We determine the fracture toughness of a duplex stainless steel using the COD-concept (crack tip opening displacement). The CODi values are obtained by stereophotogrammetric reconstruction of fracture surfaces. This is done by analyzing stereoscopic scanning electron microscope (SEM) images of the surfaces with an automatic image processing system. This system allows the automatic generation of a digital elevation model (DEM) with approximately 50 000 points for each fracture surface image. Height-profiles at the point of crack initiation can be obtained from this DEM. The examination of corresponding profiles from both specimen-halves leads to CODi.
S C I X L ~'press forging experiments on industrial equipment are carried out in order to evaluate the potential of this process for the production of jet engine disks from the direct aged nickel base alloy IN718. Metallography, electron microscopy and elevated temperature tensile tests are pel-l'ormed to analyse and quantify the strength improvements due to direct aging. The results of these analyses clearly demonstrate that the production of direct aged IN718 turbine disks is possible on ; I screw press.
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