Balitskii Alexander I, Syrotyuk Andriy M, Kolesnikov Valerii O, Balitska Valentina O, Ivaskevych Ljubomyr M, Havrilyuk Maria R
Department of Strength of the Materials and Structures in Hydrogen-Containing Environments, Karpenko Physico-Mechanical Institute, National Academy of Sciences of Ukraine, 5 Naukova Str., 79601 Lviv, Ukraine.
Department of Mechanical Engineering and Mechatronics, West Pomeranian University of Technology in Szczecin,19 Piastow Av., 70-310 Szczecin, Poland.
Materials (Basel). 2024 Dec 21;17(24):6257. doi: 10.3390/ma17246257.
Rotor shafts are the most heavily loaded and accident-prone parts of powerful turbine generators, which are cooled using hydrogen. To eliminate damage sustained during operations, repair work was carried out, including the removal of defective parts, surfacing, and turning. This study tested the machinability of the rotor shaft using prototypes made from 38KhN3MFA steel. A section of the shaft was degraded due to prolonged operation (250 thousand hours), and compared to the central part, a decrease in the average grain size from 21.57 μm to 12.72 μm and an increase in the amount of hydrogen absorbed during operation from 2.27 to 7.54 ppm were observed. With the frequency of dry turning increasing from 200 to 315 RPM, the chips changed their form from mostly rectangular with linear dimensions of 10 to 20 mm to large spiral rings with a diameter of 15 to 20 mm and a length of more than 50 mm. Cracks of 1 to 4 mm in length were found in most chip particles at both rotational speeds. Increasing the rotational speed from 200 to 315 and up to 500 RPM led to the formation of an oxide film on the surface of the specimens, as evidenced by the appearance of oxygen during local analyses of the elemental content on the chip surface. The saturation of specimens by hydrogen gas led to the formation of finer chips compared to the non-hydrated material, and the roughness of the machined surface increased at hydrogen contents of 6 and 8 ppm. In both dry and coolant cutting operations, surface roughness reflects the degradation of the rotor shaft or experimental prototypes due to hydrogenation, which can be used to diagnose the condition of the rotor after long-term operation.
转子轴是大型汽轮发电机中负荷最重且最容易发生事故的部件，采用氢气冷却。为消除运行期间遭受的损坏，进行了修复工作，包括拆除有缺陷的部件、堆焊和车削。本研究使用由38KhN3MFA钢制成的原型测试了转子轴的可加工性。轴的一部分由于长期运行（25万小时）而性能退化，与中心部分相比，平均晶粒尺寸从21.57μm减小到12.72μm，运行期间吸收的氢气量从2.27ppm增加到7.54ppm。随着干车削频率从200转/分钟增加到315转/分钟，切屑形状从大多为线性尺寸为10至20mm的矩形变为直径为15至20mm、长度超过50mm的大螺旋环。在两种转速下，大多数切屑颗粒中都发现了长度为1至4mm的裂纹。将转速从200转/分钟提高到315转/分钟再到500转/分钟，导致试样表面形成氧化膜，这在对切屑表面元素含量进行局部分析时氧气的出现得到了证明。与未氢化材料相比，氢气使试样饱和导致形成更细的切屑，并且在氢气含量为6ppm和8ppm时加工表面粗糙度增加。在干式和冷却液切削操作中，表面粗糙度都反映了由于氢化作用导致的转子轴或实验原型的性能退化，这可用于诊断长期运行后转子的状况。
