JP2679927C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention contains 2.5 to 7.0% of Si, and has a high degree of integration in the (110) [001] direction of crystal grains. Another object of the present invention is to provide a method for producing a grain-oriented electrical steel sheet having extremely low iron loss due to a finer grain size than ever before. [0002] Generally, the magnetic properties of a grain-oriented electrical steel sheet are evaluated based on both iron loss properties and excitation properties. Increasing the excitation characteristics is effective in reducing the size of equipment that increases the design magnetic flux density.
On the other hand, reducing the iron loss characteristics is effective in that when it is used as an electric device, heat loss is reduced and power consumption can be saved. further,
Aligning the <100> axis of the crystal grains of the product in the rolling direction can increase the magnetizing properties and lower the iron loss properties. In recent years, many studies have been repeated especially on this aspect, and various manufacturing technologies have been developed. Was done. [0003] As a result, there are three typical manufacturing techniques of typical grain-oriented electrical steel sheets currently industrially produced. The first technique is a production technique by a two-fold cold rolling process in which MnS functions as an inhibitor, which is disclosed in Japanese Patent Publication No. 30-3651. This manufacturing method has a relatively good iron loss due to a small particle size of the secondary recrystallization, but has a problem that a high magnetic flux density cannot be obtained. On the other hand, in order to obtain a high magnetic flux density, as a second technology,
No. 15644 was disclosed. This is a manufacturing technique in which AlN + MnS is made to function as an inhibitor and the rolling reduction in the final cold rolling step is under high pressure exceeding 80%. According to this method, the degree of integration of the (110) [001] orientation of the secondary recrystallized grains is high,
B ₈ is oriented electrical steel sheet is obtained having a high magnetic flux density of 1.870 (T) or more. Further, as a third technique, MnS disclosed in JP-B-51-13469 is disclosed.
Alternatively, a manufacturing technique by a two-fold cold rolling process in which MnSe + Sb functions as an inhibitor has been developed. [0004] In general, iron loss is roughly divided into two types: hysteresis loss and eddy current loss. Physical factors that affect the hysteresis loss include the purity of the material and internal strain in addition to the above-described crystal orientation. In addition, as a physical factor affecting eddy current loss, the electric resistance (
Component amount such as Si), plate thickness, size of magnetic domain (crystal grain size), tension applied to the steel plate, and the like. In a normal grain-oriented electrical steel sheet, the eddy current loss accounts for 3/4 or more of the total iron loss, so that it is more effective to reduce the eddy current loss than the history loss in reducing the total iron loss. For this reason, in the manufacturing method according to the second technique, (110) [0
01] orientation of high degree of integration, since the B ₈ even though oriented electrical steel sheet having a high magnetic flux density of 1.870 (T) or more is obtained, the secondary recrystallized grain size becomes large as 10mm order, The magnetic domain width affecting the eddy current loss was large. In order to improve this, a method of subjecting a steel sheet to laser treatment disclosed in Japanese Patent Publication No. 57-2252 and a method of applying a mechanical strain to the steel sheet disclosed in Japanese Patent Publication No. 58-2569, etc. Various methods of subdividing are disclosed. Therefore, there is disclosed a method for producing a grain-oriented electrical steel sheet having a fine secondary recrystallized grain size and having a lower iron loss than the conventional one. For example, in Japanese Patent Application Laid-Open No. 1-290716, a cold-rolled steel sheet is 100 ° C /
Ultra-rapid annealing to a temperature of 675 ° C. or higher at a heating rate of 275 ° C. or higher, decarbonizing the strip, performing a final high-temperature annealing to perform secondary growth, thereby reducing the strip to a reduced size. A method is disclosed that is characterized by having improved iron loss that persists without significant change after secondary particle and stress relief annealing. However, although it is true that secondary recrystallized grains can be obtained to a certain extent, this method aims at treating only rapid heating, and it has been found that a very good iron loss value cannot be obtained. [0007] The present invention provides a method for obtaining a grain-oriented electrical steel sheet having an extremely low iron loss by having a finer secondary recrystallized grain size than the method proposed above. The feature is to provide rapid heating, followed immediately by cooling. [0008] The present invention comprises C: 0.10% or less by weight, Si: 2.5 to 7.0% by weight and a usual inhibitor component, the balance being Fe and unavoidable. Starting from molten steel consisting of impurities, the strip rolled to the final product thickness is heated to a temperature range of 800 ° C or higher at a heating rate of 80 ° C / second or higher, and within 0.1 second after reaching the maximum temperature, Fifteen
By performing a cooling treatment at a cooling rate of 0 ° C./second or more to a temperature range of less than 800 ° C. and a temperature of 600 ° C. or more , and subjecting the obtained strip to decarburizing annealing and final finishing annealing, one having extremely low iron loss is obtained. It has been found that a grain-oriented electrical steel sheet can be obtained. Furthermore, the rapid heating and cooling treatment of the strip is rapidly heated by energizing between the rolls, and the method in which cooling is performed by the roll on the heated side provides a unidirectional electrical steel sheet having extremely low iron loss. I found something to be done. Hereinafter, the present invention will be described in detail. The grain-oriented electrical steel sheet can be manufactured by sufficiently causing secondary recrystallization during the final annealing in the manufacturing process to obtain a so-called Goss texture. In order to obtain this Goss texture, coarsening of primary recrystallized grains is suppressed, and only recrystallized grains of the (110) <001> orientation are selectively grown in a certain temperature range. That is, it is necessary to make a base material for secondary recrystallization. For that purpose, fine inclusions must be uniformly dispersed in the material as an inhibitor (inhibitor) for the growth of primary recrystallized grains. Also, it is said that the optimum precipitation size at this time is on the order of 100 angstroms. As described in Japanese Patent Application Laid-Open No. 1-290716, as for the effect of the rapid heating, the texture after the rapid heating is higher than that of the ordinary heating by (110) after the primary recrystallization.
