Abstract
Oxidation experiments at 500, 550, 600, 650, 700 and 800° in steam with different oxygen contents as well as in water at 300° with different amounts of chloride added, have been made on the following alloys the surfaces of which had been pickled or ground: 15/15, 18/11, 20/252 20/25 Nb, 20/35, Incoloy 800,16/75 and 13 Cr/4A1. The oxidation resistance did not show any simple relationship to the alloy composition, the order between the alloys varying according to temperature and time of exposure. At steam temperatures up to 650° ground specimens had a lower oxidation rate than did pickled specimens; at 700° this influence of surface treatment became small for long oxidation times, and at 800° this was true already at short times, the relationship even being reversed with 18/11 and 15/15. The temperature-dependence might be explained by observations made on the role of enhancement of diffusion due to the presence of dislocation. In water at 300°, ground materials had the higher oxidation rate.
Loss of oxide occurred in high-temperature tests.
To establish the amount of oxide spalling, different methods had to be used depending on test temperature and alloy compostiion.
The alloys also varied with respect to the degree of grain boundary oxidation and development of local thickening of the oxide layer. The rates of erosion found in tests at temperatures below 700° and at steam pressures below 30atm were small compared with the rate of oxidation under static condition.
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