Key takeaways
- A UNS number is one letter and five digits; N is nickel alloys, S stainless, R titanium and refractory metals, F cast irons.
- Digit patterns help (N06625 echoes alloy 625, S31603 is 316L) but they are a memory aid, not a rule.
- Trade names mislead: "Inconel 825" is Incoloy 825 (N08825) and "Alloy 500" can be Monel K-500 or Udimet 500.
- Many cast superalloys have no common UNS number and are identified by name and measured chemistry.
- Put the UNS number on every offer, packing list and invoice, and back it with readings.
A seller offers "Inconel 825". Another offers "Alloy 500". A third has "Duplex 31803". Each description sounds precise, and each one can lead a buyer to the wrong grade. A UNS number fixes that. Write N08825, N05500 or S31803 next to the trade name and there is only one alloy it can mean.
This article explains how a UNS number is built, what the prefixes and digit patterns tell you, where the system stops, and how to use it on scrap offers, packing lists and invoices. For the grade-by-grade lookup, the equivalent grade chart and the grade name converter do the work; this page explains the logic behind them.
What Is a UNS Number?
A UNS number is an identifier in the Unified Numbering System for metals and alloys: one capital letter followed by five digits, with each number assigned to one chemical composition. The system is administered jointly by ASTM International and SAE International, and the way numbers are allocated is set out in ASTM E527 and SAE J1086.
Nseries letter, nickel and nickel alloys06group within the series625digits that echo the trade numberThe system was created so that one alloy would carry one number, whatever a producer called it and whichever country or industry specified it. Before UNS, the same composition could circulate under a trade name, a producer number, an AISI type and several specification grades. Many of those names survive in the trade, which is exactly why the UNS number earns its place on a scrap description.
A UNS number identifies a composition. It says nothing about product form, heat treatment, size or test requirements; those come from a specification.
What Do the UNS Letter Prefixes Mean?
The letter prefix tells you the metal family before you read a single digit. N is nickel and nickel alloys, S is stainless and heat-resisting steels, R is reactive and refractory metals including titanium, and F is cast irons. Those four cover almost everything in the nickel alloy and stainless scrap trade.
| Prefix | Family | Examples in alloy scrap |
|---|---|---|
| N | Nickel and nickel alloys | N06625 Inconel 625, N10276 Hastelloy C-276, N04400 Monel 400 |
| S | Stainless and heat-resisting steels | S31603 316L, S32205 Duplex 2205, S31254 254 SMO |
| R | Reactive and refractory metals | R50400 Titanium Grade 2, R56400 Ti-6Al-4V |
| F | Cast irons | F41000, F41002 and F41006 for Ni-Resist Types 1, 2 and 5 |
| K, G, J | Other steels: miscellaneous, carbon and alloy, cast | Rarely met in nickel alloy lots, except as contamination |
| W | Welding filler metals | Weld wire and consumables |
| A, C, Z and others | Aluminium, copper, zinc and further non-ferrous families | Outside the nickel alloy trade |
The R series deserves a closer look, because titanium is where the paperwork carries most weight. Commercially pure Grade 1 is R50250 and Grade 2 is R50400, yet the two differ mainly in oxygen and iron, which handheld XRF cannot separate reliably. Grade 7 (R52400) and Grade 11 (R52250) add about 0.15% palladium, which XRF can see, but telling one from the other again depends on the base grade. For titanium plate and tube, the UNS number in the marking or on the certificate is often the only practical record of which grade you hold.
The prefix alone is a useful check. If a lot described as "nickel alloy" turns up with an S number on the paperwork, it is stainless steel, however high the nickel looks. If it carries a C number, it is a copper alloy such as cupronickel, not Monel.
How Are Nickel Alloy UNS Numbers Grouped?
Within the N series, the first two digits tend to cluster alloys of a similar type. Across the grades on this site, the clusters are consistent enough to be a useful memory aid, though not a rule to identify an alloy by.
