Influência dos ciclos de tratamentos térmicos nas propriedades mecânicas e no aprisionamento de hidrogênio do aço 2,25Cr-1Mo-0,25V

Abstract

The present work investigates the 2.25 Cr-1Mo-0.25V steel used under conditions of high hydrogen pressure in the construction of oil hydrotreating reactors. During manufacture and stop-repair procedures, the pressure vessels are subjected to dehydrogenation, DHT, Intermediate Stress Relieving, ISR and post-weld heat treatments, PWHT. To study the effects of these temperature cycles, heat treatments were performed to determine the changes to the microstructure, mechanical properties and to hydrogen diffusibility, solubility and trapping. To this end, 2.25Cr-1Mo-0.25V steel samples were characterized microstructurally by scanning electron microscopy, SEM, and transmission electron microscopy, TEM. Hydrogen interaction with the microstructure was analyzed via electrochemical hydrogen permeation and Thermal desorption spectroscopy, TDS, tests. Mechanical properties were evaluated by comparing tensile test results of hydrogenated and non-hydrogenated samples. Results showed the strong influence of the traps and simultaneous precipitation mechanisms such as nucleation, grown and dissolution, in the steel´s behavior due to the variations in temperature and time of the heat treatment cycles. Overaging condition was observed in samples with the highest equivalent times to heat treatment of 600°C obtained from the Larson Miller Parameter.