| The main objective of the present study is to clarify the microstructural factors such as tempered martensite matrix, coarse primary carbides, eutectic structures, and fine secondary carbides, which influence fracture properties of high speed steel (HSS) rolls. Three HSS rolls with different Cr content were manufactured by a centrifugal casting method, and the microstructures of their shell regions were investigated quantitatively. MC type primary carbides, together with eutectic ledeburite structures, were observed in the intercellular regions. The observation of fracture processes indicated that these primary carbides cleaved first to form microcracks at very low stress levels. These microcracks were easily propagated along the intercellular networks, leading to predominantly cleavage mode of fracture on fracture surfaces. To improve microstructures for use in the HSS rolls, therefore, it is suggested that the cell size must be minimized to achieve the homogeneous distribution of primary carbides |
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