2.) <001> Orientation grains increase, and these become nuclei for secondary recrystallization, and secondary recrystallized grains to some extent are obtained. Further, the mechanism achieved in the manufacturing method of the above patent includes two changes: a change in the primary recrystallization composition before the final decarbonizing annealing step and a change in the primary recrystallization structure before the high-temperature annealing step. However, it has been found that control of the primary recrystallization structure is insufficient with this manufacturing method alone. [0011] Therefore, as a result of variously examining the cause of obtaining finer secondary recrystallized grains, it was found that 800 ° C.
The above temperature range is heated at a heating rate of 80 ° C / sec or more, and the roll heated on the side within 0.1 second after reaching the maximum temperature is cooled to a temperature of 800 ° C or less at a cooling rate of 150 ° C / sec or more. By cooling to a temperature range of 600 ° C. or higher , it was found that the precipitates did not become coarse in the high temperature range and the optimum precipitate size on the order of 100 angstroms could be maintained. A secondary recrystallized grain size can be obtained, and a grain-oriented electrical steel sheet having extremely low iron loss can be obtained. Next, in the present invention, the reasons for limiting the steel composition and the production conditions as described above are as follows.
This will be described in detail. The reasons for limiting the steel components are as follows. The upper limit of 0.10% for C is limited because if it is more than this, the time required for decarburization becomes longer and it is economically disadvantageous. The lower limit of Si is set to 2.5% in order to improve iron loss, but if it is too large, it is likely to break during cold rolling and processing becomes difficult, so the upper limit is set to 7.0%. Furthermore, in order to produce a grain-oriented electrical steel sheet, it is preferable to add the following component elements as ordinary inhibitor components. When MnS is used as an inhibitor, Mn and S are added. Mn is
In order to obtain an appropriate dispersion state of MnS, 0.02 to 0.15% is desirable. S is M
It is an element necessary for forming nS, (Mn.Fe) S, and is preferably 0.001 to 0.05% in order to obtain an appropriate dispersion state. Further, when AlN is used as an inhibitor, acid-soluble Al and N are added. 0.01 to 0.04 in order to obtain a proper dispersion state of acid-soluble Al and AlN.
% Is desirable. N is also 0.003 to 0.02 in order to obtain a proper dispersion state of AlN.
% Is desirable. In addition, Cu, Sn, Sb, Cr and Bi are used for the purpose of strengthening the inhibitor.
At 0% or less, at least one kind may be added. Next, an intermediate thickness strip is obtained by subjecting the molten steel to ordinary ingot casting or continuous casting or hot rolling. At this time, the strip casting method can also be applied to the present invention. Further, when a nitride is required as an inhibitor, it is desirable to perform intermediate annealing at 950 to 1200 ° C. for 30 seconds to 30 minutes to precipitate AlN or the like. Next, a strip having a final product thickness is obtained by rolling one or more times including intermediate annealing. At this time, the final rolling reduction needs to be 50% or more in order to obtain a product having a high degree of Goss accumulation. If the lower limit is 50% or less, a necessary Goss nucleus cannot be obtained, so that it is limited. The strip thus rolled to the final product thickness is subjected to a heat treatment at a heating rate of 80 ° C./sec or more to a temperature range of 800 ° C. or more. The lower limit of the heating rate at this time is 80
° C / sec is a value below which (110) <0 after primary recrystallization, which is the core of secondary recrystallization.
