Estudo da fragilização por hidrogênio de um aço inoxidável super martensítico através da teoria da redução da energia interfacial

Abstract

One of the biggest problems faced in the production of oil and gas is the hydrogen embrittlement of steels. Throughout the years several models were proposed to explain this phenomenon. The aim of this work is to study the hydrogen embrittlement by using the theory of interfacial energy reduction. In order to apply this theory super martensitic stainless steel was used. This alloy is extensively used by the oil industry, due to its high mechanical resistance, toughness and corrosion resistance. However, this alloy is prone to hydrogen embrittlement due to the conditions in which it operates. The theory of interfacial energy reduction refers to the surface or interface energy reduction (Υ) along with the increase of the chemical potential (μ) of hydrogen, therefore favoring the formation and propagation of cracks in the material. Electrochemical permeation tests were performed by applying different cathodic potentials for the generation of hydrogen, from -950 mV/SCE to -2000 mV/SCE. Samples for tensile testes were hydrogenated by applying the same potentials. For this alloy, the hydrogen’s diffusivity obtained through low cathodic charging was of the order of 10-13 m²/s, whereas with the application of higher potentials the diffusivity was of the order of 10-12 m²/s, which corresponds to a quicker fill of the hydrogen traping sites. A reduction in the material’s ductility was observed with the increase of the hydrogen chemical potential. It was possible to apply the proposed theory and observe the reduction of the interfacial energy through the increase of the hydrogen chemical potential.