Metallic and composite systems

Investigation of steels

measured by the SANS

We have investigated by small angle neutron scattering (SANS) a duplex steel (containing two different phases) of industrial interest subjected to various ageing processes. Supposing that the scattering objects in steels have cuboid or rombohedral form, the scattering law obeys known formulae (in the case of monodisperse size distribution) and the cahracteristic size of these particles can be determined. The form factor and the contrast factor of the objects relative to the basic material give information also on the angle of orientation of the diagonal of the rhombes relatively to the main axes of investigation. We have observed the growth of cuboids with size changes from a ≈ 17 nm to a≈ 20.5 ± 6.6 nm due to thermal treatment. Further thermal treatment causes a developing of polydispersity of scattering particles. Therefore in this case only an average size was estimated. It was shown that this system becomes very polydisperse and the scattering data can be approximated by average parameter of particles as a ≈ 17 nm.

Fig

Figure 1. SANS analysis of steel samples (a) S1  as received,  (b) S2 aged at low temperature, (c)  S3 aged at high  temperature. This yields the characteristic thermal treatment to evaluate the aging process.