Study on Wear Performance of Cermet Tools in Cutting Hard Materials

1 Introduction With the development of the machinery industry, many difficult-to-machine materials (such as chilled cast iron, hardened steel, stainless steel, titanium alloy, etc.) have become increasingly widespread. 1Cr18Ni9Ti stainless steel belongs to austenitic stainless steel and has poor thermal conductivity and toughness and is difficult to process. The content of Cr and Ni in the stainless steel is high. Although Cr can improve the strength and toughness of the stainless steel, it increases the adhesion tendency of the stainless steel and the cutter; Ni can play a role in stabilizing the austenite structure, but the austenite has a large plasticity. , It will easily cause work hardening. Tungsten-cobalt (YG8, etc.) hard alloy cutting tools are generally used in actual production, but the machining effect is not very satisfactory. The C in chilled cast iron mainly exists in the form of Fe3C and other carbides, and a considerable part is distributed in the steel matrix in the form of hard spots. Therefore, the chilled cast iron has high hardness and good wear resistance and is difficult to cut. During cutting, the peeling of hard spots will cause the cutting force to fluctuate, affecting the cutting stability, making the tool easier to chip and reducing the service life. Therefore, so far there is no ideal method for cutting chilled cast iron in China. Ti(C,N)-based cermets are widely used as tool materials because of their excellent comprehensive properties such as high hardness, good wear resistance, and good thermal conductivity. In this paper, through the cutting test, the cutting performance of the TiC-based cermet tools modified with nano-TiN in the machining of hard-to-cut materials such as chilled cast iron and stainless steel was studied. Compared with YG8 cemented carbide tools, the tool was used to broaden the cermet tools. The scope of application provides the test basis for its use in the machining of hard-to-machine materials. 2 Test Methods The material composition of the Cermet Insert (Model SNUN150406) was 54TiC-10TiN (nanopow)-15Mo-20Ni-1C. TiN nanopowder is produced by Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, and has a particle size of 30 to 50 nm. When preparing, first use ZB220-T ultrasonic instrument to disperse the TiN nanometer powder, mix and then add proper amount of anhydrous ethanol and ball mill for 24 hours; after the mixture is dried, add PVA to granulate, then press molding under 170MPa pressure; Finally, it was sintered in vacuum at a temperature of 1400° C. for 1 hour. The cutting test was performed on a 6140 machine tool. The workpieces to be processed are Ø183 mm chilled cast iron rolls (hardness >50HRC) and Ø80mm austenitic stainless steel rods (1Cr18Ni9Ti). The tool mounting angle is a0=9°, g0=-8°, kr=90°, kr'=30°. The YG8 cemented carbide insert (manufactured by Zhuzhou Cemented Carbide Factory) has the same type and cutting parameters (cutting speed vc, feed f, and depth a) as the cermet insert. After cutting, the flank wear amount VB of the tool was measured under a 40-times tool microscope and the wear pattern was observed. The microstructure of the cermet cutting tool was observed with a HITACHIX-650 scanning electron microscope and an H-800 transmission electron microscope.

(a) SEM morphology (×3000)

(b) TEM morphology (×20000)

Fig. 1 The microstructure of a cermet cutting tool

(f=0.08mm/r, ap=2mm, vc=7.5m/min)
Figure 2 Wear curves of cermet and YG8 cutting chilled cast iron

(f=0.1mm/r, ap=0.4mm, vc=60m/min)
Figure 3 Wear curves of cermet and YG8 cutting stainless steel

3 Test results and analysis Microstructure of the cermet cutting tool The microstructure of the cermet cutting tool is shown in Fig. 1. It can be seen from the figure that the cermet structure consists of a ceramic phase and a metal phase (Fig. 1a); the coarser ceramic phase presents a core/shell structure (Fig. 1b), the core component is a Ti(C,N) solid solution, and the shell component is mainly composed of It is (Ti,Mo,W)(C,N) solid solution. Compared with the microstructure of the traditional Ti(C,N)-based cermets, the effect of adding nano-TiN to TiC-based cermets is more significant than that of micron-TiNs. Comparison of cutting performance of cermet cutting tools and YG8 cutting tools Comparison of tool wear curves when cutting chilled cast iron with cermet cutting tools and YG8 hard alloy cutting chilled cast iron is shown in Fig. 2. As can be seen from the figure, the cutting performance of the cermet cutting tool is quite different from that of the YG8 hard alloy tool. The initial wear of the cermet cutting tool is very fast. The wear amount VB reaches 0.4 mm in less than three minutes, but the wear rate is decreased after that. , but still faster, and there is almost no stable wear period, and the final tool chipping failure. Cutting tests were carried out under other cutting conditions. It was found that the cutting life (t) of the cermet cutting tool was low (up to several minutes) and the failure mode was generally a chipping or micro-disintegration. It can be seen that the cermet tool is not suitable for cutting chilled cast iron. This is mainly due to the low bending strength and fatigue resistance of the cermet. The fluctuating cutting force and cutting force of the cermet cutting are large, so the cermet cutting tool Easy chipping failure. The YG8 carbide tool has high strength, good toughness, and good resistance to mechanical fatigue. The tool life is longer when cutting chilled cast iron. In addition, when cutting chilled cast iron, tool geometry is also an important factor affecting tool life. In order to reduce the chip deformation and cutting force, generally smaller rake angles and relief angles are required. In order not to reduce the blade edge strength, it is necessary to round or grind the edge of the blade and grind out the negative chamfer and eliminate the blade edge defect by grinding. The wear curve of cutting stainless steel with a cermet tool and a YG8 carbide tool cutting 1Cr18Ni9Ti stainless steel is shown in FIG. 3 . As can be seen from the figure, the cutting performance of the cermet cutting tool is better than that of the YG8 carbide cutting tool, and its life span is more than three times that of the YG8 cutting tool. This is mainly due to the excellent comprehensive mechanical properties and thermal conductivity of the cermet material and its anti-adhesive property. Good for excellent physical properties [6]. The surface quality of workpieces processed with cermet tools is also better than that of YG8 tools. Therefore, it can be seen that the cermet tool is more suitable for semi-finishing and finishing of stainless steel. When processing stainless steel materials, in order to ensure the smooth cutting process and obtain a higher tool life and workpiece surface quality, the following points should be noted: 1 should be used larger rake angle and smaller lead angle to reduce the cutting force, so that Cutting is lighter; 2 Grind the front and back of the tool carefully to obtain a higher surface finish to avoid sticking to the workpiece during cutting; 3 Use a high cutting speed or very low cutting speed; 4 Stainless steel swarf Strong toughness, it should take appropriate effective measures for chip breaking, chipping and chip removal; 5 stainless steel material has poor thermal conductivity, large linear expansion coefficient, easy to produce thermal deformation under the local high temperature cutting area, easy finishing Affects the dimensional accuracy, so the tool with better thermal conductivity should be used; 6 The stiffness of the machine tool-tooling system should be improved as much as possible. 4 Conclusion Because the cermet cutting tools have low bending strength and fatigue resistance, the cutting force and cutting force fluctuate greatly during the cutting of chilled cast iron, so the tool life is low and it often fails in the form of chipping and micro collapse. The YG8 carbide tool life is relatively high. Because the cermet tool has excellent comprehensive mechanical properties and physical properties, the tool life of the 1Cr18Ni9Ti stainless steel is much longer than that of the YG8 carbide tool.

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