JP3492965B2 - Cold rolling method to obtain unidirectional electrical steel sheet with excellent magnetic properties - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet used for a core material of electric equipment such as a transformer and a generator. 2. Description of the Related Art A grain-oriented electrical steel sheet must have good magnetizing properties and iron loss properties in the rolling direction. The quality of the magnetization characteristics is determined by the level of the magnetic flux density induced in the iron core in the applied constant magnetic field, and a product with a high magnetic flux density can reduce the size of the iron core. Iron loss is power loss that is consumed as heat energy when a predetermined AC magnetic field is applied to the iron core, and the quality is determined by the magnetic flux density, plate thickness, coating tension,
The amount of impurities, the specific resistance, the size of crystal grains, and the like influence. Among them, it is important that the magnetic flux density is high and the plate thickness is thin in order to reduce iron loss. In recent years, with the progress of manufacturing technology, for example,
Excellent steel sheet with 23mm thickness, magnetic flux density B8 (value at 800A / m magnetizing force) 1.92T, iron loss W17 / 50 (value at 1.7Hz at 50Hz at maximum magnetization) 0.85W / kg Products can be produced on an industrial scale. The grain-oriented electrical steel sheet with such excellent magnetic properties is an easy axis of magnetization of iron <001>
The orientation is composed of a crystal structure highly aligned with the rolling direction of the steel sheet.During final finishing annealing in the manufacturing process, crystal grains having a so-called Goss orientation of {110} <001> orientation are formed. It is formed through a phenomenon called secondary recrystallization that preferentially grows massively. [0004] As a basic requirement for sufficiently growing the secondary recrystallized grains having the Goss orientation, an inhibitor for suppressing the growth of crystal grains having an undesired orientation other than the Goss orientation in the secondary recrystallization process. It is a well-known fact that the existence and the formation of a primary recrystallized structure in which secondary recrystallized grains having a Goss orientation are likely to develop preferentially are indispensable. Here, as inhibitors, AlN, Mn (S, Se), Cu ₂ (S,
A precipitate such as Se) is used, and a grain boundary segregation-type component such as Sn or Sb is additionally used. In the primary recrystallized structure, it is important to form a texture in which the crystal grain size and its uniformity, and the grains having the Goss orientation grains and the orientation grains corresponding to the Goss orientation are aligned in the rolling direction. A method for obtaining a grain-oriented electrical steel sheet having a high magnetic flux density has been known for a long time, for example, Japanese Patent Publication No. 46-23820.
As disclosed in Japanese Patent Publication No.
Methods using N are widely known. In this method, an inhibitor component of AlN is once dissolved by high-temperature slab heating, and AlN is finely precipitated during annealing before final cold rolling to produce a grain-oriented electrical steel sheet. [0006] On the other hand, Japanese Patent Application Laid-Open No. Sho 62-40315 discloses a method in which an AlN inhibitor is formed by a nitriding treatment in a later step to perform low-temperature slab heating. This method was developed in order to avoid the equipment and operational disadvantages of high-temperature slab heating. It is well known that a high magnetic flux density cannot be obtained without an appropriate primary recrystallization structure in a production method using these AlN inhibitors.
The formation of the primary recrystallization structure is greatly affected by the cold rolling conditions,
In general, it is preferable that the rolling reduction in the final cold rolling is as high as 81% or more. [0007] Regarding other cold rolling, (1) Japanese Patent Publication No. 54-13846 discloses that at 50-350 ° C. between passes of strong cold rolling.
The technology of aging treatment for more than a minute is also available.
Japanese Patent No. 9182 discloses a technique for holding at 300 to 600 ° C. for 1 to 30 seconds. The technique (1) is intended for reversal rolling, and the technique (2) is intended for tandem rolling. [0008] High-temperature rolling using a tandem mill is difficult in terms of equipment and operation technology, and at present, high-temperature rolling is performed using the heat generated by the processing of reversal rolling. Utilizes the aging effect. The reversing mill is generally one in which rolls such as 4-ply and 6-ply are arranged in series.However, when the work roll diameter is reduced, roll deformation is likely to occur.In general, large-diameter rolls of 250 mm φ or more will be used. . On the other hand, a Sendzimir mill or an NMS mill in which rolls of 6, 12, 12, or 20 layers are arranged in a cluster form,
The use of small diameter work rolls is possible to back up work rolls from various angles. Since a grain-oriented electrical steel sheet containing a large amount of Si and having a small product thickness has a high rolling reaction force, it is advantageous to use a small-diameter work roll. Therefore, a cluster type reversing mill is often used for high-temperature rolling of a grain-oriented electrical steel sheet. On the other hand, with respect to the work roll diameter of the cold rolling mill, (3) Japanese Patent Publication No. 50-37130 discloses a technique in which rolling is performed with a small-diameter roll having a diameter of 300 mm or less in all rolling passes or a subsequent pass.
