Electromagnetic steel sheet having excellent magnetic properties and production method thereof

Abstract: Electromagnetic steel sheet having excellent magnetic properties and a texture gratly integrated in the {100}<001> orientation, and an uncomplicated and low cost production method; with about a 15 µΩ·cm or more specific resistivity, about a 2.0 or more {100}<001> integration degree /{111}<uvw> integration degree and about a 10 pm to 500 µm grain diameter; when about 0.1 to 3.5% by weight of Si is present, the {100}<001> integration degree is about 10 or more; when about 0.2 to 1.2% by weight of P is present, the {100}<001> integration degree is about 3 or more; by applying a large reduction ratio to a steel slab in the vicinity of the final stage of hot rolling, with the hot rolling finishing temperature controlled at about 75C to 1150°C, hot rolled steel having a texture highly integrated in the {100}<001> orientation is economically produced.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic steel sheet having excellent magnetic properties, preferably to an electromagnetic steel sheet for application as a magnetic core, and a production method thereof. 2. Description of the Related Art It is preferable that an electromagnetic steel sheet (silicon steel sheet) has a texture such that the electromagnetic properties in the magnetization direction in use can be excellent. A preferable texture varies depending upon the application. However, for an EI core, which has the magnetization directions orthogonal to each other, a so-called cubic texture with a {100} rolled face orientation and a <100> rolling orientation (RD) is most preferable. In order to obtain such a texture, various methods have been advocated so far. Examples thereof include a melt quenching method disclosed in the official gazette of Japanese Unexamined Patent Publication No. 5-306438, a cross rolling method disclosed in the official gazette of Japanese Unexamined Patent Publication No. 5-271774, a tertiary recrystallization method disclosed in "Growth of (110)[001]-Oriented Grains in High-Purity Silicon Iron-A Unique Form of Secondary" (TRANSACTIONS OF THE METALLURGICAL SOCIETY OF AIME, VOL 218, 1960 P. 1033-1038), and a columnar crystal growth method disclosed in the official gazette of Japanese Unexamined Patent Publication JP-I-108345 with the application No. 1987-262997. However, since all of the above-mentioned methods excluding the melt quenching method depend on cold rolling and annealing, a complicated process is required as disclosed in the official gazette of Japanese Unexamined Patent Publication No. 4-346621. Further, the melt quenching method requires a special cooling roller. Therefore, in either of the methods, high production costs have been problematic. On the other hand, a grain oriented silicon steel sheet is known as an expensive electromagnetic steel sheet. The grain oriented silicon steel sheet has a texture having a so-called Goss orientation, {110}<001> orientation in the vicinity of the surface layer of the hot rolled steel sheet in a small amount so that secondary recrystallization can be conducted, utilizing the Goss orientation grains. The magnetic properties thus obtained are superior in the rolling direction (RD), but inferior in the transverse direction (TD). It has been a common view that Si is superior to other alloy elements from the comprehensive aspect although some elements are superior to Si in one of the characteristics including magnetic and mechanical properties, in particular, processability and alloy cost. However, the present inventors elaborately studied the application of the alloy elements other than Si into an electromagnetic steel sheet and discovered that an electromagnetic steel sheet with an Fe-P composition can obtain properties superior to those of a silicon steel sheet as disclosed in the official gazette of Japanese Unexamined Patent Publication No. 9-41101. US-A-5 258 080 discloses a non-oriented electrical strip and its production method, having a cube texture {100}<001> or having a cube on face texture {100}<0V w >, and no phase changing from ferrite to a mixed or gamma phase, by inducing in the finishing train a maximum reduction ratio of 30% at a temperature of 1000 - 1060°C. The specific C content is more than 0.005%. Relatively high cold reduction contributes to the formation of cube texture. SUMMARY OF THE INVENTION An object of the present invention is to provide an electromagnetic steel sheet having a texture that is highly integrated in the {l00}<001> orientation, at a low cost, all without the need of a complicated process. A further object is to create a method of making such an electromagnetic steel sheet. We have discovered that the texture of steel having a specific resistivity of 15 µΩ•cm or more can be improved by applying sufficient strain at a high temperature, and by large reduction condition in hot finish rolling, compared with the conditions adopted in the conventional process. The steel sheet of this invention is extremely effective for the targeted objective. The present invention include the following embodiments: 1. A finish annealed non-oriented electromagnetic steel sheet having excellent magnetic properties, with a C content of 0.005% by weight or less, as well as an Si content of 0.1 to 3.5% by weight, and/or a P content of 0.2 to 1.2% by weight a 15 µΩ•cm or more specific resistivity, a 2.0 {100}<001> integration degree /{1111<uvw> integration degree and a 10 µm to 500 pm grain size. 2. The electromagnetic steel sheet described in paragraph 1, wherein the steel sheet composition contains 0.1 to 3.5% by weight of Si and the {100}<001> integration degree is about 10 or more. 3. The electromagnetic steel sheet described in paragraph 1, wherein the steel sheet composition contains 0.2 to 1.2% by weight of P and the {100}<001> integration degree is 3 or more. 4. A production method of the electromagnetic steel sheet described in paragraph 1, wherein a large reduction ratio is applied to a steel slab in the vicinity of the final stage in a hot rolling process with the components adjusted such that the specific resistivity of the product is 15 µΩ•cm or more and the hot rolling finishing temperature is 750 to 1150°C. 5. A large strain as described in paragraph 4, specifically a rolling operation in the hot rolling final pass, with a 30% or more reduction ratio. In addition, the operation can include conducting finish rolling in the hot rolling process with 1 pass. Or the large strain described in paragraph 4 can include an operation with 50% or more hot rolling final 3 passes accumulated reduction ratio and a 10% or more final pass reduction ratio. 6. A steel slab with the components adjusted such that the specific resistivity of the product can be 15 µΩ·cm or more made according to the method described in paragraph 4. 