Abstract
Reversion (Rückbildung) test on hardness and dissolving rate and change in microstructure due to ageing were studied. Reversion test was carried out by heating the aged specimen at 200°C for 1min. (in silicone oil bath).
The results obtained were as follows.
(1) Before reaching the maximum point on dissolving rate-ageing curve (that is at the 1st stage) by heating the specimen at 200°C for 1min., both dissolving rate and hardness which had been increased due to ageing dropped to the initial values as quenched, respectively. The above period was considered to be a reversible one, when cluster and G. P. zone were formed. In the period after passing through the above maximum point, it was assumed that intermediate phase was precipitated.
(2) The equilibrium phase was preferentially precipitated in the grain boundary, and then, it was precipitated within the grains in the period after passing through the maximum point on hardness-ageing curve. At the 3rd stage of ageing, it was supposed that an equilibrium phase was precipitated.
