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The Weibull stress model and variations thereof have been used extensively topredict the probability of cleavage fracture in steels in the ductile-brittle transitionregion [1-7]. The standard Weibull stress model is based on a weakest-linkassumption. While the weakest-link model characterizes cleavage fractureinitiation, it does not account for the possibility of crack arrest in the presence of asteep stress gradient, such as occurs in front of a crack. Cleavage may initiate at atrigger near the crack tip and subsequently arrest because the crack driving forceis insufficient for propagation. This results in a minimum toughness, Kmin, belowwhich cleavage propagation is not possible.