Small-angle neutron scattering investigation of M₂₃C₆ precipitation in AISI 304 stainless steel

An investigation of the M₂₃C₆ carbide (M = metal atom) precipitation induced by aging in AISI 304 stainless steel was performed with techniques of small-angle neutron scattering (SANS) and transmission electron microscopy (TEM). The samples were aged at 873 and 923 K for different times after a solution treatment at 1323 K. The coherent neutron scattering length density for each sample was calculated from the chemical composition. As the carbide composition is dependent on aging time exact chemical compositions for each sample were determined with X-ray fluorescence techniques. Coherent scattering cross-section curves were obtained for the different aged samples, from which the total surface and total volume of precipitates per unit volume of sample were determined as a function of aging time at both temperatures. Moreover, the size distribution function of M₂₃C₆ carbide was obtained for each aging time. In general, the results obtained, taking into account the difficulty of the problem, are in satisfactory agreement with the localized TEM observations.