Dresden 2003 – wissenschaftliches Programm

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M: Metallphysik

M 41: Postersitzung

M 41.20: Poster

Donnerstag, 27. März 2003, 14:30–16:30, HSZ

Rhines-Pack Oxidation of Low-Alloyed Steel — •Jürgen Gegner — SKF GmbH, Department of Materials Physics, Ernst-Sachs-Strasse 5, D-97424 Schweinfurt

The Rhines-pack method is used to examine scale-free internal oxidation of the low-alloyed bearing steel SAE 52100 at the dissociation pressure of wüstite between 1073 and 1373 K. The surrounding powder consisting of Fe₂O₃ and Fe offers oxygen in excess. Thus, the rim concentration of carbon is maintained constantly at almost zero by oxidation. As the gaseous reaction products are rapidly removed from the surface and the low alloying content avoids the formation of an outer barrier layer, undisturbed simultaneous decarburization takes place resulting in an austenite-ferrite phase transformation in the edge zone at not too high temperatures. Here, out-diffusion of carbon controls the iron phase, in which internal oxidation occurs. This is shown by metallography, SEM and profile measurements of both micro-hardness and carbon concentration. The rate of internal oxidation characterized by subscale thickness and oxygen permeability intermediately reveals an inverse course in the narrow temperature range of gradual transition from one pure rim matrix to the other at around 1170 K, as oxygen diffuses much faster in the remaining ferrite than in austenite. This phenomenon does not arise in carbon-free iron alloys.