Metallurgical investigation on fatigue failure of stainless steel chain in a continuous casting machine

Stainless steels strips (chains) are used for the connection of dam blocks in belt casting machines. Thermal cycling and repetitive stressing under complex loading conditions due to tension and bending are the most frequent function modes during production. Samples from fractured stainless steel strips used for the connection of dam blocks in a copper rod continuous casting line, were sent for failure investigation. Optical and scanning electron microscopy for structural and fractographic evaluation along with mechanical testing are used as the principal analytical techniques in the context of the present investigation. Failure analysis findings suggest strongly that the failure was caused by bending fatigue which assisted also by thermal cycling, initiated from the strip surface and followed by ductile final overload fracture. Final fracture occurred via ductile failure, when the remaining strip cross sectional area reaches a critical size, becoming unable to sustain the operating load. Review of the service history (operating conditions, e.g. process design, applied loads, thermal cycles), in combination to the examination of a potential substitution of the material to a more heat (and fatigue) resistant one are suggested as further fatigue damage preventive actions.