CA1249764A - Grain-oriented electrical steel sheet having a low watt loss and method for producing same - Google Patents

Abstract

GRAIN-ORIENTED ELECTRICAL STEEL SHEET HAVING A LOW
WATT LOSS AND METHOD FOR PRODUCING SAME

ABSTRACT OF THE DISCLOSURE

Method for subdividing the magnetic domains of a grain-oriented electrical steel sheet is improved so that the watt loss can be further lessened and the watt-loss improving effect does not disappear during stress relief annealing. An intrudable means is formed on the finishing-annealed steel sheet on or in the vicinity of strain which promotes the intrusion of an intrudable means. Sb or Sb containing material is a preferred intrudable means and the laser irradiation is a preferred method for imparting the strain and also for attaining the removal of a surface coating.

Description

~ 2 ~t'~ ~

GRAIN-O~IENTED ELECTRICAL STEEL SHEET HAVING A LOW
WATT LOSS AND METHOD FOR PRODUCING SAME

BACKGROUND OF TH~ IN~ENTION
1. Field of the Invention The present invention relates to a grain-oriented electrical steel sheet having a low watt loss and a method for produclng the same. More particularly, the present invention relates to a grain-oriented electrical steel sheet, in which the magnetic domains are subdivided and the subdivision effect does not disappear, even if the steel sheet is subsequently heat treated. The present invention also relates to a method for producing the grain-oriented electrical steel sheet as mentioned above.

2. Description of the Related Art The grain-oriented electrical steel sheet is-used mainly as the core material of transformers andother electrical machinery and devices, and must, therefore, have excellent excitation and watt-loss characteristics. In the grain oriented electrical steel sheet, secondary recrystallized grains are developed which have a (110) plane parallel to the rolled surface and a <001> axis parallel to the rolling direction.
These grains have the so-called Goss texture formed by utilizing the secondary recrystallization phenomenon.
Products having improved exciting and watt-loss charac-teristic~ can be produced by enhancing the orientationdegree of the tllO)'001> orientation and lessening the deviation of the s001~ axis from the rolling direction.
Note, the enhancement of the (110)~001>
orientation leads to a co~rsening of the crystal grains and an enlargement of the magnetic domains due to a passing of domain walls through the grain boundaries.
There occurs accordingly, a phenomenon such that the watt loss cannot be l~ssened proportionally to enhance the orientation.
Japanese Examined Patent Publication No. 58-5968 proposes to lessen the watt loss by eliminating the nonproportional phenomenon regarding the relationship between the orientation enhancement and the watt loss--reduction. According to this proposal, a ball or the like is pressed against the surface of a finishing-annealed, grain-oriented sheet so as to form an indentation having depth o 5 ~ or less. By this indentation, a linear, minute strain is imparted to the steel sheet, with the result that the magnetic domains are subdivided.
Japanese Examined Patent Publication No. 58-26410 proposes to form at least one mark on each of the secondary recrystallized crystal grains by means of laser-irradiation, thereby subdividing the magnetic domains and lessening the watt loss.
The materials having ultra-low watt loss can be obtained, according to the methods disclosed in the above Japanese Examined Patent Publication Nos. 59-5868 and 58-26410, by means o~ imparting a local minute strain to the sheet sur~ace of a grain-oriented electrical steel sheet. Nevertheless, the watt loss-reduction effect attained in the above ultra-low watt loss materials disappears upon annealing, for example, during stress-relie annealing. For example, in the production of wound cores, the watt loss-reducing effect disappears disadvantageously ater the stress-relief annealing.
It is also known that the watt loss can be lessened by refining the crystal grains. For example, Japanese Examined Patent Publication No. 59-20745 intends to lessen the watt loss by determining an average crystal-grain diameter in the range of rom 1 to 6 ~n.
It is also known to impart tensional force to a steel sheet to lessen the watt loss. The tensional force in the steel sheet can be generated by diffexing the coefficient o~ thermal expansion between the insulating coating and the steel sheets.
The above described refining of crystal grains and strain imparting would not attain a great reduction in watt loss.
SUMMARY OF THE INVENTION
The materials having an ultra-low watt loss can be obtained by the methods for subdividing the magnetic domains. When these materials are annealed, for example, stress-relief annealed, the watt loss-reduction effect disappears. It is, therefore, an object of the present invention to provide a grain-oriented electrical steel sheet having an extremely low watt loss, and to provide a method for forming subdivided magnetic domains, in such a mannex that the watt loss-reducing effect does not disappear even during a heat treatment, for example, stress-relief annealing.
The present inventors conducted a number of e~periments for producing, by the magnetic domain subdividing method, a grain- oriented electrical steel sheet which can exhibit an extremely low watt 1GSS even after a heat ~reatment at a temperature of from 700 to 900C.
In -the experiments, intruders were penetrated into ~he finishing-annealed, grain-oriented electrical steel sheets. These intruders are distinguished from the steel of the steel sheets either in components or stxucture. The intruders were formed as a result of a reaction, in which the steel sheet or the surface coating was participated. The intruders were an alloy la~er, a reaction product of the superficial reaction, and the like, and the intruders were spaced from one another.
As a result of the experiments as descrlbed above, lt was discovered that: the nuclei of magnetic domains are generated on both sides of the intruders; these nuclei cause the subdivision of magnetic domains when ~L2~7~

the steel sheet is magneti~ed and, hence, an extremely low watt loss is obtained; the effect of reducing the watt loss does not disappear even after the steel sheet is annealed, for example, stress-relief annealed; and, an extremely low watt loss is maintained.
The term "intruder" herein expresses clusters, grains, lines, or the like formed by an intrusion of a film on the steel sheet into sheet . The film alone may intrude into the steel sheet. Alternati.vely, -the film may be combined with the components of a steel sheet including any surface coating ~ormed during the production of a grain-oriented electrical steel sheet.
The film may also be combined with the gas atmosphere of a heating furnace. The films intruded may be those combined with the components of a steel sheet, or the gas atmosphere. A preferred intruder is one formed by Sb metal, Sb alloy, Sb mixture, or Sb compoundl alone or combined with the steel body of a grain-oriented electrical steel sheet. The intruder containing Sb can cause the subdivision of the magnetic domains and drastically lessen the watt loss.
The effect of watt loss-reduction by the Sb-con-taining intruder is outstanding, since it does not disappear cluring a later stress-relief annealing at a high temperature, for example, from 7~0 to lOOO~C. The magnetic flux density of steel sheets having the Sb-containing intruders is high The term "intrudable means" or "the intrudable means for subdividing the magnetic domains" herein represents the material capable of forming the intruder, and more specifically, is the material to be deposited on the ~rain-oriented electrical steel sheet by plating.
This material includes Al, Si, Ti, Sb, Sr, Cu, Sn, Zn, Fe, Ni, Cr, Mn, P, S, B, Zr, Mo, Co~ and other metals and nonmetals, as well as mixtures, oxides, and alloys thereof. This material further includes phosphoric acid, boric acid, phosphate, borate, sulfate, nitrate, 7~i~

