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ORDERING IN COMMERCIAL SILICON STEELS
M. Shimizu, T. Honsako, K. Fujimoto
To cite this version:
M. Shimizu, T. Honsako, K. Fujimoto. ORDERING IN COMMERCIAL SILICON STEELS. Journal
de Physique Colloques, 1979, 40 (C2), pp.C2-581-C2-582. �10.1051/jphyscol:19792202�. �jpa-00218581�
JOURNAL DE PHYSIQUE Colloque C2, suppldment au
n
O 3, Tome 40, mars 1979, page C2-581ORDERING IN COMMERCIAL SILICON STEELS
M. Shimizu, T. Honsako and K. Fujimoto
Research Laboratories, Kawasaki Steel Corporation I , Kawasaki-Cho, Chiba, 280, Japan
Resum&.-La probabilitg de presence de trois types d'atomes de fer dans les aciers cotrmaerciaux au silicium
a
temperature ambiante a etb mesurge par spectrornetrie ~gssbauer. On observe un dcart notable B la loi binomiale de distribution au hasard, notamment sur un acier dgsordonng par dB-formation plastique et recuit ultt5rieurement. I1 semblerait qu'il existe deux phases de type FelsSi, avec respectivement plus et moins de 6,25 at% de silicium.
Abstract.- Probability of occurrence of three kinds of iron atoms is measured using FfAssbauer spectroscopy at room temperature in commercial silicon steels.Probability obtained shows a marked deviation from binomial distribution of random solution. The deviation is observed after the heat treatment of steel disordered by plastic deformation during manufacturing process of grain orien- ted steel. Two phases of ordering of F e ~ s S i type with more Si concentration than 6.25atX and with less Si concentration are suggested to exist in commercial steels.
1. Introduction.- In a phase diagram of iron-silicon system given by Hansen and Anderko /I/ in 1958 no ordering is indicated at the silicon concentration of commercial electrical steels. Recently, however, experimental investigations by means of electron microscopy 1 2 1 , neutron diffraction 131, specific heat 141, and theoretical calculations of free energy of silicon-iron mixture /5/ have suggested the expansion of DOs structure down to 3wt% sili- con. Kbssbauer spectroscopy in an Fe-1.08wtXC- 3.64wtXSi alloy /6/ has shown the probability of occurrence of iron atoms corresponding to FeisSi type order. In this study using the ~gssbauer method the probability of occurence of three kinds of iron atoms has been measured in silicon steels.
2. Experimental.- Sheets of comnercial grain orien- ted and grain non-oriented silicon steels and a vacuum melted silicon steel were abraded and elec- tropolished to a thickness of 2 0 microns. Table I shows the chemical compositions of specimens. For commercial steels sheets in various stages of manu- facturing process were also measured. For a vacuum melted steel only a sheet quenched from 9 0 0 ~ ~ was m'easured. Gssbauer absorption and scattering spec- tra were obtained in constant acceleration mode by spectrometer of Elsint.
Table I : The chemical compositions of three kinds of silicon steels (wtX).
Source and samples were kept at room temperature.
Analysis by the method of least square was made.
The goodness of fitting of the data to the synthe- sized curve was tested by computing the
xZ
values.3. Results.-The Mijssbauer spectrum of a vacuum mel- ted steel is quite similar to that of ideal random solution. Outermost peaks of two commercial steels show prominent bumps which appear more distingui- shed in grain non-oriented silicon steel.
The assumptions used in the decomposition of the spectra into their individual contributions are very similar to those of Wertheim et al. /7/ in disordered silicon steel, where Si atoms are assu- med to go into each atomic site with equal probabi-
lity. The probability for an Fe atom to have 8.7 and 6 nearest neighbor Fe atoms is given by binomial distribution; only these three kirds of iron atoms are assumed to exist. The spectrum of vacuum melted steel can be fitted to that obtained by using bino- mial distribution.
The spectrum can also be fitted by changing the intensity of individual peaks from that of ideal random solution where the internal field and isomer shift are fixed to those of random solution.
