EP0184891B1 - Tôle d'acier au silicium à grains orientés et son procédé de fabrication - Google Patents

Tôle d'acier au silicium à grains orientés et son procédé de fabrication Download PDF

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EP0184891B1
EP0184891B1 EP19850301496 EP85301496A EP0184891B1 EP 0184891 B1 EP0184891 B1 EP 0184891B1 EP 19850301496 EP19850301496 EP 19850301496 EP 85301496 A EP85301496 A EP 85301496A EP 0184891 B1 EP0184891 B1 EP 0184891B1
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Prior art keywords
grain
less
steel sheet
annealing
seconds
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EP0184891A1 (fr
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Kenzo C/O Nippon Steel Corporation Iwayama
Yasunari C/O Nippon Steel Corporation Yoshitomi
Katsuro C/O Nippon Steel Corporation Kuroki
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Nippon Steel Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
    • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
    • H01F1/147—Alloys characterised by their composition
    • H01F1/14766—Fe-Si based alloys
    • H01F1/14775—Fe-Si based alloys in the form of sheets
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1216—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the working step(s) being of interest
    • C21D8/1233—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
    • C21D8/1266—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest between cold rolling steps

Definitions

  • the present invention relates to a grain-oriented steel sheet having a so-called ⁇ 110 ⁇ 001> Goss texture and used as core material for transformers and other electrical machinery and apparatus.
  • the present invention also relates to a process for producing the grain-oriented silicon steel sheet.
  • one method proposes to increase the silicon content so as to raise the resistivity. This, however, impairs the workability. Thus, the maximum silicon content is restricted by the workability.
  • Japanese Examined Patent Publication (Kokoku) No. 51-12451 discloses a method for improving the quality of a forsterite coating
  • Japanese Examined Patent Publication No. 53-28375 discloses a method for top coating. While the tensional force can be increased with an increase in thickness of these coatings, the improvement attained by the effects of tensional force is restricted by the space factor of the transformer core as the space factor is lessened with the increase in the coating thickness.
  • Still other methods aim at improving the watt-loss characteristics include the marking-off methods, disclosed in Japanese Examined Patent Publication No.
  • Japanese Unexamined Patent Publication (Kokai) No. 57-41326 discloses watt-loss reduction of thin sheets by grain-refining.
  • EP-A-47,129, EP-A-101,321 and FR-A-2,511,045 inter alia discloses grain-oriented silicon steel sheets of low iron loss (watt loss) and processes for their production involving rolling, decarburization and the use of Se, S, Sb, As, Bi, Sn, AI and N as inhibitor elements.
  • the invention provides a grain-oriented silicon steel sheet, and a process for producing such a sheet, as set out in the claims appended hereto.
  • the 0.15 to 0.23 mm thick grain-oriented electrical steel sheet of the present invention is thinner than conventional ones and thus has the disadvantage of lower productivity, but it is very advantageous as an energy-saving material for electrical machinery and apparatuses.
  • the silicon steel according to the present invention is used as the core of a transformer under uninterrupted operation, the few percent of power saved accumulates and results in considerable savings.
  • the first requirement for the product relates to its components and is that the content of silicon be from 2.3% to 4.3% and the content of each of carbon, nitrogen, and sulfur, as impurities, be restricted to 0.0020% or less.
  • the above contents are critical for obtaining W 17/50 ⁇ 0.88 w/kg.
  • Such a content of silicon and impurities has hithertofore been recognized as effective for decreasing the eddy-current loss and hysteresis loss, however, that recognition was qualitative and did not establish the quantitative knowledge to reduce the W 17/50 to 0.88 w/kg or less.
  • the second requirement is that the sheet thickness of the grain-oriented silicon steel sheet be from 0.15 to 0.23 mm. It has heretofore been broadly known that the eddy-current loss characteristic can be improved by reducing the sheet thickness. Nevertheless, W 17/50 ⁇ 0.88 w/kg cannot be obtained simply by reducing the sheet thickness of conventional grain-oriented silicon steel sheets.
