Influência da microestrutura na suscetibilidade a fragilização pelo hidrogênio em aços martensíticos

Abstract

High resistance quenched and tempered steels are applied in oil and gas operations of exploration and production. Ultra-deep wells explored in the last decade led to the development of process and materials more suitable to work in high pressures and corrosive environments. In these environments there are hydrogen sulfides which are responsible for the sulfide stress corrosion, a phenomenon where the hydrogen embrittlement plays an important hole. This phenomenon is being studied by many authors in the way to find best strategies to reduce material degradation and this is the main topic of the present work. The use of alloying elements such as Nb, Ti, V and Mo is one of the possibilities to mitigate the hydrogen embrittlement. In this work, three steels, two recently developed by a company that provides pipelines for OCTG, and one that is a grade already commercialized were studied aiming to elucidate the main mechanism behind hydrogen embrittlement and the contribution of the different microstructural features. For this purpose, permeation and thermal desorption techniques were applied where it was found that the steel with higher Nb content and the most homogeneous structure was capable of trap strongly hydrogen atoms minimizing the amount of free hydrogen in the material lattice in a way to decrease the change of hydrogen interact with defects such as non-metallic inclusions, this way, mitigating the impact of the hydrogen embrittlement in the material. Thus, the best strategies of alloying design for industrial purpose were elucidated.