敏化的304L不锈钢紧凑拉伸试样在288℃的含氧循环水中发生应力腐蚀(SCC)后, 沿试样横截面将裂纹尖端区制成透射电镜(TEM)试样, 用高分辨分析型TEM观察裂尖, 测量微区成分. 结果表明,在不连续的SCC裂纹周围及裂尖前方存在几百纳米宽的氧化物区, 成分为Cr2O3, Fe3O4或其混合物. 在氧化物中存在大量的纳米级浅裂纹, 在裂尖应力集中作用下, 氧化物中首先形成不连续的微裂纹, 它们长大并和主裂纹连接就导致SCC裂纹的不连续形核及扩展.
Stress corrosion cracking (SCC) of a sensitized 304L stainless steel was carried out under slow tension of a pre--cracked sample in water containing oxygen at 288℃. Thin foil samples were prepared along its cross--section containing the pre--cracks, and the tip region of SCC was studied by analytical TEM. The observations show that there are oxides with a size of several hundreds nanometers ahead of a crack tip of SCC and around the discontinuous microcracks. Fine--probe analysis was used to determine local compositions of the oxides, indicating the oxides are Cr2O3, Fe3O4 and their mixture. Many microcracks are distributed unevenly in the oxides. Microcracks initiated discontinuously in the oxides ahead of a main crack because of a large stress concentration. The growth and connection of the discontinuous microcracks in the oxides resulted in the propagation of SCC.
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