---
title: "Monel Machining | 400 & K-500 Nickel-Copper Parts | OpenSpindle"
description: "Get quotes for custom Monel 400 and K-500 parts from qualified shops. Nickel-copper alloy for marine, seawater, and reducing-acid service. Machined, turned, and welded. Upload a drawing."
canonical: https://openspindle.com/materials/monel
---

# Get quotes for custom Monel parts

Monel is a family of nickel-copper alloys (roughly 67% Ni, 30% Cu) that resists seawater, salt spray, reducing acids, and alkaline service better than most stainless. The marine, naval, and chemical-process standard where 316 stainless corrodes. Upload your drawing and we route it to shops set up for Ni-Cu work.

## Monel grades shops run most

Two grades dominate practical specification: solid-solution Monel 400 and precipitation-hardening K-500.

### Monel 400 (UNS N04400)

The baseline nickel-copper alloy (~67% Ni, 30% Cu, balance Fe/Mn). Excellent seawater and salt-air corrosion resistance, immune to chloride-induced stress-corrosion cracking, strong in reducing acids. Not heat-treatable; strength set by cold work.

**Best for:** Marine hardware, seawater pump wet-ends, propeller shafts, valve bodies, fittings, chemical-process piping

### Monel K-500 (UNS N05500)

Monel 400 with aluminum and titanium additions for age-hardening. Roughly 2× the yield strength of Monel 400 with the same corrosion profile, used where seawater service meets a strength requirement.

**Best for:** Pump and valve shafts, fasteners for marine and oilfield, downhole hardware, propeller shafts

### Monel 404 (UNS N04404)

A low-magnetic variant with controlled low aluminum, for electronic and vacuum tube applications where magnetic properties matter.

**Best for:** Vacuum electronics, specialty magnetic applications

### Monel R-405 (UNS N04405)

A free-machining Monel 400 with added sulfur for better machinability at the cost of some corrosion resistance. For high-volume turned parts where the base alloy is too gummy.

**Best for:** High-volume machined fasteners, fittings, screw-machine parts

## Material Properties

Representative values for Monel 400 (annealed) and K-500 (aged).

| Property | Value |
| --- | --- |
| Density | 8.80 g/cm³ (0.318 lb/in³) |
| Melting range | 1300–1350 °C |
| Tensile strength (400 annealed) | ~70 ksi min |
| Yield strength (400 annealed) | ~28 ksi min |
| Tensile strength (K-500 aged) | ~130–160 ksi |
| Yield strength (K-500 aged) | ~85–120 ksi |
| Hardness (400 annealed) | ~75 HRB |
| Hardness (K-500 aged) | ~27–35 HRC |
| Machinability | 400: gummy, work-hardens; R-405 is better. K-500: machine solution-annealed, then age. |
| Welding | Readily welded with matching NiCu filler (ERNiCu-7). |

Monel work-hardens; keep the cut heavy enough to stay under the hardened layer, avoid dwelling, and use positive-geometry carbide. For K-500, machine in the solution-annealed condition and age-harden after rough machining, then finish-machine.

## Processes That Run This Material

- [CNC Turning](https://openspindle.com/capabilities/cnc-turning.md) -- Shafts, fittings, and marine hardware turned from Monel 400 and K-500 bar.
- [CNC Machining](https://openspindle.com/capabilities/cnc-machining.md) -- Milled valve bodies, pump wet-ends, and marine brackets.
- [Welding & Metal Fabrication](https://openspindle.com/capabilities/welding.md) -- TIG and MIG weldments for marine piping and chemical-process assemblies.
- [Swiss Machining](https://openspindle.com/capabilities/swiss-machining.md) -- Marine fasteners and small turned parts in free-machining R-405.
- [Precision Grinding](https://openspindle.com/capabilities/precision-grinding.md) -- Finished seal surfaces on pump and valve shafts.

## Finishes

Monel is usually left bare or passivated; the alloy itself provides the corrosion resistance.

- **As-machined** -- Standard for most marine and industrial parts.
- **Pickled & passivated** -- Removes heat tint and surface iron from machining and welding; restores full corrosion profile.
- **Electropolished** -- For pharma and semi applications where surface particulate matters.
- **Bead or glass-bead blasted** -- Uniform matte finish, common on visible marine and architectural parts.

For sour service and oil & gas, specify NACE MR0175 compliance and the heat-treat condition on the drawing (annealed vs aged).

