EFFECT OF HOT ISOSTATIC PRESSING ON MECHANICAL-PROPERTIES AND MICROSTRUCTURE OF 70-30 CUPRONICKEL CASTINGS

The present work is part of an investigation into the use of hot isost atic pressing to recover 70-30 cupronickel castings. These alloys have particularly good corrosion resistance and, when strengthened with si licon and chromium, produce a material capable of use in very severe c onditions of stress and massive corrosion. However, it is not possible to recover such castings by the application of repair welding, becaus e of the possibility of reduced corrosion resistance in the vicinity o f the weld. Hot isostatic pressing represents an alternative method of casting recovery. The results reported in the present work refer to t he effect of hot isostatic pressing on mechanical properties, microstr ucture, and the level of segregation in the alloys. Hot isostatic pres sing may be used to remove casting defects in the form of fine pores u p to total porosity of 5%. However, in cases where porosity takes the form of very large defects, the mechanical properties of the recovered region are inferior to those of the originally sound material. This e ffect is probably associated with the presence of very finely distribu ted oxide particles in the originally defective parts of the casting. The optimum hot isostatic pressing temperature for the best overall co mbination af properties was 950 degrees C.