silicate and the like, and mixtures thereof.
The term "film" hereln collectively indicates a mechanical coated ~ilm, a chemically deposited film, e.g., a plating film, and a bonded film; which films are formed on at least a part of the steel sheet. The term "film" may include partly a reaction layer and may have any thickness which is not specified in any way.
The term "surface coating" herein indica-tes the film, layer or coating ~ormed by the ordinary method for producing a grain- oriented electrical steel sheet.
The heat-resistant, subdivision of the magnetic domains can be performed as follows. Strain is imparted to the grain-oriented electrical steel sheet. The metallic or nonmetallic powder, the powder of the metallic or nonmetallic oxide, or agent, such as phosphoric acid, boric acid, phosphate, borate is applied, on the~inishing-annealed, grain-oriented electrical steel sheet, with spaced distances of the application. When the heat treatment is carried out, the applied material (intrudable means) is caused to react with the steel sheet or the surface coating and is forced into the steel sheet via the strain. The intruders therefore can be ~ormed spaced from one another and have components or a structure different ~rom those of steel.
In accordance with the present invention there is provided a grain-oriented electrical steel sheet having an ultra low watt loss, characterized in that intruders, which are spaced from one another and are distinguished ~rom the steel in component or in structure, are formed on or in the vicinity of the plastic strain region, thereby subdividing the magnetic domains.
There is also p~ovided a method for producing a grain-oriented electrical steel sheet by steps including a subdivision of magnetic domains, characterized in that, a strain is imparted to the grain-oriented electrical steel sheet, and an intrudable means for 7~'~

forming the intruders being distinguished from the steel in component or structure, is formed on the grain-oriented electrical steel sheet prior to or subsequent to imparting of the strain.
Note, the technique disclosed in Japanese Examined Patent Publication No. 54-23647 is similar to the present invention in the point that a metal or compound is intruded into the steel sheet. It is proposed irl this technique that, before the finishing annealing, the compound, metal, or element alone, which is rendered to slurry form, is applied on the steel sheet and is thermally diffused into the steel sheet thereby forming, before the finishing annealing~ the secondary recrystal-lization-regions in the steel sheet. Principally speaking, this technique allegedly stops the growth of grains other than ~110)<001> oriented grains at the secondary recrystallization regions, thereby attaining a preferential grcwth of the (110)~001> oriented grains.
The watt loss W17/50 attained in the Japanese Examined 20 Patent Publication No. 54-23647 is approximately 1.00 W/kg which is considerably inferior to ~hat which the present invention aims to attain. The present inventors believe that the watt loss according to the present invention is much less than that of the publication because diffusing me-tal and the like applied on the steel sheet at a step prior to the finishing annealing prevents the coarsening of grains to attain the watt loss reduction in Japanese Examined Patent Publication No. 54-23647, while, in the present invention, after completion of the secondary recrystal-li~ation, in order to subdivide the magnetic domains the intruder is forced into the steel sheet, in which the Goss texture is thoroughly developed.
Method for A~elying an Intrudable Means The grain-oriented electrical steel sheet, which is subjected to the subdivision of magnetic domains according to the present invention, may be produced by using any composition and under any conditions of production steps until the finishing annealing. That is, AlN, MnS, MnSe, BN, Cu2S and the like can be optionally used as the lnhibitor. The Cu, Sn, Cr, Ni, Mo, Sb, W, and the like may be con~ained if necessary.
The silicon steels containing the inhibitor elements are hot-rolled, annealed, and cold-rolled once or twice with an intermediate annealing to obtain the final sheet thickness, decarburization annealed, an annealing separator applied, and are finally finishing annealed.
The agent which is the intrudable means consists of at least one member selected from the metal- and nonmetal-group consisting of Al, Si, Ti, Sb, Sr, Cu, Sn, Zn, Ni, Cr, Mn, B and their oxides, and of at least one member selected from the group consisting of phosphoric acid, boric acid, phosphate, borate, and sulfate, and as well as these mixtures thereof. The agent is rendered to a slurry state or solution state and is applied linearly or spot-like on the finishing-annealed, grain-oriented electrical steel sheet. The lines are spacedfrom one another.
The metallic or nonmetallic powder has a size of tens of microns or less. In the slurry, the amount of metallic, nonmetallic, or oxide powder is preferably in a concentration from approximately 2 to 100 parts by weight relative to 100 parts by weight of water, since the slurry can be applied at a high efficiency at such a concentration. The metallic or nonmetallic powder or oxide can be mixed with acid or salt, which may be the stock solution or may be diluted with water.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a photoyraph showing strain in the steel sheet;
Figure 2 is an optical microscope photograph showing an example of the intruder;
Figures 3(a) and (b) are an elevational view and lateral view, respectively, of an electric plating 76'~

~pparatus;
Figure 4 is a graph showing the relationship between the current density and cathode-current density in an electroplating; and Figure 5 is a graph showing the relationship between the sheet thickness and watt loss.
Figure 6 is a graph showing a relationship between the depth of intruder and the reduction percentage in watt loss.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Method for Imparting Strain The intrudable means are applied on the finishing-annealed, grain-oriented electrical steel sheet to form a film having a weight of from approximately 0.1 to 50 g/m . The application of the intrudable means is carried out by plating, vapor-depositing, bonding, fusion-bonding, or the like, preferably by plating.
Prior to or subsequent to the formation of the film, the strain is imparted by an optical means, such as laser irradiation, or a mechanical means, such as the yrooved roll, ball point pen and mark.ing-off methods. The regions of a grain-oriented electrical steel sheet to which the strain is imparted are spaced from one another.
The method for imparting the strain is more specifically described.
The agent is applied on the grain-oriented electrical steel sheet with a space distance of from 3 to 30 mm. This grain-oriented electrical steel sheet is preliminarily subjected to a mechanical formation of minute indentations with a space distance of from 3 to 30 mm by means of a small ball, a ball point pen, marking-off, a grooved roll, a roller, or the like.
Alterna-tively, the optical method may be used, such as laser irradiation, for forming the marks~ The appli-cation amount of the agent can be from 0.1 to 50 g/m2,preferably from 0.3 to 10 g/m2 of area of marks, flaws and the like, in terms of the film weight after the application and drying. Subsequently, the heat treatment is carried out at a temperature of from 500 to 1200C, after drying the applied agent. During the heat treatment, the agent is brought into reaction with the steel sheet and/or the surface coating and forced into the steel sheet along its width to form the intruders, such as the alloy layer and/or the surface reaction product. The intruders so formed are spaced from one another.
Regarding the laser-irradiation method for imparting the s-train, the laser may be any one of a CO2 laser, N2 laser, ruby laser, pulse laser, YAG laser, and the like. The space distance between the strain-imparted regions may be from 1 to 30 mm and these regions may be equi-distant or non-equidistant.
The method for imparting the strain is not to subdivide the magnetic domains by itself, as in the conventional method, but to promote~the intruder formation due to a stably enhanced reaction between the ~0 film and the steel sheet or between the film and the surface coating. The strain and intrudable means are further explained with reference to Fig. 1 showing the strain by black shadow. In this explanation, it is assumed that the heat treatment is not carried out by the steel maker but by the user. The intrudable means, such as the plated Sb, is merely deposited on the steel sheet and does not exert an effect upon the magnetic properties until the steel sheet is annealed by the user. Upon annealing, Sb di~fuses into the steel sheet, precipitates in the steel sheet, and forms an inter-metallic compound. The surface of a grain-oriented electrical steel sheet, to which the laser is applied, is influenced by the laser so tha-t this surface and its proximity undergo plastic deformation (black shadow in Fig. 1). As a result of the plastic deformation, dislocations, vacancies and other defects increase in the crystal lattices of deformed region and its 7~

