UNS S31803 Duplex Stainless Steel

In modern industry, stainless steel is widely used for its good corrosion resistance, strength and aesthetics. UNS S31803 is one of the most popular duplex stainless steel materials, favored for its unique characteristics and uses. This article will comprehensively analyze the characteristics, standards, composition, applications and performance of duplex stainless steel UNS S31803 to help you better understand the importance of this material.

What is UNS S31803 Duplex Stainless Steel?

S31803 (F51) is a UNS (Unified Numbering System) number that represents a duplex stainless steel material. This stainless steel is also known as Duplex 2205 or F60 and is widely used in industry for its excellent corrosion resistance and high strength.

UNS S31803 Duplex Stainless Steel Pipe is a medium alloy duplex stainless steel with good chloride stress resistance. Medium alloy type - the representative grade is UNS S31803 (22Cr-5Ni-3Mo-0.15N); S31803 duplex steel pipe is the most widely used among the three duplex steels (2205 duplex stainless steel pipe, 2507 duplex stainless steel pipe, S31803 duplex stainless steel seamless pipe).

Steel material characteristics:
S31803 stainless steel belongs to austenite-ferrite duplex stainless steel, which has good corrosion resistance and mechanical properties. Its main characteristics include:

1. Corrosion resistance: Compared with traditional 304 stainless steel, S31803 shows good performance in acidic and chloride environments, which makes it suitable for a variety of harsh conditions. In particular, it has a high resistance to pitting, crevice corrosion and stress corrosion cracking, especially in chloride-containing environments.

2. Mechanical properties: Due to its unique dual-phase structure of ferrite and austenite, S31803 has higher strength than conventional austenitic stainless steel (tensile strength generally exceeds 500 MPa) while maintaining good toughness and ductility. The tensile strength and yield strength of S31803 are higher than those of 304 stainless steel and 316 stainless steel, and it can withstand greater loads.

3. Welding performance: Although the welding process requires special attention to prevent structural degradation in the heat-affected zone, good welding results can be achieved through appropriate welding techniques and post-processing methods. S31803 stainless steel can be easily welded in various processes.

Steel implementation standards:

The implementation standards of S31803 stainless steel mainly include the following:
ASTM A240/A240M – Standard specifications for stainless steel plates and strips.
ASTM A479 – Standards for stainless steel bars, wires and forgings.
ASME SA240 – Material specifications for pressure vessels.

These standards ensure that S31803 stainless steel has good quality and reliability in different application fields.

Chemical composition:
The key elements in the chemical composition of S31803 include:
Chromium (Cr): 22% – improves corrosion resistance.
Nickel (Ni): 5-6% – affects the toughness and ductility of the material.
Molybdenum (Mo): 3% – enhances corrosion resistance, especially pitting corrosion resistance.
Nitrogen (N): 0.08-0.20% – improves mechanical properties and enhances strength.

This unique ratio enables S31803 to maintain its performance in a variety of harsh environments.

Application range and processing:

The wide application of S31803 stainless steel is due to its good comprehensive performance. The main application areas include:
1. Oil and gas industry: used for oil and gas pipelines and related equipment, it can maintain strength and corrosion resistance under high temperature and high pressure environment.
2. Chemical treatment: used for reactors and storage containers, commonly found in chemical plants.
3. Marine engineering: Due to its excellent resistance to chloride corrosion, S31803 is suitable for use in marine environments. In ships, offshore platforms, etc., it can resist corrosion caused by seawater.
4. Construction field: Due to its beauty, S31803 is also often used in building exterior decoration and structural components to improve building quality and aesthetics.
5. Food industry: In the food processing industry, it is often used for equipment and pipelines for transporting and storing food.

According to the ASME B16.11 standard, S31803 duplex stainless steel can be used to manufacture pipe connection parts such as socket fittings and threaded fittings. In addition, it also meets the requirements of other relevant international and national standards, such as ASTM A240/A240M and EN 10088-2.

In terms of processing, S31803 stainless steel can be processed by traditional cutting, forging, cold working, welding, milling and other processes. However, it should be noted that due to its high hardness, suitable tools and cutting parameters should be selected during processing to avoid excessive tool wear.

Physical and mechanical properties:

The physical and mechanical properties of S31803 stainless steel are as follows:
Density: about 7.8 g/cm³, which belongs to the typical density range of stainless steel materials.
Elastic modulus: about 193 GPa, showing high stiffness.
Thermal conductivity: relatively low, suitable for use in some insulation applications.

In terms of mechanical properties, S31803 has the following characteristics:
Tensile strength: ≥620 MPa
Yield strength: ≥450 MPa
Elongation after fracture: ≥25%, with good toughness.

This combination of physical and mechanical properties shows that S31803 stainless steel is a material that is very suitable for demanding industrial applications.

In short, UNS S31803 duplex stainless steel has become an indispensable part of modern industry with its corrosion resistance, extremely high strength and wide application.

Extended information:

Classification of stainless steel pipes:

1) According to the material
Stainless steel pipes can be divided into austenitic stainless steel pipes, ferritic stainless steel pipes, duplex stainless steel pipes, etc. according to the material. Among them, austenitic stainless steel pipes have excellent corrosion resistance and are widely used in petroleum, chemical and other industries; ferritic stainless steel pipes have good oxidation resistance and are often used in high temperature environments; duplex stainless steel pipes combine the characteristics of austenite and ferrite, and have high strength and corrosion resistance.

2) According to the production process
Stainless steel pipes can be divided into welded stainless steel pipes and seamless stainless steel pipes. Welded stainless steel pipes are made by bending and welding stainless steel plates and are widely used in petroleum, chemical and other fields; seamless stainless steel pipes are made of stainless steel billets through multiple cold rolling, cold drawing and other processes, with smooth surfaces and wide applications.

3) According to chemical composition
Duplex stainless steel pipes can be divided into the following four categories according to their chemical composition:
1. Low alloy type: Representative grades include UNS S32304 (23Cr-4Ni-0.1N). This type of duplex stainless steel pipe does not contain molybdenum, and the PREN value is 24-25. It can replace AISI 304 or 316 in terms of stress corrosion resistance.
2. Medium alloy type: Representative grades include UNS S31803 (22Cr-5Ni-3Mo-0.15N), with a PREN value of 32-33, and its corrosion resistance is between AISI 316L and 6%Mo+N austenitic stainless steel.
3. High alloy type: Generally contains 25%Cr, molybdenum and nitrogen, and some also contain copper and tungsten. The standard grades include UNSS32550 (25Cr-6Ni-3Mo-2Cu-0.2N), with a PREN value of 38-39, and its corrosion resistance is higher than that of 22%Cr duplex stainless steel.

4. Super duplex stainless steel type: Contains high molybdenum and nitrogen, with standard grades including UNS S32750 (25Cr-7Ni-3.7Mo-0.3N), and some also contain tungsten and copper, with a PREN value greater than 40, suitable for harsh media conditions, with good corrosion resistance and mechanical comprehensive properties, comparable to super austenitic stainless steel.

Read more: Stainless Steel ERW vs Seamless Pipe or Stainless Steel Seamless Pipe Manufacturing Process