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首页> 外文会议>12th International Conference on Environmental Degradation of Materials in Nuclear Power Systems: Water Reactors 2005 vol.2 >EXAMINATION OF STRESS CORROSION CRACKS IN ALLOY 182 WELD METAL AFTER EXPOSURE TO PWR PRIMARY WATER
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EXAMINATION OF STRESS CORROSION CRACKS IN ALLOY 182 WELD METAL AFTER EXPOSURE TO PWR PRIMARY WATER

机译：压水一次水暴露后182合金金属的应力腐蚀裂纹检查

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Detailed metallurgical examinations have been undertaken of Primary Water Stress Corrosion Cracks (PWSCC) in an Alloy 182 weld from a prior capsule test program. The objective was to examine the relationship between crack initiation sites and the microstructure of the weld metal as well as to identify those microstructural features that facilitate or arrest PWSCC propagation. Initial examinations by Scanning Electron Microscopy (SEM) were carried out in order to locate secondary cracks on the internal surfaces associated with the main leaking crack of failed capsules. Optical and SEM-Energy Dispersive Spectroscopy examinations of transverse sections of the failed capsules on a plane close to the main cracks were used to characterize the weld microstructures, to search for possible surface flaws related to crack initiation sites, and to identify the orientation of the crack path in relation to the weld microstructure. Electron Back Scattering Diffraction was used to determine the crystal orientations of the grains on both sides of the crack flanks (I.e. grain boundary misorientation). Secondary Ion Mass Spectroscopy on metallographic cross sections in the immediate vicinity of the surface and near crack initiation sites was also employed both to try and detect any subsurface damage in the base metal and to characterize elemental segregation in the weld deposit. PWSCC initiation was associated with plastic deformation and high energy grain boundaries that were approximately perpendicular to the surface (and therefore to the applied hoop stress) in the test capsules. No evidence of crack initiation at small (acceptable) weld flaws (such as gas bubbles or slag inclusions) was found, despite the fact that such defects were observed in the most favorable zone for initiation. Cracks typically initiated between two grains that did not deform in the same way under stress. This was linked to the heterogeneity of composition (particularly niobium) between the grains. The cracks exhibited a highly unusual aspect ratio, as they never showed a large lateral surface extent (>～250 μm), even when they extended through the wall thickness (～0.6 mm). This is a very different feature compared to PWSCC in wrought nickel base alloys such as Alloy 600, where cracks that form in a uniform stress field are semi-elliptical in shape. The unusual shape of PWSCC in Alloy 182 was deduced to be due to the strong texture of the weld.
机译：根据先前的胶囊测试程序，已经对182合金焊缝中的主水应力腐蚀裂纹（PWSCC）进行了详细的冶金学检查。目的是检查裂纹萌生点与焊缝金属微观结构之间的关系，并确定有助于或阻止PWSCC传播的微观结构特征。进行扫描电子显微镜（SEM）的初步检查，以便在与破裂胶囊的主要泄漏裂纹相关的内表面上找到次要裂纹。在靠近主裂纹的平面上对失效胶囊的横截面进行光学和SEM能量色散检查，以表征焊缝的微观结构，寻找与裂纹产生部位有关的表面缺陷，并确定裂纹的方向。与焊缝微观结构有关的裂纹路径。电子背散射衍射用于确定裂纹侧面两侧晶粒的晶体取向（即晶界失取向）。在表面紧邻和裂纹产生部位附近的金相截面上的二次离子质谱法也用于尝试检测母材中的任何次表面损伤并表征焊缝中的元素偏析。 PWSCC的引发与塑性变形和高能晶界有关，高能晶界近似垂直于测试胶囊中的表面（因此垂直于施加的环向应力）。尽管在最有利的起弧区域观察到了此类缺陷，但没有发现在小（可接受）焊缝缺陷（例如气泡或夹渣）处出现裂纹的证据。裂纹通常在两个晶粒之间产生，这些裂纹在应力作用下不会以相同的方式变形。这与晶粒之间的成分（特别是铌）的异质性有关。裂纹表现出极高的长宽比，因为即使扩展到整个壁厚（〜0.6 mm），也从未表现出较大的侧面扩展（>〜250μm）。与PWSCC在变形的镍基合金（例如Alloy 600）中相比，这是一个非常不同的特征，后者在均匀应力场中形成的裂纹为半椭圆形。可以推断出182合金中PWSCC的不寻常形状是由于焊缝的牢固纹理。

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