7. The production method of an electromagnetic steel sheet described in paragraph 4, wherein the slab is made from a component to have a ferrite-austenite transformation at 750 to 1150°C and the hot rolling finishing temperature is Ar 1 - 100 to Ar 1 + 50°C. 8. The production method of an electromagnetic steel sheet described in paragraph 4, wherein the slab is made from a component to have a ferrite single phase at 750 to 1150°C and the hot rolling finishing temperature is higher than or equal to 1010°C + 100 × [Si] - 5 × reduction ratio of the final hot rolling pass (%). In general, a steel slab (about 10 to 500 mm thickness) reheated to about 900 to 1450°C is processed to be a hot rolled steel sheet with about a 0.8 to 4.0 mm thickness by hot rolling. Usually the slab is processed to be in the state of a sheet bar having about a 15 to 50 mm intermediate thickness before the state of the hot rolled steel sheet. The hot rolling operation from the slab to the sheet bar denotes a rough rolling and the hot rolling operation from the sheet bar to the hot rolled steel sheet denotes a finish rolling. In some cases, a direct rolling operation without reheating the slab, or a finish rolling by directly casting the sheet bar can be conducted. The expression "vicinity of the final stage in a hot rolling process" according to the present invention refers to the stage from the final pass of the hot finish rolling to one or several passes before the final pass. Further, the expression "Ar 1 (°C)" refers to the temperature achieving the ferrite single phase from the (ferrite + austenite) phase in the cooling of the steel. According to the present invention, a steel sheet with a cubic texture, having excellent magnetic properties, can be provided by conducting hot finish rolling at a high temperature and providing large reduction, with the subsequent cold rolling process and the annealing process conducted in an ordinary manner without the need of a special condition. The resulting steel sheet can be produced at a cost that is drastically lower than conventional steel sheet. BRIEF DESCRIPTION OF THE DRAWING The Figure is a graph showing the influence of the reduction ratio (1 pass) R in the final stand, the rolling finishing temperature T F and the Si amount [Si] on the {100}<001> integration degree. DETAILED DESCRIPTION OF THE INVENTION Initially, the present invention will be explained with reference to an explanatory example. A 50 kg steel ingot with a composition of 1.23% by weight of Si, 0.002% by weight of C, 0.003% by weight of O, 0.21% by weight of Mn and 0.23% by weight of Al, was melted in a small vacuum melting furnace, and a 5 mm thick sheet bar was obtained by hot rough rolling. In the slab composition, the specific resistivity was 28 µΩ . cm, and the Ar 1 point was 960°C. After being heated at 1150°C for 25 minutes, the sheet bar was rolled by 700 mm diameter rolls at an 800 m/min peripheral speed, using an 80% reduction ratio and a 965°C rolling finishing temperature, to obtain a hot rolled steel sheet having a thickness of 1.0 mm. The hot rolled steel sheet was subjected to heat treatment at 650°C for 2 hours for the coil winding process, washed with acid, and subjected to cold rolling so as to obtain a cold rolled steel sheet having a thickness of 0.35 mm. Then, after degreasing the steel sheet, recrystallization annealing was applied at 850°C for 20 seconds in a dry atmosphere containing 35% hydrogen and 65% nitrogen. The degree of integration of the texture and the magnetic properties of the steel sheet were examined. The integration degree in a specific orientation represents the degree of frequency of the presence of crystal grains oriented in the orientation with respect to a texture having a completely random orientation distribution. It can be determined as follows. A sheet thickness part parallel to the sheet surface of a steel specimen was abraded so that the incomplete pole figure of (110), (200), and (211) with respect to the abraded surface was measured by the X-ray diffraction Schultz method. The resulting measurement data were converted to a three dimensional orientation distribution function using a series development method as disclosed in "Texture Analysis Materials Science" by H. J. Bunge. Since the distribution function was standardized such that the existence frequency was 1 in any orientation when the distribution was completely random, in order to determine the integration degree in a specific orientation, the value of the distribution function in the direction was adopted. This value is a multiple of the integration degree with respect to a right random distribution. The (110), (200) and (211) pole figures at each position of the steel sheet, equally divided into 10 sections in the sheet thickness direction from the surface thereof, were determined by the X-ray diffraction Schultz method. The three-dimensional distribution density was calculated for each of them, and the average value was obtained. As to the magnetic properties, a specimen having the longitudinal direction as the rolling direction (hereinafter referred to as the L direction) and a specimen having the longitudinal direction orthogonal to the rolling direction (hereinafter referred to as the C direction) were obtained so as to conduct the Epstein measurement. As a result, the steel sheet had unprecedentedly excellent properties including a high {100}<001> integration degree of 18.7 and magnetic properties of 2.87 W/kg at W 15/50 and 1.842T at B 50 . A steel sheet rolled at a 700°C rolling temperature was examined similarly. The result shows that the {100}<001> integration degree declined. That is, when the rolling finishing temperature was too low, since the texture in the {110}<001> orientation is formed by the deformation derived from the shearing strain so that the {100}<001> integration degree of the steel sheet produced after the subsequent processes declines and the magnetic flux density in the C direction is deteriorated, a steel sheet having a high {100}<001> integration degree could not be obtained. Furthermore, even when the rolling finishing temperature was high, with a small reduction ratio, since a strain sufficient for the recrystallization of {100}<001> grains would not be applied, the {100}<001> integration degree of the steel sheet produced after subsequent processing declined and a steel sheet having a high {100}<001> integration degree could not be obtained. An experimental result on a P steel, which is a basis for the present invention, will be explained. A 50 kg steel ingot with a composition including 0.56% by weight of P, 0.003% by weight of C, 0.01% by weight of Si, 0.03% by weight of Mn and 0.05% by weight of Al, that is, a composition containing P and the remainder comprising Fe and incidental impurities, was melted in a small vacuum melting furnace. A 5 mm thick sheet bar was obtained from it by hot rough rolling. In the slab composition, the specific resistivity was 20 µΩ·cm, and the Ar 1 point was 970°C. After being heated at 1100°C for 30 minutes, the