Editing Quenching (section)

===Process===
The process of quenching is a progression, beginning with heating the sample. Most materials are heated to between {{convert|815|and|900|C|F}}, with careful attention paid to keeping temperatures throughout the workpiece uniform. Minimizing uneven heating and overheating is key to imparting desired material properties.

The second step in the quenching process is soaking. Workpieces can be soaked in air (air furnace), a liquid bath, or a vacuum. The recommended time allocation in salt or lead baths is up to 6 minutes. Soaking times can range a little higher within a vacuum. As in the heating step, it is important that the temperature throughout the sample remains as uniform as possible during soaking.

Once the workpiece has finished soaking, it moves on to the cooling step. During this step, the part is submerged into some kind of quenching fluid; different quenching fluids can have a significant effect on the final characteristics of a quenched part. Water is one of the most efficient quenching media where maximum hardness is desired, but there is a small chance that it may cause distortion and tiny cracking. When hardness can be sacrificed, mineral oils are often used. These oil-based fluids often oxidize and form sludge during quenching, which consequently lowers the efficiency of the process. The cooling rate of oil is much less than water. Intermediate rates between water and oil can be obtained with a purpose-formulated quenchant, a substance with an inverse solubility that therefore deposits on the object to slow the rate of cooling.

Quenching can also be accomplished using inert gases, such as nitrogen and noble gases. Nitrogen is commonly used at greater than atmospheric pressure ranging up to 20 bar absolute. Helium is also used because its thermal capacity is greater than nitrogen. Alternatively, argon can be used; however, its density requires significantly more energy to move, and its thermal capacity is less than the alternatives. To minimize distortion in the workpiece, long cylindrical workpieces are quenched vertically; flat workpieces are quenched on the edge; and thick sections should enter the bath first. To prevent steam bubbles the bath is agitated.

Often, after quenching, an iron or steel alloy will be excessively hard and brittle due to an overabundance of martensite. In these cases, another heat treatment technique known as [[Tempering (metallurgy)|tempering]] is performed on the quenched material to increase the [[toughness]] of [[iron]]-based [[alloy]]s. Tempering is usually performed after [[Hardening (metallurgy)|hardening]], to reduce some of the excess [[hardness]], and is done by heating the metal to some temperature below the [[Critical point (thermodynamics)|critical point]] for a certain period of time, then allowing it to cool in still air.