JPS60204832A - Production of grain-oriented silicon steel sheet having excellent repeated bending characteristic - Google Patents

Abstract

PURPOSE:To improve the repeated bending characteristic and magnetic characteristic of the titled steel by specifying the surface roughness of the rolling rolls in the final cold rolling pass of a silicon steel slab as well as the oxygen weight of the surface oxide formed in the stage of decarburization annealing within a prescribed range. CONSTITUTION:A silicon steel slab contg. 2.5-4wt% Si is subjected to hot rolling and further to one pass or >=2 passes of cold rolling stages including intermediate annealing. The surface roughness Ra (measured in terms of center line average height Ra and the unit is mum) of the rolling rolls in the final cold rolling pass in said cold rolling stages is controlled to <=-[Si%]X0.27+1.18. The oxygen weight of the oxide layer formed on the surface of the steel sheet in the decarburization annealing following said rolling is adjusted to 1-2.2g/m<2>. A separating agent for annealing consisting essentially of MgO is then coated thereon and the steel sheet is subjected to final finish annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a unidirectional silicon steel sheet, and particularly to a method for manufacturing a unidirectional silicon steel sheet with excellent repeated bending properties.

Generally, unidirectional silicon steel sheets are Si4. After hot rolling a silicon steel slab containing Os (wt%, same hereinafter) or less and subjecting it to hot-rolled plate annealing as necessary, one cold rolling or two or more times with intermediate annealing in between. The final product thickness is achieved through a cold rolling process consisting of cold rolling, followed by primary recrystallization annealing that also serves as decarburization, and final finish annealing (+1
0) Develop secondary recrystallized grains with the [001) orientation and form a forsterite insulating film, then apply and bake a phosphate-based insulating film and flatten to remove the coil set. Manufactured through a series of annealing steps.

When using the unidirectional silicon steel sheet produced in this way as a core material for transformers, motors, etc., it is usually subjected to slitting or punching, and when it is processed into a wound core. is subjected to deformation such as small diameter bending. If the steel plate is broken or cracked during such processing, it becomes impossible to manufacture the iron core. Therefore, JIS C2553 stipulates that grain-oriented silicon steel strips be subjected to repeated bending tests in order to prevent breakage and cracking during processing due to brittleness, and also describes the method of repeated bending tests. is JIS C2550
stipulated in If, as a result of such repeated bending tests, it is found that the repeated bending properties are poor, the product must be discarded even if the magnetic properties such as iron loss properties are excellent. Therefore, it can be seen that the grain-oriented silicon steel strip L1 not only has excellent magnetic properties such as core loss properties but also good repeated bending properties.

By the way, in recent years there has been an increasing demand for energy and resource conservation, and there has been a strong demand for low iron loss in transformers. Products with even lower iron loss have become popular, and recently there has even been a trend to achieve lower iron loss even at the expense of some degree of magnetic flux density. As described above, a well-known method for reducing iron loss in a oriented silicon-copper strip is to increase the amount of 5ill in the steel to increase the electrical resistance of the base steel and reduce eddy current loss. . However, it is known that steel sheets become brittle if the amount of Si is excessive, and research conducted by the present inventors has revealed that if the amount of Si exceeds 3.4%, the cyclic bending properties will be significantly reduced. There is.

That is, the 5iIt of a normal grain-oriented silicon steel sheet is around 3%, but the inventors have determined that the Si ii is 2.5 to 4.0.
When the influence of the amount of Si on the repeated bending characteristics of the product was investigated by changing the amount of Si within a range of 1.5%, the results shown in FIG. 1 were obtained. As is clear from Figure 1, there is a marked tendency for the repeated bending characteristics to decrease as the SI amount increases, and in particular, when 5ill exceeds 34%, the number of repeated bends decreases significantly to 5 times or less. Some product boards were also found to have been bent repeatedly 0 times. In this case, the rolling roll surface roughness (center line average roughness; Ra) of the final cold rolling bath in the process of producing unidirectional silicon steel sheets is 0.25 to 0.30 μm, which is the level normally carried out.1 The surface after decarburization annealing The oxygen basis weight of the oxidized layer was in the range of 1.5 to 2.0 bar.

