Surface Activated Recrystallization of Antimony Alloyed Non-Oriented Electrical Steel Sheet
Površinsko aktivirana rekristalizacija silicijevih elektro jekel, legiranih z antimonom
M. Jenko,* F. Vodopivec, M. Godec, D. Steiner-Petrovič, Inštitut za kovinske materiale in tehnologije, Ljubljana, Slovenia
H. Viefhaus, M. Lucas, Max-Planck-lnstitute fur Eisenforschung, Dusseldorf, Germany M. Milun.T. Valla, Institut za fiziku Sveučilišta u Zagrebu, Zagreb, Croatia
In the present paper the effect of antimony on reerystallization texture of non oriented steel sheets Is discussed. The antimony surface and grain boundary segregation vvere investigated. Since the grain boundary segregation vvas negligible one can conclude that the texture formation results from orientation dependent effects of Sb on the surface energy and through them on grain boundaries.
Key vvords: non oriented steel sheet, recrystallization, grain grovvth, adsorption, surface and grain boundary segregation.
Raziskali smo vpliv antimona na teksturo rekristalizacije neorientirane elektro pločevine, kot tudi segregacijo antimona na površini in na mejah zrn. Segregacija antimona po mejah zrn preiskovanih jekel je zanemarljiva. Predpostavljamo, da se zaradi vpliva antimona na površini pločevine površinska energija zrn z orientacijo (100) zmanjša in vpliva na oblikovanje ugodne teksture.
Ključne besede: neorientirana elektro pločevina, rekristalizacija, rast zrn, adsorbcija, površinska segregacija, segregacija po mejah zrn.
1.	Introduction
Low loss and high permeability non oriented silicon steels are needed for efficient electrical power generation and transformation. which is one of the conditions for energy conservation and environmental amelioration1 \ To attain the full potential of this highly developed material its recrystallization texture must be improved1".
It has been found that small additions of certain elements (Sb.Sn.Se.Te) cspeciallv antimony, into the steel for non oriented electrical sheets, affect the recrystallization and lead to an in-crease of the number of ferrite grains vvith favorable orientation'' The effect on grain grovvth and orientation can be caused by surface and/or grain boundarv segregation of Sb or else. The surface segregation, its kinetics and equilibrium vvere measured using Auger Electron Spectroscopy and Thermal Desorption Spectroscopv on and in steel doped vvith Sb.
2.	Experimental
Experimental steels of the composition given in Table 1, vvere prepared in laboratorv from the same base material. The specimens for the surface segregation studies, of dimensions 6 mm in diameter and thickness of 0.15 mm vvere mounted into the UHV sv stem. The samples vvere heated up to 900°C for 10 min-utes and then sputter clean, annealed in the temperature range
doc. dr. Monika Jt NKO. dipl. in/ IV1I Ljubljana. Lepi pot 1 I. 61000 Ljubljana e-mail: monika jenko (2 guesl. ames. .i
from 450 to 950°C and investigated •in situ' by AES. The anti-mony enrichment of the surface vvas determined by follovving the peak height ratio (PHR) of amplitudes betvveen the dominant Sb(MsN, SN4,) and Ee(LM, ,V). Auger transitions at kinetic en-ergies of 454 and 650 eV, rcspcctivcly''711 1 \
Table 1: Chemical composition in mass contents in Vi ofthe experimental steels:
Steel	C	Mn	Si	S	Al	Sb
1	0.005	0.18	1.85	0.001	0.19	0.05
2	0.004	0.20	1.94	0.001	0.1 1	0.1
3	0.004	0.20	2.12	0.001	0.19	-
Cylindrical specimens for grain boundarv segregation measurements vvere prepared from the ingots of the same base material. notehed, encapsulated in quartz tubes evacuated to approx-imately 10" mbar. normalized for 24 hours al 1000°C, cooled and aged at 850,700 and 550°C for different times, from I to 500 hours.
Also the grain boundary segregation vvas investigated by AES method. Cylindrical specimens vvere introduced into UHV system of AES spectrometer at basic vacuum 4x10 111 mbar and after cooling to approximately -120°C vvere impact fraetured 'in situ'. The AES analysis vvere taken from as many intergranular fracture facets as possible" 14 "'.
