An alloy material made of a hard compound of a refractory metal and a binder metal through a powder metallurgy process. Cemented carbide has a series of excellent properties such as high hardness, wear resistance, good strength and toughness, heat resistance and corrosion resistance, especially its high hardness and wear resistance, which remain basically unchanged even at a temperature of 500 °C , still has high hardness at 1000℃. Carbide is widely used as tool material, such as turning tools, milling cutters, planers, drills, boring tools, etc., for cutting cast iron, non-ferrous metals, plastics, chemical fibers, graphite, glass, stone and ordinary steel, and can also be used for cutting Difficult-to-machine materials such as heat-resistant steel, stainless steel, high manganese steel, tool steel, etc. The cutting speed of new carbide tools is now hundreds of times that of carbon steel.
Application of cemented carbide
(1) Tool material
Carbide is the largest amount of tool material, which can be used to make turning tools, milling cutters, planers, drills, etc. Among them, tungsten-cobalt carbide is suitable for short chip processing of ferrous and non-ferrous metals and processing of non-metallic materials, such as cast iron, cast brass, bakelite, etc.; tungsten-titanium-cobalt carbide is suitable for long-term processing of ferrous metals such as steel. Chip machining. Among similar alloys, those with more cobalt content are suitable for rough machining, and those with less cobalt content are suitable for finishing. General-purpose cemented carbides have a much longer machining life than other cemented carbides for difficult-to-machine materials such as stainless steel.
(2) Mold material
Cemented carbide is mainly used for cold working dies such as cold drawing dies, cold punching dies, cold extrusion dies, and cold pier dies.
Carbide cold heading dies are required to have good impact toughness, fracture toughness, fatigue strength, bending strength and good wear resistance under the wear-resistant working conditions of impact or strong impact. Medium and high cobalt and medium and coarse grain alloy grades are usually used, such as YG15C.
Generally speaking, the relationship between wear resistance and toughness of cemented carbide is contradictory: the increase of wear resistance will lead to the decrease of toughness, and the increase of toughness will inevitably lead to the decrease of wear resistance. Therefore, when selecting alloy grades, it is necessary to meet specific use requirements according to the processing object and processing working conditions.
If the selected grade is prone to early cracking and damage during use, the grade with higher toughness should be selected; if the selected grade is prone to early wear and damage during use, the grade with higher hardness and better wear resistance should be selected. . The following grades: YG15C, YG18C, YG20C, YL60, YG22C, YG25C From left to right, the hardness decreases, the wear resistance decreases, and the toughness increases; on the contrary, the opposite is true.
(3) Measuring tools and wear-resistant parts
Carbide is used for wear-resistant surface inlays and parts of measuring tools, precision bearings of grinders, guide plates and guide rods of centerless grinders, tops of lathes and other wear-resistant parts.
Binder metals are generally iron group metals, commonly cobalt and nickel.
When manufacturing cemented carbide, the particle size of the selected raw material powder is between 1 and 2 microns, and the purity is very high. The raw materials are batched according to the prescribed composition ratio, and alcohol or other media are added to wet grinding in a wet ball mill to make them fully mixed and pulverized. Sieve the mixture. Then, the mixture is granulated, pressed, and heated to a temperature close to the melting point of the binder metal (1300-1500 °C), the hardened phase and the binder metal will form an eutectic alloy. After cooling, the hardened phases are distributed in the grid composed of the bonding metal and are closely connected with each other to form a solid whole. The hardness of cemented carbide depends on the hardened phase content and grain size, that is, the higher the hardened phase content and the finer the grains, the greater the hardness. The toughness of cemented carbide is determined by the binder metal. The higher the binder metal content, the higher the flexural strength.
In 1923, Schlerter of Germany added 10% to 20% cobalt to tungsten carbide powder as a binder, and invented a new alloy of tungsten carbide and cobalt. The hardness is second only to diamond. The first cemented carbide made. When cutting steel with a tool made of this alloy, the cutting edge will wear out quickly, and even the cutting edge will crack. In 1929, Schwarzkov in the United States added a certain amount of tungsten carbide and titanium carbide compound carbides to the original composition, which improved the performance of the tool in cutting steel. This is another achievement in the history of cemented carbide development.
Cemented carbide has a series of excellent properties such as high hardness, wear resistance, good strength and toughness, heat resistance and corrosion resistance, especially its high hardness and wear resistance, which remain basically unchanged even at a temperature of 500 °C , still has high hardness at 1000℃. Carbide is widely used as tool material, such as turning tools, milling cutters, planers, drills, boring tools, etc., for cutting cast iron, non-ferrous metals, plastics, chemical fibers, graphite, glass, stone and ordinary steel, and can also be used for cutting Difficult-to-machine materials such as heat-resistant steel, stainless steel, high manganese steel, tool steel, etc. The cutting speed of new carbide tools is now hundreds of times that of carbon steel.
