UNS (Unified Numbering System) is a uniform system for identifying metals and alloys, in which one letter and five numbers create a material number. The system enables the linking of American designations with European ones, trade names, and metallurgical documentation. In practice, we encounter, among others, UNS S31603, S32205, S32750, N06625, N08800 and G43400 – in stainless steels, duplex, superduplex, structural steels and nickel alloys.
Unlike traditional markings AISI/SAEThe UNS system also applies to non-standard materials, nickel alloys, cobalt alloys, non-ferrous metals, and even cast iron. It is particularly useful for material inquiries, certification analysis, grade comparison, and compiling technical documentation.
The most important rule: UNS identifies a grade of metal or alloy but is not a stand-alone product standard. UNS N06625 does not yet specify whether bar, plate, tube, or forging is required, nor what processing and testing should be used. When ordering, the UNS number must be combined with the appropriate ASTM/ASME standard, product type, dimensions, and delivery condition.
Related articles: American steel standards and designations; ASTM – requirements for products; AISI – species designations; SAE – Steel Classification and AMS Specifications.
What is UNS and who manages the system?
Unified Numbering System for Metals and Alloys is a system jointly administered by ASTM International and SAE InternationalIts principles include, among others: ASTM E527-23 standard and SAE J1086The goal is to reduce ambiguity when a single alloy is known by multiple names or when different materials have similar trade names.
The UNS number does not replace chemical composition standards, product standards ani acceptance certificatesIts role is consistent identification. To determine the actual element content limits and delivery requirements, refer to the specification appropriate for the given application and document edition.
How to read UNS markings? A letter and five numbers.
The scheme is simple: UNS + material group letter + five digitsThe first letter indicates the material family, but the remaining five digits does not provide a universal formula for calculating the chemical compositionIn some series, the number refers to the older AISI/SAE designation; in others, it is merely an assigned identifier.
| Mark | How to read? | Meaning |
|---|---|---|
| G43400 | G + 43400 | Alloy structural steel SAE 4340, Ni-Cr-Mo family. |
| S31603 | S + 31603 | 316L steel – a low-carbon variant of the grade 316. |
| S31803 / S32205 | S + five digits | Two family-related IDs duplex 2205; chemical requirements are not identical. |
| S32750 | S + 32750 | Superduplex steel 2507 – European number 1.4410. |
| N06625 | N + 06625 | Nickel Alloy 625/Inconel 625. |
| N08800 / N08810 / N08811 | N + five digits | Related alloy variants Alloy 800, 800H and 800HT. |
Important: letter N denotes the UNS numbering family covering nickel and certain alloys, but does not automatically prove that nickel is the dominant elementFor example, 904L high-alloy steel has been designated UNS N08904, and low carbon 316L – UNS S31603.
What do the letters UNS mean? The most important series
| UNS Series | Material group | Examples |
|---|---|---|
| Sxxxxx | Corrosion and high temperature resistant steels, including stainless and duplex | S30400, S31603, S32205, S32750, S30815 |
| Nxxxxx | Nickel and nickel-based alloys and some high-alloy materials from this numbering family | N06625, N07718, N08800, N08904 |
| Gxxxxx | Carbon and alloy steels related to AISI/SAE numbering | G10450, G41300, G41400, G43400 |
| Hxxxxx | Structural steels with controlled hardenability, so-called H-steels | Variants of SAE families with hardenability requirements |
| Dxxxxx | Steels determined by mechanical property requirements | Selected structural steels |
| Fxxxxx | Cast iron | Identifiers of different types of cast iron |
| Jxxxxx | Cast steel | Separate numbers for steel castings |
| Txxxxx | Tool steels | Tool steel identifiers |
| Wxxxxx | Specific welding consumables | Welding materials classified by composition |
| Cxxxxxx | Copper and copper alloys | C11000, C36000 |
| Axxxx | Aluminum and its alloys | A96061 |
| Rxxxxx | Reactive and refractory metals and some cobalt alloys | R30035, R30605 |
In Alfa-Tech special metallurgy we most often use the series S, N and G. For the supply of foundry materials, tooling materials and other alloys will also be important J, F, T and R.