  • the third requirement is a magnetic flux density of B 10 ⁇ 1.89 T. If the magnetic flux density 8 10 is less than 1.89, the absolute value of the eddy-current loss is increased and, hence, a watt-loss W 17/50 ⁇ 0.88 w/kg cannot be attained regardless of the other conditions.
  • the fourth requirement is the crux of the present invention and involves a novel physical parameter based on a principle, i.e., a dispersive location of grains having a specified size, different from those heretofore known.
  • the fourth requirement is that 2 mm or less circle-equivalent diameter crystal grains are present in the product in an amount of from 15% to 70% by area and, further, the average nearest intergrain distance (ND) of the 2 mm or less circle-equivalent diameter grains is from 2.0 to 8.0 mm.
  • the "circle-equivalent diameter” means the diameter of-a circle which has the same area as a crystal grain.
  • the "nearest intergrain distance (ND)” means the minimum value of the distance between the centers of the 2 mm or less circle equivalent crystal grains.
  • the "average nearest intergrain distance rND)” means the average values of the nearest intergrain distance (ND) which are measured for each 2 mm or less diameter grain. The physical significance of ND is explained later.
  • the present inventors first developed a method allowing them to observe the secondary recrystallized structure (hereinafter referred to as the "macro-structure") of grain-oriented silicon steel sheets.
  • the method developed was to heat and corrode the product in an aqueous hydrochloric acid solution. This removed the surface coating, such of the forsterite coating, and made the macrostructure easily discernible.
  • the present inventors then conducted extensive experiments to produce a number of the 0.10 to 0.35 mm thick grain-oriented silicon steel sheets. These sheets were produced not only by known methods but also by test methods in which the composition of the silicon steels and the production conditions were varied in an attempt to attain a W 17/50 ⁇ 0.88 w/kg.
  • the present inventors took note of the fact that the watt-loss is lessened when the sheet thickness is small. This relationship has been previously known. The watt-loss reduction is attributable to the reduction in size of the macrostructure.
  • the present inventors then determined that a substantial amount of the data was related to the location of coarse and fine grains of the macrostructure.
  • the present inventors tried to quantitatively define the location of coarse and fine grains of the macrostructure. They subjected the steel sheets described above to data-processing by means of an image analyzing processor connected to a commercial computer.
  • This image analyzing processor was of the type which has recently come into use for research and experiments in the metallurgical field and was used for obtaining the circle-equivalent diameter, its distribution graph, and, the average nearest intergrain distance (ND) of n-mm circle-equivalent diameter crystal grains, "n" being a predetermined minimum value. They also carried out a chemical analysis of samples to obtain the residual amounts of carbon, nitrogen, and sulfur.
  • Figure 1 shows the 8 10 and W 17/50 of the products produced in the extensive experiments and having W 17/50 ⁇ 1.00 w/kg.
  • the steels of the products contained from 2.3% to 4.3% of silicon, from 0.0002% to 0.0057% of carbon, from 0.0003% to 0.0046% of nitrogen, and from 0.0003% to 0.0038% of sulfur.
  • the components of films were excluded for the determination of these contents.
  • the products had only a forsterite coating or a forsterite coating and a tension-coating applied thereon. It is apparent from Figure 1 that in order to obtain W 17/50 ⁇ 0.88 w/kg, B, o ?1.89 T is necessary. From this viewpoint, the inventors numerically limited 8 10 to be at least 1.89 T.
  • each of the sulfur, nitrogen, and carbon contents must be 0.0020% or less in order to obtain W 17/50 ⁇ 0.88 w/kg.
  • a high silicon content generally results in a low watt-loss.
  • the silicon content is the lowest value of 2.3%, the watt-loss W 17/50 exceeds 0.88 w/kg with regard to several samples.
  • silicon samples exhibiting less than 0.88 w/kg such properties other than the silicon content, such as the sheet thickness, magnetic flux density, and tensional force fall within preferred ranges.
