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LEAN DUPLEX BLOG SERIES #2: WORKING WITH DUPLEX STAINLESS STEEL

In our previous blog, we wrote about duplex and lean duplex as materials, including their brief history and mechanical properties. In this one, it is time to take a closer look at their fabrication. If you read on, you will learn about the cutting, bending, welding and drilling of duplex and lean duplex stainless steel grades.

Duplex and lean duplex stainless steels are characterized by high strength and corrosion resistance. They are durable materials with a long service life and low life cycle costs. As for their fabrication, there are a few things we will highlight in this blog.

CUTTING AND DRILLING OF DUPLEX GRADES

Duplex grades can be cut with conventional band and circular saws. The high strength of the material may, however, require a special type of saw blade. There are for example PVD coated circular saw blades with are designed for cutting high strength stainless steels.

We recommend laser cutting whenever possible.

We recommend using laser cutting whenever it is possible. It provides good surface quality and excellent tolerances. High strength of the material is not an issue for laser. For the same reasons we recommend to use laser cutting instead of drilling. For example tube laser cutting machine makes easily cutting and drilling at the same time.

If laser cutting is not possible duplex grades can be drilled with PVD coated drilling tools and because of the ferromagnetic microstructure of the duplex grades also magnetic drills can be used.

BENDING DUPLEX AND LEAN DUPLEX TUBES

Duplex and lean duplex tubes can be bent like austenitic of ferritic tubes. The main difference is the force needed for bending. The high strength of the material means that the bending machine has to withstand higher loads. Materials with high strength also have higher spring back effect compared to softer materials.

Using heat for bending or straightening of duplex grades should be avoided.

Using heat for bending or straightening of duplex grades should be avoided. It may cause changes in the microstructure which can have an effect on the material's toughness and corrosion resistance.

HOW TO WELD DUPLEX AND LEAN DUPLEX

While early duplex stainless steels were not top performers in terms of weldability, this is not the case with modern duplex grades: their weldability is considered good. Most of the common welding processes can be used to weld duplex grades.

Lean duplex grades are the easiest duplex grades to weld.

Lean duplex grades (for example EN 1.4062 and EN 1.4162) are the easiest duplex grades to weld. Even austenitic filler material can be used (type 309). Standard duplex filler (type E2209) material is still often recommended. Lean duplex grades are not sensitive for heat input. This makes the transition from conventional austenitic grades to duplex grades much easier.

Lean duplex grades can be easily welded together with austenitic or ferritic stainless steel and even carbon steel. Type 309 welding wire is suitable for that. MAG welding is commonly used and suitable shielding gas for that is Argon + 2% CO2 or 2% O2.

More alloyed duplex grades (so called standard and super duplex) are more demanding materials to weld. Standard duplex (EN 1.4462/2205) has good weldability but needs a bit more know how compared to lean duplex grades.

Common duplex filler material (E2209) shall be used for welding but more effort is needed to control heat input in order to achieve metallurgically good weld quality. Keep in mind that super duplex grades (for example EN 1.4501 and EN 1.4410) require a specific super duplex filler material and more metallurgical know-how to avoid problems in welding.

Lari Brask

Director of product Development and Technology Technical support, Welding & materials

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