| 摘要 |
PROBLEM TO BE SOLVED: To reduce the sensibility to hot-working cracking of a cast ingot by controlling the crystal grain size in the tough pitch copper cast ingot and reducing the apparent quantity of Bi per unit crystal grain boundary area in the cast ingot, at the time of hot-working to the tough pitch copper cast ingot containing Bi. SOLUTION: The crystal grain size in the tough pitch copper cast ingot is controlled so that the apparent quantity of Bi per unit crystal grain boundary area in the tough pitch copper cast ingot becomes <=9.3×10<-8> (g/mm<2> ). The apparent quantity of Bi [the apparent concn. of Bi in the grain boundary: CBi (g/ mm<2> )] is defined as CBi≡[Bi quantity of the cast ingot (g)/crystal grain boundary area (mm<2> )]. The hot-working such as rolling, forging, drawing, etc., is applied to this tough pitch copper cast ingot. The control of the crystal grain size in the tough pitch copper cast ingot is executed by casting of a molten tough pitch copper at a low temp. or giving an ultrasonic wave to the molten tough pitch copper at the time of casting or giving an electromagnetic-stirring to the molten tough pitch copper at the time of casting. By this method, even if Bi as impurity is contained, the hot-working cracking can be prevented.
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