CA1297070C - Extra-low iron loss grain oriented silicon steel sheets - Google Patents

Abstract

Abstract of the Disclosure An extra-low iron loss grain oriented silicon steel sheet comprises a base metal of silicon steel and a thin coat of nitride or carbide of Ti, Zr, Hf, V, Nb, Ta, Mn, Cr, Mo, W, Co, Ni, A?, B and Si and strongly adhered to a finished surface of the base metal through a mixed layer of the base metal and the thin coat, and has excellent electrical and magnetic properties as well as good magnetostriction characteristics and lamination factor.

Description

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60-32,935 comb.
~881-2~5 EXTRA-LOW IRON LOSS
GRAIN ORIENTED SILICON STEEI. _HEErS

This invention relates to an extra-low iron loss grain oriented silicon steel sheet, and more particularly to an extra-low iron loss grain o:riented silicon steel sheet suitable for use in electrical 05 machinery and equipment having excellent heat stability, compressive stress dependence of magnetostricti.on and lamination factor.
Lately, remarkable developments and efforts for satisfying the improvement of electrical and magnetic properties in grain oriented silicon steels, particularly ultimate demand on reduction of iron loss are gradually producing good results. However, when using such grain oriented silicon steel sheets, it is a serious problem that the degradation of the above properties is unavoidably caused when the steel sheet is subjected to a so-called strain relief annealing after its working and assembling and the use application is restricted considerably and undesirably.
Throughout the specification, the invention will be described with respect to developmental results ; on new measures for advantageousl.y satisfying the above demands irrespectively of a high temperature heat treatment such as strain relief annealing, particularly for profitably providing desirable compressive stress , ~,~

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,: , ~ 64881-2~5 dependence of magne-tostriction and lamination factor in grain oriented silicon steel sheets.
As is well-known, the grain oriented silicon steel sheet, wherein secondary recrystallized grains are highly aligned in ~(110)} <001~ orientation, namely Goss orientation, is mainly used as a core for transformers and other electrical machinery and equipment. In this case, the magnetic flux density (represented by Blo value) is hi~h, the iron 108s (represen-ted by W17/so value) is low and, in addition to these superior magnetic properties, the magnetostriction property and lamination factor are excellent.
Since these grain oriented silicon s-teel sheets are usually manufactured through many complicated steps, many inven-tions and improvements have been applied to the above steps, whereby low iron loss grain oriented silicon steel sheets having Blo of no-t less than 1.90 T and W17/so Of not more than 1.05 W/kg when the product thickness is 0.30 mm or Blo of not less than 1.89 T and W17/so of not more than 0.90 W/kg when the product thickness is 0.23 mm have been manufactured up to the present.
Lately, supreme demands on the reduction of power loss have become considerable in view of energy-saving. In particular, a system of "Loss Evaluation" wherein the iron loss is converted into an equivalent amount of money which is then added to the cost of the transformer in the manufacture of a low loss transformer, is widely spread in Europe and America.

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~?t~.70 6~ 2~5 Under the above clrcumstances, there has recently been proposed a method w~era1n local microstrain ls :Introduced i.nto khe surface o~ ~he grain oriented silicon steel sheet by irradiating a laser beam onto the steel sheet surface in a direction substantially perpendicular ~o th~ rolling direction after the finish annealing to thereby reduce the width o~ the magnetic domain and hence reduce the iron loss (Japanese Patent Application Nos. 57-2,252 published on January 14, 198~, 57-53,419 published on November 12, 1982, 58--~,968 published on February 2, 1983, 58 ~6,405 published on June 2, 1983, 58-26,406 published on June 2, 1983, 58-26,407 published on June 2, 1983 and 58-36,051 published on August 6, 1983 and all in the name of Nippon Steel Corporation).
Such a magnetic domain reductlon or refinement is effectlve ~or the grain oriented silicon steel sheet nok sub~ected to the strain relief annealing in the manu~acture of stacked lamination-core type ~rans~ormers. However~ in case of wound-core type trans~ormers, the strain relie~ annealing ls per~or~ed after the magnetic domain reEinement, so that the local microstrain produced by laser irradiation on purpose is released by the annealing treatment to make the width o~ magnetic domains wlde and consequently the laser irradiating effect is lost.
On the o~her hand, Japanese Patent Appllcatlon Publication No. 52-24,499 published on July 1, 1977 in the name of Nippon S~eel Corporation discloces a method o~ producing an extra low iron lo~s grain oriented silicon steel sheet wherein the surface of ~he grain orien-ted silicon s~eel sheet is subjected ~o . ~
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~ ~ 6~881-245 a mirror finishing aEter the final annealing. A metal thin plating may be applied to the mirror finished surface or an insulation coating may be baked thereon.
However, the mirror finishing for improving the iron loss does not sufficiently contribute to the reduction of iron loss to make up for -the increase in cost caused b~ the added manu-facturing step. Particularly, there is a problem in the adhesion property o~ the insulation coating applied and baked after the mirror finishing. Therefore, such a mirror finishing is not yet adopted in the present manufacturing step.
Further, there is proposed a snethod, wherein the steel sheet surface is subjected to the mirror finishing and then a thin coat of oxide ceramics is deposited thereon, in Japanese Patent Application Publication No. 56-4,150 published on January 28, 1981 in the name of Kawasaki ~teel Corporation. In this method, how-ever, the ceramic coat is peeled off from the steel sheet surface when subjecting to a high temperature annealing above 600C, so ~ that it can not be adopted in the actual manufacturin~ step.
-~ Moreover, the magnetostriction of the grain oriented silicon steel sheet is a phenomenon that the steel sheet is sub-jected to stretching vibrations during the magnetization of the steel sheet, which is a most serious cause on the occurrence of noise in the transformer.
The magnetostriction behavior results from the fact that the magnetization process of the steel sheet includes 90 boundary displacement and rotation ~ .
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magnetization. That is, the magnetostriction increases in accordance with compressive stress applied to the steel sheet.
Since the compressive stress is irreversibly 05 applied to the steel sheet in the manufact-ure of the transformer, it is advantageous that a tension is ~ ~rs-~
~r-e~6~y applied to the steel sheet in vie~ of the compressive stress dependence of magnetostriction.
Of course, the application of the tension to the steel sheet is effective for improving the iron loss in the grain oriented silicon steel sheet, and its effect is conspicuous.
In general, the grain oriented silicon steel sheet is subjected to a tension by a double coating consisting of a forsterite layer, which is produced by high temperature reaction between an iron oxide of fayalite (Fe2SiO4) usually formed on the steel sheet surface through decarburization and primary recrystal-lization annealing before secondary recrystalli~ation and an annealing separator composed mainly of MgO in the final annealing, and an insulation coating produced on the forsterite layer and composed mainly of phosphate and colloidal silica, whereby the magnetostriction property is improved. However, it can not be said that the compressive stress dependence of magnetostriction is sufficiently improved by such a conventional method.
In order to improve the magnetostriction property, there has been attempted the development of . . .

