Microstructural investigation, using polarized neutron scattering, of a martensitic steel for fusion reactors

Small- and wide-angle polarized neutron scattering has been used to investigate the microstructure of modified martensitic steel DIN 1.4914 ("MANET"-type) developed as a potential candidate for the "first wall" of future fusion reactors. The nuclear-magnetic interference term and the comparison of the size distribution functions, obtained from the nuclear and from the magnetic scattering components, show that for quench temperatures lower than 1200 degrees C three kinds of microstructural inhomogeneities can be identified: (a) tiny C-Cr elementary aggregates (1 nm or less in size), (b) larger (1-25 nm) Fe-carbides, (c) much larger inhomogeneities arising either from M23C6 precipitates or from fluctuations in the Cr distribution. The scattering data are also compared with those previously obtained on the same samples from a conventional SANS instrument and the influence of the available Q-range on the accuracy of the obtained size distribution functions is discussed. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.