Introduction
When engineers choose metals for rigorous applications, they consider three main criteria: toughness, corrosion resistance, and cost.
In this article, you’ll learn about duplex 2205 and super duplex 2507. These two grades belong to the duplex stainless steel family. It consists of two types of metal structure, namely austenite and ferrite.
We will look at the distinctions between these two grades and why each is suited to different purposes.
What Are They Made Of?
Both of them contain high levels of chromium, nickel, molybdenum, and nitrogen. The elements protect the metal from corrosion and increase the alloy’s hardness.
| Element | Duplex 2205 | Super Duplex 2507 |
| Chromium (Cr) | 21-23% | 24-26% |
| Nickel (Ni) | 4.5-6.5% | 6-8% |
| Molybdenum (Mo) | 2.5-3.5% | 3-5% |
| Nitrogen (N) | 0.14-0.20% | 0.24-0.32% |
A number called PREN describes a metal’s ability to resist rust. This range is 35-37 for Duplex 2205. Super Duplex 2507 has a value of 40-45. The higher the PREN number, the more resistant the material is to saltwater and other corrosive substances.
Strength and Durability
Their characteristics are significantly greater than those of normal stainless steel. This also means they can withstand heavy weight and pressure.
| Property | Duplex 2205 | Super Duplex 2507 |
| Yield Strength | ~450 MPa | ≥550 MPa |
| Tensile Strength | ~620 MPa | ≥800 MPa |
| Elongation | 25-30% | 15-25% |
Super Duplex 2507 and Duplex 2205 are strong, which means builders need less metal to create structures such as ships, tanks, and pipes. This is helpful for weight and cost savings. These steels can also bend slightly, making them easier for workers to shape.
Where Are They Used?
Duplex 2205 is commonly used in various locations. In fact, factories rely on it for the tanks that store their chemicals, the pipes that carry liquids, and the machines that heat or cool them. Water plants use it to convert saltwater into freshwater. Paper mills use it in equipment that cleans and bleaches paper.
Super Duplex 2507 is used for even more challenging applications. It is used in underwater pipes and vital parts in oil platforms at sea. Water plants use it in the saltiest areas. It is also employed in hot-water coolers and in systems that pump seawater at high pressure.
Building and Cost
Duplex 2205 costs less money. Workers find it easier to cut, bend, and weld together. It can be used with any equipment or materials.
Super Duplex 2507 is more expensive due to higher levels of special metals. It is more difficult to make things with it. Special precautions are necessary when welding, and the right material must be used.
How Do You Choose?
Choosing any of these duplex stainless steels depends on the project’s needs.
Choose Duplex 2205 if you are seeking good strength and rust protection, but do not wish to spend much. It is suitable for factories, water plants, and areas with low salt levels.
For the toughest applications, use Super Duplex 2507. It is most suitable if the metal is going to come into contact with large amounts of salt, high pressure, or strong chemicals. It is very strong, highly rust-resistant, and safe for people and machines.
Conclusion
Duplex 2205 is suitable and durable for use in machinery and pipelines under simple conditions. It can easily be formed into shape and is long-lasting in its common applications.
Super Duplex 2507 is recommended for high-stress environments and corrosion resistance. It performs optimally over the long term in the toughest situations. This characteristic makes Super Duplex 2507 suitable for safety-critical applications.
Choose your duplex stainless steel based on the application for which you intend to use it. Proper selection leads to good performance by the machinery.