Oxidation and characterization of as-cast TRIP steel surfaces

This paper presents recent results from a collaborative study between the Department of Ferrous Metallurgy at RWTH-Aachen University and the Department of Materials Science and Engineering at Carnegie Mellon University on high temperature oxide scale formation of Al and Si containing as cast TRIP steel surfaces under conditions similar to that of continuous casting and hot rolling. A combination of experimental studies consisting of (i) electron microprobe analysis and metallographic studies of the cast steel surface, (ii) direct visualization of the oxide formation through high temperature confocal scanning microscopy and (iii) Tammann furnace oxidation tests were carried out. It was found that internal oxidation of Al and Si takes place along the inter-dendritic boundaries, where Al and Si were found to have been enriched after casting. The scale formed on the steel surface was a complex mixture of solid fayalite ((FeO_n)₂(SiO₂)), wüstite (FeO _n), magnetite (fe₃O₄), hematite (Fe ₂O₃), and Fe-particulates and the rate of scale growth appears to have been controlled at high temperatures by the formation of a liquid slag layer that allows for rapid oxygen transport to the steel/scale interface.