Difference between Duplex and Super Duplex Fasteners

Difference between Duplex and Super Duplex Fasteners

There is a wide variety of different types of stainless steel fasteners, all of which share the common property of the resistance against corrosion. This property, combined with the low level of maintenance required when working with this type of metal are just some of the reasons it is popular in so many application areas.

In this blog post will highlight, the difference between a duplex and super duplex fasteners

Overview

Although the duplex and super duplex both are an alloy of chromium, Molybdenum & nickel. They also have mixed austenite and ferrite structure, which gives them enhanced mechanical and physical properties as compared to both individual austenitic and Ferritic classes of stainless steel.

Check below the detailed information to know the Difference between Duplex and Super Duplex Material.

The main difference between a duplex and super duplex steel fasteners is the amount of chromium & Molybdenum. The content of chromium in super duplex grade stainless steel ranges between 24 percent to 26 percent, while the content of chromium in duplex grade stainless steel could range anywhere between 19 percent to 32 percent.

Duplex Steel Fasteners contains about 3 percent Molybdenum & 5 percent – 6 percent nickel in their alloy while super duplex steel fasteners contain 4 percent Molybdenum & 7 percent nickel.

Another difference between duplex steel and super duplex steel is the addition of nitrogen. Adding Nitrogen in super duplex stainless steels improves its yield strength as well as its pitting resistance. Nitrogen also stabilizes the austenite effect in the presence of nickel.

The higher content of chromium & Molybdenum makes the super duplex grade stainless steel an increased resistance to corrosion and increased tensile strength that is much higher as compared to duplex stainless steel.

As super duplex stainless steel grades are highly alloyed in comparison to duplex stainless steel, they offer many advantages like – excellent resistance to chloride stress cracking, good toughness.

Welding duplex and super duplex stainless steels can be done easily because they both have good weldable properties and can be welded by the addition of filler metals. Both these stainless steel grades do not require pre and post-heat treatment for welding.

Since both duplex and super duplex fasteners have high tensile strength as compared to austenitic grade stainless steel, the consumption to design & manufacture a product can be lowered. The walls of the product can be thinned, leading to a reduction in both the weight of the product as well as the cost of the product.

The mechanical and physical properties in both duplex vs super duplex steel can be compared to a superlative degree. For instance, if the mechanical strength of duplex steel is considered as high, the mechanical strength of super duplex steels would be considered as very high.

Although the duplex and super duplex differences are visible in terms of the content of chromium, nickel, Molybdenum & tungsten, the addition of these elements makes the processing of super duplex stainless steels a little difficult. These elements added in the alloy of super duplex stainless steel, promote the formation of intermetallic phases. Intermetallic phases formed can reduce the impact strength of this grade drastically.

While the content of the elements differs in the alloy of both duplex and super duplex grades, a major difference that stands out is the improved tensile strength and the corrosion resistance.  But other mechanical and physical properties of these grades are similar to each other. Hence, both these grades of stainless steel can be considered to be the best because of their improved weldability, ductility, corrosion resistance, and high tensile strength as opposed to both Ferritic and austenitic stainless steel grades.