  • the relationship between the sheet thickness and W 17/50 was investigated with regard to products fulfilling the first and third requirements. The results are shown in Figure 2.
  • a sheet thickness of from 0.15 to 0.23 mm is necessary for obtaining W 17/50 ⁇ 0.88 (the first requirement).
  • the objective watt-loss of W 17/50 ⁇ 0.88 may occasionally not be obtained even by fulfilling the above three requirements.
  • the inventors selected samples A, B, and C ( Figure 2), having a sheet thickness of approximately 0.21 mm and fulfilling the first and third requirements, from the samples shown in Figure 2 and measured the circle-equivalent diameter (d) of individual grains and counted the number of grains having the diameter (d) by means of an image-analyzing processor. The percentage proportion of the grains with the various circle-equivalent diameters (d) is shown in Figure 3.
  • the present inventors made further extensive experiments and obtained a number of products under production conditions which easily attained the first, second, and third requirements in order to clarify the relationship between W 17/50 and the average nearest intergrain distance (ND).
  • ND average nearest intergrain distance
  • the conditions in the decarburizing step and the finishing annealing step were adjusted to thoroughly decarburize, denitride, and desulfurize the steel.
  • the second requirement was met by setting the sheet thickness of all of the test samples in the range of from 0.15 to 0.23 mm.
  • the steels were produced by melting and AIN was used as the inhibitor. Annealing followed by quenching was carried out before the final cold-rolling. The reduction at the final cold-rolling was 81% or more.
  • Figure 4 shows the relationship between W 17/50 and the average nearest intergrain diameter (ND) with regard to the samples fulfilling the first, second, and third requirements.
  • the data is classified into three groups based on the circle-equivalent diameter (d). These groups were determined by several preliminary investigations on the influence of the circle-diameter equivalent (d) upon the watt-loss. The preliminary investigations revealed that when 2 mm or less circle-equivalent diameter crystal grains are present in an amount of from approximately 15% to 70%, the watt-loss charactersitic is improved.
  • ND should be from 2 to 8 mm and the 2 mm or less circle-equivalent diameter grains should be present from 15% to 70%.
  • the grain boundaries of small-diameter grains appears to act as sites of strain and hence subdivide the magnetic domains.
  • each small-diameter grains is surrounded by large-diameter grains, even the magnetic domains of the large-diameter grains are subdivided due to the strain generated at the grain boundaries of the small-diameter grains.
  • the forsterite or tension coatings for imparting tension to a steel sheet are applied on the steel sheet, the subdivision as described above can be particularly enhanced.
  • the large-diameter grains have a high B lo , due to their close orientation to the ⁇ 110 ⁇ 001> direction. When the magnetic domains of such grains are subdivided, the watt-loss characteristic is drastically. improved.
  • the small thickness according to the present invention appears to make the coatings, such as forsterite and tension coatings, more effective than in the case of thick grain-oriented silicon steel sheets.
  • the present inventors investigated and experimented with other requirements aside from the four requirements so as to further lessen W 17/50 .
  • the present inventors discovered two additional requirements for obtaining an extremely improved watt-loss. These requirements are defined by an SF value and the tension value and are indispensable for obtaining W 17/50 ⁇ 0.86 w/kg.
  • SF is an abbreviation of shape factor.
  • the SF value is defined by:
  • the SF value indicates the shape of the grain boundary.
  • the SF value is therefore a parameter indicating the shape of the grain boundary, normalized by 1.
  • the SF value becomes smaller as the grain boundary becomes more complicated. For example, when the shape of a crystal grain is hexagonal, the SF value is equal to 0.88.
  • the present inventors conducted additional experiments similar to those for obtaining the results shown in Figure 4.
  • the data of samples which fulfilled the first to fourth requirements described above were further investigated with regard to W 17/50 , the tensional force, and the SF value.
  • the SF value was measured by means of an image-analyzing processor.
