High-hardenability case steels

Case Hardening by Surface Deformation. When a metaUic material is plastically deformed at sufficiently low temperature, eg, room temperature for most metals and alloys, it becomes harder. Thus one method to produce a hard case on a metallic component is to plastically deform the surface region. This can be accomplished by a number of methods, such as by forcing a hardened rounded point onto the surface as it is moved. A common method is to impinge upon the surface fine hard particles such as hardened steel spheres (shot) at high velocity. This process is called shot... 

The discussion so far has been limited to the structure of pure metals, and to the defects which exist in crysteds comprised of atoms of one element only. In fact, of course, pure metals are comparatively rare and all commercial materials contain impurities and, in many cases also, deliberate alloying additions. In the production of commercially pure metals and of alloys, impurities are inevitably introduced into the metal, e.g. manganese, silicon and phosphorus in mild steel, and iron and silicon in aluminium alloys. However, most commercial materials are not even nominally pure metals but are alloys in which deliberate additions of one or more elements have been made, usually to improve some property of the metal examples are the addition of carbon or nickel and chromium to iron to give, respectively, carbon and stainless steels and the addition of copper to aluminium to give a high-strength age-hardenable alloy. 

Cementation process. This process, now little used, consists of heating wrought iron or low-carbon steel in powdered charcoal or leather dust for 6 to 11 days in a closed boxlike furnace at 650 to 700°C. At these temperatures, carbon diffuses slowly into the surface of the steel, thus producing a thin coat of high-carbon steel over a core of low-carbon steel. This is essentially a case-hardening procedure, and steel produced in this manner is used largely in the manufacture of tools. 

Various iron nitrides and carbonitrides are formed during case hardening of steels and alloyed steels. " These iron nitrides are hard, highly wear resistant and usually do not lead to dimensional changes in the case-hardened items. 

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