| Group | What the grades on this site have in common | Examples |
|---|---|---|
| N04, N05 | Nickel-copper (Monel) | N04400 Monel 400, N05500 Monel K-500 |
| N06 | Mostly solid-solution nickel-chromium alloys, with or without molybdenum | N06600, N06625, N06690, N06022 C-22, N06002 Hastelloy X, N06230 Haynes 230 |
| N07 | Mostly age-hardenable nickel alloys and superalloys | N07718 Inconel 718, N07080 Nimonic 80A, N07263, N07500 Udimet 500 |
| N08 | Iron-nickel-chromium alloys | N08825 Incoloy 825, N08904 904L, N08024 20Mo-4 |
| N09 | Age-hardenable iron-nickel alloys | N09925 Incoloy 925, N09706 Inconel 706 |
| N10 | Nickel-molybdenum alloys | N10276 C-276, N10665 Hastelloy B-2 |
The groups explain a few surprises. Hastelloy C-22 and C-276 are close relatives in trade, yet C-22 sits in N06 and C-276 in N10. The chart below shows why the numbers part company: C-276 carries more molybdenum than chromium, while C-22 carries more chromium than molybdenum, closer to Inconel 625.
Nominal values from the grade pages; specification limits vary by product form.
The last three digits often echo the trade number: N06600 for alloy 600, N06625 for 625, N08825 for 825, N07718 for 718. That echo is a convenience, not a promise. Hastelloy X is N06002, Haynes 282 is N07208 and Monel K-500 is N05500, none of which you could guess from the trade name.
How Do Stainless Steel UNS Numbers Work?
For the common austenitic stainless steels, a UNS number is S, the old three-digit AISI type and a two-digit suffix that marks the variant. The suffix is where the useful detail sits: 00 is the standard grade, 03 the low-carbon L grade, 08 the S version of 310 and 09 the high-carbon H grade.
Sseries letter, stainless and heat-resisting steels316the AISI type03variant suffix, low carbonSo 316 stainless is S31600 and 316L is S31603; 304 is S30400 and 304L S30403; 310S is S31008 and 310 is S31000; 347 is S34700 and 347H S34709. The suffix matters on certificates and pressure-equipment paperwork. For scrap, carbon differences of this size do not show on handheld XRF, so the UNS number on the paperwork is often the only record of which variant you have.
Higher-alloy stainless grades break the AISI pattern. Duplex 2205 is S32205 (and the older S31803), super duplex 2507 is S32750, S32760 is its copper-and-tungsten cousin, and 254 SMO is S31254. One grade crosses families entirely: 904L is traded as a stainless steel but carries the nickel-series number N08904. Describe it by its UNS number and nobody files it in the wrong bin.
Can One Alloy Have Two UNS Numbers, or One Name Two Alloys?
Yes to both, and each causes real confusion in scrap. One grade can carry two UNS numbers when a revised composition is given its own number, and one trade name can point to two different alloys when producers reuse numbers.
Duplex 2205 is the standard example of the first case. S31803 and S32205 differ slightly in their minimum chromium, molybdenum and nitrogen, and most current material is certified to both. The guide to reading a 3.1 mill certificate covers how to read a dual-certified certificate.
The second case is more dangerous for value. "Alloy 500" can mean Monel K-500 (N05500), a nickel-copper alloy, or Udimet 500 (N07500), a cobalt-bearing superalloy. They share nothing but the number in their names.
| Name on the offer | UNS number | What it actually is |
|---|---|---|
| Inconel 825 | N08825 | Incoloy 825, an iron-nickel-chromium alloy, not an Inconel |
| Monel 500 | N05500 | Monel K-500 |
| Alloy 500 | N05500 or N07500 | Monel K-500 or Udimet 500: ask which |
| Alloy 22 | N06022 | Hastelloy C-22, not C-276 (N10276) |
| Duplex 31803 | S31803 / S32205 | Duplex 2205 |
| F44, SMO 254, 6Mo | S31254 | 254 SMO super-austenitic stainless |
The Inconel vs Incoloy comparison explains why the 825 mix-up matters: the iron and nickel contents are far apart, and so is what a melter can do with the metal.
Is a UNS Number the Same as a Specification or a W.Nr.?
No. A UNS number names the alloy; a specification such as ASTM B443 sets the requirements for a product form of that alloy, and a W.Nr. (Werkstoff number) is the European material number for a comparable composition. One UNS number usually appears in several specifications, one for each form.
| Names one composition | Defines product form and tests | Independent of producer | Common on scrap paperwork | |
|---|---|---|---|---|
| Trade name | ◐ | ○ | ○ | ● |
| UNS number | ● | ○ | ● | ● |
| W.Nr. | ● | ○ | ● | ◐ |
| ASTM or ASME specification | ◐ | ● | ● | ◐ |
● yes ◐ partly ○ no
Inconel 625 shows how the layers fit together. Its UNS number is N06625 and its W.Nr. is 2.4856. Plate is made to ASTM B443, pipe and tube to B444 and bar to B446, each of which lists N06625 as the alloy. The ASTM B specifications for nickel alloys and EN, DIN and Werkstoff numbers pages cover both systems. Treat a W.Nr. and a UNS number as close equivalents rather than identical: the composition limits behind them are set by different standards and may not match exactly.
