Whether you are looking for a high-performance material for your next project or simply want to learn more about this versatile alloy, this guide is the ultimate resource for duplex stainless steel.
By reading this guide, you will be provided with a comprehensive overview of its properties, uses, and various types available on the market.
Let us start.
What Exactly Duplex Stainless Steel is?
Duplex stainless steel consists of a balanced mix of two distinct phases, austenite and ferrite. It combines the superior strength of ferritic and the corrosion resistance of austenitic.
Its higher chromium and molybdenum content make it more resistant to pitting and crevice corrosion in harsh environments.
The Composition
The composition determines the properties of the steel and how it will perform in different applications.
Take a look at its composition stated below.
| Chromium (Cr) | 18–20% |
| Nickel (Ni) | 8–10% |
| Manganese (Mn) | 2% |
| Silicon (Si) | 1% |
| Molybdenum (Mo) | 2–3% |
| Nitrogen (N) | 0.08–0.20% |
| Phosphorus (P) | 0.045% |
| Carbon (C) | 0.03% |
| Iron (Fe) | Balance |
Where to Use Duplex-Type Stainless Steel?
Duplex-type stainless steel is used in a variety of industries. Like in the medical, marine, automotive, and aerospace industries.
Now, let’s explore its specific uses in more detail.
Medical
In the medical environment, the material is widely used in manufacturing:
- Implantable Medical Devices: This includes components such as orthopedic screws and plates, dental implants, pacemakers, and stents.
- Surgical Instruments: Duplex stainless steel is often used to produce surgical instruments such as forceps, scalpels, and clamps.
- Scanners and Imaging Machines: This enables the machines to create accurate images without interference from magnetic fields.
- Hospital Furniture: Often used in the manufacture of hospital furniture, such as beds, tables, and cabinets. This ensures that the furniture is able to withstand the rigors of a hospital environment.
Marine & Offshore
In marine applications, duplex stainless steel is used to produce:
- Ship Hulls: It is often used for the hulls of ships due to their superior strength.
- Propeller Shafts: The high strength-to-weight ratio of the material makes it an ideal choice for use in propeller shafts.
- Anchor Chains: Duplex is often used to manufacture anchor chains due to its strength.
- Piping: Duplex steel is a popular choice for shipboard piping systems due to its excellent anti-corrosion properties.
- Marine Fittings: Often used in the manufacturing of marine fittings such as valves, flanges, and fittings.
- Deck Hardware: Duplex steel is used in the manufacturing of deck hardware such as cleats, chocks, and bollards.
Automotive
In automotive applications, the said alloy is used in the fabrication of:
- Exhaust systems: Due to their high-temperature resistance and toughness, duplex is often used in automotive exhaust systems.
- Fuel systems: The material is used in fuel systems due to its impressive strength.
- Structural elements: The specific steel is used in the manufacture of structural elements like chassis frames, suspension components, and body panels.
- Engine components: Duplex durability makes it the perfect material for producing automotive engine components.
- Heat exchangers: Its outstanding anti-corrosive properties make it a great choice in heat exchanger assembly.
Aerospace
The uses of duplex stainless steel in the aerospace industry include:
- High-temperature components: The steel is used to make high-temperature components such as exhausts, turbine blades, and heat shields. This is due to its excellent performance at high temperatures.
- Structural components: The material is used in the production of structural components like landing gears, wing spars, plugs, valves, etc.
- Hydraulic systems: It includes valves and fittings.
- Fasteners: Commonly used in the production of fasteners such as bolts and nuts.
Oil & Gas
In the oil and gas industry, the material is used for producing:
- Subsea Pipelines: Duplex is highly resistant to fatigue and oxidation making it the material of choice for subsea pipelines.
- Offshore Platforms: Typically used for offshore platforms, where its fatigue resistance make it ideal for harsh environment.
- Downhole Equipment: Used in downhole equipment such as drill bits, where its superior wear resistance makes it ideal.
- Valves and Fittings: Since the material has outstanding strength, it can be used in producing valves and fittings.
Construction
In the construction industry, duplex steel is used as a structural material in the construction of bridges, buildings, and other large structures.