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insulation coating capable of applying an elastic tension to the s-teel sheet surface (Japanese Patent Application Publication No.
56-52,117 published on December 10, 1981 in the name of Kawasaki Steel Corporation or 53-28,375 published on August 1~, 1978 in the name of Nippon Steel Corporation). However, such an at.tempt was still lacking in the effectiveness.
Further, the lamination factor of the grain oriented silicon steel sheet is expressed by an amount (percentage) of base metal of the final anneali.ng. The base metal amount is obtained by removing the forsterite layer and vitreous insulation coating from the surface of the grain oriented silicon steel sheet during the final annealing. It is said that the increase of such a lami-nation factor in the grain oriented silicon steel is one of the most important objectives. In general, it is known that the sur-; face roughness of the steel sheet is made as small as possible or the thickness of each of the forsterite layer and vitreous insula-tion coating is made thin for increasing the lamination factor of the product. However, although the thinning of -these coatings increases the lamination factor, it is very difficult to stably form the thin coating having a good surface appearance and excel-; lent adhesion property and uniformity at the actual manufacturing step, so that there is a limit in the increase of the lamination factor.
It is, therefore, an ob~ect of the invention to advanta-geously improve the compressive stress dependence of magnetostric-tion and the lamination : , ` ' , :

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factor in the grain oriented silicon steel sheet while forming an extra thin tensile coat on the steel sheet surface for e-fEectively leading the improvement of iron loss by mirror finishing.
It is another object of the invention to overcome the problems of the adhesion property and durability of the insulation coating without causing the degradation of characteristics when it has been exposed to high temperature treatmen-t.
The invention is based on a novel knowledge that a thin coat of at least one layer composed of nitride and/or carbide as mentioned later, which is strongly adhered to the finished surface of the grain oriented silicon steel sheet, can extremely reduce the iron loss and simultaneously achieve the improvement of heat stability, compressive stress dependence of magnetostriction and lamination factor.
According to the invention, there is the provision of an extra-low iron loss grain oriented silicon steel sheet comprising a base metal of silicon steel and a thin coat of at least one layer composed of at least one of nitrides and carbides of Ti, Zr, Hf, V, Nb, Ta, Mn, Cr, Mo, W, Co, Ni, AQ, B and Si and strongly adhered to a finished surface of the base metal through a mixed layer of the base metal and the thin coat, the thin coat having a thickness OL 0.005-5~m. Thus, the grain oriented silicon steel sheet according to the invention has excellent magnetic properties such as high magnetic flux density, ext~a-low iron loss and ~, .

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so on, and improved heat stab-ility, compressive stress dependence of magnetostriction and lamination factor.
In the grai.n oriented silicon steel sheet according to the invention, a tension is always applied 05 to the surface of the steel shee-t owing to the difference in thermal expansion coefficient between the hase meta]
and the thin coat, whereby a fairly low iron loss is obtained. Moreover, the extra-low iron loss is stably obtained when the thin coat :is formed on the base metal surface while further applying a tension of not more than 2 kg/mm2 to the base metal.
In a preferred embodiment of the invention, an insulation coating composed mainly of phosphate and colloidal silica is formed on the thin coat for the promotion of electrical insulation.
The invention will be described with reference to the accompanying drawings, wherein:
Fig. l is a diagrammatic view of an ion plating ap'paratus used in the manufacture of the extra-low iron loss grain oriented silicon steel sheet ` ~ according to the invention;
Fig. 2 is a schematic view illustrating behaviors of accelerated ions and deposition atoms; and Figs. 3 and 4 are graphs showing compressive ~; 25 stress dependence of magnetostriction in the grain oriented silicon steel sheet having an extra thin AQN
or TiN coat according to the inventlon and the grain oriented silicon steel sheet obtained by the conventional _ 9 .
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.~' ' '- ' ' - . - , ~, manu.Eact~ring process~ respectively.
The invention will first be described with respect to experimental details resulting in the success of the invention.
05 A continuously cast slab of silicon steel comprising 0.046% by weight of C, 3.34% by weight of Si~
0.068% by weight of Mn, 0.023% by weight of Se, 0.025%
by weight of Sb and 0.025% by weight of Mo was heated at l,360C for 4 hours and t:hen hot rolled to o~tain 0 a hot rolled steel sheet having a thickness of 2.0 mm.
The hot rolled steel sheet was subjected ,~cJ
to a normalized annealing at 900C for 3 minutes~ ~eh was then subjected to a cold rolling two times through an intermediate annealing at 950C for 3 minutes to obtain a final cold rolled steel sheet having a thickness of 0.23 mm.
After the cold rolled steel sheet was subjected to decarburization and primary recrystallization anneal-ing in a wet hydrogen atmosphere at 820C, a slurry of an annealing separator composed mainly of MgO was applied onto the surface of the steel sheet. Then, the : steel sheet was subjected to a secondary recrystalliza-tion annealing at 850C for 50 hours and further to ; a purlfication annealing in a dry hydrogen atmosphere ; 25 at 1,200C for 5 hours.
~:~: Thereafter, -the thus treated steel sheet was~ pickled with a solution of H2 S04 at 80C to remove : a forsterite layer from the steel sheet surface. Next, ~ ~ - 1 0 -.,, v `
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the steel sheet was sllbjected to a chemical polishing with a mixed sol-ution of 3% HF and H202, whereby the surface of the steel sheet ~as rendered into a mirror finished state having a center-line average roughness 05 of O.l ~m.
Then, a thin coat of AQ203 or TiN with a thickness of 0.5 ~m was formed on the mirror finished surface of the steel sheet by using an ion plating apparatus shown in Fig. l.
In Fig. l, numera:L l is a m:irror finished base metal to be tested, numeral 2 a shutter, numeral 3 a crucible, numeral ~ an electron gun, numeral 5 an electron beam, numeral 6 an ionization electrode, numeral 7 a thermionic emission el.ectrode, and numeral 8 an inlet for reactive gas such as N2, C2H2, 2 or the like.
After the ion plating, the steel sheet was subjected to a coating treatment with a coating solution consisting mainl~ of phosphate and colloidal silica (i.e. the formation of an insulation baked coating).
For the comparison, the mirror finished surface of the steel sheet was subjected to a copper vapor evaporation treatment at a thickness of 0.5 ~m in the conventionally well-known manner and then the same coating treatment as described above was applied thereto.
The magnetic properties and adhesion property of the resulting products were measured to obtain results as shown in the following Table l.
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~ 64~ 2~5 As seen from Table 1, the conventional product (a) obtained by applying the coating treatment to the forsterite layer formed on the steel sheet surface in the Einish annealing has Blo ot 1.905 T and W17/so of 0.87 W/kg as magnetic properties, wherein the adhesion property of the insulation coating is good in a way.
On the other hand, when -the product: (b) is manufactured by remov-ing the forsterite layer formed on the steel sheet surface during the final annealing through pickling, rendering the forsteri-te-free steel sheet surface into a mirror finished state through chemical polishing, and then subjec:ting such a mirror finished surface to a copper vapor evaporation and a coating treatment, the magnetic properties (Blo=1.913 T, W17/so=0.73 W/kg) are moderately improved, but the adhesion property is bad.
On the other hand, in the product (c) obtained by repeating the same procedure as in the product (b) except that the ion plating of A~203 was conducted instead of ~he copper vapor evaporation, the magnetic properties (Blo=1.915 T, W17/so=0.72 W/kg) are somewhat improved, but the adhesion property of the A~2O3 thin coat including the insulation coating is still bad though it is somewhat better than that of the product (b).
On the contrary, the product (d) obtained by repeating the same procedure as in the product (b) except that the ion plat-ing of TiN was conducted instead of the copper vapor evaporation has very excellent magnetic properties of B1o=1.920 T and W17/so=0.68 W/kg and a good adhesion property.

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, ~, According to -the invention, the improvement of the mag-netic properties and adhesion proper-ty i5 based on the following fac-t. That is, as schematically shown in Fig. 2, mixed layer 9 of accelerated ions 1 and deposition atoms a i5 formed on the finished surface of the silicon steel sheet as a base metal 1 to considerably enhance the adhesion property of a thin coat 10 to the base metal 1 through the mixed layer 9. The enhanced adhesion gives rise to strong tension on the surface of the silicon steel sheet to thereby realize an extra-low iron loss which has never been attained in the prior art. In this case, the ac-tion of plas-tic microstrain is not utilized, so that there is caused no prob-lem as to the heat stability, and consequently the electrical and magnetic properties are not influenced under a high temperature heat treatment such as strain relief annealing.
In order to provide an extra-low iron loss product, the surface of the steel sheet is particularly required to be in a mirror finished state having a centerline average roughness (Ra) of not more than 0.4 ~m. However, when Ra is more than 0.4 ~m, the degree of reduction of iron loss tends to somewhat decrease, but is still superior as compared with the case of performing the conventionally well-known method. According to the invention, the effect of reducing the iron loss can be obtained even when the oxides are removed from the ' ' ' :

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steel sheet surf~ce by a chemical process swch as pickling or a mechan-lcal process such as cutting or grinding as mentioned later.
According to the invention, the thin coat is desired to have a thickness of 0.005-5 ~m, preferably 0.05-1.5 ~Im. When the thickness is less than 0.005 ~rn, the application of the required tension can not be attained, while when it exceeds 5 ~m, the lamination factor and adhesion property are unfavorably degraded.
o The strong adhesion of the thin coat to the mirror finished surface of the steel sheet through the mixed layer is advantageously produced by anyone of PVD
- (physical vapor deposition) process such as ion plating, ion implantation or the l;.ke and CVD ~chemical vapor deposition) process. Besides, there may be employed a method wherein a metal is deposited on the mirror finished surface of the steel sheet and then reacted ~; near this surface in its atmosphere to form a desired ~, thin coat.
Next, the invention will be described with respect to experimental results on the compressive stress dependence of magnetostriction in the grain oriented silicon steel sheet.
A continuously cast slab of silicon steel comprising 0.045% by weight of C~ 3 . 38% by weight of Sig 0. 063% by weight of Mn, 0.021% by weight of Se, 0.025% by weight of Sb and 0.025% by weight of Mo was heated at 1,340C for 4 hours and then hot rolled to A _ ' .' ~ ' .

