The oxidation mechanism and characterization of steam-side oxidation scale formed on the internal surface of the super-heater tubes made of T91 steel removed from the boiler of a power plant are studied by using the testing and analyzing methods of metallurgic inspection, scanning electron microscope-energy dispersive X-ray (SEM-EDX) and X-ray diffraction analysis. The results show that based on the section oxygen elemental distribution and the Fe-Cr elemental diffraction rule, the original steam-side oxidation scale normally consists of three layers. The inner layer is heterosphere oxides, which consists of Cr-enriched and Cr-depleted zones appearing alternatively; the middle layer is the loose and porous Fe3O4 with the columnar crystal microstructure; the outer layer is the thin Fe2O3. In the outer layer, there are small gaps among the oxides and the adhesion is weak, which makes it easy for the oxides to flake off during great temperature variation. The middle layer works better than the outer one.%采用金相显微镜、扫描电镜、能谱分析仪、X-射线衍射仪等试验分析手段,对某电厂锅炉过热器用9CrlMoVNb(T91)钢蒸汽侧氧化膜形态及其形成规律进行研究.结果表明,根据截面氧元素分布及Fe-Cr元素传质规律,该类合金钢蒸汽侧氧化膜分为内、次外、外3层,内层为致密的富Cr层与贫Cr层交替出现的非均质氧化层,中间层为疏松、柱状结构的Fe3O4,最外层为较薄的Fe2O3;外氧化层氧化颗粒间存在缝隙,粘附强度低,温度变化剧烈时最易剥落,次外层次之.
展开▼