01> The orientation grain size was reduced and fine secondary recrystallized grains could not be obtained. Also,
The lower limit of 800 ° C. was limited because recrystallization would not start below this lower limit. Furthermore, in order to prevent coarsening of fine precipitates in the heated temperature range, a temperature of less than 800 ° C and 600 ° C or more at a cooling rate of 150 ° C / sec or more within 0.1 second after reaching the maximum temperature. Cool the area. The upper limit of 0.1 seconds for the soaking time after reaching the maximum temperature was limited if the heating time was longer than this, because the precipitates became coarse. Below the upper limit 800 ° C. of the cooling temperature range,
Exceeding this range is limited because it greatly deviates from the precipitation nose. FIG. 1 shows the relationship between the cooling rate up to 650 ° C. after heating a 0.22 mm thick strip at a rate of 180 ° C./sec to 825 ° C. and the resulting iron loss characteristics of the product. When cooling is performed at a cooling rate of 150 ° C./sec or more, a good iron loss value is obtained. Note that the above treatment is desirably performed in a reducing atmosphere as much as possible because of problems after the formation of the film. Further, as one of the above-mentioned rapid heating and cooling treatments, there is a method of energizing between rolls. FIG. 2 shows a schematic diagram of one embodiment of the present invention. Two pairs of upper and lower rolls sandwiching the strip are provided, and electricity is supplied to the strip S between the rolls R1 and R2, so that the strip S is moved to a temperature range of 800 ° C. or more by 80 ° C. /
By heating at a heating rate of not less than 2 seconds and further cooling at point P by the roll R2 on the heated side, 150 ° C./sec by the roll on the heated side within 0.1 second after reaching the maximum temperature. At the above cooling rate, cooling is performed to a temperature range of less than 800 ° C. and 600 ° C. or more . The above processing is desirably carried out in a reducing atmosphere as much as possible for the apparatus box B from the viewpoint of problems such as film formation. It is also possible to improve the shape of the heated strip by introducing this slight distortion. Thereafter, decarburization annealing is performed in a wet hydrogen atmosphere. At this time, the carbon must be reduced to 0.005% or less so as not to deteriorate the magnetic properties of the product. Here, when the slab heating temperature in hot rolling is low and only AlN is used as an inhibitor, nitriding may be performed in an ammonia atmosphere. Further, an annealing separator such as MgO is applied and finish annealing at 1100 ° C. or higher is performed for secondary recrystallization and purification, thereby producing a grain-oriented electrical steel sheet having extremely low iron loss characteristics.
In order to further improve the iron loss of the obtained product, it is possible to subject the above-mentioned grain-oriented electrical steel sheet to a treatment for subdividing magnetic domains. EXAMPLES Example 1 A molten steel containing the composition shown in Table 1 was cast, heated to a slab, and then hot-rolled.
. A 3 mm hot rolled steel sheet was obtained. Next, annealing was performed at 1100 ° C. for 5 minutes, followed by pickling, and then cold rolling to a thickness of 0.22 mm. The rolled steel sheet was heated under various conditions by a direct current heating device having a set of heating electrodes. Further, immediately after heating, the steel sheet was subjected to various soaking times and cooling conditions. Table 2 shows the heating rate, the ultimate temperature, and the cooling conditions after heating. Next, after decarburizing annealing in wet hydrogen and applying MgO powder, high-temperature annealing was performed in a hydrogen gas atmosphere at 1200 ° C. for 10 hours. Table 2 shows the secondary recrystallized grain size and magnetic properties of the obtained product. Magnetic properties of the product, the temperature range of not lower than 800 ° C. and heated at 80 ° C. / sec or more heating speeds, within 0.1 seconds after reaching the maximum temperature, lower than 800 ° C. at a cooling rate of more than 0.99 ° C. / sec 600 By cooling to a temperature range of at least ℃, a finer secondary recrystallized grain size than before can be obtained,
A grain-oriented electrical steel sheet having extremely low iron loss has been obtained. [Table 1] [Table 2] (Example 2) A molten steel containing the composition shown in Table 3 was cast, and after slab heating, hot rolling was performed.
. A 3 mm hot rolled steel sheet was obtained. Next, annealing was performed at 1100 ° C. for 5 minutes, followed by pickling, and then cold rolling to a thickness of 0.22 mm. The rolled steel sheet was heated under various conditions by a direct current roll heating apparatus shown in FIG. Immediately after the heating, the exit roll was preheated and the sheet passing speed was controlled, so that various soaking times and cooling conditions were applied. Table 4 shows the heating rate and the ultimate temperature at that time, and the cooling conditions of the delivery roll. Next, decarburizing annealing is performed in wet hydrogen, and nitriding is performed in an ammonia atmosphere.