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obtain a hot rolled steel sheet having a thickness of 2.0 mm.
Then, the hot rolled steel sheet was subjected to a normalized annealing at 900C for 3 minutes and 05 further to a cold rolling two times through an lnter-mediate annealing at 950C for 3 minutes to obtain a final cold rolled steel sheet having a thickness of 0.23 mm.
Thereafter, the thus obtained steel sheet was 0 subjected to decarburization and primary recrystalli~a-tion annealing at g20C in a wet hydrogen atmosphere, coated with a slurry of an annealing separator composed of AQ2O3 (70%) and MgO (30%), and then subjected to a secondary recrystallization annealing at 850C for 50 hours and further to a purification annealing at ; 1,200C in a dry hydrogen atmosphere for 5 hours.
The thus treated steel sheet was pickled with a solution of HCQ at 70C to remove oxides from the steel sheet surface and then subjected to a chemical polishing with a mixed solution of 3% H~ and H2O2 to render the surface into a mirror finished state having a center-line average roughness of 0.05 ~m.
Then, a thin coat of TiN with a thickness of 0.7 ~m was formed on the mirror finished surface by CV~
process wherein the steel sheet was subjected to CVD
reaction in a mixed gas atmosphere of TiCQ~, H2 and N2 ; at 750C for 20 hours. After an insulation coating consisting mainly of phosphate and colloldal silica was : ~ .
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formed on the thin coat by baking, t:he steel sheet was subjected to a strain relief annealing at 800C for 2 hours to obtain a desired product.
The compressive stress dependence of magneto-05 striction and magnetic properties of the resultingproduct are shown in Fig. 3 together with those of a comparative product obtained by the usual manufacturing process.
Moreover, the comparative product was manufactured by subjecting the same final cold rolled steel sheet as described above to decarburization and primary recrystallization annealing at 820C in a wet hydrogen atmosphere, applying an annealing separator composed mainly of MgO to form a forsterite layer, subjecting to a secondary recrystalliæation annealing at 850C for 50 hours and a purification annealing at 1,2G0C in a dry hydrogen atmosphere for 5 hours and baking an insulation coating consisting mainly of phosphate and colloidal silica onto the forsterite layer.
As seen from Fig. 3, the product provided with the TiN thin coat according to the invention has very excellent magnetic properties of B1o=1.92 T and W17/5O=0.69 W/kg, and also the increase of magneto-S r~ q 1 /
3,1 25 striction (App) is very ~ e even when the compressive stress (o) is increàsed up to 0.6 kg/mm2.o~r h4") On the ~rt~ , in the comparative product (manufact~red by the usual manufacturing process), B1o , ~ . .

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is :L.90 T and Wl7/50 is 0.87 W/kg as magnetic properties, but the ~agnetostrlction (App) increases with the increase of the compressive stress (~). For instance, the magnetostriction exhibits a large value of 05 App=3.2x10-6 at the compressive stress (a) of 0.4 kg/mm2.
Further, the invention will be described with respect to experi.mental results on the magnetic properties, lamination factor and compressive stress dependence of magnetostriction in another grai~ oriented lo silicon steel sheet.
A continuously cast slab of silicon steel comprising 0.043% by weight of C, 3.36% by weight of Si, 0.062% by weight of Mn, 0.021% by weight of Se, 0.025% by weight of Sb and 0.025% by weight of Mo was heated at 1,360C for 4 hours and then hot rolled to obtain a hot rolled steel sheet having a thickness of 2.4 mm.
The hot rolled steel sheet was subjected to a normalized annealing at 900C for 3 minutes and further to a cold rolling two times through an inter-mediate annealing at 950C for 3 minu-tes to obtain a final cold rolled steel sheet having a thickness of 0.23 mm.
Ne~t, the cold rolled steel sheet was subjected to~decarburization and primary recrystalliza-tion annealing at 820C in a wet hydrogen atmosphere, : coated with an annealing separator composed of AQ2O3 (70%) and MgO (30/O)~ and then subjected to a secondary .

, 71) recrystallization annealing at 850C for 50 hours andfLIrther to a purification annealing at 1,200C in a dry hydrogen atmosphere for 5 hours.
Thereafter, the steel sheet was pickled with 05 a solution of HCQ at 50C to remove oxides from the steel sheet surface and then subjected to a chemical pollshing with a mixed solution of 3% HF and H2O2 to render the surface into a mirror finished state having a center-line average roughness of 0.05 ~m.
o Next, a thin coat of AQN with a thickness of 0.8 ~m was formed on the mirror finished surface by CVD
process wherein the steel sheet was subjected to CVD
reaction in a mixed gas atmosphere of AQCQ3, H2 and N2 at 800C Eor 15 hours. After an insulat:ion coating consisting mainly of phosphate and colloidal silica was formed on the thin coat by baking, the steel sheet was subjected to a strain relief annealing at gO0C for 2 hours to obtain a desired product.
The compressive stress dependence of magneto-striction, magnetic properties and lamination factor ofthe resulting product are shown in Fig. 4 together with those of another comparative product obtained b.y starting from the above cold rolled steel sheet in the same manner as described on the comparative product of Fig. 3.
As seen from Fig. 4, the product prov1ded with the ~QN thin coat according to the invention has very excellent magnetic properties of B1o=1.92 T and - 19 ~

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Wl7~50=0.71 W/kg, and is ~ ~ e in the increase of magnetostriction (App~ because App is 0.25x10-~ at a compressive stress (~) of 0.~ kg/mrn2 and 0 70x10-6 at ~ of 0.6 kg/mm2. Further, it should be noted that the 05 lamination factor is extremely increased to 98.5%.
On the contrary, in the comparative product, ~10 is 1.90 T and W1 7~50 iS O . 87 W/kg as magnetic properties, but the magnetostriction (App) cons:iderably increases with the increase of the cornpressive stress (a).
0 For instance, the magnetostriction (App) becomes 3.2 at a=0.4 kg/mm2. Further, the lamination factor of this comparative product is 96~5%~ which is worse by abowt 2% than that of the product according to the invention.
As apparent from the results of Table 1 and Figs. 3 and 4, the grain oriented silicon steel sheets according to the invention have good magnetic properties such as high magnetic flux density, extra-low iron loss and so on and are excellent in the compressive stress dependence of magnetostriction and the lamination factor.
The manufacture of the grain oriented silicon steel sheet according to the invention will be descrLbed in the order of the manufacturing steps.
As a base metal for the manufacture of grain oriented silicon steel sheets, there may be used any of ; conventionally well-known silicon steels, a typical example of which is a silicon steel comprising, on a weight ratio, 0.0l-0.06% of C, 2.0-4.0% of Si, : - 20 -. . .