proximity. During the annealing, the restoration of the regions influenced by the laser is made in such a manner that polygonization occurs and subgrains form due to the rearranging of the dislocations. The grain boundaries of the subgrains and defects still remaining at the annealing facilitate the diffusion of the Sb into the steel. The diffused Sb forms an intermetallic compound at the grain boundaries of the subgrains and similar sites of crystals and the intermetallic compound is precipitated. Unless the defects remain as explained above, not only does the diffusion occur at a slow rate but also a uniform diffusion occurs such that Sb penetrates into the steel in all directions. In the diffusion under the utilization of regions influenced by the plastic deformation, the diffusion rate is high and the diffusion does not spread unlimitedly but is limited to occur only in the regions mentioned above.
Accordingly, the Sb can penetrate into the steel sheet to a depth of, for example, from 5 to 30 ~m, and form a distinct phase which is highly effective for subdividing the magnetic domains.
The method for imparting the strain is described more specifically.
The degree of strain is appropriately determined depending upon the kind of agents used, the temperature-elevating rate and holding-temperakure of heat treatment, and the like. The strain-imparting by the laser irradi-ation can be carried out at an energy density of from 0.05 to 10 J/cm2. The strain-imparting by marking-off can be carried out at a depth of 5 ~m or less.
According to the discoveries made by the present inventors during their research into conventional me-thods of subdividing the magnetic domains by imparting strain, the effect of subdividing the magnetic domains can be made to disappear by holding the temperature at 700-900C for a few hours. It is therefore believed that the stress induced by strain decreases at a temper-7~

ature of from 700 to 900C~ On the other hand, such atempera-ture range promotes the formation of intruders in the method utilizing the imparted strain according to the present invention. It is therefore believed that, prior to the disappearance of the stress induced by strain, the material of a film actively propayates into the steel sheet. The temperature- elevating rate and the holding time and tempera-ture can therefore be advantageously determined so that the stress induced by strain does not disappear during the active propagation.
The appropriate temperature-elevating rate and the holding time and temperature, as well as their appropri-ate ranges for stably forming the in-truder, are dependent upon the component or kind of film, the concentra-tion of agent in the film, and the like.
Referring to Fig. 2, the intruder is shownO The intruder was formed by utilizing the stress generated by a mar~ing off method. As is apparent ~rom Fig. 2, which is a microscope photograph at the magnification of 1000, 2~ the intruder sharply penetrates into the steel sheet along its width.
Mote that the laser irradiation can be carried out after application of the agent, which may be made as either an entire or partial formation of film on the finishing annealed, grain- oriented electrical steel sheet. Also in this case, the strain, which is imparted to the film, contributes to a stable formation of the intruder when the subsequent heat treatment is carried out, since the strain enhances the reactions of film with the surface coating and steel sheet during the temperature-elevation and holding. However, the strain-imparting causes the destruc-tion of a film in many cases. Such destruction can be prevented by a thick application of -the agent or by strengthening the film by, for e~ample, a heat treatment at approximately 500C.
Platin~ Method A glass film, o~ide film, and occasionally an insulating coating (surface coating), are formed on the finishing annealed, grain-oriented electrical steel sheet. These films and coating can be removed entirely or with a space distance by laser-irradiating, grinding, machining, scarfing, chemical polishing, pickling, shot-blasting or the like, to expose the steel body o~ the grain-oriented electrical steel sheet. The intrudable means, such as metal, nonmetal, a mixture thereof, alloy, oxide, phosphoric acid, boric acid, phospha-te and borate, as well as a mixture of phosphoric acid, boric acid, phosphate and borate, are plated on the steel sheet. When the glass film and the like are removed with a space distance, an electroplating, a hot dipping, or the like is employed for plating. When the glass film and the like are removed entirely, a partial electroplating is employed for plating. The building up amount is 0.1 g/m2 or more.
The oxide film mentioned above is formed during the decarburization annealing and is mainly composed of SiO~
The glass film is formed by a reaction between the oxide film and the annealing separator mainly composed of MgO
and is also referred to as the forstellite film. The insulating coating mentioned above is formed by applying colloidal silica, chromic acid anhydride, aluminum phosphate, magnesium phosphate, and the ].ike on the steel sheet and then baking them. The oxide film, glass film and the insulating coating suppresses the intrusion of an intrudable means. By removiny such oxide film and the like, the reactivity between the intrudable means and the steel body o~ the grain-oriented electrical steel sheet is enhanced. The intrudable means deposited in a building up amount o~ 0.1 g/m2 can then effectively and stably be caused to penetrate into the steel sheet, thereby forming the intruder. Since the intrusion depth and amount can be easily changed by controlling the building up amount, it becomes also possible to dis-tinguishably produce products having different grades of 37~'~

watt loss characteristics by controlling the building up amount. In addition, due to an enhanced reactivity, the heat treatment after plating may be omitted, but carried out if necessary to increase the intrusion depth and amount.
The spaced removal of the oxide film, the glass film, and the insulating coating can be carried out by laser-irradiation, grinding, shot-blasting machining, scarfing, local pickling and the like. The removed regions are spaced from one another by the distance of 1 mm or more, preferably from 1 ~ 30 mm, with an equal or nonequal distance, and are oriented preferably at an angle of from 30 to 90 degrees relative to the rolling direction of steel sheet. The removal operation may be continuous, with the aid of pickling or shot-blasting, or discontinuous. The width of each of the removed regions is preferably from 0.01 to 5 mm in the light of an effective formation of the intruder. The steel body of a grain-oriented electrical steel sheet is exposed by removing the oxide film and the like. During this exposure, the steel body is partly slightly recessed and the s~rain is imparted simultaneously with the recess ~ormation.
After the removal as described above, the electro-plating of an intrudable means is carried out.
In a case of the spaced remo~al of the surfacecoatiny, the steel sheet is conveyed, for the electro-plating, through the electrolytic solution, into which is incorporated an intrudable means, such as metals and nonmetals, e.g., Al, Si, Ti, Sb, Sr, Sn, Zn, Fe, Ni, Cr, Mn, P, S, B, Zr, Mo, Co, and a mixture, oxide, or alloy thereof, as well as phosphate, borate, sulfate, nitrate, silicate, phosphoric acid, and boric acid. An electro-chemical reaction occurs, during the electroplating, only where the surface coating is removed with a distance and the steel body of a steel sheet is thus exposed. The intrudable means is therefore electropla-ted on only , . ..