(4) According to Japanese Patent Application Laid-Open No. 02-282422, 30 to 10
Technology of warm rolling at 150 to 230 ° C with a small diameter roll of 0 mm φ, (5) Japanese Patent Application Laid-Open No. 05-33056,
The technology of warm rolling at 150 to 350 ° C. with a small diameter roll of 150 mm φ, and (6) Japanese Patent Application Laid-Open No. 09-287025 discloses that the rolling temperature (100 to 100 mm) is increased as the diameter of a work roll (40 to 500 mm φ) is increased.
(~ 350 ° C). [0011] As a cluster mill used for conventional magnetic steel sheets, a Sendzimir mill represented by a 21 or 22 type is mainly used, and from the viewpoint of ensuring thin rollability,
Mainly, small-diameter work rolls of 95 mmφ or less were used. For example, in the technique (5), the roll diameter is set to 50 to 15
Although 0 mm φ is set, only 80 and 90 mm φ are described in the embodiment. Further, in the production of an Al-containing grain-oriented electrical steel sheet, as disclosed in the above-mentioned publication (3), a cold rolled work roll is considered to have a small diameter, and a cluster mill advantageous for thinning is provided. This request was met. Also, as disclosed in the above-mentioned publications (4) to (6), it has been considered that small-diameter rolls are advantageous from the viewpoint of magnetic properties also in rolling on the assumption of an aging temperature between passes. Since the Sendzimir mill represented by the 21 and 22 types basically has an integral housing, the work roll diameter is a fixed value. However, recently, due to technical and technological advances in cluster and mills composed of split housings and the development of NMS mills, work rolls with a diameter of 95 mmφ or more have become available. Then, the present inventors examined in detail the influence of the work roll diameter on the magnetic properties when manufacturing the Al-containing grain-oriented electrical steel sheet by performing aging treatment between passes using a reversing mill. As a result, when using a work roll with a small diameter of 90 mm or less, the magnetic properties are found to deteriorate rather, and a new finding that magnetic properties improve as the work roll diameter increases in the range of 95 to 170 mm φ is improved. discovered. The present invention provides a cold rolling method for obtaining a grain-oriented electrical steel sheet having good magnetic properties based on this finding. [0014] The gist of the present invention is that the mass%
And C: 0.025 to 0.100%, Si: 2.5 to
4.5%, Mn: 0.03 to 0.45%, and A
l: 0.007 to 0.040% .
Cu up to 50%, Sn up to 0.12%, 230pp
m or less of Sb containing at least one of Sb is subjected to hot rolling, then hot-rolled sheet annealing is performed, and then one or two or more times of intermediate annealing are inserted. Rolling, then, primary recrystallization annealing, then, in the method of manufacturing a grain-oriented electrical steel sheet to be subjected to secondary recrystallization annealing, the final cold rolling, the work roll diameter 95-170mm φ cluster type reversal rolling This is a cold rolling method for obtaining a grain-oriented electrical steel sheet with excellent magnetic properties, characterized in that it is held in a temperature range of 100 to 350 ° C. for 1 minute or more at the thickness stage during rolling. . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, test results on which the present invention is based will be described. In mass%, C: 0.055%, S
i: 3.3%, Mn: 0.1%, S: 0.0070%,
Al: 0.0282%, N: 0.0084%, and
An electromagnetic steel slab containing Sn: 0.07% was heated at a low temperature of 1150 ° C. and then hot-rolled to obtain a hot-rolled coil having a thickness of 2.0 mm. After annealing this hot-rolled coil at 1100 ° C.,
Cold rolling was performed at a rolling reduction of 89.0% using a heavy-duty Sendzimir mill to finish the sheet thickness of 0.22 mm. At that time, the work roll diameter of the rolling mill was changed in the range of 50 to 185 mmφ, and the rolling was performed under the same conditions as the pass schedule and the number of passes (six times). Further, at the thickness stage in the second, third, fourth and fifth passes, aging treatment was performed at 200 ° C. for 5 minutes. Then, the primary recrystallized grain size of the cold rolled sheet is 23
After decarburizing annealing by adjusting the temperature to become μm,
Nitriding annealing was performed so that [N] became 215 ppm, and then magnesia was applied to form a coil. After subjecting this coil to finish annealing by a usual method, "insulating coating of phosphoric acid + colloidal silica" was applied, and coating baking and shape correction annealing were performed to obtain a product. Then, the magnetic flux density B8 of this product was measured. FIG. 1 shows the relationship between the work roll diameter and the magnetic flux density B8. From Fig. 1, the work roll diameter is 95-185mm φ
