Process for manufacturing double oriented electrical steel sheet having high magnetic flux density

Abstract: The present invention provides a process for manufacturing a double oriented electrical steel sheet having a high flux density by suppressing the growth of the secondary recrystallization of {110} <uvw> oriented grains from the surface of the steel sheet in the hot-rolling stage or cold-rolling stage, which process comprises subjecting a hot rolled sheet comprised of 0.8-6.7% by weight of Si, 0.008-0.048% by weight of acid soluble Aℓ, 0.010% by weight or less of N, and the balance being Fe and unavoidable impurities to a cold-rolling at a reduction rate of 40-80%, and then subjecting the resulting sheet to another cold-rolling in the direction vertical to the above cold-rolled direction at the reduction rate of 30-70% in the final thickness, followed by the steps of annealing for the primary recrystallization, applying an annealing separator, and applying finishing annealing for the secondary recrystallization and purification of steel, wherein the rolling in the finishing hot-rolling stage is carried out at the accumulated reduction rate of 20% or more under the condition that the friction coefficient between the rolls and the steel sheet is not more than 0.25; or wherein the accumulated reduction rate in the last three passes in the hot-rolling is not more than 80%; or wherein material of more than 1/10 of the total thickness is removed from both surfaces of the hot-rolled sheet; or wherein the cold-rolling is carried out using a work roll having a diameter of not less than 150 mm.

Description: This invention relates to a process for manufacturing a double oriented electrical steel sheet including recrystallized grains whose easy axis <001> of magnetization is oriented both in the longitudinal orientation and in the direction vertical thereto, together with the rolled surfaces exhibiting {100} planes; these crystallographic orientations can be represented as {100} <001> in the Miller indices. Since the double oriented electrical steel sheet has excellent magnetic properties in two different directions, because of its easy axis (<001> axis) in the rolled direction and in the direction vertical thereto, it can be more advantageously used for a magnetic core material of an apparatus, e.g., a large-scale rotating machine, where the magnetic flux flows in two different directions in comparison with a grain oriented electrical steel sheet which exhibits excellent magnetic properties in only one rolled direction. Non-oriented magnetic steel sheet, whose easy axis is not densely accumulated, is generally used for small stationary machinesor installations. The use of double oriented electrical steel sheet, however,makes it possible to miniaturize the machine with increased efficiency. The double oriented electrical steel sheet, which has excellent magnetic properties as described above, has long been expected to be put into mass production, but the general use of such a type of sheet as an industrial product is still limited at present. The following two methods in the prior art have been proposed for manufacturing a double oriented electrical steel sheet: 1) A method wherein an initial steel sheet is annealed at a high temperature in an atmosphere containing a polar gas, e.g., hydrogen sulfide, to secondarily recrystallize out {100} <001> oriented grains with the aid of surface energy, as described in US-A-3163564. This method is inadequate for mass production, however, because it requires very accurate control of the surface energy of the sheet. 2) A method wherein a steel sheet is cold-rolled in one direction and then cold-rolled in a direction vertical thereto, i.e., a cross cold rolling method, as described in Japanese Examined Patent Publication No. 35-2657. The magnetic flux density (B 8 ) of the products obtained by this method is not more than 1.85 Tesla, and accordingly, a significant improvement of the magnetic properties can not be obtained in spite of the complicated manufacturing process, which in turn requires increased cost. The double oriented electrical steel sheet obtained by this method is not preferable to the conventional grain oriented electrical steel sheet. The magnetic flux density (B 8 ) of grain oriented electrical steel sheet has steadily improved, since the techniques disclosed in Japanese Examined Patent Publication No.40-15644 and Japanese Examined Patent Publication No. 51-13469 were disclosed. At present, the magnetic flux density (B 8 ) of the commercially available products is as high as 1.92 T. An improved method has been proposed to enhance the magnetic properties in