Fatigue fracture of cutter blade made of high-speed steel

• Engraving process when heat is emitted can provide to effect of structural notch.
• Electrical engraving process can cause local melting of the material.
• Local melting of the material let to structure change and form the micro dendrites.
• Dendritic structure cause internal stresses, cracks and propagation of fatigue fracture.
• It is recommended to use more safety identification marks such as adhesive labels.

The quality of the surface of cyclically loaded components is very important. Many observations confirm that the root cause of the micro cracks (causing the fatigue fracture) are primarily a surface's defects appearing during production process. These surface defects can be also caused by engraving processes used to perform identification marks. This paper presents the failure analysis of broken blade of the cutter Ku 500VX. The blade was subject of standard metallographic examination, hardness measurements, fractography analysis and metallographic studies using stereoscopic, light and scanning electron microscopes. The damage of the blade was caused by changes of the structure (formation of the brittle micro dendritic structure) that occurred during manual electric engraving process when the material was heated till its melting point. As a result the stresses occurred in surface what provided to micro cracking and to propagate the fatigue fracture. The origin of this fatigue fracture was in the place where the inscription was made.