In this study, machining tests have been performed by means of machining method so that effects of changes in microstructure and mechanic features of hot rolled aisi 5140 steel of which microstructures and mechanic features were changed by heat treatment on tool wearing and cutting forces will be examined. The tests were carried out with four different cutting speeds (90-110-130-150 m/min.), development of 0.1mm/rev and cutting depth of 1mm under dry cutting conditions. During tests, it has generally been observed that cutting forces are obviously decreased while cutting speeds are increasing. The highest cutting force (593.78 N) has been obtained in the result of processing the sample which was hardened in oil having 755 degrees C temperature was machined in cutting speed of 90 m/min. It has been thought that max. hardness and strength of this sample resulted in highest cutting force. It has been observed that apparent tool wearing occurred in materials of which hardness is relatively high.