Where Does the UNS System Run Out?
UNS runs out at many cast superalloys, which are made to engine and turbine manufacturers’ own specifications and have no commonly used UNS number. On this site, the René, MAR-M and GTD families and IN-939 fall into that group, while a few older cast or cast-and-wrought alloys, such as Inconel 713C (N07713) and Udimet 500 (N07500), do carry one.
For these alloys, the trade name and the measured chemistry are the identification. A box of blades described only as "superalloy" tells a buyer very little; "René 80 blades, uncoated" plus readings tells them a lot. Because several of these alloys differ only in tantalum, hafnium or aluminium, they are usually confirmed by XRF and then by OES or laboratory analysis, as described in how superalloy revert returns to the melt.
How Should You Use UNS Numbers on a Scrap Lot?
Use the UNS number as the anchor of every lot description: next to the trade name on the offer, on the packing list and on the invoice, checked against the readings. It costs nothing and removes the commonest cause of disputes, which is two people meaning different alloys by the same name.
- 1Read the markingpipe, plate and bar often carry the UNS number beside the specification
- 2Convert trade namesuse a grade chart for anything without a marking
- 3Confirm the metalXRF readings should match the grade behind the number
- 4Write it everywhereoffer, photographs, packing list and invoice
- 5Keep one number per lotsplit lots that read as two grades
Never let the number outrun the evidence. A UNS number on an offer is a claim; readings, markings or a matching certificate are what back it up. For the testing side, see how handheld XRF sorts nickel alloys. When you send us an enquiry, include the UNS number if you know it along with photographs and readings; we’ll review your enquiry against them.
Submit a requirement with the grade, form, quantity and delivery location.
Source a GradeFAQ
What does the N in a UNS number like N07718 mean?
N is the UNS prefix for nickel and nickel alloys. N07718 is Inconel 718. The other prefixes common in alloy scrap are S for stainless and heat-resisting steels, R for reactive and refractory metals such as titanium, and F for cast irons such as Ni-Resist. The five digits after the letter identify the specific alloy within that family.
Who assigns UNS numbers?
UNS numbers are administered jointly by ASTM International and SAE International. The way numbers are requested and allocated is described in ASTM E527 and SAE J1086. Producers and standards committees request numbers for new compositions, so each established alloy should have one number that is recognised regardless of who makes it or what trade name it is sold under.
How do I find the UNS number for a trade name?
Look up the trade name in the equivalent grade chart or the grade name converter, which list UNS numbers, W.Nr. and aliases for every grade on this site. On new material, the UNS number is usually printed in the marking beside the ASTM specification, and it also appears in the product line of the mill certificate.
Is 904L a stainless steel or a nickel alloy?
In trade, 904L is sold and described as a high-alloy austenitic stainless steel. Its UNS number, however, is N08904, in the nickel series. It carries about 25% nickel, 20% chromium, 4.5% molybdenum and 1.5% copper on an iron base. Quote the UNS number on a lot description so the buyer knows exactly which grade you mean.
Does every alloy have a UNS number?
No. Many cast superalloys used for turbine blades and vanes, such as the René, MAR-M and GTD families, are made to manufacturers’ own specifications and have no commonly used UNS number. They are identified by trade name and chemistry. Some proprietary or very new alloys may also lack a number, or be traded under a producer designation first.
Can a UNS number tell 304 from 304L in scrap?
On paperwork, yes: 304 is S30400 and 304L is S30403, and the difference is the carbon limit. In the metal itself, handheld XRF cannot measure carbon, so the two cannot be told apart that way. Spark OES or laboratory analysis can. For most stainless scrap, the distinction only matters when the material is sold with traceable paperwork.
Is a UNS number enough to describe a scrap lot?
No. The UNS number names the alloy, but a buyer also needs the form, such as solids, pipe or turnings, the quantity, the condition, any coatings or contamination, and the evidence behind the grade. A good description reads: grade and UNS number, form, weight, location, plus photographs and XRF readings. See common nickel alloy scrap grades.
