Fragilização por hidrogênio em aços 41XX utilizados em ambientes marinhos contendo H2S

Abstract

The present work analyzes the mechanisms of hydrogen diffusion and trapping in a quenched and tempered 41XX steel, evaluating its susceptibility to embrittlement. Through the addition of a recombination poison and application of different cathodic currents in permeation tests, the hydrogenation conditions were adjusted to obtain a hydrogen flow similar to those reported in H2S tests. Then, electrochemical permeation and thermal desorption tests were performed on thin and thick samples, as well as uniaxial tensile tests after different hydrogenation times and analysis of fractures by SEM. It was observed that there is a critical thickness between 0.5 mm and 2.3 mm where a drastic change in diffusion kinetics occurs, and it was noted that the Fick’s laws conditions are achieved only in thick membranes. An apparent diffusivity of 2.3x10−10 m2/s and a solubility of 9.9 mol/m3 were measured in the thick samples. The traps have an activation energy of 35.7 kJ/mol, with desorption of 34.5 molH/m3 after 24 h of hydrogenation. The tensile tests showed that after hydrogenation times above 50 min the material suffers strong embrittlement. Promoting less than 2% of total elongation, the fracture generates a surface with a mixture of quasi-cleavage, intergranular and flat features.