steel sheet bar was rolled by a rolling apparatus having 700 mm diameter rolls with a 800 m/min peripheral speed, a 86% reduction ratio and a 950°C rolling finishing temperature so as to obtain a hot rolled steel sheet having a 0.7 mm thickness. After annealing the hot rolled steel sheet for 1 minute, the integration degree of the texture and the magnetic properties of the steel sheet were examined. As a result, the hot rolled steel sheet had unprecedented excellent properties including a high {100}<001> integration degree of 5.8 and a 1.816T magnetic flux density at B 50 although a 6.2 W/kg iron loss at W 15/50 is just like a middle grade silicon steel sheet. A sheet thickness middle portion parallel to the sheet surface of a steel specimen was abraded so as to be measured by X-ray diffraction for calculating the three-dimensional orientation distribution function. A steel sheet rolled with a 700°C rolling temperature condition with the same composition was examined similarly and the result shows that the {100}<001> integration degree declined. Furthermore, after cold rolling the hot rolled steel sheet obtained as mentioned above to a 0.5 mm thickness and annealing at 850°C for 1 minute, the texture and the magnetic properties of the steel sheet were examined. As a result, when the hot rolling finishing temperature was 950°C, an {100}<001> integration degree of 5.5, which indicates that the integration degree at the hot rolled steel sheet stage was substantially maintained, a 4.6 W/kg iron loss at W 15/50 , a 1.821T magnetic flux density at B 50 were measured. An electromagnetic steel sheet having a magnetic flux density much higher than a conventional non-oriented electromagnetic steel sheet with the similar iron loss was obtained. On the other hand, when the hot rolling finishing temperature was 700°C, the {100}<001> integration degree declined in the cold rolled steel sheet. Furthermore, hot rolled steel sheets were prepared with the same kind of the steel as mentioned above with a 950°C rolling finishing temperature so as to have a 1.25 mm sheet thickness. They were cold rolled with 30, 40, 60, 80, 90, 92% reduction ratios to have a 0.88, 0.75, 0.50, 0.25, 0.12, or 0.10 mm thickness, and annealed at 850°C for 1 minute. The result of the examination on the texture and the magnetic properties thereof shows the {100}<001> integration degrees and the magnetic flux densities B 50 in the C direction as shown in Table 1. Cold reduction ratio (%) {100}<001> integration degree {111}<uvw> integration degree {100} <001> integration degree / {111} < uvw > integration degree Magnetic flux density in C direction (T) 30 4.2 1.98 2.12 1.83 40 7.3 1.68 4.53 1.86 60 12.0 1.30 9.23 1.88 80 10.9 1.86 5.86 1.87 90 8.5 4.00 2.13 1.86 92 5.8 4.53 1.28 1.83 With a 40 to 90% reduction ratio, the {100}<001> integration degree is further improved to be 7 or more compared with the hot rolled steel sheet and the magnetic flux density B 50 in the C direction was 1.86T or more. That is, an electromagnetic steel sheet having a high magnetic flux density was obtained. The present invention is based on the above-mentioned experimental facts where the composition ratio as well as the hot rolling condition are important. That is, only when the temperature of a steel sheet at the time of finishing hot rolling is sufficiently high and the reduction ratio is sufficiently large, can a good texture be obtained. By further applying cold rolling with an appropriate reduction ratio, the texture became reinforced. Although the reason thereof is not completely understood, it is believed that crystal grains with the right cubic orientation dominantly appear in the recrystallization at the rolling deformation in a specific condition of hot rolling. As to the degree of integration improvement of the texture by cold rolling and annealing, this is surprising. Although in conventional knowledge the texture had been considered to be destroyed by a large amount of reduction, and to reduce the integration degree conversely, the actual integration degree was improved. This phenomenon is considered to relate to the special texture of the hot rolled steel sheet. However, a full explanation of the phenomenon has not so far been realized. In order to examine the influence of the Si amount and the hot rolling condition in a ferrite single phase steel sheet, silicon steel slabs with a composition including 1.9%, 3.0%, and 3.4% by weight of Si were heated to 1250°C, and 1.4 to 10 mm thickness sheet bar was obtained by hot rough rolling. Finish rolling was applied in various conditions to have a 1.0 mm sheet thickness. The hot rolled steel sheets were applied with a heat treatment at 650°C for 2 hours for the coil winding process, washed with acid, and cold rolling so as to obtain a cold rolled steel sheets having a 0.35 mm thickness. Then, after degreasing the steel sheet, recrystallization annealing was applied at 850°C for 20 seconds in a dry atmosphere containing 35% hydrogen and 65% nitrogen. The specific resistivities were 34, 49, and 53 µΩ·cm. The average values of the three dimensional orientation distribution density in the sheet thickness direction of the steel sheet accordingly obtained calculated as mentioned above are shown in the Figure. As shown in the Figure, in order to obtain a desired texture in a ferrite single phase steel sheet, it is important to satisfy a certain relational formula with respect to the final stand reduction ratio (1 pass) R, the rolling finishing temperature T F , and the Si amount [Si]: 1150 ≥ T F ≥ 1010 + 100 × [Si] - 5 × R. Only when hot finish rolling is conducted in the condition satisfying the relational formula, can the targeted purpose be achieved. In the present invention, the steel slab needs to have the composition ratio such that the specific resistivity of the product is higher than an ordinary steel. Specifically, a 15 µΩ·cm or more value is required. With a lower value, the eddy current loss becomes large and, thus, the product cannot be used as an electromagnetic steel sheet. An example of the specific composition capable of providing such a specific resistivity will be described below. Si and P independently serve to increase the specific resistivity and reduce the eddy current loss. Thus, the desired properties can be obtained provided that at least one of Si and P is present within the respective ranges mentioned below. Si has an effect to increase the specific resistivity and reduce the eddy current loss. With an Si amount less than about 0.1% by weight, the effect cannot be achieved sufficiently. On the other hand, with an Si amount exceeding about 3.5% by weight, the magnetic flux density drastically declines and the processability also deteriorates. Therefore, the range of the Si amount is defined to be about 0.1 to 3.5% by weight. P has the effect to increase the specific resistivity and reduce the eddy current loss. That is, although the magnetic flux density