  • the investigation results are shown in Figure 6 with regard to 0.20 mm thick samples.
  • Figure 6 the average SF value (SF), which is obtained by taking the average SF over the crystal grains of a steel sheet, is shown.
  • the tensile stress which is applied, before the stress-relief annealing, to a steel sheet, by a forsterite coating or tension coating be in the range of from 0.20 to 1.0 kg/mm 2 .
  • the other additional requirement is therefore a tensional stress of from 0.20 to 1.0 kg/mm 2. How these requirements influence the watt-loss is not clear, but is considered as follows.
  • each crystal grain has a difference in orientation at the grain boundries. Such a difference is approximately 4° to 5° at the maximum.
  • strain sites generate at the grain boundaries and their vicinity. The strain at the strain sites become great when the shape of the grain boundaries is intricate, that is, the SF value is small. The strain sites therefore effectively lessen the width of the magnetic domains when the SF value is small. As a result, the eddy-current loss and, thus, the total power loss, are lessened.
  • the essential components of the starting material are from 2.3% to 4.3% of silicon, from 0.02% to 0.10% of carbon, from 0.015% to 0.040% of acid-soluble aluminum, and from 0.0040% to 0.0100% of nitrogen. These components are contained in the starting material.
  • the acid-soluble aluminum and nitrogen act as inhibitors.
  • Silicon is an element for outstandingly improving the eddy-current loss.
  • the transformation phase is disadvantageously formed during the finishing annealing, so that the secondary recrystallization becomes difficult.
  • the silicon content is more than 4.3%, the steel drastically embrittles. Silicon concentrates, during the finishing annealing, on the surface of a steel sheet and is included in the oxides, such as forsterite. The silicon content of the steel is therefore decreased as compared with that of the starting material, generally, in an amount of from 0.1% to 0.2%.
  • the carbon content is less than 0.02%, the amount of deformation phase, which is formed until the decarburization annealing, becomes too small to obtain good primary-recrystallized grains.
  • the carbon content is more than 0.10%, the decarburization property is impaired. The carbon content is therefore from 0.02% to 0.10%.
  • Aluminum and nitrogen are used in the present invention as the principal inhibitor elements, since the AIN inhibitor makes it possible to easily obtain a macrostructure in which coarse grains having a high 8 10 and fine grains are present.
  • the content of acid-soluble aluminum is less than 0.015%, and, further, the nitrogen content is less than 0.0040%, an appreciable amount of AIN effective as the inhibitor cannot be ensured.
  • the content of acid-soluble aluminum is more than 0.040% and the nitrogen content is more than 0.0100%, the acid-soluble aluminum and nitrogen are solid-dissolved insatisfactorily.
  • inhibitor elements for example, 0.04% or less of sulfur and selenium and 0.4% or less of one or more of manganese tin, antimony, arsenic, bismuth, and copper may be additionally contained in the starting material. When these elements exceed the maximum limits, the growth of secondary recrystallized grains is retarded.
  • a hot-rolled steel plate which fulfills the composition requirements described above is the starting material for producing a grain-oriented silicon steel sheet.
  • the hot-rolled steel plate is annealed, if necessary, and cold-rolled appropriately.
  • the annealing before the final cold-rolling is carried out with the plate held at 900°C to 1200°C for 10 to 600 seconds, or 1050°C to 1200°C for 300 seconds or less followed by being held at 800°C to 1000°C for 30 to 500 seconds, and cooling down to 100°C in 5 to 50 seconds.
  • the annealing step before the final cold-rolling is important for finely dispersing the inhibitor, thereby enhancing B lo .
  • This step is also important for providing a condition of steel matrix appropriate for improved shape and distribution of crystal grains in the finishing annealing step.
  • annealing at 900°C to 1200°C for 10 to 600 seconds, the lowest temperature of 900°C and the shortest time of 10 seconds are determined for preventing incomplete precipitation of the inhibitor.
