation must reflect the required delivered condition.
Does every steel shipment need the same certificate?
No. The required document and testing depend on the contract and application. Confirm what is needed and what can be supplied for the selected source before ordering.
Define the material before requesting a firm quotation
Send the complete grade and product standard, required condition, drawings, quantities and material-document requirements. Identify whether alternatives may be considered.
Part 5 of our international buyer guide. Return to Precision CNC Machining in Vietnam.
Sources and technical reference notes
- worldstainless: similar-composition designations, ISO 15510:2010 reference
- China Steel Corporation: product manual, steel specifications and comparison tables
- Ovako Steel Navigator: 42CrMo4 grade information
- Aktif Çelik: JIS/EN/SAE steel grade comparison
- Outokumpu: Prodec 303/4305 machining guidance
- Alleima: Sanmac 316/316L material information
Technical literature describes its referenced products and editions. This guide is not a substitute for the applicable purchase specification, and it does not declare current stock availability or authorize a material substitution.
