JPH06104865B2 - Non-oriented electrical steel sheet manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a non-oriented electrical steel sheet exhibiting particularly excellent suitability as an iron core material for rotating equipment such as electric motors and generators.

[Conventional technology]

Energy saving is an important issue regardless of the field. In the electric equipment field as well, in recent years, there has been an increasing demand for reduction of electric power consumption, improvement of equipment characteristics, miniaturization of equipment, and the like.

Non-oriented electrical steel sheet is mainly used as a core material for stationary equipment such as transformers and ballasts and rotating equipment such as electric motors and generators. To achieve this, low iron loss and high magnetic flux density are required.

In this case, for non-oriented electrical steel sheet for stationary equipment,
Since the magnetization direction is limited, there is no problem even if the magnetic properties have anisotropy (direction) in terms of device performance, and in some cases it may be advantageous to have anisotropy. Since it is magnetized in all directions of the plate surface, the anisotropy of magnetic properties must be extremely small. As its name implies, non-oriented electrical steel sheets have a certain level of performance regardless of the direction, but when we look at actual non-oriented electrical steel sheets, they usually have anisotropy. . Therefore, a non-oriented electrical steel sheet for iron cores of rotating equipment is required to have low anisotropy of magnetic properties and low iron loss and high magnetic flux density as an average value in all directions of the plate surface. Of.

Here, in the case of a non-oriented electrical steel sheet, the iron loss and the magnetic flux density are usually measured as specified in JIS-C-2550.
Epstan-in samples are taken from the rolling direction and the direction perpendicular to the rolling, but this method cannot properly evaluate the performance of the iron core of equipment that is magnetized in all directions of the plate surface, such as rotating equipment. When a rotating device is used, it is important to evaluate the magnetic properties of a ring sample close to its excited state, and it is important that good properties can be obtained by this test method.

As a method for manufacturing a non-oriented electrical steel sheet, a method called a single cold rolling method is most common. This is a hot rolled steel strip
Cold rolling is performed once with a reduction rate of about 70 to 80%, and then annealing is performed. In this case, even if good characteristics are obtained in the JIS test method of collecting and measuring Epstein samples from the rolling direction and the direction perpendicular to the rolling direction, the anisotropy is large, so that it is not always good when measured with ring samples. In many cases, the characteristics could not be obtained.

From these things, in recent years, good iron loss and magnetic flux density can be obtained even when measured with a ring sample, and the development of a non-oriented electrical steel sheet having good magnetic properties in the sheet surface non-direction has been promoted. Proposals have been made regarding manufacturing methods.

For example, in JP-A-59-123715, the winding temperature after hot rolling is 700 to 900 ° C. and the grain size is 4 or less.
Furthermore, a method has been proposed in which the reduction ratio of cold rolling is set to 85% or more. In addition, JP-A-59-104429 and JP-A-
In 60-125325, the hot rolling end temperature is 600 to 700 ° C.
It has been proposed to combine the cold rolling reduction with 75 to 85%. However, both methods have problems.

[Problems to be solved by the invention]

In the former method, it is difficult to stably coarsen the grain size of the hot-rolled sheet, and good magnetic properties are not always obtained, mainly because the consideration of the component side is insufficient as described later. Absent.

The latter method requires hot rolling under a low temperature condition of 600 to 700 ° C, but hot rolling at such a low temperature is realized from the viewpoint of mill power in the current hot rolling mill. Is difficult.

In view of the above, the present invention has an object to provide a method capable of stably producing a non-oriented electrical steel sheet having excellent iron loss and magnetic flux density in the sheet surface non-direction without performing low temperature hot rolling. .

