Microstructure and Composition of Grain Boundary- and Intragranular Oxides in Low Alloy Mn-Cr, Mn-Al-Si and Si-Al-P Hot-rolled Steel Sheets

Abstract

Abstract During hot rolling, coiling and subsequent cooling of low-alloy steel sheets, internal oxides are formed at the grain boundaries (intergranular) and within the grains (intragranular) as a consequence of oxygen diffusion into the steel and segregating alloy elements. The assembly/microstructure and composition of the oxides found were investigated via transmission electron microscopy (TEM) and electron energy loss (EELS)- or energy-dispersive X-ray (EDX) spectroscopy therein. Our spectroscopic data reveal various simple oxide species, located separately or side by side. Those findings apply to grain boundary oxides and intragranular oxides, for all the steel compositions investigated (Fe-Mn-Cr, Fe-Mn-Al-Si, Fe-Si-Al-P). For example, within the Mn-Cr-alloyed steel we find Mn oxide at all oxide locations (inter- and intragranular), but Cr oxide is not present always. We also discuss the sequences of oxide formation, which follow the thermodynamic rules of oxide formation.