3~

portions of the steel sheet where the steel body is exposed, and the other portions are not electroplated with the intrudable means. The distance between the portions of electroplating or between the intruders as well as the location of such portions can be controlled optionally. Such controlling can be attained without incurring a reduction in the strip conveying speed of a plating line at all. No reaction of the remaining surface coating with the plating solution also brings about an advantage in that a beautiful appearance of the surface coating is maintained.
In the case of an entire removal of the surface coating, the partial electroplating is employed for plating the intrudable means with a space distance, as described with reference to Fig. 3. The electroplating roll shown in Fig. 3 is provided with conductive zones 1, which ar~ spaced from one another. In the roll body, a passage 2 for the electrolyte solution is formed.
Injection apertures 3 for the electrolyte solution are formed through the conductive zones 1 or in their neighbourhood. By varying the distance between and arrangement of the conductive zones 1, the distance between and arrangement of the plated metals also can be varied. The electrolyte solution, into which the intrudable means is incorporated as described above, is also used for the partial electroplating, and the portions of a steel sheet through which -the current is conducted are plated with the intrudable means and the intruder is formed in such portions. The width of each of the portions mentioned above is preferably from 0.01 to 5 mm.
In the plating method, the building up amount is important, since, at a small ineffective amount, the amount of intruder formed is too small to subclivide the magnetic domains. A-t a building up amount of 0.1 g/m2 or more, a heat-resistant subdivision of the magnetic domains can be achieved. In addition, by controlling a ~ 15 ~

the building up amount, the intrusion depth and amount can be varied~ For example, by increasing the building up amount, the intrusion depth and amount can be increased and the watt loss characteristics can thus be greatly improved and, further, the products having different grades of watt loss characteristics can be distinguishably produced.
It is to be noted that, for exposing the steel body of a steel sheet, either only the glass and o~ide films or all of the glass and oxide films and the insulating coating may be removed. The latter removal method is employed for plating after the formation of the insulating coating, while the former removal method is employed for plating directly after forming the glass film.
Sb-based Intrudable_~leans and Plating Method According to a preferred method for locating the intrudable means on the finishing-annealed, grain-oriented electxical steel sheet, one or more members selected from the group consisting of Sb alone, Sb-Sn, Sb-Zn, Sb-Pb, Sb-Bi, Sb-Sn-Zn, Sb~Co, Sb-Ni, other Sb alloys, a mixture of Sb with one or more of Sn, Zn, Pb, Bi, Co, Ni, A1 and the like, Sb oxide, Sb sulfate, Sb borate, and other Sb compounds are incorporated into the electrolyte solution, through which a steel sheet is conveyed for electroplating. In a pre~erred electro~
plating method, the plating bath is a fluoride bath or borofluoride bath which contains fluoric acid, borofluoric acid, boric acid, and further selectively ~o contains sodium sulfate, salt (NaCl), ammonium chloride, and caustic soda. A preferred building up amount is 1 g/m or more.
By means of plating with the fluoride bath or borofluoride bath, a distinctly crystalline electro-deposition is obtained at a high current efficiency, thedensity of which current, as shown in E'ig. ~, ranges from a low to a high value. The electrolyte solution used in the electroplating solution is a borofluoride bath which consists of borofluoric acid, and boric acid~
and Sb.
The 0.23 m thick and 914 mm wide grain-oriented electrical steel sheet is subjected to removal of a glass film and an insulating coating with a space distance of 5 mm and width of 0.2 mm. The samples obtained from the steel sheet are then conveyed through the electrolyte solution, while varying the current density. The relationship between the apparent current density and cathode current efficiency is shown in Fig. 4. For comparison purposes, the electrolyte solution containing a complex citrate is used for the electroplating.
As is apparent from Fig. 4, the precipitation efficiency of the intrudable means is high, and the stability of the precipitation is high, at a high current density.
Effects similar to this are attained by using a ~luoride bath for the electroplating.
The borofluoride bath and fluoride bath also can be used for electroplating Sn, Zn, Fe, Ni, Cr, Mn, Mo, Co and their alloys. The boro~luoride bath contains borofluoric acid, boric acid, and in addition, one or more of the conductive salts.
The borofluoride bath and fluoride bath are advantageous over other baths, such as the sulfate-, chloride-, and organic salt-baths, in the points as e~plained with reference -to Fig. 4. The former baths can therefore attain a low watt loss at a low metal-deposition amount as compared with the latter baths, possibly because for the following reasons. ~enerally speaking, when the glass film and the like of a grain-oriented electrical steel sheet is subjected to the removal by laser-irradiating, grinding, machining, shot-blasting, and the like, part of the glass film and thelike are usually left on the steel sheet. The unremoved film occasionally impedes during plating of an intruda~le 7~i~

means, the forcing of the intrudable means satisfactorily into the steel sheet. Hydrofluoric acid (HF) as a component of the fluoride bath etches vigorously the steel base and slightly dissolves the glass film and oxide film. Borofluoric acid (HBF4) as a component of the borofluoride bath is believed to decompose in the bath and partially generates the hydrofluoric acid ~HF) according to the ~ollowing ~ormula.
HBF4 + 3H2O ~ ~HF ~ H3BO3 In the fluoride bath and boro~luoride bath, the general nature of hydrofluoric acid can be advantageously used for dissolving the surface coating which partially remains due to a failure of complete removal by the laser irradiation and the like, and also for etching the steel base. The metal precipitated in the electroplating process can be firmly deposited on the steel sheet and can be brought into direct contact with the steel base via a broad contact area. ~n improved watt loss can therefore be attained at a small deposition amount of metal.
Typical watt loss values W13/50 and W17/50 and magnetic flux density attained by the present invention are shown in the following tabl~.

7 ~ L~a ~ 18 -~ Table 1 Magnetic Sheet Thickness (mm) Properties 0.18 0.20 0.23 0.27 0.30 W13/50 (W/kg) 0.33 0.37 0.40 0.45 0.51 material W17/50 (W/kg) 0.64 0.67 0.69 0.80 0.87 Blo (T) l.91 1.92 1.93 1.94 1.94 Conven- Wl3/50 (W/kg) 0.40 0.45 0.47 0.52 0.61 tlonal Material W17/50 (W/kg) 0.80 0.84 0.88 0.94 0.98 plating) Blo (T) 1.92 1.92 1.94 1.94 1.95 The relationships between the W17/50 and ~he sheet thickness are shown in Fig. 5, in which the solid and chain lines indicate the Sb plated material and conventional materials~ respectively, of Table 1. Note that the grain-oriented electrical steel sheet having Wl7/50 dependent upon sheet thickness essentially coincident with ''INVENTIONI' is considerably improved over the conventional material.
In the case of the borofluoride bath and fluoride bath, the building up amount is also important as described hereinabove. A preferred building up amount is l g/m2 or more.
It is another outstanding feature of the boro-fluoride bath and fluoride bath that the intruder is effectively formed in an extremely short period of time, namely a-t a high productivity, and further, the surface appearance of the steel sheets is excellent.
The heat treatment can be carried out, if necessary, to increase the intrusion depth or to further ~orce the intrudahle means into the steel sheet. The hea~ treat-ment can be carried out at a temperature of from 500 to 1200~C~ either by continuous annealing or box annealing.
Zn is another preferred intrudable means. After the Zn plating, metal having a vapor pressure lower than that of Zn is preferably plated on the Zn, and sub-sequently, the plating is preferably carried out in an electrolyte solution containing one or more of Ni, Co, Cr, Cu, and their alloys.
In a case of using the citric acid bath, such an efficient plating as in the case of using the boro-fluoride bath can be attained by preliminarily light pickling prior to the plating.
Heat Treatment Method During the heat treatment at a temperature of from 500 to 1200C, a reaction between the agent and steel body or surface coating of a grain-oriented electrical steel sheet is advanced. This reaction is activated by the strain in the temperature-elevating stage or holding stage of the heat treatment. The intruders are formed so that they are forced with a space therebetween, into the steel body and are structurally distinguished from the secondarily recrystallized structure having Goss orientation or are distinguished from the composition of the steel body.
The heat treatment is carried out in a neutral atmos-phere or a reducing atmosphere containing H2. The intruder can be an aggregate of the spot-form materials.
As described above, the temperature-elevating rate and holding temperature are preferably determined depending upon the kind of intrudable means. This is because, during t.he intruding procedure, the intrusion depth and amount are inEluenced by thermal and diffusion conditions. The intrusion depth and amount appears to be influenced by whether or not the film thermally firmly adheres to the steel sheet prior to initiation of the intrusion. Since the effect of improving the watt 105s characteristics becomes generally great with an 7~

