Abstract: Analysis on defect and the work of contrast about microstructure and fatigue life are carried out at same time between the materials of home and Germen back wheel hub axle. On base of the above, the reason of early fatigue inactivation occurred in home back wheel hub axle are founded. The test results show that mass of metallurgical defect exist in the material and a great amount of Mo, Cr, Ca, Cl, O, Na, K are founded in the zone of rarefaction cavity defect, but there is no element Mo in the substrate. This proves that the substrate isn’t alloyed. The occurrence of cavity is the real reason about over early generation of fatigue crack. The test results may be treated as the theoretical rule about material choosing for back wheel hub axle of home car.

Key words: Early fatigue, Fatigue life, Wheel hub axle