is slightly lowered with a P increase, P is more advantageous than Si due to less decline in the magnetic flux density when P and Si are compared in the same specific resistivity level. With a P amount less than about 0.2% by weight, the above-mentioned effect cannot be provided sufficiently. On the other hand, with a P amount exceeding about 1.2% by weight, Fe 3 P, and the like is precipitated along the grain boundary so that the magnetic flux density drastically declines, iron loss increases and processability deteriorates. Accordingly, the range of the P amount is defined to be about 0.2 to 1.2% by weight. Al: about 2.0% by weight or less, Mn: about 2.0% by weight or less . These elements may be independently included as optional elements in the steels of the present invention. Al and Mn have the effect of increasing the specific resistivity like P and Si and, thus, are preferable in the present invention. However, an Al or Mn amount exceeding about 2.0% by weight causes the cost to rise. Therefore, the amount of Al and Mn is preferably about 2.0% by weight or less. Since C deteriorates the magnetic properties, it is advantageous to minimize the amount thereof, specifically, it is about 0.005% by weight or less. Similarly, if O is contained in a large amount, since a bad influence is cast on the formation of a texture integrated in {100}<001> orientation in hot rolling, and further, the texture and the magnetic properties of the product are deteriorated, it is more preferable to restrain the amount to about a 0.005% by weight or less level. Sb: about 0.1% by weight or less, Sn: about 0.1% by weight or less Since Sb and Sn improve the texture and are effective in improving the magnetic properties, at least one of Sb and Sn can be added optionally as needed. Concerning the crystal integration degree, the {100}<001> integration degree/{111}<uvw> integration degree is about 2.0 or more. Here the {100}<001> integration degree represents the value of the three dimensional orientation density in the {100}<001> orientation, and the {111}<uvw> integration degree represents the geometric mean of the three dimensional orientation density in the {111}<uvw> orientation. The reason why the above-mentioned ratio is about 2.0 or more is that a good property cannot be obtained with a smaller ratio since the ratio of {111}<uvw> oriented grains, which deteriorates the magnetic characteristics, becomes large. Concerning the crystal grain size, each crystal grain size is from about 10 µm to 500 µm. The crystal grains are obtained by etching with Nital (a liquid mixture of nitric acid and ethyl alcohol). By measuring the average grain area by microscope observation, the size corresponding to the circle equivalent diameter may be obtained as the grain size. The reason of setting the upper limit and the lower limit of the crystal grain size at about 10 to 500 µm is that the hysteresis loss is increased to deteriorate the magnetic properties with a crystal grain size less than about 10 µm. On the other hand, the punching property of the product is deteriorated with a crystal grain size exceeding about 500 µm. Furthermore, concerning the texture, since the texture integrated in the {100}<001> orientation is characteristic of the present invention, it is important to have about a 10 or more {100}<001> integration degree in order to sufficiently utilize the effect as an Si steel material. Since the integration in the {111}<uvw> orientation, which is disadvantageous in terms of the magnetic properties, becomes strong in an Si steel, the above-mentioned integration degree is necessary. Further, in a P steel, it is important to have the integration degree in the {100}<001> orientation about 3 or more. Since the integration in the {111}<uvw> orientation is not particularly strong in a P steel, the above-mentioned integration degree is sufficient. An electromagnetic steel sheet of the present invention can be obtained by the following method. That is, in the production of an electromagnetic steel sheet by hot rolling a slab with the steel composition adjusted to have about a 15 µΩ·cm or more specific resistivity in the product, a sufficient strain is applied in a predetermined temperature range in the vicinity of the hot rolling final stage. The application of sufficient strain refers to rolling with a reduction ratio larger than an ordinary hot rolling. That is, recrystallization is not generated until midway through hot rolling, but is drastically generated in the vicinity of the hot rolling final stage under a large strain. This is one of the most important features of the present invention. A sufficient strain is introduced into the steel sheet thereby so that the rolling texture can be effectively improved to obtain a preferable texture. That is, a texture having a higher integration degree in the vicinity of {100}<001> can be obtained compared with the texture by ordinary rolling and, thus, the texture in the hot rolling stage provides excellent characteristics in the product electromagnetic steel sheet. Accordingly, without the need of strictly controlling the cold rolling condition or the annealing condition after hot rolling, a product with excellent electromagnetic properties can be obtained. An example of a further specific hot rolling condition will be described later. The reduction ratio in the latter stage stand in hot finish rolling specifically needs to be about a 30% or more reduction ratio in the final pass, or about a 10% or more reduction ratio in the final pass and about a 50% or more total reduction ratio in the final 3 passes. Since application of a sufficient amount of a strain energy to the steel sheet in the latter stage of hot finish rolling is important in the present invention, with less than about a 30% reduction ratio in the final pass, or a less than about a 50% total reduction ratio in the final 3 passes when the reduction ratio in the final pass is from about 10% to less than about 30%, a sufficient strain cannot be introduced into the steel sheet and, thus, the rolling texture cannot be improved effectively. Therefore, even if cold rolling and annealing are applied with an ordinary condition in the rolled texture state, improvement of the magnetic properties cannot be expected. Accordingly, a reduction ratio in the final pass is defined to be about 30% or more, and the total reduction ratio in the final 3 passes is defined to be about 50% or more (the reduction ratio in the final pass is about 10% or more) in hot finish rolling in the present invention. Furthermore, it is particularly preferable to have the finish rolling with about a 30% or more 1 pass reduction ratio. The upper limit of the total reduction ratio in the final pass and the final 3 passes is preferably about 80% and about 90%, respectively, since a total reduction ratio in the final pass and in the final 3 passes exceeding about 80% or about 90% deteriorates the passing property of the steel sheet