Abstract
Vicker;s hardness tests were made on the view point of the formative conditions of G. P. Zones (G. P. 1), θ" zones (G. P. 2) and θ' phase. Quench hardening caused by θ" zones and G. P. zones is found at quenching temperatures from 300° to 500°C. The θ" zones are easily formed at the quenching temperature bellow the solubility limit (490°C). The first step age hardening of this alloy at 140°C is attributed to θ" zones and not to G. P. zones. Those zones are completely reversed at 200°C (solubility limit of G. P. zones TG.P. = 190°C for this alloy). The second step hardening at 140°C is due to θ' phase being formed independently of θ" zones in the solution. The θ' phase is formed more rapidly at 200°C in the supersaturated solid solution in which zones have been already formed than in the solid solution yet free from the zones.