UNS G – structural, carbon and alloy steels SAE/AISI
In the case of the classic four-digit SAE designations, the UNS number often reproduces their digits: SAE 4340 → UNS G43400, SAE 4140 → UNS G41400This rule should not be extrapolated to all material groups, as the method of assigning numbers depends on the relevant UNS family.
| SAE / AISI steel | US | Family/Character | EN comparison or note |
|---|---|---|---|
| 1020 | G10200 | Carbon – nominally approx. 0,20% C | Compare with specific EN standard |
| 1045 | G10450 | Carbon – nominally approx. 0,45% C | C45 is a similar species, not identical by definition |
| 4130 | G41300 | Chromium-molybdenum Cr-Mo – approx. 0,30% C | 25CrMo4 / 1.7218 – similar grade, not a 1:1 substitute |
| 4140 | G41400 | Chromium-molybdenum Cr-Mo – approx. 0,40% C | Composite with 42CrMo4 / 1.7225; verify requirements |
| 4340 | G43400 | Nickel-chromium-molybdenum Ni-Cr-Mo – approx. 0,40% C | It is not an ASTM standard number |
| 5160 | G51600 | Chrome spring steel | Check equivalents according to composition and delivery condition |
| 6150 | G61500 | Chrome-vanadium Cr-V | Differences from EN require checking |
| 8620 | G86200 | Ni-Cr-Mo, case hardening steel – nominally approx. 0,20% C | Not to be confused with SAE 4340 |
Practical example: SAE 4340 = UNS G43400 identifies the Ni-Cr-Mo steel grade. In a query about bars, you can indicate, for example, ASTM A29/A29M as the appropriate product specification, but the required standard version, dimensions, heat treatment and testing must still result from the order.
UNS S – popular austenitic and high-alloy steels
Among austenitic steels, UNS designations allow for easy distinction between variants with reduced carbon content, compositional modifications, or stabilization with titanium and niobium. The most common classifications include: 304/304L and 316 / 316L / 316TiA similar number alone is not sufficient to establish interchangeability.
| Species name | US | Related designation EN / W.Nr. | Card / Note |
|---|---|---|---|
| AISI 301 | S30100 | 1.4310 | Steel card 301 / 1.4310 |
| AISI 304 | S30400 | 1.4301 / X5CrNi18-10 | Card 304 / 1.4301 |
| AISI 304L | S30403 | 1.4307 (common equivalent) / 1.4306 | Low carbon 304 grade |
| AISI 304H | S30409 | High Carbon Variant 304 | Selection based on temperature operating requirements |
| AISI 316 | S31600 | 1.4401 / X5CrNiMo17-12-2 | 316 / 316L steel card |
| AISI 316L | S31603 | 1.4404 / X2CrNiMo17-12-2 | Card 316L / 1.4404 |
| AISI 316Ti | S31635 | 1.4571 / X6CrNiMoTi17-12-2 | Titanium stabilized variant |
| AISI 321 | S32100 | 1.4541 / X6CrNiTi18-10 | Titanium stabilized |
| AISI 347 | S34700 | 1.4550 / X6CrNiNb18-10 | Niobium stabilized |
| AISI 317L | S31703 | 1.4438 / X2CrNiMo18-15-4 | Increased molybdenum content |
| 254 SMO / 6Mo | S31254 | 1.4547 / X1CrNiMoCuN20-18-7 | Superaustenitic steel |
| 904L | N08904 | 1.4539 / X1NiCrMoCu25-20-5 | Warning: the designation belongs to the N series |
| Alloy 926 | N08926 | 1.4529 / X1NiCrMoCuN25-20-7 | High-alloy 6Mo steel – N series |
| AL-6XN | N08367 | Material similar to 1.4529, but not identical | Do not automatically equate with N08926 |
Ferritic, martensitic and precipitation hardening steels
| Type | US | Example EN / W.Nr. | Description |
|---|---|---|---|
| 409 | S40900 | 1.4512 | Ferritic; e.g. elements operating in the exhaust gas environment |
| 430 | S43000 | 1.4016 | Card 430 / X6Cr17 |
| 444 | S44400 | 1.4521 | Ferritic with addition molybdenum |
| 410 | S41000 | 1.4006 | Martensitic |
| 420 | S42000 | Compiled with 1.4021 and other varieties | Don't treat the entire 420 family as one EN |
| 431 | S43100 | 1.4057 | AISI 431 / 1.4057 card |
| 440C | S44004 | 1.4125 | Martensitic high-carbon steel |
| 17-4PH / AISI 630 | S17400 | 1.4542 | Card 17-4PH / 1.4542 |
UNS for duplex and superduplex steel – the most important markings
In steel duplex and superduplex UNS numbers are the primary way to identify material varieties. It is crucial to distinguish, for example, UNS S31803 and S32205, which belong to the duplex 2205 family, but do not have identical chemical composition limits. Also, the names 2507, 255, Zeron 100 and their corresponding identifiers are not generic synonyms for "superduplex".
