Quenching refers to the process of rapidly cooling metal products from the austenitizing or solution treating temperature, typically from within the range of 815 to 870 °C (1500 to 1600 °F) for steel. Stainless and high-alloy steels may be quenched to minimize the presence of grain boundary carbides or to improve the ferrite distribution but most steels including carbon, low-alloy, and tool steels, are quenched to produce controlled amounts of martensite in the microstructure. Successful hardening usually means achieving the required microstructure, hardness, strength, or toughness while minimizing residual stress, distortion, and the possibility of cracking. The selection of a quenchant medium depends on the hardenability of the particular alloy, the section thickness and shape involved, and the cooling rates needed to achieve the desired microstructure. The ability of a quenchant to harden steel depends on the cooling characteristics of the quenching medium. Quenching effectiveness is dependent on the steel composition, type of quenchant, or the quenchant use conditions.

Tempering of steel is a process in which previously hardened or normalized steel is usually heated to a temperature below the low critical temperature and cooled at a suitable rate, primarily to increase ductility and toughness, but also to increase the grain size of the matrix. Steels are tempered by reheating after hardening to obtain specific values of mechanical properties and also to relieve quenching stresses and to ensure dimensional stability. Tempering usually follows quenching from above the upper critical temperature; however, tempering is also used to relieve the stresses and reduce the hardness developed during welding and to relieve stresses induced by forming and machining. 

Martempering is a term used to describe an interrupted quench from the austenitizing temperature of certain alloy, cast, tool, and stainless steels. The purpose is to delay the cooling just above the martensitic transformation for a length of time to equalize the temperature throughout the piece. This will minimize the distortion, cracking, and residual stress. 

Austempering is the isothermal transformation of a ferrous alloy at temperature below that of pearlite formation and above that of martensite formation. Austempering of steel offers several potential advantages: increased ductility, toughness, and strength at a given hardness; reduced distortion, which lessens subsequent machining time, stock removal, sorting, inspection, and scrap; the shortest overall time cycle to through-harden within the hardness range of 35 to 55 HRC, with resulting savings in energy and capital investment.

The majority of all spheroidizing activity is performed for improving the cold formability of steels. It is also performed to improve the machinability of hypereutectoid steels, as well as tool steels. After spheroidizing, that is, heated and cooled to produce a structure of globular carbides in a ferritic matrix. A spheroidized microstructure is desirable for cold forming because it lowers the flow stress of the material. The flow stress is determined by the proportion and distribution of ferrite and carbides. The strength of the ferrite depends on its grain size and the rate of cooling. Whether the carbides are present as lamellae in pearlite or spheroids radically affects the formability of steel. 

Ultrahigh-strength steels are heat treated by use of equipment and techniques similar to those employed for heat treating constructional alloy steels. With ultrahigh-strength steels, emphasis is placed on the maximum section size that a given alloy will respond to during heat treatment, and thus machining is generally done prior to heat treatment to optimize final property response. The ultrahigh-strength steels ordinarily are quenched and tempered to specific hardness, but for critical applications it may be necessary to pull tensile specimens to ensure that a required combination of strength and ductility has been achieved. In still other instances, it may be necessary to conduct impact or fracture-toughness tests to ensure that a required level of resistance to brittle fracture has been attained. The majority of ultrahigh-strength steels are available in varying quality levels. The quality level is usually dictated by the method of primary or secondary melting used in the manufacture of that alloy. The widely used in refining techniques such as argon-oxygen decarburization (AOD) and vacuum oxygen decarburization (VOD) along with vacuum induction melting (VIM) as primary melting techniques. Remelting is typically performed with vacuum arc remelting (VAR) techniques to further enhance microstructural cleanliness. Currently some of the grades are being processed by electroslag remelting (ESR). Although heat treatment of the different quality level materials is similar, the premium quality provides increased fracture toughness, tensile ductility, and fatigue life at a given strength level.

Maraging steels are highly alloyed low-carbon iron-nickel martensites that process an excellent combination of strength and toughness superior to that of carbon-hardened steel. As such, they constitute an alternative to hardened carbon steels in critical applications when high strength and good toughness and ductility are required. Hardened carbon steels derive their strength from transformation-hardening mechanisms (such as martensite and bainite formation) and the subsequent precipitation of carbides during tempering. In contract, maraging steels derive their strength from the formation of a very low-carbon, tough, and ductile iron-nickel martensite, which can be further strengthened by subsequent precipitation of intermetallic compounds during age hardening.

Economic and technical demands have forced the globe steel industry to undergo a series of important changes. These changes were made imperative by the need of the steel industry to maintain a competitive and leadership position in relation to other engineering materials. Significant advances have been made in both process metallurgy and product metallurgy. These advances have transferred the steel industry into a modern, cost-effective, and high-quality manufacturing force in the world marketplace. The improvements in steelmaking, ladle refining and continuous casting practices have been matched with other advances in the science and technology of microstructural control in the final product. It is this ability to control microstructure during processing that has allowed significant and cost-effective improvements in the final properties of steel to be achieved. Central to the concept of controlled processing is thermomechanical controlled processing (TMCP). It is a procedure in which both the temperatures and size reductions are strictly controlled and in which rolling is completed at a specified temperature close to, and may be less than, that at which ferrite formation is complete. This results in a microstructure and mechanical properties which cannot be obtained by a normalizing heat treatment. Because the goal of thermomechanical processing is the refinement of the austenite grain structure, the control of recrystallization and/or grain coarsening during processing are among the metallurgical techniques available. The presence of minute quantities of elements such as niobium, titanium, and vanadium have been shown to be particularly useful during thermomechanical processing because of the change in the solubilities of their carbides /carbonitrides/nitrides in austenite as a function of temperature. These elements are known as microalloying elements (MAE) because they are generally present at levels at or below 0.1 wt%. Hence, the use of these microalloying elements enables the goal of thermomechanical processing to be easily achieved because these elements permit forces retarding recrystallization and grain coarsening to be governed by controlled precipitation during processing.