铁素体-马氏体钢P91和P92在超临界水中腐蚀后氧化膜多孔性分析

用X射线衍射（XRD）和扫描电镜-电子能谱（SEM-EDX）技术研究P91、 P92在500℃/25 MPa和550℃/25 MPa超临界水中腐蚀后氧化膜的多孔性成因。结果表明，两种材料氧化膜均为双层结构，外层氧化膜为 Fe₃O₄相，内层氧化膜为Fe₃O₄和FeCr₂O₄相，P92在接近氧化膜区域的基体内存在一个内氧化区。P91和P92在超临界环境中腐蚀后氧化膜的多孔性与外层氧化膜Fe₃O₄的缺陷类型有关，富氧Fe₃O₄中的缺陷主要类型为氧空位，在超临界状态下，当氧空位浓度达到一定程度后，空位坍塌即形成小孔。

CHARACTERIZATION OF THE POROSITY OF THE OXIDE SCALES ON FERRITIC-MARTENSITIC STEEL P91 AND P92 EXPOSED IN SUPERCRITICAL WATER

The porosity of P91 and P92 exposed to 500, 550℃/25 MPa supercritical water (SCW) environment have been investigated. The oxidized samples were characterized by scanning electron microscopy (SEM)/energy dispersion X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The oxide scale is composed of a dual-layer structure: the outer magnetite (Fe₃O₄) and the inner magnetite-chromite (Fe₃O₄-FeCr₂O₄). An innermost internal oxidation zone was also observed in P92. The formation of pores is related to the defect types present in the magnetite structure, there are two major defect types in magnetite, one is interstitial Fe²⁺, and another is vacancy which may collapse into pores when vacancy concentration is high enough in supercritical water.