[en] Among the existing approaches approaches to predict J_c, in the transition region of the ferritic steels, there are statistical and deterministic methods. Among the formers we have the methodology based on the two-parameter J-Q theory and the weakest-link concept with its characteristic distance, r_wl. For this work, an experimental program was developed using 65 fracture mechanics specimens made from an A508 steel, in three geometries with thickness B < 1T = 25.4 mm, and tested at four transition temperatures. After the tests to measure J_c, all specimen fracture surfaces were observed by scanning electron microscopy to identify the cleavage trigger points (weak-links) and to measure their characteristic distances r_wl to the crap tip. The J_c and r_wl values were presented and compared with the theoretical ones. (author)