a double oriented electrical steel sheet, as disclosed in Japanese Examined Patent Publication No. 35-17208 and Japanese Examined Patent Publication No. 38-8213. Nevertheless, the magnetic flux density of the resulting products has not been made higher than that of the grain oriented electrical sheet. EP-A-0138051 discloses that only {100} <001> oriented grains are preferentially grown by annealing at a particular secondary recrystallization temperature; this annealing is based on the discovery that the temperature at which said oriented grains formed in the primary recrystallization structure preferentially grow in the secondary recrystallization annealing is different from the temperature at which {110} <uvw> oriented grains formed in the primary recrystallization structure preferentially grow in the secondary recrystallization annealing. An object of this invention is to provide a process for stably manufacturing a double oriented electrical steel sheet having a high magnetic flux density. Specifically, the object of this invention is to suppress the growth of {110} <uvw> oriented grains which are initiated from the surface of the steel sheet due to the secondary recrystallization, since these grains impair the magnetic properties of the double oriented steel sheet. The present invention provides a process for manufacturing a double oriented electrical steel sheet which comprises subjecting a hot rolled sheet comprised of 0.8 - 6.7% by weight of Si, 0.008 - 0.048% by weight of acid soluble Aℓ, 0.010% by weight or less of N, balance Fe and unavoidable impurities to cold-rolling at a reduction rate of 40 - 80%, and then subjecting the resulting sheet to another cold-rolling in the direction vertical to the above cold-rolled direction at a reduction rate of 30 - 70% in the final thickness, followed by the steps of annealing for primary recrystallization, applying an annealing separator, and applying finishing annealing for secondary recrystallization and purification of steel, wherein the {110} texture formed in the surface of the hot rolled steel sheet is reduced whereby the growth of {110}<uvw> oriented grains from the surface on secondary recrystallization of the steel sheet is suppressed. The {110} texture is reduced by cold rolling the hot rolled sheet by a rolling machine possessing work rolls having a diameter of 150 mm or more; or by defining the accumulated reduction rate in the last three passes in the hot-rolling to be at most 80%; or by removing at least 1/10 of the whole thickness of both surfaces of the hot rolled steel sheet in the thickness direction; or by carrying out the rolling in the finishing hot rolling at an accumulated reduction rate of 20% or more under the condition that the friction coefficient between the rolls and the steel sheet is not more than 0.25. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 shows (200) pole figures representing the texture of surface layer (a) and center layer (b) in the primary recrystallization; Fig.2 shows the texture at various depths of the hot-rolled sheet; Fig.3 shows (200) pole figures showing the orientation distribution of secondary recrystallized grain with the starting material of the surface layer of the hot-rolled sheet (a) and the center layer of the hot rolled sheet (b); Fig.4 shows the relationship between the magnetic flux density (B 8 ) of a product and the friction coefficient at hot-rolling; Fig.5 shows the relationship between the magnetic flux density (B 8 ) of a product and the accumulated reduction rate at which hot-rolling of the final stage is made with a low friction coefficient: Fig.6 shows the relationship between the magnetic flux density (B 8 ) of a product and the accumulated reduction rate at the final three passes of hot-rolling; Fig.7 shows the relationship between the magnetic flux density (B 8 ) of a product and the thickness of the removed layer; Fig.8 shows the relationship between the magnetic flux density (B 8 ) of a product and the diameter of a work roll in the cold-rolling; and Fig.9 shows (200) pole figures representing the distribution of grain orientation in the secondary recrystallization in the caseswhere a work roll diameter in cold-rolling is 50 mm (a) and 400 mm (b). The inventors studied products of double oriented electrical steel sheet manufactured by the cross cold-rolling method, and found the following. The crystalline orientation optimal for a double oriented electrical steel sheet is {100} <001>. In crystalline grains after the secondary recrystallization, however, {110} <uvw> oriented grains exist together with the above-mentioned {100} <001>, grains, and the former lower the magnetic