Influence of Stress and Temperature on Stress Corrosion Cracking of Welded Duplex Stainless Steel Joints under Drop Evaporation Test

摘要

Drop evaporation test at three different temperatures was conducted with duplex stainless steel for studying the influence of temperature, strain and heat input on its stress corrosion cracking (SCC) suitability. Three welding conditions were performed: regular heat input of 1.0 kJ/mm; low heat input 0.5 kJ/mm, inducing high ferrite content in the melting zone; and high heat input 3.5 kJ/mm, in order to induce the precipitation of deleterious phases in the heat affected zone. The specimens were tested with three different tensile stresses with four point bending device for 500 hours under the drop of synthetic sea water solution with flow rate of 10 ± 1 drops per minute and temperatures of 70 °C, 90 °C and 110 °C. All specimens tested at temperature of 110 °C showed a fracture in the region adjacent to the dropping zone, below the salt deposit and away from the weld bead, with the presence of multiple nucleation and branched crack propagation. The fracture surface showed topography similar to cleavage with small regions of α/γ interface propagation. The test specimens tested at 90 °C only showed localized preferential corrosion of the ferrite; it also occurred in the region adjacent to the dropping zone. The same tests were made with the dropping aiming adjacent, moved 25 mm from the specimen's center for formation of the salt deposit above the weld bead, at temperatures of 70 °C and 90 °C, but there was no evidence of SCC.