  • the highest temperature of 1200°C and the longest time of 600 seconds are determined for facilitating uniform and fine inhibitor phases.
  • the annealing pattern of 1050°C to 1200°C for 300 seconds or less and then 800°C to 1000°C for 30 to 500 seconds is particularly advisable for steel having a high silicon content, since the holding is first carried out for a short period of time at a temperature of from 1050°C to 1200°C, which is effective for decomposing Si 3 N 4 , and then AIN and other inhibitors are precipitated in the latter holding.
  • the conditions of cooling after the holding are also important for stable secondary recrystallization and ensuring the magnetic properties.
  • the secondary recrystallization at the final production step is not attained.
  • the cooling rate is slower than cooling in still air, it is difficult to obtain the 2 mm or less circle-equivalent diameter grains.
  • a cooling time more than 50 seconds is disadvantageous, since it becomes difficult to obtain products having a high magnetic flux density.
  • the annealed sheet is pickled so as to sufficiently remove the scale formed on the sheet surface and completely expose the sheet surface.
  • the degree of removal of scale must be higher than in the conventional methods for producing a grain-oriented silicon steel sheet. The reason is not clear. Otherwise, the growth of secondary recrystallization is considerably impeded, in the case of insufficient scale removal, when the sheet-thickness is thin.
  • the preferred thickness of the hot-rolled steel strip is in the range of from 1.6 to 2.5 mm.
  • the optimum thickness varies in this range depending upon the silicon content, number of cold-rolling steps, and the sheet thickness of the product.
  • the hot-rolled steel strip is desirably thin in the light of the bending embrittlement.
  • the product is thin, such as approximately 0.15 mm, double-stage cold-rolling is carried out and the hot-rolled steel strip must have a thickness enabling the double-stage cold-rolling.
  • the screw-down degree at the final cold-rolling is from 81 % to 93%. If the screw down degree is less than 81 %, B 10 ⁇ 1.89 T is difficult to obtain. On the other hand, if the screwdown degree is more than 93%, stable secondary recrystallization becomes difficult.
  • the known decarburization annealing is then carried out at a temperature of from 800°C to 860°C.
  • the decarb.uziation-annealing time is short when the sheet thickness is thin.
  • a decarburization-annealing time longer than the usual time is preferred so as to decrease the carbon content to a level not detrimental to the magnetic properties.
  • An annealing separator mainly composed of MgO is then applied on the decarburization-annealed sheet surface, and the finishing annealing is carried out at a temperature of 1150°C or more for 10 hours or more.
  • the soaking time of the finishing annealing is preferably 30% to 50% longer than the conventional one so as to thoroughly purify nitrogen and sulfur.
  • a tension coating is applied on the grain-oriented silicon steel sheet.
  • the heating for baking of the tension coating must be very carefully carried out so as not to generate thermal strain in the steel sheet, because, due to the thin sheet-thickness, any temperature-nonuniformity, especially during cooling, occasionally results in compression stress in parts of a steel sheet.
  • the watt-loss is considerably impaired due to compression stress.
  • the decarburization-annealed steel strip is advisably held at a temperature range of from 900°C to 1100°C for a time period of from 1 to 1000 seconds.
  • This heat-treatment considerably mitigates the destabilization of secondary recrystallization of the thin, 0.15 to 0.23 mm thick sheet product by the thin sheet thickness.
  • This heat-treatment thus makes it possible to easily obtain a high 8 10 value. It appears that, since the temperature of this heat treatment is higher than the decarbuziation-annealing temperature, the primary recrystallized grains are rectified and rather stabilized. However, if the temperature is excessively high and the time is excessively long, the inhibitor deteriorates and thus the secondary recrystallization becomes difficult.
  • Figure 5A shows the macrostructure of the product produced by the above-described process.
  • Figure 5B shows the macrostructure of the product produced by a conventional process. Particulars of these products follow:
  • Imposition of a production condition related to heat-treatment between the cold-rolling passes is effective for further lessening the watt-loss.
