Effect of Oxidation Process on Characteristics and Mechanical Properties of Iron Oxide Scale Formed on Q355B Steel

High temperature oxidation tests of Q355B steel were conducted at different temperatures (1100,1150,1200 ℃) and different times (180,240, 300 min) in dry atmosphere with different oxygen content (5%, 10% and 21%, volume fraction) using three-factor three-level orthogonal expertmental scheme. The characteristics and mechanical properties of the iron oxide scale formed on Q355B steel were studied by SEM, XRD and nanoindentation instrument. The results show that the iron oxide scale is composed of FeO, Fe₃O₄ and Fe₂O₃ phases, and the influence of temperature, time and oxygen content on the content of the phases in the iron oxide scale is complicated. The relationship between oxidation weight gain and iron oxide scale thickness with temperature, time and oxygen content can be characterized by multiple linear regression equations. The order of the effect of temperature, time and oxygen content on the average oxidation weight gain and average iron oxide scale thickness is temperature> time>oxygen content. The effects of temperature and time on oxidation weight gain and iron oxide scale thickness are significant and positively correlated. The effect of oxygen concentration on oxidation weight gain and iron oxide scale thickness is not as significant as temperature and time. The iron oxide scale may be characterized by looseness, densification and delamination. The plastic deformation occurs during the nanoindentation test of the iron oxide scale, and the phenomena of pop-in and pop-out occur on the loading and unloading curves respectively. The larger the preset depth of penetration, the more pronounced the pop-in and pop-out phenomena.