The master reason is the harder rigidity of the formation rock, and the badder drill ability of rock, and the better rock abrasiveness. Drill string receives the complicated stress which is tension-compression stress, torsion stress, bending stress, etc.

其主要原因是：地层岩石的硬度高、可钻性差以及研磨性强；在长期工作中，钻具承受拉伸、压缩、弯曲和扭转等复杂应力。

The results of the measurement of the hardness has shown:the abrasiveness will improved largely. At last,the indication was verified by the wear experiments.

硬度测量结果表明:其耐磨性将大幅提高,这一点通过试样的磨损试验最终得以证实。