A Guide to Duplex Stainless Steel

Duplex stainless steels come with numerous benefits compared to other stainless steel alloys. For instance, they provide high levels of yield and impact strength, along with excellent corrosion resistance, the ability to hold up in temperatures ranging from -50° C to 250° C, and optimal weldability and machinability. They’re also more cost-effective than other more expensive alloys.

In this blog post, we’ll cover the different types of duplex stainless steel, including their structure and applications.

Introduction to Duplex Steels

Duplex stainless steels feature an even combination of ferritic and austenitic microstructures. The alloy’s microstructure defines the atoms’ crystal structure, which is crucial in determining the alloy’s specific properties. While 3xx and 4xx stainless steels contain solely austenitic or ferritic structures respectively, duplex stainless steels feature both, combining the best features of each structure.

Duplex and Super Duplex Stainless Steels

Based on their specific needs, different applications can use either duplex or super duplex stainless steel alloys.

Duplex Stainless Steels

Pulp and paper manufacturing applications first used duplex stainless steels in the 1930s, replacing 3xx grades to provide more corrosion resistance and strength. Originally, the designation for duplex stainless steels was UNS S31803 (F51), but later enhancements made to increase corrosion resistance led to a re-designation of UNS S32205 (F60). 

Super Duplex Stainless Steels

Off-shore oil and gas exploration and other developments requiring improved alloys led to the creation of super duplex stainless steels. Specifically, Ferralium came first in 1967 as the original super duplex stainless steel. Following the launch of this alloy, Alloy 32760 and Alloy 32750 came along with varying compositions.

Applications for Duplex and Super Duplex Stainless Steels

Many applications use duplex and super duplex stainless steel alloys. The following are some of the most common applications.

Oil & Gas

Downhole tooling, subsea and well equipment, pumps, and valves use super duplex stainless steels. H2S-containing environments such as sour service wells also frequently use these materials.

Bolts and Fasteners

Many bolts and fasteners feature super duplex stainless steel construction. This is due to the material’s high strength and ease of hardening for added strength. 

Pollution Control Scrubbers

Pumps, fans, and precipitators often use super duplex stainless steels. They offer superior corrosion resistance in systems using seawater and acids.

Marine Applications

Shafts, seals, rudders, and propellers frequently use super duplex stainless steel. Specifically, they will use this metal if austenitic stainless steels such as XM-19 are incompatible with an application.

Chemical Process Industry

Chemical processes often use phosphoric, sulphuric, and nitric acid during production. Super duplex stainless steels offer the wear, corrosion, and abrasion resistance needed in these applications.

Vegetable Processing

Equipment used for processing vegetables and grains often features duplex stainless steels. Ferralium 255 offers reliable resistance to wear and corrosion in sugar cane processing, centrifuges, and mixers.

Water Treatment

Some water treatment applications for super duplex stainless steel include swimming pools, desalination, and sewage treatment. Many of these environments use seawater, brackish, or contaminated solutions that require sufficient corrosion resistance.

Paper and Pulp

Components used to produce pulp and paper are often made with super duplex stainless steels. While duplex and lean duplex alloys are sometimes used, areas at a greater risk of failure typically use super duplex alloys.

Pump Shafts

Super duplex stainless steels often appear in pump shaft components. The popularity of these alloys in these applications comes down to the material’s combined strength and resistance to wear and corrosion.

Reliable Metal Material Services from Continental Steel

Both duplex and super duplex stainless steels offer plenty of benefits that make them popular in many applications. If you would like high-quality metal material services, the experts at Continental Steel & Tube can provide fabrication, forging, exporting, and industrial metal processing services based on your individual project needs. To learn more about our service offerings, contact us today or request a quote for our services at any time.