Values of the crack tip opening stretch (COS), the stress intensity factor, Keff, and the energy integral J were determined for 22 Ni Mo Cr 3 7 steel at room temperature. A material-dependent linear relationship between COS and J resulted. The critical values of COS and J determined for the onset of stable crack growth using the electrical potential method and the interrupted loading procedure were independent of specimen type and crack length for thicknesses smaller than 30 mm. A dependence on crack length, although accompanied by large scatter, was indicated for 75-mm-thick specimens with an instability type of fracture behavior.