increase in the depth of an intruder measured from the steel base surface of a grain-oriented electrical steel sheet, the above described influences should be desirably used for forming deep intruders. When the temperature-elevating rate is too slow, the amount of intruderformed becomes small and the total heat treatment-time becomes long. On the other hand, when the tempera-ture-elevating rate is too high, there is a danger, especially for the intrudable means having a low meltlng temperature-point, that the intrudable means are lost due to vaporization or the like before completion of a satisfactory reaction with the surface coating and steel base of a grain-oriented electrical steel sheet. When the holding temperature is too low, the reaction of the intrudable means becomes unsatisfactory. On the other hand, if the holding temperature is too high, the electrical insulating propert~ o~ the insulating coating is impaired, the heat energy is consumed undesirably, and a failure in the shape of the steel sheets occurs.
Generally, the holding temperature should be in the range of from 500 to 1200C. The kinds of intrudable means should be appxopriately selected depending upon the temperature elevating rate and holding temperature selected within these ranges.
Film Recoating Method After the formation of the intrudable means, the solution for the insulating coating can be applied on the grain-oriented electrical steel sheet and baked at a temperature of, preferably 350C or more. The solution for the insulating coatiny, for example, can contain at least one member selected from the group consisting of phosphoric acid, phosphate, chromic acid, chromate, bichromate, and colloidal silica.
The plated intrudable means do not peel off the steel sheets during handling due to coil slip and do not ~aporize during the annealing, since the plated in-trudable means are covered with the insulating coatingO

The formation of in~ruders can therefore be further stabilized. In addition, the corrosion resistance and insulating property of portions of the steel sheets where intruders are formed are improved by the insulating coating.
Depth of Intruder Samples having various intruder depths were prepared by varying the temperature and time of the heat treat-ment. The composition of the slabs, from which the 0.225 mm thick grain-oriented electrical steel sheets were manufactured by well known steps starting at the slab heating and ending at the finishing annealing, was as follows.
C: 0.05 ~ 0.08~, Si: 2.95 ~ 3.33~, ~In: 0,0 0.12~, Al: 0.010 ~ 0.050~, S: 0.02 ~ 0.03%, N:
0.0060 ~ 0.0090~.
The depth of grains or clusters forced into the steel sheet was measured. The watt loss W17/50 after the finishing annealing (W117/50) and the watt loss W17/50 after the formation of the intruder (W 17/50~ were measured and the watt loss-improving percentage (~W) was calculated as follows.
~W = {(W117~50 ~ W 17/50)/W 17/50}
The influence of the depth of the intruders measured from the surface of steel body of grain~oriented elec-trical steel sheets upon the watt-loss improving per-centage (~W) was investigated. The results are shown in Fig. 6. As is apparent from Fig~ 6, an appreciable improvement in terms of ~W is obtained at an intruder depth of 2 ~m or more, and this improvement is enhanced with an increase in the intruder depth. The improvement in terms oE ~W saturates at an intruder depth of approxi-mately 100 ~m. Such a relationship as described above can be found not only in the steel composition of the above samples but also in the steel compositions con-taining one or more of Cu, Sn, Sb, Mo, Cr, Ni and the like. ~ preferred depth of the intxuders according to the present inven-tion is 2 ~m or more. The maximum lntruder dep~h is not specifically limited but is determined by taking into consideration the thickness of the steel sheets and the like. Although the intruder depth should be specified as described above, the distances therebetween need not be specified at all, and may be, for example, from approximately 1 to 30 mm. When the space distance between the intruders is de-termined narrowly, the grains, clusters and the like of the intruders appear virtually continuous.
The present inventi~n is now explained with refe-rence to the examples.
Example 1 Silicon steel slabs, which consisted of 0.077 o C, 3.28% of Si, 0.076% of Mn, 0.030% of Al, 0.024~
of S, 0.15~ of Cu, 0.15% of Sn and iron essentially in balance, were subjected to well known steps for producing a grain-oriented electrical steel sheet of hot-rolling, annealing, and cold-rolling. The 0.250 mm thick cold-rolled steel sheets were obtained. Subsequently, thewell known steps of decarburization annealing, appli-cation of annealing separator and finishing annealing were carried out.
The finishing annealed coils were subjected to application of an insulating coating and heat-flattening.
Samples of 10 cm in width and 50 cm in length were cut from these coils and irradiated with laser to Eorm minor flaws which extended perpendicular to the rolling direction and were spaced from one another by a distance of 10 mm, as seen in the rolling direction. These samples are denoted as "before treatment".
Subsequent to the laser irradiation, the agent A
(ZnO: 10 g -~ Sn: 5 g~, the agent B (Sb2O3: 10 g + H3BO3: 10 g), the agent C (Sb: 10 g ~ SrSO4: 20 g), and the agent D (Cu: 10 g + Na2B4O7: 20 g) were respectively applied on the samples in an amount of 0.5 g/m2 in terms of weight after application and 7~i~

drying. The samples were then laminated one upon another and dried at a furnace temperature of 400C.
The samples were then heat treated at 800C for 30 minutes. The samples subjected to this heat treatment are denoted as "after treatment". The samples were further subjected to a stress-relief annealing at 800C
for 2 hours. These samples are denoted as "after stress-relief annealing". The magnetic properties of the samples before and after treatment and after stress relief annealing were measured. The measurement results are shown in Table 2.

Table 2 Ma~netic Properties Before trea~t After treatment After stress-relief annealing (After laser- (800C x Agent irradiation 30 minutes,b~d~q) (800C x 2 hours) BloW17~50 BloW17~50 Blo W17~50 (T~(W/kg) (T)lW/kg) IT) (W/kg) _ . _ . , .
A 1.925 0.79 1.9260.80 1.926 0.80 B 1.928 0.76 1.9290.77 1.930 0.77 C 1.923 0.75 1.9230.75 1.923 0.75 D 1.931 0.78 1.9320.78 1.933 0.79 E (non-appli- 1.9280.76 - - 1.9350.89 cation of agent.
ca~xrative example) _ Example 2 Silicon steel slabs, which consisted oE 0.077% of C, 3.30% of Si, 0.076% of Mn, 0.028% of Al, 0.024% of S, 0.16% of Cu, 0.12% of Sn and iron essen-tially in balance, J'~

were subjected to well known steps for producing a grain-oriented electrical steel sheet of hot-rolling, annealing, and cold rolling. The 0.225 mm thick cold-rolled steel sheets were obtained. Subsequently, the well known steps of decarburization annealing, appli-cation of annealing separator and finishing annealing were carried out. The finishing annealed coils were subjected to application of an insulating coatin~ and heat-flattening. Samples of 10 cm in width and 50 cm in length were cut from these coils and then marked-off to impart the strain which extended perpendicular to the rolling direction and were spaced from one another by a distance of 10 mm. These samples are denoted as "before treatmentl-.
Subsequent to the mar~ing-off, the Sb2O3 powder in the powder form, as the agent, was rendered to a slurry containing the powder in an amount of 10 g/H2O-50 cc. The slurry was applied on the samples in an amount of 0.6 g/m2 in terms of weight after application and drying. After drying the heat treatment was carried out while varying the conditions in a temperature ranging from 800 to 900C and a time ranging from 5 to 120 minutes so as to vary the intruding depth of the intruder. The samples subjected to this heat treatment are denoted as "after treatment". The samples were further subjected to a stress-relief annealing at 800C
for 2 hours. These samples are denoted as "after stress-relief annealing". The magnetic properties of the samples before and after treatment and after stress relief annealing were measured. The measurement results are shown in Table 3.

