Recrystallization diagrams for induction heating

Abstract

1. The following annealing conditions, with heating by induction, may be recommended for the metals investigated: a) for technical-grade iron-heat at 50°C/sec to 1000°C, or at 200–650°C/sec to 1100°C; b) for 1Kh18N9T [18-9Ti] steel-heat at 50–60°C/sec to 1200°C; c) for copper-heat at 50°C/sec to 500–600°C, or at 200–500°C/sec to 600–700°C. These conditions ensure a fully recrystallized structure, for all degrees of deformation, with the minimum grain size. 2. Increase in the rate of induction heating is accompanied by increase in the recrystallization threshold temperature; with induction heating, this temperature is considerably higher than when heating in a furnace. 3. With induction heating the rain growth associated with lighter reductions is less than with furnace heating. Increase in temperature has less effect on grain size when heating by induction than with normal methods of heating. 4. The reason why there is no well-defined maximum for grain size at critical degrees of deformation lies in the special features of induction heating and the brief periods of holding at maximum temperature. In this case, the rate at which recrystallization nuclei are formed is much more rapid than the grain growth. 5. The rate of induction heating has little effect on grain size. Grain size decreases slightly, other conditions being equal (temperature and degree of deformation) as the heating rate is increased. 6. The recrystallized structure is in every case finer after induction heating than after heating in a furnace. The reason lies in thesimultaneous formation of large numbers of recrystallization nuclei at higher annealing temperatures.