Research performed at Ghent University, regarding new production methods for
electrical steel, has shown that high silicon steel suffers an ageing phenomenon at room
temperature. Recent studies carried out by the same group using different analysis techniques
(Mossbauer spectroscopy, neutron diffraction, etc) brought to light a probable process of ordering
towards the D03-structure, which is responsible for the observed low ductility during cold rolling
and makes the processing of steel extremely difficult. In addition, the Si-steels become more brittle
as the delay time between hot and cold rolling is increased.
Frequency dependent internal friction (FDIF) studies were performed on different Fe - Si alloys
with a Si content varying from 3.73 at. % to 8.7 at. % immediately after several thermal treatments
and compared with ultra-low carbon steel. The evolution of relaxation peaks during the IF
measurements, performed at constant room temperature, helps to understand the ageing
mechanisms. Three processes have been observed: firstly, as expected, addition of Si reduces the
carbon Snoek peak. Secondly, a peak associated to C - Si is formed. Thirdly, a low frequency peak
associated with Zener relaxation (Si atom pairs) appears for a content of approximately 3.77 wt. %
Si. The two latter peaks decrease with ageing time and in the case of the Zener peak there is a
notable displacement to higher frequencies with a small increase of the Si content. The reduction of
the peaks during the ageing after annealing is more noticeable in quenched specimens than in air
cooled ones, and in furnace cooled specimens the reduction is even smaller, indicating that the
process is really an ageing phenomenon.
Room temperature short-range ordering might explain both the lowering of the Zener peak and
the observed macroscopic embrittlement.
Softening Behaviors of Severely Deformed Zn Alloy Studied by the Nanoindentation