| Name / family | US | EN / W.Nr. | Alfa-Tech Connections |
|---|---|---|---|
| Lean Duplex 2101 / LDX 2101 | S32101 | 1.4162 | Card 1.4162 / S32101 |
| Duplex 2304 | S32304 | 1.4362 | Card 1.4362 / S32304 |
| Duplex 2205 – basic variant | S31803 | 1.4462 | Duplex card 2205 / 1.4462 |
| Duplex 2205 – a variety with narrower composition requirements | S32205 | 1.4462 | Duplex card 2205 / S32205 |
| Duplex 329 | S32900 | 1.4460 | Card 1.4460 / AISI 329 |
| Super Duplex 2507 | S32750 | 1.4410 | Card 1.4410 / S32750 |
| Super Duplex Zeron 100 | S32760 | 1.4501 | Card 1.4501 / S32760 |
| Super Duplex 255 / Ferralium 255 | S32550 | 1.4507 | Card 1.4507 / S32550 |
Do not confuse: Duplex 2205 (UNS S32205) it's not the same as Super Duplex 2507 (UNS S32750)Differences arise in composition, corrosion resistance, and performance parameters. When comparing materials, consideration should also be given to the product standard, required testing, weldability, and operating environment.
UNS heat-resistant and creep-resistant steels
For steels intended for use at elevated temperatures, the UNS number does not specify the allowable operating temperature. Suitability is determined by factors such as: oxidation, creep, long-term durability, working atmosphere and product condition. Designation H in the traditional species name it usually refers to the version intended for specific high-temperature conditions, but the limits should be checked in the standard.
| Name / family | US | Example EN / W.Nr. | Note/card |
|---|---|---|---|
| 304H | S30409 | High temperature variety 304 | Other requirements than 304L |
| 316H | S31609 | High temperature variety 316 | Not to be confused with 316L |
| 321H | S32109 | High temperature variant 321 | Pay attention to pressure documents |
| 347H | S34709 | High temperature variant 347 | Stabilized grade Nb |
| 309S | S30908 | 1.4833 | Austenitic heat-resistant steel |
| 310S | S31008 | 1.4845 | Card 1.4845 / 310 / 310S – verify variant |
| 314 | S31400 | 1.4841 | Card 1.4841 / AISI 314 |
| 253 MA | S30815 | 1.4835 | Card 253 MA / 1.4835 |
UNS N – nickel alloys, heat-resistant superalloys and corrosive materials
Door Line N is of particular importance in special materials. It covers a wide range of nickel alloys – from pure nickel through alloys Ni-Cr, Ni-Cr-Mo, Ni-Mo, Ni-Cu to precipitation-strengthened superalloys. In trade, in addition to the UNS number, you'll also find names such as Inconel, Incoloy, Monel, Hastelloy, or Haynes, which should be associated with a specific specification.
