Fracture Analysis on 10.9 Grade High Strength Bolts for Glued Insulated Rail

A small amount of high strength bolts used for glued insulated rail on turnout of passenger line fractured after service for about one year. By means of macro analysis, chemical compositions analysis, mechanical properties testing, metallographic examination, SEM fracture observation and so on, the fracture reason of the bolts was analyzed. The results show that the main reason for fracture of the high strength bolts was attributed to the one-step temper brittleness, and a little amount of upper bainite which formed during quenching accelerated the fracture. Finally improvement measures were put forward.