Table 3 Magnetic Properties Before treat~ent After stress-Depth of In- (After laser- After treat~ent relief Annealing truder inadiation) (~) BloW17~50 BloW17~50 Blo W17~50 (T)(W/kg) (T)(W/ky) (T) (W/kg) 2 3 3 1.930 0.78 1.923 0.7~ 1.920 0.76 5 ~ 7 1.928 0.76 1.918 0.75 1.913 0.73 10 ~ 12 1.933 0.74 1.915 0.72 1.908 0.69 30 ~ 34 1.930 0.77 1.905 0.75 1.899 0.69 Example 3 Silicon steel slabs, which consisted of 0.077 of C, 3.30~ of Si, 0.076% of Mn, 0.032% of Al, 0.024~
of S, 0.16% of Cu, 0.18% of Sn and iron essentially in balance, were subjected to well known steps for producing a grain-oriented electrical steel sheet of hot-rolling, annealing, and cold-rolling. The 0~225 mm thick cold-rolled steel sheets were obtained. Subsequently, thewell known steps of decarburization annealing, appli-cation of annealing separator and finishing annealing were carried out.
The finishing annealed coils were subjected to application of an insulating coating and heat-flattening.
Samples of 10 cm in width and 50 cm in length were cut from these coils and irradiated with laser to Eorm minor strain which extended perpendicular to the rolliny direction and were spaced from one another by a distance of 10 ~n, as seen in the rolling direction. These samples are denoted as "before treatment".
Subsequent to the laser irradiation, the agent A

(ZnO: 10 g + Sn: 5 g), the agent B (Sb2O3: 10 g +
H3so3: 10 g), the agent C (Sb: 10 g + SrSO4: 20 g), and the agent D (Cu: 10 g + Na2B4O7: 20 g) were respectively applied on the entire surface of samples in an amount of 0.5 g/m in terms of weight after appli-cation and drying. The samples were dried at a furnace temperature of 400C, laminated upon one another, and heat-treated at 800C for 30 minutes. The samples subjected to this heat treatment are denoted as "after treatment". The samples were further subjected to a stress-relief annealing at 800C for 2 hours. These samples are denoted as "after stress-relief annealing".
The magnetic properties of the samples before and after treatment and after stress relief annealing were measured. The measurement resulted are shown in Table 4.

Table 4 Magnetic ProFerties Eefore treatment After treatment After stre~s-relief annealing (After laser (800C x Agent irradia-tion 30 minutes, ~ing) (800C x 2 hours) BloW17~50 BloW17~50 BloW17~50 (T)(W/kg) (T)(W/kg) (T)(W/kg) _ A 1.9400.77 1.9370.73 1.9210.73 B 1.9350.78 1.9250.80 1.9200.69 C 1.9300.77 1.9200.76 1.9050.72 D 1.9350.75 1.9350.71 1.9330~72 E (non-aFpli- 1.9320.78 ~ _ 1.9320.91 cation of agent.
ccmparative e~le) -7~

Example 4 Silicon steel slabs, which consisted of 0.077~ of C, 3.15% of Si, 0.076~ of Mn, 0.030% of Al, 0.024~ of S~
0.007~ of N and iron essentially in balance, were subjected to well known steps for producing a graln oriented electrical steel sheet of hot-rolling, annealing, and cold-rolling. The 0.225 mm thick cold-rolled steel sheets were obtained. Subsequently, the well known steps of decarburization annealing, appli-cation oE annealing separator and finishing annealingwere carried out. Samples of 10 cm in width and 50 cm in length were cut from these coils and stress-relief annealed. These samples are denoted as "before treat-ment". Subsequents to the stress-relief annealing, the agent A IZnO: 10 g + Sn: 5 g), the agent B (Sb2O3:
10 g + H3BO3: 10 g), the agent C (Sb: 10 g + SrSO4:
20 g), and the agent D (Cu: 10 g + Na2B4O7: 20 g) were respectively applied on the surface, i.e., the ~lass film, o~ samples in an amount of 0 g g/m2 in terms of weight after application and drying. These samples were irradiated with laser in a direction extending virtually perpendicular to the rolling direction and with distance spaces of 12 mm, to impart to the samples minute strain.
The samples were heat-treated at 800C for 30 minutes.
The samples subjec-ted to this heat treatment are denoted as "after treatment". The samples were further subjected to a stress-relief annealing at 800C for ~ hours. These samples are denoted as "after stress-relief annealing".
The magnetic properties of the samples before and after treatment and after stress relief annealing were mea-sured. The measurement results are shown in Table 5.

3~

Table 5 Magnetic Prop~Xies Before treatment After treatment After stress-relief Annealing (After laser- (800C x Agent ~ adiation 30 minutes, baking) (800C x 2 hours) __ BloW17~50BloW17~50 BloW17~50 (T)(W/kg)(T)(W/ky) (T)(W/kg) A 1.931 0.771.930 0.73 1.931 0.73 B 1.935 0.741.895 0.76 1.880 0.70 C 1.928 0.7~1.903 0.78 1.870 0.71 D 1.925 0.851.925 0.81 1.925 0.81 E (non-appli-1.930 0.80 - - 1.930 0.91 cation of agent.
o~Lative example) Example 5 Silicon steel slabs, which consisted of 0~080%
of C, 3.20~ of Si, 0.068% of Mn, 0.032% of Al, 0.024~
of S, 0.10% of Cu, 0.08% of Sn and iron essentially in balance, were subjected to well known steps for pro-ducing a grain-oriented electrical steel sheet of hot-rolling, annealing, and cold rolling. The 0.250 mm thick cold-rolled steel sheets were obtained. Sub-sequently, the well known steps of decarburizationannealing, application of annealing separator mainly composed of MgO and finishing annealing were carried out. Samples obtained from the steel sheets, which were subjected to the finishing annealing, are denoted as "before treatment".
The steel sheets were irradiated with CO2 laser in a direction virtually perpendicular to the rolling direction and with a distance space of 5 mm, so as to remove the glass film and oxide film. The steel sheets were then subjected to an electroplating using elec-trolyte solutions Nos. 1 - 5 containing, as plating metals, Sb (No. 1), Mn (No. 2), Cr (No. 3), Ni (No. 4), and none (No. 5), so as to deposit the intrudable means (plating me-tal) in a building up amount of 1 g/m2.
The samples obtained from the so treated steel sheets are denoted as "after treatment". The steel sheets were further subjected to a stress-relief annealing at 800C
for 2 hours. The samples obtained Erom the so annealed steel sheets are denoted as "after stress-relief an-nealing". The magnetic properties of the samples before and after treatment and after stress relief annealing were measured. The measurement results are shown in Table 6.

