The influence of cold work on the initially formed oxide layer on the stainless steels AISI 304 and Incoloy 8OOH has been studied by XPS. Oxidations were performed at pressures of 10-6-10-4Pa and temperatures of 300-800 K. All samples showed a similar oxidation behaviour. The oxidation rates of iron and chromium are of the same order of magnitude at temperatures below 650 K. Subsequent oxidation results in an iron oxide on top of a chromium oxide layer. At temperatures above 650 K the metal surface becomes enriched in chromium, which is preferentially oxidized at these temperatures and pressures. Even prolonged oxidation does not result in an iron-rich oxide surface. Nickel has never been found in its oxidized form. The binding energy of oxygen, in the various oxide layers, is independent of the extent of oxidation and is 530.6 eV.

AISI 304, 314, 321, and Incoloy 800H have been subjected to several pretreatments: polishing, milling, grinding, and

Oxidation experiments, performed by means of light interference microscopy, give information of the initial oxidation on a microscopic scale. A thin oxide layer on the substrate gives rise to an interference colour, which is directly correlated to the thickness of this layer. It is shown that not all stainless steels react in the same way to the same pretreatments. The oxidation behaviour of drawn AISI 304 and AISI 321 is completely different from that of Incoloy 800 H, while the undeformed and recrystallized samples all show the same oxidation behaviour. It is suggested that this behaviour of AISI 304 and AISI 321, is caused by the formation of a' martensite in the deformed austenitic matrix.Oxidationsversuche in Verbindung mit optischer Interferenzmikroskopie liefern Aussagen iiber die Anfangsstadien der Oxidation im Mikrobereich. Die auf dem Substrat entstehende diinne Oxidschicht fiihrt zum Auftreten einer Interferenzfarbe, die direkt mit der Dicke dieser Schicht korrelierbar ist. Es wird gezeigt, dal3 das Verhalten der nichtrostenden Stahle auch bei gleicher Vorbehandlung verschieden ist. So ist das Oxidationsverhalten von gezogenem Stahl AISI 304 und 321 vollkommen anders als das von Incoloy 800 H, wahrend unverformte und rekristallisierte Proben sich gleich verhalten. Dieses Verhalten der Stahle 304 und 321 ist wahrscheinlich der Bildung von a'-Martensit in der verformten austenitischen Matrix zuzuschreiben.

The interaction of oxygen with clean surfaces of stainless steels has been studied by spectroscopic ellipsometry and AES. The reaction involves chemisorption and dissolution of oxygen into the surface of the metal via a place-exchange mechanism.Oxide thickening occurs via cation and anion migration under the influence of an electric field. The activation energy increases with increasing oxide thickness and the final activation energy equals the energy needed to break the bonds between oxygen and metal ions in the oxide, suggesting diffusion via lattice sites.