  • the final cold-rolling step is carried out at a screw-down ratio of from 81 % to 93% so as to obtain the sheet thickness of from 0.15 to 0.23 mm.
  • heat-treatment of the steel strip is carried out at least twice by heating it to a temperature range of from 150°C to 300°C for 30 seconds or more. Heat-treatment carried out under the conditions described above considerably facilitates an of less than 0.60.
  • the maximum passes of the final cold-rolling step are eight from a practical point of view, since more passes are wasteful.
  • the ingots were produced by a vacuum-melting furnace.
  • the ingots contained silicon in an amount of from 1.1 % to 3.6%, carbon in an amount of from 0.0055% to 0.071 %, and different amounts of acid-soluble aluminum, nitrogen, manganese, sulfur, and selenium.
  • the principal inhibitor was AIN.
  • the ingots were heated to 1350°C and then hot-rolled to a sheet-thickness of 2.0 mm.
  • the composition of hot-rolled sheets is shown in the left column of Table 2.
  • the hot-rolled sheets were divided into two groups X, Y, for each charge.
  • the hot-rolled sheets of the Y group were pickled.
  • the hot-rolled sheets of the X, Y groups were cold-rolled to a thickness of 1.4 mm and subsequently loaded into a furnace, the temperature of which was set at 1140°C.Assoon as the temperature of the steel sheets rose to 1135°C, the steel sheets were loaded into a furnace, the temperature of which was set to 930°C.
  • the steel sheets were kept in the furnace for 100 seconds and then immersed in hot water of 70°C to cool.
  • the steel sheets were further divided into U and V groups as to carry out two kinds of pickling.
  • the appearance of the steel sheets was checked in the course of pickling to detect the time at which the scale disappear.
  • the pickling was carried out twice.
  • the pickling was carried out for a time period of approximately 7/10 time the time at which the scale apparently disappears.
  • the cold-rolling was carried out.
  • the sheet of the X group and Y group were cold-rolled to 0.23 mm and 0.18 mm, respectively.
  • the sheets were immersed in an isothermal tank of 250°C for 20 minutes in the course of cold-rolling to 0.17 mm, 0.12 mm, 0.07 mm, and 0.04 mm with regard to the X group and 1.1 mm, 0.07 mm, and 0.04 mm with regard to the Y group.
  • the decarburization annealing was carried out at 800°C for 300 seconds in a wet-hydrogen stream.
  • MgO was applied on the steel sheet.
  • the steel sheets were then heated to 1200°C at a temperature-elevation rate of 20°C per hour, and then purification-annealed at 1200°C for 25 hours.
  • Insulative tension coating known from Japanese Examined Patent Publication No. 53-28375, was applied on the steel sheet. The insulative tension coating was baked while imparting the tension to the steel sheets. The coil set was removed simultaneously with the baking.
  • the magnetic properties of the steel sheets were measured.
  • the tensional force of both the forsterite coating and the insulative coating was measured.
  • the macrostructures were investigated to determine the number of 2 mm or less circle-equivalent diameter grains, their proportion in total grains, and the average nearest intergrain distance of the 2 mm or less circle-equivalent diameter grains.
  • the impurities of steel sheet were chemically analyzed.
  • composition C and Group U were carried out except for an additional step directly after the decarburization-annealing.
  • additional step the steel sheets were held at 970°C for 50 seconds in a furnace where a dry nitrogen protective atmosphere was established.
  • the magnetic properties of the products were:
  • a number of 2.3 mm thick hot-rolled sheets containing 2.5% to 4.3% silicon, 0.04% to 0.09% carbon, 0.020% to 0.032% acid-soluble aluminum, 0.0050% to 0.0100% nitrogen, 0.050% to 0.150% manganese, 0.014% to 0.035% sulfur, 0.08% to 0.15% copper and 0.05% to 0.20% tin were prepared.
