The C Curves Determined by Isothermal Treatments in the Age-Hardening Cu–Cr, Cu–Be and Cu–Co₂Si Alloys

Abstract

In an age-hardening copper base alloy subjected to the solution treatment at a slow cooling rate, a supersaturated solid solution cannot be obtained at room temperature, and its age-hardenability deteriorates considerably. The critical cooling rate (CCR) in solution treatment was studied by the isothermal heat treatment methods.
The C curves which showed the precipitation behaviors of the alloying element in solution treatment were obtained in the Cu-0.7% Cr alloy, the Cu-2.5% Be-0.3% Co, and Cu-4% Co₂Si alloys. The CCR was determined to be 20°C/sec at 925°C (the nose temperature of the C curve) for the Cu–Cr alloy, 60°C/sec at 500°C for the Cu–Be alloy, and 20°C/sec at 940°C for the Cu–Co₂Si alloy. In the preceding paper the CCR of each alloy was determined by the Jominy test, i.e., continuous cooling, whereas in this paper the CCR was determined by the isothermal method, i.e., discontinuous cooling. There were good agreement in CCR determined by both methods.