通过对某锅炉水冷壁管20G材质水环境下内壁沉积物下腐蚀氧化膜进行金相、扫描电镜、能谱分析、XRD等试验分析，研究了水环境下沉积物氧化腐蚀微观特征及其机理。结果表明，沉积物腐蚀下氧化膜主要为磷酸盐水垢、氧化铁垢混合物，分为内、外两层。内层为致密层/疏松层交替出现的带状组织，主要以Fe3O4为主;外层为疏松、多孔及细小颗粒组成的沉积物、Fe2O3等非均质层。内壁沉积物下腐蚀改变了水冷壁内壁氧化膜的形态及其氧化机制，使外氧化层成为疏松、多孔的细小粒状组织，内氧化层富含孔洞，促进了其反应产物氢与氧向内传质过程，且腐蚀产物氢与金属晶界处渗碳体反应，造成材质组织脱碳、晶界空隙增加以及微裂纹的萌芽与发展，加速了晶界氧化。

The corrosion oxidation mechanism and characteristics of steam-side oxidation scale formed on the internal surface of water-wall tube made of 20G steel which was removed from a boiler of a power plant were investigated by metallurgic inspection, SEM-EDX and X-ray diffraction analyses. The results show that the original steam-side oxidation scale normally consists of phosphate and iron oxide with two layers, the inner layer consists of compact and loose zone appearing alternatively and being identified as Fe3O4, the outer layer is loose, porous and identified as Fe2O3 with the deposition of phosphate. The deposition corrosion changed the steam-side oxidation mechanism and characteristics, which promoted the diffusion and mass transfer process of corrosion products (hydrogen and oxygen). And the reaction process of hydrogen and cementite in grain boundarier caused decarburization of water-wall tube, void fraction increase and grain boundar cracking initiation and propagation, then accelerated the oxidation of grain boundaries and materials.