Reduction of Oxide Scales Formed on Low Carbon Steel Sheet in Synthesized Combustion Gas

Reduction of oxide scale, which formed on low carbon steel sheet at 973K for 4.5 ks in 10.9 kPa CO2–14.5 kPa H2O–bal. N2, was studied at 673–1073K in pure H2. Reduction was slow at 673K and it became fast up to 823K. Between 823–873K, however, the reduction became slower than that at lower temperatures and showed a minimum at 873K. Then the reduction became faster with increasing temperature above 873K. The temperature at which the reduction was the slowest coincides with that of transformation between magnetite and wüstite. Surface appearance of scales was different in these two temperature regions; surface cracks increased with reduction time at low temperature, whereas surface sintering proceeded with the time at high temperatures. The reason for the sudden reduction manner change around 873K was considered in terms of morphology, type and porosity of the oxide scales. It is concluded that the formar two can be the reason for the sudden change of reaction manner.