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The quenched steel, being placed in or very near its hardest possible state, is then tempered to incrementally decrease the hardness to a point more suitable for the desired application. The hardness of the quenched steel depends on both cooling speed and on the composition of the alloy.
The earliest examples of quenched steel may come from ancient Mesopotamia, with a relatively secure example of a fourth-century BC quench-hardened chisel from Al Mina in Turkey. [6] Book 9, lines 389-94 of Homer's Odyssey is widely cited as an early, possibly the first, written reference to quenching: [3] [7]
Only steel that is high in carbon can be hardened and tempered. If a metal does not contain the necessary quantity of carbon, then its crystalline structure cannot be broken, and therefore the physical makeup of the steel cannot be altered. Frequently, the term "hardening" is associated with tempered steel. Both processes are used hand in hand ...
Martensite in AISI 4140 steel 0.35% carbon steel, water-quenched from 870 °C. 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. [1]
A514 is a particular type of high strength steel, which is quenched and tempered alloy steel, with a yield strength of 100,000 psi (100 ksi or approximately 700 MPa). The ArcelorMittal trademarked name is T-1. [1] A514 is primarily used as a structural steel for building construction.
In austempering the heat treat load is quenched to a temperature which is typically above the Martensite start of the austenite and held. In some patented processes the parts are quenched just below the Martensite start so that the resulting microstructure is a controlled mixture of Martensite and Bainite.
This process is often used for knife making, by heating only the edge of a previously quenched and tempered blade. When edge turns the proper color temperature, it is quenched, hardening only the edge, but leaving most of the rest of the blade at the lower hardness. The knife is then tempered again to produce the final differential hardness. [16]
A tempered outer ring of martensite, 2. A semi-tempered middle ring of martensite and bainite, and 3. a mild circular core of bainite, ferrite and pearlite. This is the desired micro structure for quality construction rebar. In contrast, lower grades of rebar are twisted when cold, work hardening them to increase their strength.