Soldagem subaquática de aço baixo carbono com eletrodo inoxidável austenítico

Abstract

Wet underwater welding studies have been carried out for some time using electrodes with a low carbon steel composition and all sorts of flux. The microstructure of the molten zone (ZF) and heat effected zone(HAZ) obtained after welding show low solubility of hydrogen and oxygen, resulting in varied discontinuities. To evaluate an alternative that may have less sensitivity to the negative effects of these elements, the present study has as main objective to study metallurgical and operational aspects, comparing the use of austenitic stainless steel and carbon steel core wires. It is expected that, with this change, its possible to keep the hydrogen in the molten zone and thus minimize its diffusion to the heat affected zone, where it can cause problems of embrittlement and cracking. By maintaining an austenitic structure in the molten zone, it is also expected to avoid embrittlement by hydrogen in this region of the joint. Finally, the higher tenacity and ductility of the austenitic material contribute to an improvement of these characteristics in the welded joint. It will be analyzed aspects such as porosity formation, mechanisms and sensitivity to cracking, formation of microconstituents, and inclusions in the molten zone and heat affected zone, comparing the results to those found with a carbon steel electrode. The welding will be by gravity in a hyperbaric tank of the Laboratory of Robotics, Welding and Simulation, capable of simulating underwater welding at different depths. It is intended to evaluate welding with electrodes of different classes in different depths of water: 0.5, 10, 30 and 50 meters below the water line. Initially, the study will be done with the deposition of the weld beads to evaluate operational aspects (bead format, penetration and formation of discontinuities) and metallurgical aspects (dilution effect, inclusions, formation of the microstructure, cracking mechanisms and formation of porosity). Subsequently, a comparative study of the effect of hydrogen on underwater wet welds with ferritic and austenitic core wires will be done. The tests will include diffusible hydrogen measurements and weldability tests involving tests for cold cracking sensitivity