In modern machining, cemented carbide and high-speed steel are the most used tool materials, accounting for almost half of each. The invention and application of high-speed steel has a history of a whole century, and cemented carbide has been around for half a century. However, both have developed many new varieties, and their performance is constantly improving, which plays an important role in machining. cemented carbide with rare earth elements is one of the new varieties of tool materials. Rare earth elements refer to atomic numbers 57~71 (from La to Lu) in the periodic table of chemistry, plus 21 and 39 (Sc and Y), a total of 17 elements. Adding certain rare earth elements to traditional cemented carbide grades in a certain way can effectively improve their mechanical properties and cutting properties. our country is rich in rare earth element resources, and the research and development of rare earth cemented carbide is ahead of other countries. The following grades of rare earth cemented carbide for tools have been developed: YG8R (equivalent to ISOK30 grade), YG6R (K20), YW1R (M10), YW2R (M20), YT5R, YT14R (P20), YT15R (P10), YS25R (P25). There are also mines and geological tools grades YG11CR. The authors systematically study the cutting properties of P, M and K rare earth cemented carbides, and discuss their cutting mechanisms.

　　Mechanical and physical properties of rare earth cemented carbide

　　After adding rare earth elements such as Ce and Y to YG8, YT14 and YW1 cemented carbide, rare earth cemented carbide YG8R, YT14R and YW1R are formed. YG8R is mainly used for roughing cast iron and non-ferrous metals; YT14R is mainly used for semi-finishing steel processing; YW1R is a general grade that can be used for semi-finishing of various workpiece materials.

　　After testing, the structure of cemented carbide is relatively dense after the addition of rare earth elements. Room temperature hardness and high temperature hardness have improved; The fracture toughness and flexural strength are significantly improved, increasing by more than 20% and 10%, respectively.

　　Wear resistance and service life test of rare earth cemented carbide

　　Through experiments, we know that compared with the original blades without rare earth elements, the wear resistance and service life of YG8R, YT14R and YW1R blades have been improved to varying degrees.

　　We also carried out impact resistance tests of rare earth cemented carbide, using YG8R, YT14R, YW1R and other cemented carbide inserts with rare earth elements, and YG8, YT14, YW1 inserts without rare earth elements, turning spline shaft steel parts, and the tip of the knife was impacted until the tip was broken. After many repeated tests, the number of impacts that YG8R, YT14R and YW1R blades can withstand before the tip is damaged is more than 1~2 times higher than that of YG8, YT14 and YW1 blades, respectively.

　　Cutting force test of rare earth cemented carbide

　　Turning 45# steel (HB200) with cemented carbide inserts YT14R and YW1R with rare earth elements is compared with YT14 and YW1 inserts. Use a three-way resistive force gauge to measure and record the three-way cutting force: main cutting force Fc, cutting force Fp in the depth of cutting direction, and cutting force Ff in the feed direction. In the case of changing the cutting parameters many times, the statistical results are as follows: the Fc of YT14R and YW1R inserts is about 5% lower than that of YT14 and YW1 inserts, respectively, while their Fp and Ff are reduced by more than 10%~15% compared with YT14 and YW1 inserts.

　　The test formula for the main cutting force is:

　　YT14R车削45#钢Fc=2059ap0.89f0.84N

　　YT14车削45#钢Fc=2104ap0.86f0.80N

　　YW1R车削45#钢Fc=1771ap0.98f0.79N

　　YW1车削45#钢Fc=2196ap1f0.87N

　　Cutting mechanism

　　Rare earth elements exist in (W,Ti)C or (W,Ti,Ta,Nb)C solid solutions, which can strengthen the hard phase; It can also inhibit the uneven growth of WC grains, make them tend to be uniform, and the average grain size is reduced. A small amount of rare earth elements are also solid dissolved in the bonded phase Co, which strengthens the bonding phase. Rare earth elements are enriched at the phase interface of WC/Co and between the (W,Ti)C/(W,Ti)C phase interfaces, and are often combined with impurities S and O to form RE2O2S and other compounds, which improves the cleanliness of the interface and improves the wettability of the hard phase and the bonded phase. As a result, the impact toughness, flexural strength and impact resistance of rare earth cemented carbide during operation are significantly improved. Its hardness, wear resistance, and resistance to diffusion and oxidation on the surface of the tool are also improved.

　　After electron microscopy testing, it was also found that the surface of rare earth cemented carbide inserts is rich in cobalt during cutting, so it can reduce the friction coefficient between chips, workpieces and tools, so as to reduce the cutting force.

　　Rare earth elements are rich in nature and not expensive, and their addition to cemented carbide can significantly improve the mechanical, physical properties and use performance, so they have broad application prospects.

　　Application examples

　　1. Beijing Construction Machinery Factory uses YT14R and YT14 cemented carbide turning 45# steel shaft (quenched and tempered, hardness HB250), cutting speed v=60m/min, cutting depth ap=0.5mm, feed f=0.51mm/r. The service life of YT14R is 2 times higher than that of YT14, and the quality of the processed surface is slightly improved

　　2. Beijing Internal Combustion Engine General Factory uses YT14R and YT14 cemented carbide tools to turn 45# camshafts (quenched and tempered, HRC28~32), v=92m/min, ap=3mm, f=0.6mm/r. YT14R can process an average of 80~100 pieces, while YT14 can only process 40~50 pieces. And the YT14R has less knife phenomenon than YT14.

　　3. YW1R and YW1 carbide turned 45# camshaft (quenched and tempered, HRC28~32) for Beijing Internal Combustion Engine General Plant, v=92m/min, ap=3mm, f=0.6mm/r. YW1R can process an average of 60~70 pieces without knife punching, while YW1 can only process 30~32 pieces, and sometimes punch.

　　4. The 502nd Research Institute of the Fifth Academy of China Aerospace Industry Corporation uses YW1R and YW1 tools to turn stainless steel 1Cr18Ni9Ti (tensile strength sb=0.55GPa) and superalloy GH3128 (sb=0.84GPa), v=30~60m/min, ap=0.7~1.5mm, f=0.08mm/r. The service life of YW1R is more than twice that of YW1, and the machining surface roughness of YW1 is Ra=3.2mm, and YW1R is Ra=1.6mm.

　　5. YG8R and YG8 carbide turned gray cast iron HT200 (hardness HB170~180) for Beijing No. 1 Machine Tool Factory, v=80m/min, ap=2mm, f=0.3mm/r. The service life of YG8R is 1.5~2 times that of YG8, and the impact resistance is improved.