Duplex stainless steel has excellent strength and corrosion resistance. It can handle high pressure and high corrosion working conditions. QD is a manufacturer of duplex stainless steel castings. We will help you determine when to invest in duplex stainless steel castings. And we will provide you with practical decision-making basis.
What is duplex stainless steel?
Duplex stainless steel is a high performance alloy. Its name comes from its unique microstructure. It is made up of about 50 percent austenite and 50 percent ferrite phases. The austenite phase provides excellent toughness and weldability. The ferrite phase contributes high strength and resistance to chloride stress corrosion cracking. When combined, these two phases let duplex stainless steel keep good workability. At the same time, its performance is much better than traditional austenitic stainless steel.
The balance of microstructure is key. If the proportion of ferrite is too high, the material may become brittle. If there is too much austenite, the strength will decrease. So precise control of phase proportion during casting is very important. Today, duplex stainless steel has become a key material in marine engineering, chemical processing and energy industries.
Three Core Advantages of Duplex Stainless Steel
1. Doubled Strength: Reduce Weight and Cost
The yield strength of duplex stainless steel can be more than twice that of traditional austenitic stainless steel such as 304 or 316L. For example, the typical yield strength of 316L is about 170-200 MPa. But the yield strength of standard duplex steel like 2205 can reach 450-550 MPa. This high strength allows the design of thinner wall thickness. It thus reduces the weight of components. It also cuts down material usage and transportation costs.
2. Excellent Resistance to Stress Corrosion Cracking
Stress corrosion cracking is the brittle fracture of metals. It happens when tensile stress and corrosive media act together. Duplex stainless steel performs well in this aspect. Its ferrite phase can effectively stop the spread of cracks. For example, in high temperature chloride solutions, 316L may fail quickly. But duplex steels like 2205 can operate stably for a long time. This makes it especially suitable for seawater cooling systems or chemical pipelines.
3. Excellent Resistance to Pitting and Crevice Corrosion
Pitting and crevice corrosion are forms of localized corrosion. They are common in stagnant areas or crevices. The corrosion resistance of duplex stainless steel is usually measured by the Pitting Resistance Equivalent Number (PREN). The formula for PREN is %Cr + 3.3×%Mo + 16×%N. A higher PREN value means better resistance to pitting corrosion. For example:
- The PREN of 316L stainless steel is about 24-26.
- The PREN of duplex steel 2205 is about 35-40.
- The PREN of super duplex steel 2507 can reach 40-45.
This means duplex steels can effectively resist localized corrosion in harsh environments. They also reduce the need for maintenance.
Comparison of Mainstream Grades: 2205 vs. 2507
2205 and 2507 are the most commonly used representatives of duplex stainless steel. The table below compares their properties in detail. It helps you make a choice based on your project needs.
| Properties | 2205 | 2507 |
| Typical yield strength (MPa) | 450-550 | 550-700 |
| PREN value | 35-40 | 40-45 |
| Main alloying elements | Cr: 22 – 23%, Ni: 4.5 – 6.5%, Mo: 3 – 3.5%, N: 0.14 – 0.20% | Cr: 24 – 26%, Ni: 6 – 8%, Mo: 3 – 4%, N: 0.24 – 0.32% |
| Cost-effectiveness | Economical and practical. Balance between performance and cost | Higher cost. But suitable for extreme environments |
| Applicable temperature range | -50°C to 300°C | -50°C to 350°C |
| Common applications | Chemical containers, heat exchangers | Offshore platforms, desalination equipment, high pressure valves |
Duplex Steel 2205: 2205 is one of the most commonly used duplex stainless steels. It achieves a perfect balance between strength, corrosion resistance and cost. It is widely used to replace 316L in moderate corrosion environments. Such environments include chemical processing and pulp industries. It has good weldability and formability. It is suitable for complex castings.
Super Duplex Steel 2507: 2507 super duplex steel has higher contents of chromium, molybdenum and nitrogen. These elements improve its strength and corrosion resistance. It is especially suitable for environments with high chloride ion concentration and high pressure. Its cost is higher. But in extreme working conditions such as deep sea oil and gas extraction, its long service life and low maintenance cost can bring higher return on investment.
Typical Application Scenarios
Equipment for Offshore Oil Platforms
Examples include pump casings, valves and pipeline systems. These components are exposed to high chloride seawater and acidic media. The corrosion resistance and high strength of duplex steel ensure the reliability of the equipment in harsh marine environments. They also reduce downtime.
Storage Tanks for Chemical Tankers
When transporting corrosive chemicals such as acidic solutions, storage tanks need to resist pitting and stress corrosion. Duplex steel has a high PREN value. It provides an extra safety margin. It also meets international shipping standards.
Pumps and Valves for High Pressure and Highly Corrosive Media
In oil refining or chemical processing, these components bear high temperature, high pressure and corrosive fluids. The strength of duplex steel allows the design of more compact components. At the same time, it extends the service life.
Contact Us
Is your project facing the double challenge of strength and corrosion? Let QD evaluate the feasibility of using duplex stainless steel. We can calculate the PREN value based on your working conditions. We can also provide cost performance analysis. This helps you make the best decision.
Whether it is the design of a new project or the upgrade of existing equipment, we can provide customized solutions. Please contact our expert team to get free consultation.
FAQ
1. Is the cost of duplex stainless steel much higher than that of 316L?
Yes. Its initial cost is higher. It is about 1.5 to 2 times that of 316L. But due to its high strength and long service life, the total cost of ownership is often lower.
2. Is duplex stainless steel suitable for high temperature environments?
Yes. But the temperature needs to be controlled below 300°C for 2205. Or below 350°C for 2507. This is to avoid phase transformation. We can recommend the right grade according to your temperature range.
3. Is it difficult to weld duplex stainless steel?
No. But professional processes are needed to prevent phase imbalance. QD can provide welding guidance and support.
4. How does the PREN value help with material selection?
The PREN value measures pitting corrosion resistance. The higher the value, the better the performance. We can calculate the PREN requirement in your environment. Then we match the best material for you.
5. How does duplex stainless steel perform in acidic environments?
It performs excellently. This is especially true in environments with chloride ions or weak acid media. But for strong reducing acids such as hydrochloric acid, extra evaluation is needed. QD can conduct corrosion tests.
6. What size of castings can QD’s foundry handle?
We can produce castings from a few kilograms to several tons. We rely on investment casting technology. This ensures high precision for complex geometric shapes.