0.01-0.20% of Mn, 0.005-0.05% in total of at least one of S and Se, and -the remainder being substantial].y Fe.
The other base metals include a silicon steel cornprising 0.01-0.06% of C, 2~0-4.0~/o of Si, 0.01-0.20% of Mn, os 0.005-0.05% in total of at least one of S and Se, 0 . OOS-0 . 20% of Sb, and the remainder being substantially Fe; a silicon steel comprising 0.01-0.06% of C, 2.0-4.0%
of Si, 0.01-0.20% of Mn, 0.()05-0.05% in to~al of at least one of S and Se, 0.005-0. 20% of Sb, 0.003-0.1%
0 of Mo, and the remainder being substantiall~ Fe;
a silicon steel comprising 0.01-0. 06% of C, 2 . 0-4 . 0%
of Si, 0.01-0.20% of Mn, 0.005-0.05% in total of at least one of S and Se, 0.005-0.06% of sol. AQ, 0.001-0.01% of N, and the remainder being substantially Fe;
a silicon steel comprising 0.01-0.06% of C, 2.0-4.0%
of Si, 0 . 01-0 . 20% of Mn, 0.005-0.05% in total of at least one of S and Se, 0.005-0.06% of sol . AQ, O . 001-0 . 01% of N, 0 . 003-0 .1% of Mo, and the remainder being substantially Fe; a silicon steel comprising 0.01~0. 06%
20 of C, 2 . 0-4 . 0% of Si, 0 . 01-0 . 20% of Mn, 0.005-0.05% in total of at least one of S and Se, 0.005-0.06% of sol . AQ, 0 . 001-0 . 01% of N, 0 . 01-0 . 5% of Sn, 0 01-1.0%
: of Cu and the remainder being substantially Fe; a silicon steel comprising 0.01-0.06% of C, 2 . 0~4.0% of Si, 2s 0 . 01-0 . 2% of Mn, 0 . 005-0 . 05% in total of at least one : of S and Se, 0.0003-0.02% of B, 0.001-0.01% of N, and the remainder being substantially Fe; a silicon steel comprising 0.01-0.06% of C~ 2.0-4.0% of Si, 0.01-0.2%
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of Mn, 0.005-0.05% in total of at ]east one of S and Se, 0. 0003-0 . 02% of B, 0.001-0.01% of N, 0.01-1.0%
of Cu, and the remainder being substantially Fe, and so on.
05 The reason why the compositions of the silicon s-teels according to -the invention are limited to the above ranges is as follows:
C: 0.01-0.06%
When -the amount of C is less than 0.01%, the o control of hot rolled texture is difficult and large elongated grains are prodwced during hot rolli.ng and consequently the magnetic properties are degraded.
While, when it exceeds 0.06%, the decarburization takes a long time and is uneconomical. Therefore, the C
amount is necessary to be within a range of 0.01-0.06%.
Si: 2.0-4.0%
When the amount of Si is less than 2.0%, the electric resistance is low and the value of iron loss based on the increase of eddy-current loss becomes larger, while when it exceeds 4.0%, the brittle rupture is apt to be caused in the cold rolling, so that the Si amount is necessary to be within a range of 2.0-4 0%.
Mn: 0.01-0.2%
Mn is an element required for the formation of MnS or MnSe as a dispersed precipitate phase (or an inhibitor) controlling the secondary recrystal-lization of the graLn oriented silicon steel sheet.
When the amount of Mn is less than 0.01%, the amount of ' -~
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~?~o~ 64881-245 MnS or MnSe required for causing the secondary recrystallization is lacking as a whole, so that the secondary recrystallization is incompletely caused and at the same time the surface defect called a blister increases. While, when the amount exceeds 0.2%, the dissolution/solution of MnS or MnSe and the like is difficult when heating the slab, and even if the dissolution/solution is perform-ed, the dispersed precipitate phase or MnS or MnSe is apt to be coarsened during the hot rolling and consequently the optimum size distribution of the dispersed precipita-te phase as an inhibitor is undesirably damaged and the magnetic properties are degraded.
Therefore, the Mn amount is necessary to be within a range of 0.01-0.2%.
S and/or Se: 0.005-0.05% in total When the amount of each of S and Se i5 less than 0.005%, the effect for inhibition of normal grain growth of MnS and MnSe is weak, while when each amount of S and Se exceeds 0.05%, the hot and cold workabilities are considerably degraded. Therefore, the ; amount of each of S and Se is necessary to be within a range of 0.005-0.05% and also the total amount of S and Se is necessary to be limited to a range of 0.005-0.05%.
Mo: 0.003-0.1%
Mo is an inhibitor for normal grain growth as disclosed in Japanese Patent Application Publication Nos. 56-4,613 published on Januar~ 31, 1981 and 57-14,737 published on March 26, 1982, both in the name of Kawasaki Steel Corporation. When the amount of Mo is less than 0.003%, the effect for inhibition of normal ;~ .

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graln growth is no-t clea~, wh:Lle when it exceeds 0.1%, the hot and cold workabilitles are degraded and also the iron loss increases, so ~hat the Mo amount is necessary to be within a range of 0.003-O. 1'~.
Sb: 0.005-0.20%
As disclosed ln Japanese Patent Application Publlcation Nos. 38-8,214 published on June 6, 1963 and 51-13,469 publ:lshed on April 28, 1976, both in the name of Kawasaki ~teel Corporation, lt is known that the normal gra:Ln growth is inhibited by including 0.005-0.2% of Sb in silicon steel together with a slight arnount of S or Se. When the amount of Sb ls less than 0.005%, the effect for inhibition of normal recrystallized grain is lit~le, while c~e C r e c~ s ~: 5 when it exceeds 0.2~, the magnet:Lc flux density ~ to degrade the magnetic properties. Therefore, according to the invention, the Sh amount ls necessary ~o be within a range of 0.005-0.20%.
Sol. A : 0.005 0.06~
A acts a~ a strong inhlbitor by bonding with N
contained in silicon steel to for~ a fine precipitate of A N.
Particularly, in order to grow secGndary recrystallized grains in the heavy cold rolling at a draft of 80-95~, it is necessary to include A in an amount of 0.005-0.06~ as sal. A in the silicon steel. When the amount o~ sol. A is less than 0.005~, the a~ount of A ~ fine precipitate as an inhibitor is lacking and the growth o~ secondary recrystalli~ed grain with {110}~001> orientation i~
;~ insufficient, while when it exceeds 0.06~, the growth of secondary .. ~,, ", ~ ~,.....

- :
, :

~ t7~

recrystallized grain with {110}<001> orientation hecomes rather bad.
B: 0.0003-0.02%
B bonds with N contained in the silicon steel 05 to form fine precipitate of BN, but when the amount of B is too large, it is difficult to grow the secondary recrystallized grain with {110~<001> orientation, so that the B amount is limited to a range of 0.0003-0.02%.
Moreover, it is already known from ~I.E. Grenoble, 0 IEEE Trans. Mag. ~G-13 (1977), p.l427 and H.C. Fiedler, IEEE Trans. Mag. MAG-13 (1977), p. 1433 that the slight amount of B or BN fine precipitate e-Ffectively inhibits the grain boundary migration as an inhibitor.
N: 0.001-0.01%
N forms fine precipitate of AQN or BN by bonding with sol. ~Q or B contained in the silicon steel and acts as a strong inhibitor for inhibiting the growth of normal recrystallized grain. Therefore, -the amount of N is necessary to be within a range of 0.001-0.01%. When the N amount is less than 0. 001%~
the amount of AQN or BN fine precipitate is lacking and the inhibition eff~ct is weak and consequently the growth of secondary recrystallized grain with ~110~<001>
orientation is insufficient. While~ when it exceeds 0.01%, the amouht of solute N increases -to bring about the increase of iron loss.
According to the invention, a small amount of at least one inhibitor-forming element selected from :

- ,:
.
.~ .

, ~
.
' . ~ ' ' .

