The investigation of the effects of cryogenic treatment applied to cutting tools on tool life in machining AISI 316 austenitic stainless steel

In this study, the effects of the duration of cryogenic treatment applied to cutting tools on tool life in machining of AISI 316 austenitic stainless steel have been investigated. The uncoated cutting tool, TiCN, TiAlN and TiCN/Al2O3/TiN coated tungsten carbide tools were used. The cutting tools were subjected to deep cryogenic processing for five different durations namely 12, 24, 36, 48, and 60 hours at -145ºC. Machinability tests were carried on a CNC lathe with dry machining conditions and tool wear, cutting forces and surface roughness were investigated. The depth of cut was kept constant in all experiments (2.4 mm) and three different feed rates (0.15, 0.3 and 0.45 mm/rev) were used. The cutting speeds, for the uncoated and TiCN coated tools 100, 120, 140 and 160 m/min and for TiAlN ve TiCN/Al2O3/TiN coated tools 120, 160, 200 ve 240 m/min were used. In all machining experiments flank wear and crater wear were observed. The analysis of the microstructure and measurements of the microhardness of cutting tools were also carried out. As a result of the hardness measurements it was determined that the cryogenic process provides an increase in micro-hardness of the cutting tool and the highest increase was obtained with 24 hours duration of the cryogenic treatment. The machining experiments were carried out at 0.3 mm/rev feed rate and four different cutting speeds (100, 120, 140 ve 160 m/min) in order to determine the optimum duration of cryogenic treatment and Kİ24 tool exhibited the best wear resistance and surface roughness among the tools that cryogenic treatment was applied at five different durations. In the cutting forces, Kİ24 exhibited the highest cutting forces and the lowest cutting forces were measured with the untreated tool. According to these data, the optimum duration of the cryogenic treatment was determined as 24 hours for tungsten carbide cutting tools used in this the study. The machining experiments were carried out with only the 24 hours cryogenic treated and untreated tools using 0.15 mm/rev and 0.45 mm/rev feed rate and four different cutting speeds. In all experiments, the cryogenic treated tools exhibited lower wear rates and surface roughness. Cutting forces of cryogenic treated coated tools were slightly lower than the cryogenic treated uncoated tools.