Carbide can also be used to make rock drilling tools, mining tools, drilling tools, measuring tools, wear-resistant parts, metal abrasives, cylinder liners, precision bearings, nozzles, metal molds (such as wire drawing dies, bolt dies, nut dies, and Various fastener molds, the excellent performance of cemented carbide gradually replaced the previous steel molds).
Later, coated cemented carbide also came out. In 1969, Sweden successfully developed a titanium carbide coated tool. The base of the tool is tungsten-titanium-cobalt carbide or tungsten-cobalt carbide. The thickness of the titanium carbide coating on the surface is only a few microns, but compared with the same brand of alloy tools, The service life is extended by 3 times, and the cutting speed is increased by 25% to 50%. In the 1970s, a fourth generation of coated tools appeared for cutting difficult-to-machine materials.
How is cemented carbide sintered?
Cemented carbide is a metal material made by powder metallurgy of carbides and binder metals of one or more refractory metals.
Major producing countries
There are more than 50 countries in the world that produce cemented carbide, with a total output of 27,000-28,000t-. The main producers are the United States, Russia, Sweden, China, Germany, Japan, the United Kingdom, France, etc. The world cemented carbide market is basically saturated. , the market competition is very fierce. China’s cemented carbide industry began to take shape in the late 1950s. From the 1960s to the 1970s, China’s cemented carbide industry developed rapidly. In the early 1990s, China’s total production capacity of cemented carbide reached 6000t, and the total output of cemented carbide reached 5000t, second only to In Russia and the United States, it ranks third in the world.
WC cutter
①Tungsten and cobalt cemented carbide
The main components are tungsten carbide (WC) and binder cobalt (Co).
Its grade is composed of “YG” (“hard and cobalt” in Chinese Pinyin) and the percentage of average cobalt content.
For example, YG8 means the average WCo=8%, and the rest is tungsten-cobalt carbide of tungsten carbide.
TIC knives
②Tungsten-titanium-cobalt carbide
The main components are tungsten carbide, titanium carbide (TiC) and cobalt.
Its grade is composed of “YT” (“hard, titanium” two characters in Chinese Pinyin prefix) and the average content of titanium carbide.
For example, YT15 means average WTi=15%, and the rest is tungsten carbide and tungsten-titanium-cobalt carbide with cobalt content.
Tungsten Titanium Tantalum Tool
③Tungsten-titanium-tantalum (niobium) cemented carbide
The main components are tungsten carbide, titanium carbide, tantalum carbide (or niobium carbide) and cobalt. This kind of cemented carbide is also called general cemented carbide or universal cemented carbide.
Its grade is composed of “YW” (the Chinese phonetic prefix of “hard” and “wan”) plus a sequence number, such as YW1.
Performance characteristics
Carbide Welded Inserts
High hardness (86～93HRA, equivalent to 69～81HRC);
Good thermal hardness (up to 900～1000℃, keep 60HRC);
Good abrasion resistance.
Carbide cutting tools are 4 to 7 times faster than high-speed steel, and the tool life is 5 to 80 times higher. Manufacturing molds and measuring tools, the service life is 20 to 150 times higher than that of alloy tool steel. It can cut hard materials of about 50HRC.
However, cemented carbide is brittle and cannot be machined, and it is difficult to make integral tools with complex shapes. Therefore, blades of different shapes are often made, which are installed on the tool body or mold body by welding, bonding, mechanical clamping, etc. .
Special-shaped bar
Sintering
Cemented carbide sintering molding is to press the powder into a billet, and then enter the sintering furnace to heat to a certain temperature (sintering temperature), keep it for a certain time (holding time), and then cool it down to obtain a cemented carbide material with the required properties.
The cemented carbide sintering process can be divided into four basic stages:
1: In the stage of removing the forming agent and pre-sintering, the sintered body changes as follows:
The removal of the molding agent, with the increase of temperature in the initial stage of sintering, the molding agent gradually decomposes or vaporizes, and the sintered body is excluded. The type, quantity and sintering process are different.
The oxides on the surface of the powder are reduced. At the sintering temperature, hydrogen can reduce the oxides of cobalt and tungsten. If the forming agent is removed in vacuum and sintered, the carbon-oxygen reaction is not strong. The contact stress between the powder particles is gradually eliminated, the bonding metal powder begins to recover and recrystallize, the surface diffusion begins to occur, and the briquetting strength is improved.
2: Solid phase sintering stage (800℃–eutectic temperature)
At the temperature before the appearance of the liquid phase, in addition to continuing the process of the previous stage, the solid-phase reaction and diffusion are intensified, the plastic flow is enhanced, and the sintered body shrinks significantly.
3: Liquid phase sintering stage (eutectic temperature – sintering temperature)
When the liquid phase appears in the sintered body, the shrinkage is completed quickly, followed by crystallographic transformation to form the basic structure and structure of the alloy.
4: Cooling stage (sintering temperature – room temperature)
At this stage, the structure and phase composition of the alloy have some changes with different cooling conditions. This feature can be used to heat the cemented carbide to improve its physical and mechanical properties.
Post time: Apr-11-2022
