Material properties of the cemented carbide

The material properties

Cemented carbide with high hardness of the refractory metal carbides (WC, TiC) micron grade powder as main ingredients, with cobalt (Co) and nickel (Ni), molybdenum (Mo) as the binder, sintering in vacuum furnace or hydrogen reduction furnace of powder metallurgy products.

Ⅳ, Ⅴ B, B Ⅵ B group metal carbide, nitride, boride, etc, due to the hardness and particularly high melting point, collectively known as tungsten carbide. Here, with emphasis on the carbide to illustrate the structure of hard gold, characteristics and application.

Ⅳ, Ⅴ B, B Ⅵ B group metal and carbon form type metal carbides, due to the carbon atom radius is small, can fill the gap in the metal lattice and retain the original metal lattice form, form interstitial solid solution. Under appropriate conditions, this kind of solid solution can also continue to dissolve its constituent elements, until it is saturated. As a result, they can be changed in a certain range of (such as the composition of titanium carbide on the changes of between TiC0.5 ~ TiC), chemical formula does not comply with the rules of valence. When dissolved carbon content exceeds a certain limit, such as titanium carbide Ti: C = 1:1), lattice pattern will change, and make the original metal lattice transformed into another form of metal crystal lattice, at this time between the solid solution is called filling between filling compound.

Type metal carbides, especially Ⅳ, Ⅴ B, B Ⅵ B group the melting point of metal carbides are above 3273 k, hafnium carbide, tantalum carbide at 4160 k and 4150 k respectively, is the current know the melting point of a material of the highest. Most of the carbide hardness is very big, the microhardness is greater than 1800 kg, was (microhardness is one of the hardness of the representation, usually for hard alloy and hard compound, microhardness, 1800 kg was equivalent to Morse, a diamond hardness of 9). Many of the carbide under high temperature is not easy to decompose, antioxidant capacity than the metal components. Titanium carbide in thermal stability, best of all the carbide is a very important metal type carbides. However, in the oxidizing atmosphere, all carbide under high temperature easy to oxidation, can say this is a major weakness of carbide.

In addition to the carbon atom, the nitrogen atoms, boron atoms can enter the space lattice of metal, the formation of interstitial solid solution. They are similar to the nature of the clearance type carbide, conductive, thermal conductivity, high melting point, high hardness, brittleness is big at the same time.

Cemented carbide substrate consists of two parts: part of hardening phase; The other part is a metal bonding.

Hardening phase is the periodic table of transition metal carbides, such as tungsten carbide, titanium carbide, tantalum carbide, their high hardness, melting point 2000 ℃ or more, some even more than 4000 ℃. In addition, transition metal nitride, boride, silicides have similar features, can also serve as a hardening phase of cemented carbide. The existence of hardening phase determines the alloy with high hardness and wear resistance.

Carbide requirement for tungsten carbide WC particle size according to the different USES of cemented carbide with different particle size of WC (tungsten carbide). Cemented carbide cutting tools, such as cutting blade, the V - CUT foot machine finishing such as alloy using super fine, fine, fine grain WC, magnesium alloy used in the WC particles, gravity and heavy cutting of the alloy, coarse particle in WC is applied to make the raw material; Mining tools: rock high hardness, high impact load, the coarse grain WC, small rock impact small impact load using WC particles do in raw materials; Wearing parts: when to emphasize its wear resistance, compressive strength and surface finish, is made of super fine, fine, fine, WC particles do in raw materials, impact resistant raw materials of tool use, coarse particle in WC.

WC theory carbon content is 6.128% (50%) of atoms, when WC carbon content is greater than the theory of carbon content, the free carbon in the WC (WC + C). The existence of free carbon, sintering when around the WC grain growth, uneven carbide grain size. Compound carbon tungsten carbide is high (6.07% or higher), free carbon (0.05%) or less, the total carbon is decided by the production technology of hard alloy and using range.

Under normal circumstances, paraffin wax process vacuum sintering with WC before total carbon mainly depends on the sintering pressure combine oxygen content within the block. Contains an oxygen to increase 0.75 carbon, namely the WC + oxygen % x 0.75 = 6.13% of total carbon (assuming sintering furnace for the neutral atmosphere, in fact most of the vacuum furnace for carburizing atmosphere, the WC is less than the calculated value of total carbon).

At present, China's total carbon content of WC roughly divided into three types: paraffin wax process vacuum sintering with WC about 6.18 + / - 0.03% of total carbon (free carbon will increase). Paraffin wax process hydrogen sintering with WC total carbon content was 6.13 + / - 0.03%. Rubber process hydrogen sintering with WC = 5.90 + / - 0.03% of total carbon. The above process sometimes cross, thus determine the WC total carbon according to the specific circumstances.

Different scope, different Co (cobalt) content, grain size of alloy WC total carbon used to do a few small adjustments. Low cobalt tungsten carbide alloy can choose high total carbon, high cobalt alloy can choose low carbon tungsten carbide. In short, needs to use cemented carbide is different to the requirement of tungsten carbide particle size.

Bonding metal is iron group metals commonly, commonly used is cobalt and nickel.

Manufacturing cemented carbide, the raw materials of powder particle size between 1 ~ 2 microns, and the purity is very high. The proportion of raw materials in accordance with the provisions of the ingredients, addition of alcohol or other medium wet in wet ball mill grinding, make them fully mixing, crushing, after drying, sieving join such kind of wax or gel forming agent, after drying, sieving mixture system. Then, put the mixture granulating, pressed, heated to close to bond metal melting point (1300 ~ 1500 ℃), the hardening phase bonding metal form a eutectic alloy. After cooling, hardening phase distribution in the bonding of metal mesh, closely linked each other, forming a solid overall. Carbide hardness depends on the content of hardening phase and grain size, namely, the higher the content of hardening phase, the fine grain size, the greater the hardness also. Carbide toughness is determined by bonding metal, the higher the bonding metal content, the greater the bending strength. SGS hard alloy cutter