クロム銅およびベリリウム銅合金の溶体化処理における臨界冷却速度

抄録

It is shown that certain high strength and high electrical conductivity copper alloys, Cu-Cr and Cu-Be, do not undergo sufficient age-hardening by slow quenching. This problem has been recently highlighted by the increasing demand for high strength alloys in the form of a large section. In order to find out the effect of the cooling rate on the formation of a supersaturated solid solution for Cu-Cr and Cu-Be alloys, the Jominy end quench tests and the isothermal treatment and ageing tests were performed. A 25φ×100 mm test bar similar to the standard bar for steel was used for the Jominy tests and the 1.0 mmφ wire for the isothermal treatment and ageing tests to determine the C curve.
The results obtained are as follows. (1) Cu-0.68%Cr alloy. It was found by the Jominy tests that the supersaturated solid solution of this alloy was obtained at room temperature, when the cooling rates (at 1050°∼800°C) were faster than 10°C/sec at 1000°C and 17°C/sec at 900°C. The nose of the C curve was observed at 900°∼950°C. It may be concluded that the critical cooling rate of this alloy on solution treatment is 17°∼20°C/sec at 900°∼950°C. (2) Cu-2.46%Be-0.23%Co alloy. It was found by the Jominy tests that the Cu-Be alloy could be age-hardened satisfactorily, when the cooling rates from 800°C were faster than 55°C/sec (at 800°∼500°C). The upper C curve was obtained at about 700°C, higher than the β-phase eutectoid temperature, and the critical cooling rate at which the cooling curve did not intersect with the upper C curve was relatively low (about 3°C/sec). The lower C curve was obtained at about 500°C lower than the eutectoid temperature, and the critical cooling rate was as high as 60°C/sec. The ageing characteristics were particularly influenced by the cooling rate in the temperature range near the nose of the lower C curve. It is concluded that the critical cooling rate on solution treatment of this alloy is 55°∼60°C/sec at about 500°C.