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Annealing
Annealing is a heat treatment process used to alter the physical and chemical properties of metals. It involves heating metals above their recrystallization temperature, holding at that temperature, and then slowly cooling. This allows the development of an equilibrium structure. The goals of annealing include increasing ductility, reducing hardness, removing internal stresses, increasing toughness, and decreasing brittleness. The annealing process consists of three stages - recovery, recrystallization, and grain growth. Recovery involves the movement and annihilation of dislocations to reduce strain energy. Recrystallization results in the formation of new strain-free grains. Grain growth occurs with further heating and causes the grains to increase in size.
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Annealing
- 1.
- 2. Annealing is oneof the heat treatment process in which the metal is heated to a temperature above its recrystallization temperature, kept at that temperature some time and then very slow cooling to develop equilibrium structure in the metal or alloy. Annealing is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and to make it more workable.
- 3. To - Increaseductility Reduce hardness Remove internal stresses Increase toughness Decrease brittleness Decrease electrical resistance etc.
- 4. Annealing process consistsof three stages such as– 1. Recovery 2. Recrystallization 3. Grain Growth
- 5. No change occursin microstructures. It occurs at low temperature. During this point defects are created. Dislocations of opposite sign come together annihilate each other. Point imperfections and dislocations are associated with strain energy.
- 6. Fig-1 Rearrangement ofdislocations Recovery
- 7. Strained grains becomesstress free, strain free grains. Microstructure at the end of recrystallization is much similar to the original structure prior to the cold working. Recrystallization temperature- The temperature at which the normal cold worked material recrystallizes in one hour. Recrystallization temperature is high in case of metal having high melting point. Recrystallization temperature - Iron-450oc Steel- 727oc
- 8. Degree of coldwork Initial Grain size Temperature of Cold Working Purity or composition
- 9. It occurs dueto the heating the metal beyond the time given for recrystallization. Diffusion occurs between grain boundaries. This results in increase in grain size. Due to Grain growth larger grains reduces the strength and toughness of metal and curve boundary becomes planar. Grain growth is useful for single crystal. Fig-1
- 10. Fig-2 Changes inMicrostructure during different stages of Annealing
- 11. Fig-3 Schematic Representationof cold worked and Anneal cycle showing the effects of Properties and Microstructures
- 12. Textbook of MaterialTechnology by O.P. Khanna http://www.brighthhubengineering.com/manufacturing-technology http://www.engineersedge.com/materials/annealing http://info.lu.farmingdale.edu/depts/met/met205/ANNEALING.html