~ .~>~ '7~
Cr, Ti, V, Zr, Nb, Ta, Co, Ni, Cu, Sn, P, ASJ Bi, Te and the like may be adcled to the silicon steel.
For instance, as shown in the following Table 2, composition (c) or in I~. Iwayama et al, "Roles of Tin 05 and Copper in the 0.23 mm-Thick High Permeability Grain Oriented Silicon Steel", J. Appl. Phys., 55(198~
p 2136, it is effective to add small amounts of Cu and Sn to the silicon steel according to the invention.
Lately, a tendency of thinning the product thickness f~S ~-CO~C' 0 for the reduction of iron -~o~-~eeom-es- stronger, but in this case the secon~ary recrystallization becomes unstable. Therefore, it is desirable t~ add about 0.01-0.5% of Sn, and further the addition of about 0.01-1.0% of Cu is favorable for the stabilization of the thin coat.
The grain oriented silicon steel sheet according to the invention is manufac-tured as follows.
At first, the components having a given base metal composition are melted in -the conventionally well-known steel making furnace such as LD converter, electric furnace, open hear-th or the like and then cast into a slab. It is a matter of course that vacuum treatment or vacuum dissolution may be applied during the melting.
After the resulting slab is subjected to a hot rolling in the usual manner, the resulting hot rolled steel sheet is subjected to a normalized annealing at a temperature of 800-1,200C, and, if necessary, to :, , a swbseqwent quenching treatment. Then, the thus treated steel sheet is cold rolled -to a final product thickness of 0.lS~0.35 mm by a heavy cold rolling at once or by a two-times cold rolling through an inter-05 mediate annealing usually performed at 850-l,050C.
In the latter case, the draft is 50-80% in the first cold rolling and 30-80% in the second cold rolling.
The final cold roll.ed steel sheet is degreased and subjected to decarburization and primary recrystal-0 lization annealing in a wet hydrogen atmosphere at750-~50C.
Then, the thus treated surface of the steel sheet is coated with an annealing separator. In this case, according to the invention, the feature that forsterite always produced after the final annealing in the prior art is not formed is effective for simplifying the subsequent mirror finishing of the steel sheet surface. Therefore, it is preferable to use an annealing separator composed mainly of MgO as well as a mixture of MgO and not less than 50% of .
AQ2O3 3 ZrO2~ TiO2 or the like.
After the application of the annealing : separator, a secondary recrystallization annealing is performed for sufficiently growing secondary recrystal-lized grains w1th {110}COO1> orientation. In general, : this treatment is carried out by box annealing wherein the temperature of the steel sheet is rapidly raised to more than l,000C and then held at that temperature for :
'; ~
.
- - . . . .

a given time. Moreover, it is advclntageous that the isothermal annealing at a temperature of 820-900C is carried out in order to highly grow the secondary recrystallized texture with {110}<001> orientation.
05 Besides, a slow temperature-rise annealing at a rate of 0.5-15C/hr may be performed.
After the secondary recrystallization anneal-ing, it is required that a purification annealing is carried out in a dry hydrogen atmosphere at a temper-0 ature above 1,100C for 1-20 hours.
Then, the forsterite layer or oxide layer produced on the steel sheet surface is removed from this surface by a chemical removing process such as well-known pickling or the like, a mechanical removing process such as cut-ting, grinding or the like, or a combination of these processes.
After the removal of the oxide, the steel sheet surface is rendered into a mirror finished state having a center-line average roughness of not more than 0.4 ~m by the conventional process such as chemical polishing, electropolishing, buffing, or a combination thereof, if necessary.
After the removal of the oxide or the mirror finishing, a thin coat of at least one layer composed of at least one of nitrides and carbides of Ti, Zr, ~f, V, Nb, Ta, Mn, Cr9 Mo, W, Co, Ni, AQ, B and Si is formed on ~he steel sheet surface by CVD process, PVD
process (ion plating, ion implantation) or the like.

~ .

. ' .

. .

;3!7~
In this case, the thin coat is effective to have a thickness of about 0.005-5 ~m.
Further, an insulation coating consisting mainly of phosphate and colloidal silica is formed on the thin coat by the conventionall~ well-known process such as baking or the like. The formation of such an insulation coating is, of course, required in the manufacture of transformers having a capacity as large as 1,000,000 KVA.
The following examples are given in illustra tion of the invention and are not intended as limitations thereof.
; Example 1 _.
(a) C=0.043%, Si=3.36%, Mn=0.072%, Sb=0.025%, Mo=0-.025%, Se=0.023%
(b) C=0.036%, Si=3.08%, Mn=0.065%~ S-0.018%
(c~ C=0.055%, Si=3.43%, Mn=0.078%, sol.A~=0.028%, S=0.030%, N=0.0068%, Sn=0.08%, Cu=0.1%
(d) C=0.03$%, Si=3.26%, Mn=0.058%, S=0.0~6%, B=0.0038%, Cu=0.3%, N=0.0059%
Three hot rolled steel sheets of the above chemical compositions (a), (b) and (d) were subjected to a normalized annealing at 950C for 3 minutes, respectively. A hot rolled s-teel sheet of the above chemical composition (c) was subjected to a normalized annealing at 1,150C for 3 minutes and then quenched.
Thereafter, the steel sheets (a~ and (b) were subjected to a cold rolling two times through an intermediate ~ ~ .

, -. - .
- .

, 3"~D
annealing at 950C to obtain final cold rolled steel sheets (a) and (b) of 0.23 mm in thlckness. 'L'he s-teel sheets (c) and (d) were subjected to a heavy cold rolling to obtain final cold rolled sheets (a) and (d) 05 of 0.23 mm in thickness. Then, these cold rolled steel sheets were subjected to decarburization and primary recrystallization annealing in a wet hydro~en atmosphere at 820C, and coated with a slurry of an annealing separator composed of AQ203 (70%) and MgO (30%).
Subsequently, the steel sheet (a) was subjected to a secondary recrystallization annealing by holding at 850C for 50 hours, and then to a purification annealing in a dry hydrogen atmosphere at 1,200C
for ~ hours. On the other hand, each of the steel sheets (b), (c) and (d) was subjected to a secondary recrystallization annealing by raising the temperature from 850C to l,050C at a rate of 8C/hr, and then to a purification annealing in a dry hyd'rogen atmosphere at 1,200C for l0 hours.
Thereafter, the surface of each of these steel sheets was pickled to remove oxides therefrom, and then rendered into a mirror finished state by electropolishing. Then, after a thin coat of TiN
(0.8 ~m thickness) was formed on the finished surface ~5 of the steel sheet by using an ion plating apparatus, ` an insuIation coating was further formed thereon.
The magnetic properties and the lamination factor of the resulting products are shown in the following :~

:, . :
'- ~ , :

~ :
.

o Table 2.
For comparative purpose, comparative products were obtained according to the conventional method.
That is, after the decar~urization and primary recrystal-05 lization annealing, the surface of the s-teel sheet was coated with a slurry of an annealing separa-tor composed mainly of MgO, and then subjected to secondary recrystal-lization annealing and purification annealing in the same heat cycle as mentioned above. Thereafter, an insulation coating was formed thereon, and results are also shown in Table 2.

.

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~ ~Q _ _ ..._ _ _...

O aJ rl .~J~s) ~:) ~s:) ~D
~; ~a l5\ C5~ a~
r~ ~ 4~ _ _ ~ ~ O~ co ~ O
,~ ~ co c;~ a~
. ~-r~ 3~ O O O O
~r-l ~ ~ r~ ~

r~ r--~ r-~ r--i r;
r~ _ .~
c^ ~ ~ L~ u) u~
r~ O J-- ri ~ cO cO ~0 00 ~ ~ O ~ ~ ~ ~
_ 5~ C~ r--r ~r~Z 3~ O O O O
~ O ~
E~ P~ J ~ E~ ~ o ~ c~
O ~ ~ c~
' '~ r--i r--i ._ ... _ ..._ o~ ~! ~ o~
. 0~ 0 ~0 O ~ O
O ~ O ~ o-o~ o o~
~n ~ O ~ ~ ~ O
o~ o~ o~O~ o~
a) I ~ o oo c~ O ~ ~
O ~O O ~v~O ~O
: O ~ ~ ~r~ ~ r l c~ u~ u~ u~ ~ ,c4 r~u ~ ~ ~ ~
: ~ cr)~J ~000 1~^) ~ 00~) L~
0 ~r) r--l ~ O c~ ~I O
v~ O ~ O O O ~ O O O O
: r~ O O
c~ u~ c~ u~ z t ) u~ z ,n : _ . _ :: :
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As seen from Table 29 as compared with the comparative proclucts, the products provided with TiN
thin coat according to the invention e~hibit much improvement in that B1o, W17~50 and the lamina-tion 05 factor were enhanced by 0.01-0.03 T, 0.17-0.20 W/kg, and 2-2.5%, respectively.
Example 2 A hot rolled silicon steel sheet (1.~ mm thickness) containin~ 0.056% of C, 3.39% of Si, 0.068%
of Mn, 0.018% of S, O. 025% of sol. AQ and 0.0076% of N
was subjected to a normalized annealing at 1,050C Eor 3 minutes, and then to a cold rolling two times through an intermediate anneaLing at 950C to obtain a final cold rolled steel sheet of 0.23 mm in thickness. Then, after decarburization and primary recrystallization annealing was carried out at 820C for 3 minutes, the resulting steel sheet was coated with a slurry of ; an annealing separator composed of AQ203 (6b%), MgO (25%), ZrO2 (10%) and TiO2 (5%).
Thereafter, secondary recrystalli~ation ,:
annealing was carried out by holding the temperature at 850C for 50 hours. Subsequently, after purification annealing was carried out in a dry hydrogen atmosphere at 1,200C for 6 hours, oxides were removed from the surface of the steel sheet through pickling, and the steel sheet surface was rendered into a mirror ~inished state by e:Lectropolishing. Then, various thin coats (about 0.6-0.7 ~m in thickness~ were formed onto the :`

