Why Cemented Carbide Also Called Cermet
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- Category: Tungsten Information
- Published on Tuesday, 01 September 2015 16:37
- Written by zhihua
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The main use of tungsten (in the form of tungsten carbide) is now in the manufacture of cemented carbide. Cemented carbide, or hard metal as it is often called, is a material made by "cementing" very hard tungsten mono-carbide (WC) grains in a binder matrix of tough cobalt metal by liquid phase sintering. This material is classified technically as a “brittle” material since it exhibits little or no plastic deformation preceding the initiation of a crack. All materials contain some amount of defects in the form of voids, pores or micro-cracks. These defects lead to reduced material strength. In the case of ductile materials such as aluminum, mild steels or copper, the frequency of defects is less critical than in brittle materials.
Sintered tungsten carbide exhibits a broader range of scatter-of-fracture stresses, due primarily to the existence of micro-voids, when compared to ductile materials. The value of the stress at fracture can also vary widely with size, stress state (tensile, bending, torsion), shape, and type of loading. Despite the significant variability of the stress at failure, cemented carbide has considerably high strength for what some consider to be a “ceramic” or cermet material.
The definition of a ceramic material is the marriage of a metal to a nonmetal, for example silicon (metal) carbide (carbon, non-metal), aluminum oxide, silicon nitride or tungsten carbide. A cermet is a composite material composed of ceramic (cer) and metallic (met) materials. A cermet is ideally designed to have the optimal properties of both a ceramic, such as high temperature resistance and hardness, and those of a metal, such as the ability to undergo plastic deformation. The metal is used as a binder with oxide, boride, carbide, or alumina. Generally, the metallic elements used are cobalt, nickel, and molybdenum. It is the addition of the metallic binder, i.e. cobalt or nickel that makes the cemented carbide (WC - Co) a cermet and differentiates it from truly brittle materials, that is, the ceramic family of materials.
The combination of WC and metallic cobalt as a binder is a well-adjusted system not only with regard to its properties, but also to its sintering behavior. The high solubility of WC in cobalt at high temperatures and a very good wetting of WC by the liquid cobalt binder result in an excellent densification during liquid phase sintering and in a pore-free structure. As a result of this, a material is obtained which combines high strength, toughness and high hardness.
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Advantage of Tungsten Resources Promotes Rapid Development of Tungsten Carbide Industry
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- Category: Tungsten Information
- Published on Tuesday, 01 September 2015 16:28
- Written by zhihua
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Tungsten is very valuable as a rare metal resources. Tungsten industry is significant to be one of the important material industries in modern time.
Tungsten has high hardness, high melting point, high strength, and it’s widely used in machinery, special steel, defense industry and other fields. Its main application is the carbide industry, which is often said as tungsten steel. Carbide is called the teeth of modern industry. As an important strategic resource, tungsten resource is emphasis protected by world powers. Our country has also set up Tungsten Industry Association since 1990s, introduced a number of laws and regulations, and keeps strict supervision on tungsten resources.
Global reserves of tungsten resources are scarce and centralizedly distributed. 65.5% of the world’s reserves are in China, which has obvious advantages. Since 2001, China began to imply tungsten resource extraction quotas and export quotas, effectively inhibited the global tungsten supply. Coupled with decreasing amount of foreign supply and limited availability of recycling waste tungsten, tungsten supply growth was slow.
Tungsten is mainly used in carbide, steel and alloys, chemical industry etc. About 50% of tungsten materials are used for carbide industry. In China production of carbide cutting tools only accounts about 25% of total production, while 65% of consumption in developed countries accounts for carbide cutting tool consumption. China hass broad space for development of carbide in the future. "Twelfth Five-Year Plan" clearly encourages new materials containing tungsten may become a new impetus to the demand of tungsten.
Tungsten resources are rare metal which has absolute advantage in China. As the country gradually strengthen the industry consolidation, supply growth will gradually slow down, while demand in areas such as carbide rapid growth in the long term, the future supply of tungsten would be probably in the tight state. Our carbide industry will get more rapid developement relied to the absolute advantage of tungsten resouces.
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System and Method for processing Ferrotungsten and Other Tungsten Alloys Articles forward Therefrom and Methods for Detecting the Same
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- Category: Tungsten Information
- Published on Tuesday, 01 September 2015 16:23
- Written by xinyi
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Systems and methods for refining or otherwise processing tungsten alloys, including ferrotungsten powder and articles formed therefrom, and methods for detecting the presence of the same. The methods include at least one of magnetically-separating and particle-size-separating ferrotungsten or ferrotungsten-containing powder. In some embodiments, powder may be separated to remove fine particles, and optionally to separate the remaining particles into fractions containing selected particle size distributions. The powder additionally or alternatively may be separated into at least magnetic and non-magnetic fractions. In some embodiments, portions of two or more size and/or magnetism fractions are mixed to provide a ferrotungsten-containing feedstock. Selected fractions resulting from the size and magnetism separation steps may be utilized to provide a ferrotungsten-containing feedstock from which articles are produced and which may include additional components.
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A New Technological Process for Smelting Ferro-Tungsten-Molybdenum
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- Category: Tungsten Information
- Published on Tuesday, 01 September 2015 16:28
- Written by xinyi
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The paper introduces the use of W and Mo in alloy steel, describes the mechanism of ferro-tungsten-molybdenum smelting in three-phase AC working frequency plasmafurnace directly with mixed charge of W and Mo concentrates and gives the pilot experiment results. The ferro-tungsten-molybdenum, obtained with Mo/W of 0. 05~0.5 at recovery of Mo and W 90% respectively, is applicable to smelting ahoy steel. This new technologicalroute is open to utilization of the W-Mo intergrowth mineral resource.
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Determination of Lead,Tin and Bismuth in the Ferrotungsten by Inductively Coupled Plasma Atomic Emission Spectrometry
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- Category: Tungsten Information
- Published on Tuesday, 01 September 2015 16:20
- Written by xinyi
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Determination of lead,tin and bismuth in the ferrotungsten by inductively coupled plasma atomic emission spectrometry.
A method for the determination of lead,tin and bismuth by inductively coupled plasma atomic emission spectrometry was studied.The sample was decomposed with oxalic acid and hydrogen peroxide.In the medium of ammonia at pH≥9,Pb,Sn and Bi were precipitated and separated from W in the solution.The residual tungsten in the sediment was less than 0.7% after twice precipitation with ammonia liquor.The interferences from residual tungsten could be eliminated by the background correct mode.The restraining influence from iron on the intensity of Pb,Sn could be overcome by matrix matching.The method has been applied to the determination of Pb,Sn and Bi in ferrotungsten with the recovery of 96%-102% and relative standard deviation of 1.3%-1.5%.
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