density. Accordingly, {110} <uvw> oriented grains after the secondary recrystallization must be suppressed to obtain a high magnetic flux density. After a further study in detail of the orientation of these grains, it was found that the sheet created by the primary recrystallization prior to the secondary recrystallization exhibited different textures over the thickness of the sheet, i.e., {110} <uvw> oriented grains start to grow from the surface layer, whereas {100} <001> oriented grains grow from the central layer. This has been confirmed by the following experiments: A hot-rolled 1.8 mm thick sheet containing 0.055% of C, 3.3% of Si, 0.028% of acid soluble Aℓ, 0.007% of N, balance Fe and unavoidable impurities,was annealed at 1125°C for 2 minutes, and then cold-rolled at a reduction rate of 55% in the same direction as the hot-rolling, and further, cold cross-rolled at a reduction rate of 55% in the direction vertical to the above rolled direction to form a sheet having a final thickness of 0.35 mm. The sheet thus cold rolled was annealed for the primary recrystallization at 810°C for 210 seconds in a wet hydrogen atmosphere; this heat treatment also served for decarburization of the sheet. An examination of the texture in the sheet thus recrystallized showed that the main orientations of the grains were {110} <001> and {111} <uvw> in the vicinity of the surface shown in Fig.1 (a), whereas they were {211} <124> and {211} <231> at the central portions, as shown in Fig.1 (b). This implies that the crystalline orientation of major grains varies from sheet depth to sheet depth. It should be noted that the orientation of grains in the secondary recrystallization is strongly influenced by the texture in the primary recrystallization as reported, for instance, by K.T. Aust, J.W. Rutter in Trans. Met. Soc. AIME, 215 (1959), pp. 119-127., and by Ushigami et al. in Abstract of 96th Symposium of Metallurgy Society of Japan, pp. 375. The dependence of the texture on the depth of the sheet treated by the primary recrystallization was further studied, and as shown in Fig.2, it is found that the dependence is largely influenced by the inclination of the texture versus the depth of the hot-rolled sheet. To determine this, test pieces were selectively prepared by cutting same from the hot-rolled sheet at the surface and central portions, respectively. These pieces were primarily recrystallized under the conditions for the primary recrystallization as mentioned above, and then annealed in the finishing stage after an annealing separator containing MgO as a main component was applied. Fig.3 shows the orientation distribution of the secondary recrystallized grains of the respective test pieces thus prepared. From Fig.3, it can be seen that grains having {110} <uvw> orientations grow from the surface of the hot-rolled sheet, whereas grains having {100} <001> orientations grow from the central area. Therefore, it is considered that {110} <uvw> oriented grains formed, resulting in a decreased magnetic flux density , may be successfully suppressed by reducing the {110} texture in the hot rolled sheet. On the basis of the above finding, a further study was made of the conditions of hot- and cold-rolling in detail, and the following means for suppressing such an undesirable texture determined: (1) By setting the friction coefficient between a steel sheet and hot-rolling rolls to an amount of less than 0.25, {110} <uvw> oriented grains grown from the surface areas are suppressed in the secondary recrystallization due to the change of the texture in the hot-rolled sheet, thereby ensuring the stable manufacture of a double oriented electrical steel sheet having a high magnetic flux density. The experimental results obtained are now described. Slabs containing the same components as mentioned above were hot-rolled with varied friction coefficients,and then annealed at 1050°C for 2 minutes. Thereafter, the sheets thus rolledwere cold-rolled at a reduction rate of 50% in the same direction as for hot-rolling, and further cold cross-rolled at a reduction rate of 50% in the direction vertical to the above-mentioned direction. Moreover, the sheets were annealed for both the primary recrystallization and decarburization at 800°C for 90 seconds in a wet hydrogen atmosphere, and further annealed for finishing after applying an annealing separator. Fig.4 shows the relationship between the friction coefficient employed and the magnetic flux density (B 8 ) of the products obtained at an accumulated reduction rate of 50% in the finishing rolling process of the hot rolling. It can be seen from Fig.4 that a product having a high magnetic flux density