The effect of the addition of alloying elements on carbide precipitation and mechanical properties in 5% chromium martensitic steels

Carbide-forming elements (W, Mo, Nb, V), as well as elements that influence only the tempering kinetics (Co, Ni), were added to a 5% Cr tempered martensitic steel in order to modify its precipitation. The main goal was to shift the secondary hardening peak towards higher tempering temperatures. Small angle neutron scattering and X-ray diffraction experiments, as well as transmission electron microscopy, were performed to characterize the precipitation of nanometric carbides. A significant modification of the volume fraction and/or chemistry of the very fine secondary precipitation was observed only for Mo, V and Ni additions. Moreover, the mechanical properties showed that the volume fraction of small precipitates (VC, Fe3Mo3C) directly influences the mechanical resistance at high temperature but has a detrimental effect on Charpy impact energy.