By the way, as a method for improving the repeated bending characteristics of a unidirectional silicon steel sheet, a method described in Japanese Patent Publication No. 58-32216 has already been proposed. According to this proposal, in the manufacturing process of grain-oriented silicon steel sheets, the final finish annealing conditions are regulated so that the N in the product sheet is 1 Oppm or less and the S is 0.0.
It is said that the repeated bending characteristics of the product will be improved by reducing it to 0.01 inch or less. However, even if this proposed method is adopted, if the SL amount is 3.4 inches or more, the desired repeated bending characteristics cannot be obtained. In other words, the data shown in FIG. 1 based on the experiments conducted by the present inventors is based on the manufacturing process proposed above. As mentioned above, although an improvement in the characteristics is observed, the repeated bending characteristics deteriorate rapidly.

On the other hand, it is known that by improving the surface condition of unidirectional silicon steel sheets, even lower iron loss values can be obtained.
For example, literature (Journal of AppliedP
hysics; Vol, 41.47. June
1970: pp. 2981-2984) describes that an extremely low core loss value can be obtained by removing the glass film on the surface of a silicon steel product plate and chemically polishing it to improve the surface roughness. Therefore, according to this method, SIJ! It is considered that it is possible to improve the iron loss value without causing deterioration of the repeated bending characteristics due to the increase. However, in the case of the method described in this document, the glass film film on the product board is removed and chemically polished, so the glass film must be attached in a separate process using one of the methods after chemical polishing. It is extremely difficult to put this method into practical use on a mass production scale, and even if it were put into practical use, the process would become complicated and the cost would rise significantly, making this method impractical.

This invention was made against the background of the above-mentioned circumstances, and it is an object of the present invention to develop a method for actually producing a unidirectional silicon steel sheet that simultaneously satisfies excellent repeated bending properties and excellent magnetic properties (particularly low core loss). The purpose is to provide

In order to achieve the above object, the present inventors conducted various experiments and studies on the factors that affect the cyclic bending characteristics of unidirectional silicon steel sheets, and found that the cyclic bending characteristics It has been found that the decarburization is greatly affected by the degree of decarburization and the oxygen basis weight of the surface oxide layer formed on the surface of the steel sheet during decarburization annealing.

As a result of further investigation, the surface roughness of the rolling roll in the final cold rolling pass was set to be below a certain value depending on the amount of Si.
At the same time, by adjusting the oxygen weight of the surface oxide layer generated during decarburization annealing within a certain range, excellent repeated bending properties can be obtained, and by increasing the amount of Si under these conditions, repeated bending properties can be obtained. They discovered that it is possible to achieve a low iron loss value without causing any deterioration of the iron, leading to the creation of this invention.

That is, the method of the present invention hot-rolls a silicon steel slab containing 2.5 to 4.0% Si, and further cold-rolls it once or twice or more with intermediate annealing in between to reduce the thickness of the final product. Then, after performing primary recrystallization annealing that also serves as decarburization,
In a method for manufacturing a unidirectional silicon steel sheet that includes a series of steps of final finish annealing, the surface roughness of the rolling roll in the final cold rolling pass of the cold rolling step is adjusted to a center line average roughness Ra according to the SI amount. ) and Ra (ttm)≦−(Si amount) X O,27+
1.18, and the oxygen basis weight of the surface oxide layer generated on the steel plate surface by subsequent decarburization annealing is adjusted within the range of 1.0 to 2.2 f/rrl. It is characterized by:

The method for producing a unidirectional silicon steel sheet according to the present invention will be explained in more detail below.