It can be seen that the magnetic flux density B8 is improved in the range. The magnetic flux density of the grain-oriented electrical steel sheet is affected by the inhibitor and the primary recrystallization structure. In this test, since the inhibitor was not changed, it is presumed that the work roll diameter influenced the magnetic flux density through the change in the primary recrystallization structure. Therefore, primary recrystallization samples corresponding to work roll diameters of 50 mm, 110 mm and 165 mm were taken,
The primary recrystallization texture was investigated. X-ray analysis was performed by sampling at a plate thickness of 1 / 5t and analyzed by the SGH method (Harase et al .: Bulletin of the Japan Institute of Metals, Vol. 29, No. 7, P552). FIG. 2 shows the intensity (I _N ) of the Goss orientation around the ND axis and the intensity (IcΣ9) of the azimuth corresponding to Σ9. FIG. 2 shows that when the work roll diameter is large, I _N decreases near 25 ° and IcΣ9 becomes sharper. In order to obtain a grain-oriented electrical steel sheet having a high magnetic flux density, the condition that the primary recrystallization texture should have is that the Goss orientation and the orientation in which goss is preferentially grown are sharp. When the diameter of the work roll is controlled in accordance with the present invention, the degree of Goss accumulation of secondary recrystallization is particularly high in the surface layer portion of the sheet thickness, and a suitable texture is obtained. The above is the result of the low-temperature slab heating method using an AlN inhibitor. As shown in Example 1, the present inventors have found that MnS, AlN + MnS (MnSe) inhibitor and Sn, Sb A high-temperature slab heating method to which Cu, Cu and the like were added as supplementary materials was similarly investigated. As a result, it was confirmed that when the work roll diameter was large, the effect of improving the magnetic properties was remarkable for all the component materials containing AlN as an inhibitor. It is known that AlN has a higher inhibitor strength than MnS (MnSe) and the like and is thermally stable. When such an AlN inhibitor is used, it is presumed that the primary recrystallized texture obtained in the present invention effectively exerts a magnetic flux density improving effect. The mechanism relating to the relationship between the work roll diameter and the primary recrystallization texture is not clear at present, but is presumed as follows.
When the work roll diameter is small, the shear deformation component on the steel sheet surface increases during cold rolling, and after primary recrystallization, (1
It is known that the 10) plane increases and the (111) plane decreases (see Kono et al., Iron and Steel, 68 (1982), p. 58). At this time, with respect to the (110) plane, it is estimated that the orientation group rotated around the ND axis from the Goss orientation increases, resulting in a broad texture that is not preferable for the grain-oriented electrical steel sheet. Next, the reasons for limitation of the component composition of the grain-oriented electrical steel sheet according to the present invention and the preferred composition range will be described. The unit of the amount added is mass%. C is an important element for austenite formation, and 0.025% or more is necessary. If too much, decarburization becomes difficult, so the upper limit is set to 0.100%. If the content of Si is too small, the electric resistance becomes small and good iron loss characteristics cannot be obtained. On the other hand, if the content of Si is too large, cold rolling becomes difficult. Therefore, the content of Si is set to 2.5% or more and 4.5% or less. Mn has a lower limit of 0.03% as an unavoidable component.
On the other hand, if the amount is too large, it is difficult to form a solution of MnS and MnSe on the assumption of high-temperature slab heating.
0.45%. S and Se are appropriately added depending on the type of the inhibitor to be used. These combine with the Mn to form MnS and MnSe which act as inhibitors. The composition range of S and Se is preferably 0.01% or more and 0.04% or less in both cases of single use and combination use. However, MnS
In order to precipitate MnSe finely, high-temperature slab heating is required. On the other hand, in a low-temperature slab heating method in which an inhibitor is formed by a post-step nitriding method, fine MnS,
Since MnSe is an obstacle, S and Se are desirably 0.01% or less. In the present invention, the inclusion of Al as an inhibitor component is indispensable for obtaining a high magnetic flux density, and it is necessary to add a certain amount or more.
