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Quenching and tempering of steel are carried out to provide mechanical properties that are suitable for the intended future use. The steel is heated to the appropriate hardening temperature of the, held at this temperature and then cooled in various media. This is followed by tempering that provides the final mechanical properties and relieves the tensions in the steel. The actual conditions of the process parameters depend on the composition of the steel, the size of the workpiece, and the required final properties given by the client. The workpiece receives a rough mechanical treatment in its soft state prior to the quenching and tempering to ensure the final mechanical properties of the material.
Solution annealing is a common heat treatment process for many different metal types. Stainless steel, aluminium alloys, nickel-based superalloys, titanium alloys, and some copper-based alloys may require a process of melt annealing.
The purpose of solution annealing is to dissolve any precipitates in the material and transform the material at the solution annealing temperature into a single-phase structure. At the end of the solution annealing process, the material is rapidly cooled to room temperature in order to prevent the formation of precipitates during cooling in the lower temperature range. The single-phase annealed material will be in a soft state after the treatment.
The solution annealing process must be carried out prior to age hardening or precipitation hardening. The composition, size, and number of precipitates formed during ageing will determine the hardness, strength, and mechanical properties of the finished product after ageing.
Age hardening process, also called precipitation hardening, is used to increase the tensile strength of alloys that are based on magnesium, titanium, nickel, and certain stainless steels. Age hardening creates changes in physical and mechanical properties by creating fine precipitates which impede the movement of disslocations or defects in the crystal lattice. Dislocations are often the predominant cause of plasticity or flexibility, so this process is used to harden the material.
Precipitation hardening properties
Mechanical treatments such as bending, welding, grinding, rolling, quenching, punching, and other operations can introduce new stresses into the structure of metal parts. Stress relief is a heat treatment process designed to relieve residual internal stresses in the material caused from such manufactoring processes. Because these stresses result in changes in the granular structure of the metal, they can present challenges when working with metal component in the future. This process must be controlled based on the metal or alloy. The temperature reached, and duration of the heating and the cooling process precisely based on the material bing treated.
During the recrystallising annealing of electromagnetic metals, a marked orientation or texture appears, which enables a hysteresis loop shape with a precisely defined induction and coercivity value. Such treatment of soft magnetic iron, soft magnetic metal, and alloys is used for applications such as power transformers, various relay metals, magnetic switches, and special alloys based on Ni and Fe, e.g. mumetall, vacoperrm, permenorm, vacofer, and vacoflux.
The duration of the annealing is 2–6h at a specified temperature with controlled cooling.
Following the heat treatment cycles, deep freezing can be applied to increase hardness and wear resistance. The cryogenic treatment/deep freezing procedure is usually performed immediately after the quenching and before the tempering procedure.
Cryogenics is often used for gears, bearings, tools and other items that require high wear resistance and durability. The highest efficiency of the transformation of residual austenite into martensite is achieved in high-alloy and high-carbon steels.
