材料期刊网

对于D_6AC钢(σ_b=203.5kgf/mm~2)和24CrMnSiNi钢(σ_b=161.0kgf/mm~2),在裂纹张口处滴水的条件下进行了应力腐蚀开裂实验。在光学显微镜和干涉显微镜下观察并研究了应力腐蚀开裂所引起的试样表面形变现象。结果表明,表面形变对于不同强度级别的钢具有不同的特征。在试样表面上所观察到的应力腐蚀裂纹的开裂路径,大多沿着一侧形变带或两形变带的会合处。讨论了产生这种表面形变现象的机制,认为与观察到的应力腐蚀裂纹在试样厚度上呈舌形扩展有关,此时未开裂的薄的试样表面层在外力作用下经受剪切变形,因而造成所观察到的试样表面形变现象。

Stress corrosion cracking (SCC) experiments were conducted with steel D6AC (σ_b=203.5 kgf/mm~2) and 24CrMnSiNi (σ_b=161kgf/mm~2) by dropping water onto the crack opening mouth. The phenomenon of surface deformation induced by SCC has been observed by means of optical and interference microscopes. It was shown that the surface deformation started at the tip of fatigue precrack, then stretched separately into two branches with an angle of 45° to tbe direction of crack propagation and finally turned to parallel to it. For steel D6AC, the width between two deformation bands distributed on both sides of crack propagating direction was narrower and two deformation bands stretched forward by joining together and separating apart alternately. However, for steel 24CrMnSiNi, the two deformation bands, the width between which was found to be wider, did not join together even after stretching forward a long distance. It can be seen from the interference photographs that the fringes were largely displaced at deformation bands, indicating that the surface deformation was mainly concentrated within the deformation bands. In contrast, the fringes corresponding to the area between two deformation bands maintained nearly parallel to each other. The optical microscope observation certified that this area was contracted along the thickness direction. The cracking paths on specimen surface were observed to extend mostly either along the deformation band on one side or the confluence of deformation bands on both sides. The mechanism of surface deformation was discussed. It is considered to be related with the tongue shape expansion of stress corrosion crack over the specimen thickness. Apparently, the uncracking thin surface layers of specimen were subjected to a shear deformation under the action of applied force, resulting in the observed phenomenon of surface deformation.