Publications

High temperature oxidation of 304L stainless steel and its effects on glass-to-metal joining

Susan, D.F.; Van Den Avyle, James A.; Monroe, Saundra L.; Sorensen, Neil R.; McKenzie, Bonnie B.; Michael, Joseph R.; Christensen, J.E.; Walker, Charles A.

An oxidation treatment, often termed "pre-oxidation", is performed on austenitic stainless steel prior to glass/metal joining to produce hermetic seals. The resulting thin oxide acts as a transitional layer and a source of Cr and other elements which diffuse into the glass during the subsequent bonding process. Pre-oxidation is performed in a low pO 2 atmosphere to avoid iron oxide formation and the final oxide is composed of Cr 2O 3, MnCr 2O 4 spinel, and SiO 2. Significant heat-to-heat variations in the oxidation behavior of 304L stainless steel have been observed, which result in inconsistent glass/metal seal behavior. The objectives of this work were to characterize the oxidation kinetics, the oxide morphology and composition, and the stainless steel attributes that lead to robust glass/metal seals. The oxidation kinetics were determined by thermogravimetric (TG) analysis and the oxide layers were characterized using metallography, SEM, focused ion beam (FIB) analysis, and image analysis. The results show that poor sealing behavior is associated with slower oxidation kinetics and a more continuous layer of SiO 2 at the metal/oxide interface. In addition, the effects of 304L heat composition on oxidation behavior will be discussed. Copyright © 2006 ASM International®.