  • the hot-rolled sheets were annealed by one of the following heat cycles: holding at 1150°C for 30 seconds, then holding at 900°C for 1 minute, and water-cooling down to 100°C in 20 to 30 seconds; and holding at 1150°C for 30 seconds, then holding at 900°C for 1 minute, and air-cooling down to 100°C in 60 to 70 seconds.
  • the sheets were then cold-rolled down to 0.21 mm or 0.18 mm in five passes with or without intermediate heat-treatment.
  • heat-treatment the steel sheet were immersed, three times, in an isothermal bath of 250°C for 20 minutes.
  • decarburization annealing and application of annealing separator were carried out by a known manner.
  • the annealing atmosphere before the secondary recrystallization was 10% N 2 -90% H 2 or 80% N 2 -20% H 2 .
  • the tension coating known from Japanese Examined Patent Publication No. 53-28375 was applied on the steel sheets.
  • grain-oriented silicon steel sheets were obtained.
  • the magnetic properties and the tension of steel sheets resulting from the surface coatings were measured. Subsequently, the surface coatings were removed by means of fluoric acid and nitric acid, and the NO and SF of crystal grains, which appear on the sheet surface, were measured by using an image-analyzing processor. The silicon, tin, carbon, nitrogen, and sulfur contents in the steel were measured. The results are given in Table 3.
  • Sample Nos. 10, 11, and 12 in which the cooling time in the annealing of the hot-rolled sheets did not fall within the range of the present invention, exhibited an SF of more than 0.60 and high W 17/50 .
  • W 17/50 of Sample Nos. 2 and 6 exceeded the level of 0.88 w/kg.
  • Sample No. 4 (80% N 2 and 20% H 2 ) did not attain an SF of 0.60 or less.

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  • Soft Magnetic Materials (AREA)

Claims (6)

1. Tôle d'acier au silicium à grains orientés, constituée de 2,3% à 4,3% de silicium, 0,0020% ou moins de carbone, 0,0020% ou moins de chacun des éléments azote et soufre, et contenant du manganèse et éventuellement d'autres éléments formateurs d'inhibiteur, ou leurs résidus, le reste étant constitué de fer et d'impuretés, la tôle ayant une épaisseur de tôle de 0,15 à 0,23 mm, caractérisée en ce que des grains de cristaux ayant un diamètre du cercle équivalent de 2 mm ou moins sont présents dans une proportion de 15% à 70% par superficie, par rapport à la totalité des grains de cristaux; que la valeur moyenne intergranulaire la plus rapprochée (ND) desdits grains de cristaux ayant un diamètre du cercle équivalent de 2 mm ou moins est de 2,0 à 8,0 mm (N-D-=2,0 à 8,0 mm); B10≤1,89 T; et W17/50≤0,88 w/kg.
2. Tôle d'acier au silicium à grains orientés selon la revendication 1 caractérisée en ce que la totalité des grains de cristaux comprenant lesdits grains de cristaux ayant un diamètre du cercle équivalent de 2 mm ou moins, présentent une forme des limites de grains qui est indiquée par 0,60 ou moins d'un SF moyen par rapport à la totalité des grains de cristaux SF étant défini par
Figure imgb0009
3. Tôle d'acier au silicium à grains orientés selon la revendication 1 ou 2, dans laquelle il existe une contrainte le tension résiduelle de 0,20 à 1,0 kg/mm2 mesurée avant tout traitement de stabilisation.
