On the Influence of the Microstructure upon the Fatigue and Corrosion Fatigue Behavior of UNS N07718

Abstract

Due to the challenging operational conditions occurring during drilling, e.g., in the oil and gas industry, the corrosion fatigue (CF) behavior of materials used in drillstring components needs to be well understood. The combination of cyclic mechanic loads and a corrosive environment can affect significantly the integrity of a material, which has to be taken into account when selecting and qualifying materials for drilling equipment. Nickel alloys such as the precipitation-hardenable alloy 718 (UNS N07718) are widely used in many industrial applications including subterranean drilling. In the present study, the fatigue and CF behavior of alloy 718 in three different metallurgical conditions was investigated. The CF behavior of the different conditions was determined using customized rotating bending machines enabling testing in a simulated drilling environment at 125 °C. Results have shown that the fatigue and CF strength of alloy 718 is affected by its microstructural particularities, for instance, the amount of strengthening phases and δ-phase.