In modern machining, cemented carbide and high-speed steel are the most used cutting tool materials, accounting for almost half of each. The invention and application of high-speed steel has a history of a whole century, while cemented carbide has a history of half a century. However, both of them have developed many new varieties, and their performance has been improved continuously, which plays an important role in machining. Cemented carbide with rare earth elements is one of the new cutting tool materials. Rare earth elements refer to 17 elements in the periodic table with atomic numbers of 57-71 (from LA to Lu), plus 21 and 39 (SC and y). The mechanical and cutting properties of some rare earth elements can be effectively improved by adding them to the traditional cemented carbide grades in a certain way. China is rich in rare earth resources, and its research and development of rare earth cemented carbide is ahead of other countries. Rare earth cemented carbides of the following grades have been developed: yg8r (equivalent to isok30), yg6r (K20), yw1r (M10), yw2r (M20), yt5r, yt14r (P20), yt15r (P10), ys25r (P25). There are also mine and geological tool brand yg11cr. The cutting properties of the above-mentioned P, m and K rare earth cemented carbides are systematically studied and their cutting mechanism is discussed.
Mechanical and physical properties of rare earth cemented carbide
After adding CE, y and other rare earth elements to YG8, YT14 and yw1 cemented carbides, yg8r, yt14r and yw1r are formed. Yg8r is mainly used for roughing of cast iron and non-ferrous metals; yt14r is mainly used for semi finishing of steel; yw1r is a general brand, which can be used for semi finishing of various workpiece materials.
After testing, the structure of the cemented carbide is relatively compact after adding rare earth elements; the hardness at room temperature and high temperature is improved; the fracture toughness and bending strength are significantly increased by 20% and 10% respectively.
Wear resistance and service life test of rare earth cemented carbide
Through the test, we know that the wear resistance and service life of yg8r, yt14r and yw1r blades are improved in different degrees compared with the original blades without rare earth elements.
We also carried out the impact test of rare earth cemented carbide, using yg8r, yt14r, yw1r and other cemented carbide blades with rare earth elements, and YG8, YT14, yw1 blades without rare earth elements, turning spline shaft steel, the tool tip was impacted until the tool tip was damaged. After repeated tests, the impact times of yg8r, yt14r and yw1r blades were 1-2 times higher than those of YG8, YT14 and yw1 blades before the tip was damaged.
Cutting force test of rare earth cemented carbide
45 × steel (hb200) was turned with yt14r and yw1r cemented carbide blades added with rare earth elements, compared with YT14 and yw1 blades. The three-way cutting force is measured and recorded with a three-way resistance force measuring instrument: the main cutting force FC, the cutting force FP in the cutting depth direction and the cutting force FF in the feed direction. In the case of changing cutting parameters for many times, the statistical results are as follows: FC of yt14r and yw1r blades is reduced by about 5% compared with that of YT14 and yw1 blades respectively, while their FP and FF are reduced by more than 10% ~ 15% compared with that of YT14 and yw1 blades.
The test formula of the main cutting force is:
Yt14r turning 45 × steel FC = 2059ap0.89f0.84n
YT14 turning 45 × steel FC = 2104ap0.86f0.80n
Yw1r turning 45 × steel FC = 1771ap0.98f0.79n
Yw1 turning 45 × steel FC = 2196ap1f0.87n
Rare earth elements exist in (W, Ti) C or (W, Ti, Ta, Nb) C solid solution, which can strengthen the hard phase, inhibit the uneven growth of WC grains, make them tend to be uniform, and reduce the average grain size. A small amount of rare earth elements are also dissolved in the bonding phase Co, so that the bonding phase is strengthened. Rare earth elements are concentrated at the interface of WC / CO and the interface of (W, Ti) C / (W, Ti) C. they are often combined with impurities such as s and O to form re2o2s and other compounds, which improves the cleanness of the interface and the wettability of the hard phase and the bonding phase. As a result, the impact toughness, bending strength and impact resistance of the rare earth cemented carbide are obviously improved. The hardness, wear resistance and the ability of anti diffusion and anti-oxidation on the surface of the cutting tool are also improved.
It is also found that there is cobalt rich phenomenon on the surface of rare earth cemented carbide blade during cutting, so the friction coefficient between chip, workpiece and tool can be reduced, so the cutting force can be reduced.
Rare earth elements are abundant in nature and low in price. Adding them to cemented carbide can improve its mechanical, physical and service properties, so it has a broad application prospect.
1. Yt14r and YT14 cemented carbide are used in Beijing construction machinery plant to turn 45 × steel shaft (hardened and tempered, hardness hb250), cutting speed v = 60m / min, cutting depth AP = 0.5mm, and feed rate f = 0.51mm/r. The service life of yt14r is 2 times longer than that of YT14, and the quality of machined surface is slightly improved
2. Yt14r and YT14 cemented carbide tools are used in Beijing internal combustion engine works to turn 45 × camshaft (tempering, hrc28-32), v = 92m / min, AP = 3mm, f = 0.6mm/r. Yt14r can process 80-100 pieces on average, while YT14 can only process 40-50 pieces. And yt14r is less than YT14.
3. The 45 × camshaft (quenched and tempered, hrc28-32) is turned by yw1r and yw1 cemented carbide in Beijing internal combustion engine works, v = 92m / min, AP = 3mm, f = 0.6mm/r. Yw1r can process 60-70 pieces on average, without cutting phenomenon, while yw1r can only process 30-32 pieces, and sometimes cutting.
4. Yw1r and yw1 tools are used 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 in the 502 Research Institute of the Fifth Institute of China Aerospace Industry Corporation. The service life of yw1r is more than 2 times of yw1, and the surface roughness of yw1 is ra = 3.2mm, y