Its high strength and anti-corrosive properties make it an ideal choice for structures in corrosive environments. Or even areas where the weather or temperature can fluctuate greatly.
Chemical
In the chemical industry, the duplex type is used for a wide range of applications. It can be used as pumps, valves, tanks, and heat exchangers. Also, it is well suited for handling highly hazardous chemicals. As well as for the storage and transport of chemicals.
Thanks to its exceptional anti-corrosion properties, it became widely used in the production of chemical catalysts and other materials used in the chemical industry.
Benefits of Using Duplex SS
There will be no regrets if you choose duplex steels for your fabrication projects. Using this specific steel will deliver you numerous benefits.
Its major benefit is its resistance to corrosion. Because of its higher chromium content, duplex steel can resists corrosion from chlorides better than other steels available.
Another considered benefit is its durability. It is extremely resistant to wear and tear. For that reason, you can use it to manufacture pumps, valves, and other components without worrying. It is also less prone to fatigue and creep, making it suitable for applications that require high strength levels.
Lastly, steel is more cost-effective than other types of stainless steel. It is usually less expensive to produce. In addition, it is also easy to fabricate, making it simpler and quicker to produce components. Plus it is also easier to maintain than other steels, so it is excellent for projects that require long-term durability.
Disadvantages
Though duplex steel is gaining immense popularity due to its amazing properties, it is not without its downsides. The following are some of the disadvantages of using this specific steel:
- High Cost: The metal is much more expensive than other types of stainless steel due to its high alloy content and the difficulty in manufacturing it.
- Difficult to Weld: It is much more difficult to weld than other steels due to its high alloy content. This can be a problem for certain types of applications.
- Low Temperature: You cannot use it in temperatures below -50°C. This can be a problem for certain applications, such as in cryogenic systems.
- Hot Tearing: Hot tearing can occur during the welding process of stainless steel. Its high alloy content causes the weld center to solidify faster than the edges.
- Toughness: Duplex stainless steel is a very tough material and can be difficult to machine. This means that it can take longer to get the desired shape and finish, and can significantly increase the production cost.
Duplex Stainless Steel Grades
The most common grades included are 2205, 2304, 2101, and 2003. Other grades include 2507, 2202, and Z100.
Let’s get to know each common grade more.
Type 2205. It became a duplex SS grade because of its combination of properties. It has high strength, excellent anti-corrosive properties, and good weldability. It also has higher yield strength than conventional austenitic steel grades.
Type 2304. The most common grade used is 2304, which is a combination of 23% chromium, 4% nickel and 2% molybdenum. The combination of these materials provides excellent strength compared to traditional austenitic and ferritic grades.
Type 2101. The 2101 stainless steel became a duplex grade because it has a combination of austenitic and ferritic microstructures. This combination of microstructures provides a balance between strength and ductility. Which then makes it a great choice in industries such as chemical processing, oil and gas, and food processing.
Type 2003. It is a duplex grade because it has a high chromium level, nickel, and molybdenum content. It is highly resistant to pitting and crevice corrosion. Additionally, its resistance to chloride-induced stress corrosion cracking makes it suitable for environments exposed to chlorides, such as seawater and brackish water.
The Difference Between Duplex VS 316 Stainless Steel
Duplex stainless steel is a type of steel that is composed of both ferritic and austenitic steel.
Whereas, 316 stainless steel is austenitic stainless steel composed of iron, chromium, nickel, and molybdenum. This alloy is one of the widely used grades of stainless steel due to its excellent anti-corrosive properties and strength. It is also highly resistant to pitting, which can occur when certain chemicals come into contact with the surface of the steel.
The main difference between the two is their composition. Duplex stainless steel is composed of both ferritic and austenitic steel. However, the 316 stainless steel is composed of just austenitic steel. That difference in composition makes the duplex more resistant to corrosion than 316. However, the 316 stainless steel is stronger and more resistant to pitting than the duplex type.
Duplex Stainless Steel VS 304
Duplex stainless steel is composed of two or more phases and has a high strength-to-weight ratio. This material is particularly useful in applications that require good corrosion resistance and strength, such as oil and gas pipelines.
