The machinebilities of 1050, 4140 and 8620 steels related to changing microstructures and mechanical properties before and after the heat treatment

THE MACHINABILITTES OF 1050, 4140 AND 8620 STEELS RELATED TO CHANGING MICROSTRUCTURES AND MECHANICAL PROPERTIES BEFORE AND AFTER THE HEAT TREATMENT Ph.D Thesis Yusuf ÖZÇATALBAŞ GAZI UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY September 1996 ABSTRACT In this study, the machinabilities of 1050, 4140 and 8620 rolled steels have been investigated related to changing microstructures and mechanical properties before and after full annealing and normalizing heat treatments. In laboratory tests, while the cutting forces have been measured by a shope made strain gauge dynamometer for lathe work on one hand, one the other hand, the morphologies of chip roots have been studied by using a quick stop device. For these three types of steels the maximum tool life has been observed at as rolled state. However, it has been observed that the tool life for full annealed 4140 steel has been increased when the cutting speed is over 200 m/min. The least surface roughness has been obtained for 1050 and 4140 steels at their as rolled state and for 8620 after normalizing. All samples with full annealed condition exhibited the tendency of decreasing the cutting forces (Fcand Ff). The minimum built-up edge width on normalized 1050 steel has been up to 35 m/min and on the rolled 4140 and 8620 steels up to 13 m/min and 72 m/min cutting speeds respectively. In all three samples, full annealing process increased the tendency of having built-up edge and increasing built-up edge width increased the surface roughness. Keywords: Machinability, Mechanical Properties, Tool Life, Cutting Forces, Surface Roughness, Chip Roots Morphology Science Code: 225.01.00.225.01.01 Number of Pages: 184 Thesis Supervisor: Prof.Dr. Fevzi ERCAN