Análise do comportamento em fadiga do recobrimento de uma liga zinco-níquel como substituição ao cádmio eletrodepositado para o aço AISI 4140

Abstract

Studs are applied in the Brazilian petrochemical industry to join together flanges or equipment connectors in marine environments, where fluctuations of the tensile stress at the studs occur due to the variation of the pressure in the oil well or due to the ocean waves movement, causing the fatigue mechanism. Due to the corrosive operating environments, frequently the studs undergo a cadmium electrodeposition process. However, cadmium is harzadous to the environment and to human health. Anticorrosive coatings influence the fatigue resistance, and its influence has to be evaluated in order to ensure structural integrity. The feasibility with respect to the fatigue behavior of the substitution of electrodeposited cadmium for a zinc-nickel alloy on AISI 4140 steel was investigated in this work. The fatigue behavior comparation was made through the analysis of AISI 4140 steel S-N curves in axial fatigue for studs, specimens in accordance with standard, and threaded specimens. The Weibull distribution was used to perform the statistical analysis of the fatigue behavior. The finite element analysis was used to quantify the stress concentration. The optical and scanning electron microscopies were used to perform the microstructure and fracture surface analysis, respectively. The stress concentration effect due to the threads of the studs had more influence than the cadmium or zinc-nickel coatings in the fatigue behavior of AISI 4140 steel. The material covered with electrodeposited cadmium presented a similar fatigue behavior to the base material, which can be attributed to dehydrogenation treatment. The material covered with a zinc-nickel alloy presented a small increase in the axial fatigue resistance, which may be related to a lower tensile residual stress value than the presented by the base material. The substitution of the ... (Complete abstract click electronic access below)