First, to explain the relationship between the rolling roll surface roughness in the final cold rolling pass of the cold rolling process in the normal manufacturing process of unidirectional silicon steel sheets, the present inventors have developed unidirectional silicon steel sheets with various Si contents. In manufacturing the product, the surface roughness of the rolling roll in the final cold rolling pass (measured by centerline average roughness Ra) is changed, and the number of repeated bending of the product is determined according to JIS C
As a result of the repeated bending test specified in 2550, it was found that there was a relationship as shown in FIG. At this time, the oxygen basis weight line of the surface oxide layer after decarburization annealing was 1.5 to 1.9 Y/mj. As shown in Figure 2, even if the Si content of the steel plate increases, the rolling roll surface roughness (Ra) can be reduced to increase the smoothness of the steel plate surface. , it can be seen that a good repeated song can maintain its characteristics. In order to obtain 5 or more repeated bending times, which can be evaluated as having good repeated bending characteristics, the rolling roll surface roughness Ra should be adjusted to fall within the area below line A in Figure 2 according to 5iill. It turned out that it was necessary to control the That is, the area below line A in FIG. 2 is Ra (ttm)≦-[Si'%)Xo
, 27+1.18. Therefore, good repeated bending characteristics can be obtained by controlling the rolling roll surface roughness Ra according to the amount of Si so that it satisfies the above formula.

In addition, the final rolling roll surface roughness Ra in the cold rolling process is
Magnetic properties are also improved by reducing the amount of Si in proportion to the amount of Si and increasing the smoothness of the surface of the steel sheet.In particular, increasing the amount of Si makes it possible to simultaneously improve the iron loss value and ensure sufficient repeated bending characteristics. .

As described above, reducing the surface roughness of the mill roll in the final cold rolling pass can be achieved by making the abrasive grain finer during final polishing of the mill roll.

That is, the abrasive grain size in conventional general final polishing of cold rolling rolls is about 120 J, and the roll surface roughness Ra in this case is 0.25 to 0.3011 m. The amount of Si on straight line A in the figure is 3.44 to 3.
26%, it is difficult to ensure that the number of repeated bending of a steel plate with 5ilj13.4% or more is 5 times or more, and in particular, with a steel plate with a Si content of 3.45% or more, the repeated bending characteristics are significantly reduced. I end up.

On the other hand, if the abrasive grain size during final polishing is set to 600J, for example, and the roll is polished for the final cold rolling pass, the surface roughness f'i will be reduced by 0.05 to 0.1 μm Km,
Even when the sl amount is 3.45% or more, it is possible to reliably ensure repeated bending times of 5 or more times and maintain excellent repeated bending characteristics. Furthermore, in order to make the surface roughness 0.05 μm or less, the abrasive grain size may be made finer than ÷600. In this way, by simply increasing the abrasive grain size during final polishing of the rolling rolls in the final cold rolling bath, it is possible to reduce the roll surface roughness and improve the cyclic bending characteristics even with a high Si content, which leads to an increase in costs. It is possible to implement it on a mass production scale without any problems.

Next, the relationship between the number of oxygen per unit area of the steel sheet in the oxide layer on the surface of the steel sheet generated during decarburization annealing after the final cold rolling, that is, the oxygen basis weight, and the repeated bending characteristics of the product sheet will be explained.

Generally, in the manufacturing process of unidirectional silicon steel sheets, after the final product thickness is achieved through a cold rolling process, decarburization annealing is performed which also serves as primary recrystallization annealing. In this decarburization annealing, SiO□ and An oxide layer mainly composed of iron oxide is generated. After that, an annealing separator mainly composed of MgO is applied onto the oxide layer, and the annealing separation agent is applied to the oxide layer in a hydrogen atmosphere.
By performing final annealing at 1200° C., a forsterite-based insulating film is formed on the surface of the steel sheet, and excellent magnetic properties are obtained. Therefore, the generation of a surface oxide layer during decarburization annealing is essential for ultimately forming a forsterite insulating film and obtaining excellent magnetic properties. The present inventors have newly discovered that the amount has a large effect not only on the magnetic properties of the final product but also on the repeated bending properties.