of more than 1.90 Tesla can be obtained when the friction coefficient is less than 0.25. An examination of the texture of the hot-rolled sheet obtained with a friction coefficient of less than 0.25 reveals that the grains having {110} surfaces are markedly eliminated. The results suggest that secondary recrystallization of {110} <uvw> oriented grains grown from the surface areas is suppressed. Taking into account these results, the effect of the accumulated reduction rate in the hot-rolling was further studied under the fixed condition of a friction coefficient of 0.22 in the finishing rolling process. As shown in Fig.5, products having a high magnetic flux density of more than 1.90 Tesla can be successfully obtained when the accumulated reduction rate is not less than 20%. Since the difference in the texture obtained with varied friction coefficients is concealed due to the recrystallization, etc., in the initial stage of the hot-rolling, the coefficient may be adjusted at the final stage, i.e.,the finishing rolling stage at which difference in the texture is clarified. (2) By setting an accumulated reduction rate of less than 80% in the final three passes of the hot-rolling process,and preferably a temperature of 950°C or more for finishing hot-rolling, the growth of {110} <uvw> oriented grains from the surface is suppressed due to change of texture in the hot-rolled sheet, thereby ensuring the stable manufacture of a double oriented electrical steel sheet having a high magnetic flux density. The experimental results obtained will be described; 40 mm-thick slabs having the same components as described previously were hot-rolled into 2.0 mm thick sheets, using six passes with varied pass schedules. The temperature in the final hot-rolling was 900-950°C. The sheets were then annealed for 2 minutes at 1050°C. Subsequently, the sheets, were cold-rolled at a reduction rate of 50% in the same direction as for hot-rolling, and further cold cross-rolled at a reduction rate of 50% in the direction vertical to the above rolled direction. Furthermore, the sheets were annealed for primary recrystallization and decarbonization at 800°C for 90 seconds in a wet hydrogen atmosphere. Finally, the sheets were annealed for finishing after applying an annealing separator. Fig.6 shows the relationship between the accumulated reduction rate in the final three passes of the hot-rolling and the magnetic property (B 8 value) of the product obtained. From this diagram, it can be seen that a product having a high magnetic flux density of more than 1.90 Tesla was obtained at an accumulated reduction rate of less than 80%. On the basis of the experimental results, the effect of the final temperature in the stage of hot-rolling on the magnetic property was studied at an accumulated reduction rate of 80% in the final three passes with varied delay time, and as a result, it was found that the magnetic flux density was further increased when the temperature of the final hot-rolling was not less than 950°C. An examination of the texture in the hot-rolled sheet reveals that a hot-rolled sheet having a high magnetic flux density always contained less {110} oriented grains in the vicinity of the surface layer. In accordance with the present invention, therefore, it can be concluded that {110} texture formed is further reduced, in which case the crystal rotation due to the shear deformation at the surface is further suppressed, when the accumulated reduction rate at the final three passes is kept at less than 80%, and the temperature of the final hot-rolling is kept at more than 950°C. (3) By removing the surface layers at both faces of a hot-rolled sheet by a depth of 1/10-1/3 total thickness, {110} texture formed at the surface layers of a hot-rolled sheet was reduced to suppress {110} <uvw> oriented grains grown from both surfaces in the secondary recrystallization, thereby ensuring the stable manufacture of a double oriented electrical steel sheet having a high magnetic flux density. The experimental results obtained will be described. Slabs containing the same components as described above were hot-rolled into 1.8 mm thick hot-rolled sheets under the same conditions. The surface layers of the 1.8 mm thick hot rolled sheets were removed by a grinder. In Fig.7, the relationship between the amount of material removed from both surfaces of the hot-rolled sheet and the magnetic flux density (B 8 ) value of the product is given. It can be seen from the results that a double oriented electrical steel sheet having a high magnetic flux density can successfully be obtained, when material of more than 1/10, preferably 1/5, of the total thickness