JP3458683B2 - Method for producing non-oriented electrical steel sheet with excellent magnetic properties after strain relief annealing - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet having excellent magnetic properties after strain relief annealing and a method for producing the same, and particularly to Ti which is a harmful element in the production process. It is intended to stably obtain excellent magnetic properties without causing variations in properties after annealing for strain relief even when steel is mixed into steel. 2. Description of the Related Art Non-oriented electrical steel sheets are mainly used as iron cores for rotating equipment and transformers. In order to increase the energy efficiency of these devices, non-oriented electrical steel sheets as core materials are used. It is important to reduce iron loss. In recent years, with the increasing demand for higher efficiency of rotating equipment, etc., there has been a growing demand for non-oriented electrical steel sheets to improve their magnetic properties, especially high magnetic flux density and low iron loss. As for the characteristics, a material of 3.5 W / kg or less at _W15 / ₅₀ is required. [0003] Conventionally, materials having a low iron loss as described above have not been taken into account in the strain relief annealing process, and steel plate manufacturers have been using such materials.
Annealed in a high temperature range exceeding 00 ° C. and controlled to obtain a predetermined particle size, that is, iron loss, and supplied to a motor manufacturer. On the other hand, recently, as a form of use of high-performance electrical steel sheets, a product steel sheet is punched into a predetermined shape by a motor maker or the like, and then subjected to strain relief annealing at 750 ° C. for 2 hours to be used as a motor part. The method of doing is becoming common. The original purpose of the strain relief annealing was to recover the magnetic deterioration (about 0.1 to 2.0 W / kg) due to the strain during shearing. However, at present, the particle size must be reduced at the product stage in order to secure the punching accuracy during shearing.
While it is about 20 to 30 μm, the idea of improving the characteristics by growing crystal grains by subsequent strain relief annealing is becoming popular. As a technique for improving magnetic properties based on the above idea, the present inventors have previously disclosed in Japanese Patent Application Laid-Open Nos. 8-3699 and 8-325678, etc., Ti, Zr, which are impurity elements.
We have proposed a manufacturing technology that focuses on reducing inclusions and controlling inclusions by adding REM, and demonstrated that it is possible to manufacture non-oriented electrical steel sheets with excellent magnetic properties after strain relief annealing. However, when producing a non-oriented electrical steel sheet according to the above-described production technique, sometimes the amount of Ti in the steel fluctuates greatly and the target characteristics cannot be achieved accordingly. Was scattered. Such fluctuations in characteristics not only cause a decrease in product yield, but also pose a problem as threatening stable supply of products. [0007] The inventors of the present invention have conducted analysis in order to solve the above-mentioned problems, paying particular attention to the behavior of Ti.
Ti is reduced by Al and returned to the steel, and the Ti concentration rises.If the Ti concentration rises in this way, 750
It has been found that the magnetic properties of the product tend to fluctuate due to magnetic deterioration after the strain relief annealing at 2 ° C. for 2 hours. Such a reversion of Ti is a phenomenon that is inevitable in current refining metallurgy when the Al content is large, so in order to minimize the property deterioration due to the variation of Ti, it is necessary to use auxiliary raw materials, flux and slag. Strict refining management of Ti contained in the steel is required, which leads to an increase in cost and a decrease in productivity due to a decrease in yield. The present invention advantageously solves the above-mentioned problems. Even when Ti is contained to some extent, excellent magnetic properties can be stably obtained without causing magnetic deterioration after strain relief annealing. An object of the present invention is to propose a non-oriented electrical steel sheet together with its advantageous production method. [0009] The details of the invention will be described below. Table 1 shows that the amount of Al in the steel and the ratio of the magnetically deteriorated coil (iron loss after strain relief annealing was 0.5 W
The following table shows the results of investigations on the relationship between the steel and the steel that has deteriorated by more than / kg) in relation to the increase in the amount of Ti in steel (Ti ≧ 15 ppm). In addition,
Components other than Al were fixed. [Table 1] As shown in Table 1, as Al increases,
The percentage of magnetically degraded coils has increased. Especially, 0.6wt% of Al
In the case of the materials exceeding the above, the effect of improving the magnetism after annealing decreased due to the increase of Ti. It is considered that the increase in Ti in the high Al component system is due to the reduction of Ti oxides in auxiliary materials and slag by Al and returning to Ti in the steel. Turned out to be a problem. As described above, such a phenomenon is unavoidable in the current refining metallurgy process, and in order to minimize the deterioration of characteristics due to the variation of Ti, it is necessary to strictly control the amount of Ti contained in auxiliary materials, flux and slag. Although refining management is required, it is very limited by the current technology, and therefore, the problems of reduced yield and unstable characteristics due to Ti variations are inevitable. Therefore, in order to realize stable production of a product, it is essential to stably obtain excellent magnetic properties after strain relief annealing even in a steel containing Ti to some extent. Under the above-mentioned background, the present inventors have developed Ti
As a result of intensive studies on the relationship between the amount and the low-temperature grain growth property, if the content of Ti, which was conventionally extremely detrimental to grain growth, is within the range of 0.0070 wt%, it can be desulfurized by adding REM. In addition, after reducing O, S, and N to a predetermined level or less and optimizing the processes after hot rolling, 75
It has been found that grain growth can be ensured in strain relief annealing at 0 ° C. for 2 hours, and that the characteristics can be stabilized. The present invention is based on the above findings. That is, according to the present invention, C: 0.005 wt% or less, Si: 0.1 to 3.5 wt%, Mn: 0.1 to 1.5 wt%, Al: 0.