If the amount is too large, the heating time of the high-temperature slab for solution becomes long, and the productivity deteriorates.Therefore, the Al content is 0.007% or more.
0.040% or less. N is contained in the range of 0.003% or more and 0.020% or less, assuming that high-temperature slab heating is required, since it is necessary to form AlN in annealing before final cold rolling. On the other hand, in the low-temperature slab heating method, since AlN is formed by nitriding after the primary recrystallization annealing, it is not essential to contain N in the steelmaking stage. In addition to the above, in order to improve magnetism,
n, Sb, Cu, Ni, Cr, P, V, B, Bi, Mo, Nb and Ge
And the like can be appropriately added within a known range.
Next, conditions related to the manufacturing process will be described. In the present invention, a known production method is applied to the production of the steel material. The manufactured ingot or slab is processed as necessary, adjusted in size, heated, and hot-rolled. The slab heating temperature is set in the range of 1100 ° C. to 1450 ° C. as necessary, and a normal gas heating furnace or an induction heating furnace is used for heating. The steel strip after the hot rolling is made to have a final thickness by a single cold rolling method or a multiple cold rolling method. Before cold rolling, it is necessary to perform annealing under known conditions. When high-temperature slab heating is premised, annealing before cold rolling is important to ensure insufficient AlN fine precipitation by hot rolling. On the other hand, when low-temperature slab heating is assumed, hot-rolled sheet annealing for controlling AlN precipitation is not essential, but for controlling carbide and solid solution C,
The combined use of methods such as rapid cooling after annealing, addition of processing strain during the cooling process, and retention for carbide precipitation does not impair the effects of the present invention. Thereafter, the steel sheet is subjected to final cold rolling by reversal rolling. At this time, in order to obtain a high magnetic flux density, a reduction rate of 81% or more is conventionally known. preferable. In the present invention, aging treatment during cold rolling and warm rolling are important for improving magnetic properties. In particular, in the case of high-temperature slab heating, it is known that it is effective from the viewpoint of preventing the generation of linear fine particles, in addition to the effect of fixing solid solution C and N. And in this invention, as shown in Example 2, at the board | substrate thickness stage in the middle of rolling,
It is necessary to maintain the temperature in the temperature range of 100 to 350 ° C. for 1 minute or more. Another feature of the present invention is to produce a grain-oriented electrical steel sheet having excellent magnetic properties by increasing the work roll diameter. As shown in FIG. 1, the magnetic flux density is remarkably inferior when the work roll diameter is 90 mmφ or less,
It is improved at 95mmφ or more, and tends to be almost saturated at 120mmφ or more. Therefore, in the present invention, the work roll diameter is 95 mmφ or more, preferably 120 mmφ or more. The upper limit is set to 170 mmφ, which enables stable rolling of 0.35 mm or less, which is the thickness of a normal unidirectional magnetic steel sheet. Rolling mills are limited to cluster type reversing rolling mills such as 6-high, 12-high and 20-high rolls from the viewpoint of the stability of high-temperature rolling and thin rolling. In addition, rolling mills having such large-diameter work rolls are known as Sendzimir mills or NMSs composed of split housings.
