Microstructure changes in welded duplex stainless steel and their effects on hardness and corrosion resistance

Duplex stainless steels (DSS) are extensively used in various applications because of their favorable properties, which result from equal proportions of the two phases, ferrite and austenite, along with specific percentages of alloying elements. These combined characteristics provide the materials with superior strength, corrosion resistance, and good welding capacity. During the welding process of DSS, the balance between the two phases is disrupted, and precipitates form, leading to reduced mechanical properties and corrosion resistance. To investigate this phenomenon, this study analyzes the effect of changes in welding current by mixing 10% N? with 80% Ar as a shielding gas on microstructure changes of DSS weldment. The changes were evaluated through measurements of hardness and corrosion resistance. The study found that increasing the welding current causes \ce{Cr2N} precipitates to disappear in the weld zone (WZ), with only a small amount appearing in the heat-affected zone (HAZ). However, very low welding current leads to the formation of \ce{Cr2N} precipitates in both the WZ and HAZ. The results indicate a direct relationship between the volume fraction of austenite and the welding current. Reducing the welding current increases the hardness of DSS welds due to a higher ferrite volume fraction. The results also show that the linear polarization resistance and the critical pitting potential of DSS weldment increase with higher welding current, mainly due to the increased austenite volume fraction and suppression of \ce{Cr2N} precipitation. Moreover, as the welding current increases, the corrosion rate of DSS weldments decreases.