Cracking Analysis of Inner Ring of Bearing in Engine

There was a visually visible crack found on the end of the inner ring of a bearing in an engine after 3 hours’ test. Macroscopic and microscopic observation, microstructure examination and hardness testing were carried out to analyze the cause of the crack. The results show that the crack was due to the shrinkage residual defects in the raw material, which were flattened into a closed linear oxide inclusion in the process of forging, and then cracked in the following testing. The shrinkage residual defects in the raw material should be the shrinkage residual or the secondary shrinkage nearing the feeder head of the cast ingot. The distribution of the shrinkage residual is concentrative in the raw material, so they can be found by the macroscopic examination. In the later stage, macroscopic examination was added before they came into market, and the finished parts had no such defects.