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Dear users, do you know those commonly used professional terms in the cemented carbide tungsten carbide industry? So, today we will give you a popular science term that is used every day in the tungsten carbide industry.
According to our habits, it is often called cemented carbide, tungsten alloy, tungsten-cobalt alloy, and cemented carbide tungsten carbide. It refers to a sintered composite material composed of refractory metal tungsten carbide and metal binder. Among the metal carbides currently used, tungsten carbide WC, titanium carbide TiC, tantalum carbide TaC and niobium carbide NbC are the most common components . Cobalt Co metal is used as a binder, which is widely used in the production of cemented carbide tungsten carbide; other metal binders can also be applied, such as nickel Ni, iron Fe, etc. The more common tungsten carbide material combination is: tungsten carbide + Cobalt + tantalum carbide, used as tungsten carbide tool material. There are also some cost-saving tungsten carbide material combinations, such as: tungsten carbide + iron. tungsten carbide manufacturers flexibly adjust the ratio of tungsten carbide for some special purposes and special users. First, the hardness of tungsten carbide. The hardness of tungsten carbide refers to the ability of a material to resist plastic deformation. Rockwell hardness HRA is another hardness measurement method that is more commonly used. It uses the penetration depth of a standard diamond cone to measure the hardness. Vickers hardness HV is widely used internationally. This hardness measurement method refers to the hardness value obtained by measuring the size of the indentation by penetrating the surface of the sample with diamond under a certain load condition. Both the Vickers hardness measurement method and the Rockwell hardness measurement method can be used to measure the hardness of tungsten carbide, and the two can be converted correspondingly.
Second, the density of tungsten carbide. The density of tungsten carbide is measured by the drainage method (Archimedes' law). The density of tungsten carbide refers to the ratio of the mass and volume of the material. Its volume also includes the volume of pores in the material. Also called specific gravity. The density of tungsten carbide WC is 15.7g/cm3, and the density of cobalt Co is 8.9g/cm3. Therefore, as the content of cobalt and Co in tungsten carbide decreases, its overall density will increase. The density of titanium carbide TiC is lower than that of tungsten carbide, only 4.9g/cm3, so if TiC or other components with lower density are added, the overall density will decrease. In the case of a certain chemical composition of the tungsten carbide material, the increase of the pores in the tungsten carbide will lead to a decrease in density. "tungsten carbide Density Test"="tungsten carbide Density Test"
Third, the bending strength of tungsten carbide. Multiply the sample as a simply supported beam on two fulcrums, apply a load on the center line of the two fulcrums until the sample breaks, and use the value calculated by the bending formula according to the load required for fracture and the cross-sectional area of the sample. Also known as transverse breaking strength or flexural strength. In tungsten carbide WC-Co, the flexural strength increases with the increase of the cobalt-Co content. When the cobalt-Co content reaches about 15%, the flexural strength of the tungsten carbide begins to decrease after reaching the maximum value. The flexural strength of tungsten carbide adopts the average of several measured values as its measured value. With the change of sample geometry, surface finish, internal stress and internal defects of the material, this value will also change. Therefore, the flexural strength of tungsten carbide is only a strength measurement method, and the flexural strength value cannot be used as the basis for selecting tungsten carbide grades. The above three commonly used terms of hardness, density, and bending strength of tungsten carbide materials are the basic three elements for selecting tungsten carbide materials. Users should first understand.
Fourth, the porosity of tungsten carbide. The reduction of porosity can effectively improve the overall performance of the product. The pressure sintering process is an effective means to reduce porosity. tungsten carbide is made by pressing and sintering powder through powder metallurgy technology. Due to the characteristics of the process, a small amount of residual pores may exist in the metallographic structure of the product. The residual void volume is evaluated using a map comparison program of the pore size range and distribution. A-type: less than 10μm. B-type: between 10μm-25μm.
Fifth, the decarburization and carburization of tungsten carbide. The decarburization of tungsten carbide we often say refers to the insufficient carbon content of tungsten carbide after sintering. When the product is decarbonized, the organization changes from WC-Co to W2CCo2 or W3CCo3. The ideal carbon content of tungsten carbide in tungsten carbide (WC) is 6.13% by weight. When the carbon content is too low, there will be an obvious carbon-deficient structure in the product. Decarburization will greatly reduce the strength of tungsten carbide and increase its brittleness. Carburizing refers to the excessive carbon content after the cemented carbide is sintered. The ideal carbon content of tungsten carbide in tungsten carbide (WC) is 6.13% by weight. When the carbon content is too high, there will be an obvious carburized structure in the product. There will be significant excess free carbon in the product. Free carbon will greatly reduce the strength and wear resistance of tungsten carbide. The relationship between the decarburization and carburization of tungsten carbide is like the coexistence of human male and female hormones. The male and female hormones of normal people are balanced. No one has more or less. Once the balance mechanism between them is disrupted, they are all in an abnormal state. The same is true for the decarburization and carburization of tungsten carbide. In a word, decarburization will reduce the strength of tungsten carbide, leading to increased brittleness; carburizing will reduce the strength and wear resistance of tungsten carbide.
Sixth, the coercivity of tungsten carbide. The coercive force is the residual magnetic force measured by magnetizing the magnetic material in the tungsten carbide to a saturated state and then demagnetizing it. There is a direct relationship between the average particle size of the carbide phase of tungsten carbide and the coercive force: the finer the average particle size of the magnetized phase, the higher the coercive force value.