6-2.0 wt%, REM: 0.0002-0.020 wt%, and Ti: 0.0015-0.0070 wt% (but 0.0015 wt%
%, Except for S, O, and N, where S: 50 ppm or less, and O:
40 ppm or less, N: suppressed to 60 ppm or less, the balance is Fe and
Hot-rolling a steel slab that has the composition of unavoidable impurities ,
Then, after performing cold rolling, and performing finish annealing to produce a non-oriented electrical steel sheet, at least once between the finish hot rolling and before the final cold rolling, at a temperature range of 700 to 900 ° C. After heating for minutes to 10 hours, at least
By performing an annealing treatment to cool to 500 ° C at a cooling rate of 50 ° C / min or less, the crystal grain size before strain relief annealing is 35 μm
Below, and the crystal grain size after strain relief annealing at 750 ° C for 2 hours
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties after strain relief annealing characterized by having a steel structure of 65 μm or more. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, experimental results on which the present invention is based will be described. Si: 0.6 wt%, Al: 1.5 wt
%, Mn: 0.6 wt%, P: 0.02 wt%, C: 15 to 20 ppm,
S: 35 ppm, O: 16 ppm, N: 45 ppm and REM: 0.00
A steel ingot containing 5 wt% and changing Ti from 5 ppm to 90 ppm was prepared, and after hot rolling, A: heated at 810 ° C for 2.5 hours, cooled to 500 ° C at 20 ° C / min B: 810 After heating at 500 ℃ for 2.5 hours, cool to 500 ℃ at 100 ℃ / min. C: After annealing at 950 ℃ for 30s, cool to 500 ℃ at 100 ℃ / min, then roll to 0.5mm thickness. Then
Annealed at 850 ° C for 10 seconds to obtain a product. At this time, the particle size of the obtained product plate was 23 to 25 μm. Then 750
After performing the strain relief annealing at ℃ for 2 hours, the magnetic measurement was performed.
The effect of Ti content on grain growth was investigated. FIG. 1 shows the relationship between the amount of Ti and iron loss after strain relief annealing. In addition, the figure also shows the results of the investigation for the case where REM was not added for comparison. Under the conditions of B and C, the magnetism after annealing is not improved in the range where the content of Ti is 15 ppm or more.
It can be seen that the magnetism is improved up to ppm. Also,
It can be seen that the magnetism is further improved by adding REM. Therefore, in the case of Al-added steel, the temperature and cooling rate of heat treatment before cold rolling are important to stably improve grain growth inhibition by Ti, and REM addition contributes effectively. There was found. This phenomenon is thought to be due to the fact that Ti-based precipitates were coarsened and rendered harmless by annealing before cold rolling, resulting in improved grain growth at 750 ° C. It is thought that the form of the object was changed. The fact that the iron loss is reduced more than annealing at a low temperature for a short time when hot-rolled sheet annealing is performed has been a well-known phenomenon for low Ti materials. About Ti by hot rolled sheet annealing with controlled cooling rate
It is a fact discovered for the first time in the present invention that the adverse effect of Ti can be wiped out and the adverse effect can be further reduced by adding REM. Despite the addition of the above process, a non-oriented electrical steel sheet with low iron loss can be obtained stably without variation in operation. Further, according to the study of the inventors, in order to ensure the above-mentioned annealing effect of the hot-rolled sheet, S, O,
It was also determined that the reduction of N was important. Table 2 shows the Si:
1.1 wt%, Al: 1.5 wt%, Mn: 0.6 wt%, P: 0.02 wt
%, Ti: 25 to 30 ppm and REM: 0.001 to 0.002 wt%, and ingots having variously changed S, O, and N contents were subjected to the above-described condition A until strain relief annealing was performed. The result of having carried out the magnetic measurement about the annealed plate which has been shown is shown. [Table 2] As is clear from the table, it is understood that this effect cannot be obtained unless S, O, and N are all reduced. Therefore, in order to effectively improve the magnetic deterioration phenomenon of the strain relief annealing, the reduction of S, O, and N is also an important factor. Next, in the present invention, the reason why the composition of the steel sheet is limited to the above range will be described. C: 0.005 wt% or less C deteriorates magnetic properties due to precipitation of carbides.
