Development of coated electrodes for welding of Super Duplex steel

The microstructure, tensile strength and impact strength following welding of Super-Duplex-Stainless-Steel using coated electrodes were investigated. It was observed that the lower the basicity index of the coating, the higher the reduction of oxygen in the weld pool. This can be explained by the interference of the basic elements with the oxygen reduction by the acidic elements of the coating. The change in the microstructure of the weld indicates the different cooling rate in each zone: The cooling rate during welding, from the highest to the lowest, is as follows: Interface area >>> Root area >>> Face area. In the face area, the highest content of austenite and lowest content of ferrite were observed, which indicates that this area has experienced the lowest cooling rate. In the interface area, the lowest content of austenite and the highest content of ferrite were observed, hence indicating that this area has experienced the highest cooling rate. All welds showed the presence of Widmanstatten austenite, grain boundary austenite, sigma phase and large grains of ferrite. It can be deduced that the sigma phase cannot be avoided in the welds; however, the secondary austenite can be avoided, by employing an appropriate "low heat input policy". It was found that the higher the content of the secondary austenite and sigma phases in the weld, the lower the yield stress, due to the brittle characteristics of these phases. However, the higher the austenite content in the weld, the higher the elongation.