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The high temperature of annealing may result in oxidation of the metal's surface, resulting in scale. If scale must be avoided, annealing is carried out in a special atmosphere, such as with endothermic gas (a mixture of carbon monoxide, hydrogen gas, and nitrogen gas). Annealing is also done in forming gas, a mixture of hydrogen and nitrogen.
This produces steel that is much stronger than full-annealed steel, and much tougher than tempered quenched steel. However, added toughness is sometimes needed at a reduction in strength. Tempering provides a way to carefully decrease the hardness of the steel, thereby increasing the toughness to a more desirable point.
This is the most common state for finished articles such as tools and machine parts. In contrast, the same steel composition in annealed state is softer, as required for forming and machining. Depending on the temperature and composition of the steel, it can be hardened or softened. To make steel harder, it must be heated to very high temperatures.
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 ]
A gas cylinder is used to store gas or liquefied gas at pressures above normal atmospheric pressure. [2] In South Africa, a gas storage cylinder implies a refillable transportable container with a water capacity volume of up to 150 litres. Refillable transportable cylindrical containers from 150 to 3,000 litres water capacity are referred to as ...
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.
If a disordered state is not in thermodynamic equilibrium, one speaks of quenched disorder. For instance, a glass is obtained by quenching (supercooling) a liquid. By extension, other quenched states are called spin glass, orientational glass. In some contexts, the opposite of quenched disorder is annealed disorder.
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]