This paper presents a procedure to characterize deformation behavior applicable to various engineering materials in machining processes. Orthogonal machining tests are used to obtain the relationship between shear stress, strain, strain rate and temperature. Shear plane temperature is measured by an infrared thermal imaging system and compared with the Loewen and Shaw model. A new procedure to determine strain rate in the shear zone is proposed based on a triangular shear zone model and grain boundary determined by optical microscopy. Finally, a constitutive model for a low carbon steel, determined by the procedure, is presented and compared with existing results.