Establishing the cause of failure in continuous casting rolls.

• Failure analysis of continuous casting rolls is methodically studied. • Microstructural evolution during service exposure of rolls is investigated. • The correlations between the microstructure and observed failure are discussed. • The failure is related to the formation of sigma phase in the microstructure. This paper investigates failure of repair welded continuous casting rolls. Observed failures are in the form of localized corrosion, initiated at boundaries between two welding passes. Defects were categorized into three typical damages: zebra lines, partially interconnected zebra lines, and fully connected zebra lines. In some cases, star like features were also distributed on the surface of the roll. Optical microscope, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to characterize microstructure of failed rolls. Damage is appeared to be initiated from elongated greyish phases, which are rich in Cr. These phases are at intermediate states between delta ferrites and sigma phase. Cr enrichment of delta ferrite during service is associated with Cr depletion of the matrix and this in turn makes these phases susceptible to the initiation of corrosion. [ABSTRACT FROM AUTHOR]