In comparison to 304 stainless steel, duplex steels have a higher strength-to-weight ratio and better weldability. It is also more resistant to stress corrosion cracking, which is a common problem in certain environments. But in terms of cost, the duplex is more expensive than 304, but its superior properties make it well worth the extra cost.
Overall, the duplex type is an excellent choice for applications that demands superior strength and weldability. It is a great alternative to 304 SS when the cost is a major factor.
Fabrication & Welding Methods
Duplex SS requires different welding methods and specific heat treatments. Studying this will be the best way to ensure that the material is handled correctly. And that it will perform as expected when used.
- One of the most common methods of welding and fabricating duplex steel is Gas Tungsten Arc Welding (GTAW). This method uses a non-consumable tungsten electrode to form an arc between the material and the filler metal. The heat generated melts the material and the filler metal together, forming a strong bond. This method is widely used for welding thinner gauges of duplex steel and is ideal for welding in tight spaces.
- Plasma arc welding (PAW) is a newer method of welding duplex steels. This method uses an electric arc to form plasma between the filler metal and the material. The plasma creates a hot and turbulent environment, ideal for welding thicker gauges of duplex stainless steel.
Does Duplex SS Rust?
Duplex steel is known for its high strength and durability. But does it rust?
The answer is yes, this type of steel does rust. However, it is much more resistant to rust than regular steel due to its higher chromium content and dual-phase microstructure. Also, its ferritic and austenitic components provide additional protection against rust.
When exposed to harsh environmental conditions such as seawater, acids, and high temperatures, duplex will still corrode but at a much slower rate. It is because the two alloy components form a protective coating over its surface, preventing the spread of corrosion.
The rate of corrosion in this specific steel is also dependent on the environment and the maintenance level. Proper maintenance and regular inspections are essential to keep the steel in good condition and prevent corrosion. Regular cleaning and coating with specialized corrosion inhibitors can also help to protect it from rust.
Tips to Prolong the Quality
Like all materials, duplex stainless steel is susceptible to damage and degradation over time. Fortunately, there are a few simple tips you can follow to help prolong the quality of your material.
- Proper Cleaning and Maintenance: The most important step in maintaining the quality of the steel is to ensure that it is properly cleaned. This means removing any dirt, debris, or corrosion that may be present on the surface. Cleaning should be done with a mild detergent, warm water, and a soft cloth or brush. After cleaning, be sure to dry the surface thoroughly.
- Avoid Abrasive Cleaners: Abrasive cleaners can cause scratches and other damage to the surface of duplex steel, which can lead to deterioration over time. As such, it is important to avoid using any abrasive cleaners when cleaning.
- Prevent Rust: Rust can be a major problem when it comes to duplex stainless steel. To prevent it, make sure to keep the steel dry and clean. Also, use a protective coating, such as paint or a special oil, to keep the metal safe from moisture and other corrosive elements.
- Keep It Cool: Heat can be damaging, so be sure to keep it away from extreme temperatures. If necessary, use an insulating material to keep the metal cool.
- Use the Right Tools: Make sure to use the right tools when handling duplex steel. It’s important to use tools that are specifically designed for stainless steel to avoid any damage.
- Store Carefully: Make sure to store the metal properly to protect its quality. Store it away from extreme temperatures and in a dry, clean environment. Also, avoid contact with other metals or corrosive substances that may damage the surface of the steel.
- Inspect Regularly: Inspect the steel regularly for signs of wear and tear. Look for any indications of rust or other damage that could affect its quality. Repair any damages or replace the steel if necessary.
The Lifespan
The lifespan of duplex stainless steel depends on a variety of factors, such as the environment in which it is used.
Generally speaking, a duplex is known for its long life span. It can last for up to 30 years, depending on the application and environment.
In addition to its long life span, the duplex is also known for its extreme resistance to chloride-induced stress corrosion cracking. Therefore it is perfect for applications requiring long lifespan metals, such as in the marine and chemical processing industries.
CONCLUSION
We can conclude that duplex stainless steels are advantageous for most projects. As they have their own unique advantages and drawbacks compared to other stainless steels.
The information provided above is certainly useful in helping you determine if it is suitable for your applications.
If you need help, contact us now!