Table 6 Magnetic Prop~rties After stress-Before treatment After treatment relief Annealing Electrolyte (800C x 2 hours) Solution Nos.
BloW17~50 BloW17~50 BloW17~50 tT)IW/kg) (T)(W/kg) (T)(W/kg) 1 1.938 0.821.937 0.801.940 0.78 2 1.940 0.841.938 0.811.943 0.74 3 1.935 0.821~936 0.791.940 0.75

4 1.948 0.811.947 0.801.949 0.76

5 (non-appli- 1.940 0.83 - - 1.945 0.97 cation of agent, ccmparative example) _ -7~

Example 6 Silicon steel slabs, which consisted of 0.078%
of C, 3.25% of Si, 0.068% of Mn, 0.026% of A1, 0.024%
of S, 0.15% of Cu, 0.08% of Sn and iron essentially in balance, were subjected to well known steps for pro-ducing a grain-oriented electrical steel sheet of hot-rolling, annealing, and cold rolling. The 0.225 mm thick cold-rolled steel sheets were obtained. Sub-sequently, the well known steps of decarburi2ation annealing, application of annealing separator mainly composed of MgO and finishing annealing were carried out. The samples obtained from steel sheets, which were subjected to the finishing annealing are denoted as "before treatment".
The steel sheets were irradiated with CO2 laser in a direction virtually perpendicular to the rolling direction and with a distance space of 10 mm~ as seen in the rolling direction, so as to remove the glass film and oxide film. The steel sheets were then subjected to an electric plating using the electrolyte solution ~os. 1 - 5 containing Sb (No. 1), Zn (No. 2), Cr (No. 3), Sn (No. ~), and none (No. 5, comparative example), so as to deposit the intrudable means (plating metal) in a building up amount of 1 g/m2. The solution containing for insulating coating, containing aluminum phosphate, phosphoric acid, chromic acid anhydride, chromate, and colloidal silica was then applied on the surface of steel sheets and baked at 850C to form an insulating coating. The samples obtained from the steel sheets with insulative coating are denoted as "after treat-ment".
The steel sheets were further subjected to a stress-relief annealing at 800C for 2 hours. These samples are denoted as "after stress-relief annealing".
The magnetic properties of the samples before and after treatment and after stress relief annealing were measured. The measurement results are shown in Table 7.

7~j;L~

~ 31 -Table 7 Magnetic Properties __ _ After Stress-Before ~eatment After trea~ent relief Annealing Electrolyte ~800C x 2 hours) Solution Nos. ~
BloW17~50 Blo W17~50 Blo W17~50 (T)(W/kg) (T) (W/kg) (T) (W/kg) l 1.943 0.971.939 0.90 1.93~ 0.87 2 1.942 0.981.940 0.92 1.938 0.92 3 1.945 0.961.940 0.91 1.940 0.90 4 1.950 0.961.943 0.90 1.946 0.89 5 Inon-appli- 1.946 0.98 _ _ 1.947 0.98 cation of agent.
co~r2tive example) Example 7 Silicon steel slabs, which consisted of 0.080%
of C, 3.30% of 5i, 0.070% of Mn, 0.028% of Al, 0.025~
of S, 0.0080~ of N and iron essentially in balance were subjected to well known steps for producing a grain-oriented electrical steel sheet of hot-rolling, annealing, and cold-rolling. The 0.225 mm thick cold-rolled steel sheets were obtained. Subsequently, the well known steps of decarhurization annealing, appli-cation of annealing separator mainly composed of MgO and finishing annealing were carried out. Solution for forming insulating coating was then applied on the finishing-annealed steel sheets and baked. During the baking, the heat-flattening annealing was also per-formed. The samples obtained from the steel sheets withthe insulating coating, are denoted as "before treat-ment". These steel sheets were irradiated with CO2 laser in a direction virtually perpendicular to the rolling direction and with a space distanGe of 5 mm, so as to remove the glass film and the insulating coating.
The steel sheets were then subjected to an electric plating using the electrolyte solutions given in Table 8 and containing the intrudable means. The building up amount of the electric plating was from 0.05 -to 10 g/m2.
The solution for insulating coating aluminum phosphate, chromic oxide anhydride, and colloidal silica was then applied on the steel sheets and baked at 350C to form the insulating coating. The samples obtained from the steel sheets wi-th an insulative coating are denoted as "after treatment". The steel sheets were further subjected to a stress- relief annealing at 800C for 2 hours. The samples obtained from these steel sheets are denoted as "after stress-relief annealing". The magnetic properties of the samples before and after treatment and after stress relie~ annealing were mea-sured. The measurement results are shown in Table 9.

~lr3~7~

Table 8 Electrolyte Buildiny up Solu-tionKind of Plated Metal n No. ~ /m ) 1 - (1) Sb 0.05 (2) " 1.00 (3) " 10.00 2 - (1) Mo 0.05 (2) " 1.00 (3) " 10.00 3 - (1) Cu O.05 (2) i, 1.00 (3~ " 10.00 4 - (1) Sb + Zn 0.05 (2) " 1.00 (3) " 10.00 Non application of agent IccmParative example) I ~ u~ ~ co ~ o ~ ~r o ~n ~1 5: ~.Y I` r~ 1 u~ ~ r-~ .
3 o o o o o o o o o o o o o U~ X
O In ~ U~0~ 0 U~ CO LO ~D ~ n o r-~1 o o ~! a) a~ ~ E~ a~

~n r~ O ~ ~ r~ ~ O In o~
_ ~ ~
:~1 3 o o o o o o o o o o o o ~:4 ~ ~
U ~ ~
~ 1 S~ (~ l ~ O CS~
o ~ ~ t~ ~~r ~ t~) ~ eJI ~r ~') c~
,, ~ ~ ~
a~
o ~ c;~ ~ ~co o ~ ~ o a~ ~ cc ~ o E~ ~ r ~ co a~
.~ ~ 3 o o o o o o o o o o O o o O
~ a :q ~ ~D CO ~ ~ O ~ O U~ r o a~ co o ~ er r~ In U~ Lt~ ~ ~r ~r ~ ~r Ln ~ ~r ~ ~ ~ ~ CJ cr~

a a) ~ O ~
p ~ ~ ~
~ ~ o ~
u~

6~

Example 8 Silicon steel slabs, which consisted of 0.075%
of C, 3.22% of Si, 0.068% of Mn, 0.030% of A1, 0.02~%
of S, 0.08% of Cu, 0.10% of Sn and iron essentially in balance, were subjected to well known steps for producing a grain-oriented electrical steel sheet of hot-rolling, annealing, and cold rolling. The 0.225 rnm thick cold-rolled steel sheets were obtained. Subsequently, the well known steps of decarburization annealing, applica-tion of annealing separator mainly composed of MgO, and finishing annealing were carried out.
A solution for forming an insulating coating was then applied on the finishing-annealed steel sheets and baked. During the baking, the heat-flattening annealing was also performed. The samples obtained from the steel sheets with the insulating coating, aré denoted as "heat treatment". These stee~ sheets were irradiated with C2 laser in a direction virtuall~ perpendicular to the rolling direction and with a space distance of 5 mm.
The steel sheets were then sub~ected to an electroplating using the electrolyte solutions Nos. 1 - 6 containing Sb and Zn (No. 1), Sb and Zn (No. 2), Sb and Sn (No. 3), Sb and SbO (No. ~), Sb (No. 5), and none (No. 6, comparative example). The building up amounts of 25 electroplating were 0.1, 1, and 10 g/m2. The samples obtained from the steel sheets plated as above are denoted as "after treatment". The steel sheets were further subjected to a stress-relief annealing at 800C
for ~ hours. These samples are denoted as "after stress-xelief annealing". The magnetic properties of the samples before and af-ter treatment and after stress relief annealing were measured. The measurement results are shown in Table 10.

