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Heat Treating

Heat Treating

Today, metal parts manufacturers frequently change the properties of metal by applying heat treating. These processes permit the modification of the physical characteristics of steel, for instance. Heat treating in general involves the use of heating or cooling.

The Heat Treating Process

The process of heat treating varies. Important factors include:

  • The metal undergoing heat treating;
  • The maximum temperature;
  • The duration of heating;
  • The speed of cooling;
  • The initial cooling temperature.

In general, heat treating hardens metal parts. This process may ultimately impact other properties of the metal work piece also. Some modifications include ductility, strength, toughness, the presence of internal stresses and the ability to withstand machining without fracturing or growing brittle.

Since heat treating sometimes changes the interior grains of the constituent metal, industrial manufacturers must exercise great care in obtaining desired results through the application of this process. Usually, a metallurgist will examine the interior of a sample work piece carefully on a microscopic level.

Common Heat Treatments

Over the centuries, metal manufacturers have developed a number of heat treating technologies. These include quenching, annealing, case hardening, induction hardening, normalizing and tempering.


Quenching involves cooling a hot metal part very quickly in order to enhance hardness. Rapid cooling impacts the structure of the metal at a microscopic level.

Process Details

Typically metal manufacturers heat metals to high temperatures and then quench them in a bath of liquids, such as water or oil. Some production facilities substitute inert gases for liquid baths. Quenching sometimes generates brittle parts unless combined with tempering.


Hard metal parts result from the process of quenching.


Metal fabricators use quenching to generate hardened metal parts, including gears.


During annealing, a metal manufacturer softens metal to obtain greater ductility.

Process Details

Softening occurs by re-heating metal above the indicated temperature for re-crystallization for a designated period of time before cooling.


This process enhances the ductility of many types of metal, including silver, brass, steel and copper.


Annealing occurs extensively in the semiconductor and electronics industry.

Case Hardening

Case hardening generates hard, wear-resistant surfaces. It’s used widely today.

Process Details

Typically case hardening relies upon carburizing or nitriding in conjunction with a heat source to toughen exterior surfaces through the diffusion of carbon or nitrogen atoms.


Modern case hardening occurs under highly controlled conditions.


This process helps produce gears, cams and cylinder sleeves.

Induction Hardening

Manufacturers employ electromagnetic currents to produce hardened metal surfaces.

Process Details

An induction coil typically surrounds a work piece. It heats the metal.


This process occurs in mass-production settings.


This process hardens auto axles.


Normalization involves the annealing of ferrous alloys.

Process Details

The re-heating usually occurs at very elevated temperatures.


Normalizing will reduce brittleness, making metal parts less likely to fracture.


Steel parts requiring extensive machining often benefit from normalization.


Tempering can soften metal after hardening in order to reduce brittleness.

Process Details

During tempering, a metal fabricator re-heats metals, often to very high temperatures, then allows the work pieces to cool gradually for a designated period. The temperatures utilized during tempering vary based upon the component.


Tempering decreases brittleness.


Springs and metal tools often undergo tempering.

Heat Treating Applications and Benefits

Heat treating metal components offers numerous benefits. These include hardening and softening metals to enhance wear resistance and reduce brittleness. In many circumstances, heat treated parts last for longer periods of time and resist corrosion in harsh environments more effectively. Softening enables manufacturers to alleviate interior stresses.

Softening Metal

Industrial metal parts manufacturers employ two processes very widely to achieve metal softening: annealing and tempering. Softening typically helps decrease the hardness and brittleness of a work piece. It tends to increase ductility by reducing interior stresses which might cause strain or fracturing.

Overall, this stress relieving process usually increases the toughness of metal. It may also further refine interior grain structures and, in some cases, modify the electromagnetic properties of the constituent metal.

Hardening Metal

Some metal heat treating processes, such as case hardening and induction hardening, enhance the hardness of metal work pieces. Metal parts manufacturers may employ these processes in order to improve a component’s strength and wear properties. For instance, engine gear manufacturers often harden the metal in order to augment a component’s ability to withstand a lot of friction and stress during daily operations.

The specific metal hardening process can make a significant difference in the costs and manufacturing resources required. For instance, case hardening usually relies upon a continuous heat source, such as a blast furnace. By contrast, induction hardening utilizes an electromagnetic current during heating.

Materials Modification

Heat treating may alter other properties of a metal in addition to impacting hardness or softness. In the past, manufacturers have employed these processes to augment stress relieving properties of parts intended for use in harsh environments, for instance. Softening usually makes a part less brittle and more resilient.

Companies sometimes employ heat treating during the finishing stages in order to enhance the anticipated lifespan of a metal component. For example, heat treating may improve the metal’s internal stress relieving capabilities. Softening hard metal parts promotes greater toughness.


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