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Nickel Alloy

Monel 400

Monel 400 is a nickel-copper alloy renowned for resistance to seawater, hydrofluoric acid, and reducing acids where stainless steels fail. With a corrosion rating of 4.5, 550 MPa tensile, and good ductility at 40% elongation, it is a single-phase, non-hardenable alloy whose value lies in its chemistry. It serves marine and acid piping that demand reliable corrosion performance.

How Monel 400 machines

Machinability is 2.0/5. Monel 400 is tough and work-hardens, behaving gummy like other nickel alloys. Use sharp tooling, low to moderate speeds, firm positive feeds to stay under the work-hardened layer, rigid setups, and generous coolant. Avoid dwelling and rubbing, which harden the surface and accelerate tool wear.

Manufacturing & processing

Monel 400 is processed by CNC, forging, sheet metal, and extrusion. It is not hardenable by heat treatment; strength comes from cold work. It welds well with matched filler and inert shielding and retains toughness over a wide temperature range, making it suitable for fabricated piping, valves, and fittings.

Typical applications

Best for marine and acid service piping. Typical uses include seawater valves, pumps, and piping, hydrofluoric acid equipment, heat-exchanger and condenser tubing, marine fasteners, and chemical-process hardware exposed to reducing acids and brines that attack ordinary stainless.

When to choose it

Choose Monel 400 for seawater, hydrofluoric acid, and reducing-acid service where stainless corrodes. If you need high strength as well as corrosion resistance, a duplex stainless or nickel superalloy fits better. For oxidizing acids, other alloys may outperform Monel.

Suitable surface finishes

Common finishes for Monel 400: electropolishing, passivation. Use the finish selector →

FAQ

Why is Monel 400 used for seawater and HF acid?
Its nickel-copper chemistry resists seawater, brines, and hydrofluoric and other reducing acids that pit or corrode stainless steel. This specific resistance, rated 4.5, is the main reason to specify Monel 400 for marine and acid piping.
Can Monel 400 be hardened by heat treatment?
No. Monel 400 is a single-phase solid-solution alloy and cannot be hardened by heat treatment; additional strength comes only from cold working. It is selected for corrosion resistance and toughness rather than high mechanical strength.
Is Monel 400 hard to machine?
Moderately, rated 2.0/5. It is tough and work-hardens like other nickel alloys, so it can be gummy. Sharp tools, firm positive feeds, rigid setups, adequate coolant, and avoiding dwell are needed for clean cuts and reasonable tool life.

Property values are typical/nominal for early guidance and vary by temper, grade, supplier and heat treatment. Confirm critical specs against a certified datasheet or with an mfgiq engineer.