Abstract
The oxidation behavior of 22Cr25NiWCoCu stainless steel with 0–0.86 wt.% Nb addition was investigated at 900 °C in air. With an increase in Nb addition, the volume fraction and average particle size of Nb (C, N) increased, but the grain size decreased. The results of grazing incidence X-ray diffraction indicated that the steels with Nb additions promoted Cr2O3 formation. After 10–100 h of oxidation, Cr depletion occurred at the region with Nb (C, N) precipitates because of its high Cr consumption rate, leading to Fe oxide generation. Finally, after 100 h of oxidation, the outer layer of Fe2O3 and the inner layer of (Cr, Fe, Mn)3O4 were formed.
Highlights
According to a global energy report from the International Energy Agency, the amount of CO2 emissions increased from 23 gigatons (Gt) to 32.5 Gt from 2000 to 2017 [1]
For 0.29-Nb addition, the average grain size decreased to 146 ± 25 μm, and the fine precipitates of
When the Nb addition was raised to 0.86 wt.%, the volume fraction of large-sized precipitates of Nb (C, N) increased significantly, few fine particles were observed, and the average grain size decreased to 90 ± 12 μm
Summary
According to a global energy report from the International Energy Agency, the amount of CO2 emissions increased from 23 gigatons (Gt) to 32.5 Gt from 2000 to 2017 [1]. Alloys with high Cr content, such as AISI 310SS and 20Cr-25Ni-Nb stabilized stainless steel, were chosen to improve the high oxidation resistance because they form a protective Cr2 O3 oxide layer [3,4]. A reduction in grain size is beneficial in oxidation resistance because the grain boundaries act as fast diffusion paths for Cr to form a protective Cr2 O3 layer [14,15,16,17,18] Otherwise, some phenomena, such as different morphologies of the oxides, could possibly be induced by the precipitates [18,19,20]. EBSD was employed to analyze the orientation and phase distribution of the oxide scales, and energy-dispersive X-ray spectroscopy (EDS) was applied to help distinguish Cr2 O3 and Fe2 O3 in the oxide layer
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