and the production cost. Concerning the above-mentioned certain temperature in the vicinity of the hot rolling final stage, the hot rolling finishing temperature is set to be about 750 to 1150°C. With less than about 750°C, the {100}<001> integration degree is less than about 10. On the other hand, at more than about 1150°C, the time from sending out from the heating furnace to rolling is limited, and heating at a high temperature is required so that the cost is raised. Therefore, the rolling temperature is defined in the range from about 750 to 1150°C. The optimum range of the temperature of the steel sheet at the time of finishing rolling and the reduction ratio varies depending upon the component and, thus, it is advantageous to conduct control according thereto. As the reason thereof, the phase condition of the steel at the time of finishing rolling seems to be important. That is, one having the y single phase at the time of finishing rolling has a random orientation distribution subsequently so as to influence the texture of the steel sheet produced after subsequent processes and, thus, the {100}<001> integration degree and the magnetic flux density are deteriorated. Therefore, it is important to have the a single phase or the (α + γ) two phase region at the time of finishing rolling. The {100}<001> integration degree of the steel sheet produced after subsequent processes becomes less than about 10 if the hot rolling finishing temperature is less than Ar 1 - 100°C in a steel having the ferrite-austenite transformation in the temperature range from about 750 to 1150°C. On the other hand, the texture becomes random if the temperature exceeds Ar 1 + 50°C. Therefore, it is preferable to finish rolling in the temperature range from Ar 1 - 100°C to Ar 1 + 50°C. In a steel having the ferrite single phase in the temperature range from about 750 to 1150°C, sufficiently satisfying characteristics cannot always be obtained only by satisfying the above-mentioned rolling temperature and reduction ratio. The reason is that the hot rolling strain amount at a high temperature, which is necessary for forming the texture oriented in {100}<001>, increases with a large Si content. Therefore, in this case, it is important to conduct hot finish rolling in the condition satisfying the below-mentioned formula with respect to the final stand reduction ratio (1 pass) R (%), the rolling finishing temperature T F , and the Si amount [Si]: 1150 ≥ T F ≥ 1010 + 100 × [Si] - 5 × R. By further conducting cold rolling and annealing after the above-mentioned hot finish rolling, a cold rolled electromagnetic steel sheet having excellent magnetic properties can be obtained. Specifically, the reduction ratio is selected in cold rolling so as not to ruin the preferable texture obtained in the hot rolling, preferably to further improve the texture. Since the texture is disturbed to deteriorate the integration degree with a more than about 90% cold reduction ratio, it is preferably about 90% or less. Even with a low cold reduction ratio, the magnetic characteristics cannot be worse than the hot rolled steel sheet. However, in order to improve the same, about a 40% or more reduction ratio is preferable. By selecting the cold reduction ratio in the range from about 40 to 90%, further better characteristics including a high {100}<001> integration degree and the magnetic properties such as about 1.80T or more B 50 at 2 to 3 W/kg of W 15/50 , and about 1.86T or more B 50 at 3 to 4 W/kg of W 15/50 can be provided. Hot rolled sheet annealing can be conducted as needed. The upper limit of the temperature is defined to be about 1100°C or less in view of production cost, or the A 1 transformation point or less in the case of a steel to be transformed. On the other hand, since the effect of annealing cannot be provided with less than about 600°C, it is preferable to have the lower limit at about 600°C. The condition of finish annealing need not be particularly limited. However, the condition in the about 750 to 1100°C temperature range for about 10 seconds to 2 hours is recommended. In particular, since the texture becomes random and, thus, a desired texture cannot be obtained in a steel to be transformed if the annealing temperature exceeds the A 1 transformation point, it is preferable to have finish annealing at lower than the A 1 transformation point. The above-mentioned is simply intended as illustrative examples of embodiments of the present invention and various modifications can be introduced in the range of the appended claims. EXAMPLES Example 1 100 kg steel ingots with compositions shown in Table 2 were melted in a small vacuum melting furnace, and sheet bars with a 1.5 to 8.0 mm thickness were obtained by hot rough rolling after heating at 1150°C. After being heated at 1100°C, the steel sheet bars were rolled at a 800 m/min rolling speed with the rolling finishing temperature controlled at 700, 750, 950, and 1050°C so as to obtain a 1.0 mm thickness by 1 pass. Then, a heat treatment was applied at 750°C for 2 hours. The heat treatment is for self annealing by the coil winding process. After being washed with acid, the hot rolled steel sheets were cold rolled so as to have a 0.35 mm thickness. Then, finish annealing was applied at 850°C for 1 minute. The pole figure of (110), (200), and (211) of each of the steel sheets accordingly obtained was sought by X-ray diffraction. Three dimensional orientation analysis was conducted using a series development method mentioned above. The magnetic measurement was conducted with a specimen with the L direction and a specimen with the C direction combined half and half for seeking the iron loss amount at the time of 1.5T excitation; W 15/50 , and the magnetic flux density; B 50 at the time of the excited magnetic field; 5000 A/m. Concerning the magnetic flux density, each B 50 in the L direction and the C direction was measured so as to seek the difference ΔB 50 between the L direction and the C directionThe obtained results are shown in Table 3. Kind of steel C (%) Si (%) Mn (%) P (%) S (%) Al (%) N (ppm) O (ppm) Ar 1 point (°C) Specific resistivity ρ (µΩ·cm) I 0.005 0.45 025 0.005 0.001 0.25 23 24 892 19 II 0.004 1.03 0.23 0.25 0.001 0.21 16 18 925 26 III 0.004 3.1 024 0.001 0.001 0.60 8 9 - 54 IV 0.003 3.8 0.21 0.001 0.001 0.045 10 12 - 56 Nos. 1, 5 and 8 are comparative examples with a low rolling temperature. Nos. 2 and 6 are Comparative Examples with the reduction ratio outside the range of the present invention. In both of them, the {100}<001> integration degree is less than the targeted value, the magnetic properties, particularly the magnetic flux density are poor, and the difference between the L direction and the C direction is large. Nos. 11 and 12 are comparative examples with the Si amount outside the range of the present invention. Even if the rolling condition is in the preferable range (No. 12), the magnetic flux density is poor, and the difference