After applying the O powder, high-temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. Table 4 shows the secondary recrystallized grain size and magnetic properties of the obtained product. The magnetic properties of the product are heated at a heating rate of 80 ° C / sec or more to a temperature range of 800 ° C or more by energizing,
By cooling to a temperature range of less than 800 ° C. and 600 ° C. or more at a cooling rate of 150 ° C./sec or more by a roll on the side heated within 0.1 second after reaching the maximum temperature, a finer than before can be obtained. A grain-oriented electrical steel sheet having a secondary recrystallized grain size and extremely low iron loss has been obtained. [Table 3] [Table 4] Example 3 A molten steel containing the composition shown in Table 5 was cast, heated with a slab, and then hot-rolled.
. A 3 mm hot rolled steel sheet was obtained. This was annealed at 1100 ° C. for 5 minutes, pickled, and then cold rolled to a thickness of 0.27 mm. The rolled steel sheet is heated directly to 825 ° C at a heating rate of 250 ° C / sec by a current-carrying heating roll, and cooled to 680 ° C at a cooling rate of 23000 ° C / sec 0.01 seconds after reaching the maximum at the delivery roll. did. Next, after decarburizing annealing in wet hydrogen and applying MgO powder, high-temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. The average secondary recrystallized particle size of the obtained product was 3.5 mm. Also,
Magnetic properties, B ₈ = 1.94T, grain-oriented electrical steel sheet having a very low iron loss of _{W 17/50 = 0.89 (W / kg} ) was obtained. Further, the obtained steel sheet was subjected to magnetic domain refinement by laser treatment, and the magnetic properties were as follows: B ₈ = 1.92 T, W _17/50 = 0.81 (W / kg) An electrical steel sheet was obtained. [Table 5] Example 4 Molten steel containing the component compositions shown in Table 6 was cast, and after slab heating, hot rolling was performed.
. A 3 mm hot rolled steel sheet was obtained. This was annealed at 1100 ° C. for 5 minutes, further pickled, and then cold rolled to a thickness of 0.22 mm. The rolled steel sheet is heated to 851 ° C. at a heating rate of 250 ° C./sec by two pairs of direct current heating rolls, and after reaching the maximum at the delivery roll 0.01 seconds after reaching the maximum, to a cooling rate of 24500 ° C./sec to 790 ° C. And cooled. Next, decarburization annealing was performed in wet hydrogen. Further, the same steel plate was heated to 746 ° C. by induction heating at a heating rate of 250 ° C./second, and was not cooled as it was, but was further heated to 850 ° C. at 15 ° C./second and decarburized and annealed in wet hydrogen. After applying MgO powder to the above two types of decarburized annealed plates, high-temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. Table 7 shows the magnetic properties of the obtained products. Satisfactory magnetism of the product was obtained by the energized roll method. [Table 6] [Table 7] According to the present invention, the unidirectionality having a smaller secondary recrystallized grain size, a higher magnetic flux density, and extremely low iron loss characteristics than ever before by the rapid heating method and the rapid cooling method. Since an electromagnetic steel sheet can be manufactured, the industrial contribution is extremely large.

[Brief description of the drawings]       FIG.   It is a chart of the relationship between the cooling rate in an outlet roll, and an iron loss value.       FIG. 2   FIG. 3 is a schematic view of an embodiment of an electric heating method according to the present invention.

Claims (1)

Claims: 1. A molten steel containing, by weight, C: 0.10% or less, Si: 2.5 to 7.0% and a usual inhibitor component, with the balance being Fe and unavoidable impurities. As a starting material, the strip rolled to the final product thickness is heated to a temperature range of 800 ° C. or more at a heating rate of 80 ° C./sec or more, and within 0.1 second after reaching the maximum temperature,
An extremely low iron loss characterized by performing a cooling treatment at a cooling rate of 150 ° C./sec or more to a temperature range of less than 800 ° C. to 600 ° C. or more , and subjecting the obtained strip to decarburizing annealing and final finishing annealing. A method for manufacturing a grain-oriented electrical steel sheet. 2. The strip according to claim 1, wherein the rapid heating and cooling of the strip is carried out by applying a current between the rolls, whereby the strip is rapidly heated, and the strip is heated on the side on which the strip is heated. Method. 3. The method according to claim 1, wherein the grain-oriented electrical steel sheet is subjected to a treatment for subdividing magnetic domains.