Silicon nitride wire rolling tools: Damage analysis and correlation with rolling-contact fatigue

Failure mechanisms of silicon nitride wire rolling tools used in forming high strength steels were investigated. Wire rolling experiments and FEM were carried out to analyze the thermomechanical loading in this metalforming process. Based on the experimental observations and numerical computations, a model was proposed to describe the failure mechanisms in work rolls. Thermal stresses were found to comprise a minuscule portion of the overall thermomechanical stresses developed in the rolls. Surface wear played a fundamental and decisive role in the damage evolution and lifetime of the rolling tools. Tensile stress, which is relevant to the fracture of Si3N4, exhibited a peak on the caliber flanks. Both the value and location of this peak were found to be dependent on wire reduction. Furthermore, failure of Si3N4 rolls under rolling-contact fatigue was investigated by means of twin-disk experiments and FEM. The results emphasized the impact of tribomechanical aspects on the failure of ceramic components. Such observations could be transferred to wire rolling to improve the reliability of ceramic-based rolling tools.