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 pipingcomponents (e. g. flanges or T-pieces) or structural parts in oil and gasexploration. With the expansion of the oil and gas recovering area inthe arctic region, resistance to brittle fracture at low temperatures is ofgreat importance for all components, regardless of their manufacturingprocess. Since forgings generally have larger wall thicknesses than e.g.tubes, it is more difficult to realize the required properties over theentire cross-section.In this article, the investigation of two fine-grained structural steels ofdifferent grades (ASTM A694 F65 and F70) in the form of twodifferent forging geometries is presented. The work has been carriedout under the Arctic Materials Project. Both, the influence of chemicalcomposition and the impact of forging process on the mechanicalproperties have been evaluated. The main focus of the investigationwas placed on the impact strength and fracture toughness. Transitioncurves were recorded to characterize low-temperature toughnessbehavior of the different material grades. Many CTOD measurementsat –60℃ with different notch depths were carried out to gain a statistic.The results of these experiments are interpreted by means of opticalmicroscopy.