Welding Guidelines for Stainless Steel and Nickel Alloys – Part 2/2

Welding Guidelines for Duplex Stainless Steel

In the previous article, we discussed welding guidelines for stainless steel and nickel alloys. The present article focuses on welding duplex stainless steel.

Special Considerations for Duplex Stainless Steels

Duplex alloys are quite different from standard stainless steel. They contain approximately 50% each of ferrite and austenite. If not properly welded, this class of alloy can be susceptible to the formation of embrittled phases or the formation of precipitates that are susceptible to pitting. By recognizing this, and properly following recommended procedures, mechanically sound and corrosion-resistant fabrications are easily accomplished.

Exaton provides welding guidelines to successfully join duplex base materials.

The following parameters are required to be followed when welding duplex stainless steel:

Joint design

Due to the sluggish nature of ferritic materials, weld pool flow tends to be sluggish. To prevent lack of fusion it is recommended to use wider joint angles and larger root openings than commonly used in stainless steels. Refer Exaton Welding Guidelines for more specific information.

Shielding and backing gas selection

Due to the nature of ferritic materials, weld pool flow is sluggish. This can be compensated for by the proper shielding gas selection, which can also benefit the proper austenite and ferrite balance. The selection of backing gas can have a beneficial effect on corrosion resistance.

Refer Exaton Welding Guidelines for more specific information.

Heat input

In order to achieve the optimum ferrite to austenite ratio, the heat input must be properly controlled. The recommended heat input range is dependent on the grade of duplex stainless steel being fabricated. Refer Exaton Welding Guidelines for more specific information.

Interpass temperature

Duplex alloys have specific interpass temperatures recommended, to prevent the formation of brittle intermetallic phases. The proper interpass temperature is dependent on the grade being welded and the base metal thickness. Refer Exaton Welding Guidelines for more specific information.

Welding of Ferritic Steels

Ferritic stainless steel alloys, by their nature, tend to weld sluggishly due to their poor flow characteristics.

Exaton has developed special chemistries for several grades of ferritic stainless steel to improve this condition. Contact Exaton for more information.

Weld Overlay

For many industrial applications, it is necessary to contain relatively high pressures conforming to various pressure vessel codes such as ASME. At the same time, corrosion protection is required to extend the life of the vessel.

A common solution is to fabricate the vessel with high strength, low alloy steel, and weld clad the container, with various higher alloy materials, utilizing various processes. Common processes used can be MIG, TIG, SMAW, and SAW using bare wire or wire and flux combinations. In the last several decades, the utilization of Strip Electrodes has become increasingly common in either a submerged arc or electroslag process.

ESAB has developed an extensive line of consumable wire, strip, and fluxes that can achieve fully alloyed weld overlays in as little as one layer with deposition rates exceeding 90 lb/hr (40 kg/hr).

It is necessary to apply the first layer with an over-alloyed welding consumable to achieve a mechanically sound weld deposit. Subsequent layers can be achieved using a filler metal with the final deposit chemistry desired.

Contact your Exaton Sales Associate to find out more about the grades available in wire, strip, or flux combinations.