The mechanical properties of sixteen back-up roll materials produced by various practices were investigated to assess their spalling resistance in service. Axial fatuigue tests showed that most rolls had adequate fatigue endurance limits to resist fatigue initiation by the cyclic shear stress even under relatively high mill loads. The rate of fatigue crack growth, which varied by a factor of 7 among the rolls evaluated, correlated primarily iwth the hardness and fracture toughness properties of the roll material. A stress model describing the cyclic propagation of a circumferential fatigue band leading to a spall is discussed. The forged rolls with similar chemical compositon and heat treatment as the cast rolls had generally higher fatigue endurance limits, but similar tensile strength, fracture toughness, and fatigue crack growth properties.
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