Propagação de trincas por fadiga na zona fundida de soldas obtidas em único passe com altíssima energia de soldagem através do processo SAW com adição de arame frio em um aço EH36

Abstract

The submerged arc welding (SAW) with high heat input and various wires has been used to weld thick plates in order to reduce the number of passes and consequent increase of productivity in the shipbuilding and oil industry. Additional characteristics of SAW such as high penetration and relative ease of producing welds with good finishing and without discontinuities contribute to this process being widely applied. However, the use of very high heat inputs leads to the formation of a large melting pool and large amount of liquid metal which submits the region of the weld to long-term thermal cycles with low cooling rates. This contributes to the formation of thick solidification structures and, at the end of the cooling, results in a microstructure consisting mainly of grain boundary ferrite with low mechanical strength and large grain size. This research evaluated the fatigue crack growth rates in welding metals made by high heat input SAW with cold wire. Single pass welds were made on a 25 mm thick TMCP EH36 steel varying the chemical composition of the wire and heat inputs from 10 kJ/mm. Microstructure, mechanical properties and da/dN x K graphics were constructed with the propagation of the crack in the longitudinal direction of the weld. For all tested conditions, propagation rates were similar to those of base metal in Paris Region. However, the welds presented a crack propagation threshold higher than base metal, and this threshold was increased for welds made with higher heat input by the use of a molybdenum-containing addition metal. This was attributed to content of a higher amount of acicular ferrite in weld.