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Properties and applications of engineering materials
Published in Alan Darbyshire, Charles Gibson, Mechanical Engineering, 2023
Alan Darbyshire, Charles Gibson
Mild steel does not respond to quench hardening because of its low carbon content. Case hardening increases the surface hardness of the material whilst leaving the core in its soft and tough condition. The first part of the process is known as carburising where the components are ‘soaked’ for a period of time at high temperature in a carbon-bearing material. The traditional method is to pack them in cast iron boxes with a carbon rich powder. This may be purchased under a variety of trade names or made up from a mixture of charcoal and bone meal. The carbon slowly soaks into the steel to give an outer case with a high carbon content. The depth of the case depends on the time of soaking.
Gear Materials
Published in Stephen P. Radzevich, Dudley's Handbook of Practical Gear Design and Manufacture, 2021
Nitriding is a case-hardening process in which the hardening agents are nitrides formed in the surface layers of steel through the absorption of nitrogen from a nitrogenous medium, usually dissociated ammonia gas.
Materials for motorcycles
Published in Andrew Livesey, Motorcycle Engineering, 2021
Low-carbon steel is soft, ductile, and malleable and therefore can be easily formed into shape. It cannot be hardened and tempered by heating and quenching, but it can be case-hardened and it will work-harden. Case-hardening is a process of coating the surface of the steel component with a high-carbon content chemical and heating it to a set temperature. When the component cools, the surface is hard like high-carbon steel and the underside remains soft and malleable. This process is used on hub bearing surfaces. If you look at a hub cone closely, you will be able to see the different colors of the metal. The advantages of this are that the axle and cones can be made of low-carbon steel, which is both easier to machine and cheaper to buy, and then given a wear-resistant surface for the bearing.
Crack initiation and early propagation in case hardened sintered PM steels under cyclic load
Published in Powder Metallurgy, 2023
Anders Holmberg, Urban Wiklund, Per Isaksson, Åsa Kassman Rudolphi
Machine components of PM steels, such as gears, are almost always hardened in some way. The most common is case hardening, which provides the surface with a hard, wear-resistant martensitic layer while keeping the ductility and toughness of the interior. The case hardening procedure involves surface heating, resulting in phase transformations from ferrite and pearlite to austenite. As the material is then rapidly cooled, the austenite is transformed into martensite. The relevant structure to relate to after case hardening is thus prior austenite grains rather than prior particle grains. For sintered steel, the pores, if they are large enough, will pin down grain boundaries and retard austenitic grain growth. Therefore the initial particle size practically restricts the maximum size of the austenite grains [10,11], meaning that the size of a prior austenite grain depends on the size of the prior particle grain size.