Microscopic examination of the fracture surfaces of a cold working die due to premature failure

► Poor design, improper use and absence of stress removing, led to premature fracture. ► Deficiency of design concerning both shape and mechanical properties of the die. ► Metallographic analysis of the fracture surface has evidenced three distinct areas. The paper studies the fracture surfaces of a rotary cold working die that broke down during the setup process on the machine it was designed for. The die was manufactured using AISI D2 tool steel and was intended for cutting paper at room temperature. The tool failed during the setup process on the machine. Initially, historical data were collected: operating conditions, lifetime, restitution of sound operation, collection of recorded service history. This was followed by measurement of temperatures, hardness control, optical inspection and selection and preparation of samples. The cutting edges, fracture surfaces and the structure, not affected by the failure, were investigated by optical microscopy. The quality of the nitrated layers were inspected. Additional information concerning the fracture was obtained by examining the fracture surfaces using a scanning electron microscope. Local chemical analysis of the material was made using an EDX spectrometer. Fracture mechanism, the type of the fractures, and the principal causes that led to the premature failure of the die are discussed. Justification of these causes facilitates the prevention of future failures and sometimes contributes to an increased service life of the tools.