is removed from both surfaces. When the material is removed from the both surfaces to a thickness of approximately 1/3 the total thickness, the magnetic property is saturated. (4) By using work rolls having a diameter of more than a specific value for cold-rolling, the state of the metal flow at the surfaces of a hot-rolled sheet can be varied to suppress the growth of {110} <uvw> grains from the surface in the secondary recrystallization, thereby ensuring the stable manufacture of a double oriented electrical steel sheet having a high magnetic flux density. The experimental results obtained will be described. Slabs containing the same components as described previously were hot-rolled and cold cross-rolled under the same conditions as described above to obtain cold-rolled sheetshaving a final thickness of 0.35 mm. Five different work rolls having diameters of 60 mm, 100 mm, 150 mm, 270 mm, or 490 mm were used in the cold-rolling. The sheets thus cold-rolled were annealed for 210 seconds in wet hydrogen for both decarburization and primary recrystallization. Thereafter, the sheets were finally annealed after applying an annealing separator containing MgO as a main ingredient. Fig.8 shows the relationship between the diameter of work roll used and the magnetic flux density (B 8 ) of a product. It can been seen from Fig.8 that a product having a high maqnetic flux density (B 8) value of more than 1.90 Tesla results when the work roll diameter for cold-rolling was more than 150 mm. This effect becomes saturated at a diameter of more than 270 mm. Fig.9 shows the distribution of crystal grain orientations of the products in the secondary recrystallization where the work roll diameter in the cold-rolling is 60 mm (a) or 490 mm (b). From both pole figures, it can be seen that the growth of {110} <uvw> oriented grains can be successfully suppressed by an increased diameter of the work rolls. The reasons for this are probably as follows: The work roll diameter in the cold-rolling exerts a significant influence on the metal flow in the thickness direction, and the rotation of crystals in the vicinity of the surface promotes an increased growth of {110} <uvw> oriented grains in the recrystallization as the diameter of the work rolls becomes larger. Other limited conditions or elements will be described. A molten sheet used in the present invention may be prepared in any manner, such as in a revolving furnace or electric furnace, and must contain the following components in the following contents: A high content of Si improves iron loss properties, but decreases the magnetic flux density inevitably. Watt loss is minimum at an Si content of approximately 6.5%, while no improvement can be obtained with further increase of the content. The upper limit of Si content should, therefore, be specified to be 6.7%. An increased content of Si makes the product brittle, and cold cracks appear at an Si content of more than 4.5%, but worm-rolling can be principally applied to solve this problem. On the other hand, a lower content of Si provides an increased transformation of α into γ, thereby impairing the crystal orientation. The lower limit of the Si content should be determined at 0.8%, which has no substantial influence. Acid soluble Aℓ forms nitrides such as AQN, (Aℓ,Si)N, which act -as inhibitors. The Aℓ content is restricted to be 0.008-0.048%, preferably 0.018-0.036%, where the magnetic flux density of the product increases. If the content of N exceeds 0.010%, gaps called blisters appear, and thus the upper limit is defined as 0.010%. For the lower limit, the content of N can be adjusted via nitriding in intermediate process steps, and thus it need not be specified. Furthermore, inhibitor constitution elements such as Mn, S, Se, B, Bi, Nb, Sn, Ti, and Cr may be added. The molten steel of the above-mentioned components can be used in the present invention as a hot-rolled sheet in the usual manner. The hot-rolled sheet is cold-rolled directly or after a short time annealing. This annealing is usually carried out at 750-1200°C for 30 seconds to 30 minutes, and effectively enhances the magnetic flux density of products. Therefore, this annealing should be adopted in accordance with the desired level of the magnetic flux density. The successive reduction rates in the cold-rolling can be selected in the same manner as disclosed in Japanese Examined Patent Publication No. 35-2675 or Japanese Examined Patent Publication No. 38-8213. The material after being cold-rolled can be annealed for the primary recrystallization at a temperature of 750-1000°C for a short time of 30 seconds to 10 minutes. Usually, this annealing serves for