Microstructural evolution, under tempering at 700 degrees C, in a steel for fusion reactors

This work presents the results of SANS measurements carried out on samples of modified martensitic steel DIN 1.4914 (MANET-type) submitted to tempering at 700 degrees C for times up to 20 h. The size distribution functions determined from the nuclear and from the magnetic SANS components show the presence of: (1) very large (> 100 Angstrom) particles with strong magnetic contrast to be possibly identified as M23C6 precipitates (non-magnetic, imbedded in a magnetic matrix); (2) much finer scattering centers (similar to 10 Angstrom) with different magnetic contrast to be identified with C-Cr aggregates. The microstructural evolution under tempering is discussed in the light of the SANS results.