4. Procédé de fabrication d'une tôle d'acier au silicium à grains orientés selon les revendications 1, 2 ou 3, comprenant les étapes de laminage à chaud du matériau de départ constitué de 0,02% à 0,10% de carbone, 2,3% à 4,3% de silicium, 0,015% à 0,040% d'aluminium soluble dans les acides, 0,0040% à 0,0100% d'azote, et au moins un autre élément inhibiteur, ledit élément inhibiteur étant le manganèse, l'étain, l'antimoine, le cuivre, l'arsenic ou le bismuth, dans une proportion de 0,4% ou moins, ou le soufre ou le sélènium dans une proportion de 0,04% ou moins, le reste etant constitué de fer et d'impuretés, recuit et laminage à froid préliminaire de la tôle laminée à chaud, si nécessaire traitement thermique, avant le laminage à froid final, par (a) maintien dans une plage de températures de 900°C à 1200°C pendant 10 à 600 secondes ou (b) maintien dans une plage de températures de 1050°C à 1200°C pendant 300 secondes ou moins, suivi d'un refroidissement à 100°C en une période de 5 à 50 secondes, décapage laminage a froid final avec un rapport de serrage de 81 % à 93%, obtenant ainsi une tôle laminée à froid ayant une épaisseur finale de 0,15 à 0,23 mm, décarburation application à la surface de la tôle d'un séparateur de recuit essentiellement constitué de MgO; et recuit de finition, obtenant ainsi une tôle d'acier au silicium à grains orientés ayant une perte d'énergie de Wl,/60=0,88 w/kg.
5. Procédé selon la revendication 4 dans lequel la tôle d'acier est chauffée, au moins deux fois, entre les passes du laminage à froid dans une plage de températures de 150°C à 300°C, et elle est maintenue dans ladite plage de températures pendant une période d'au moins 30 secondes.
6. Procédé selon la revendication 5, dans lequel la tôle d'acier decarburée est maintenue, avant le recuit de finition dans une plage de temperatures de 900°C à 1100°C pendant une periode de 1 à 1000 secondes.
EP19850301496 1985-03-05 1985-03-05 Tôle d'acier au silicium à grains orientés et son procédé de fabrication Expired EP0184891B1 (fr)

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EP19850301496 EP0184891B1 (fr) 1985-03-05 1985-03-05 Tôle d'acier au silicium à grains orientés et son procédé de fabrication
DE8585301496T DE3571464D1 (en) 1985-03-05 1985-03-05 Grain-oriented silicon steel sheet and process for producing the same

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JPS62202024A (ja) * 1986-02-14 1987-09-05 Nippon Steel Corp 磁気特性の優れた一方向性電磁鋼板の製造方法
JPH0768580B2 (ja) * 1988-02-16 1995-07-26 新日本製鐵株式会社 鉄損の優れた高磁束密度一方向性電磁鋼板
US4992114A (en) * 1988-03-18 1991-02-12 Nippon Steel Corporation Process for producing grain-oriented thin electrical steel sheet having high magnetic flux density by one-stage cold-rolling method
JP2951852B2 (ja) * 1994-09-30 1999-09-20 川崎製鉄株式会社 磁気特性に優れる一方向性珪素鋼板の製造方法
JP3598590B2 (ja) * 1994-12-05 2004-12-08 Ｊｆｅスチール株式会社 磁束密度が高くかつ鉄損の低い一方向性電磁鋼板
KR100440994B1 (ko) * 1996-10-21 2004-10-21 제이에프이 스틸 가부시키가이샤 방향성전자강판및그제조방법
DE69706388T2 (de) * 1996-10-21 2002-02-14 Kawasaki Steel Co Kornorientiertes elektromagnetisches Stahlblech
KR19990088437A (ko) * 1998-05-21 1999-12-27 에모또 간지 철손이매우낮은고자속밀도방향성전자강판및그제조방법

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JPS5920745B2 (ja) * 1980-08-27 1984-05-15 川崎製鉄株式会社 鉄損の極めて低い一方向性珪素鋼板とその製造方法
JPS6048886B2 (ja) * 1981-08-05 1985-10-30 新日本製鐵株式会社 鉄損の優れた高磁束密度一方向性電磁鋼板及びその製造方法
EP0101321B1 (fr) * 1982-08-18 1990-12-05 Kawasaki Steel Corporation Procédé pour la production de tôle ou de bande en acier au silicium à grain orienté présentant une haute induction magnétique et faible perte dans le fer

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