Forgings for Low Temperature Applications – Influences of the Alloying Concept and Advanced Forging Procedures on Impact Strength and Fracture Toughness

摘要

Forgings are widely used in offshore applications such as piping components (e. g. flanges or T-pieces) or structural parts in oil and gas exploration. With the expansion of the oil and gas recovering area in the arctic region, resistance to brittle fracture at low temperatures is of great importance for all components, regardless of their manufacturing process. Since forgings generally have larger wall thicknesses than e.g. tubes, it is more difficult to realize the required properties over the entire cross-section. In this article, the investigation of two fine-grained structural steels of different grades (ASTM A694 F65 and F70) in the form of two different forging geometries is presented. The work has been carried out under the Arctic Materials Project. Both, the influence of chemical composition and the impact of forging process on the mechanical properties have been evaluated. The main focus of the investigation was placed on the impact strength and fracture toughness. Transition curves were recorded to characterize low-temperature toughness behavior of the different material grades. Many CTOD measurements at –60°C with different notch depths were carried out to gain a statistic. The results of these experiments are interpreted by means of optical microscopy.