Abstract: The coated steel roller is subjected to bending moment and torque during operation. Under the effect of a small alternative load, the roller shaft prematurely experiences fatigue fracture failure, and the fracture mode is brittle fracture. The occurrence of fatigue fracture is a result of combined actions of several factors. The main factors are as follows: alternating cyclic stress; stress concentration at the root of the shaft caused by the change in shaft diameter; the change of microstructure in the welded joint region of steel roller caused by the fusion welding process ; the welding defects in weld joint region;surface state after welding. These factors lead to defects in welded joint region and surface of the components to become the origin of fatigue microcrack initiation. Existence of welding residual stress increases the average stress, which causes the weld defects to accelerate toward the inside of the adjacent shaft body and causes the roller shaft to prematurely experience fatigue fracture failure.

Key words: coating steel roller, fatigue fracture, welding defects, failure analysis