Restricted to 0.0050 wt% or less. Si: 0.1 to 3.5 wt% Si is a main element of electrical steel sheets and effectively reduces iron loss by increasing the specific resistance.
If it is less than wt%, the effect is not sufficient, while 3.5 wt%
Exceeds 0.1, the cold workability deteriorates.
Limited to the wt% range. Mn: 0.1 to 1.5 wt% Mn has a function of fixing S as coarse MnS, and for this purpose, it is necessary to contain 0.1 wt% or more. On the other hand, an increase in the amount of added Mn deteriorates the magnetic flux density, so the upper limit is 1.
5 wt%. Al: 0.6 to 2.0 wt% Al, like Si, is a useful element that effectively contributes to the reduction of iron loss by increasing the specific resistance and does not cause the height to rise as much as Si. If the Al content is less than 0.6 wt%, the above-mentioned increase in Ti does not occur, and therefore, the hot-rolled sheet annealing treatment as in the present invention is not particularly required. Therefore, the lower limit of the Al content is set to 0.6 wt%. . However, if the content exceeds 2.0 wt%, the magnetic flux density is greatly reduced.
wt%. REM: 0.0002 to 0.020 wt% REM effectively contributes as a desulfurizing agent, and forms coarse precipitates which suppress the formation of MnS and the like and do not adversely affect the grain growth. However, if the content is less than 0.0002 wt%, the effect of the addition is poor, while if the content exceeds 0.020 wt%, the domain wall movement is hindered and the magnetic properties are deteriorated.
It was to be contained in the range of 020 wt%. The reason why the addition of REM alleviates the degree of grain growth inhibition of Ti is as follows.
Although it is not clear, it is considered that the addition of REM causes some change in the precipitate morphology of Ti, which affects the change in Ti during hot-rolled sheet annealing. S: 50 ppm or less, O: 40 ppm or less, N: 60
S, O, and N, which are less than ppm, are all mixed into steel as impurity elements, and it is desirable to reduce them as much as possible. In particular, S
> 50 ppm, O> 40 ppm, N> 60 ppm, sulfides, oxides and nitrides inhibit domain wall motion and grain growth,
Since it is difficult to improve the magnetic properties, it was limited to the above ranges. Ti: 0.0015 to 0.0070 wt% (however, 0.0015 wt%
Except) Ti is%, carbides, nitrides, to form a sulfide, a great influence component grain growth during strain relieving annealing. In the past, it was necessary to reduce as much as possible.
In Al-containing steel, it is difficult to stably reduce it.
Here, when the Ti content is less than 0.0015 wt%, although the product yield is lowered and the cost is increased, even if the hot-rolled sheet annealing as in the present invention is not performed, the harmful effects of Ti do not particularly occur . If the Ti content exceeds 0.0070 wt%, Ti precipitates hinder domain wall movement and grain growth, leading to deterioration of magnetic properties.
Ti content is 0.0015 to 0.0070wt% (excluding 0.0015wt%)
Limited to the range . Other components are not particularly limited, but elements such as Zr, Mo, V, Cu, Nb, and B, which form sulfides, oxides, and nitrides, should be reduced as much as possible. Is desirable. Further, even when conventionally known Sb, Sn, or Ca is added, the obtained effect is not affected.
