Nickel Alloy Cross-Reference: UNS, GB/GH, JIS, AMS

A nickel alloy cross-reference table maps one alloy across the numbering systems that different buyers, mills and airframe primes use. The same material can be ordered as UNS N06625 in an American mill certificate, 2.4856 in a German enquiry, GH3625 on a Chinese drawing and AMS 5666 on an aerospace purchase order — four strings of characters that describe one metal. The table below puts those systems side by side, and the sections after it explain where cross-referencing is safe and where it quietly causes failures.

What does each numbering system actually control?

Most cross-reference tables list numbers without saying what each number governs. That is the root of most substitution errors, because the six systems do not cover the same ground.

The distinction matters most for AMS. UNS N06625 tells a mill what to melt. AMS 5666 tells an aerospace supplier how to melt it, how to forge it, what grain size to reach, which mechanical tests to run and how to certify the result. Two bars with identical chemistry can satisfy UNS and fail AMS.

Nickel alloy cross-reference table

Blank cells mean the alloy has no grade in that system, not that the grade is unknown. A tilde (≈) marks a pair that is compositionally close but produced under separate specifications — treat them as equivalents for engineering discussion, not as automatically interchangeable for procurement.

Two rows deserve attention because they break the pattern people expect. A-286 (UNS S66286) is an iron-base alloy and it is the only grade in this table that JIS files outside the NCF family — SUH 660 lives in the heat-resisting steel series. And Hastelloy C-276 carries a Chinese corrosion-resistant grade (NS3304) while carrying no JIS grade at all, which is why Japanese enquiries for it usually arrive quoting ASTM ASTM B575 or ASTM B619 directly.

Titanium cross-reference table

Titanium follows its own logic. The American system uses Grade numbers, the Chinese system uses alloy designations (TA for commercially pure, TC for alpha-beta alloys), and JIS H 4600 uses Class numbers. Werkstoff numbers for titanium are widely quoted in European enquiries.

Grades 1 through 4 are unalloyed titanium separated by oxygen content — and oxygen content is what sets strength. Increasing oxygen from 0.18% to 0.25% moves the same metal from Grade 1 to Grade 2 and raises minimum yield from 170 MPa to 275 MPa. This is why a Grade 1 to Grade 2 substitution is almost always acceptable upward and never downward without a re-check.

How do Chinese grades map back to UNS numbers?

Chinese drawings typically quote the GB grade, so the reverse lookup is the one that gets used most often in day-to-day enquiry work. GH grades come from GB/T 14992, which covers wrought superalloys; NS grades come from GB/T 15007, which covers corrosion-resistant alloys. The two series were written for different service environments and cannot be merged into one list.

The GH designation is a grade family, not a single specification. GH4169 sets a composition window; it does not set the heat treatment cycle, the grain size or the acceptance tests. Those live in the product standard — GB/T 14994 for cold drawn bar, or the applicable ASTM or AMS specification when the drawing calls for one. Read GH4090 cold drawn bar as an example of how a single GB grade fans out across product forms.

Why does one alloy carry six different numbers?

Each numbering system grew out of a different problem, and none of them was designed to be read alongside the others.

UNS was created in the 1970s when North American industry could no longer keep track of trade names — "Hastelloy", "Inconel" and "Nimonic" are trademarks owned by specific companies, and a mill cannot put a competitor's trademark on a certificate. The UNS number is deliberately trademark-free so that anyone can claim compliance with it.

Werkstoff numbers encode the same information in a numeric tradition that predates computer databases. The five-digit number is an index, not a description; 2.4856 carries no more meaning than N06625 does.

The GH series was built for the Chinese aeroengine and gas turbine programmes, and it borrowed composition ranges from the British Nimonic and American Inconel families while writing its own grade names. This is why GH4033 and Nimonic 80A sit almost on top of each other.

AMS exists because aerospace buyers needed more than composition. A single AMS specification can lock down melting practice, forging temperature, grain size, tensile properties at elevated temperature, stress rupture life and the exact certification paperwork.

When is a cross-reference safe to use for substitution?

A cross-reference table is a translation aid, not an approval. Before any grade in it is substituted for another on a live job, three conditions must hold at the same time.

The third row is the one that catches experienced buyers. Composition equivalence says nothing about which product standard applies, and different product standards set different minimum properties for identical chemistry. A tube to ASTM B444 and a plate to ASTM B575 can both be N10276 and still carry different specified minimum yield strengths.

Where a substitution is being considered for a pressure boundary, the three checks above are the minimum. Weldability, thermal expansion matching and corrosion performance in the specific medium sit on top of them, and none of those can be read off a cross-reference table.

Where do cross-reference tables go wrong?

The mistakes are consistent enough to list.

A further category of error comes from tables that are simply wrong. Grade equivalences circulated on the web are frequently copied from one another without verification, and a single mistyped digit propagates across hundreds of documents. Any equivalence that matters commercially should be confirmed against the current edition of the specification, not against a table.

How should a purchase order be written?

A purchase order should carry the specification, the grade and the delivery condition — three fields, never fewer.

For a European enquiry for corrosion-resistant tubing, that is: ASTM B622, UNS N06022 (Werkstoff 2.4602), solution annealed and pickled. For an aerospace forging it may be: AMS 5663, UNS N07718, solution treated and aged to a specified hardness range. For a Chinese project it may be: GB/T 14994, GH4090, cold drawn and solution treated.

When a customer supplies only one of the three, the supplier has to assume the rest, and the assumption is where disputes begin. Two useful habits follow from this. Ask for the product standard whenever a drawing quotes only a grade — it settles the mechanical property question immediately. And quote the delivery condition explicitly even when the standard defines a default, because defaults differ between systems.

The site's piping grade matching guide applies the same three-field discipline to pipe, fittings, flanges and filler metal, which is where most cross-system confusion on a project actually surfaces.

Continue reading

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