Nickel-alloy names are often used as shorthand, but an alloy trade name, UNS number, chemistry limit, product form, and heat-treated condition describe different things. This table compares three selected INCONEL products from Special Metals bulletins: alloys 600, 625, and 718. It preserves the supplier’s UNS identifiers and selected composition limits, and it labels the reported density condition. It is a source-specific orientation aid, not a material certificate or design-allowable table.

Nickel alloy designations and properties

How to read the names and identifiers

INCONEL is a supplier trade name, while UNS N06600, N06625, and N07718 identify the corresponding standardized alloy designations. A UNS match is useful for material identification, but it does not prove the supplied product meets a purchase specification, form, condition, or heat-lot chemistry. Verify the exact standard and certificate required for the component.

The chemistry column contains selected limits, not a complete chemical analysis. “Minimum,” “maximum,” and “balance” are not interchangeable: balance indicates that iron or another element predominates after the specified limits, not that the material contains only that element. The source bulletin contains additional limits. Use its full table or the governing specification for procurement and acceptance.

Compare alloy families without assuming equivalence

Special Metals describes alloy 600 as a nickel-chromium-iron material that is not precipitation hardenable and is strengthened by cold work. Alloy 625 is a nickel-chromium-molybdenum-niobium alloy, with molybdenum and niobium contributing to strength. Alloy 718 is age hardenable; its bulletin describes solution treatment followed by precipitation hardening. The similar product names therefore do not imply the same strengthening mechanism or manufacturing condition.

The table lists supplier-stated densities of 8.47 g/cm³ for alloy 600 and 8.44 g/cm³ for alloy 625. For alloy 718, the bulletin lists 0.296 lb/in³ in the annealed condition; the displayed 8.19 g/cm³ is a unit conversion from that stated annealed value. Density is a physical-property reference, and the 718 bulletin says properties can vary slightly with composition and specimen condition. It is not a basis for comparing strength.

Worked material-selection check

Suppose a drawing calls out “INCONEL 718” and a purchase order requires an age-hardened product to a particular specification. First match the UNS number N07718, then verify the product form and required specification against the supplier certificate. The bulletin explains that 718’s precipitation-hardening treatment is essential to its high strength; a matching alloy number in an annealed or otherwise different condition is not automatically equivalent for a strength-critical part.

For a different example, choosing alloy 625 because its UNS number or chemistry resembles another nickel alloy is not enough. The intended corrosion environment, temperature, form, heat treatment, weldability, and design code matter. Use material-specific allowable stresses and supplier guidance for the actual condition rather than borrowing a tensile value from a different form or heat treatment.

Common mistakes and limits

Do not treat composition limits as typical heat analysis. Do not assume a trade name alone identifies the required product condition. Do not compare room-temperature tensile properties taken from different forms as if they were the same test. The Special Metals bulletins include extensive property tables and cautions that typical values are not necessarily specification values; consult the applicable product specification and certificate.

Alloy selection also needs corrosion and oxidation testing appropriate to the service environment. Media, temperature, stress, fabrication, weld procedure, and crevices can change performance. This abbreviated reference omits many alloy families and properties, and it cannot approve a component design or replace materials engineering review.

Sources

Identifiers and chemistry limits are drawn from the manufacturer’s INCONEL 600, INCONEL 625, and INCONEL 718 technical bulletins. Check their full tables, editions, product form, and current governing specification before ordering or using an alloy.