Premature Failure Analysis of the High-Speed Steel Work Roll of Hot Strip Mill

Failure analysis was performed on a prematurely failed high-speed steel work roll of a hot strip mill in an integrated steel plant to identify the root cause of failure. Visual observation of the fractured surface revealed that the surface was rough and spalled with no indication of fatigue marks. Microstructure investigation was conducted using an optical microscope and scanning electron microscope (SEM) with energy dispersive x-ray spectroscopy (EDS). The microstructure of the roll comprises MC, M₂C and M₂₃C₆ carbides in a martensitic matrix. Acicular-shaped, coarse M₂C carbides were distributed along the cell boundaries in the microstructure and these carbides escalate the sensitivity for crack propagation and decrease the spalling resistance of work roll during service. X-ray diffraction analysis of failed sample also confirmed the presence of M₂C carbides. The microstructure constituents of the failed work roll were compared with the equilibrium solidification diagram generated from the chemical composition by JMat Pro. It is recommended from this study that the precipitation of coarse intercellular M₂C carbides in high-speed steel work roll should be controlled by modifying the chemical composition and optimising the solidification/cooling rate.