Confirm the exact UNS identifier
One digit can represent a different composition. Do not shorten or infer the number from an informal grade name.
Technical guide
UNS Stainless Steel Grades
UNS stainless steel grades use a unified identifier for an alloy chemistry, but the UNS number is not a product specification. A purchase order must also define product form, governing standard, dimensions, condition, finish, tests and inspection documents.
Identifier formatLetter plus five digits
Stainless family prefixCommonly S
Critical limitUNS is not a quality specification
Decision summary
Use the UNS number as one part of the material callout
The identifier reduces ambiguity between trade names and standards, while the product specification establishes manufacturing, condition, dimensions, properties, testing and acceptance.
Add the product specification
State the current ASTM, ASME, EN or other applicable product document for sheet, plate, bar, tube, pipe, forging or casting.
State form and condition
Annealed, cold worked, solution treated, precipitation hardened and other conditions can materially change properties.
Control dual certification
Accept dual marking only when the material and product meet every invoked requirement, not because two names appear similar.
Check code acceptance
Pressure, structural or regulated applications may limit permitted specifications, grades, conditions and design allowables.
Verify the delivered identity
Reconcile markings and inspection documents to the purchase order, heat or lot and physical product.
Reference table
Common UNS stainless identifiers and families
The examples support identification only. Composition limits and product requirements must be taken from the current invoked standards.
| UNS identifier | Common designation | Family | Procurement note |
|---|---|---|---|
| S30400 | 304 | Austenitic Cr-Ni | Specify product standard, form, condition and finish; low-carbon variants have separate identifiers |
| S30403 | 304L | Low-carbon austenitic Cr-Ni | Commonly selected for welding, but weld procedure and service suitability remain separate |
| S31600 | 316 | Austenitic Cr-Ni-Mo | Molybdenum improves resistance in many environments but does not make the alloy universally chloride-proof |
| S31603 | 316L | Low-carbon austenitic Cr-Ni-Mo | Confirm whether dual 316/316L certification is required and permitted by the product specification |
| S32100 | 321 | Titanium-stabilized austenitic | Condition, product specification and elevated-temperature design requirements must be stated |
| S40900 | 409 | Ferritic | Surface appearance and corrosion behavior differ from common 300-series grades |
| S43000 | 430 | Ferritic chromium stainless | Magnetic response is not a reliable grade-verification method by itself |
| S41000 | 410 | Martensitic | Mechanical properties depend strongly on heat-treatment condition |
| S31803 / S32205 | Duplex identifiers associated with 2205 products | Austenitic-ferritic duplex | Do not treat the two UNS compositions as automatically interchangeable; invoke the exact required identifier and standard |
| S32750 | 2507-type super duplex | High-alloy duplex | Requires exact product, heat-treatment and fabrication controls for the intended service |
| S17400 | 17-4 PH | Precipitation-hardening | Specify solution and aging condition because strength and toughness vary by condition |
Common names such as 304, 316L, 2205 and 17-4 PH are convenient labels, but the purchase specification must resolve the exact composition and product requirements.
Working method
Translate a grade name into a complete order description
Use a short verification sequence so an alloy identifier is not mistaken for a finished-product requirement.
Resolve the identifier
Confirm the full UNS number and any common, national or trade designation used by the design.
Select the product document
Choose the specification for the actual form and service, then confirm edition and any supplementary requirements.
Add delivery condition
State heat treatment, strength condition, dimensions, tolerance, finish, testing and inspection-document type.
Verify receipt
Check physical marks, heat or lot, document identifiers, reported results and ordered product before release to production.
Limits and escalation
Avoid equivalence claims based on a name alone
UNS does not set product quality
ASTM E527 explicitly treats UNS as an identification system, not a specification of form, condition or quality.
Cross-standard grades may differ
Nominal counterparts can have different composition ranges, mechanical requirements, dimensions or test rules.
Strength depends on condition
The same composition can be supplied annealed, cold worked or precipitation hardened with very different properties.
Corrosion depends on service
A familiar UNS grade does not establish suitability for chlorides, acids, high temperature or hygienic duty.
Interactive planning aid
Build the missing part of a UNS material callout
Select what is currently known and the product form. The result shows the next specification element to add.
Frequently asked questions
UNS stainless steel grades FAQ
UNS is the Unified Numbering System for metals and alloys. Stainless identifiers commonly use the letter S followed by five digits.
No. The UNS number identifies an alloy composition. An ASTM product specification adds form, manufacturing, condition, properties, dimensions, testing and acceptance.
S31603 is the UNS identifier commonly associated with 316L. The complete order still needs the applicable product specification and delivery requirements.
State the exact UNS identifier, governing product specification and edition, form, dimensions, tolerance, condition, finish, tests, inspection document and any supplementary requirements.
Method, sources and review
Traceable sources and review status
Current ASTM practice for numbering metals and alloys in the Unified Numbering System.
SAE practice describing the UNS system and number-assignment procedure.
Current SAE handbook compiling UNS designations for metals and alloys.
SAE composition reference for wrought stainless steels and major UNS series groupings.
This table is an identification aid, not a substitute for licensed current standards. Confirm composition limits, product requirements and code acceptance before procurement or design.
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UNS designation context
Read the UNS identity alongside product form and governing specification.
A UNS number is a controlled material designation, not a substitute for the product standard, delivery condition or acceptance criteria that apply to the order.
UNS identityRecord the complete UNS identifier before comparing grade names.
Product scopeMatch the requested form and product specification to the order.
Acceptance basisUse the stated standard and certificate for final acceptance.
Visual reference
Show the designation, product form and evidence together.
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Designation reference
Reserved for designation and cross-reference context.
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Documented acceptance
Reserved for certificate and specification review.
Engineering and sourcing support
Convert the UNS identifier into a complete specification
Send UNS number, product standard, form, dimensions, tolerance, condition, finish, service, testing, inspection-document type, quantity and destination.