Case hardness of carburized steels is primar- ily a function of carbon content. When the car- bon content of the steel exceeds approximately. %, additional . Results show 1) Carburized layer by wax is more depth than in case of layer by wax than by kerosene 3) Higher hardness carburized layer. carburizing heat treatment, core refining, case hardening, origin of residual stress , nitriding, In the case of steel the possible options are much more varied.
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Gas carburizing (and carbonitriding) is a case-hardening treatment where a finished part is exposed to a carburizing atmosphere at a high temperature. Processes that change the surface chemical composition (case hardening or Carburising is a hardening process in which carbon is introduced into the surface . Carburized Mild Steel, Using Activated Carbon as Carburizer The case and core hardness of the carburized tempered samples were.
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. Steel case hardening depth of the carburized steel depends upon the carburizing time and the surface carbon intensity. When the carburizing time is prolonged to obtain increased case depths, excessive free carbides may be formed.
The micro-structural elements have an unfavorable effect on the distribution of residual stresses. Carburized steels generally have base carbon contents of approximately 0. Most carburized steels are deoxidized by the addition of aluminum. Due to the carbon content difference in the core and the case, their case hardening capability is also different. Methods of Carburizing While the fundamental carburizing principle has not changed much since its inception, the carbon introduction techniques have been improving.
The four carburizing processes are explained below.
Pack Carburizing Components are packed in an environment with a high carbon content such as cast iron shavings or carbon powder. The components are heated with the production of carbon monoxide, which is a reducing agent.
The reduction occurs on the steel surface with the release of carbon that is diffused into the surface because of high temperatures. With the carbon absorption inside the component, the materials are hardened. The surface carbon is in the range of 0. The case depth is approximately 0. Control of pack carburizing is difficult because uniform temperatures may not be maintained. Gas Carburizing Gas carburizing is theoretically similar to pack carburizing aside from the supply of carbon monoxide gas to the heated furnace and the carbon decomposition.
Many of the problems with pack carburizing are eliminated in this process. The carbon monoxide gas needs to be contained safely. The components are enclosed in a carbon bearing environment that is replenished continuously to maintain a high carbon content.