~ 36 --u~,~ I oL~o ~
~a x ~ 3 o o o o o o o o o o o o o o o o ~2- ~ ,,~ o~ o o _ a~ o ~D co co o o ~ co O
~ ~ ~ 3~ 3 o o o o o o o o o o o o o o o .~ ~ m~ E~ ~ 9 o o ~ ~ ~ ~ o -~1 ~ _ ,, ,, ~1 o~ ~ o~
g~l 3 o o o o ~ o o o o o o o o o o o O ~ ~ ~ O ~ O ~ n Lr) Ch O
E~ ~ ~ ~ c~
_ IQ~ ~ ~oo ~0~ ~ ~ ~ ~b~
~ d O ~i u~ o ,i u~ o ~i ui o ~i ~ o ~i u~ ~ o ~
. ~4 O ;~,~ g , ,î ~1 ~ ~1 ~ ~ ,~ ~ ~ ~1 ~ ~ ,~ ~ ~ g ~d ~
~1 ~ '~ Z

7~;~

Example 9 Silicon steel slabs, which consisted of 0.080%
of C, 3.15% of Si, 0.075% of Mn, 0.029% of Al, 0.024%
of S, 0.10% of Cu, 0.08~ of Sn and iron essentially in balance, were subjected to well known steps for producing a grain-oriented electrical steel sheet of hot-rolling, annealing, and cold rolling~ The 0.225 mm thick cold-rolled steel sheets were obtained. Subsequently, the well known steps of decarburization annealing mainly composed of MgO, application of annealing separator and finishing annealing were carried out.
The samples obtained from the steel sheets having an insulating coating are denoted as "before t~eatment".
These steel sheets were irradiated with laser in a direction virtually perpendicular to the rolling direc-tion and with a space distance of 5 mm, so as to remove the glass film, insulating coating and oxide film. The steel sheets were then subjected to an electric plating using the electrolyte solutions Nos. 1 - 5 containing, as plating metals, Sb ~No. 1 - borofluoride bath), Mn ~No. 2 - borofluoride bath), Sn (No. 3 - fluoride bath); Ni ~No. 4 - fluoride bath), and none (No. 5, comparative example). The samples obtained from the steel sheets plated as above are denoted by "after treatment'l. The steel sheets were further subjected to a stress-relief annealing at 800C for 2 hours. The samples obtained from these steel sheets are denoted as "after stress-relief annealing". The magnetic properties of the samples before and after treatment and after stress relief annealing were measured. The measurement results are shown in Table 11.

_ 38 -Table 11 _ Magnetic Properties After Stress-ElectrolYte sefore treatment After treatment relief An~ealing Solution Nos.
BloW17~50 BloW17~50 Blo W17~50 (T)(W/kg) (T)(W/kg) (T) (W/kg) 1 1.9380.75 1.9370.74 1.940 0.67 2 1.9400.74 1.9380.73 1.943 0.70 3 1.9350.77 1.9360.75 1.940 0.71 4 1.9480.75 1~9470.75 1.9490 r 72 5 (non-appli- 1.9400.76 - - 1.945 0.97 cation of agent/
ccmparati~e example) _ _ Example 10 Silicon steel slabs, which consisted of 0.078 of C, 3.27% of Si, 0.073% of Mn, 0.029~ of Al, 0.024~
of S, 0.16~ of Cu, 0.008% of Sn and iron essentially in balance, were subjected to well known steps for producing a grain-oriented electrical steel sheet oE hot-rolling, annealing, and cold rolling~ The 0.225 mm thick cold-rolled steel sheets wexe obtained. Subsequently, the well known steps of decarburization annealing, applica-tion of annealing separator and finishing annealing were carried out. Samples 10 cm in width and 50 cm in length were cut from the finishing annealed coils and stress--relief annealed at 800C for 4 hours. These samples, which are free of stress and coil-set, are denoted as "before treatment". Each of agents A ~AlPO~), B (Sb pow~
der), C (Sb powder ~ Al powder (1 : 1~) and D (MnSO4) in an amount of 10 g per 50 ml o H2O, was applied on the steel sheets and dried to foxm as films. The Eilms 7~i~

were irradiated with an electron beam with a distance space of approximately 20 mm to impart heat to the films at 860C for 20 hours. The samples subjected to this heat treatment are denoted as "after treatment". The samples were further subjected to a stress-relief annealing at 800C for 2 hours. These samples are denoted as "after stress-relief annealing". The magnetic properties of the samples before and after treatment and after stress relief annealing were measured. The measurement results are shown in Table 12.

Table 12 _ Magnetic Properties After Stress-Before treatment After treatment relief Annealing Agent BloW17~50 BloW17~50 BloW17~50 (T)(W/kg) ~T)~W/kg) (T)(W/kg) __ . __ _ _ A 1.934 0.891.930 0.831.930 0.82 B 1.945 0.871.943 0.751.885 0.70 C 1.937 0.911.937 0.771.890 0.75 D 1.920 0.921.936 0.841.930 0.85 E ~non-appli- 1.935 0.89 - - 1.935 0.88 cation on of agent, comparative example) _ _

Claims (12)

1. A grain-oriented electrical steel sheet having an ultra low watt loss, characterized in that intruders which are spaced from one another and are distin-guished from the steel in component or in structure, are formed on or in the vicinity of plastic strain regions, thereby subdividing the magnetic domains of the grain-oriented electrical steel sheet.

2. A grain-oriented electrical steel sheet according to claim 1, wherein the intruders intrude by a depth of 2 µm or more.

3. A grain-oriented electrical steel sheet according to claim 2, wherein the space distance between the intruders is 1 mm or more.

4. A grain-oriented electrical steel sheet according to any one of claims 1 through 3, wherein intrudable means is one or more of Sb, Sb alloy, Sb compound, or Sb mixture and is plated, at a building up amount of 1 g/m2 or more, on the portions of the grain-oriented electrical steel sheet at which surface coating is removed.

5. A method for producing a grain-oriented electrical steel sheet by the steps including a subdivi-sion of magnetic domains, characterized in that a strain is imparted to the grain-oriented electrical steel sheet, and an intrudable means for forming intruders being distinguished from the steel in component or structure is formed on the grain-oriented electrical steel sheet prior to or subsequent to imparting of the strain.

6. A method according to claim 5, wherein a heat treatment is subsequently carried out to intrude the intrudable means into the steel body.

7. A method according to claim 6, wherein the grain-oriented electrical steel sheet is subjected to thermal irradiation so as to intrude the intrudable means.

8. A method according to claim 5, wherein a surface coating is removed and then the intrudable means is plated, at a building up amount of 1 g/m2 or more on the grain-oriented electrical steel sheet where the surface coating is removed.

9. A method according to claim 8, wherein one or more of Sb, Sb alloy, Sb compound, and Sb mixture is plated at a building up amount of 0.05 g/m2 or more on the portions of the grain-oriented electrical steel sheet where the surface coating is removed with a space distance.

10. A method according to claim 9, wherein the plating is carried out using a fluoride bath or a borofluoride bath and at a building up amount of 1 g/m2 or more.

11. A method according to claim 9 or 10, wherein the removal of the surface coating and the strain-imparting are carried out by laser.

12. A method according to any one of claims 8 through 10, wherein an insulating coating is applied on the grain-oriented electrical steel sheet, after formation of the intrudable means.