The HT 80 steel welds have been investigated by means of welded and surface notched wide plate specimens. Effects of the plate thickness on the fracture characteristics were clarified through this series of experiments. Then, it was shown that the plane-strain stress intensity factor K _IC would be calculated with help of exprimental formula, after K _C at onset of unstable crack growth was obtained. In this experiment, it has also been shown that the high tensile strength steels with large plate thickness will have considerably superior fracture characteristics. Furthermore, investigations have been conducted to determin the correlation between K _IC and the results of standard Charpy impact test in the transition-temperature range to assist both the materials engineer and the structural designer. The results showed that the satisfactory correlations do exist between K _IC and the absorbed energy in Vee notch Charpy test for the weld fusion line of HT 60 and HT 80 steels. One of the correlations is shown in next equation. ( K _IC/100) ²= 300 (_v E /σ_y)