Comprehensive analysis of precipitates in rich chromium steels by means of electron energy loss spectrometry spectrum imaging

This paper give insight into the microstructural evolution during heat treatment and creep testing of a boron alloyed 9% Cr steel, with special emphasis on the role of boron, by using advanced analytical transmission electron microscopy methods. Electron energy loss spectrum images acquired in scanning transmission electron microscopy mode provide full elemental information in the form of compositionally quantified maps (atoms/nm³) of C, N, Fe, Cr, V and B with high spatial and energy resolution. MX precipitates embedded in the M₂₃(C, B)₆ particle were identified and analysed with respect to their boron concentration. Energy filtered TEM elemental maps have been processed by applying bivariate histogram analysis in order to recognise an early stage transformation of vanadium nitride particles to the complex nitride named modified Z phase. Moreover, pre-austenite grain boundaries in the creep tested specimens have been charted and the phases were identified via energy filtering TEM, electron energy loss and X-ray spectrometry.