Difference Between Duplex and Super Duplex

 

What Is The Difference Between Duplex And Super Duplex?

Both standard duplex and super duplex steels have a specialty that they have ferritic and austenitic phases in their metallurgic microstructure. This means they have the ferritic and austenitic properties combined in them. The composition includes chromium, nickel and molybdenum with other elements in smaller quantities.

The duplex stainless steels have chromium content up to 22% of the composition where the super duplex steels have up to 25% chromium content. This increased content with varying nickel and molybdenum content provides the super duplex material with additional corrosion resistance.

Price Difference Between Duplex And Super Duplex

Since the super duplex material has more chromium, nickel and molybdenum content, it is expensive than the standard duplex grades. There are different grades of standard duplex and super duplex materials. Each different type has different material composition. Based on the material composition, the prices vary. In general, super duplex is more expensive than the standard duplex grades.

Welding Duplex And Super Duplex Stainless Steels

One of the major issues in welding metallic components is the chromium carbide precipitation which can cause intergranular corrosion and localized corrosion in the long term. Since both duplex and super duplex materials have high chromium content in the composition, they both have the risk of chromium carbide precipitation.

But the amount of carbon in these materials determines the carbide precipitation as well. Both the materials have to be preheated for welding and post weld heat treatment has to be carried out. Since both these materials are less prone to corrosion, they are both suitable for welding given the correct procedures are carried out and the correct parameters are maintained.

Duplex And Super Duplex Corrosion Resistance

The corrosion resistance is one of the most important aspects of the duplex and super duplex stainless steels. These are being used as replacement for more traditional types of steels. The corrosion resistance of both grades are higher than those of most austenitic stainless steels but the super duplex has even higher corrosion resistance.

The super duplex can be used in chemical, marine, sea water and food grade applications as it is resistant to most general corrosive components, mild acids and oxidizing agents. Depending on the different grades of super duplex, the corrosion resistance properties vary.

Duplex & Super Duplex Stainless Steel Cutting Speed

Duplex materials can be cut and formed with machining techniques. Compared to the super duplex, the duplex grades can be cut and machined faster. The super duplex is hard to machine compared to the duplex grades due to the increased chromium, nickel and molybdenum composition.

Precise and strong tools have to be deployed with slow cutting and machining speeds. There are certain tests to ensure the optimum speeds of cutting on duplex and super duplex materials. Tests such as the turning test, chip formation test and drilling tests can be performed to determine the cutting and machining aspects of various grades of duplex and super duplex stainless steels.