Metal Treatment Methods and Processes

Solid Solution Hardening

Solid solutions cause an increase in the hardness of the metal.

Treatment of Metals

Treatments are categorized based on how they alter the properties of the metal:

• Heat treatment: The metal is subjected to thermal processes that do not vary its chemical composition, but do alter its structure.
• Thermochemical treatments: Metals undergo heating and cooling while amending the chemical composition of their outer surface.
• Mechanical treatments: Features are enhanced by mechanical deformation of metals, with or without heat.
• Surface treatments: Improves the metal surface without changing its bulk chemical composition.

Note: Treatments should not change the chemical composition of the metal; otherwise, it would be classified as a different type of process.

Heat Treatments

These are operations of heating and cooling metals to amend their crystal structure. There are three primary treatments:

• Annealing: The metal is heated for a period and then cooled slowly.
• Quenching: The metal is heated and then cooled sharply.
• Tempering: Applied to quenched metals; it is a complementary treatment to quenching.

Thermochemical Processing

These operations consist of heating and cooling metals, supplemented with the addition of other elements to the surface of the pieces. There are five types:

• Cementation: The addition of carbon into the surface of steel that has a low content of this element.
• Nitriding: A process of hardening steel through nitrogen absorption at a given temperature.
• Cyaniding: A treatment intermediate between cementation and nitriding.
• Carbonitriding: Increases the hardness of steels by the absorption of carbon and nitrogen at a given temperature.
• Sulfinization: Achieved by immersing the metal in a special bath to incorporate a layer of carbon, nitrogen, and sulfur.

Mechanical Treatment

These improve the characteristics of metals by mechanical deformation, with or without heat. There are two types:

• Hot mechanical treatment: Consists of heating a metal to a certain temperature, then hitting it strongly to deform it.
• Cold mechanical treatment: Consists of deforming the metal at ambient temperature through impact.

Surface Treatment

• Metallization: A molten metal is projected onto the surface of another.
• Chromium plating: Chromium is deposited onto the metal surface.