Improving Duplex Steel Welding with ESAB's unique Exaton 22.8.3.LSi

By Peter Stones CEng IWE/EWE IEng MWeldI

Improve the appearance, quality and productivity of your Duplex welding by using the unique grade Exaton 22.8.3.LSi from ESAB.

Several austenitic grades are available with additional silicon in their composition. For example, AWS A5.9 ER 308LSi & 316LSi have been available for several years, and the benefits that arise as a consequence for adding the additional silicon are outlined in this article. However, ESAB are the only manufacturer who are able to manufacture a DUPLEX grade of wire, AWS A5.9 ER 2209, with added silicon.

Enhanced Metallurgical Properties

Adding silicon to stainless steel welding wire grades significantly influences the metallurgical properties of the weld metal. Silicon primarily acts as a deoxidizer, reacting with oxygen to form silicon oxides, which are less detrimental than iron oxides. This deoxidation process, by definition, reduces the oxygen content in the weld pool, thereby minimising the formation of inclusions and other impurities that could compromise weld integrity.

Improved Fluidity and Wetting Action

The addition of silicon improves the fluidity of the molten weld pool. This enhanced fluidity allows for better wetting action, meaning the molten metal spreads more evenly over the base material. This is particularly advantageous in welding thin sections and complex joint geometries, as it reduces the likelihood of incomplete fusion and lack of penetration. The improved fluidity also facilitates better bead shape and smoother transitions, which are crucial for the mechanical performance and aesthetic quality of the weld. Practically, for the welder it means that the typical ‘chewing gum like’ weld pool associated with welding higher alloys is greatly reduced and consequently it is much easier to weld, hence productivity can be improved. For both automatic GTAW and robotic GMAW, welding speeds have been increased by up to 17% over standard duplex.

Arc Stability and Spatter Reduction

Silicon contributes to a more stable welding arc, which is essential for consistent weld quality. It affects the electrical conductivity and thermal characteristics of the weld pool, promoting a steadier arc and reducing spatter. Spatter reduction is particularly important in maintaining a clean weld area and minimising post-weld cleaning and finishing operations. A stable arc also ensures uniform heat distribution, reducing thermal stresses and the risk of weld defects.

Mechanical Properties

Silicon promotes the formation of a finer and more homogeneous microstructure, which is beneficial for improving the toughness and ductility of the weld. A fine-grained microstructure is less susceptible to crack initiation and propagation, thereby enhancing the overall durability of the weld.

Corrosion Resistance

While chromium is the primary element responsible for corrosion resistance in stainless steels, (assisted by molybdenum in some grades,) additional silicon content is particularly valuable in oxidising environments, where it supplements the protective effects of chromium oxide.

Mitigation of Hot Cracking

Hot cracking, or solidification cracking, is a significant concern in stainless steel welding. Silicon influences the solidification behaviour of the weld metal by modifying the solidification temperature range and promoting a more favourable solidification path. This reduces the susceptibility to hot cracking, which typically occurs due to high tensile stresses during the final stages of solidification. By reducing the incidence of hot cracking, silicon enhances the reliability and integrity of the weld.

Solidification Behaviour and Microstructure Control

Silicon affects the solidification sequence and microstructure of the weld metal. It promotes a eutectic-type solidification, which can refine the dendritic structure of the weld. This refinement leads to a more uniform microstructure with smaller dendrite arm spacing, which is beneficial for both mechanical properties and corrosion resistance. A controlled solidification process helps in achieving a desirable balance of ferrite and austenite phases in duplex stainless steels, enhancing their performance characteristics.

Cost-Effectiveness

Silicon is a relatively inexpensive alloying element, making it a cost-effective choice for improving the properties of stainless steel welding wires. The addition of silicon provides significant metallurgical and mechanical benefits without substantially increasing the overall material cost. This cost-effectiveness is particularly advantageous in large-scale welding operations where material efficiency and budget considerations are critical.

What about existing procedures requiring AWS A5.9 ER2209?

The composition of the grade Exaton 22.8.3.LSi contains additional silicon, but the amount is still within the permissible limits of AWS A5.9 ER2209 and ISO 14343-A/B 22 9 3 L / (2209). This means that the ‘LSi’ duplex grade can be substituted for standard duplex without any modifications to the procedure.

Conclusion

The inclusion of silicon in stainless steel welding wire grades offers numerous technical benefits, including improved deoxidation, enhanced fluidity and wetting, better arc stability, and significant mechanical property enhancements. Additionally, silicon contributes to superior corrosion resistance, mitigates hot cracking, and aids in controlling the solidification behaviour and microstructure of the weld metal. With Exaton 22.8.3.LSi from ESAB, all of the above advantages are available in a DUPLEX grade, and this is unique on the market.

Learn more about Exaton 22.8.3.LSi HERE