Fracture Analysis of the Chain Pin Shaft of an Escalator Ladder

Abstract

This study analyzed the cause of fracture for the chain pin shaft of an escalator ladder, and found that the pin material satisfied the chemical composition content requirements of the GB 20CrMo steel standard and similar to ASTM A29/A29M-2012 grade 4120. Abnormal metallurgical quality defects were not found in the pin. The pin shaft was carburized, and internal oxidation defects were not observed on the surface as a result of carburization. The internal structure of the material was uneven, there existed a mixed grain structure, and the martensite structure was coarse at particular regions, to seven grade. Additionally, the martensite structure in the carburized layer was slightly coarser, four to five grade, which had an adverse effect on the pin strength. The pin break was a fatigue fracture caused by multiple cumulative damages. The fracture originated on the surface of the pin, and may have been caused by indentation on the pin's surface.