The antimony desorption from the surface segregated iayer vvas investigated by performing Thermal desorption
Speclrometrv - TDS. The specimen vvas introduced in the UHV system of AES spectrometer additionally equipped vvith TDS and heated several times up to 950°CIS.
The grain orientation vvas determined by X-ray difractome-trv vvith Mo K<r radiation.
3. Results and discussion
The highest antimony surface segregation vvas established al 700 C until no further inerease in Sb concentration eould be observed and the sulfur concentration vv as acceptable lovv, figure E
Kinetic Energy/eV
Figure 1: AES spectra of maximum equilibrium antimonv segregation obtained al 70(I°C for steel vvith 0.057, Sb.' Slika 1: AES spekter maksimalne ravnotežne segregacije antimona dosežene pri 700 C za jeklo legirano z 0.057, Sb.
Table 2: Antimony to iron peak height ratios for ali reeordered AES spectra of Sb surface segregation measured on the different grains, shovvn in figure 2.
Grain	PHR (Sb/Fe650eV)
1	0.32
2	0.39
3	0.2K
4	0.44
5	0.43
6	0.37
7	0.38
S	0.42
Table 2 shovvs antimony to iron peak height ratios for ali reeordered Auger spectra. The corresponding points on the different grains are noted on the SEM images, figure 2. The Sb/Fe650 eV peak height ratio varies betvveen 0.28 and 0.44. There is not always a correlation of the peak height ratios and the intensity vvithin the Sb SAM images and this may be due to a channeling effect of the primary electron beam. The intensity, es-pecially of the iron Auger signal, depends on the angle of inci-dence for the primary electron beam vvith respect to the crystal-lographic orientation of the grains". If vve negleet this influence of possible channeling effects vve can estimate the Sb surface concentration by comparison vvith the results on Sb surface segregation on single crystal surfaces of defined orientation. For the same primary energv of exciting electrons the follovving satura-tion peak height ratios vvere measured for single crystal surfaces of (100), (110) and (111) orientation: Sb/Fe 650 eV = 0.42 for the (11 I) oriented surface Sb/Fe 650 eV = 0.58 for the (110) oriented surface Sb/Fe 650 eV = 0.40 for the (100) oriented surface
For the (100) oriented surface saturation coverage is half of a monolaver corresponding to a LEED c(2x2) overlayer pattern. For the other surface orientations no vvell defined ordered structure of surface coverage vvas observed". But the peak height ratios are in the same order as for the polvcristalline samples. The peak height ratio at saturation for the (100) surface vvas used as a calibration and the surface concentration for the polvcrvstalline samples at saturation vv ere in the range of 0.2 to 0.6 of a monolaver.
i
2
4
7
1 Ok e M SE M
Figure 2: AES measurements of Sb surface segregation on the different grains. Antimonv to iron peak height ratios for ali reeordered spectra are given in Table 2.
Slika 2: AES meritve površinske segregacije Sb na različnih zrnih. Razmerja vrhov antimona napram železu za posnete spektre so podana v tabeli 2.
It vvas found that even in one grain the antimonv segregation layer is not uniform, close by grain boundarv the segregated laver vv as thieker. figure 3.
Figure i: SEM image of the grain vv ith segregated antimony lav er.
Close to grain boundarv the segregated laver vvas found thieker. Slika 3: SEM posnetek zrn s segregirano plastjo Sb. Ob meji zrna je bila segregirana plast Sb debelejša.
The kinetics of surface antimonv segregation measured bv AES at 700 and 800°C is shovvn in figure 4. It vvas found that at elevated temperatures T > 750°C, antimony surface segregation rate decreases. There are tvvo possible explanation for this effect;
s
lil* w *
2Qu bi
simultaneouslv antimonv and sulfur segregation and/or Sh des-orption from scgrcgatcd laver.
Time , min
Figure 4: Kinetics of maximum equilibrium Sb surface segregation of steel alloved with 0.05% Sb. obtained at 700°C. Slika 4: Kinetika maksimalne ravnotežne površinske segregacije antimona /a jeklo z 0.05% Sb. dobljena pri konstantnem žarjenju na temperaturi 700°C.
Sb desorption from the segregated layer was investigated by Thermal Desorption Spectrometry in temperature range from 20 to 950°C. In Figure 4 the results of TDS investigation are shovvn. Sb as vvell as S desorption from the segregated layer vvas estab-lished at T > 750°C.
