In this study, the performance of cryogenically treated tungsten carbide inserts in the milling of Hadfield steel (X120Mn12) was evaluated in terms of surface roughness (Ra) and tool wear (VB). Cutting tools were assessed under three conditions: untreated (U), cryogenic treated (CT) and cryo-tempered (CTT). For the cutting parameters, three different cutting speeds (70, 100 and 130 m.min(-1)) and feed rates (0.08, 0.14 and 0.2 mm.rev(-1)) were used. The experiments were carried out under a fixed depth of cut and dry cutting conditions. To determine the factorial effects, the procedure Taguchi L27 (33) was used. For the estimation of Ra and VB, the response surface method (RSM) was employed and mathematical models were developed. In terms of Ra, the effective parameter was feed rate (89.45 %) and in terms of VB, it was the cutting speed (60.42 %). For Ra and VB, the optimum levels of factors were determined as A3B3C1 and A3B1C1, respectively. The effects of the factors were also assessed by RSM.