Causes Analysis on Fracture of the Rear Cover Shaft of a Reinforcing Cylinder

The fracture failure happened to the 40Cr steel rear cover shaft of a reinforcing cylinder. The fracture causes of the rear cover shaft of the reinforcing cylinder were analyzed by macroscopic observation, microscopic observation, nonmetallic inclusion evaluation, metallographic inspection and hardness testing. The results show that the heat treatment technology of the shaft material was unreasonable, leading to the abnormal surface microstructure and the strength and hardness reduction of the shaft material; stripped nonmetallic inclusions were seriously overproof and they destroyed the continuity of the metal base; the above factors of two aspects resulted in the generation of fatigue cracks in the variable diameter area of the rear cover shaft of the reinforcing cylinder under the action of alternating stress, and then caused the early fracture failure.