Duplex 2507 Stainless Steel: Uses, Composition, Properties
Duplex 2507 stainless steel is known for its corrosion resistance and exceptional strength. It has about 50-50 ferrite-austenite, though the exact balance may vary with heat treatment. Duplex 2507 stainless steel excels in various demanding industrial applications such as: offshore oil platforms, chemical processing equipment, and marine components.
In this article, we’ll take a closer look at Duplex 2507 stainless steel, including its uses, composition, characteristics, and properties.
What Is Duplex 2507 Stainless Steel?
Duplex 2507 stainless steel is a super duplex stainless steel containing low carbon (up to 0.03%), chromium (~25%), nickel (~7%), and molybdenum (~4%). Duplex 2507 stainless steel is engineered to meet the rigorous demands of applications that require exceptional strength and resistance to corrosion. These applications include equipment used in chemical processes, petrochemical industries, and equipment used in seawater environments. This steel boasts outstanding resistance to chloride-induced stress corrosion cracking. Thanks to its elevated levels of chromium, molybdenum, and nitrogen, it offers superb protection against pitting, crevice, and general forms of corrosion.
How Is Duplex 2507 Stainless Steel Made?
Duplex 2507 stainless steel is typically produced in a similar manner to other modern high-alloy steels. Scrap steel and the desired alloy additions are melted in an electric arc furnace. Once the steel is in a molten state, it's transferred to an AOD (argon oxygen decarburization) converter, where several key processes take place such as: decarburization, sulfur refining, and elimination of dissolved gasses.
Nitrogen is typically introduced into the steel during the AOD process. Following this, the steel proceeds to the ladle furnace, where adjustments are made to the inclusions.
With these preliminary steps completed, the next step in the process is to transfer the molten steel to the casting operation, which can take the form of individual ingots (large metal blocks) or continuously cast blooms (long, solid sections). These solid steel blooms or ingots undergo further refinement — they are reheated and then either forged or rolled to attain the desired thickness. To ensure uniform internal structure, a heat treatment known as solution annealing is applied, followed by a water quenching process.
Duplex 2507 piping materials can be produced through either hot forming or cold forming techniques. For hot forming, the temperature range should be set between approximately 1024 °C and 1232 °C. Following the hot forming step, a solution annealing process should be carried out, with a minimum temperature of about 1052-1125 °C, followed by a rapid water quench. In the case of cold forming, which encompasses actions like bending, deep drawing, extruding, and pressing, a subsequent heat treatment involving solution annealing and quenching is also necessary.
How Does Duplex 2507 Stainless Steel Differ From Duplex Steel?
Duplex 2507 stainless steel is classified as a super duplex stainless steel. Duplex stainless steels are a special class of stainless steels with a microstructure containing both ferrite and austenite in about equal measure. They combine some of the most useful characteristics of each of these phases. This unique blend gives duplex stainless steel exceptional resistance to corrosion coupled with robust mechanical strength. However, different duplex steel grades offer varying degrees of protection against corrosion. While they generally exhibit good resistance to localized corrosion such as pitting, crevice corrosion, and stress corrosion cracking, the exact level of resistance can vary based on the specific grade and alloy composition. Duplex stainless steels can be subdivided into four distinct categories, categorized according to the PREN (Pitting Resistance Equivalent Number) range of these alloys. Among these categories, super duplex stainless steel is characterized by a PREN number ranging from 38 to 45.
To learn more, see our guide on Duplex Steel Composition.
What Are the Uses of Duplex 2507 Stainless Steel?
Some common applications of Duplex 2507 stainless steel include:
- Desalination.
- Oil and gas industry equipment, including offshore platforms, pipelines, and well casings.
- Chemical processing equipment, especially for handling corrosive chemicals.
- Pulp and paper industry, particularly bleaching process equipment.
- Petrochemical industry applications, including PVC strippers.
- Water desalination plants.
- Power industry equipment, such as flue gas desulfurization (FGD) systems.
- Marine components, including ship propellers and shafts.
- Pollution control equipment such as scrubbers.
- Fittings are crucial components for connecting and controlling the flow of fluids in pipelines and systems. This includes elbows, tees, stub-ends, returns, caps, crosses, reducers, and pipe nipples, among others.
What Is the Chemical Composition of Duplex 2507 Stainless Steel?
The chemical composition (in weight percentage) and the PREN number of super duplex 2507 stainless steel are given in Table 1 below. Take note that the balance, which is not listed in the table, comprises iron.
| Name | 2507 |
|---|---|
Name UNS | 2507 S32750; S39275 |
Name En No. | 2507 1.441 |
Name C (max.) | 2507 0.03 |
Name Mn | 2507 1.2 |
Name Si | 2507 0.8 |
Name Cr | 2507 24.0-26.0 |
Name Ni | 2507 6.0-8.0 |
Name Mo | 2507 3.0-5.0 |
Name N | 2507 0.24-0.32 |
Name Cu | 2507 0.5 |
Name Other | 2507 S 0.020 max; P 0.035 max |
Name PREN | 2507 40-43 |
Table Credit: https://www.imoa.info/molybdenum-uses/molybdenum-grade-stainless-steels/duplex-stainless-steel.php
| Property | Value |
|---|---|
Property Density (g/cm3) | Value 7.8 |
Property Melting point (°C) | Value 1350 |
Property Modulus of Elasticity (GPa) | Value 200 |
Property Elongation (%) | Value 15 |
Property Tensile Strength (MPa) | Value 795 |
Property 0.2% Yield Strength(MPa) | Value 550 |
Property Hardness (Brinell) | Value 310 |
Table Credit: https://www.azom.com/article.aspx?ArticleID=9185
What Is the Machinability Rating of Duplex 2507 Stainless Steel?
