Classification and Study on Cemented Carbide Cutting Tools

Part one

Tool is an indispensable tool in cutting processing, whether it is an ordinary machine tool, or an advanced numerical control machine tool (NC), machining center (MC) and flexible manufacturing system (FMC), must rely on the tool to complete the cutting process. The development of tools has a direct impact on improving productivity and processing quality. Material, structure and geometry are the three factors that determine the cutting performance of the tool, in which the performance of the tool material plays a key role.

As an important part of tool materials, cemented carbide plays an irreplaceable role in modern cutting processing. Cemented carbide is a high hardness, refractory metal carbide (WC, TiC, etc.) of the micron order of magnitude powder, sintered with Co, Mo, Ni and other binder powder metallurgy products, of which the high temperature carbide content exceeds the high-speed steel, the allowable cutting temperature up to 800 ~ 1000℃, the normal temperature hardness of HRC89 ~ 93, 760℃ hardness of HRC77 ~ 85, cutting speed up to 100 ~ 300m/min, far more than high-speed steel, life is several times to dozens of times of high-speed steel, but the strength and toughness is only 1/30 ~ 1/8 of high-speed steel, poor ability to withstand shock and impact. Now it has become one of the main tool materials.

The International Organization for Standardization (ISO) divides carbide for cutting tools into six categories:

1. Type P

Composed of WC, Co and 5% ~ 30% TiC, also known as tungsten titanium cobalt carbide, grade YT5, YT14, YT15, YT30, of which the TiC content is 5%, 14%, 15%, 30%, the corresponding Co content is 10%, 8%, 6%, 4%, hardness HRA91.5 ~ 92.5. The bending strength is 900 ~ 1400MPa. TiC content increased, Co content decreased, hardness and wear resistance increased, but the impact toughness decreased significantly. This kind of alloy has high hardness and wear resistance, good adhesion and diffusion resistance and oxidation resistance. But the bending strength, grinding performance and thermal conductivity decrease, low temperature brittleness, toughness is poor. Suitable for high speed cutting steel material. The higher the Co content of the alloy, the better the bending strength and impact toughness, suitable for roughing. The Co content is reduced, the hardness, wear resistance and heat resistance are increased, and it is suitable for finishing. The affinity between the Ti element in the alloy and the Ti element in the work-piece will produce a serious sticking tool phenomenon, which will aggravate the tool wear in the case of high temperature cutting and large friction factor, and is not suitable for processing stainless steel and titanium alloy.

2. Type K

Composed of WC and Co, also known as tungsten cobalt tungsten carbide, commonly used grades YG6, YG8, YG3X, YG6X, containing Co of 6%, 8%, 3%, 6%. Hardness HRA89 ~ 91.5, bending strength 1100 ~ 1500GPa. The structure is divided into coarse grain, medium grain and fine grain. Generally (such as YG6, YG8) for the medium grain structure, fine grain carbide (such as YG3X, YG6X) containing the same amount of Co than the medium grain hardness, its wear resistance is slightly higher, bending strength and toughness are slightly lower. This kind of alloy toughness, grinding, thermal conductivity is good, suitable for processing brittle materials.

3. Type M

On the basis of WC, TiC and Co, TaC(or NbC) is added to the composition, adding TaC(NbC) to YT can improve its bending strength, fatigue strength, impact toughness, high temperature hardness, strength and oxidation resistance, wear resistance and so on. Commonly used grades YW1 and YW2. Can be used to process cast iron, non-ferrous metals and steel, but also can process high-temperature alloy, stainless steel and other difficult-to-process materials.

4. Type H

Mainly used for cutting high hard materials, such as hardened steel, chilled cast iron and so on. Cubic boron nitride PCBN is listed in Class H.

5.Type S

Used for cutting heat-resistant materials, super-alloys, etc.

6.Type H

Used for cutting non-ferrous metals. Polycrystalline diamond PCD is included in class N.

In this article, I mentioned six types of cemented carbide by classifying cutting tools, next part, there will be more new types of cemented carbide to conclude, please don’t forget to check the next half if you are interested.

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