In particular, Sb is well known for its effect of suppressing nitriding during annealing, and can be advantageously applied to this material in the range of about 0.005 to 0.10 wt%. Next, the manufacturing process will be described. Converter
The slab is melted by a conventional steelmaking method such as a degassing method, and is made into a slab by continuous casting or ingot-bulking method. Then, the slab is hot-rolled, and both a method of hot-rolling after reheating the slab and a method of direct hot rolling after continuous casting without slab heating are suitable. In addition, REM
It is necessary to desulfurize at the same time, and this is also possible by using a common flux. The heat treatment of the hot-rolled sheet after the hot rolling is the point of the present invention, and an annealing treatment as described below is performed at least once after the completion of the hot rolling and before the start of the cold rolling. . The heating conditions are a temperature of 700 ° C to 900 ° C and a time of 30 minutes or more and 10 hours or less. This is because if the heating temperature is lower than 700 ° C, the effect of improving the grain growth is not seen, whereas if it exceeds 900 ° C, the processing in the subsequent process will increase due to the development of scale etc., causing problems in productivity. Because. If the treatment time is less than 30 minutes, the effect of improving the magnetic properties cannot be obtained, while if it exceeds 10 hours, the productivity also deteriorates. Next, cooling is performed. In the present invention, this cooling treatment is particularly important, and is at least 500 ° C.
Cooling rate to 50 ° C: Slow cooling at 50 ° C / min or less is required. In such a cooling process, the cooling rate is 50 ° C
The reason for limiting the grain growth inhibition caused by Ti is that the grain growth is not improved at cooling rates exceeding 50 ° C / min. Is considered to be related to the growth of Ti precipitates, even if a relatively large amount of Ti is contained, by annealing under the above-described appropriate conditions, the adverse effects of Ti can be eliminated. is there. The above-described hot-rolled sheet annealing may be performed as a heat-retaining heat treatment immediately after the hot-rolling winding, or the hot-rolled sheet may still be heated for 10 minutes.
It may be carried out after controlling the crystal grain size before cold rolling by performing annealing at a high temperature of about 00 ° C. for a short time (10 s), or may be performed using a normal box annealing furnace. Although such hot-rolled sheet annealing causes a slight increase in cost due to an increase in the number of steps, it is a low cost as compared with a decrease in yield and a decrease in productivity due to slippage of Ti in steelmaking, and therefore has a great merit as a total cost. Thereafter, cold rolling and finish annealing are performed. These treatments include a method in which the product thickness is obtained by one cold rolling, followed by finish annealing, and a method in which the product thickness is obtained by performing cold rolling two or more times including intermediate annealing to obtain the product thickness, followed by finish annealing. Is also good. In the case of finish annealing, it is necessary to reduce the particle size to 35 μm or less. This is indispensable for obtaining the punching accuracy of the product, and when the particle size exceeds this, the punching accuracy is deteriorated. In order to obtain such a grain size, it is important to appropriately select the final annealing temperature, and annealing in the range of 700 to 900 ° C is appropriate. This is because, when the final annealing temperature exceeds 900 ° C, the grain growth becomes remarkable, causing not only a problem in the punching accuracy but also excessive grain growth during the final annealing, and the subsequent low-temperature strain relief annealing at 750 ° C. This is because the product does not grow at all, and is no different from the conventionally known low-loss full-process material. It goes without saying that an insulating film may be subsequently formed on the steel sheet surface by a known method. Further, in the present invention, the crystal grain size must be 65 μm or more after the strain relief annealing at 750 ° C. for 2 hours. This is the minimum particle size required to obtain a predetermined iron loss, and unless it is 65 μm or more, an iron loss of W _15/50 = 3.5 W / kg or less cannot be stably obtained. The steel structure that causes such grain growth can be formed by the annealing treatment in consideration of the cooling rate as described above. Conventionally, in high Ti content steels, it has been extremely difficult to reduce the grain size after finish annealing to 35 μm or less and to reduce the grain size to 65 μm or more by 750 ° C. strain relief annealing. Even if the amount is large, a predetermined particle size can be obtained. EXAMPLE 1 Continuous steel casting of molten steel having the composition shown in Table 3 by converter refining and degassing was performed, and the resulting continuously cast slab was reheated and then hot rolled. Thereafter, hot-rolled sheet annealing was performed under the conditions shown in Table 4. Subsequently, a cold-rolled sheet having a thickness of 0.5 mm was formed by one cold rolling, and then subjected to finish annealing at 800 ° C. for 12 s, and further, an insulating film was formed thereon to obtain a product. The particle size of each of the obtained products was 35 μm or less. Then, after shearing to a predetermined size, the steel was subjected to strain relief annealing at 750 ° C. for 2 hours in a nitrogen atmosphere. Then, the crystal grain size was measured, and the magnetic measurement was performed by a 25 cm Epstein method. The results obtained are also shown in Table 4. [Table 3] [Table 4] No. 1 is a low Al material in which the amount of Ti is reduced. However, since such a reduction of Ti requires strict refining management of Ti as described above, the operation is difficult. It was extremely difficult. In addition, although the amount of Ti was reduced, it was contained in excess of the allowable upper limit of 15 ppm, so that a sufficient magnetic improvement effect could not be obtained even by strain relief annealing. In No.3, since the hot-rolled sheet annealing temperature was too low,
Since the cooling rate to 500 ° C. was too high, a sufficient magnetic improvement effect could not be obtained by strain relief annealing. No. 10 is an example where the hot-rolled sheet annealing time was too long.
