High Temperature Oxidation of Some Iron-Chromium Alloys

Abstract

The sealing eharoeteristics of three Fe-Cr alloys have been investigated by determining their weight goin vs. time curves at 1600° to 2000°F. The scoles formed thereby hove been examined using the techniques of X-ray diffraction ond speetrographic and metallographie analyses in an attempt to explain the discontinuities in the eurves and to elucidote the meehanism of scaling.D ESPITE the considerable number of investigations that have been carried out on heat resistant alloys, the characteristics of the scales formed at high temperatures are not fully known. The research reported here was undertaken in an attempt to ascertain the mechanism of scaling of the stainless steels. Scaling experiments were carried out first, the weight increase of the specimens being followed continuously with time. It was observed that, as weIl as showing the expected decrease in oxidation rate with time, the oxidation curves showed breaks corresponding to intermediate periods of accelerated oxidation, after which protectiveness again increased. This phenomenon was observed with austenitic stainless steels (types 302, 309, and 330) and with Fe-Cr alloys (types 410, 430, and 446), but only the latter are treated in this report. An examination of the scales was made using the techniques of X-ray diffr action and spectrographic and metallographie ana~ yses in an attempt to obtain a correlation between the nature of the scales and the oxidation curves.

Effect of Si Addition on Oxidation Behavior of Nb Containing Ferritic Stainless Steel

“…5,6) The other is that Si makes thin amorphous SiO 2 layer at the scale/metal interface and prevents the outward diffusion of metal ion and the inward diffusion of oxygen. [7][8][9] In this study, based on the observation results by means of FE-SEM and FE-TEM, an amorphous SiO 2 layer was confirmed to form under Cr 2 O 3 . Therefore, the later mechanism is likely to act.…”

“…The two kinds of mechanism were proposed for improving oxidation resistance. One is that Si decreases the defects in the Cr 2 O 3 scale, leading to the pure and fine Cr 2 O 3 scale, as proposed by Fransis 5) and Radavich et al 6) The other is that Si forms a thin SiO 2 layer at the scale/metal interface and prevents the outward diffusion of metal ion and the inward diffusion of oxygen, as proposed by Caplan and Cohen, 7) and Nakayama and Oshida. 8) Shoji et al 9) tried to elucidate these two ideas using austenite stainless steels with the high Si addition.…”

“…Many previous papers [5][6][7][8][9][10][11] reported that Si addition improved oxidation resistance and Si has recognized to be the element improving oxidation resistance. Wood et al 10) and Fujikawa et al 11) reported that Si addition improved oxidation resistance using ferritic stainless steels with various Si contents.…”

“…The effect of Si on oxidation resistance was studied by many previous researchers. [5][6][7][8][9][10][11] Si has been recognized as the element improving oxidation resistance. The two kinds of mechanism were proposed for improving oxidation resistance.…”

Measurement of the Mechanical Properties of Growing Surface Films in oxidising environments

“…I t would therefore appear that this technique will also be eminently suitable for examining facets of oxidation behaviour of high-temperature alloys such as 'breakaway' in stainless steels (7,8,9) and oxide spalling on nickd-base alloys. The results on Nimonic 90 at 900 "C suggest that some mechanical discontinuities in the oxide scale do occur during growth.…”