GAS CARBURISING PDF

During the thermal cycle the components are subject to an enriched carbon atmosphere such that nascent species of carbon can diffuse into the surface layers of the component. The rate of diffusion is dependent on the alloy and carbon potential of the atmosphere. Care must be taken to ensure that only sufficient carbon is available in the atmosphere at any one time to satisfy the take up rate of the alloy to accept the carbon atoms. In practice, this is defined in a carbon potential setpoint profile which runs concurrently with the temperature cycle.

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Method[ edit ] Carburization of steel involves a heat treatment of the metallic surface using a source of carbon. The process depends primarily upon ambient gas composition and furnace temperature, which must be carefully controlled, as the heat may also impact the microstructure of the remainder of the material. For applications where great control over gas composition is desired, carburization may take place under very low pressures in a vacuum chamber.

Plasma carburization is increasingly used to improve the surface characteristics such as wear, corrosion resistance, hardness , load-bearing capacity, in addition to quality-based variables of various metals, notably stainless steels. The process is environmentally friendly in comparison to gaseous or solid carburizing. It also provides an even treatment of components with complex geometry the plasma can penetrate into holes and tight gaps , making it very flexible in terms of component treatment.

The process of carburization works via the diffusion of carbon atoms into the surface layers of a metal. If the carbon remains in solid solution, the steel is then heat treated to harden it.

Both of these mechanisms strengthen the surface of the metal, the former by forming pearlite or martensite, and the latter via the formation of carbides. Both of these materials are hard and resist abrasion. In oxy-acetylene welding , a carburizing flame is one with little oxygen, which produces a sooty , lower-temperature flame. It is often used to anneal metal, making it more malleable and flexible during the welding process.

A main goal when producing carburized workpieces is to ensure maximum contact between the workpiece surface and the carbon-rich elements. In gas and liquid carburizing, the workpieces are often supported in mesh baskets or suspended by wire.

In pack carburizing, the workpiece and carbon are enclosed in a container to ensure that contact is maintained over as much surface area as possible. Pack carburizing containers are usually made of carbon steel coated with aluminum or heat-resisting nickel-chromium alloy and sealed at all openings with fire clay.

Hardening agents[ edit ] There are different types of elements or materials that can be used to perform this process, but these mainly consist of high carbon content material. A few typical hardening agents include carbon monoxide gas CO , sodium cyanide and barium carbonate , or hardwood charcoal. In gas carburizing, the CO is given off by propane or natural gas.

In pack carburizing, carbon monoxide is given off by coke or hardwood charcoal. Geometrical possibilities[ edit ] There are all sorts of workpieces that can be carburized, which means almost limitless possibilities for the shape of materials that can be carburized. However careful consideration should be given to materials that contain nonuniform or non-symmetric sections.

Different cross sections may have different cooling rates which can cause excessive stresses in the material and result in breakage. The amount of these changes varies based on the type of material that is used, the carburizing process that the material undergoes and the original size and shape of the work piece. However changes are small compared to heat-treating operations.

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Gas Carburising Process

Method[ edit ] Carburization of steel involves a heat treatment of the metallic surface using a source of carbon. The process depends primarily upon ambient gas composition and furnace temperature, which must be carefully controlled, as the heat may also impact the microstructure of the remainder of the material. For applications where great control over gas composition is desired, carburization may take place under very low pressures in a vacuum chamber. Plasma carburization is increasingly used to improve the surface characteristics such as wear, corrosion resistance, hardness , load-bearing capacity, in addition to quality-based variables of various metals, notably stainless steels. The process is environmentally friendly in comparison to gaseous or solid carburizing.

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Carburising Gas Reactions

Home Heat Treatment Solutions Heat Treatment Applications Carburising Gas Reactions Carburising Gas Reactions In the gas carburising process, a low carbon bearing carrier gas is used, which is enriched with a hydrocarbon gas, such as propane or methane natural gas , to increase and control the carbon availability of the atmosphere. The carrier gas is usually of the Endothermic gas type produced from a sub stoichiometric mixture of a hydrocarbon and air at elevated temperature in the presence of a catalyst. The production of Endothermic gas is usually carried out in an external gas generator. Alternatively, a nitrogen — Methanol mixture, injected into the furnace can be used to produce a synthetic Endothermic gas.

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Gas Carburizing

Gas Carburizing Abstract: Carburizing is a case-hardening process in which carbon is dissolved in the surface layers of a low-carbon steel part at a temperature sufficient to render the steel austenitic, followed by quenching and tempering to form a martensitic microstructure. The resulting gradient in carbon content below the surface of the part causes a gradient in hardness, producing a strong, wear-resistant surface layer on a material, usually low-carbon steel, which is readily fabricated into parts. Carburizing is a case-hardening process in which carbon is dissolved in the surface layers of a low-carbon steel part at a temperature sufficient to render the steel austenitic, followed by quenching and tempering to form a martensitic microstructure. In gas carburizing, commercially the most important variant of carburizing, the source of carbon is a carbon-rich furnace atmosphere produced either from gaseous hydrocarbons, for example, methane CH4 , propane C3H3 , and butane C4H10 , or from vaporized hydrocarbon liquids. In the most primitive form of this process, the carbon source is so rich that the solubility limit of carbon in austenite is reached at the surface of the steel and some carbides may form at the surface. Such atmospheres will also deposit soot on surfaces within the furnace, including the parts. While this mode of carburizing is still practiced in parts of the world in which resources are limited, the goal of current practice in modern manufacturing plants is to control the carbon content of furnace atmospheres so that: The final carbon concentration at the surface of the parts is below the solubility limit in austenite.

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