[Means for solving problems]

Generally, in a non-oriented electrical steel sheet, in order to enhance the magnetic properties in the non-oriented sheet surface without having anisotropy, see
As shown in the -123715 publication, the winding temperature after hot rolling is set to 700 to 950 ° C, the grain size of the hot rolled sheet is coarsened, and cold rolling is performed at a high pressure reduction rate of 85% or more. It is valid. However, this method cannot obtain stable characteristics, and the characteristics are not significantly improved. It is considered that one of the causes for this is that the grain size coarsening of the hot rolled sheet cannot be stably performed.

Therefore, the present inventors have focused on a method for obtaining coarse grains stably in a hot-rolled sheet, especially various experiments from the viewpoint of the material steel composition,
As a result of the examination, it was found that the following facts are effective to obtain coarse grains by limiting the Mn and S in the material to below specified amounts and annealing the hot-rolled sheet. In this case, the rolling end temperature of hot rolling is set to the ferrite region temperature, and the winding temperature is set to 600 ° C. or lower. Then, after that, the hot rolled sheet is completely recrystallized by annealing at 700 to 1000 ° C. and the grain size is coarsened. By carrying out the cold rolling of the hot-rolled sheet with the coarsened grain size in this way at a reduction ratio of 85% or more, stable magnetic properties can be obtained in a non-directional manner on the sheet surface.

The present invention is based on the above findings, C0.005% or less, Si4.0% or less, Mn0.20% or less, P0.200% or less, S0.00
Finishing temperature of steel material containing 6% or less, less than 0.002% Sol.Al or 0.150 to 1.0%, and the balance Fe and inevitable impurities, or steel material further containing P0.050 to 0.200%. Is hot-rolled at a temperature in the ferrite region of 700 ° C or higher, followed by winding at a temperature of 600 ° C or lower, then annealing at a temperature of 700 to 1000 ° C before or after descaling, and 85% or higher. The gist is a method for manufacturing a non-oriented electrical steel sheet, which is characterized by performing annealing after cold rolling at a reduction ratio of.

[Action]

Fig. 1 shows about C0.003%, Si1.
0%, P0.015%, Sol.Al0.250%, S 0.002% and 0.010%
The ferrite region temperature (800 ° C) for steel materials with various Mn contents varying from 0.05 to 0.55%
At the end temperature of rolling to hot rolling to a plate thickness of 4.5 mm, then winding at 530 ° C, followed by continuous annealing at 950 ° C for 30 seconds and subsequent descaling by pickling, followed by rolling down. Cold rolled at 0.5% to 0.5mm, then at 850 ℃
It is the result of investigating the magnetic properties of a ring sample for the thus obtained material after continuous annealing for 20 seconds.

When S is 0.010%, the iron loss rapidly increases with a decrease in Mn, but when S is as low as 0.002%, the iron loss does not increase even if Mn decreases. Moreover, the magnetic flux density increases with the decrease of Mn, and the tendency is remarkable especially when Mn is 0.2% or less. That is, by reducing the Mn and the S, the iron loss and the magnetic flux density are increased in the non-direction of the plate surface.

Although there is no clear reason why low iron loss and high magnetic flux density can be achieved without reducing the Mn and low S in the plate surface direction, the cleanliness of the steel sheet is improved, the grain size of the hot-rolled sheet is coarsened, and the high cooling rate is high. It is considered that the combination of the rolling reductions formed the texture that was advantageous to the magnetic properties during the final annealing.

Note that Mn in steel is conventionally required to suppress hot embrittlement of steel due to S, and is also required to coarsen inclusions MnS in steel, and at least 0.2% is added. It was customary to run.

In the present invention, this Mn is regulated to 0.2% or less, while S
Since it is limited to 0.006% or less, neither hot brittleness nor grain growth poses practical problems.

Hereinafter, the method of the present invention will be described in detail in the order of specific description and examples.

[Specific explanation]

〇 First, the reasons for limiting the components of the steel material used are as follows.

C: C is preferably as small as possible from the viewpoint of reducing iron loss. C is 0.005
%, The iron loss increase due to magnetic aging becomes particularly remarkable, so 0.005% was made the upper limit. It should be noted that the lower limit is not particularly limited because the smaller C is, the more preferable.

