Annealing
Processing of copper, such as wire drawing or rolling, at room temperature involves crystal strain following the deformation, and crystal grains become smaller with the progress of the processing. Depending on the degree of the strain, the resistance against deformation increases, and the elastic limit, yield point, tensile strength, and hardness become higher, while the elongation becomes smaller.
If a copper product that has been work-hardened as a result of cold-working is heated, the crystals with the smaller grains will recrystallize and soften at about 200°C. With the progress of the recrystallization, the tensile strength and hardness gradually decrease, while the elongation increases. The higher the degree of processing, the lower the softening temperature. The properties will be almost stabilized when the softening has progressed to a certain level. Further raising of the temperature causes the crystal grains to markedly grow, and the tensile strength and hardness to decrease. For this reason, the annealing temperature for copper is set to 350–500°C for industrial purposes depending on the core wire size and the quantity.
If a copper product that has been work-hardened as a result of cold-working is heated, the crystals with the smaller grains will recrystallize and soften at about 200°C. With the progress of the recrystallization, the tensile strength and hardness gradually decrease, while the elongation increases. The higher the degree of processing, the lower the softening temperature. The properties will be almost stabilized when the softening has progressed to a certain level. Further raising of the temperature causes the crystal grains to markedly grow, and the tensile strength and hardness to decrease. For this reason, the annealing temperature for copper is set to 350–500°C for industrial purposes depending on the core wire size and the quantity.