A mill or the like is suitable. [0029] The steel sheet after the final rolling is subjected to a degreasing treatment, and thereafter subjected to an annealing for both decarburization and primary recrystallization. In the case of the low-temperature slab heating method in which the slab heating temperature is 1250 ° C. or less, it is effective to perform a nitriding treatment between the primary recrystallization and the secondary recrystallization to form an AlN inhibitor. As a nitriding method, there is a method in the middle of finish annealing disclosed in Japanese Patent Application Laid-Open No. 60-179885 or a method of mixing "hydrogen + nitrogen + ammonia" while running a strip disclosed in Japanese Patent Application Laid-Open No. 1-82393. There is a method of annealing in gas. Nitrogen amount is 120p for stable development of good secondary recrystallized grains
pm or more, preferably 150 ppm or more. When the primary recrystallization grain size control disclosed in Japanese Patent Application Laid-Open No. 1-82939 is used in combination, the magnetic properties are further improved. Next, the steel sheet is coated with an annealing separator containing MgO as a main component, and then wound into a coil and subjected to final finish annealing. After that, apply insulation coating as needed, laser, plasma, mechanical method, etching,
It is also effective to perform the magnetic domain refining process by another method. (Example 1) An electromagnetic steel slab containing the components shown in Table 1 was heated to high-temperature slabs a), b) and c) at 1350-1400 ° C, and a low-temperature slab at 1150-1290 ° C. Heating d), e) and f)
Hot rolling by the method described above to obtain a hot rolled steel strip. A), c) and f) are two-time cold rolling methods with intermediate annealing, b) and e) are one-time cold rolling methods after hot-rolled sheet annealing, d)
Was a single cold rolling method without annealing of a hot rolled sheet. In the final cold rolling, a reversing mill was used, and the rolling reduction was 63 to 90%. The intermediate plate thickness and the final plate thickness are as shown in Table 1. The cold rolling was performed in three to seven passes while changing the work roll diameter as shown in Table 1. Under all conditions, an intermediate plate thickness of at least two passes during rolling was selected, and aging treatment was performed at 200 ° C. for 5 minutes. The cold-rolled steel strip is subjected to decarburizing annealing in the usual manner. Among them, for d) and e), nitriding annealing is added after decarburizing annealing, and the amount of nitriding shown in the table (after nitriding-before nitriding) Inhibitors were reinforced to become Thereafter, magnesia application, finish annealing, insulating coating, shape correction and baking annealing were performed in a usual manner. The magnetic properties (B8, W17 / 50) of the obtained product steel strip were measured. As shown in the table, it can be seen that a product having excellent magnetic properties can be obtained by controlling the Al-containing component system within the condition range of the present invention. [Table 1] (Example 2) An annealed material having an intermediate thickness of 1.8 mm shown in a) of Table 1 was subjected to 12 different passes shown in Table 2 using a reversing mill having a work roll diameter of 120 mm φ. Under the conditions of holding temperature and time, cold rolling was performed to a final thickness of 0.22 mm. The cold rolled steel strip was subjected to decarburizing annealing, magnesia coating, finish annealing, insulating coating, shape correction and baking annealing in the usual manner. Magnetic properties of the obtained product steel strip (B8, W17 / 50)
Was measured. As shown in Table 2, at the thickness stage during rolling,
It can be seen that a product having excellent magnetic properties can be obtained by maintaining the temperature in the temperature range of 100 to 350 ° C. for 1 minute or more. [Table 2] According to the present invention, it is possible to obtain a grain-oriented electrical steel sheet having excellent magnetic properties in a grain-oriented electrical steel sheet using AlN as an inhibitor. Therefore, the present invention contributes to low iron loss and miniaturization of transformers and the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a relationship between a work roll diameter and a magnetic flux density. FIG. 2 is a diagram showing an analysis result of a primary recrystallization texture of a steel sheet when a work roll diameter is changed.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Shinya Hayashi 1-1, Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works (72) Inventor Toshiyuki Shiraishi 20-Shintomi, Futtsu-shi, Chiba 1 Nippon Steel Corporation Technology Development Division (56) References JP-A-62-40315 (JP, A) JP-A-5-33056 (JP, A) JP-A-9-287025 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) C21D 8/12 B21B 3/02 H01F 1/16 C22C 38/00 303 C22C 38/06

Claims (1)

(57) [Claims 1] C: 0.025 to 0.100 by mass%
%, Si: 2.5 to 4.5%, Mn: 0.03 to 0.4
5% and Al: 0.007 to 0.040%
And 0.50% or less of Cu, 0.12% or less of
Any one or more of Sn and Sb of 230 ppm or less
After hot-rolling the electromagnetic steel slab containing , subjected to hot-rolled sheet annealing, and then subjected to one or two or more cold-rolling interposed intermediate annealing, then, primary recrystallization annealing ,
Next, in the method for producing a grain-oriented electrical steel sheet to be subjected to secondary recrystallization annealing, the final cold rolling is performed by a cluster type reversing mill having a work roll diameter of 95 to 170 mmφ, and at a plate thickness stage during rolling, A cold rolling method for obtaining a grain-oriented electrical steel sheet having excellent magnetic properties, characterized in that the sheet is held in a temperature range of 100 to 350 ° C. for 1 minute or more.