Stainless steels are classified into different classes based on the differences in their microstructural phases. While each class has its own microstructural phase, duplex stainless steels have a microstructure that is comparable to those of two other classes, ferritic and austenitic stainless steel.
Duplex stainless steels have a microstructure that is a mix of austenite and ferrite. Both of these crystalline structures have an equivalent ratio, meaning that duplex steels contain 50 percent austenite and 50 percent ferrite.
Duplex stainless steel is broken further into three subcategories, one of which is super duplex stainless steel. Because of this, super duplex grades have a dual microstructure as well. The PREN, or pitting resistance equivalent number, values of duplex grades are extremely high. The range of these numbers is 22 to 45.
The Price Difference Between a Duplex and a Super duplex-
While both grades have stronger corrosion resistance than normal austenitic SS alloys, super duplex SS grades have a higher resistance to pitting. Pitting resistance is a key feature, which is obtained by increasing the chromium concentration to around 27%, as opposed to the pre-existing 22% in ordinary duplex grades.
The dual microstructure of the alloy changes when the chromium concentration is increased. As a result, super duplex stainless steels’ chemistry will include nickel additions in addition to the other components. Nickel, a traded commodity metal, is costly due to its fluctuating price. However, because molybdenum is a scarce element, it is costly. The cost of super duplex alloys tends to rise as the amount of nickel and molybdenum in the alloy increases.
Welding Duplex and Super Duplex Stainless Steels-
In contrast to traditional austenitic stainless steel alloys, where the base metals are damaged during welding, the HAZ in these alloys has problems. For example, during welding, main difficulties in the HAZ, or heat-affected weld zone, include loss of toughness, cracking after welding, and a deterioration in the alloy’s corrosion resistance qualities. This is why professional welders must use SAW, TIG, and MIG procedures to weld either grade, with the alloys receiving suitable post-welding processing.
Duplex and Super Duplex Corrosion Resistance-
As previously stated, chromium, nickel, molybdenum, nitrogen, and tungsten are added to their alloys to improve corrosion resistance. Pitting resistance could be as high as 45 percent. Furthermore, they may be used at high temperatures without experiencing oxidative corrosion. These alloys are also resistant to a wide range of alkaline, acidic, and neutral solutions.
For more information Visit Duplex Pipe Fitting Suppliers