decarburization of the steel under a controlled dew point in the atmosphere. Thereafter, the sheet is subjected to an annealing separator (e.g. containing MgO as a main component and to annealing finishing. This finishing annealing effects the secondary recrystallization and purification. In particular, it is desirable to carry out the secondary recrystallization and the purification separately under specific conditions. In this case, the sheet can be secondarily recrystallized at a temperature of 950-1100°C, and then heated to a temperature of more than 1100°C for purification. Example (1) A slab containing 0.05% by weight of C, 3.2% by weight of Si, 0.1% by weight of Mn, 0.03% by weight of acid soluble Aℓ, 0.008% by weight of N was heated to 1150°C, reduced to a 25 mm thickness by coarse rolling, and subsequently rolled for finishing into a 1.8 mm thick sheet. A lubricant was applied at the time of finishing rolling to reduce the friction coefficient. Thereafter, the sheet was annealed at 1100°C for 2 minutes, cold-rolled at a reduction rate of 55% in the same direction as for hot-rolling, and then cold cross-rolled in the direction vertical to the above-mentioned cold-rolled direction at a reduction rate of 50%. After annealing for primary crystallization (which also served for decarburization) was carried out at 800°C for 210 seconds in a wet hydrogen atmosphere, an annealing separator was applied, followed by annealing for finishing. The finishing annealing was carried out by heating to 1200 °C at a heating rate of 15°C/hr in an atmosphere of 50% N 2 + 50% H 2 , and then continuing with the atmosphere changed to 100% H 2 . The properties of the resulting products are as follows. Lubricating Properties Friction Coefficient at hot-rolling Magnetic Flux Density (B 8 : Tesla) Hot-rolled Direction Direction vertical thereto No 0.30 1.84 1.79 Yes 0.15 1.92 1.91 (2) Slabs having a 26 mm thickness and containing 0.05% by weight of C, 3.2% by weight of Si, 0.1% by weight of Mn, 0.03% by weight of acid soluble Aℓ, and 0.08% by weight of N were heated to 1150°C, and then hot-rolled to a thickness on the following order: (1) 26 → 20 → 18 → 15 → 8 → 4 → 2 (mm) or (2) 26 → 15 → 7 → 3.5 → 3 → 2.5 → 2 (mm) to prepare hot-rolled sheets having a 2.0 mm thickness. After the completion of hot-rolling, each sheet was air-cooled for 1 second, cooled to 550°C in water, maintained at this temperature for 1 hour, and then cooled by the furnace. The hot-rolled sheets were annealed at 1120 C° for 2 minutes, cold-rolled in the hot-rolled direction at a reduction rate of 50%, and then cold cross-rolled in the direction vertical to the above-mentioned cold-rolled direction at a reduction rate of 50%. An annealing for primary crystallization, which also served as decarbonization, was carried out at 800°C for 210 minutes, an annealing separating agent was applied, and then a finishing annealing for the purpose of secondary recrystallization and purification was carried out. The magnetic properties of the resulting products are shown in Table 2. Hot-Rolling Conditions Accumulated reduction rate in the last 3 passes(%) Magnetic Flux Density (B 8 : Tesla) Remarks Hot-rolled Direction Direction vatical thereto (1) 87 1.83 1.75 Comp. Ex (2) 73 1.91 1.90 Ex. (3) The same slabs as in Example 2 were hot-rolled at at initial hot rolling temperature of (1) 1100°C, (2) 1000°C, or (3) 900°C via the following six passes, i.e., 26 → 15 → 6 → 3.2 → 2.8 → 2.4 → 2 (mm) to prepare sheets having a 2 mm thickness. Each sheet was then annealed for finishing under the same conditions as in Example 2. The magnetic properties of the resulting products are shown in Table 3. Hot-rolling Initiation Temp. (°C) Hot-rolling complete Temp.(°C) Magnetic Flux Density (B 8 : Tesla) Hot-rolled Direction Direction vertical thereto 1100 1000 1.92 1.92 1000 910 1.91 1.90 900 830 1.90 1.90 (4) Two samples (of hot rolled steel sheet containing 0.048% by weight of C, 3.40% by weight of Si, 0.14% by weight of Mn, 0.023% by weight of acid soluble AQ, balance Fe and unavoidable impurities, having a 1.8mm thickness), in one of which both surfaces had been ground down to 1/4 of the total thickness by a grinder (sample A), and the other of which had not been ground (sample B), were prepared. Cold cross-rolling was applied to these samples by cold-rolling in the same direction as for hot-rolling at a reduction rate of 55%,and then cold-rolling in the direction vertical to the former cold rolled direction at a reduction rate of 55%. These cold rolled sheets were subjected to annealing for primary crystallization, which also served for decarburization, at 810°C for 120 minutes. Subsequently, MgO