| Material/family | US | EN / W.Nr. | Alfa-Tech Card or Note |
|---|---|---|---|
| Nickel 200 / pure nickel | N02200 | 2.4066 (also other numbers depending on the character) | Nickel 200 / 201 – comparison chart |
| Nickel 201 / pure low-carbon nickel | N02201 | 2.4068 (also other numbers depending on the character) | Nickel 200 / 201 – comparison chart |
| Monel 400 / Alloy 400 | N04400 | 2.4360 | Monel 400 – Alloy Card |
| Monel K-500 / Alloy K-500 | N05500 | 2.4375 | Monel K-500 – Alloy Card |
| Alloy 600 / Inconel 600 | N06600 | 2.4816 | Alloy 600 - Alloy Card |
| Alloy 601 / Inconel 601 | N06601 | 2.4851 | Alloy 601 - Alloy Card |
| Alloy 617 / Inconel 617 | N06617 | 2.4663 | Alloy 617 - Alloy Card |
| Alloy 625 / Inconel 625 | N06625 | 2.4856 | Alloy 625 - Alloy Card |
| Alloy 718 / Inconel 718 | N07718 | 2.4668 | Alloy 718 - Alloy Card |
| Alloy X-750 / Inconel X-750 | N07750 | 2.4669 | Precipitation hardening alloy |
| Alloy 725 | N07725 | Depending on the documentation | High-strength Ni-Cr-Mo alloy |
| Alloy X / Hastelloy X | N06002 | 2.4665 | Hastelloy X / Alloy X – card |
| Alloy C-22 / Hastelloy C-22 | N06022 | 2.4602 | Alloy C-22 – card |
| Alloy C-276 / Hastelloy C-276 | N10276 | 2.4819 | Alloy C-276 – card |
| Haynes 230 / Alloy 230 | N06230 | 2.4733 | Haynes 230 – card |
| Alloy 825 / Incoloy 825 | N08825 | 2.4858 | Alloy 825 – card |
| Alloy 20 / Incoloy 020 | N08020 | 2.4660 | Alloy 20 – card |
| Nimonic 75 | N06075 | 2.4951 | High-temperature superalloy |
| Nimonic 80A | N07080 | 2.4952 | High-temperature superalloy |
| Nimonic 90 | N07090 | 2.4969 | High-temperature superalloy |
Alloy 800, 800H and 800HT – one family, three UNS numbers
At the feet Alloy 800 / Incoloy 800 It's worth keeping their family list, as on the existing Alfa-Tech card. These are related materials Ni-Fe-Cr, differing in specific compositional requirements and suitability for high-temperature service. We do not create an artificial division into unrelated alloys, but we also do not treat all variants as automatically interchangeable.
| Alloy 800 Family | US | EN / W.Nr. – frequently used | Reference |
|---|---|---|---|
| Alloy 800 / Incoloy 800 | N08800 | 1.4876 | One card: Alloy 800, 800H and 800HT |
| Alloy 800H / Incoloy 800H | N08810 | 1.4958 (1.4876 is also found in documents) | Comparison of the composition and designations of alloy 800H |
| Alloy 800HT / Incoloy 800HT | N08811 | 1.4959 | Comparison of the composition and designations of the 800HT alloy |
Material note: for 800, 800H and 800HT Select the variant according to the actual technical requirements (including composition, structure, and operating conditions). A common family table alone does not determine the possibility of substituting a variant in an industrial device.
UNS and ASTM, ASME, EN and AMS – how to complete the markings in the documentation?
