Avaliação do efeito da fragilização por hidrogênio na tenacidade à fratura do aço AISI 4340 calculada pelo método da integral J

Abstract

Hydrogen embrittlement is a physical-chemical process that affects steels used in the aeronautic and oil and gas industries, degrading its mechanical properties. This phenomenon can generate notable problems in structures since it affects their ability to meet the requirements for which they were designed to. This work aims to evaluate the influence of hydrogen on the fracture toughness of quenched and tempered AISI 4340 steel (32 HRC) using the J Integral method. The calculation of toughness is performed from tests conducted according to ASTM E1820. For this purpose, a factorial design was proposed with a single factor (hydrogenation level) int three levels, namely: air condition, without exposure to an environment propitious to hydrogenation, this one used as a reference value for comparison purposes; and two hydrogenation conditions, one of those being more aggressive. From the obtained results and with the help of fractured region images, the influence of microstructurally diffused hydrogen on the fracture toughness of AISI 4340 material and on the variation of the fracture mechanism presented was evaluated. It was verified, therefore, that the most softly hydrogenated condition presented little variation in the fracture toughness value and maintained the fracture mechanism as ductile. For the hydrogenates specimens in a more aggressive condition, the J Integral method was not effective for toughness measuring, since the embrittlement effect, denoted by the change of the fracture mechanism from ductile to brittle, was aggressive to the point of invalidating the results for this condition. The Kruskal- Wallis test showed that microstructural Hydrogen promoted a statistically significant change in the fracture toughness of AISI 4340 steel, denoted by the deterioration of the property as its concentration increases.