Quenching
A process to heat the steel to form austenite and transform it to martensite by quickly cooling it in water or oil. Quenching is also a conventional mean used to forge Japanese swords.
Quenching is done to harden the steel but since its toughness decreases, the steel is generally tempered after quenching. Quenching and tempering may be collectively called QT treatment. |
Tempering
A process to provide toughness to the hardened steel after quenching. The martensitic steel is reheated, held at a specific temperature range for a certain period of time, and gradually cooled. A desired structure can be attained by changing the holding temperature. If the steel is tempered at about 600ｼC, sorbite is formed, while troostite forms if it is tempered at around 400ｼC. A series of processes subsequent to quenching that form sorbite is especially called thermal refining. |
Annealing
A process to remove internal stresses caused by hardening, soften the structure, and improve toughness for flattening. The steel is held at a particular temperature in the austenite region for sufficient time and then slowly cooled in a furnace.
Taken from this process, the term ﾔannealingﾕ is also used for an operation that rebinds nucleic acid (DNA, RNA) after heat denaturation followed by slow cooling down. It may indicate a binding of a single-strand DNA, whose base sequence is known, or of a PCR primer with DNA. |
Normalizing
A process to remove internal stresses caused by previous processes, restore as-cast properties, or refining austenite grins. Normalizing increases intensity and ductility. This is also used as preliminary treatment for quenching. The steel should be held at a specific temperature range to fully convert the structure into austenite, and then cooled in the air.
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