Influence of Ordering Phenomena on the Thermomechanical Processing of High-Si Electrical Steel Studied by Mossbauer Spectroscopy

Fe-Si alloys with Si-contents up to 14 at.%Si (7.6 wt.%Si ) were produced by conventional casting and hot/cold rolled with different conditions of temperatures, pass reductions and cooling rates. The obtained thickness of the final sheet was between 0.5 and 0.7 mm for Si-steel up to 10 at.%Si (5.5 wt.%). Mossbauer spectroscopy was used to characterize the order evolution with the Si-content and the thermomechanical processing of the material. A new fitting program was developed for this purpose due to the known complexity of the Fe-alloys spectra. Results show that there is never complete disorder, i.e. binomial distribution of the atoms, whatever the Si-concentration is. Moreover, a clear tendency towards D03 ordering is observed. The obtained long-range order parameters prove a patent increase of the D03 order above 7 at.%Si (3.6 wt.%) which can be associated to the observed brittleness beyond this Si-amount. Concerning the relationship between order and thermomechanical processing, no big effect was found for low Si-contents (up to 6 at.%Si), while for higher amounts two results are clearly observed: (i) the slower the cooling after the hot rolling is, the higher the order is and (ii) cold deformation removes order in a great way. This agrees with the need of fast cooling after hot rolling in order to increase the cold workability of the Si-steel.