copper heat treatment Methods and types
The purpose of quenching is to make the steel obtain high hardness and wear resistance. The hardness of quenched steel can generally reach HRC60~65. But the internal stress of the steel is produced after quenching, which makes the steel become brittle. Therefore, the steel should be eliminated by tempering.
Commonly used heat treatment methods for copper materials
The purpose of tempering is to eliminate the internal stress produced during quenching and stabilize the microstructure of the steel, reduce the brittleness during quenching and increase the plasticity and toughness. Tempering is not only the heat treatment process after quenching, but also the final process of heat treatment. It plays a decisive role in the final required properties and microstructure of products. After quenching, the hardness and strength of the steel are greatly improved, but the plasticity and toughness are obviously reduced, which is called quenching brittleness.
The purpose of annealing is to reduce hardness, improve plasticity, improve cutting performance, eliminate internal stress, such as forging, casting, prevent deformation after processing, refine grain, uniform structure, improve mechanical properties. The purpose of annealing mentioned above is not attainable for all steels, but only for one or more purposes.
The heat treatment methods of copper alloys are mainly as follows: solid solution quenching, aging treatment, recrystallization annealing, high temperature homogenization annealing, low temperature stress relief annealing, low temperature strengthening annealing (such as tin phosphorus, zinc white copper).
Heat treatment of copper alloys: homogenization annealing. The main purpose is to eliminate the segregation of ingots during casting. The diffusion velocity of solute is directly proportional to the diffusion coefficient D, D = D0exp (- Q / RT), [R gas constant, Q activation energy, D0 frequency factor cm2 / s], Q indicates the energy required for an atom to move from one location to another, and the movement of an atom must overcome the energy barrier. The activation energy of pure phase is large and the diffusion coefficient is small, but if the concentration is not uniform, the relative Q is smaller. As the temperature rises, the number of atoms that overcome the energy barrier increases with the help of thermal fluctuations. Vacancies at high temperatures also help to diffuse the atoms. Generally, the homogenization temperature is 100 degrees higher than the annealing temperature. The relationship between diffusion velocity and time is parabolic, i.e. R2 = kt (r diffusion distance, K constant). Generally, tin bronze needs homogenization annealing because of its large crystallization range and serious component segregation.
What are the methods and kinds of heat treatment for copper?
The main purpose of intermediate recrystallization annealing is to eliminate work hardening. The intermediate annealing temperature is above the recrystallization temperature, and the softening degree of the material depends on the cold working rate, annealing temperature and holding time. Generally, high temperature annealing is used in the early stage of processing, and low temperature annealing is used in the late stage of processing to ensure uniform grain size.
Empirical formula of recrystallization temperature of alloy: T re = 0.4T melt (k) = 0.4t melt - 164 (?), low temperature annealing, brass cold working residual stress, will lead to stress corrosion, resulting in seasonal cracking phenomenon. The main purpose of low temperature annealing is to eliminate the residual stress, so the low temperature annealing temperature should be as low as possible to avoid the softening of the material. The hardness of Tin Phosphorus and zinc white copper at low temperature can also be significantly improved.
Aging hardening: The purpose of aging heat treatment is to precipitate solute atom strengthening alloy after solution and quenching. The aging temperature requirements are stricter and the furnace temperature must be kept as uniform as possible.
Solid solution quenching (SSQ) is a heat treatment process prior to ageing. Its purpose is to quench rapidly after holding at the solution temperature in order to obtain the maximum supersaturated solid solution.