High-resolution topochemical analysis and thermochemical simulations of oxides and nitrides at grain boundaries and within the grains of a low alloy Mn-Cr hot-rolled steel sheet

Highlights: • high-resolution maps of grain boundaries show non-uniform element distribution. • Central nitride strand in oxides may originate from pre-existing nitrides. • Numerical calculations for> 40 potentially stable phases are presented. • Differences between experiment and theoretical results will be discussed. • Existing knowledge on grain boundary oxide structure is strongly simplified. -- Abstract: The selective oxidation underneath the scale layer of an industrially hot rolled Fe-1.8Mn-0.8Cr steel at temperatures between 600 and 700 ^°C has been investigated. The spatial distribution and composition of formed precipitates has been studied by high-resolution topochemical analysis via TEM-EELS and NanoSIMS and revealed heterogeneities in chemical composition, especially along grain boundaries. It could be shown that grain boundary oxides are predominantly composed of aluminium, chromium or silicon oxides/nitrides, surrounded by manganese-rich oxides. Experimental results of phase stability have been compared to numerical simulations, considering the distribution of more than 40 potentially stable oxide-, nitride- and carbide phases, and differences are critically discussed.