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Quench polish quench (QPQ) is a specialized type of nitrocarburizing case hardening that increases corrosion resistance. It is sometimes known by the brand name of Tufftride, Tenifer or Melonite. [1] Three steps are involved: nitrocarburize ("quench"), polish, and post-oxidize ("quench"). [2]
Colt Peacemaker, showing discoloration from case-hardening. Case-hardening or carburization is the process of introducing carbon to the surface of a low-carbon iron, or more commonly a low-carbon steel object, in order to harden the surface. Iron which has a carbon content greater than ~0.02% is known as steel.
A few typical hardening agents include carbon monoxide gas (CO), sodium cyanide and barium carbonate, or hardwood charcoal. In gas carburizing, carbon is given off by propane or natural gas . In liquid carburizing, the carbon is derived from a molten salt composed mainly of sodium cyanide (NaCN) and barium chloride (BaCl 2 ).
Surface carburizing, or case hardening, is one example of solid solution strengthening in which the density of solute carbon atoms is increased close to the surface of the steel, resulting in a gradient of carbon atoms throughout the material. This provides superior mechanical properties to the surface of the steel without having to use a ...
Carbonitriding forms a hard, wear-resistant case, is typically 0.07 mm to 0.5 mm thick, and generally has higher hardness than a carburized case. Case depth is tailored to the application; a thicker case increases the wear life of the part.
Case hardening is specified by "hardness" and "case depth". The case depth can be specified in two ways: total case depth or effective case depth. The total case depth is the true depth of the case. For most alloys, the effective case depth is the depth of the case that has a hardness equivalent of HRC50; however, some alloys specify a ...
The hardenability of a ferrous alloy is measured by a Jominy test: a round metal bar of standard size (indicated in the top image) is transformed to 100% austenite through heat treatment, and is then quenched on one end with room-temperature water. The cooling rate will be highest at the end being quenched, and will decrease as distance from ...
At 0-D there is precipitate and solid solution strengthening with particulates strengthening structure, at 1-D there is work/forest hardening with line dislocations as the hardening mechanism, and at 2-D there is grain boundary strengthening with surface energy of granular interfaces providing strength improvement.