Cemented carbide is an alloy material made of refractory metal carbide and metal binder by powder metallurgy.
Cemented carbide has a series of excellent properties such as high hardness, wear resistance, good strength and toughness, heat resistance and corrosion resistance.
In particular, its high hardness and wear resistance remain basically unchanged even at 500 ℃ and still have high hardness at 1000 ℃.
Cemented carbide is widely used as cutting tool materials, such as turning tool, milling cutter, planer, drill bit and boring cutter.
It is used to cut cast iron, non-ferrous metals, plastics, chemical fiber, graphite, glass, stone and ordinary steel.
It can also be used to cut refractory materials such as heat-resistant steel, stainless steel, high manganese steel and tool steel.
The manufacturing process of cemented carbide blade is shown in Fig. 2-8.
The basic characteristics of cemented carbide tool are as follows:
(1) High hardness and wear resistance.
(2) High modulus of elasticity.
(3) High compressive strength.
(4) Good acid and alkali resistance.
(5) Low impact toughness.
(6) The coefficient of expansion is low, and the thermal conductivity and conductivity are similar to that of iron and its alloys.
Fig. 2-8 manufacturing method of cemented carbide
Classification and characteristics of cemented carbide tool materials
1. Classification and characteristics of ordinary cemented carbide
(1) Tungsten cobalt (WC + Co) (corresponding to ISO and national standard class K).
The higher the cobalt content of the alloy, the better the toughness, which is suitable for rough machining;
Low cobalt content, suitable for finishing.
Tungsten cobalt cemented carbide is sintered from WC and Co.
Class K alloy has good thermal conductivity and is conducive to reducing cutting temperature.
Class K alloy has good grinding performance and can grind sharp cutting edges.
It is generally suitable for processing cast iron, non-ferrous metals, fiber lamination and other materials.
Its organization is shown in Fig. 2-9.
Fig. 2-9 microstructure of WC + CO cemented carbide
(2) Tungsten titanium cobalt (WC + TiC + Co) (corresponding to national standard class P).
This kind of alloy has high hardness, heat resistance, good adhesion and oxidation resistance.
When machining steel, it has large plastic deformation, intense friction and high cutting temperature.
P-type alloy has slow wear and high tool life.
If the tic content in the alloy is high, the wear resistance and heat resistance are improved, but the strength is reduced.
Generally, the brand with less tic content is selected for rough machining and the brand with more tic content is selected for finish machining.
Tungsten titanium cobalt cemented carbide is sintered with WC as matrix, tic added and Co as binder, code named P.
It is generally suitable for high-speed processing of steel.
However, when the amount of TiC increases, the thermal conductivity of the alloy becomes poor, and cracks are easy to occur during welding and grinding.
Its organization is shown in Fig. 2-10.
Fig. 2-10 microstructure of WC + TiC + Co cemented carbide
(3) Tungsten titanium tantalum (niobium) cobalt (WC + TiC + TAC (NB) + Co) (corresponding to national standard class M).
M alloy is added with an appropriate amount of rare refractory metal carbides to improve the properties of the alloy.
YW alloy is suitable for semi finishing of chilled cast iron, non-ferrous metals and alloys, as well as semi finishing and finishing of high manganese steel, quenched steel, alloy steel and heat-resistant alloy steel.
Tantalum (niobium) cemented carbide is another kind of cemented carbide formed by adding a small amount of other carbides (such as Ta C or NbC) to the above two kinds of hardness alloys.
It is code named m.
It is suitable for processing both brittle materials and plastic materials.
Common brands M10 and M20.
(4) Titanium carbide based (WC + TiC + Ni + Mo) (corresponding to national standard P01).
P01 alloy is titanium carbide based, which takes tic as the main component and Ni and Mo as bonding metals.
Suitable for high-speed finishing alloy steel, hardened steel, etc.
The main characteristics of TiC based alloy are very high hardness, good wear resistance, high bonding temperature with steel, and strong resistance to crater wear.
It has good wear resistance and oxidation ability, and can still be cut at 1000 ~ 1300 ℃.
The alloy has good chemical stability and low affinity with materials.
It can reduce the friction with workpieces and is not easy to produce chip nodules.
It is suitable for rough machining and low-speed cutting with impact load, and has poor resistance to plastic deformation and edge collapse.
2. Characteristics of Ultrafine Grain Cemented Carbide
Ultrafine grain cemented carbides are mostly used in class K alloys.
Their hardness and wear resistance have been greatly improved, their bending strength and impact toughness have also been improved, and their properties are close to high-speed steel;
It is suitable for small-size milling cutter, drill bit, etc., and can be used to process high hardness and difficult to process materials.
Cemented carbide is widely used in high-speed cutting tools with good rigidity and simple edge shape.
With the progress of technology, the application of complex cutting tools is gradually expanding.
Cemented carbide has high melting point, high hardness, high carbide content, good hot melt, good thermal hardness, high cutting speed, but high brittleness, weak bending strength and impact toughness.
The bending strength is only 1 / 3 ~ 1 / 2 of that of high-speed steel, and the impact toughness is only 1 / 4 ~ 1 / 35 of that of high-speed steel.
It is mainly determined by the type and quantity of cemented carbide, the thickness of powder particles and the content of tackifier.