of brittle phase such as cementite. The reason has been, however, not clarified completely. Particularly, it has been
difficult to quantitatively predict the fracture toughness based on only information of microstructures.
The cleavage fracture of steel is generally interpreted by the weakest-link mechanism differently from the
yielding and the work hardening. Scatter is thus found in fracture toughness as its essential feature. This is a
principal reason of the difficulty to quantify the influence of microstructures on fracture toughness. A formulation to
evaluate the variation of fracture toughness was proposed by Beremin (1984) based on the weakest-link theory. We
c
an find its effectiveness on quantitative evaluation of fracture toughness including its scatter. However, this model
is not able to clarify the relationship between the f
racture toughness and microstructures.
In the present paper, we propose a model to quantitatively predict th
e influence of microstructures on the fracture
toughness of ferrite-cementite steels, based on the formulation of the cleavage fracture initiation process.