Monel® 405: Uses, Composition, Properties

Monel® 405 belongs to the Monel alloy family, renowned for its exceptional resistance to corrosive environments, especially those involving acids, seawater, and alkaline solutions. It is a free-machining version of R-400. It has a small amount of extra sulfur compared to R-400 which enhances machinability. Monel 405 is a nickel-copper alloy that offers outstanding performance, making it an attractive choice for critical applications where durability and longevity are paramount.

Monel 405 comprises a minimum of 63% nickel and 28-34% copper, enhancing its mechanical and physical characteristics. The addition of sulfur in small amounts gives Monel 405 the added benefit of improved machinability when compared to Monel 400. This alloy demonstrates excellent strength up to approximately 480 °C, making it useful for many high-temperature applications in challenging corrosion environments.  This article will discuss Monel 405, its uses, composition, and notable properties.

What Is Monel 405?

Monel 405 (or R-405) is a free-machining grade of Monel. Monels are a group of nickel-copper alloys known for their excellent corrosion resistance and high strength. Monel 405 has improved machinability compared to R-400, to which it is otherwise identical, because of the addition of a small amount of sulfur (0.025-0.060%).

The composition of Monel 405 typically consists of approximately 63% nickel and 28-34% copper. It also contains small amounts of carbon, iron, manganese, silicon, and sulfur. The addition of sulfur in Monel 405 leads to the formation of nickel-copper sulfides, which enhance its machinability, making it easier to work with.

Monel 405 exhibits excellent corrosion resistance, making it suitable for applications in marine environments, chemical processing plants, and the aerospace, electrical equipment, and oil and gas industries. It is commonly used in components such as pump shafts, propeller shafts, seawater valves, heat exchangers, fasteners, and electrical connectors.

Monel 405 is primarily utilized as an automatic screw machine stock. It is governed by various standards and specifications, including ASME SB-164, ASTM B-164, and Federal QQ-N-281. For more information, see our guide on What is Monel.

What Is Monel 405 Used For?

Monel R-405 has gained a significant foothold as the alloy of choice for corrosive environments requiring high strength and resistance to high temperatures. Listed below are some of its uses:

1. Meter and valve parts in the oil and gas industry
2. Fasteners for assembled structures in marine, chemical, and offshore petroleum production
3. Screw machine products for manufacturing precision components
4. Piping in oil refineries
5. Heat exchangers in marine and chemical processing industrial settings
6. High-temperature heating coils in industrial furnaces and heating systems

How Is Monel 405 Made?

The exact details of the manufacturing process for Monel 405 may be proprietary and specific to each manufacturer's practices. Here is a general overview of how Monel 405 is typically made:

1. The primary components of Monel 405 (nickel and copper) are accurately weighed and measured according to the desired proportions. The materials are melted together to form a homogeneous liquid.
2. During the melting process, any necessary alloying elements, such as: sulfur, iron, manganese, silicon, and carbon, are added to the molten metal to achieve the required composition of Monel 405. Refining agents may also be used to remove impurities and enhance the quality of the alloy.
3. Once the alloying and refining are complete, the molten Monel 405 alloy is cast into a specific shape or solidified into a desired form, such as ingots, billets, or continuous casting for larger sections.
4. The solidified Monel 405 alloy is then subjected to various forming and processing techniques such as: hot rolling, cold rolling, extrusion, machining, and heat treatment, based on the intended final product. These processes help shape the alloy into the desired forms, such as sheets, bars, plates, rods, or wires. Heat treatment processes such as annealing may be required. 
5. After the necessary forming and processing steps, the Monel 405 material may undergo additional finishing processes, such as polishing, or coating, to achieve the desired appearance, dimensions, and surface characteristics.

What Is the Chemical Composition of Monel 405?

Monel 405 is a nickel-copper alloy modified from Monel 400 for improved machinability. It has nickel and copper contents of about 63 and 28-34%, respectively. The exact chemical composition of Monel 405 typically includes:

What Are the Properties of Monel 405?

Table 2 shows some important properties of Monel 405:

Machinability Rating of Monel 405

Monel 405, or R-405, has a machinability rating of 44%. Machinability ratings are typically established by comparing the performance of a material to Steel SAE 1112, which serves as a reference material, with a fixed machinability rating of 100%. A machinability rating below 100% indicates a relatively more difficult material to machine.

What Are the Thermal Properties of Monel 405?

Monel 405 has a melting temperature range of 1300-1350 °C. Other thermal properties of Monel 405 (R-405) are given in Tables 3 below:

a Annealed material

b Extrapolated data (source: https://www.specialmetals.com/documents/technical-bulletins/monel-alloy-r-405.pdfbulletins/monel-alloy-400.pdf)

What Are the Common Forms of Monel 405 Material?

Monel 405 is available in a number of forms, including:

Sheet

Monel 405 is available in sheet form, which is typically used for applications such as cladding, roofing, and general fabrication.

Bar

Monel 405 is also available in bar form, with either round or rectangular cross sections. Monel 405 bars can be used for applications including fasteners, shafts, and structural components. This is also the dominant product form of Monel 405. 

