Fracture Analysis on High Strength Screws for Elevator

A batch of high strength screws used in elevator fractured after assembling for two months, and the fracture reason was analyzed by using photoelectric direct reading spectrometer, N, H, O joint tester, optical microscopy and scanning election microscopy. The results show that not in time dehydrogenation after galvanization resulted in the high hydrogen content in the screws, and no turning process after cold drawing which resulted in the formation of a large number of small defects on the surface of the screws before galvanization. They were the two main reasons for the fracture of this batch of high strength screws. These small defects acted as hydrogen traps and caused stress concentration. With the enrichment of hydrogen in the defects and under the load of static pulling stress, the high strength screws happened hydrogen-induced delayed e-brittle fracture finally.