LAUSR

Oxidation kinetics and oxide scale characteristics of two steels with 7.5 wt% Ni (7.5Ni) and 8.4 wt% Ni (8.4Ni) are investigated in temperature range of 1100–1250 °C by the thermogravimetric analysis, scanning electron microscope, and X‐ray diffraction. In the results, it is shown that oxidation kinetics for both steels obey the parabolic rate law, and oxidation activation energy of 8.4Ni steel is slightly larger than 7.5Ni steel. Thickness of outer oxide scale has an important effect on thickness of inner scale. The inner oxide scale is entangled with the steel matrix, and consists of Ni metal and its surrounding Fe oxide. Compared with 7.5Ni steel, the thicker inner oxide scale of 8.4Ni steel implies that the severer internal oxidation occurs in the 8.4Ni steel than 7.5Ni steel when the temperature exceeds 1200 °C. The decreases in Ni content and heat‐treatment temperature contribute to alleviating surface quality defects of Ni‐containing steel caused by surface oxidation.