,- ' mirror finished s~Lrfaces of the steel sheets by using CVD (no mark in Table 3), ion plating ("o" in Table 3), or ion implantation ("~" in Table 3), and an insulation coating consisting mainly of a phosphate and colloidal silica was formed thereon. The magnetic properties of the resulting products are shown in the following Table 3.

Table 3 Magnetic properties Run No. Kind of compound ~10 (T) wl7/50 (W/kg) (1) TiN o 1.95 0.76 (2) BN 1.96 0.72 (3) Nitride Si 3 N4 1.95 0.71 (4) ZrN 1.94 0.70 (5) AQN 1.94 0.76 (6) Ti(CN) ~ 1.96 0.69 (7) TiC o 1.95 0.71 (8) SiC o 1.95 0.68 : (9) Carbide ZrC 1.95 0.71 (10) WC 1.96 0.70 : . (11) Mo2C 1.94 0.69 (12) Cr7C3 1.95 0.68 Example _ ~: A hot rolled steel sheet containing 0.043%
of C, 3.37% of Si, 0.063% of Mn, 0.025% of Mo, 0.022%
of Se, and 0.025~o of Sb was prepared.

, . .
.

~.2 ~
This hot rolled steel sheet was sub;jected to a normalized annealing at 900C for 3 minutes, and then to a cold rolling two times through an intermediate annealing at 950C to obtain a final cold rolled steèl 05 sheet of 0.23 mm in thickness.
Thereafter, the resulting steel sheet was subjected to a decarburization anneali-ng in a wet hydrogen atmosphere at 820C, and coated with a slurry of an annealing separator composed of AQ203 (75%), MgO (20%~, and ZrO2 (5%). The coatecl steel sheet was subjected to a secondary recrystallization annealing at 850C for 50 hours, and then to a purification annealing : in H2 at 1,200C for 8 hours.
Subsequently, the surface of the steel sheet was pickled to remove oxide layer therefrom, and ~ subjected to a chemical polishing with a mixed solution : of 3% H~ and H2O2 to render the surface into a mirror finished state. Thi.n coats of various compounds, that is, Cr2N, BN, Si3N4, ZrN and AQN as nitrides, and TaC, : 20 NbC, SiC, ZrC, WC, Mo2C and Cr7C3 as carbides were formed all in a thickness of 0.7-0.9 ~m by using CVD
(no mark in Table 4), ion plating ("o" in Table 4) or : ion implantation ~'~" in Table 4).
Then, an inslllation coating consisting mainly : 25 of a phosphate and colloidal silica was baked onto the surface of each of the thin coats, which was subjected to a strain relief annealing at 800C for 2 hours.
: The magnetic properties, compressive stress : , .

'~ ' .
: .

:il",~17~

clependence of magnetostriction (values App of magneto-striction when the compressive stress a is 0.4 and 0.6 kg/mm2) of the resulting products are shown in the following Table 4.

Table 4 _ _ , . . ._ _ Run Magnetic properties A (X10-~) No Kind of compound _ _ _ PP
. Blo(T) Wl7~50(W/kg) a:O.4kg/mm2 a:O.6kg/mm2 _ .............. . ~ __ (1) Cr2N o1.91 0 78 0.15 -------¦
(2) BN 1.92 0.82 0.21 0.63 (3) Nitride Si3N~ 1.92 0.84 0.23 0.62 . . _ (4) ZrN 1.91 0.73 0.21 0.53 . _ _ (5) AQN 1.91 0.72 0.18 0.63 ... _ . ... .__ (6) TaC ~ 1.92 0.78 0.19 0.66 . . ___ . ___ (7) NbC o 1.91 0.76 0.22 0.67 (8) SiC o 1.92 0.76 0.13 0.68 . _ (9) Carbide ZrCl.91 0 74 0.10 0.78 ~10) WC1'.91 0.73 0.21 ~ 0.72 (11) Mo2C1.91 0.81 0.22 0.76 (12) ¦ Cr7C31.91 0.82 0.11 0.49 Example 4 A grain oriented silicon steel sheet containing 0.056% of C, 3.29% of Si, 0.078% of Mn, 0.025% of AQ, 0.030% of S, 0.1% of Cu and 0.05% of Sn was heated at 1,440C for 5 hours, and then hot rolled to obtain ; a hot rolled steel sheet of 1.6-2.7 mm in thickness.
Then, the steel sheet was subjected to ., .

!

a normalized annealing at l,100C for 3 minutes, and then quenched. Thereafter, the resulting steel sheet was warm rolled at 350C to obtain a final rolled steel sheet of 0.20, 0.23, 0.27 or 0.30 mm in thickness.
05 Subsequently, the rolled steel sheet was subjected to decarburization and primary recrystalliza-tion annealing in a wet hydrogen atmosphere at 850C, and then coated with a slurry of an annealing separator composed of AQ203 (70%), MgO (20%), TiO2 (5%), and lo ZrO2 (5%). The coated steel sheet was subjected to a secondary recrystallization annealing at 850C for 50 hours, and then to a purification annealing in a dry hydrogen atmosphere at 1,200C for 5 hours.
Then, the steel sheet was pickled to remove oxides therefrcm, and subjected to an electropolishing to render the surface into a mirror finished state.
: Thereafter, a -thin coat of Cr2N was formed by using PVD (ion plating apparatus), and then an insulation coating consisting mainly of a phosphate and colloidal silica was baked thereon. The baked steel sheet was ; subjected to a strain relief annealing at 3~0C for 3 hours. The thickness of Cr2N thin coat, and the magnetic properties, compressive stress dependence of magnetostriction (values App of magnetostriction when the compressive stress a is 0.4 kg/mm2 and 0.6 kg/mm2), and the lamination factor ~%) of the resulting products are shown in the following Table 5.

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~ ~ o ~ ~ ~ ~
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~ o C~l U~ o . o o ~.

