Effect of shielding gases on mechanical and metallurgical properties of duplex stainless-steel welds

Abstract

Duplex stainless steels (DSS) are well known for their higher mechanical strength and better corrosion resistance. DSS is commonly used in the marine construction, petrochemical, and chemical industries. DSS (2205) has equal amounts of α and γ phases. However, unlike the parent metal, the solidification microstructure of the fusion zone in the weld does not have nearly equal amounts of the α and γ phases. Thus the mechanical properties and corrosion resistance of DSS welds are degraded. The interpass temperature plays a vital role in achieving balanced α and γ phases, which in turn results in improved mechanical and corrosion resistance. Gas tungsten arc welding (GTAW) is employed for welding of thin sheets/plates. The GTAW process ensures small amounts of slag formation during welding, which eliminates slag crevices and sites for corrosion attack. Standard 2205 (UNS S31803) DSS sheets of 5 mm thickness, with 22.37% Cr and 5.74% Ni, were used in this study. Weld beads were produced with Zeron-100 super DSS filler wire with higher alloy content (26% Cr and 8% Ni). Argon (Ar) and helium (He) were employed as shielding gases. Heat input was maintained <1 kJ/mm. Interpass temperatures were maintained at 120°C. The ferrite number of the weld metal for the two different shielding gases was investigated. Mechanical properties of joints such as impact strength and hardness were evaluated. Microstructure evaluation was also carried out.