Stainless Steel Workshop: Duplex stainless and its alloys

Practical Welding Today January/February 2008
January 15, 2008
By: Jeff Heagey

What is duplex stainless steel?

Duplex stainless is fast becoming the material of choice when improved corrosion resistance and mechanical properties are required. Through the combined efforts of the steel producers and the filler metal manufacturers, the market is better equipped to use these alloys for general fabrication. Whether your need is for GTAW, SMAW, GMAW, FCAW, or SAW, there is a duplex alloy for your application.

As the name implies, duplex means two. The microstructures of duplex steels consist of both ferrite and austenite to form a ferritic-austenitic structure. This Cr-Ni-Mo-N composition produces good strength and toughness, resistance to pitting corrosion, and an excellent resistance to stress-corrosion cracking. These unique properties make these alloys like no other stainless steel grades.

Duplex stainless steel comes in various grades, including a base metal grade known as 2205 (22 percent Cr, 5 percent Ni, 3 percent Mo, and 0.15 percent N), sometimes referred to as UNS S32205. This alloy is welded with a 2209 filler metal. Super- duplex grades are available too. One such grade is the base metal 2507 (25 percent Cr, 7 percent Ni, 4 percent Mo, and 0.25 percent N), commonly referred to as UNS S32750. This alloy is welded with a 2509 filler metal. Other variations of superduplex stainless containing copper and tungsten are available commercially that provide better mechanical properties. Two such grades are UNS S32550 and UNS S32760, better known as Ferralium® 255 and Zeron® 100. These grades also can be welded with 2509 filler metal, provided that no sulfuric acid is present in the service.

Jeff Heagey

ESAB Welding & Cutting Products
Hanover, PA
Phone: 717-630-3445

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