Through methods such as macroscopic observation of fracture's appearance

test of chemical composition

test of tensile property

shock test

hardness measurement

microscopic observation of fracture's appearance

and metallographic organization examination etc.

the causes leading to chain-rings' breakage of the slag-dredger used for boilers have been analysed.Results show that the type of failure concerning chain rings' breakage of the slag-dredger is fatigure fracture.In operation of the slag-dredger

the inner near surface in bent section of the chain-rings had been repeatedly compressed and wornout under effect of the residual tensile stress and pulling-bending fatigue load at the near surface of chain-rings

the grain-boundary microflaws being sprouting and expanding from the inner near surface up to final breakage.