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Exam~
Hot rollecl steel sheets having the following chemical composition were prepared:
(a) C=0.042%, Si=3.36%, Mn=0.062%, Mo=0.024%, 05 Se=0.021%, and Sb=0.025%; and (b) C=0.056%, Si=3.36%, Mn=0.068%, AQ=0.026%, S=0.029%, N=0.006~%, Cu=0.1%, and Sn=0.05%
First, the hot rolled steel sheet (a) was subjected to a normalized annealing at 900C for 3 minutes, and then to a cold rolling -two times through an intermediate annealing at 950C to obtain a final cold rolled steel sheet of 0.20 mm in thickness.
On the other hand, the hot rolled steel sheet (b) was subjected to a normalized annealing at 1,080C for 3 minutes and quenched, and then warm rolled at 300C to obtain a final rolled steel sheet of O.20 mm in thickness.
Then, each of the rolled steel sheets was subjected to decarburization annealing in a wet hydrogen atmosphere at 830C, and coated with a slurry of ~ ~ an annealing separator composed of AQ2O3 (75%), : . MgO (20%), and ZrO2 (5%). The resulting sample with : the composition (a) was subjected to a secondary : recrystallization annealing at 850C for 50 hours, and ; 25 then to a purification annealing in a dry hydrogen atmosphere at 1,200C for 5 hours. The resulting sample with the composition (b) was heated from 850~
to 1,050C at 5C/hr for second recrystallization, and ; 39 ,: :

, , , : , ': .
- , , Y~7~) then subjected to a purification annealing in a dry hydrogen atmosphere at 1,200C for 8 hours.
Thereafter, an oxide layer was removed through pickling, and then a chemical polishing was carried out os with a mixed solution of 3% HF and H2O2 to effect mirror finishing.
Then, by using a (VD device, (i) TiN thin coat, (ii) Ti(C~j thin coat and (iii) TiC thin coat were formed all in a thickness of 0 7 ~Im from a mixed gas of TiCQ4, H2 and N2, a mixed gas of TiCQ4, H2, N2 and CH4, and a mixed gas of TiCQ4, H2, N2 and CH~, respectively. By using an ion plating or ion implanta~
tion apparatus, thin coats of (iv) Ti(CN) and (v) TiC
were formed in a thickness of 0.7-0.9 ~m.
Subsequen-tly, an insulation coating consisting mainly of a phosphate and colloidal silica was baked onto the surface of the thus treated sample, which was subjected to a strain relief annealing.
The magnetic properties and compressive stress dependence of magnetostrict1on (values App of magnetostriction when compressive stress a is 0.4 and O.6 kg/mm2) of the resulting produc-ts are shown in the following Table 6.

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.
, ~.fJ~'7 Example 6 A grain oriented silicon steel sheet containing 0.043% of C, 3.42% of Si~ 0.069% of Mn, 0.021% of Se, 0.025% of Sb and 0.025% of Mo was heated at 1,/-~00C for 05 3 hours, and then hot rolled to obtain a hot rolled steel sheet of 1.8-2.7 mm in thickness. Thereafter, the hot rolled steel sheet was subjected to a normalized annealing at 900C for 3 minutes, and -then to a cold rolling two times through an intermediate annealing at 950C for 30 minutes to obtain a final cold rolled steel sheet of 0.20, 0.23, 0.27 or 0.30 mm in thickness.
Thereafter, the cold rolled steel sheet was subjected to decarburization and primary recrystalliza-tion annealing in a wet hydrogen atmosphere at 830C
and then coated with a slurry of an annealing separator composed of MgO (20%), AQ2O3 (70/O)~ TiO2 (5%), and ZrO2 (5%). Then, the coated steel sheet was subjected to a secondary recrystallization annealing at 850C for 50 hours, and then to a purification annealing in a dry 20 hydrogen atmosphere at 1,200C for 5 hours. After oxides on the surface of the steel sheet were remo~ed through lightly pickling, the surface of the steel : sheet was rendered into a mirror finished state by electropolishlng.
Then, a TiN thin coat was formed by using PVD
(ion plating apparatus) 9 and an insulation coating consisting mainly o~ a phosphate and colloidal silica : was baked thereon, which was subjected -to a strain ~ - 42 -- ~ .
' , ' :~

relief annealing at 800C for 3 hours. The thickness of the TiN thin coat and the magnetic properties, compressive stress dependence of magnetostriction (values App of magnetostriction when the compressive stress a is 0.4 kg/mm2 and 0.6 kg/mm2) of the resulting products are shown in the following Table 7.

Table 7 _ _ .
Compr~ssiv~ stress Thickness Thickness Magnetic properties dependence of of product o TiN magnetostriction (mm)thin coat A (X10-6) (~m) PP
, BlotT) Wl7j50(W/kg) c~:O.4kg/mm2 o:O.6kg/mm2 : 0.30 1.10 1.92 0.90 0.2 0.3 . _ 0.27 1.02 1.92 0.82 0.1 0.15 0.23 0.75 1.91 0.74 0.1 0.2 . .
:' ._ ~ 0.20 0.50 1.92 0.69 0.2 0.35 : , Example 7 A grain oriented silicon steel sheet containing O . 044% of C, 3.45~/O of Si, 0.066% of Mn, 0.023% of Se, 0.025% of Sb, and 0.026% of Mo was heated at 1,360C
for 4 hours, and then hot rolled to obtain a hot rolled ::
steel sheet of 2.2 mm in thickness. Then, the hot rolled steel sheet was subjected to a normalized annealing at 900C for 3 minutes, and then to a cold _ 43 _ :
-' '7~'7~

rolling two times through an intermediate annealing at950C for 3 minutes to obtain a ~inal cold rolled steel sheet of 0.23 mm in thickness.
Then, the cold rolled steel sheet was subjected 05 to decarburization and pri.mary recrystallization annealing in a wet hydrogen atmosphere at 820C, and coated with a slurry of an annealing separator composed of A~2O3 (60%), MgO (30%), ZrO2 (5%) and TiO2 (5%).
The coated steel sheet was subjected to a secondary recrystalli~ation annealing at 850C for 50 hours, and then to a purification annealing in a dry hydrogen atmosphere at l,200C for 8 hours. Thereafter, oxides on the surface of the steel sheet were remove~ through lightly pickling, and the surface of the steel sheet was rendered into a mirror finished state through electropolishing.
Then, a TiN thin coat was formed by using ~arious ion plating apparatuses according to ta) magnet ron sputtering method, (b) EB (Electron Beam) ~ RF (~adio Frequency) method, (c) HCD (Hollow Cathode Discharge) method, or (d) Multi Arc method. The results on the X-ray diffraction of the TiN thin coat and the magnetic properties of the resulting products are shown in the following Ta~le 8.

!

64~81-2~5 Table 8 Magnetic properties X-ray diffrac Run Kind o-f ion . .__ _ tometry of No. plating method Blo(T) W:L7/50(W/kg) thin coat . . _ _ _ . . .
(a) Magnetron 1.91 0.70 TiN peaks only sputtering .. . _ _ ..... ~ ...... _~
TiN peaks mainly (b) EB~RF 1.92 0.70 small . _ _ _ . _ TiN peaks mainly (c) HCD 1.92 0.69 Ti2N peaks small Ti peaks small _ . . __ ._ ______ . . __ (d) Mul-ti Arc 1.920.72 TiN peaks only . _ .. . . ~ .. _ ~ As apparent from Table 8, the magnetic properties in the ; formation of the Ti~ thin coa-t according to four types of the ion plating methods are extremely excellent in that .Blo is 1.91-1.92 T
and W17/so is 0.69-0.72 W/kg. According to the results on the X-ray diffraction of the thin coats on the surface of the steel sheet, only TiN peaks were detected in the condition of (a) and (d), and in the condition (b), although the TiN peaks were main peaks, Ti peaks were slightly detected, while in the conditi.on (cj, TiN peaXs were main peaks, but Ti2N and Ti peaks were slight-ly detected. However, such slight amounts of other peaks than those of TiN will not greatly affect the magnetic properties.

~ !

?'~1~3'7 Ex~ e 8 A hot rolled steel sheet containing 0.043/~
of C, 3.36% of Si, 0.063% of Mn, 0.026% o-f Mo, 0.021%
of Se and 0.025% of Sb was subjected to a cold rolling 05 two times through an intermediate a process annealing at 950C for 3 minutes to obtain a final cold rolled steel sheet of 0.23 mm in thickness. Then, the cold rolled steel sheet was subjected to decarburization and primary recrystallization annealing in a wet hydrogen atmosphere at 820C, and coated with a slurry of an annealing separator composed of AQ203 (70%), MgO (25%) and ZrO2 (5%). The coated stee:L sheet was : subjected to a secondary recrystallization annealing at 850C for 50 hours, and then to a purification annealing in a dry hydrogen atmosphere at 1,200C for 7 hours.
Thereafter, an oxide layer on the surface of the steel sheet was removed through pickling, and a chemical polishing was carried out to render the surface into a mirror finished state having a center-line average roughness of not more than 0.04 ~m. Then, a metal or a semimetal as shown in the following Table 9 was deposited thereon at a thickness of 0.7-0.8 ~m.
Next, the resulting product was annealed in an atmosphere containing N2 or CH4 to form a mixed ~hin coat consisting of various carbides and nitrides.
Then, an insulation coating con`sisting mainly of a phosphate and colloidal silica was formed onto the . ~ ~ ' ' " ~'' ,.'"'' " ~ ~

~l ~r~ 7~

thin coat. The magnetic properties and adhesion property of the resulting product were examined to obtain results as shown in Table 9.