That is, when hot rolled silicon steel material containing 3.50% Si is cold rolled to obtain the final product thickness, the surface roughness Ra of the roll roll of the final cold rolling bath in the cold rolling process is set to 0.0!5.
/jm, (controlled at 3 levels of 1, 2 μm, 0.5 μm,
Next, when performing decarburization annealing, the atmosphere was changed to adjust the oxygen basis weight of the surface oxide layer produced by the decarburization annealing to a range of 0.3 to 3.5. After that, an annealing separator mainly composed of MgO (i-) was applied in accordance with a conventional method and final annealing was performed, and the repeated bending characteristics of each product sheet obtained were examined by a repeated bending test specified in JIS C2550. It has been found that there is a relationship as shown in FIG. 3 between the oxygen basis weight of the surface oxide layer by decarburization annealing, the roll surface roughness of the final cold rolling bath, and the repeated bending characteristics.

As is clear from FIG. 3, if the oxygen basis weight exceeds 2.2 bar, the repeated bending characteristics of the product sheet will deteriorate significantly even if the roll surface roughness in the final cold rolling bath is extremely small.

The reason for this is thought to be that when the amount of oxygen per unit area is large, the unevenness at the interface between the base metal becomes significantly large and deteriorates the repeated bending characteristics, regardless of the roll surface roughness in the final cold rolling bath. . On the other hand, when the oxygen basis weight is less than 1.0 f/m, the repeated bending properties of the product plate do not deteriorate and are actually good, but the magnetic properties deteriorate significantly and the appearance of the coating is significantly impaired. Therefore, it has been found that in order to satisfy both magnetic properties and repeated bending properties, the oxygen basis weight needs to be within the range of 1.0 to 2.277 m. Therefore, in the method of the present invention, the roll surface roughness Ra of the final cold rolling bath is controlled according to the amount of Si as described above, and the decarburization annealing step is performed with the oxygen basis weight of the surface oxide layer produced thereby. The amount was adjusted so that it was within the range of 10 to 22".

In order to adjust the oxygen basis weight in this way, it is sufficient to adjust the atmosphere of warm coal annealing, but it goes without saying that it is also affected by the annealing time and annealing temperature.

As described above, in the method of the present invention, control of the roll surface roughness of the final cold rolling waste and adjustment of the oxygen basis weight in decarburization annealing are basically essential requirements, and other steps and conditions are not considered. may be the same as a conventionally known method. That is, after hot rolling a silicon steel slab, hot-rolled plate annealing and pickling are performed as necessary, and cold rolling consists of one cold rolling or two or more cold rolling with intermediate annealing in between. The thickness of the final product is obtained through the process, and after decarburization and primary recrystallization annealing, an annealing separator containing MgO as a main component is applied and final annealing is performed.

Examples of the present invention will be described below along with comparative examples.

Example 1 Three samples with Si contents of 3.05, 3.35, and 3.55
Above the standard, both Mn0.0 as an inhibitor.
Six 200-day thick continuously cast silicon steel slabs containing 70%, SeO, 025%, and SbO, 028% were prepared, and after heating each slab to 1380°C for 1 hour, 2. It was hot rolled to a thickness of 5 cm and wound into a coil. Next, each coil was held at 980° C. for 30 seconds, cold rolled to a thickness of 0.75 tll, and then intermediate annealed at 950° C. for 2 minutes. Then, when final cold rolling was carried out to finish to a thickness of 0.30111, the surface roughness (Ra) of the rolling roll of the final scrap was changed to three conditions: 0.13 μm, 10.38 μm, and 0.55 μm. After that, when performing primary recrystallization annealing that also serves as decarburization in wet hydrogen at 800°C, the atmosphere was changed to g#1
The oxygen basis weight of the surface oxide layer was adjusted to 1.7 t/m.
Two levels of 2.5 P/m' were applied, and then an annealing separator mainly containing MgO was applied, final annealing was performed by box annealing, and an insulating coating was applied to obtain a unidirectional silicon steel sheet product. The final annealing was performed at 860°C during the heating process for 30°C.
After holding for a certain time, annealing was subsequently performed at 1200° C. for 10 hours. Table 1 shows the results of examining the repeated bending properties and magnetic properties of the product thus obtained.