The machinability range of super duplex 2507 is between 10 and 30%. This means that it is considered relatively difficult to machine. Machining Duplex 2507 stainless steel requires more cutting force, specialized tooling, and slower machining speeds to achieve the desired results compared to materials with higher machinability ratings.
Is Duplex 2507 Stainless Steel Magnetic?
Yes, the presence of ferritic grains within its composition renders 2507 duplex stainless steel a magnetic material.
Can Duplex 2507 Stainless Steel Be Welded?
Yes. Duplex 2507 stainless steel has good weldability and can be effectively joined to itself and other materials through various welding methods, including: SMAW (shielded metal arc welding), PAW (plasma arc welding), GTAW (gas tungsten arc welding), FCW (flux cored wire), and SAW (submerged arc welding). When welding 2507, it is recommended to use 2507/P100 filler metal.
Preheating of 2507 is generally not recommended, except when it's required. It's essential to maintain an interpass weld temperature below 100 °C to avoid compromising the integrity of the weld.
Does Duplex 2507 Stainless Steel Rust?
Yes. Although duplex 2507 stainless steel has excellent corrosion resistance it can still rust in extreme conditions. It is, however, less prone to rust than other types of stainless steel. 2507's elevated levels of chromium and molybdenum give it exceptional resistance against uniform corrosion induced by organic acids such as formic and acetic acid. 2507 steel's excellent corrosion resistance makes it suitable for use in environments with corrosive substances, such as seawater, acids, and chemicals, where it maintains its integrity and does not easily rust or corrode.
What Are the Thermal Properties of Duplex 2507 Stainless Steel?
The thermal properties of Duplex 2507 stainless steel are given in Table 3 below:
| Property | 2507 |
|---|---|
Property Thermal Conductivity (W/m·K) | 2507 19 at 20-100 ºC |
Property Thermal Expansion (m/m·K) | 2507 14.5 up until 300 °C |
Property Specific Heat 0-100 °C
(J/kg·K) | 2507 460 |
What Are the Common Forms of Duplex 2507 Stainless Steel Material?
Duplex 2507 stainless steel material is available in an assortment of common forms, each tailored to suit specific industrial applications:
Sheet
Duplex 2507 stainless steel is often provided in sheet form. It is suitable for a wide range of applications in the construction, manufacturing, and marine industries.
Plate
Plate made from Duplex 2507 is ideal for projects requiring larger, thicker sections of this corrosion-resistant alloy, such as pressure vessels, tanks, and structural components.
Bar
Duplex 2507 stainless steel bar is available in different cross-sectional shapes and sizes, offering flexibility for machining and fabricating components such as shafts, valves, and fasteners.
Pipe & Tube (Welded & Seamless)
Duplex 2507 stainless steel is used extensively in the manufacturing of pipes and tubes, both welded and seamless, to handle various applications in such industries as oil and gas, chemical processing, and desalination.
Weld Wire
Weld wire made from Duplex 2507 is designed for welding and joining applications, ensuring the strength and corrosion resistance of the alloy in critical structural and repair work.
What Are the Equivalents of Duplex 2507 Stainless Steel?
The equivalents of Duplex 2507 stainless steel are outlined in Table 4 below:
| Grade | UNS No. | Euronorm No. | Euronorm Name |
|---|---|---|---|
Grade 2507 | UNS No. S32750 | Euronorm No. 1.441 | Euronorm Name X2CrNiMoN25-7-4 |
What Are the Advantages of Using Duplex 2507 Stainless Steel?
The advantages of using Duplex 2507 stainless steel include:
- It has high pitting corrosion resistance, with a PREN number of up to 43. This means that it has superior corrosion resistance compared to stainless steel grades like 254SMO. Duplex 2507 also demonstrates exceptional resistance to other forms of corrosion, including Stress Corrosion Cracking (SCC), crevice corrosion, and general corrosion. These combined corrosion-resistant properties make Duplex 2507 a versatile and reliable choice for a wide range of applications in aggressive environments.
- 2507 offers double the yield strength of 300 series stainless steel. This strength advantage allows for thinner steel sections and reduced material costs for equipment under the same load conditions.
- It exhibits double the yield strength and tensile strength of ordinary stainless steel. This results in significantly improved wear resistance.
What Are the Disadvantages of Using Duplex 2507 Stainless Steel?
Some disadvantages of Duplex 2507 stainless steel are:
- One of the significant concerns with Duplex 2507 stainless steel is the potential formation of brittle phases such as alpha prime (α') and sigma prime (σ') within specific temperature ranges. These phases can lead to a reduction in toughness and impact resistance, which is a critical consideration for structural applications subjected to varying temperatures.