o.12 is an example in which the hot-rolled sheet annealing temperature was too high. However, although the iron loss properties were good, pickling was extremely difficult due to the remarkable scale development. No.13 is an example of high-temperature and short-time hot-rolled sheet annealing, and No.14
Are examples of cooling at higher speed, but none of them could obtain good iron loss characteristics. On the other hand, those obtained according to the present invention (Nos. 2, 4 to 5, 7 to 9, 11, 15 to 17) were all Ti
Although iron was contained in a relatively large amount of 20 to 30 ppm, excellent iron loss characteristics could be obtained under good grain growth. In view of this, in order to improve magnetic properties by strain relief annealing for steel materials containing a relatively large amount of Al and therefore unavoidable increase of Ti, according to the present invention, RE
Inclusion control by adding M and annealing temperature: 70
0 to 900 ° C, annealing time: 0.5 to 10 hours, then 50
It turns out that it is extremely effective to perform annealing treatment in which cooling is performed at a cooling rate of not more than ℃ / min. Example 2 A continuously cast slab produced in the same manner as in Example 1 and having the composition shown in Table 5 was hot-rolled, and then subjected to hot-rolled sheet annealing under the conditions shown in Table 6. 0.5mm in one cold rolling
After forming a thick cold-rolled sheet, it was subjected to finish annealing at 800 ° C. for 12 seconds, and an insulating film was formed thereon to obtain a product. The particle size of each of the obtained products was 35 μm or less. Then, after shearing to the specified size, 750 ° C, 2
After performing the strain relief annealing for h, the crystal grain size was measured, and the magnetic measurement by the 25 cm Epstein method was performed. Table 6 shows the obtained results. [Table 5] [Table 6] As shown in Table 6, when no REM was added (No. 3) and when the amount of REM added was too large (N
o.5), and when the amounts of S, O, and N in the steel exceeded the allowable upper limits (Nos. 6, 8, and 10), good iron loss characteristics were not obtained. According to the present invention,
Good iron loss characteristics could be obtained in any of the samples to which REM was added and the amounts of S, O, and N were suppressed to predetermined levels. As described above, according to the present invention, it is possible to effectively eliminate the deterioration of the grain growth during strain relief annealing caused by the increase in the amount of Ti mixed in with the addition of a large amount of Al. A non-oriented electrical steel sheet having excellent magnetic properties can be stably obtained without variation in properties.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the influence of the amount of Ti in steel on iron loss characteristics after strain relief annealing, using hot rolled sheet annealing conditions as parameters.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-8-3699 (JP, A) JP-A-5-5126 (JP, A) JP-A-59-100217 (JP, A) JP-A-11- 158550 (JP, A) Table 6-503609 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 8/12 C22C 38/00 303 C22C 38/12 H01F 1/16

Claims (1)

(57) [Claims] [Claim 1] C: 0.005 wt% or less, Si: 0.1 to 3.5 wt%, Mn: 0.1 to 1.5 wt%, Al: 0.6 to 2.0 wt%, REM: 0.0002 to 0.020 wt.%, and the inclusion of Ti: 0.0015 to 0.0070 wt% (excluding 0.0015 wt%) as an impurity is allowed, and for S, O and N, the mixing thereof is S: 50 ppm or less, respectively. : 40ppm or less, N: suppressed to 60ppm or less, the balance is Fe and unavoidable impurities , hot-rolled, then cold-rolled, then subjected to finish annealing and non-directional electromagnetic In producing the steel sheet, after finishing hot rolling, heat at least once in the temperature range of 700 to 900 ° C for 30 minutes to 10 hours before the final cold rolling, and then heat up to at least 500 ° C to 50 ° C / By performing the annealing treatment to cool at a cooling rate of min or less, the crystal grain size before strain relief annealing is 35 μm or less. And 750 ° C., the manufacturing method of the non-oriented electrical steel sheet grain size after stress relief annealing of 2h is excellent in magnetic properties after stress relief annealing, characterized in that the steel structure to be more 65 .mu.m.