From Table 1, it can be seen that the product sheet of the present invention example that was manufactured satisfying the final cold-rolled bath roll surface roughness conditions and the decarburization annealing oxygen basis weight conditions of the present invention satisfies one or both of these two conditions. It is clear that the repeated bending characteristics are extremely superior by 9 points compared to the product sheet of the comparative example which was manufactured with a deviation from the standard, and the magnetic characteristics are also good.

Example 2 3 with S1 content of 3.00%, 3.35%, and 3.55%
levels, and both contain Mn as an inhibitor.
0.067 Z, SO, 22 containing 0.023%
Prepare 6 continuous cast silicon steel slabs each with a thickness of 0W, heat each slab to 1360℃ for 1 hour, and then heat the slab to 2.5℃ using a conventional method.
It was hot rolled to a thickness of 11011 mm and wound into a coil. These hot-rolled coils were then pickled and cold-rolled into a 9.75m5 warehouse, followed by intermediate annealing at 900°C for 5 minutes, and then final cold-rolled to a temperature of 0.30 days. The rolling roll surface roughness is 0.13 μm.

Finishing was carried out under three conditions: 0.38 μm and 0.55 μm. Thereafter, for decarburization and primary recrystallization annealing in wet hydrogen at 800°C, the atmosphere was adjusted to give two levels of oxygen basis weight: 1.7 f/rrl and 2.5μ, and then MgO was added. After applying the annealing separator as the main component, a final annealing was performed in which the temperature was immediately raised to 1170° C. and held for an IQ time using box annealing to obtain a unidirectional silicon steel sheet product. Regarding the product sheet obtained in this way, the repeated bending characteristics
Table 2 shows the results of examining the magnetic properties.

From Table 2, according to this invention, ll! It is clear that the remaining product plates of the inventive examples have significantly superior repeated bending properties and magnetic properties compared to those of the comparative examples.

As is clear from the above explanation, the method of the present invention has the effect of making it possible to actually KIR-manufacture a unidirectional silicon steel sheet that has excellent repeated bending properties and excellent magnetic properties at the same time. In particular, iron loss characteristics should be improved (S
Excellent cyclic bending properties can be ensured even when the amount of i is increased, so even in that case, the failure rate in cyclic bending tests can be significantly reduced, contributing to improved yields and, ultimately, to lower production costs. can. Further, the method of the present invention has the advantage that there is no particular problem in implementing it on a mass production scale, and it does not particularly cause an increase in manufacturing costs.

[Brief explanation of drawings]

Figure 1 is a correlation diagram showing the relationship between 5iil in steel and the number of repeated bending of a unidirectional silicon steel plate manufactured under conventional general method and process conditions. Figure 2 is a unidirectional silicon steel plate product. A correlation diagram showing the effect of the final cold rolling pass roll surface roughness (Ra) and the amount of Si in the steel on the number of repeated bending. FIG. 2 is a correlation diagram showing the influence of unidirectional silicon steel sheet products on the number of repeated bendings. Applicant: Kawasaki Steel Co., Ltd. Agent: Taketo Toyota, patent attorney (and one other person)

Claims (1)

[Claims] Si2.5 to 4. A silicon steel slab containing Owt % is hot-rolled, and then subjected to one or more cold-rolling steps with intermediate annealing to achieve the final product thickness, and then subjected to primary recrystallization annealing that also serves as decarburization. A method for manufacturing a grain-oriented silicon steel sheet comprising a series of steps of applying an annealing separator containing MgO as a main component and subjecting it to final finish annealing. Roughness is expressed as center line average roughness (Ra) depending on the amount of Si: na (pm)≦-(84%:] X O, 27+
1.18, and adjust the oxygen basis weight of the surface oxide layer generated on the steel plate surface in the subsequent decarburization annealing to be within the range of 1.0 to 2.2 ff7m. A method for producing a unidirectional silicon steel sheet with excellent repeated bending properties.