## Applications

- Marine propeller shafts, rudder bearings, and fittings
- Seawater pump wet-ends and valve trim
- Naval and submarine hardware
- Offshore oil & gas (umbilicals, downhole hardware)
- Hydrofluoric acid service (specialty)
- Salt-production equipment
- Fasteners for marine and oilfield
- Chemical-process piping and heat exchangers

Monel wins when the service is seawater, salt spray, or reducing acids where stainless pits or stress-corrosion cracks.

## How It Compares

How Monel compares to the alloys buyers consider alongside it.

### [316L stainless steel](https://openspindle.com/materials/stainless-steel.md)

- Monel resists seawater pitting and chloride stress-corrosion cracking; 316L is vulnerable to both
- 316L is far cheaper per pound and more widely available
- For general industrial corrosion where chlorides are moderate, 316L is usually adequate

**Verdict:** Choose Monel for seawater and chloride-rich service. Choose 316L for general industrial and food-grade service.

### [Hastelloy C-276](https://openspindle.com/materials/hastelloy.md)

- Hastelloy handles mixed oxidizing + reducing media better than Monel
- Monel is better in hot HF (hydrofluoric acid), where Hastelloy and stainless both fail
- Monel is less expensive than Hastelloy and more widely available

**Verdict:** Choose Monel for seawater, salt, and HF. Choose Hastelloy for mixed-acid chemical process and higher-temperature service.

### [Inconel 625](https://openspindle.com/materials/inconel.md)

- Inconel 625 covers a wider temperature range and more aggressive mixed media
- Monel is better suited to seawater and reducing-acid wet service
- Monel is more machinable and typically less expensive

**Verdict:** Choose Inconel for high-temperature or mixed-oxidizer service. Choose Monel for marine and reducing wet service.

## Frequently Asked Questions

### What is the difference between Monel 400 and K-500?

Both have the same corrosion profile (seawater, salt spray, reducing acids, HF). Monel 400 is a solid-solution alloy with strength set by cold work. K-500 adds aluminum and titanium so it can be age-hardened to roughly double the yield strength (85–120 ksi vs 28 ksi for annealed 400). Use K-500 where you need both the corrosion resistance and the strength -- pump shafts, downhole fasteners, propeller shafts.

### Can Monel be welded?

Yes, readily. Use matching NiCu filler (ERNiCu-7 for TIG and MIG) and clean preparation; Monel is sensitive to sulfur contamination (grinding wheels, cutting fluids), which causes hot cracking. K-500 welds, then age-hardens post-weld to restore strength in the weldment.

### Why does Monel cost more than stainless?

Composition. Monel is roughly 67% nickel and 30% copper -- both commodity metals that drive the price. 316L stainless is roughly 10% nickel, 2% molybdenum, balance iron, so it rides on the far cheaper iron base. Expect 3–5× the per-pound cost of 316L stainless for Monel 400 bar.

### What is Monel R-405 and when do I use it?

R-405 is Monel 400 with added sulfur (0.025–0.060%) for free-machining performance. It cuts and chips far more easily than standard 400 and is the go-to for high-volume Swiss and screw-machine fasteners and fittings. Corrosion resistance is slightly reduced; for critical marine or chemical service, specify 400 or K-500.

### Is Monel magnetic?

Monel 400 is weakly ferromagnetic at room temperature and loses magnetism above about 20–50 °C depending on composition. K-500 is non-magnetic in the aged condition. If magnetic properties matter (vacuum electronics, MRI compatibility), specify Monel 404 or K-500 aged.

### Does Monel work for sour service?

Yes, Monel K-500 is NACE MR0175-compliant for sour service in the aged condition, and it is widely used for downhole bolting, pump shafts, and well-head hardware in H2S-containing environments. Call out the NACE requirement on the drawing with the heat-treat condition.

## Related Materials

- [Inconel / Nickel Superalloys](https://openspindle.com/materials/inconel.md)
- [Hastelloy](https://openspindle.com/materials/hastelloy.md)
- [Stainless Steel](https://openspindle.com/materials/stainless-steel.md)
- [Titanium](https://openspindle.com/materials/titanium.md)
- [Copper](https://openspindle.com/materials/copper.md)

## Need Monel 400 or K-500 parts?

Upload a drawing and we route it to shops set up for nickel-copper work, with marine, oilfield, or chemical-service experience as the project requires.