Investigation of machnability and chip morphology of AISI 1050 steel turned with cryogenically heat-treated and untreated cutting inserts

Cryogenic process (C.P.) is a type of heat treatment that allows the material to gain metallurgical and micro-structural properties by cooling the material at very low temperatures below zero degrees. This heat treatment provides positive contributions to the structure of the material by creating improvements in the mechanical structure of the material such as removing residual and internal tensions, increasing toughness, increasing wear and fatigue strength. Cryogenic process, besides being applied to materials, is also applied to cutting tools, improving the properties of cutting tools such as wear resistance, hardness, toughness and thermal conductivity. In this experimental study carried out for this purpose, cryogenic heat treatment applied to CVD coated carbide cutting tools due to these properties that cryogenic process brings to the cutting tools. In this target, deep C.P applied to cutting tools was applied for 24 hours at -146 0C. Then, these cutting tools were brought to room temperature and tempered twice at 200 °C for 2 hours each. Turning experiments was carried out by C.P and untreated cutting tools with four different cutting speeds (180, 200, 220 and 240 m/min) three different feed rates (0.1, 0.2 and 0.3 mm/rev) and 2 mm constant depth of cut under dry cutting conditions. AISI 1050 steel has been chosen as the workpiece material. The cutting forces obtained during the turning of AISI 1050 steel, with cutting tools on which treated and untreated were measured with the help of a KISTLER brand dynamometer. Surface roughness values were obtained by measuring surface roughness from 3 different surfaces of the machined workpiece. Then, the values of average surface roughness were calculated by taking the arithmetic mean of these three values. After processing experiments, SEM imaging device was used to determine the wear conditions of applied and unapplied cutting tools and the morphology of the chips formed during the cutting process. As a result of the experiments carried out, the lowest cutting force has been obtained with cryogenically heat treated cutting inserts from 240 m/min cutting speed and 0.1 mm/min feed. The lowest surface roughness value has been observed with CHT Cutting insert at 180 m/min cutting speed and 0.1 mm/rev feed. As a result, while comparing CHT cutting insert with untreated cutting insert, less tool wear, lower cutting forces and lower surface roughness values have observed with CHT inserts. In addition, in terms of chip morphology, when SEM images are compared, It was determined that the chips obtained from CHT cutting tools formed smaller serration shapes.