Thus one can conclude that the effect of decrease of antiinonv segregation rate at elevated temperature T > 750°C is the re-sult of both phenomena: antimony desorption and simultaneous-ly segregation of Sb and S as vve proposed in our earlier paper.1"
Temperature ( °C) Figure 5: The antimonv' desorption from the segregated layer vvas established at T > 750°C. by Thermal Desorption Spectrometry. Slika 5: Odparevanje antimona iz segregirane plasti smo izmerili z metodo TDS pri temperaturah T > 750°C.
Also grain boundaries of the material vvere analyzed by AES after annealing at 850. 700. 600 and 550°C for I to 500 hours. We found that the grain boundary segregation of antimony and also of other solute elements vvas negligible8 vvhich is not in agreement vvith our earlier findings\ Hovvever the Sb grain boundary segregation vvas established in a crack open to the surface of cylindrical specimen. It is therefore possible that in the earlier vvork the surface antimony segregation and not grain boundarv segregation vvas measured. Strong interaetion and cosegregation of Ni and Sb vvas observed at the grain boundaries" 1 but in our investigation it is not to be expected because of very lovv Ni content. Bryant1'' and Gas17 reported that they found grain boundary segregation of antimony in pure Fe-Sb al-loy after 200 and 500 hours of annealing in vacuum at 550°C. After the same thermal treatment of the investigated steels, the present investigation revealed that grain boundary segregation of antimony and also of other solute elements vvas negligible.
The influence of antimony on recrystallization and grain grovvth vvas studied on steel alloyed vvith 0.05% Sb and on com-parative steel. The kinetics of grain grovvth and the final grain size vvas determined in the temperature range from 700 to 800°C, there vvas no clear effect of Sb on the rate of the grain grovvth. vvhile the recrystallization vvas slovv in the antimony alloyed steel. figure 5.
The grain orientation for both steel alloyed vvith Sb and comparative steel vvas determined vvith X-ray difractometry,
Annealing time min
Figure 6: Grain size in dependence of annealing time for steels vvith 0.05% Sb and vvithout SblO. Slika 6: Velikost zrn v odvisnosti od časa žarjenja za jeklo z 0.05% Sb in primerjalno jeklo brez SblO.
Figure 7: Pole figures of steels alloyed with 0.05% Sb. 0.1% Sb and comparative steel established by X-rav difractometry. using Mo-K«
radiation. Small share of grains with the texture 1100)(001) was obtained in 0.05% Sb steel(a). for 0.1% Sb steel a vveak texture \vith (lil)(()()!) orientation was established. Slika 7: Polove figure jekel legiranih z 0.05% Sb. 0.1% Sb in za primerjalno jeklo brez Sb smo določili / metodo rentgenskega uklona / uporabo Mo K« sevanja. V jeklu /. 0.05'i Sb je bil ugotovljen manjši delež zrn z orientacijo (1001(001) (a); za jeklo / 0.1% Sb pa je bila določena šibka tekstura (111)(110). (b).
using Mo Ka radiation. Ordered pole figures are shown in figure 6, for comparative steel. For both steels alloved with anti-mony a week orientation is estimated. Small share of grains vvith the texture (100) (001) vvas obtained in steel with 0.05'v Sb, vvhile for the steel alloyed with 0,1 r/< Sb a vveak texture of (111) (110) orientation was established. Similar results of grain orientation were obtained by performing an etch pits method. as reported already\
The results of this investigation, support the hvpothesis that the texture formation results from orientation dependent effects of Sb on the surface energv. but not from effects on the grain boundary stability and mobility.
4. Conclusions
The antimony surface segregation depends on grain orientation. The maximum antimonv surface segregation coverage at saturation vvas found at 700°C by AFS.
The Sb surface segregation depends on grain orientation. The peak height ratio at saturation for the (100) single crystal surface vvas used as a calibration and the maximal surface con-centration for the polvci vstallinc samples at saturation uas 0.6 of a monolaver.
Grain boundan segregation of antimony and of other solute elements e.g.. S. C. P. Si. Al. in the experimental stecls were neg-ligible.
The desorption of antimonv and sulfur was established at T > 750 C. by TDS method. Tluis one can conclude that the de-crease in antimony segregation rate at elevated temperature is the result of simultaneously segregation of antimony and sulfur as well as of antimonv and sulfur desorption.
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