X80管线钢高温氧化膜的生长机理

观察并研究了X80钢在800～1 200℃下氧化1 mmin的氧化膜以及氧化圆点的形成规律.结果表明:X80管线钢在1 050℃以下具有良好的抗氧化特性,从1 050℃开始整个氧化膜层明显增厚,抗氧化能力下降;在1 000℃以下氧化膜内侧区域存在明显的Si、Cr富集带,温度升高到1 050℃,基体界面开始出现氧化圆点,同时内侧元素富集氧化膜的完整性遭到破坏,此种现象主要与Cr2O2进一步氧化形成CrO3有关.通过热力学和动力学分析发现,低于1 000℃.Si、Cr的氧化物稳定性高,自扩散系数小,利于形成界面处稳定的氧化膜.同时发现,1 050℃属于X80钢氧化质点形成的临界温度,低于此温度主要形成致密的界面氧化膜,它起到明显的抗氧化作用.

Growth mechanism of oxidized film of X80 pipeline steel at high temperature

The formation rules of oxidized film and round spot of hot rolled X80 steel heated from 800 ℃ to 1 200 ℃ for 1 min were studied through thermo-gravimetric analysis.The results show that good antioxidant property could be expected while temperature is less than 1050 ℃ and the antioxidant property decreases obviously as the temperature increases up to 1 050 ℃ to result in formation of thick oxidized film.The microstructure of scale varies with temperature.An enrichment band of Si and Cr is found at the inside of oxidized film below 1 000 ℃.With temperature increasing up to 1 050 ℃,the integrity of oxidized film is destroyed by the formation of oxidized round spot at the interface between matrix and scale due to further oxidation behavior of Cr,transforming from Cr2O3 to CrO3.Through thermodynamics and kinetics analysis,small self-diffusion coefficients and stable oxidation productions of Si and Cr are helpful to formation of stable oxidized film while temperature is below 1 000 ℃.Compact oxidized film between matrix and scale of X80 steel forming below the critical temperature of 1 050 ℃ has obvious antioxidant effect and 1 050 ℃ is critical temperature of formation of oxidized round spot defect.