between the L direction and the C direction is large. On the other hand, examples of the present invention in Nos. 3, 4, 7, 9 and 10 have a 10 or more {100}<001> integration degree, and excellent magnetic properties with a small difference between the L direction and the C direction. Example 2 50 kg steel ingots with a composition including 0.53% by weight of Si and Fe substantially in the remainder (kind of the steel in Table 4: A), and with a composition including 1.21% by weight of Si and Fe substantially in the remainder (kind of the steel in Table 4: B) were melted in a small vacuum melting furnace, and sheet bars with a 1.2 to 8.0 mm thickness were obtained by hot rough rolling after heating at 1150°C. After being heated at 1100°C, the steel sheet bars were rolled by a 800 m/min rolling speed with the rolling finishing temperature controlled between 700 to 1050°C so as to obtain a 1.0 mm thickness by 1 pass. Then, a hot rolled sheet annealing was applied at 800°C for 10 minutes. After being washed with acid, the steel sheets were cold rolled so as to have a 0.35 thickness. Then, finish annealing was applied at 850°C for 1 minute. The three dimensional orientation distribution density, W 15/50 , and B 50 of the accordingly obtained steel sheets were calculated as in Example 1. The obtained results are shown in Table 4. Nos. 1, 2 and 9 are comparative examples with a low rolling temperature. In either of them, the {100}<001> integration degree is less than the targeted value, and the magnetic properties are drastically deteriorated. Nos. 7, 8 and 13 are comparative examples with a high rolling temperature. The {100}<001> integration degree is low, the orientation is random, and the magnetic properties are deteriorated. No. 4 is an example with a low rolling ratio, where satisfactory magnetic properties are not obtained. On the other hand, examples of the present invention in Nos. 3, 5, 6, 10, 11 and 12 have a 10 or more {100}<001> integration degree, and excellent magnetic properties. Example 3 50 kg steel ingots with compositions shown in Table 5 were melted in a small vacuum melting furnace. In Table 5, the steels (C), (D) and (E) are of a composition ratio according to the present invention. The steel (D) contains P alone, the steels (C) and (E) contain Si, Al and Mn added thereto. The steels (A) and (B) are comparative examples with an ordinary silicon steel sheet composition. Furthermore, the steel (F) is an example with the Si, Al and Mn amount outside the range of the present invention. After heating the steel ingots at 1150°C, sheet bars having a 1.1 to 4.0 mm thickness were obtained by hot rough rolling. After being heated at 1100°C, the steel sheet bars were rolled by a 800 m/min rolling speed with the rolling finishing temperature controlled between 600 to 950°C so as to obtain a 0.8 mm thickness by 1 pass (reduction ratio: 27 to 80%). Then, a heat treatment was applied at 750°C for 2 hours, and further, a heat treatment was applied at 950°C for 1 minute. The former heat treatment is for self annealing by coil winding. The (110), (200), (211) pole figure of each of the hot rolled steel sheets accordingly obtained was sought by the X-ray diffraction, and the three dimensional orientation analysis was conducted using the above-mentioned series development method so as to seek the three dimensional orientation distribution density. The magnetic measurement was further conducted to seek the iron loss value W 15/50 at the time of the 1.5T excitation and the magnetic flux density B 50 at the time of the excited magnetic field 5000 A/m. The obtained results are shown in Table 6. Nos. 1 to 3 are comparative examples of an ordinary silicon steel sheet composition. As can be seen from the comparison between Nos. 1 and 2, in general, with the alloy amount increased, the iron loss is reduced but the magnetic flux density is declined as well. No. 3 is a comparative example with a conventional silicon steel composition although the rolling condition is fit to the present invention. In No. 3, the {100}<001> integration degree is higher due to rolling at a high temperature and a large reduction. As a result, the magnetic properties in the C direction are particularly improved compared to Nos. 1 and 2. On the other hand, examples of the present invention in Nos. 4 and 5 with the rolling condition the same as No. 3, have a high magnetic flux density particularly in the magnetic properties in the C direction compared to the No. 3, which has the similar iron loss value. That is, the steel sheets Nos. 4 and 5 with the rolling condition and the composition according to the present invention have excellent characteristics including a low iron loss in the C direction and a particularly high magnetic flux density compared with the steel sheet No. 3 with a conventional composition obtained in the rolling condition of the present invention. The same can be applied to Nos. 6 and 8 according to the present invention. No. 10 is an example of the present invention containing Si and Al in addition to P. In this case, a particularly high magnetic flux density is achieved in the similar iron loss level compared with the conventional comparative example No. 1. On the other hand, since the rolling condition of Nos. 7 and 9 is outside the range of the present invention although the composition ratio is in the range of the present invention, the characteristics are at a similar level as No. 3 although they are better than the characteristics of No. 2 with a conventional composition. Since the total amount of Si, Al and Mn of No. 11 exceeds the range of the present invention, it cannot exceed the conventional level of the magnetic properties. Example 4 50 kg steel ingots with compositions shown in Table 5 were melted in a small vacuum melting furnace. After heating the steel ingots at 1150°C, sheet bars having a 1.1 to 4.0 mm thickness were obtained by hot rough rolling. After being heated at 1100°C, the steel sheet bars were rolled at a 800 m/min rolling speed with the rolling finishing temperature controlled between 600 to 950°C so as to obtain a 0.8 mm thickness by 1 pass (reduction ratio: 27 to 80%). Then, the scale on the hot rolled sheet surface was eliminated by a shot blast treatment. Cold rolling was conducted to have a 0.5 mm thickness. Annealing was applied at 850°C for 1 minute in an atmosphere containing 35% of hydrogen and 65% of nitrogen. The (110), (200), (211) pole figure of each of the cold rolled steel sheets accordingly obtained was sought by X-ray diffraction, and the three dimensional orientation analysis was conducted using the above-mentioned series development method so as to seek the three dimensional orientation distribution density. The magnetic measurement was further conducted to seek the iron loss value W 15/50 at the time of the 1.5T excitation and the magnetic flux density B 50 at the time of the excited magnetic field 5000 A/m. The obtained results are shown