History of Duplex Stainless Steel
A duplex alloy containing 1.5% molybdenum, 5% nickel, and 26% chromium. Also known as 1.4460, this alloy. The requirement for stainless steels with high corrosion resistance, high strength, and good workability increased along with the rise in demand for oil and natural gas in the 1980s, as well as the corresponding rise in the need for new conveyor systems. The most popular duplex stainless steel grade at the time was "2205." In accordance with EN 10088-2 and VdTÜV-material datasheet 418, it is also known as 1.4462 (X2CrNiMoN 22-5-3), or UNS S31803 or UNS S32205 in accordance with ASTM/ASME (ASTM A240, ASTM A789/A790, ASTM A928).
The most common Duplex stainless steel grade in use today is 1.4462, which accounts for about 75 percent to 80 percent of the total output of Duplex. Austenitic and ferritic steels form a two-phase microstructure in duplex stainless steels. The relative proportions of the components that produce ferrite and austenite in the 1.4462 Chemical Composition determine the mechanical properties of duplex stainless steel.
The Basics of Duplex Steel Composition
The essential elements of an alloy are chromium (Cr), molybdenum (Mo), nitrogen (N), and nickel (Ni). Because it forms ferrite, Cr offers the required corrosion resistance even at high temperatures. Mo enhances the effects of Cr and significantly strengthens the resistance to pitting and crevice corrosion in environments containing chloride. Although it can also produce ferrite, its concentration is typically capped at a maximum of 7.5%.
Nitrogen has a significant impact on the characteristics while being a cheap alloying element. N helps the duplex steel's ability to resist corrosion and significantly boosts its toughness and strength. By delaying intermetallic phase formation and preserving the dual microstructure throughout the production phases, it also plays a crucial role in fabrication. It might replace some of the alloy's pricey nickel because it is a strong austenitic former.
Last but not least, Ni is the austenitic stabilizer that encourages the transformation of the crystal structure from body-centered cubic (ferritic) to face-centered cubic (austenitic). Duplex stainless steel with a high level of alloy, often known as Alloy 2205, has the UNS number 1.4462. In general, the 1.4462 Chemical Composition consists of 22-23% chromium, 4.5-6.5% nickel, 3.5% molybdenum, 0.14–0.2% nitrogen, 0.03% carbon, and a balanced amount of iron.
1.4462 Chemical Composition
Ferritic and austenitic stainless steel are combined to create duplex steel S32205 seamless pipes. They can withstand corrosion in a range of conditions because of this combination, which also gives the alloy ductility and strength.
This grade exhibits exceptional resistance to stress corrosion, cracking, pitting, and crevice corrosion. Additionally, it is resistant to reduction and oxidation. It is frequently employed in a variety of industrial settings, including the petrochemical, chemical processing, and power generation sectors. Heat exchangers and oil and gas pipelines benefit the most from it.
At 150 degrees Celsius, the grade is not susceptible to chloride stress corrosion cracking. However, embrittlement prevents it from being used above 300 degrees C. Only a complete solution through annealing will be able to fix this.
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