When ordering materials, it is worth including at least UNS number, grade name, product standard, material form, dimension and delivery conditionFor example, alloy N06625 supplied as sheet is not automatically subject to the same requirements as bar stock of the same alloy. Similarly, for S32205, you must indicate whether you are ordering sheet stock, bar stock, tube stock, or forging.
| Sample material | UNS Identification | Example product standard | What else to check? |
|---|---|---|---|
| 316L steel | S31603 | ASTM A240/A240M – sheets and strips | Product type and appropriate standard edition |
| Duplex 2205 | S32205 | ASTM A240/A240M – flat products | Composition compared to S31803; delivery status |
| Super Duplex 2507 | S32750 | ASTM A182/A182M – forgings (appropriate grade) | Conformity of specific product class and documentation |
| Alloy 625 | N06625 | ASTM B443 – flat products; ASTM B446 – rods | Required form and condition of the product |
| Alloy 800 / 800H / 800HT | N08800 / N08810 / N08811 | ASTM B409 – sheets, strips; ASTM B408 – bars | Alloy variant and additional requirements |
| SAE 4340 | G43400 | ASTM A29/A29M – rods | Delivery condition, properties and heat treatment |
The European EN and DIN systems are a separate set of requirements that may differ in terms of composition, tolerances, testing, and acceptance documents. Especially for substitutes, it is necessary to compare the composition limits with PN-EN 10088-1, appropriate product standards and manufacturer's documentation.
Common errors when reading UNS numbers
- Treating UNS as a standard number: S31603 indicates the material, not the specification for a specific sheet or pipe.
- Automatic acceptance of interchangeability: proximity to UNS numbers or a common EN number does not imply identical composition and requirements.
- Confusing duplex families: S31803 and S32205 need to be distinguished, and S32750 is a superduplex material.
- Assigning the letter S to each alloy: e.g. 904L has UNS N08904 even though it is a high alloy steel.
- Splitting the 800 family into unbound materials: N08800, N08810 and N08811 form related variants of the same family, with different requirements.
- Use of trade names without identification: the name Inconel, Monel, Nimonic or Hastelloy is not sufficient to indicate a specific alloy.
Frequently Asked Questions – FAQ
Is UNS a steel standard?
No. UNS is a system for identifying metals and alloys. The composition range and product requirements are defined by the relevant technical specifications.
What does the letter S in a UNS number mean?
Refers to a family of corrosion- and high-temperature-resistant steels, including stainless, duplex and superduplex steels.
What does the letter N in a UNS number mean?
This is a numbering series covering nickel and numerous nickel alloys, as well as some high-alloy materials. The letter N alone is not sufficient to identify the dominant element.
What is the difference between UNS S31803 and S32205?
Both designations refer to the Duplex 2205 family, but they do not have identical chemical composition requirements. The specific variant must be specified in the order and standard.
Is UNS S32750 1.4410 steel?
Yes, S32750 is the designation for superduplex 2507, usually associated with the European number 1.4410. You must also check the product standard and delivery condition.
Are Alloy 800, 800H and 800HT three completely different alloys?
These are three related variants of the same Ni-Fe-Cr family, designated N08800, N08810, and N08811, respectively. However, the technical requirements of the variants differ.
What does UNS G43400 mean?
Identifies SAE/AISI 4340 steel from the nickel-chromium-molybdenum family of structural steels. It is not a product standard number.
Are UNS N06625 and Inconel 625 the same?
N06625 is the material identifier for the material commonly known as Alloy 625 / Inconel 625. The correct product standard is still required when ordering.
Is UNS N08926 the same as UNS N08367?
No. Alloy 926 (N08926) and AL-6XN (N08367) are 6Mo materials of similar nature, but their chemical specifications are not automatically the same.
Summary – why know UNS numbers?
UNS organizes the identification of steels and alloys regardless of whether the seller uses the name AISI, SAE, Alloy, Inconel, Monel, Haynes or European number. G series includes popular carbon and alloy steels; S series – stainless, duplex and heat-resistant steels; N series – a broad group of nickel alloys and other high-alloy materials. All identifiers must be related to the technical requirements of a specific product.
Need steel or alloy according to UNS, ASTM, ASME or EN? Send the material number, product type and dimensions to kontakt@alfa-tech.com.plAlfa-Tech will help analyze the designation and prepare a grade proposal for verification in a given application.
Back to section: American steel standards and designations – ASTM, AISI, SAE, UNS, ASME.