Abstract:  Based on the experimental observations of the high-speed turning for medium carbon steel‚the forming courses and characteristics of the microtopography and microstructure of the workpiece surface were analyzed．The re-sults show that the cutting speed and material hardness are the main factors affecting the material deformation in the high-speed cutting process‚and the cutting heat makes the material in the cutting zone soften as well as causes particu-lar furrows and side flow on the workpiece surface．It is also shown that there exist a second quenching and tempering due to the high cutting temperature‚thus causing the change of the micro-hardness and the appearance of a hard and fragile white-layer contexture on the workpiece surface．The motion between the cutting tool and the workpiece‚along with the cutting heat greatly affects the formation of the machined surface profile‚that is‚with the increasing of cutting parameters‚the cutting heat and the friction heat increase‚thus forming the particular microtopography and microstruc-ture of the workpiece surface machined with high-speed turning．

Key words:  high-speed turning, surface quality, microtopography, microstructure, feed movement