Stainless steel is a group of corrosion-resistant iron-based alloys consisting of at least 10.5% chromium by mass. It also includes other alloying elements such as carbon, nickel, manganese, and other metals. The exact components and ratios depend on the required grade and the steel’s intended use. Stainless steel is broadly categorized into five families: austenitic, ferritic, martensitic, duplex, and precipitation hardening. The names come from its crystal structure, thus determining its metallurgical behavior.
Duplex stainless steels are iron, nickel, and chromium (Fe-Ni-Cr) alloys. Because of its two-phase microstructure, it bears the name ‘duplex.’ It combines the characteristics of both austenitic and ferritic grades. Thus, the end-users can leverage the benefits of both and experience fewer downsides. The exact ratios depend on the grade; however, generally, the structure has 50-percent austenite and 50-percent ferrite. Various components are alloyed together to produce duplex stainless steel, including carbon, chromium, silicon, manganese, nickel, sulfur, and phosphorus. Additionally, copper, nitrogen, and molybdenum are alloyed into the mix to bring out the desirable properties.
Grade 2205 is a popular type in the Duplex stainless steel family. Alloy 2205 duplex stainless steel comprises of 22% Chromium, 3% Molybdenum, and 5-6% Nickel nitrogen alloyed in the composition. It is a nitrogen-enhanced grade that can effectively combat common corrosion problems which the 300 series cannot endure. You can contact 2205 Duplex pipe supplier to ensure that you get access to the desirable properties so that it fits the end-user. It provides enhanced pitting and crevice corrosion resistance. 2205 Duplex pipe is suitable for oil and gas pipeline infrastructure, desalination plants, heat exchangers, and more.
Various attractive properties of Duplex Stainless Steel
Duplex stainless steel has a mixed microstructure of austenite and ferrite. Thus, its tensile strength and yield strengths are typically superior to that of the austenitic grades. The strength of a material refers to its capability to withstand an applied load without suffering any deformation or failure.
- The Yield strengthof duplex stainless steel is 440 MPa.
- Its Young’s modulusof elasticity is 200 GPa.
Duplex stainless steel is twice as strong as regular ferritic or austenitic stainless steel. The high strength is also a result of alloying the metal with nitrogen.
Duplex stainless steel has good weldability properties. Welding refers to a fabrication process that helps join metals together. Most welding processes suitable for Austenitic stainless steel apply to the Duplex family. Some of the popular welding methods include:
- Shielded metal arc welding (SMAW)
- Gas metal arc welding MIG (GMAW)
- Gas tungsten arc welding TIG (GTAW)
- Flux-cored arc welding (FCW)
- Submerged arc welding (SAW)
- Plasma arc welding (PAW)
- Resistance welding
- Laser welding
- High-frequency welding
Duplex stainless steel is welded with relatively low inter-pass temperatures and high heat input. Since welding duplex stainless steel is not a fool-proof process, it is recommended to perform quality checks. When developing a welding procedure, the manufacturers must test the corrosion resistance, impact toughness, and the austenite/ferrite mix within the weld qualification.
Toughness and ductility
Since duplex stainless steel has both ferritic and austenitic microstructures, the impact toughness is limited due to the presence of ferrite. The ductile-to-brittle transition temperature for the Duplex family is approximate –50°C. It, however, exhibits greater toughness, ductility, and better weldability than ferritic steel. It does not, however, reach the excellent values of austenitic grades. Since Duplex stainless steel is ductile, you can stretch and form it into various shapes without breaking it.
High Corrosion Resistance
Duplex stainless steel is very highly corrosion-resistant. It can effectively resist oxidation, corrosion due to chloride, and stress corrosion cracking. Despite the presence of corrosive substances, Duplex stainless steel can thrive. It shows enhanced resistance to intergranular corrosion. For chloride pitting and crevice corrosion resistance, the presence of chromium, nitrogen, and molybdenum within the mix is crucial. Even in chloride and sulfide environments, it displays very high resistance to stress corrosion cracking (SCC). It has “inherited” the SCC resistance properties from its ferritic side. SCC can be a problematic issue under specific circumstances (chlorides, humidity, elevated temperature) for standard austenitic grades. Thus, deploying a duplex stainless-steel plate will ensure that it will display the desired integrity, reliability, and corrosion resistance properties.
Duplex stainless steel is relatively more cost-effective than other types of stainless steel. The nickel content is comparatively low in the Duplex family. Since nickel is an expensive metal, the low requirement contributes to cost savings. It requires much lower nickel and molybdenum contents than the austenitic counterparts to display similar resistance to corrosion. Easy welding and machining also make it a cheaper option than other materials. Moreover, one can reduce its section thickness because of its increased yield strength. The high mechanical strength provides considerable weight and therefore cost savings as compared to austenitic stainless steels.
Thus, the improved corrosion resistance, affordable pricing, and increased strength of Duplex Stainless Steel make it a valuable material. The alloy of austenite-ferrite in its microstructure ascribes it to various valuable properties as compared to its parent grades providing it with excellent value. You can contact the best-in-class manufacturers to deploy the Duplex stainless steel within your industrial environment.
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