What is cemented carbide? What are its characteristics?
cemented carbide is a composite material produced by powder metallurgy and composed of refractory metal compounds (hard phase) and bonding metals (bonding phase).
High hardness and wear resistance;
High compressive strength (up to 6000mpa);
compared with tool steel, cemented carbide has the following advantages:
Greatly improve the tool life, several times to dozens of times;
The cutting speed and labor efficiency are improved;
The accuracy and smoothness of the workpiece are improved.
Composition, structure and properties of cemented carbide
the main components of cemented carbide are WC, CO and tic, and the secondary components are tin, Ni, Mo, TAC, NBC, VC, Cr3C2, etc. Among them, WC (including TIC) accounts for more than 80% and co accounts for less than 20%. The proportion of other components is very small.
the normal structure of tungsten cobalt alloy is the two-phase structure of WC phase and co phase. The former is also called hard phase or α Phase, the latter is adhesive phase or β Phase. There are two normal structures of tungsten titanium cobalt alloys, one is (Ti, w) c+co two-phase structure, and the other is (Ti, w) + wc+co three-phase structure.
The main performance indicators of cemented carbide include density, bending strength, hardness, coercive force, cobalt magnetism, etc. Density is the most basic index of cemented carbide quality, and it is the basis of other properties. Hardness and bending strength are the two main mechanical properties of cemented carbide, which directly affect the application effect of the alloy. These three properties basically determine the comprehensive quality of cemented carbide, which is not only the evaluation index of products leaving the factory, but also the index that users pay most attention to, and an important basis for the rational selection of cemented carbide.
Functions of several commonly used substances in tool materials:
WC – wear resistant phase, the main component of tool material;
Co – ductile phase, with the increase of CO content, the strength and toughness of the alloy increase and the hardness decreases;
TiC – hard phase, with the increase of TiC content, the anti crater wear ability of the alloy increases, but the strength and toughness of the alloy decreases, and the brittleness of the alloy increases;
TAC, NBC – hard phase, which can significantly improve the high temperature performance and wear resistance of the alloy. The alloy with TAC and NBC has good versatility;
CRC, VC inhibitors, inhibit the growth of WC grains.
Classification of cemented carbide
According to different compositions, cemented carbide can be divided into five categories.
Tungsten carbide based cemented carbide
including WC Co, WC tic Co, WC TAC Co, WC tic tac (NBC) -co, etc. These alloys are mainly composed of WC.
Titanium carbide based or titanium carbonitride based cemented carbide
a kind of cemented carbide usually composed of tic or Ti (C, n) as the basic component and Ni Mo as the binder. Such as tic Mo Ni, tic WC TAC (NBC) -mo Ni, Ti (C, n) -mo Co Ni, etc.
Coating cemented carbide
deposit a layer of tic, tin, TiB2, ZrN, CrN, AI2O3, TiCN, B4C, SiC, BN, TiAIN, diamond and other substances on the alloy surface, so as to double the service performance of the tool.
Steel bonded cemented carbide
a kind of cemented carbide whose main component is steel and whose hard phase is tic or WC. Its remarkable feature is that it can be heat treated and machined. It is a kind of intermediate alloy between tool steel and cemented carbide.
Other cemented carbide
such as Cr3C2 based cemented carbide, which is composed of Cr3C2 as the main component and Ni or Ni-W as the binder. It is usually used as wear-resistant and corrosion-resistant parts.
In addition, there are two important tool materials. One is ceramic materials, including alumina (white pottery), silicon nitride and Theron ceramics (si3n4/al2o3). The other is superhard materials, polycrystalline diamond (PCD) and polycrystalline cubic boron nitride PCBN.
Classification by purpose
Cemented carbide has a series of excellent properties and is widely used. With the passage of time, its use is expanding. The main uses are as follows:
cemented carbide can be used as a variety of cutting tools. The cemented carbide consumption of cutting tools in China accounts for about one third of the total cemented carbide output (about 3000 tons), of which about 78% are used for welding tools and about 22% are used for indexable tools. The cemented carbide used for numerical control tools only accounts for about 20% of the cemented carbide used for indexable tools. In addition, there are cutting tools such as integral cemented carbide drill bits, integral cemented carbide small circular saw blades, and cemented carbide micro drills.
Geological mining tools
geological mining tools are also a major use of cemented carbide. Cemented carbide for mining in China accounts for about 25% of the total production of cemented carbide. It is mainly used for drill bits for impact drilling, bits for geological exploration, down the hole drills for mines and oil fields, roller drills, coal cutter picks, impact drills for building materials industry, etc.
cemented carbide used as various molds accounts for about 8% of the total production of cemented carbide, including wire drawing dies, cold heading dies, cold extrusion dies, hot extrusion dies, hot forging dies, forming dies, and drawing tube mandrels, such as long mandrels, spherical mandrels, floating mandrels, etc. in recent decades, the consumption of various cemented carbide rolls used for rolling wire materials has increased rapidly, and the cemented carbide used for rolls in China has accounted for 3% of the total production of cemented carbide.
there are many products made of cemented carbide for structural parts, such as rotating seal rings, compressor pistons, lathe chucks, grinder spindles, bearing journals, etc.
Wear resistant parts
wear resistant parts made of cemented carbide include nozzles, guide rails, plungers, balls, tire anti-skid nails, snow shovel plates, etc.
Cavity for high pressure and high temperature resistance
the most important use is to produce top hammer, cylinder and other products for synthetic diamond. Cemented carbide for top hammer and cylinder has accounted for 9% of the total cemented carbide production in China.
cemented carbide is used more and more widely, and has been expanding in the civil field in recent years, such as watch chain, watch case, zipper head of high-grade luggage, cemented carbide trademark, etc.