Si: Si is an element that increases specific resistance and effectively contributes to iron loss reduction, but if it exceeds 4.0%, the steel strip becomes brittle and problems such as plate cracking occur during cold rolling, so 4.0% or less. And is appropriately determined within this range according to the application. From the viewpoint of magnetic flux density and iron loss, the more preferable range is approximately 0.1 to 1.
%.

Mn: An element having the most important meaning in the present invention.
As described above, conventionally, S is used to prevent hot brittleness and
From the viewpoint of coarsening of MnS, it was usual to add more than 0.2%, but in the present invention, it is 0.2% or less.

Under low S condition, if Mn content is 0.2% or less,
As described above with reference to FIG. 1, low iron loss and extremely high magnetic flux density are also realized in the ring sample. Mn
At around 0.2%, as is apparent from Fig. 1, the magnetic flux density is particularly reduced. Therefore, in the present invention, the upper limit of Mn is set to 0.2%.

The lower limit of Mn is 10 in terms of Mn / S from the viewpoint of hot brittleness.
The above is desirable, but not specified.

P: P is an element capable of increasing hardness and improving punchability without deteriorating magnetic properties, and is added as necessary.
When the amount of Si is low, the hardness of steel tends to be low, but the addition of P is effective in such a case.

The effect of increasing the hardness of P does not appear unless it is contained at least 0.050%. However, if it exceeds 0.200%, the steel sheet becomes brittle, and cold rolling fracture tends to occur. Therefore, when P is positively added, the addition amount needs to be in the range of 0.050 to 0.200%.

Even if P is an unavoidable impurity level (less than 0.050%, usually 0.001 to 0.030%), there is no increase in hardness,
There is no particular problem.

It forms MnS with S: Mn, acts to hinder grain growth during annealing and hinders reduction of iron loss, and causes a hot brittleness when present in a large amount. It is also harmful in promoting recrystallization and grain growth of the hot rolled steel sheet. Such an adverse effect is particularly remarkable in the low Mn steel targeted by the present invention, and therefore, it is required to strictly control the S content.

From such a viewpoint, S is set to 0.006% or less. This S0.00
6% or less is a level that is sufficiently possible with the current melting technology of clean steel.

Regarding S, it is not necessary to specify the upper and lower limits of the characteristics. However, in practice, the feasible range is naturally determined from the viewpoint of steelmaking technology and economic efficiency.

Like Si, Sol.Al:Al is an element that increases the specific resistance and contributes to the decrease of iron loss, but on the other hand, it forms AlN and deteriorates the grain growth property during annealing and acts to increase iron loss. However, this unfavorable effect can be eliminated by increasing the amount of addition and coarsening AlN. In order to bring out the effectiveness against iron loss and eliminate the adverse effects of AlN, it is necessary to add 0.150% or more. However, the addition exceeding 1% causes a decrease in magnetic flux density.

Further, the addition of Al is not always necessary in terms of characteristics. To abandon iron loss effectiveness, one way to eliminate the adverse effects of AlN is to limit the amount of Al to low levels, in which case the allowable amount should be 0.002% or less.

From the above, the amount of Sol.Al is 0.150 to 1% or 0.002%
The range was less than.

○ Next, the manufacturing process will be described.

The raw material steel having the above components is melted in a converter or the like according to a conventional method, and is first cast into a slab by continuous casting or ingot-slab rolling.

This slab is then hot rolled, then wound,
Before or after descaling, annealing is performed, cold rolling is performed, and annealing is performed.

Each step after hot rolling will be described in detail below.

Hot rolling / winding This process is conditioned on the rolling end temperature being 700 ° C or higher and the ferrite region temperature being 600 ° C or lower.

