The failure analysis of the rolls with grooves on the 3-high-roughing mill stand for hot rolling is presented. Detailed analysis of all the elements which influenced the failure was carried out, namely: the position and the place of all failures are determined and all fracture surfaces are described; the rolling forces are determined by analytical and experimental methods; numerical analysis of the local stresses due to rolling forces is performed with finite element method; stress time history of the individual local stress and stress spectrum are obtained from service loads; properties of the roll material (strength, hardness, toughness and ductility) is determined by experimental testing. Based on the results of investigation, main causes of failures are presented.

The failure analysis of two slipper couplings showed that both couplings fractured as a result of fatigue. In both cases, the fracture started in the corner between the paddle and the coupling body and propagated around the corner. Both fractures were caused by the deficient design of the fillet between the paddle and the coupling body with high stress concentration. In order to extend actual service life, three design modifications were considered. Numerical analysis showed that the redesign of the coupling with stiffener between the paddle and the coupling body reduced maximum local and actual service life of couplings and can be improved from finite to infinite.

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