Cause analysis of premature fracture in the welding position of special lifting tool for aero-engines

Abstract

A specialized lifting tool for aero-engine in a workshop broke down after two months of use, resulting in damage to the workpiece and significant economic losses. The incident also posed a serious production hazard in the workshop. In this study, a series of characterization methods including macroscopic trace observation, fracture analysis, physical and chemical testing, microstructure observation, and hardness testing were conducted to analyze the cause of the lifting tool fracture. Based on simulation methods, the reliability of the lifting tool design was evaluated. The results show that the lifting tool design itself is reliable, and the main reason for the fracture is poor welding quality of the welded structure. It is suspected that there are welding cold cracks in the heat affected zone, which propagate during the use of the lifting tool and eventually lead to fracture. The root cause is that the quality of the base material of the weld did not meet the design requirements, resulting in a higher carbon equivalent in the base material, lower weldability, and increased sensitivity to welding cracks, which was also the reason for the fracture occurring in the welding heat-affected zone. The unqualified material composition affects the process parameters of the pre-welding preheating and the post-welding heat treatment, resulting in the formation of high hardness (724.0HV1) and brittle martensite structure in the welding heat-affected zone.