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Heat Treatment of Metals

Modern metallurgists have developed ways to increase the strength of steel and reduce brittleness through the careful application of heat treatment protocols.

Both the specific alloys utilized in a work piece and the goals of the manufacturer ultimately impact the selection of hardening and tempering processes.

In most instances, tempering increases the toughness of ferrous metal alloys. This process usually occurs following hardening (which may promotes brittleness).

Steel producers reduce undesirable aspects of hardening by re-heating the metal at a lower-than-critical temperature for a designated period of time. The work piece then undergoes gradual cooling in still air. Taking this step can minimize brittleness.

Additionally, the process of “tempering” sometimes refers to hardening steel by reheating a work piece and then quenching it in a bath of oil.

The type of tempering technology used in a production environment ultimately depends upon the goals of the manufacturer.

The History of Tempering

Today, historians believe metalworkers relied upon the process of tempering-and-quenching as early as 1200 B.C.

While skilled blacksmiths could employ tempering to improve the quality of weapons and other metal objects, the use of this process necessarily involved trial-and-error: early forges could not accurately measure temperatures.

By the 1800s and 1900s, better tools existed for microscopy and for measuring forge temperatures. Metallurgists began studying the effects of tempering on metal grains.

As knowledge increased concerning different metal alloys and the effects of temperature settings on the parts fabrication process, tempering assumed greater importance in mass production environments.

The Tempering Process

The tempering process involves re-heating metal to a high temperature below the critical melting point and then cooling it again. The method selected for cooling depends upon the manufacturer’s specific goals for the work piece.

For instance, tempering and then quenching rapidly through immersion in oil, water or a forced-air environment helps harden steel.

By contrast, tempering and gradual cooling enhances the toughness of the metal by reducing internal stresses and helping to minimize brittleness.

Today, metallurgists examine the interior grains of steel microscopically to confirm the effect of tempering at specific temperatures. By enhancing the toughness of steel, the tempering process makes it less likely the metal will fail due to a sudden fracture.

The composition of the metal alloys used in a particular steel product significantly influence the tempering process.

Tempering will influence the internal structure of carbon steels, for instance. In most cases, it contributes to the formation of more finely grained microstructures.

Manufacturers may temper a steel work piece evenly to obtain uniform “through tempering” or they may selectively temper. By controlling heating and cooling temperatures rigorously, numerous options exist for creating tough, ductile yet hardened steel components.

Tempering: Materials And Applications

Tempering occurs in both “high tech” and comparatively “low tech” manufacturing settings today.

However, in order to perform this process effectively, a production facility must have the ability both to control metal heating and cooling temperatures for specified periods of time and to examine the interior grains of metal constituents.


Tempering ultimately depends upon the ability to re-heat metal. While cooling may occur gradually at room temperatures, production environments do require reliable ways to heat alloys under highly controlled conditions for sustained periods.

Blast furnaces, open flame forges, industrial ovens and a number of automated heating technologies contribute to the production of tempered metal parts in different settings.

Cooling technologies vary from open air to forced-air environments, oil baths and water immersion tanks.


Numerous applications for tempering exist today.

Industrial metal parts manufacturers frequently perform tempering to enhance the toughness of components and reduce fracturing and brittleness without sacrificing hardness.

Illustrative tempered metals include the steel beams and rivets used in construction projects to specialized aerospace, aircraft, marine and automotive components.

Agricultural and industrial machinery, electrical and plumbing parts, oil and gas drilling equipment and numerous consumer wares also frequently undergo tempering.


Tempering offers numerous benefits:

By carefully considering the composition of an alloy and the specific temperature requirements of a tempering protocol, manufacturers can produce steels displaying desired characteristics, such as enhanced hardness or ductility.

When performed correctly, tempering helps save valuable time during the production process. It helps ensure the metal used in a particular component will prove suitable for the customer’s intended purpose.

A manufacturer may temper the steel selected for a ductile spring at one temperature and the steel used in a construction beam at a different setting, for instance.

Today manufacturers typically integrate tempering protocols smoothly into a production line.

They value the ability to precisely control this heat treatment process in order to generate uniformly tempered metal work pieces in high volumes.

Tempering offers cost savings benefits because it reduces waste resulting from defects in the metal.

For instance, by tempering a brittle work pieces, a manufacturer may still obtain the benefits of hardness will reducing risks associated with fracturing.

By tempering steel, a manufacturer can promote desirable properties, such as an enhanced ability to perform load-bearing.

Tempering may improve the suitability of the metal for its intended purpose, ultimately enhancing product quality.

In many situations, tempering increases the durability of metal parts. This process may help enhance the expected product lifespan of a steel component, for instance.

Tempering offers numerous benefits for manufacturers. The widespread use of tempering in metal parts production facilities testifies to the utility of this process!


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From a contract manufacturing firm, BuntyLLC evolved into a full service custom machined, forged and cast metal parts fabrication enterprise. We supply global solutions from our headquarters in Greenville, South Carolina.

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