- Due to its relatively high ferrite content, Duplex 2507 stainless steel has a distinct Ductile-to-Brittle Transition Temperature (DBTT). This means it is not suitable for cryogenic applications and is generally limited to use at temperatures above approximately -50 °C, making it less ideal for extremely cold environments.
- Duplex 2507 stainless steel can become soft at annealing temperatures, which can lead to warping or distortion during hot forming processes. Careful control of the annealing process is required to minimize these issues.
- While Duplex 2507 stainless steel offers excellent corrosion resistance in many environments, it can be susceptible to rapid corrosion when in contact with ferrous materials and dust. This is particularly relevant in shipyards and industrial settings where exposure to such contaminants is common. Additionally, elevated seawater temperatures can increase the risk of corrosion, which may limit its use in certain marine applications
- The microstructure of super duplex stainless steel 2507 typically consists of approximately 50% ferrite and 50% austenite. Achieving the equilibrium relationship between these phases in welded joints can be challenging. It is influenced by factors such as: alloy content, filler metal, welding thermal cycles, and shielding gas. Attention must be paid to potential root cracking and stress relief heat treatment after multi-layer welding.
Is Duplex 2507 Stainless Steel Better Than Regular Stainless Steel?
It depends on the particular application and its requirements. Duplex 2507 is prized for its exceptional corrosion resistance, particularly in aggressive environments rich in chlorides. Austenitics are easier to weld, and the high strength of a super duplex can sometimes be inconvenient. Regular stainless steel, such as 304 or 316, also offers good corrosion resistance but may not perform as well as Duplex 2507 in highly corrosive conditions. Duplex stainless steels exhibit approximately double the strength of austenitic stainless steels and offer enhanced resistance to localized corrosion, specifically addressing issues like pitting, crevice corrosion, and stress corrosion cracking. Therefore, when corrosion resistance is required, Duplex 2507 often emerges as the superior choice. However, super duplex stainless steel is limited in terms of temperature capabilities. Additionally, 2507 boasts higher strength than many regular stainless steel grades, potentially allowing for the use of thinner material, which can reduce both weight and costs. However, it's important to note that 2507 is generally more expensive due to its higher alloy content. Welding Duplex 2507 also demands more care and expertise, while regular stainless steel is typically easier to work with in this regard.
To learn more, see our guide on Stainless Steel Characteristics.
Is Duplex 2507 Stainless Steel Expensive?
Yes, duplex 2507 is an expensive metal. This is primarily due to its high alloying content, but it comes with the added benefit of exceptional corrosion resistance in extreme environments.
What Is the Difference Between Duplex 2507 Stainless Steel and Super Duplex Steel?
Duplex 2507 stainless steel and super duplex steel are both members of the duplex stainless steel family. Super duplex stainless steels have a dual-phase microstructure consisting of roughly equal proportions of ferrite and austenite phases and their high PREN numbers (40-45).
PREN is a numerical parameter used to assess and compare the corrosion resistance of various stainless steel alloys. It is especially valuable in evaluating the susceptibility of stainless steel to pitting corrosion, which is a localized form of corrosion that can lead to the formation of small pits or craters on the metal's surface. There are other super duplex stainless steels, such as: Z100,4501, UR 52N+, and 255. All of these have their own composition, properties, and use cases.
What Is the Difference Between Duplex 2507 Stainless Steel and Duplex 2205?
The alloy known as 2205 is a duplex stainless steel, while 2507 is a super duplex stainless steel. Duplex 2507 contains higher levels of molybdenum, chromium, and nitrogen compared to Duplex 2205, with roughly twice the molybdenum content. This composition gives Duplex 2507 better corrosion resistance and higher strength than 2205.
In terms of physical properties, Duplex 2507 outperforms Duplex 2205. It boasts higher yield strength, tensile strength, and impact toughness. However, these advantages come at the cost of reduced ductility.
When it comes to corrosion resistance, the differences in chemical composition become crucial. Duplex 2507, thanks to its higher molybdenum and nitrogen content, exhibits greater resistance to corrosion, particularly in chloride-rich and acidic environments. It has fair wear resistance, exceptional pitting resistance, and excellent resistance to intergranular corrosion, surpassing Duplex 2205 in these aspects.
What Is the Difference Between Duplex 2507 Stainless Steel and Zeron 100 Stainless Steel?
The chemical compositions of Duplex 2507 and Zeron 100 (Z100) are similar. Z100, which is also considered to be super duplex stainless steel, contains slightly higher levels of copper and tungsten than 2507. Specifically, the copper content in Z100, ranging from a minimum of 0.5% to a maximum of 1.0%, imparts exceptional resistance to corrosion, particularly in various non-oxidizing and mineral acids such as hydrochloric and sulfuric acid. This heightened copper content enhances its capacity to withstand corrosive environments effectively.
Summary
This article presented duplex 2507 steel, explained it, and discussed its various applications and properties. To learn more about duplex 2507 steel, contact a Xometry representative.
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