The obtained probabilities of occurrence of three kinds of iron atoms do not differ so much from that of binomial distribution in vacuum melted steel and is considered to reflect the actual distribution of Si atoms in the alloy.
In figure 1.a are shown the probabilities of occurrence of three kinds of iron atoms in three kinds of silicon steels and in random solution. In
comercial silicon steels pure iron atoms (n
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792202
C2-582 JOURNAL DE PHYSIQUE
decrease markedly and iron atoms with one Si atom(n1) found not to be the present case. The probability and two Si atoms (nz) increase. Degree of deviation
from random solution depends on the kinds of sili- con steel; grain non-oriented steel shows marked deviation.
0 vacuum melted 0 m rdled 0 as rolled
number ot SI atoms In Fe n n .
Fig. 1 : Probability of occurrence of iron atoms;
a) commercial silicon steels and vacuum melted steel.
b) various stages of manufacturing process of grain oriented steel.
c) various stages of manufacturing process of grain non-oriented steel.
Probabilities in different stages of manufacturing process of grain oriented steel are shown in figure
1.b. The as-rolled state is quite close to the ideal random solution. Deviation is observed after primary recrystallization process; pure i.ron atoms, n
0'
remarkably decrease and nl and nl increase. After second recrystallization followed by furnace cooling the steel shows the same characteristics of orde- ring as those after primary recrystallization. For grain non-oriented steel the deviation is developed early in the as-rolled state as shown in figure I.c.
The n m b e r of pure iron atoms is about 30% less than that of random distribution. The deviation changes little after the following heat treatment.
4. Discussion.- For the probabilities of Fe envi- ronment in commercial silicon steels two kinds of solid solution can be considered. One is a local fluctuation of silicon concentration and the other is an ordering.
For the local fluctuation model, the proba- bility of occurrence of pure iron atoms is calcula- ted to be the same as that of random distribution when the intensity of fluctuation is small, and is calculated to increase when the intensity of fluc- tuation is large. The results obtained for the commercial silicon steels contradict with this mo- del.
For the ordering model, ordering of DO3 type leads to the increase of pure iron atoms, and is
obtained in grain non-oriented silicon steel is qui- te close to that of FelsSi type which was observed in an Fe-1.08wtXC-3.64wtXSi alloy /6/. Since orde- ring of FelsSi type does not hold the component of, iron with two Si atoms (nz), in order to increase n2,itisnecessary to add some Si atoms to the lattice in the commercial silicon steels.
The grain oriented steel in which atomic sili- con concentration is less than 6.25% and nz is lar- ger than random solution is presumed to consist of two phases which are the islands of ordering with more Si concentration than 6.25atZ and the matrix of ordering with less Si concentration. Disordering features, which can be observed by cold rolling about 50% reduction, is due to this two phase struc- ture. In grain non-oriented steel ordering is very stable against the heating up to 9 0 0 ~ ~ followed by oil quenching and cold rolling about 90%. The stabi- lity is considered to come from the higher effective Si concentration including A1 for the formation of Fel sSi type order.
In conclusion, the occurrence of the ordered configuration described above is considered to be the basic mixing characteristic of low Si Fe-Si sys- tem.
References
/I/ Hansen, M. and Anderko, K., "Constitution of Binary Alloys", (New York, McGraw-Hill Book Company, Inc. ) 1958.
/2/ Schlatte, G. and Pitsch, W., 2. Metallkd.
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(1975) 660; Swann, P.R., GranHs, L. and Lehtnen, B., Metal Sci.
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(1975) 90./3/ Inden, G. and Pitsch, W., Z. Metallkd.
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(1972) 253./4/ Ettwig, H.H. and Pepperhoff, W., Z. Metallkd.2 (1972) 453.
/5/ Inden, G. and Pitsch, W., 2. Metallkd.
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(1971)627; Schlatte, G., Inden G. and Pitsch, W., 2. Metallkd.
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(1974) 94./6/ Papadimitriou, G. and Genin, J.M., Phys. Status Solidi (a)
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(1972) K19./7/ Wertheim, G.K., Jaccarino, V., Wernick, J.H.
and Buchanan, D.N.E., Phys. Rev. Lett.
2
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