was applied to the sheets as an annealing separator, the sheets were heated to 1025°C at a heating rate of 15°C/hr, and then were maintained at 1025°C for 20 hours to complete secondary recrystallization. Thereafter, purification and annealing were carried out at 1200°C for 20 hours in 100% H 2 atmosphere. The magnetic properties of these products are as shown in Table 4. Sample No. Grinding hot-rolled Sheet Magnetic Flux Density (B 8 : Telsla) Hot-rolled Direction Direction vertical thereto (A) Yes 1.88 1.87 (B) No 1.84 1.85 (5) Samples A and B were prepared as in Example 4 except that they were annealed at 1070°C for 2 minutes, followed by the same treatments in the same stages as in Example 4. The magnetic properties of these products are as shown in Table 5. Sample No. Grinding hot-rolled sheet Magnetic Flux Density (B 8 : Tesla) Hot-rolled Direction Direction Vertical thereto (A) Yes 1.95 1.93 (B) No 1.92 1.92 (6) A hot rolled sheet having a 1.6 mm thickness, comprised of 0.05% by weight of C, 3.3% by weight of Si, 0.15% by weight of Mn, 0.027% by weight of acid soluble Aℓ, balance Fe and unavoidable impurities,was annealed at 1120°C for 2 minutes. Subsequently, the sheet was cold-rolled in the rolled direction mentioned above at a reduction rate of 50%, and then cold cross-rolled in the direction vertical to the cold-rolled direction at a reduction rate of 50%. Thereafter, the sheet was annealed at 800° for 210 seconds in a wet hydrogen atmosphere, which also served for decarburization; an annealing separator was applied thereto, and then a finishing annealing was carried out. The schedule of cold rolling was changed by using work rolls for the cold-rolling having diametersof 50 mm or 270 mm. The magnetic properties of these products are as shown in Table 6. From the results, it can be understood that the use of working rolls having a larger diameter in at least one of two cold rolling steps is most effective. Work roll Diameter in 1st Cold-Rolling (mm) Work roll Diameter in 2nd Cold-Rolling (mm) Magnetic Flux Density (B 8 : Tesla) Remark Hot-rolled Direction Direction vertical thereto 50 50 1.85 1.79 Comp. Ex. 50 270 1.90 1.91 Ex. 270 50 1.92 1.90 Ex. 270 270 1.92 1.91 Ex.

Claims: A process for manufacturing a double oriented electrical steel sheet which comprises subjecting a hot rolled sheet comprised of 0.8 - 6.7% by weight of Si, 0.008 - 0.048% by weight of acid soluble Aℓ, 0.010% by weight or less of N, balance Fe and unavoidable impurities to cold-rolling at a reduction rate of 40 - 80%, and then subjecting the resulting sheet to another cold-rolling in the direction vertical to the above cold-rolled direction at a reduction rate of 30 - 70% in the final thickness, followed by the steps of annealing for primary recrystallization, applying an annealing separator, and applying finishing annealing for secondary recrystallization and purification of steel, wherein the {110} texture formed in the surface of the hot rolled steel sheet is reduced whereby the growth of {110}<uvw> oriented grains from the surface on secondary recrystallization of the steel sheet is suppressed, said reduction of the {110} texture being effected by [a] cold rolling the hot rolled sheet by a rolling machine possessing work rolls having a diameter of 150 mm or more; or [b] defining the accumulated reduction rate in the last three passes in the hot-rolling to be at most 80%; or [c] removing at least 1/10 of the whole thickness of both surfaces of the hot rolled steel sheet in the thickness direction; or [d] carrying out the rolling in the finishing hot rolling at an accumulated reduction rate of 20% or more under the condition that the friction coefficient between the rolls and the steel sheet is not more than 0.25. A process according to claim 1 wherein there is reduction of the {110} texture by defining the accumulated reduction rate in the last three passes in the hot rolling to be at most 80%, wherein the hot rolling is completed at a temperature of 950°C or more. A process according to claim 1 wherein there is reduction of the {110} texture by removing at least 1/10 of the whole thickness of both surfaces of the hot rolled sheet in the thickness direction, wherein the thickness removal is followed by annealing at a temperature of 750 to 1200°C for 30 seconds to 30 minutes.

Inventors: ARAI SATOSHI, SENUMA TAKEHIDE, SUGA YOZO, TAKAHASHI NOBUYUKI, USHIGAMI YOSHIYUKI, YOSHITOMI YASUNARI, ARAI, SATOSHI, SENUMA, TAKEHIDE, SUGA, YOZO, TAKAHASHI, NOBUYUKI, USHIGAMI, YOSHIYUKI, YOSHITOMI, YASUNARI
Applicants: NIPPON STEEL CORP, NIPPON STEEL CORPORATION
Application year: 1991
Main classification: C21D8
IPC codes: C21D8