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The aim of the project was to determine the kinetics and equilibria of P grain boundary segregation in 9-12%Cr-steels and its effect on ductility. The study was conducted on a laboratory melt of 12%CrMoV steel with 0.057% P, annealed at 450 C, 550 C and 600 C up to 7000 h. The free energy of segregation value indicates relatively low grain boundary concentrations. The diffusivity value indicates slow diffusion due to trapping of P. Using these data grain boundary concentrations can be predicted in dependence on bulk concentration, temperature and time - for this steel relatively low values result. Notch impact tests were also conducted, after aging at 500 C and 600 C up to 7000 h. The impact energy versus temperature curves show a shift of transition temperature with annealing time to lower values and an increase of the upper shelf impact energies (an improvement of toughness). This cannot be caused by the increasing grain boundary concentration but by microstucture changes, which have been characterized by transmission electron microscopy (TEM). It is concluded that grain boundary segregation of P is not decisive for the properties of the 9-12%Cr-steels during long term application but mainly changes in microstructure.

Additional information

Authors: MACKENBROCK M, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf (DE);GRABKE H J, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf (DE)
Bibliographic Reference: EUR 15575 DE (1996) 60pp., FS, ECU 8.50
Availability: Available from the (2)
ISBN: ISBN 92-827-6183-5
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