What does American standard cemented carbide grain size C mean?
Then, when the mixture is granulated and pressed and heated to a point near the bonding metal (1300~1500 DEG C), the eutectic alloy is formed by the hardening and bonding of the metal. After cooling, the hardened phases are distributed in a grid of bonded metals that are closely related to each other and form a solid whole. The hardness of cemented carbide depends on the content of the hardened phase and grain size. The higher the content of the hardened phase and the finer the grain, the greater the hardness. The toughness of cemented carbide is determined by bonding metal. The higher the bonding metal content is, the greater the bending strength is. The effect of grain size on the mechanical properties of metals has a curve diagram: the strength of both ends is large and the middle is low. Explain: the mechanical properties of single crystals are very good. The finer the grain, the better the mechanical properties, but the mechanical properties of the single crystal with infinite size are much better than the grain's infinitesimal! A lot of grain size control method, the main principle of two: 1, increase the metal crystallization undercooling of 2, increase the crystal nucleus specific methods: electromagnetic stirring, adding grain refiner (such as Aluminum Alloy plus Al-Ti-C master alloy as grain refiner), lower solidification temperature, and fine grain of alloy elements and so on many.
Hard alloy with high hardness of refractory metal carbides (WC, TiC) micron powder as the main ingredient, with cobalt or nickel (Co) (Ni), molybdenum (Mo) as the binder, powder metallurgy products in vacuum furnace or hydrogen reduction sintering furnace. IV, B, V, B, VI, B group of metal carbides, nitrides, boride, etc., because of hardness and melting point is particularly high, collectively referred to as cemented carbide. The structure, characteristics and application of hard gold content are described with carbide as the key point. IV, A, V, A, VI, A group metals and carbon formed in the metal type carbide, because the carbon atom radius is small, can be filled in the gap of the metal character, and retain the original lattice form of metal, forming interstitial solid solution. Under appropriate conditions, such solid solution can continue to dissolve its constituent elements until it reaches saturation.
In addition to carbon atoms, nitrogen atoms and boron atoms can also enter the voids in the metal lattices to form interstitial solutions. They are similar to those of interstitial carbides, which can conduct electric conduction, heat conduction, high melting point, hardness and brittleness. The matrix of cemented carbide consists of two parts: one is a hardening phase, and the other is a bonding metal. Is the hardening phase transition metal carbides in the periodic table of elements, such as tungsten carbide, titanium carbide, tantalum carbide, their hardness is very high, the melting point of 2000 DEG C, and some even more than 4000 DEG C. In addition, transition metal nitrides, boride and silicides have similar properties and can also act as hardening phases in cemented carbides. The presence of the hardened phase determines the alloy's extremely high hardness and wear resistance. Bonding metals are generally iron based metals, and cobalt and nickel are commonly used. In the manufacture of cemented carbide, the size of the raw material powder is between 1~2 microns and the purity is very high. Raw materials according to the provisions of the proportion of added alcohol or other medium in the wet ball mill in wet grinding, making them fully mixing, crushing, drying, sieving after adding wax or gel forming agent of a class, and then drying and sieving to prepare a mixture.
Therefore, their composition can change in a certain range (such as the composition of titanium carbide in TiC0.5 ~ TiC changes), chemical formula does not conform to the rules of valence. When the dissolved carbon content exceeds a certain limit (such as titanium carbide in Ti: C=1: 1), the lattice type will be changed, the original metal lattice metal lattice into another form, then the interstitial solid solution called interstitial compounds. Metal carbides, especially B, B, IV V VI B metal carbide melting point is above 3273K, the TAC hafnium carbide, respectively 4160K and 4150K, is the highest point currently know material. Most of the carbide hardness large, their microhardness is higher than 1800kg mm2 (micro hardness is hardness says one way for hard alloy and hard compound, microhardness 1800kg mm2 is equivalent to a diamond a Mohs hardness of 9). Many carbides are difficult to break down at high temperatures, and their antioxidant power is stronger than their constituent metals. Titanium carbide has the best thermal stability in all carbides, and is a very important metal type carbide. However, in an oxidizing atmosphere, all carbides are readily oxidized at high temperatures, which can be said to be a major weakness of carbides.
