Size dependence at the beginning of the upper shelf for ferritic steels

The determination of a value for the fracture toughness of ferritic steels in the ductile-brittle transition is difficult due to the scattered results. When the test temperature increases, the ductile mechanisms become more active and in some cases no cleavage is observed. Close to the upper shelf, and contrary to what happens when only cleavage occurs, as the temperature increases scattering decreases, depending on the size: greater scattering is observed for greater thicknesses than for smaller test pieces. The start of the ductile behavior occurs at lower temperatures in smaller pieces, with a temperature at the start of the upper shelf dependent on size. This work presents an interpretation of the phenomena that occur between the start of the upper shelf and the high transition zone, with an explanation for the difference in scattering and toughness for difference test piece sizes, and also showing that the start of the upper shelf depends on the size of the piece