Estudo da deformação e do carregamento catódico de hidrogênio nos aços inoxidáveis duplex 2101 e 2404

Abstract

The behavior of steels when deformed by stress changes with temperature, chemical composition and strain rate, so experiments varying the strain rate and temperature are essential to analyze the effects that changes in these parameters cause on mechanical properties and in the microstructure of the duplex stainless steels. Thermomechanical tests with in situ X-ray diffraction allow obtaining relatively accurate data on micro strain and dislocation density throughout the tests, and it is also possible to separate these data relating to the phases (ferrite and austenite) of the duplex stainless steel and their respective contributions. The decrease in the temperature of the tests increased the density of defects inside the materials, especially in the austenitic phase, resulting in an increase in mechanical strength. The high density of defects resulted in a reduction in the elongation capacity of the duplex stainless steel

2101, while the 2404 maintained practically the same elongation. The influence of pre- strain on hydrogen embrittlement was evaluated in terms of percentage of elongation.

Initially, a pre-strain of 11% tends to increase hydrogen embrittlement, but a more

pronounced pre-strain (22%) causes the hydrogen susceptibility to be reduced. Pre- strain increases the total amount of hydrogen in the materials, but the amount of

diffusible hydrogen decreases, indicating that hydrogen is trapped at trapping sites and diffusivity is reduced with increasing pre-strain. The results of dislocation density and silver decoration of the 22% pre-strained samples of duplex stainless steel 2404 indicate that the preferential path of deformation occurs in the ferrite, since there is a significant increase in the dislocation density, causing the preferential cracking of this phase. This expressive increase in the dislocation density in ferrite significantly reduced its apparent diffusivity, when compared to the apparent diffusivity of austenite; the preferred deposition sites of silver particles were changed to austenite, indicating that the apparent diffusivity of austenite was higher in this condition.