As described above, the present invention has an important point in improving magnetic properties by promoting recrystallization and grain growth in the stage of annealing a hot rolled sheet. In order to sufficiently promote recrystallization and grain growth during annealing of hot-rolled sheet, sufficient strain must be accumulated at the end of hot rolling, and the strain energy must remain unreleased until after winding. I won't. From such a viewpoint, in hot rolling, it is preferable to set the rolling end temperature to a temperature in the ferrite region and to set the winding temperature to a low temperature at which strain energy is not released as much as possible.

In this case, as for the rolling end temperature, from the meaning of recrystallization and grain growth during annealing of the hot rolled sheet, the upper limit of the temperature within the ferrite region is sufficient, but in reality, the rolling end temperature is
Below 700 ° C, the rolling load becomes too large and it becomes difficult to operate with ordinary rolling mills.

From the above, the rolling end temperature was set to 700 ° C or higher and within the ferrite region.

Regarding the winding temperature, when the temperature exceeds 600 ° C, recovery of the steel sheet progresses, recrystallization also begins to occur, strain energy is not accumulated, and grain growth during subsequent annealing of the hot rolled sheet is poor. Become. Therefore, the upper limit of the coiling temperature was set to 600 ° C. It is not necessary to set the lower limit from the viewpoint of suppressing the release of strain energy. Recently, the winding temperature is 200 ℃ due to the improvement of the cooling capacity on the hot rolling hot run table.
Front and back temperatures are also possible.

Annealing of hot-rolled sheet This step is for recrystallizing and grain-growing the hot-rolled sheet that has been hot-rolled and wound.

As the type of annealing, either box annealing or continuous annealing can be adopted. Box annealing 700 to 950 ℃, continuous annealing
800-1000 ℃ is the proper range of annealing temperature. Annealing temperature 7
The rule of 0-100 ℃ is based on this.

The lower limit value of each appropriate range is the temperature required to stably complete the recrystallization in the process. Similarly, the upper limit value is a temperature limit that is allowable from the viewpoint of the balance between the effect of performance improvement and the equipment cost. That is, originally, it is advantageous that the annealing temperature is higher from the viewpoint of effect, but very expensive equipment is required to set the temperature above the above upper limit, and in this case, performance improvement commensurate with the equipment cost can be expected. There will be nothing.

Descaling Descaling is often carried out by pickling, but various mechanical descaling methods such as a combination of shot blasting and a roll bender may be used. Descaling may be performed before or after annealing the hot rolled sheet, or both before and after annealing.

Cold rolling The rolling reduction of cold rolling is one of the important conditions of the present invention.
It must be 85% or more. By performing cold rolling at such a high pressure reduction ratio, the in-plane anisotropy of the magnetic properties of the product is reduced. The upper limit is not set because it is determined solely by operational regulations. In the case of the most common product with a thickness of 0.5 mm, the hot-rolled plate thickness can reach 10 mm at a reduction rate of 95%.
It can be said that further reduction is practically impossible.

Annealing after cold rolling In this annealing, continuous annealing is usually performed for the purpose of recrystallizing the worked structure after cold rolling and adjusting hardness.

Non-oriented electrical steel sheets are full-process products that are shipped with given magnetic properties, and after shipping, they are subjected to stress relief annealing (750 ° C x 2h) after punching and other processing. There are semi-processed products that have magnetic properties.

Even in the case of the full process product, the strain relief annealing may of course be performed on the user side. As a full process product, the specified magnetic properties are exhibited not only at the time of shipment but also when the strain relief annealing is performed by the user side. Is required.

The present invention is intended for both such a full-process product and a semi-process product, but the annealing after cold rolling is generally about 650 to 1000 ° C. × 5 seconds or more for the full-process product,
In the case of a semi-processed product, the temperature is set to 600 to 800 ° C. for about 5 seconds or more, and in the case of the present invention, conditions similar to this may be set.

