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 and B Ⅵ B metal carbide, nitride, boride, etc, due to the particularly high melting point and hardness, collectively known as carbide. Here, with emphasis on the carbide to illustrate the structure of hard gold, characteristics and application.
Ⅳ, Ⅴ, Ⅵ B B B metal and carbon type metal carbide formation, due to the carbon atom radius is small, can fill in the gaps between 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 within a certain range of changes (such as the composition of titanium carbide in TiC0.5 ~ TiC change), chemical formula does not conform to the rules of valency. When dissolved carbon content exceeds a certain limit (such as titanium carbide in Ti: C = 1:1), lattice pattern will change, make the original metal crystal lattice transformed into another form of metal crystal lattice, at this time between the solid solution called filling filling compound.
Type metal carbides, especially Ⅳ, Ⅴ B and B Ⅵ B group the melting point of metal carbides are above 3273 k, the hafnium carbide, tantalum carbide, 4160 k and 4150 k respectively, is the current know material with the highest melting point. Most of the carbide hardness is very big, the microhardness is greater than 1800 kg, was (microhardness is one of the hardness of representation, used in hard alloy and hard compound, microhardness, 1800 kg was equivalent to Morse, a diamond hardness of 9). Many carbide under high temperature is not easy to decompose, antioxidant ability stronger than the metal components. Titanium carbide in thermal stability is best in all of carbide, carbide is a very important metal type. 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 atoms, nitrogen and boron atoms can enter the metal lattice in the gap, gap formation of solid solution. Them with the clearance type carbides are of a similar nature to conductive, thermal conductivity, high melting point, high hardness, brittleness also big.
Cemented carbide substrate consists of two parts: part of hardening phase; The other part is a metal bonding.
Hardening phase is the periodic table 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, the transition metal nitride, boride, silicides have similar features, can also serve as a carbide in the hardening phase. The existence of the hardening phase determines the alloy with high hardness and wear resistance.
For tungsten carbide WC particle size requirements according to the different USES of cemented carbide with different particle size of WC (tungsten carbide). Cemented carbide cutting tools, such as CUT foot machine blade, the V - CUT finish machining alloy using ultra fine, fine, fine grain WC, magnesium alloy used in the WC particles, gravity alloys used for cutting and heavy cutting, coarse particle in WC do raw material; Mining tools: rock, high hardness, high impact load, using coarse grain WC, small rock impact shock load using WC particles do raw materials; Wearing parts: when to emphasize its wear resistance, compressive strength and surface finish, is made of super fine, fine, fine, medium grain WC do raw material, the impact resistance raw materials of tool use, coarse particle in WC.
Carbon content is 6.128% (50%) of atoms, WC theory 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, when sintering around the WC grain growth, causing 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 cemented carbide production technology and using range.
Under normal circumstances, paraffin 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 content % x 0.75 = 6.13% of total carbon (assuming that sintering furnace for the neutral atmosphere, in fact most of the vacuum furnace for carburizing atmosphere, WC general carbon used less than calculated value).
At present, China's total carbon content of WC roughly divided into three types: paraffin process vacuum sintering with WC about 6.18 + / - 0.03% of total carbon (free carbon will increase). Paraffin 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 overlapping, so determine the WC total carbon according to the specific circumstances.
Different scope, different Co (cobalt) content and grain size of alloy WC total carbon used to do a few small adjustments. Low cobalt alloy can choose high total carbon tungsten carbide, high cobalt alloy can choose low carbon tungsten carbide. Anyway, to tungsten carbide carbide needs to use different size have different requirements.
Bonding metal is iron group metals commonly, commonly used is cobalt and nickel.
Manufacturing hard alloy, the selection of raw material powder particle size between 1 ~ 2 microns, and the purity is very high. Ratio 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, drying, sieving after join such kind of wax or rubber molding agent, after drying and sieving system have to mix again. Then, granulating, pressure type, the mixture is heated to close to bond metal melting point (1300 ~ 1500 ℃), the hardening phase bonding metal form a eutectic alloy. After cooling, the hardening phase distribution in binding of metal mesh, closely tied to each other, form a solid whole. Carbide hardness depends on the hardening phase content and grain size, namely the hardening phase content is higher, the fine grain size, the hardness. Carbide toughness is determined by the matrix metal, the higher the bonding metal content, the greater the bending strength.
