Cause of Fracture on 40Cr Steel Automobile Steering Bending Arm

The 40Cr steel steering automobile bending arm fractured. The causes of fracture on steering bending arm were analyzed by means of macro analysis, micro analysis, chemical composition analysis, hardness test, metallographic inspection, stress analysis and strength check. The results show that the fracture form of steering bending arm is bidirectional bending fatigue fracture. The root cause of the fracture was that there were machining tool marks on the R corner surface of bending arm, resulting in stress concentration. And the strengthening effect of induction quenching surface heat treatment was insufficient, so that the R corner of the transition area with cross-section change can not be effectively quenched and there was residual tensile stress, resulting in crack initiation here, and the crack expanded until fatigue fractured under the action of steering cyclic stress.