Abstract: The chain of the slag scraper of a certain thermal power generation unit broke. The causes of chain fracture were analyzed using macroscopic observation, chemical composition analysis, depth testing of the carburized layer, metallographic examination. The results show that the fracture property of the chain was fatigue fracture, and the inadequate carburizing process on the surface of chains, led to a decrease in the resistance to fatigue and wear of chains. Under the combined action of large loads and alternating stresses, the chain ultimately underwent fatigue brittle fracture.