# Alloy 400

Specifying UNS N04400 nickel-copper alloy by product form and condition, with producer-specific properties and corrosion-service limits.

Reviewed: 2026-11-01

Tags: materials, nickel-alloys, specialty-metals, corrosion

## Identity and specification

Special Metals describes **Alloy 400** as resistant in **flowing seawater** and warns of **pitting and crevice corrosion in stagnant conditions**. Assess sheltered joints, deposits and shutdown pockets alongside flowing operation. VDM also identifies stress-cracking exceptions involving mercury or moist, aerated hydrofluoric-acid vapor. [Special Metals seawater comparison](https://www.specialmetals.com/documents/technical-bulletins/monel-alloy-400.pdf), [VDM corrosion guidance](https://www.vdm-metals.com/fileadmin/user_upload/Downloads/Data_Sheets/Data_Sheet_VDM_Alloy_400.pdf)

Alloy 400 commonly denotes the nickel-copper alloy **UNS N04400**. **MONEL** is a Special Metals group trademark; **VDM Alloy 400** is another producer's identified product. A generic alloy designation does not establish either producer's provenance. Special Metals describes its alloy as a solid solution hardened by cold working. [Special Metals, MONEL alloy 400 bulletin](https://www.specialmetals.com/documents/technical-bulletins/monel-alloy-400.pdf)

Do not confuse Alloy 400 with a higher-strength, similarly named alloy or a free-machining variant. For a substitution, verify the complete designation and governing requirements before comparing individual property numbers. Retain heat identification through cutting and machining.

## Chemistry and physical-property example

Special Metals gives these limiting mass percentages for **MONEL alloy 400**. They describe that bulletin's composition basis, rather than a certificate for unidentified material. [Special Metals, Table 1](https://www.specialmetals.com/documents/technical-bulletins/monel-alloy-400.pdf)

| Constituent | Listed limit, mass % |
| --- | ---: |
| Nickel plus cobalt | ≥63.0 |
| Copper | 28.0–34.0 |
| Iron | ≤2.5 |
| Manganese | ≤2.0 |
| Carbon | ≤0.3 |
| Silicon | ≤0.5 |
| Sulfur | ≤0.024 |

VDM's named product has its own composition table, including tighter limits for some constituents. Use the specified producer/product and standard when judging a chemical analysis; a cross-producer table assembled from selected limits would create an unsupported specification. [VDM Alloy 400 data sheet, Table 2](https://www.vdm-metals.com/fileadmin/user_upload/Downloads/Data_Sheets/Data_Sheet_VDM_Alloy_400.pdf)

VDM reports **8.82 g/cm³ at 20°C**. **Calculated illustration:** a solid blank measuring 100 × 100 × 10 mm has volume 100 cm³. Estimated mass is 100 × 8.82 = **882 g**, or **0.882 kg**, using that density. This is a nominal geometry calculation, not a supplied-weight tolerance or a guarantee for every producer. [VDM physical properties](https://www.vdm-metals.com/fileadmin/user_upload/Downloads/Data_Sheets/Data_Sheet_VDM_Alloy_400.pdf)

Special Metals also notes that some heats are magnetic at room temperature and others are not. Do not specify guaranteed nonmagnetic behavior by the alloy name alone. [Special Metals, physical-property discussion](https://www.specialmetals.com/documents/technical-bulletins/monel-alloy-400.pdf)

## Mechanical properties belong to a condition

VDM's room-temperature table for **sheet/plate and rod/bar**, in the listed specification categories, distinguishes the following conditions. These are its published product-property entries, not universal design allowables. Dimensions outside the sheet's scope require agreement. [VDM data sheet, mechanical-properties section and Table 5](https://www.vdm-metals.com/fileadmin/user_upload/Downloads/Data_Sheets/Data_Sheet_VDM_Alloy_400.pdf)

| Condition and listed category | Rp0.2, MPa | Rm, MPa | Elongation A |
| --- | ---: | ---: | ---: |
| Annealed; ASTM/ASME/QQN | ≥195 | ≥480 | ≥35% |
| Stress-relieved; ASTM/ASME | 275–415 | 550–600 | ≥20% |

The table labels elongation as A; do not silently assign it an unreported gauge length. Reconcile the actual ordered form, dimensions, test specimen and specification with the material certificate. The quoted rows are not evidence that every annealed or stress-relieved Alloy 400 product has those same limits.

## Corrosion: define the medium and exposure

Special Metals contrasts favorable behavior in flowing seawater with **pitting and crevice corrosion in stagnant conditions**. “Marine alloy” therefore does not settle the behavior of a sheltered joint, deposit-covered surface or stagnant pocket. [Special Metals, corrosion-resistance section](https://www.specialmetals.com/documents/technical-bulletins/monel-alloy-400.pdf)

VDM warns that oxidizing conditions can substantially increase corrosion rates and identifies stress-cracking exceptions involving mercury or moist, aerated hydrofluoric-acid vapors. Its general resistance statements should not be read as immunity in every chemical environment. [VDM corrosion-resistance section](https://www.vdm-metals.com/fileadmin/user_upload/Downloads/Data_Sheets/Data_Sheet_VDM_Alloy_400.pdf)

Check aeration, contaminants, velocity, deposits, crevices and stress during operation, shutdown and cleaning.

Define acceptable corrosion and leakage criteria before testing. Where service is safety-critical, connect the material decision to the governing engineering assessment and inspection plan rather than a generic compatibility label.

## Fabrication and finished-part acceptance

VDM's machining guidance warns of work hardening and recommends cutting below the previously hardened zone. Its heating guidance emphasizes avoiding contamination, including sulfur, phosphorus, lead and other low-melting metals. [VDM processing and heat-treatment sections](https://www.vdm-metals.com/fileadmin/user_upload/Downloads/Data_Sheets/Data_Sheet_VDM_Alloy_400.pdf)

Develop cutting parameters for the actual condition, tool and machine; this page supplies no universal speed or feed. Plan fixturing, machining allowance and inspection around the finished geometry. For welding or thermal processing, establish a qualified route with appropriate cleanliness, consumables and acceptance requirements. A general statement of weldability does not qualify a pressure boundary or dissimilar-metal joint.

At release, connect the drawing to the exact material, certificate, processing history and final inspection. Review any change in producer, form, condition, surface treatment or service chemistry against those linked requirements. Confirm current standard editions and order-specific certification instead of treating a historical bulletin's code listing as present approval for a finished assembly.

## Source versions

The Special Metals bulletin prints **SMC-053, ©2005 (Feb 05)**. The VDM document prints **Material Data Sheet No. 4110, Revision 01, November 2020**; its primary download was checked directly. Sources reviewed **2026-11-01, America/Los_Angeles**. Dates describe the documents consulted, not a guarantee that their standards references remain current.

See [grades, tempers and conditions](../grades-tempers-and-conditions.md).