in Table 7. Nos. 1 to 3 are comparative examples of an ordinary silicon steel sheet composition. As can be seen from the comparison between Nos. 1 and 2, in general, with the alloy amount increased, the iron loss is reduced but the magnetic flux density declined as well. No. 3 is a comparative example with a conventional silicon steel composition although the rolling condition is fit to the present invention. In No. 3, the {100}<001> integration degree is higher due to rolling at a high temperature and a large reduction. As a result, particularly the magnetic properties in the C direction are improved compared with Nos. 1 and 2. On the other hand, examples of the present invention in Nos. 4 and 5 with the rolling condition the same as No. 3, have a high magnetic flux density particularly in the magnetic properties in the C direction compared with the No. 3, which has the similar iron loss value. That is, the steel sheets Nos. 4 and 5 with the rolling condition and the composition according to the present invention have excellent characteristics including a low iron loss in the C direction and a particularly high magnetic flux density compared with the steel sheet No. 3 with a conventional composition obtained in the rolling condition of the present invention. The same can be applied to Nos. 6 and 8 according to the present invention. No. 10 is an example of the present invention containing Si and Al in addition to P. In this case, a particularly high magnetic flux density is achieved in the similar iron loss level compared with the conventional comparative example No. 1. On the other hand, since the rolling condition of Nos. 7 and 9 is outside the range of the present invention although the composition ratio is in the range of the present invention, the characteristics are at a similar level as No. 3 although they are better than the characteristics of No. 2 with a conventional composition. Since the total amount of Si, Al and Mn of No. 11 exceeds the range of the present invention, it cannot exceed the conventional level of the magnetic properties. Example 5 An example with a higher cold reduction ratio for obtaining further better magnetic properties will be described. 50 kg steel ingots with compositions shown in Table 5 were heated at 1150°C so as to obtain sheet bars having a 1.7 to 6.2 mm thickness by hot rough rolling. After being heated at 1100°C, the steel sheet bars were rolled at a 800 m/min rolling speed with the rolling finishing temperature controlled between 600 to 950°C so as to obtain a 1.25 mm thickness finish hot rolled sheet with 1 pass (reduction ratio: 26 to 80%). Then, the scale was eliminated by applying a shot on the surface of the finish hot rolled sheet. Cold rolling was conducted to have a 0.5 mm thickness with a 60% reduction ratio. Annealing was applied at 850°C for 1 minute in an atmosphere containing 35% of hydrogen and 65% of nitrogen. The (110), (200), (211) pole figure of each of the electromagnetic steel sheets accordingly obtained was by X-ray diffraction, and the three dimensional orientation analysis was conducted using the above-mentioned series development method so as to obtain the three dimensional orientation distribution density. The magnetic measurement was further conducted to obtain the iron loss value W 15/50 at the time of the 1.5T excitation and the magnetic flux density B 50 at the time of the excited magnetic field 5000 A/m. The obtained results are shown in Table 8. Nos. 1 to 3 are comparative examples of an ordinary silicon steel sheet composition. As can be seen from the comparison between Nos. 1 and 2, in general, with the alloy amount increased, the iron loss is reduced but the magnetic flux density declined as well. No. 3 is a comparative example with a conventional silicon steel composition although the rolling condition is fit to the present invention. In No. 3, the {100}<001> integration degree is higher due to rolling at a high temperature and a large reduction. As a result, the magnetic properties in the C direction are particularly improved compared with Nos. 1 and 2. On the other hand, examples of the present invention in Nos. 4 and 5 with the rolling condition the same as No. 3, have a high magnetic flux density particularly in the magnetic properties in the C direction compared to No. 3, which has a similar iron loss value. That is, the steel sheets Nos. 4 and 5 with the rolling condition and the composition according to the present invention have excellent characteristics including a low iron loss in the C direction and a particularly high magnetic flux density compared to the steel sheet No. 3 with a conventional composition obtained in the rolling condition of the present invention. The same can be applied to Nos. 6 and 8 according to the present invention. No. 10 is an example of the present invention containing Si and Al in addition to P. In this case, a particularly high magnetic flux density is achieved in the similar iron loss level compared to the conventional comparative example No. 1. On the other hand, since the rolling condition of Nos. 7 and 9 is outside the range of the present invention although the composition ratio is in the range of the present invention, the characteristics are at a similar level as No. 3 although they are better than the characteristics of No. 2 with a conventional composition. Since the total amount of Si, Al and Mn of No. 11 exceeds the range of the present invention, it cannot exceed the conventional level of the magnetic properties. Example 6 The influence of the cold reduction ratio will be described. Sheet bars with a 3.75 to 14 mm thickness were produced using the steel (C) shown in Table 5 by hot rough rolling. After being heated at 1100°C, the steel sheet bars were rolled at a 800 m/min rolling speed with a 950°C rolling finishing temperature so as to obtain a 0.75 to 7.0 mm thickness with 1 pass (reduction ratio: 50 to 80%). The scale was eliminated by applying a shot on the surface of the finish hot rolled sheet. Cold rolling was conducted to have a 0.5 mm thickness with a 33 to 63% reduction ratio. Annealing was applied at 850°C for 1 minute in an atmosphere containing 35% of hydrogen and 65% of nitrogen. Then the evaluation the same as Example 3 was conducted to obtain the results shown in Table 9. No. 13 is an example of the present invention with the cold reduction ratio in the preferable range, where the {100}<001> integration degree is high, and the magnetic flux density in the C direction is particularly high. Since the cold reduction ratio in No. 12 is too low, and the cold reduction ratio in No. 14 too large, the integration degree cannot be large and the magnetic flux density slightly declined in both cases. Example 7 Steel slabs with composition ratios shown in Table 10 were heated at 1100°C and rolled by hot rough rolling. With a 5% reduction ratio at the final pass of the hot finish rolling, hot rolled sheets with a 2.0 mm thickness were