Quenching
Rapid cooling prevents the formation of cementite structure, instead forcibly dissolving carbon atoms in the ferrite lattice.
[1] In steel alloyed with metals such as nickel and manganese, the eutectoid temperature becomes much lower, but the kinetic barriers to phase transformation remain the same.
High-speed steel also has added tungsten, which serves to raise kinetic barriers, which, among other effects, gives material properties (hardness and abrasion resistance) as though the workpiece had been cooled more rapidly than it really has.
In these cases, another heat treatment technique known as tempering is performed on the quenched material to increase the toughness of iron-based alloys.
Tempering is usually performed after hardening, to reduce some of the excess hardness, and is done by heating the metal to some temperature below the critical point for a certain period of time, then allowing it to cool in still air.
Stage B: Vapor-transport cooling Once the temperature has dropped enough, the vapor layer will destabilize and the liquid will be able to fully contact the object and heat will be removed much more quickly.
There is evidence of the use of quenching processes by blacksmiths stretching back into the middle of the Iron Age, but little detailed information exists related to the development of these techniques and the procedures employed by early smiths.
[3] Although early ironworkers must have swiftly noticed that processes of cooling could affect the strength and brittleness of iron, and it can be claimed that heat treatment of steel was known in the Old World from the late second millennium BC,[4] it is hard to identify deliberate uses of quenching archaeologically.
[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] as when a man who works as a blacksmith plunges a screaming great axe blade or adze into cold water, treating it for temper, since this is the way steel is made strong, even so Cyclops' eye sizzled about the beam of the olive.However, it is not beyond doubt that the passage describes deliberate quench-hardening, rather than simply cooling.
[10] Chapters 18-21 of the twelfth-century De diversis artis by Theophilus Presbyter mentions quenching, recommending amongst other things that 'tools are also given a harder tempering in the urine of a small, red-headed boy than in ordinary water'.
[3] One of the fuller early discussions of quenching is the first Western printed book on metallurgy, Von Stahel und Eysen, published in 1532, which is characteristic of late-medieval technical treatises.
The modern scientific study of quenching began to gain real momentum from the seventeenth century, with a major step being the observation-led discussion by Giambattista della Porta in his 1558 Magia Naturalis.