In addition, when a magnetic steel sheet is manufactured, a step of applying an insulating coating is usually added, but in the case of the present invention, it is possible to add a coating step as a final step of the production. Includes such cases.

〔Example〕

〇Example 1 Steels having the respective compositional components shown in Table 1 were melted in a converter and formed into slabs by continuous casting, followed by hot rolling, hot rolled sheet annealing, cold rolling and continuous annealing. went. The manufacturing conditions are shown in Table 1.

The Ar ₁ transformation point of each sample steel is 850 ° C or higher, and in all cases, hot rolling is completed at a temperature within the ferrite region.

For each test steel plate thus obtained, the outer diameter is 80 mm and the inner diameter is
A 60 mm punched ring test piece was taken to investigate the magnetic properties. The results are shown in the right column of Table 1.

Nos. 1 and 2 show differences in the coiling temperatures of the component systems within the scope of the present invention. No. 2 manufactured at a coiling temperature higher than the range of the present invention is the condition of the present invention. No.1 manufactured in
Both iron loss and magnetic flux density are worse than

Nos. 3 to 7 show the effect of the amount of S, and No. 7 higher than the range of the present invention has poor magnetic properties. No. 8 was manufactured under the same conditions as Nos. 4 and 5, but No. 8 was produced by adding high Al.
4 and 5 show better iron loss.

Nos. 9 to 13 are test materials whose magnetic property results are shown in FIG. 1. Nos. 11 to 13 having Mn outside the scope of the present invention have poor magnetic properties as compared with Nos. 9 and 10 within the scope of the present invention.

Nos. 14 and 15 show the effect of cold rolling reduction. No. 14, which has a rolling reduction lower than the range of the present invention, is inferior in magnetic properties to No. 15 within the range of the present invention. This comparison is based on the ring sample and the difference in characteristics is slight, but as shown in Table 2, in the measurement of the magnetic flux density of the Epstein test piece (width 30 mm x length 280 mm) that is generally performed, No. 14 is better. The variation in magnetic flux density with direction is much larger.

[Effects of the Invention] As is clear from the above description, the method of the present invention is capable of producing a non-oriented electrical steel sheet having excellent magnetic properties with low iron loss in the sheet surface non-direction and high magnetic flux density. Moreover, unlike the prior art, it does not require hot rolling at a low temperature, which is practically difficult, and does not cause a problem in a normal facility for operation.

Therefore, the present invention can be said to be a very significant invention in practice as an improvement of the performance of the non-oriented electrical steel sheet for iron core materials for rotating equipment such as electric motors and generators.

[Brief description of drawings]

FIG. 1 is a plot diagram showing the relationship between the amount of Mn and magnetic properties under low S conditions.

Claims (2)

[Claims] 1. A steel containing C0.005% or less, Si4.0% or less, Mn0.20% or less, S0.006% or less, and Sol.Al less than 0.002%, and the balance Fe and unavoidable impurities. The material, or a steel material containing P0.050 to 0.200%, is hot-rolled at a rolling finish temperature of 700 ° C or higher in the ferrite region, followed by winding at 600 ° C or lower, and then de-rolling. A method for producing a non-oriented electrical steel sheet, which comprises performing annealing at a temperature of 700 to 1000 ° C before or after the scale, cold rolling at a reduction rate of 85% or more, and then annealing. 2. C0.005% or less, Si4.0% or less, Mn0.20% or less, S0.006% or less, Sol.Al 0.150 to 1.0%, with the balance being Fe and inevitable impurities. For steel materials or steel materials containing P0.050 to 0.20%,
Hot rolling at a temperature in the ferrite region above 700 ° C,
Subsequently, winding is performed at a temperature of 600 ° C or less, and then annealing is performed at a temperature of 700 to 1000 ° C before or after descaling,
A method for manufacturing a non-oriented electrical steel sheet having a high magnetic flux density, which comprises performing cold rolling at a reduction rate of 85% or more and then annealing.