Assessment of recovery and recrystallisation behaviours of cold rolled IF steel through non-destructive electromagnetic characterisation

The recovery and recrystallisation behaviours of cold
rolled IF steel have been investigated by destructive
(optical microscopy and hardness) and non-destructive
electromagnetic sensor, (which allows direct measurement
of strip samples with no surface preparation) techniques.
The onset and completion of recrystallisation are clearly
monitored through destructive techniques of optical
microscopy and hardness measurements. The nucleation of
new recrystallised grains is observed in the sample annealed
at 600 °C/15 min, while completion of recrystallisation takes
place at 700 °C/15 min. The destructive techniques are not
very accurate in monitoring recovery, for example, changes
in hardness of <20% are seen. In contrast, the magnetic
properties of annealed steel show the onsets of both recovery
and recrystallisation, with recovery accounting for ≈60%
change in the coercivity value. Therefore, the measurement of
magnetic softening through an electromagnetic sensor acts
a crucial role for understanding recovery and recrystallisation
behaviours of steels during industrial processing. The present
investigation is aimed not only for controlling product
quality but also saving characterisation time through off line
monitoring during steel processing at industry.