AN ADVANCED APPROACH TO THE CHARACTERIZATION OF PRECIPITATES IN SECONDARY HARDENING STEELS

摘要

Understanding the prevailing precipitation reactions is of vital importance for the development of advanced steels. A comprehensive characterization of all stable and metastable phases, however, is still demanding in these complex multiphase, multi-component materials. Transmission electron microscopy (TEM) is widely used, but the prevailing ferromagnetism makes the analysis of small precipitates extremely difficult. Furthermore, the investigated specimen volume is very small, making statistically relevant findings time-consuming. Therefore, in our study, TEM measurements are complemented by small-angle neutron scattering (SANS) and atom-probe field ion microscopy (APFIM). These methods were used to characterize the precipitates in a model steel which hardens by secondary hardening carbides and an intermetallic NiAl-based phase. Assets and drawbacks of each method are discussed and it will be demonstrated that an appropriate combination of the differently obtained findings leads to an almost complete description of the precipitation behavior.