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Conventional Heat Treatments


       
  Conventional Carburizing Normalizing Carbon Restoration
  Conventional Carbonitriding Conventional Annealing  
  Conventional Hardening / Quenching Stress Relieving  
  Conventional Tempering Age/Precipitation Hardening  
  Conventional Quench & Temper Austenitizing  
       

 

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Conventional Carburizing


 

Carburizing is a process of controlled diffusion of carbon into the surface of a component, followed by quenching and tempering, with the objective of increasing the component’s surface hardness. The process is generally applicable to low carbon steels. When conducted in a "conventional", rather than in a vacuum furnace, we can refer to the process as conventional carburizing.

In this thermal process ferrous alloys are heated to above their transformation temperature and exposed to carbon rich medium. Processing temperatures fall in the 1450°F - 1900°F (790°C - 1040°C) range. The diffusion of carbon into the part and the subsequent quench leads to a part with a hard, wear resistant surface and a tough shock resistant core.

Solid, liquid and gaseous carbon-carrying medium may be employed, however, the first two are rarely used. Nitrex-offered carburizing is conducted in computer controlled integral quench and pit gas carburizing furnaces. A full range of case depths if feasible with an economically derived limit of approximately 0.250" (6.4 mm).

In addition, Nitrex is capable of selective carburizing where only specific areas of the part are to be treated.

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Conventional Carbonitriding


Carbonitriding is a process similar to carburizing whereby ammonia is added to the carburizing atmosphere, which results in supplementary nitrogen diffusion into the surface of a treated component.

Note: carbonitriding is sometimes confused with nitrocarburizing. Please read the descriptions of both processes to avoid misunderstandings.

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Conventional Hardening / Quenching


Hardening is one of the oldest metallurgical processes known to man, originally in the form of heating a sword in the fire and then throwing it into the lake to make it harder. The more modern approach is to heat components in an atmosphere furnace followed by quenching, generally in heated oil.

The expression "conventional hardening" is used here to differentiate the process from vacuum hardening. It should also be noted that "hardening" is usually referred to as "quenching".

A more refined version of this process is Vacuum Hardening.

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Conventional Tempering


Tempering is almost always required after hardening (both in an atmosphere furnace as well as in vacuum, as described further), to reduce the hardness (and brittleness) to a desirable level.

The expression "conventional tempering" is used here to differentiate the process from "vacuum tempering".

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Conventional Quench & Temper


The words “quench and temper” are not a technology but just an expression. We have included this paragraph for the sake of completeness and to help those unfamiliar with these processes in absorbing these concepts more easily.

Quenching and tempering are the most fundamental heat treatments available in that most ferrous alloys must first be hardened (quenched) and then tempered to the appropriate hardness. The expression “quench and temper” (or “harden and temper”, which is the same thing) is so entrenched that some of us forget that in a sequence of conventional processes the two are done in different furnaces, with parts transferred, as quickly as possible, from one to the other.

Quenching and tempering are described separately in this section.

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Normalizing


Normalizing is a relatively simple process whose parameters, however, depend greatly on the type of steel and the desired result. The main purpose will usually be an improvement and homogenization of the grain structure.

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Conventional Annealing


The main purpose of Annealing is to soften the metal. This process is used as one of the preliminary heat treating operations or as a rescue procedure when a hardening or tempering cycle fails to meet the specification requirement, and one has to start over. (Also vacuum annealing)

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Stress Relieving


As the name of the process clearly indicates, Stress Relieving is used to reduce the residual stresses in the microstructure after machining or certain heat treating operations, to prevent distortion from occurring later.

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Age/ Precipitation Hardening


Age or Precipitation Hardening (also Aging) is a change in material properties (generally hardening) effected by holding parts at moderately elevated temperatures, without any change in the chemistry of the alloy.

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Austenitizing


Austenitizing is a process designed to induce the formation of austenite on the alloy.

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Carbon Restoration


In the event that in a heat treating operation the components suffered from decarburization (loss of carbon content) of the surface, we are capable of salvaging them using the Carbon Restoration technique.

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