What Is Duplex And Super Duplex Stainless Steel?

As a result of differences in their microstructural phases, stainless steels are categorised into various classes. While each class of stainless steel has its own microstructure, stainless steels that belong to the duplex category have a similar microstructure to two other classes, i.e. ferritic and austenitic. In the Duplex Round Bar, austenite and ferrite are mixed microstructures. 

Due to their equivalent ratio, duplex steels contain both austenite and ferrite in a 50% ratio. Duplex stainless steels can be further divided into three subcategories, one of which is super duplex stainless steel. Due to this, super duplex grades also have dual microstructures. There are very high values for PREN, or pitting resistance equivalent number, in duplex grades. The values range from 22 to 45.

It is the super duplex kind of stainless steel that offers the highest corrosion resistance out of all three duplex categories. PRENs for super duplex grades range from 38 to 45. Stainless steel grades of this type are highly alloyed, more so than conventional stainless steel alloys, such as 304 or 316. Since they are highly alloyed, they tend to offer superior corrosion resistance. 

The mechanical strength of these materials is also very high. These stainless steel metals are highly alloyed, and this is the reason for their strength and corrosion resistance, but also why super Duplex Round Bar grades are more difficult to work with. 

Moreover, due to the higher content of elements such as chromium, nickel, molybdenum, nitrogen, and even tungsten, intermetallic phases are more easily formed. These intermetallic phases reduce the impact resistance of super duplex stainless steel.

As a result, buyers need to deal with manufacturers or suppliers who are not only experienced but also deliver high-quality products. When either stainless steel grade is manufactured using faulty methods, the end product will perform very poorly.

A Comparison Of The Prices Of Duplexes And Super Duplexes

The resistance to pitting, in particular, is a quality that is higher in super duplex stainless steel grades than conventional austenitic Stainless Steel Round Bar. By increasing the chromium content to about 27%, instead of the pre-existing 22% in standard duplex grades, the material is more resistant to pitting. 

The dual microstructure of the alloy is altered by increasing the chromium content. Nickel will be added to the chemistry of super duplex stainless steels along with the other elements. The price of nickel, which is a traded commodity, is volatile, making it an expensive commodity. Molybdenum, however, is an expensive element due to its rarity. The cost of super duplex alloys tends to increase as the nickel and molybdenum content increases.

Duplex And Super Duplex Stainless Steel Welding

As opposed to conventional austenitic stainless steel alloys, where the base metals are affected during welding, these alloys have problems with the HAZ. A loss in toughness, post-weld cracking and a decrease in the alloy’s corrosion resistance properties are among the major issues noted in the HAZ during welding. It is for this reason that experienced welders are required to weld either grade using SAW, TIG, and MIG techniques, with proper post-weld processing applied to the alloys.

Duplex And Super Duplex Corrosion Resistance

The addition of chromium, nickel, molybdenum, nitrogen, and tungsten to their alloys improves their corrosion resistance. Pitting resistance could reach 45. Furthermore, they are resistant to oxidation corrosion at elevated temperatures. A number of alkaline, acidic, and neutral solutions are also resistant to these alloys.

Duplex & Super Duplex Stainless Steel Cutting Speed

Due to their tendency to work hard, these alloys may be machined keeping some parameters in mind. Due to the alloy’s high strength and low thermal conductivity properties, manufacturers may use machines that are both stronger and rigid, as well as inserts with high performance. 

There may also be a need for a large amount of coolant during the machining process. Furthermore, correct speeds and feeds are essential for efficient machining of duplex and super duplex stainless steel alloys.