The Effects Of Heating Process On The Oxidation Behavior Of Si-containing Steels

The effects of heating process on the oxidation behavior of Si-containing steels were investigated on the Setaram Setsys Evo STA using heating process similar to the industrial reheating routes.The microstructures and construction of oxide scale were anlayzed by SEM?scanning electron microscopy?,XRD?X-ray diffraction?and EDS?energy dispersive spectrometer?.In addition,the Image-Pro Plus 6.0 software was used to determine the penetration depth of the Fe₂SiO₄ layer.The melting process of Fe₂SiO₄ was observedin-situ using LSCM?VL2000DX laser scanning confocal microscope?.On the basis of a large number of experimental results and theoretical analysis,the main conclusions of the study are as follows:?1?There is a critical time point for the oxidation kinetics of Si-containing steel.After the critical time point,the oxidation rate constant increases with the increase of oxidation temperature;the mass gain with time follows a parabolic law and the model coefficient A in kinetics equation of oxidation is a constant.Before the critical time point,the oxidation rate constant remains unchanged;the mass gain with time follows a linear law and the model coefficient A decreases with the increase of temperature.But in most previous studies,the mass gain versus time shows a parabolic relationship during the isothermal oxidation of Si-containing steels.In addition,the critical time is postponed with the increase of isothermal oxidation temperature.This is one of the main innovation points of this paper.?2?When the isothermal holding temperature is higher than the melting temperature of fayalite,the oxidation rate has no relationship with temperature and time,and linear increase with oxygen concentration.The total mass gain is independent on temperature and only linear increases with oxygen concentration and time.This is another main innovation point of this paper.?3?The distribution of silicon in silicon-containing steel mainly has three types:fistly,distribution in the innermost layer of substrate with the form of Fe₂SiO₄;secondly,distribution as the silicon-containing particles in the iron substrate;thirdly,continuously distribution on the metal grain boundary.Moreover,Fe O distributes on Fe₂SiO₄ with a punctiformor lamellar morphology.This is also one of the main innovation points of this paper.?4?The total mass gain increases with the decrease of silicon content.However,the silicon content has no significant effect on the oxidation rate at high temperatures?higher than the melting point of Fe₂SiO₄?.Fe₂SiO₄ appears in a net-like form when the heating temperature higher than the melting point of Fe₂SiO₄.The morphology and penetration depth of the Fe₂SiO₄ are mainly related to the oxygen concentration and time.?5?The addition of P could reduce the melting point of the eutectic compound Fe₂SiO₄/FeO,which is helpful for descaling the oxide scale.?6?The net-like distribution of Fe₂SiO₄ becomes less apparent using reheating technologywith the slow heating rate at low temperature and at fastheating rate at high temperature.The results of the present study clarify the effects of heating process?oxygen concentration,heating temperature,heating rate?and silicon content on the oxidation behavior of silicon-containing steel,especially on the morphology,distribution and penetration depth of Fe₂SiO₄.It will provide theoretical reference for controlling oxide scale defects of silicon-containing steels.