:

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of C, 3.38% of Si, 0.065% of Mn, 0.025% of Mo, 0.022%
of Se, and 0.025% of Sb was subjected to a normalized 05 annealing at 900C for 3 minutes, and then to a cold rolling two times through an intermediate annealing at 950C to obtain a final cold rolled steel sheet of 0~20 mm in thickness.
Then, the cold rolled steel sheet was subjected to decarb~lrization annealing in a wet hydrogen atmosphere at 320C, and coated with a slurry of an annealing separator composed of AQ203 (70%), ZrO2 (5%), TiO2 (1%), and MgO (24%). The coated steel sheet was subjected to a secondary recrystallization annealing at 850C for 50 hours, and then to a purification annealing in a dry hydrogen atmosphere at 1,200C for l0 hours.
Thereafter, the surface of the steel sheet was pickled to remove an oxide layer, and a chemical polishing was carried out with a mixed solution of 3% HF and H2O2 to render the surface into a mirror finished state.
After TiN (0.3 ~m in thickness) was ion plated as shown in the formations of thin coats, (1)-(5), o~ Table l0, ion plating of (l) 0.4 ym thickness of BN, (2) 0.3 ym thickness of Si3N4, (3) G.2 ym thickness of ZrN, (4) 0.3 ym thickness of AQN, or (5) 0.3 ym thickness of TiC was carried out. In (6) and (7) of Table l0, Ti(CN) (0.3 ym in thickness) was ion plated _ ~9 _ , and then the ion plat:ing of (6) 0.5 ~m thickness of Cr2N or (7) 0.5 ~m thickness of HfN was carried ou-t.
The magnetic properties of the thus obtained products are shown in Table 10.

_able 1 Run Formation of Magnetic properties No. thin coats B~(T) W17/50(W/kg) (1) TiN (o 3~mm)frmed on 1.91 0.69 (2) on TiN (033~m))formed l.91 0.71 (3) ~irN (0 3 ~m) formed on 1.91 0.68 ...__ (4) TiN (0 3 ~m) 1.92 0.66 (5) TiN (0 3 ~m) 1.92 0.65 (6) Cr2N (0 5 ~m) formed 1.92 0.64 (7) Ti(CN) (0~3)~f)rmed on 1.92 0.66 !
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Example 1_ (a) C=0.042%, Si=3.09%, Mn=0.065%, Sb=0.026%, Se=0.021%
(~) C=0.046%~ Si=3.07%, Mn=0.072%, sol.AQ=0.026%, 05 N=0.0063%, S=0.028%
(c) C=0.052%, Si=3.39%, Mn=0.074%, sol.AQ=0.028%, N=0.0073%, Se=0.024%, Mo=0.028%
(d) C=0.042%, Si=3.06%, Mn=0.055%, B=0.0026%, N=0.0069%
~our hot rolled steel sheets were subjected to a normalized annealing at 900C for 3 minutes in case of the chemical composition (a), at l,150C for 3 minutes in case of the chemical compositions (b) and (c), and at 1,000C for 3 minutes in case of the chemical composition (d), respectively. Thereafter, each of the above steel sheets was subjected to a cold rolling two times through an intermediate annealing at 950C to obtain a final cold rolled steel sheet of 0.23 mm in thickness~
; 20 Then, these cold rolled steeI sheets were ;~ subjected to decarburization and primary recrystalllza-tion annealing in a wet hydrogen atmosphere at 820C, and coated with a slurry of an annealing separator composed of AQ2O3 ( 60%) ~ MgO (35%), ZrO2 (3%) and TiO2 (2%).
Subsequently, the steel sheet (a) was subjected o a secondary recrystalIization annealing by holding at ~850C for 50 hours, and then to a purification . :
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for 8 hours. On the other hand, each of the steel sheets (b), (c) and (d) was subjected to a secondary recrystallization annealing by raising the temperature from 850C to 1,050C at a rate of 10C/hr, and then to a purification annealing in a dry hydrogen atmosphere at l,200C for 10 hours.
Thereafter, the surface of each of these steel sheets was lightly plckled to remove oxides therefrom, and then renderecl into a mirror finished state by electropolishing. Then, a~ a thin coat of TiN (about 1.0 ~m thickness) was formed on the finlshed surface of the steel sheet by using a CVD apparatus.
The magnetic properties and the lamination factor of the resulting products are shown in the following Table 11.

Table 11 ; Magnetic properties Lamination Steel components factor Blo(T) wl7/50(w/kg) t%) (a) C 0.042%, Si 3.09%, Mn 0.065%, 1 2 Sb 0.026%, Se 0.021% .9 0.76 98.5 _ ~b) C 0.046%, Si 3.07%, Mn 0.072%, S 0.028%, sol.AQ 0.026%,1.94 0.77 98 N 0.0063%
(c) C 0.052/~, Si 3.39%, Mn 0.074%, _ sol.A~ 0.028b, N 0.0073%, 1.94 0.73 98.5 Se 0.024%, Mo 0.028%
(d) C 0.042%, Si 3.06%, Mn 0.055%, B 0.0026%, N 0.0069%, 1.93 0.78 98 Se 0.021% _ _ .

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Claims (12)

1. An extra-low iron loss grain oriented silicon steel sheet comprising a base metal of silicon steel and a thin coat of at least one layer composed of at least one of nitrides and carbides of Ti, Zr, Hf, V, Nb, Tar Mn, Cr, Mo, W, Co, Ni, A?, B
and Si and strongly adhered to a finished surface of the base metal through a mixed layer of the base metal and the thin coat, the thin coat having a thickness of 0.005-5µm.

2. The extra-low iron loss grain oriented silicon steel sheet according to claim 1, wherein said base metal is obtained by starting from a silicon steel comprising 0.01-0.06% by weight of C, 2.0-4.0% by weight of Si, 0.01-0.20% by weight of Mn, 0.005-0.05% by weight in total of at least one of S and Se, and the remainder being substantially Fe.

3. The extra-low iron loss grain oriented silicon steel sheet according to claim 2, wherein said silicon steel further contains 0.005-0.20% by weight of Sb.

4. The extra-low iron loss grain oriented silicon steel sheet according to claim 2, wherein said silicon steel further contains 0.005-0.20% by weight of Sb and 0.003-0.1% by weight of Mo.

5. The extra-low iron loss grain oriented silicon steel sheet according to claim 2, wherein said silicon steel further contains 0.005-0.06% by weight of sol. A? and 0.001-0.01% by weight of N.

6. The extra-low iron loss grain oriented silicon steel sheet according to claim 2, wherein said silicon steel further contains 0.005-0.06% by weight of Sol.A?, 0.003-0.1% by weight of Mo and 0.001-0.01% by weight of N.

7. The extra-low iron loss grain oriented silicon steel sheet according to claim 2, wherein said silicon steel further contains 0.005-0.06% by weight of sol. A?, 0.001-0.01% by weight of N, 0.01-0.5% by weight of Sn and 0.01-1.0% by weight of Cu.

8. The extra-low iron loss grain oriented silicon steel sheet according to claim 2, wherein said silicon steel further contains 0.0003-0.02% by weight of B and 0.001-0.01% by weight of N.

9. The extra-low iron loss grain oriented silicon steel sheet according to claim 2, wherein said silicon steel further contains 0.0003 0.02% by weight of B, 0.001-0.01% by weight of N
and 0.01-1.0% by weight of Cu.

10. The extra-low iron loss grain oriented silicon steel sheet according to claim 1, wherein said thickness is 0.05 1.5µm.

11. The extra-low iron loss grain oriented silicon steel sheet according to claim 1, wherein said thin coat is under a tension.

12. The extra-low iron loss grain oriented silicon steel sheet according to claim 1, wherein said thin coat is provided thereon with an insulation coating consisting essentially of phosphate and colloidal silica.