and H2), humidity (dew point) and temperature (540 °C), since the quality and thickness of Fe3O4 film are strongly related to these parameters [5]. Nevertheless, bluing is enough to provide some rust protection, burr reduction and electrical insulation between laminates. Due to cast process of small and low cost rotors, the cage aluminum and rotor laminate steel are in direct electrical contact. Therefore, the bluing film, also found in the internal surface of rotor slots, contributes to reduce this electric contact or increase the inter-bar resistance. However, even with this coating, some currents flowing in rotor bars do not reach the end rings and flow amongst rotor bars, through rotor teeth steel. These inter-bar currents are, induced by stator fundamental m.m.f. wave and its harmonics, affecting negatively the motor torque-speed curve and efficiency (increasing the stray-load loss) [4][6]. For the torque-speed curve, the most noticeable influence is the reduction of maximum torque, which decreases as the cross-resistance decreases. To evaluate the influence of inter-bar resistance in the motor performance, tests were, carried out with rotor cages produced with semi-processed electrical steel having different coatings (zinc phosphate, manganese phosphate, thin and thick Fe3O4 films). All rotors used in this analysis were, fabricated by highpressure die-casting process and tested in dynamometer before and after the rotor annealing. The use of zinc and manganese as coating is not new. Zinc and manganese phosphates are, extensively used to improve corrosion resistance of finished products ranging from structural steelworks for buildings and bridges to tubes and screws [8]. However, its application as coating of electrical steels is not usual and was chosen due to its electrical insulation characteristics and availability for tests.