Seventh, the magnetic saturation of tungsten carbide. Cobalt Co is magnetic, while tungsten carbide WC, titanium carbide TiC, tantalum carbide TaC and vanadium carbide VC are non-magnetic. Therefore, by first measuring the magnetic saturation value of cobalt in a material, and then comparing it with the corresponding value of a pure cobalt sample, the alloying level of the cobalt binder phase can be obtained. This is because the magnetic saturation is affected by alloying elements. Therefore, any change in the binder phase can be measured. This method can be used to determine the deviation of the ideal carbon content because carbon plays an important role in composition control. The low magnetic saturation value indicates the possibility of low carbon content and decarburization. High magnetic saturation values indicate the presence of free carbon and carburizing. Eighth, the cobalt pool of tungsten carbide. After the cobalt-Co binder and tungsten carbide are sintered, excess cobalt may be produced. This phenomenon is called "cobalt pool". This is mainly caused by too low sintering temperature, insufficient material molding density, or filling of pores with cobalt during HIP (pressure sintering) processing. The size of the cobalt pool is determined by comparing metallographic photos. The presence of the cobalt pool in the cemented carbide may affect the wear resistance and strength of the material.
Eighth, cobalt magnetism and re-burning of tungsten carbide. In the production process of tungsten carbide, due to carbon fluctuations, abnormal sintering equipment, improper dewaxing process, etc., the magnetic properties of tungsten carbide and cobalt are often low, which has a greater impact on product performance and products. The tungsten carbide cobalt magnetic performance index is one of the core of the quality control of the sintering process. The level of cobalt magnetism directly reflects the level of carbon content in the alloy, and the carbon content controls the composition and phase structure of the binder phase in the main components of the tungsten carbide. It has an important influence on the strength performance of tungsten carbide and is an important reference for the performance of tungsten carbide. The common unqualified type of sintering in the control of cobalt magnetism is low cobalt magnetism. The reprocessing measure often used for products with low cobalt magnetism is reburning. The principle is to place tungsten carbide under the condition of a certain amount of liquid phase. In the carburizing environment, physical and chemical reactions occur to achieve the purpose of replenishing carbon, thereby increasing the cobalt magnetic value of the alloy. Method: Put the tungsten carbide into a vacuum furnace and heat it to 1350°C for 30 minutes; pass methane gas into the vacuum furnace, heat the tungsten carbide to 1360 1380°C, and hold it for 30 to 60 minutes, and it is complete. In the whole process, methane is used as the carbon supplement medium, and the carbon supplement uniformity is better; after the carbon supplement, there will be no residual pollution in the furnace, the material box and even the vacuum pipeline, and there is no need to clean up, and the next product can be sintered directly .
The above illustrates the importance of cobalt magnetism in tungsten carbide and the necessity of re-burning. Generally speaking, many people have varying degrees of resistance to re-burning. They all believe that the re-burning of tungsten carbide is due to quality problems. In fact, it is not entirely true. What we think is the return of fever is actually a good remedy. In fact, in these cemented carbide tungsten carbide industry terms, users should care about hardness, density and flexural strength. With these three items, the grade of tungsten carbide can basically be determined.
The development of wire drawing dies in the Chinese market has not been very long. Even now, many places still need such wire drawing dies, because our country's demand for such wire drawing is greater and more refined, so press the wire die, in It can be said that my country's future development potential is still very large. When buying a drawing die, we always hope that the product we buy is the best, and it is best if there are no defects, so we must learn to analyze the quality of a drawing die when we buy it, and we can only watch it. , You can choose the most suitable drawing die for yourself. If you look at the price, the price of the natural diamond wire drawing die must be more expensive, but it is expensive for his reason, because this type of wire drawing die itself is more complicated in processing. Of that kind. The natural diamond wire drawing die has a very high-quality hardness, but it is easy to cause friction, so this type of wire drawing die can only be used on some materials with a relatively small diameter, but its wear resistance is the best. There is also a cemented carbide die. The hardness of this film is relatively low, and the surface is not very rough, but its wear resistance is relatively poor, and its hardness is relatively low, usually it is not recommended to buy of. You need to be very careful when choosing a drawing die. Only after you pay attention to it, it will give you a piece of peace of mind. Drawing dies of different materials have different characteristics. To put it simply, the current materials for making wire drawing dies are: alloy steel, cemented carbide, natural diamond, artificial single crystal diamond, artificial polycrystalline diamond, ceramics and other materials, and through various chemical heat treatments, chemical vapor deposition, physical vapor deposition Wire drawing die made by other methods.
The difference is as follows:
Drawing die material-advantages-disadvantages-application range
Alloy steel mold is easy to make-poor wear resistance and short life-basically eliminated
Natural diamond-high hardness, wear resistance-brittleness, difficult to process-wire molds with a diameter of less than 1.2mu
Cemented carbide-good polishability, low energy consumption-poor wear resistance, difficult to process-wires of various diameters
Polycrystalline synthetic diamond-high hardness, good wear resistance-difficult to process, high cost-small wire, wire
cV coating material-high smoothness, good temperature resistance-complex process, difficult to process a small wire, wire
Porcelain material-good wear resistance, high temperature resistance, corrosion resistance-thermal shock, poor toughness, difficult to process-no large-scale application
The cemented carbide buttons have excellent wear resistance and impact toughness, and the drilling speed is fast. The spherical tooth series bit has a long passivation period, and its unwear life is about 5-6 times the life of the same diameter blade bit bit. It is beneficial to save auxiliary man-hours, reduce workers' physical labor and speed up the construction speed.
Wedge-shaped teeth: used to inlay special-shaped DTH drill bits and roller cone bits, suitable for soft rock formations with high drilling speed and low tooth fracture.
3. Repairing old parts and thermal spraying processing can not only restore the size of the parts, but also strengthen the performance of the surface of the parts and double their life, which is of great economic significance.
Second, the process selection principle of thermal spraying