Milling hardened steels has emerged as a key technology in mold and die manufacturing industries. In cutting, a portion of work material is pushed upward by the tool rake face to form the chip while the other portion below this layer is ploughed under the cutting edge to become the machined surface. Although the ploughed material is a very small fraction of the uncut chip thickness, it determines surface integrity after machining. In this study, a 3D finite element simulation model of milling hardened AISI H13 tool steel (HRC 50) has been developed to study material deformation under the cutting edge of a milling insert. The ploughed depth in the range of 0.6 μm to 3.0 μm is used to study the material flow under the cutting edge. Friction between the cutting edge and workpiece surface has a significant influence on the ploughed depth. Different coefficients of friction are used to study their effects on stresses/strains and temperature during ploughing. The Johnson-Cook model is used to model the plastic behavior of workpiece material. The 3D finite element analysis gives an insight into some key issues in a milling process. The FEA model illustrates the effects of micro cutting edge geometry on pile-up in front of the cutting edge, transient stresses and temperatures, and a transition from ploughing to cutting in a milling process.