obtained. The sheets were applied with cold rolling so as to have a 0.5 mm thickness in the cold rolling condition in producing an ordinary non-oriented electromagnetic steel sheet. Then, annealing was applied with the condition the same as mentioned above. The magnetic measurement was conducted for the electromagnetic steel sheets accordingly obtained by the electromagnetic steel sheet testing method stipulated in the JIS C 2550 for obtaining the iron loss value W 15/50 per 1 kg with respect to the 1.5 tesla (T) maximum magnetic flux density and a 50 Hz frequency, and the magnetic flux density B 50 at a 5000 A/m magnetic force. The results are shown in Table 11. Kind of steel Composition ratio (wt%) Specific resistivity ρ (µΩ·cm) C Si Al Mn S N O Sb Sn 1 0.003 0.12 0.31 0.31 0.002 0.003 0.003 - - 17 2 0.005 0.54 0.25 0.29 0.002 0.004 0.004 - - 21 3 0.002 1.01 0.21 0.24 0.001 0.003 0.003 - - 25 4 0.003 1.17 0.23 0.26 0.001 0.003 0.003 - - 28 5 0.003 1.45 0.21 0.25 0.002 0.003 0.003 - - 31 6 0.002 1.84 0.22 0.25 0.001 0.003 0.003 - - 35 7 0.003 1.23 0.23 0.25 0.001 0.004 0.003 0.04 - 28 8 0.003 1.05 0.21 0.24 0.001 0.003 0.003 - 0.035 26 As is apparent from Table 11, the examples of the present invention have magnetic properties superior to those of the conventional examples in any kind of steel. Example 8 A steel slab containing 1.24% by weight of Si (kind of the steel: A), a steel slab containing 3.46% by weight of Si (kind of the steel: B), and a steel slab containing 3.80% by weight of Si (kind of the steel: C) were heated at 1120°C and rolled by hot rough rolling. With the conditions shown in Table 12 in terms of a total reduction ratio in the final 3 passes and a reduction ratio in the final pass, hot finish rolling was applied for obtaining hot rolled sheets with a 1.2 mm thickness. The sheets were applied with hot rolled sheet annealing at 900°C for 2 minutes. The scale was eliminated by washing with acid. Then cold rolling was applied so as to have a 0.5 mm thickness. Then, finish annealing at 850°C for 20 seconds in an atmosphere containing hydrogen and nitrogen. In any of the steel kinds A to C, the amount of C, Al, and Mn was adjusted to the preferable range of the present invention. The magnetic measurement was conducted for the electromagnetic steel sheets accordingly obtained in the method the same as Example 1 for obtaining the iron loss value W 15/50 and the magnetic flux density B 50 . The results are shown in Table 12. From Table 12, steel Nos. 3, 5, 7, 9, which do not meet the condition of a 30% or more reduction ratio in the final pass or a 10% or more reduction ratio in the final pass and a 50% or more total reduction ratio in the final 3 passes in hot finish rolling, have poor magnetic properties compared with the other examples in the same steel kind. Steel Nos. 10 and 11 have a low magnetic flux density since the Si amount is more than the preferable range of the present invention although the reduction ratio thereof is in the preferable range of the present invention. On the other hand, steel Nos. 1, 2, 4, 6 and 8, which meet at least one of the conditions of a 30% or more reduction ratio in the final pass or a 10% or more reduction ratio in the final pass and a 50% or more total reduction ratio in the final 3 passes in hot finish rolling, have excellent magnetic properties compared with the other examples in the same steel kind.

Claims: A finish annealed non-oriented electromagnetic steel sheet having excellent magnetic properties, said steel sheet having a C content of 0.005% by weight or less, as well as an Si content of 0.1 to 3.5% by weight and/or a P content of 0.2 to 1.2% by weight, a specific resistivity of 15 µΩ•cm or more, a ratio of {100}<001> integration degree to {111}<uvw> integration degree of 2.0 or more, and crystal grains of 10 µm to 500 µm in diameter. The electromagnetic steel sheet according to claim 1, said sheet comprising 0.1 to 3.5% by weight of Si, and its {100}<001> integration degree being 10 or more. The electromagnetic steel sheet according to claim 1, said sheet comprising 0.2 to 1.2% by weight of P, and its {100}<001> integration degree being 3 or more. A method of producing a non-oriented electromagnetic steel sheet having excellent magnetic properties as claimed in claim 1 which comprises, a) preparing a steel slab whose composition is adjusted such that the C content is 0.005% by weight or less, whilst the Si content is 0.1 to 3.5% by weight and/or the P content is 0.2 to 1.2% by weight, and the specific resistivity of the resulting product sheet is 15 µΩ•cm or more, and b) subjecting said slab to hot rolling, wherein the reduction ratio applied to said steel slab in the final rolling stage is 30% or more in the final pass or 50% or more in total in the final 3 passes with 10% or more reduction in the final pass, and wherein the finishing temperature is adjusted to 750 to 1150°C. The method according to claim 4, wherein said reduction ratio is 30% or more. The method according to claim 5, wherein said final rolling stage is conducted in 1 pass. The method according to claim 4, wherein the total reduction ratio of the final 3 passes in said hot rolling step is 50% or more, and wherein the reduction ratio in the final pass is 10% or more. The method according to any one of claims 5, 6 and 7, wherein said slab contains 0.1 to 3.5% by weight of Si and the {l00}<001> integration degree of said product sheet is 10 or more. The method according to any one of claims 5, 6 and 7, wherein said slab contains 0.2 to 1.2% by weight of P, and wherein the {100}<001> integration degree of said product sheet is about 3 or more. The method according to claim 8, wherein said slab is made from a component providing a ferrite-austenite transformation temperature of 750 to 1150°C, and wherein the finishing hot rolling temperature is not lower than 750° and not lower than Ar 1 - 100 and not higher than 1150°C and not higher than Ar 1 + 50°C. The method according to claim 8, wherein said slab is made from a component to have a ferrite single phase at about 750 to 1150°C, and wherein the finishing hot rolling temperature is not lower than 750° and not lower than 1010°C + 100 x [Si] - 5 x reduction ratio of the final hot rolling pass(%) and not higher than 1150°C. The method according to claim 9, wherein said slab is made from a component to have a ferrite-austenite transformation at 750 to 1150°C, and wherein the finishing hot rolling temperature is not lower than 750°C and not lower than Ar 1 - 100 and not higher than 1150°C and not higher than Ar 1 + 50°C.

Inventors: KONDO OSAMU, MATSUZAKI AKIHIRO, TAKAJO SHIGEAKI, KONDO, OSAMU, MATSUZAKI, AKIHIRO, TAKAJO, SHIGEAKI, Kondo, Osamu, c/o Kawasaki Steel Corporation, Matsuzaki, Akihiro, c/o Kawasaki Steel Corporation, Takajo, Shigeaki, c/o Kawasaki Steel Corporation
Applicants: JFE STEEL CORP, JFE STEEL CORPORATION
Application year: 1998
Main classification: C21D8
IPC codes: C21D8, H01F1