Estudo de fragilização pelo hidrogênio em aço 9%Ni temperado e revenido

Abstract

Seeing that 9 % Ni steel has been sugested for use in FPSO’s gas treatments pipelines, and that the presence of H2S as a contaminant can promote the generation of hydrogen, which can possibly result in material embrittlement. This work aimed to correlate the microstructure with the susceptibility to hydrogen embrittlement, as well as characterize the formation and stability of the film formed in low H2S concentration solution, as weel as the possibility of the film act as a diffusional barrier blocking the entrance of atomic hydrogen into the material. Thermal treatments of quenching and tempering were carried out at temperatures between 565oC and 605oC in order to evaluate the behavior of the different microstructures of the steel. The results show that when 9% Ni steel is immersed in low H2S concentration solution there is formation of an iron sulphide film (Mackinawite and Pyrrhotite). But the formation of the film can be inhibited by applying a cathodic potential. The hydrogen permeation tests show that the hydrogen flux at steady state depends on the fraction of retained austenite in the matrix, and that the presence of the iron sulphide film causes the flow to fall significantly. The slow strain rate tests showed a ductility loss when the steel was immersed in low H2S concentration solutio. And that the loss was more intense loss when the tests were carried out in OCP. This ductility loss is attributed to a the effect of both the dissolution at the surface of the material and the hydrogen embrittlement.