Plate

Monel 405 plates are thicker than sheets and can be used for applications that require higher strength and load-bearing capacity. Plate forms of Monel 405 are commonly used in industries such as marine, chemical processing, and oil and gas.

Hot Rolled

Monel 405 is available in a hot-rolled form. Hot rolling involves heating the material above its recrystallization temperature and then passing it through rollers to shape it into the desired form. Hot-rolled Monel 405 is typically used for applications that require larger sizes or specific structural properties.

Annealed

Annealing is a heat treatment process that involves heating the material to a specific temperature and then slowly cooling it to relieve internal stresses and enhance ductility. Annealed Monel 405 is softer and more machinable compared to its as-rolled or as-cast counterparts. It is often used for applications that require extensive forming or machining.

Cold Drawn 

Cold drawing is a process that involves pulling the material through a die to reduce its diameter or change its shape. Cold-drawn Monel 405 is typically used when precise dimensions, improved surface finish, and increased strength are required. It finds applications in industries such as aerospace, automotive, and precision engineering.

What Are the Advantages of Using Monel 405?

Here are some advantages of using Monel 405:

1. It exhibits exceptional resistance to a number of corrosive environments, including seawater, acids, alkalis, and atmospheric conditions. This makes it highly suitable for applications in marine and offshore petroleum production, chemical processing plants, and other environments where corrosion is a concern.
2. It offers good mechanical properties, including high tensile strength and yield strength. This makes it suitable for applications that require strength and durability, such as marine hardware, pump shafts, valve components, and heat exchangers.
3. It provides good weldability and can be joined to itself or other materials without significant issues. This allows for ease of fabrication and enables the creation of complex structures or components.
4. Offers resistance to stress corrosion cracking, making it suitable for applications where materials may be subjected to high-stress levels in corrosive environments, such as seawater or chemical processing plants.
5. It retains its mechanical properties at elevated temperatures, making it suitable for applications involving high-temperature environments. It can withstand thermal cycling and exhibits good dimensional stability even under varying temperature conditions.
6. It is suitable for applications where magnetic interference needs to be reduced because of its low magnetic permeability. It is commonly used in electronic and electrical equipment.

What Are the Disadvantages of Using Monel 405?

While Monel 405 has many advantages, there are also some potential disadvantages associated with its use. Here are a few considerations:

1. It tends to be more expensive than other common materials such as stainless steel or carbon steel. The higher cost can make it less economical for certain applications, particularly when a lower-cost alternative can provide sufficient performance. Monel is usually used only when a cheaper alternative cannot meet the requirements of the application. 
2. It has a lower melting point than some other nickel alloys. This limits its suitability for extremely high-temperature applications where materials with higher melting points are necessary.
3. It can still be more challenging to machine than some other materials, such as carbon steel or stainless steel. It tends to work harden, leading to increased tool wear due to slower machining speeds. Special tooling and machining techniques may be required to achieve desired results.
4. While it is generally resistant to many corrosive environments, it may not be suitable for highly concentrated strong acids, such as sulfuric or hydrochloric. In such cases, alternative materials with superior acid resistance may be preferred.
5. Although Monel alloys are generally resistant to stress corrosion cracking, they can be susceptible to chloride stress corrosion cracking in certain conditions. This limits their use in environments where chloride ions are present, such as seawater or chloride-containing solutions.

What Is the Difference Between Monel 405 and Monel 400?

Monel R-405 (UNS N04405) is a variant of Monel alloy 400 designed specifically for enhanced machinability. The increased sulfur content in R-405 improves its machinability characteristics. Alloy R-405 has essentially the same physical properties as alloy 400. However, it shows a different range of properties including variations in hardness, strength, and other mechanical attributes.

What Is the Difference Between Monel 405 and Monel K500?

Monel alloy K500 (UNS N05500/W.Nr. 2.4375) is an advanced version of Monel with minor additions of aluminum and titanium to its base composition. While Monel 400 and R-405 can only be strengthened by cold work, K500 exhibits the capability of being both work-hardened and precipitation hardened. K500 offers a combination of the outstanding corrosion resistance found in Monel alloy 400, along with the additional benefits of enhanced strength and hardness through precipitation hardening treatments. 

While it exhibits excellent corrosion resistance in many environments, it is indeed more susceptible to stress-corrosion cracking (SCC) in specific conditions when it is in the age-hardened condition. SCC is a type of corrosion that occurs under combined tensile stress and exposure to a corrosive environment.

Compared to its annealed or solution-treated condition, Alloy K500 in the age-hardened condition is more prone to stress-corrosion cracking. The age-hardening process involves heating the alloy to a high temperature and then cooling it rapidly to achieve precipitation hardening. This treatment enhances the mechanical properties of the alloy but can increase its susceptibility to SCC in certain environments.

However, Monel K500 finds particular suitability in marine service, especially for centrifugal pump shafts. It is commonly employed in applications such as oil-well tools, marine propellers, electronic components, rotary impellers, pump shafts, scrapers, doctor blades, and oil-well drill collars.

Summary

This article presented Monel 405, explained it, and discussed its various properties. To learn more about Monel 405, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

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