| Popis: |
1. Even when it has been cooled slowly to room temperature, annealed rimmed technically pure iron is sub ect to precipitation hardening (age hardening). After this metal has been held at room temperature for 20.000 h, or at 150°C for 300 h, the coercive force is almost doubled. 2. The coagulation of particles of the precipitated phases causes the coercive force of annealed iron to decrease to the initial value when it is heated at temperatures up to 350°C. When this is done however, particularly when the heating is for long periods, partial resolution of the phases takes place, and for this reason further heating at 150°C for 50 h again greatly increases the coercive force. Heating articles previously held at room temperature for 20,000 h, for short periods at 150–350°C causes a recovery process, and further heating for 50 h at 150°C also greatly increases the coercive force. 3. Holding annealed iron at about 250°C for 4 h stabilizes it, since in this case there is very little re-solution of phases. The coercive force proves to be about the same as after annealing. The conditions for this stabilizing treatment should, however, be found separately for each batch of iron. 4. The processes of precipitation and solution of phases in annealed iron are most rapid in the grain boundaries. |
