The process of increasing the hardness of a substance is known as hardening or quenching. Tempering is the process of heating a substance to a temperature below its critical range, holding it for a period of time, and then cooling it. The purpose of tempering is to improve the quality of the material by modifying its physical properties.
Hardness and temper brittleness are two important factors that determine the suitability of steel for particular uses. Hardness can be increased by either cold working or heat treatment. Heat treatment includes annealing, which restores some of the strength lost during manufacturing; and temping, which increases the hardness of low-carbon steels.
Tempering was originally used with carbon steel because it improved their toughness without affecting their hardness too much. Today's high-strength steels require tempering to achieve maximum benefits from their hardness increase. The amount of temper produced in a steel depends on several factors including the grade of steel, heat treatment procedures, and the tool used during cold working. Tempered metals exhibit greater resistance to fracture than non-tempered materials of similar composition. This property makes tempered steels useful in applications where fatigue failure may be likely.
Heat treatment also affects the ductility and yield strength of steel. If heat treated too hard, it will become brittle and unable to be worked before heat treating further.
Quenching, also known as quench hardening, is a process that includes heating the material and then rapidly cooling it in order to fix the components into position as soon as possible. Tempering is accomplished by heating the quenched material to below the critical point for a certain amount of time, then cooling it in still air. This treatment leaves the metal in its original state but with a very small number of internal stresses removed.
The purpose of temping is to remove residual stress from the quenched material. If left in place, these stresses would cause the steel to contract when it cools down and become more brittle. Also, if the temperature at which the steel is tempered is too high, the alloy may lose some of its beneficial properties such as ductility and resistance to corrosion.
In general, steel should be cooled slowly from the heat-treatment temperature to below 100°C (212°F) to allow for complete recovery of strength and other properties. Rapid cooling can cause the formation of martensite, which reduces the strength of the material.
However, fast cooling is necessary to obtain full hardness from carbon steels quickly enough for them to be useful in industrial applications. For example, knife blades made of S30V steel can be hardened to Rockwell C 35-40 using slow cooling, while those same knives can be hardened to Rockwell C 60-65 using fast cooling.
Tempering is often regarded as an efficient method of easing stresses caused by quenching, as well as lowering hardness to within a given range or satisfying particular mechanical property criteria. When cooling metals below the recrystallization temperature, tempering can lead to greater strength due to the development of finer grains and larger amounts of boundary-rich material.
The term "tempering" refers to any treatment that lowers the hardness of a metal alloy systemically below its original value. The most common form of tempering is heat treatment, but some alloys can also be tempered by cold working or solution treating followed by rapid cooling from the liquid state. In general, the harder the alloy, the more rapidly it must be cooled to achieve effective tempering. For example, if heat treated in a furnace at 1000°F (538°C), steel would need to be cooled quickly (in less than 100 hours) to avoid rehardening; if heat treated at 500°F (260°C), it could be cooled slowly (more than 150 hours) without losing effectiveness.
Alloy systems can be classified into two major groups: hardenable and non-hardenable. Hardenable alloys can be hardened further by additional heat treatments. Non-hardenable alloys cannot be hardened by such treatments.
Tempering is commonly done after quenching, which is the quick cooling of the metal to harden it. Tempering is done by regulating the heating of the quenched work-piece to a temperature lower than its "lower critical temperature." At this lower temperature, the metal becomes more elastic and can be formed into thinner walls with equal strength. Thin walls are important for producing lighter vehicles.
Critical temperatures vary greatly between different alloys. For example, aluminum alloys can be quenched in water if they are below 200 degrees Fahrenheit (93 degrees Celsius). On the other hand, iron alloys need to be cooled slowly with oil or air if they are to be temped below 500 degrees Fahrenheit (260 degrees Celsius).
In general, all alloys have a lowest temping temperature. Any alloy that can't be temped below this temperature cannot be used for vehicle body panels. However, some alloys may be able to be temped well above their lowest temping temperature. For example, stainless steel can be temped at up to 1,000 degrees Fahrenheit (540 degrees Celsius), but it must be cooled quickly to avoid burning off surface layers that protect it from further heat treatment.
The lowest temping temperature varies between different manufacturers' products because they use alloys with different properties.
Steel and other iron-based alloys are strengthened through the processes of quenching and tempering. These techniques fortify alloys by heating the material while cooling it in water, oil, forced air, or gases such as nitrogen. The heat treatment creates a combination of martensite and bainite in the steel, which provides strength and hardness to the alloy.
Quenching and tempering improves the ductility of steels without adding more metal. The technique also helps reduce stress within the steel when it changes shape during manufacturing processes.
In conclusion, quenching and tempering is an effective method for strengthening low-alloy steels.
The primary distinction between quenching and tempering is that quenching involves the quick cooling of a workpiece, whereas tempering involves the heat-treating of a workpiece. Quenching and tempering are significant operations for strengthening and hardening materials such as steel and other iron-based alloys. The terms are used interchangeably in many cases, but they have different applications.
Cooling too quickly when quenching can result in substrate failure (the formation of cracks or other defects on the surface or inside the body due to a sudden change in temperature). Cooling too slowly can also be problematic because it may not be fast enough to avoid crystallization of the alloy. For these reasons, quenching tools must be able to control the rate at which they cool metal so that they do not cause defect formation.
Tempering is used to improve the mechanical properties of metals by inducing a solid-state transformation through heat treatment. During heat treatment, alloys are typically heated to a specific temperature range called the austenite region, held there for some time, and then cooled rapidly. This process causes certain components of the alloy to become enriched with carbon and nitrogen while other elements are depleted. The resulting structure is known as "austenite" which has different properties from "ferrite", the original structure of the alloy. By controlling the heating and cooling rates during heat treatment, one can control the amount of carbon and nitrogen incorporated into the alloy.