Efeito da soldagem com dupla camada na microestrutura e dureza da zona termicamente afetada do aço 9%Ni

Abstract

This work evaluated the HAZ of the 9%Ni steel through the Higuchi Modified Technique, which defines selection criteria for welding parameters for double layer from the microstructural results of HAZ of a welding by simple deposition. The aim of the technique is to find a combination of parameters that allows to obtain a fine grain and low hardness HAZ. Based on the results obtained via the Modified Higuchi Technique, the buttering of a 9%Ni steel pipe was performed in order to apply those results to a dissimilar joint. All samples obtained in this work were analyzed by micro hardness, macrography and optical microscopy. The samples that presented the best results were investigated by Electron Backscatter Diffraction (EBSD) and by computer simulation of welding thermal cycles with the Sysweld® software. As a result of the work, it was verified that the HAZ of the 9%Ni steel is predominantly martensitic and that multipass welding promotes the formation of bainitic phase of low hardness, mainly in regions of overlapping passes. The buttering of the 9%Ni steel, although forming a bainitic phase of low hardness, results in a heterogeneous HAZ, with peaks of hardness of the order of 350 HV. Therefore, the 9%Ni buttering technique developed in this work is not suitable for application in CO2 reinjection wells, containing H2S, which requires a structure with a maximum hardness of 250 HV.