Martempering is also known as
stepped quenching or interrupted quenching. In this process, steel is heated above the upper critical point (above the
transformation
Transformation may refer to:
Science and mathematics
In biology and medicine
* Metamorphosis, the biological process of changing physical form after birth or hatching
* Malignant transformation, the process of cells becoming cancerous
* Trans ...
range) and then quenched in a hot-
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) and lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...
,
molten-salt, or molten-
lead
Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...
bath kept at a temperature of 150-300 °C. The workpiece is maintained at a temperature above the martensite start (Ms) point until uniform temperature is achieved throughout its cross-section. It is then cooled to room temperature, typically in air or oil. The steel is then
tempered. In this process,
austenite
Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 ...
is transformed to
martensite
Martensite is a very hard form of steel crystalline structure. It is named after German metallurgist Adolf Martens. By analogy the term can also refer to any crystal structure that is formed by diffusionless transformation.
Properties
Mar ...
by
step quenching, at a rate fast enough to avoid the formation of
ferrite,
pearlite
Pearlite is a two-phased, lamellar (or layered) structure composed of alternating layers of ferrite (87.5 wt%) and cementite (12.5 wt%) that occurs in some steels and cast irons. During slow cooling of an iron-carbon alloy, pearlite for ...
, or
bainite
Bainite is a plate-like microstructure that forms in steels at temperatures of 125–550 °C (depending on alloy content). First described by E. S. Davenport and Edgar Bain, it is one of the products that may form when austenite (the face ...
.
[
In the martempering process, austenitized metal part is immersed in a bath at a temperature just above the martensite start temperature (Ms). Interrupted quenching involves halting the cooling process at a temperature above the martensite transformation region, allowing sufficient time for the center of the workpiece to reach the same temperature as the surface. The metal part is then removed from the bath and cooled in air to room temperature to permit the austenite to transform to martensite. Martempering is a technique used to control the stresses and strains that develop during the quenching of a steel component. In this process, the steel is heated above the critical range to transform it entirely into austenite.
The drawback of this process is that the large section cannot be heat treated by this process.
]
See also
* Austempering
*Tempering (metallurgy)
Tempering is a process of heat treating, which is used to increase the toughness of iron-based alloys. Tempering is usually performed after Hardening (metallurgy), hardening, to reduce some of the excess hardness, and is done by heating the metal ...
References
External links
Heat Treating Terms and Definitions
Engineers Edge
{{Iron and steel production
Metal heat treatments