In rod (or bar) rolling process, the roll surface is not flat for the groove on the roll, so the roll radius is not constant along the roll axis direction. In this paper, a suitable spread formula was determined to calculate the maximum spread of alloyed steel, then the surface profile of outgoing workpiece and the critical point on the contact boundary has been predicted. Furthermore, the formula of the equivalent contact section area has been proposed and the mean roll radius has been obtained.
The validity of the new model has been examined by the bar rolling experiment and the rigid-plastic FEM simulation. Compared with the existing models, the mean roll radius obtained by the new analytical model approach the experiment data more closer than other models. So, it can be used as a available reference in practice and the theoretical derivation.