<p>This paper relates to the issue of ductile fracture in forming processes. Particular emphasis is put on the problem of crack formation induced by the Mannesmann effect. For the accurate modelling of material fracture in cross wedge rolling (CWR), a new calibration test is proposed, which involves rotary compression (RC) of a tapered specimen. The new calibration test and failure criteria developed by Oyane, Cockcroft and Latham, as well as Rice and Tracey are used to determine the critical damage values for C45 steel subjected to forming in the temperature range 950–1150&#xa0;°C. Given the differences in stresses in the CWR process and the RC test, the critical damage values are calibrated by modelling material fracture in CWR. The effectiveness of the proposed fracture modelling method is validated by experiments in which the CWR process is conducted with variable parameters. The numerical results are also used to determine the effect of crack formation in the axial zone of the workpiece on the state of stress.</p>