Estudo da fragilização por hidrogênio de aços inoxidáveis austeníticos

Abstract

Austenitic stainless steels are usually resistant to hydrogen embrittlement due to higher solubility and lower hydrogen diffusivity in the austenite. However, in some applications, certain levels of deformation are required to obtain higher mechanical resistance, which can modify the diffusivity and hydrogen trapping in the microstructure of these steels. Understanding the interaction of hydrogen with deformation microstructures, such as dislocation structures, deformation twins, and strain-induced martensites, is fundamental in the search for safe deformation levels and processing routes. In this work, two austenitic stainless steels, AISI 304 and AISI 316L, were studied with several degrees of pre-strain by rolling (0%, 22%, 33%, 44% and 55%) and hydrogenated by cathodic charging. Advanced microstructural characterization techniques were used, such as X-ray diffraction simultaneously with strain (in situ), carried out in the synchrotron ring of the National Center for Research in Energy and Materials (CNPEM, Brazil), allowing the exploration of the effects of hydrogen diffused during microstructural evolution in deformation. The evaluation of hydrogen embrittlement indexes showed slopes in pre-strain degrees of 22% and 33% in the AISI 316L steel and 33% in the AISI 304 steel, associated with a decrease in susceptibility to hydrogen embrittlement. Both processing conditions and deformation microstructures were related to beneficial effects of low degrees of deformation on the hydrogen embrittlement susceptibility (such as the hydrogen retention in the hydrogenated layer, lower amounts of mechanical twins and strain-induced martensites, a more random texture, the introduction of compressive stresses on the surface during rolling, and the increase in the dislocations density) with detrimental effects resulting from high degrees of deformation (the coalescence of α ′ -martensite, increased mechanical twinning, the emergence of harmful texture components, and the increase of heterogeneities generated in rolling). These effects, if controlled, allow the definition of strategies to prevent hydrogen embrittlement and the development of more resistant alloys.