JPH0788530B2 - Manufacturing method of non-oriented electrical steel sheet with high magnetic flux density - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a non-oriented electrical steel sheet having excellent magnetic properties, particularly a high magnetic flux density.

[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 sheets are mainly used as iron core materials for transformers, ballasts, electric motors, generators, etc., but to meet the demands for improved characteristics and downsizing of such equipment, low iron loss is required. A non-oriented electrical steel sheet with high magnetic flux density is required.

By the way, a so-called single cold rolling method is well known as a method for producing a non-oriented electrical steel sheet. This is one in which a hot-rolled steel strip is cold-rolled once with a relatively large reduction rate, specifically, a reduction rate of about 70 to 80%, and then annealed.

However, the conventional single cold rolling method cannot completely meet the recent high demands.

Regarding iron loss, there is a measure to reduce eddy current loss by adding an element that increases specific resistance such as Si or Al, but Si and Al have a side effect of reducing magnetic flux density,
Therefore, it is impossible to achieve both low iron loss and high magnetic flux density at a high level even with this kind of measure.

Under such circumstances, various studies have been conducted on non-oriented electrical steel sheets in order to achieve both low iron loss and high magnetic flux density, and various proposals have been made regarding manufacturing methods thereof. For example, in JP-A-58-204126, C0.02% or less, S
i or the total amount of Si and Al is 1.5% or less, Mn is 1.0% or less, P
Using a material of 0.20% or less, rolling end temperature 600 ~ 700 ℃,
Hot rolling is performed at a coiling temperature of 500 ° C or higher, and then Ar ₃
A method of annealing at a temperature below the point for 30 seconds or more and 15 minutes or less has been proposed.

[Problems to be solved by the invention]

This method requires hot rolling under a low temperature condition of 600 to 700 ° C. This is necessary for coarsening the crystal grains during annealing after hot rolling.

However, such hot rolling at low temperatures is difficult to realize from the viewpoint of mill power with the current hot rolling mills.

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

[Means for solving problems]

Generally, in a non-oriented electromagnetic iron plate, if the grain size of the hot rolled plate is coarsened, the grain size and texture of the product stage after the subsequent cold rolling / annealing will be affected and the magnetic properties (iron loss , Magnetic flux density). The method disclosed in the above-mentioned JP-A-58-204126 is also based on this idea, in which low temperature hot rolling and annealing of the hot rolled sheet are combined to increase the grain size of the hot rolled sheet. -ing

In order to find a method for effectively coarsening the crystal grains during annealing of a hot rolled sheet without hot rolling at a significantly low temperature, the present inventors,
In particular, as a result of various experiments and studies from the viewpoint of the steel composition of the raw material, if S and Mn in the raw material were each limited to a specific amount or less, recrystallization and grain growth during hot-rolled sheet annealing were significantly accelerated. It was found that the crystal grains are effectively coarsened by.

In this case, the rolling end temperature of the hot rolling is set to the ferrite region temperature and the winding temperature is set to 600 ° C or lower.

The present invention is based on the above findings, C0.010% or less, Si0.1-1.0%, Mn0.20% or less, P0.200% or less, S0.0
06% or less, Sol.Al less than 0.002% or 0.150 to 1.0%, balance F
Steel material consisting of e and unavoidable impurities, or a steel material containing P0.050 to 0.200% in addition to this steel material is hot-rolled at a rolling end time of 700 ° C or more and at a temperature in the ferrite region, Subsequently, it is wound at a temperature of 600 ° C. or lower, then annealed at a temperature of 650 to 950 ° C., descaled before or after or both, and then cold rolled and annealed. The gist is a method of manufacturing a non-oriented electrical steel sheet having excellent magnetic properties.

FIG. 1 is experimental data showing the relationship between the amount of Mn in steel and the iron loss and magnetic flux density under low S. This is C0.003
%, Si0.5%, P0.085%, S0.002%, Sol.Al0.0008%, and the steel material with various Mn contents in the range of 0.05 to 0.50% has ferrite region temperature (790 ℃). At the end temperature of rolling to a plate thickness of 2.3 mm, then wound at 550 ° C, then descaled and pickled, and then annealed at 800 ° C for 30 minutes for box annealing, and then a 0.5 mm plate. The results are obtained by cold rolling to a thickness, then performing continuous annealing at 760 ° C. for 20 seconds, and investigating the magnetic properties of the thus obtained material.

In the figure, the magnetic flux density tends to be improved as the Mn content in steel decreases, and this tendency is particularly remarkable when Mn is 0.2% or less.

On the other hand, iron loss does not change so much in the range of 0.07 to 0.50% Mn. It is considered that this is because an increase in Mn causes a decrease in iron loss through an increase in resistivity, and as a result, a good iron loss value was obtained even in the high Mn region.

However, the increase of Mn tends to decrease the magnetic flux density.

In any case, low iron loss and high magnetic flux density can both be achieved by lowering S and Mn satisfying the conditions of the present invention.

Incidentally, in the past, Mn in steel is required to suppress hot embrittlement of steel due to S, and is further required to coarsen MnS inclusions in steel, and at least 0.2%.
Was usually added.

Regarding the hot brittleness, the present inventors have confirmed that under the condition of low S, even if the amount of Mn is reduced, there is no practical problem.

Hereinafter, the method of the present invention will be described in more detail.

○ First, the reasons for limiting the ingredients of the steel materials used are as follows.

C: C is preferably as small as possible from the viewpoint of reducing iron loss. C is 0.010
%, The iron loss increase due to magnetic aging becomes particularly remarkable, so the upper limit was made 0.010%. 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 the specific resistance and effectively contributes to the reduction of iron loss, but it also causes the reduction of the magnetic flux density. 1%
Above this, the magnetic flux density is significantly reduced, and the high magnetic flux density, which is the object of the present invention, cannot be achieved. If it is less than 0.1%, a sufficient effect cannot be expected in terms of iron loss. Therefore, 0.
The range was 1 to 1.0%.

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 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 explained with reference to FIG. 1 above, a very high magnetic flux density is realized together with a low iron loss. This is because recrystallization at the time of hot-rolled sheet annealing and coarsening of crystal grains are promoted. The reason why recrystallization and grain growth are accelerated by lowering S and Mn is still unclear, but it is considered that the reason is that the amounts of solute Mn and MnS are both extremely low. To be At a Mn of around 0.2%, the magnetic flux density is particularly reduced, as is apparent from FIG. 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 the amount of P is an unavoidable impurity level (0.001 to 0.030%), the hardness does not increase and no particular problem occurs.

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.
The level of 006% or less is a level that is sufficiently possible with the current clean steel melting technology.

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 removed 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 and Al is 0.150 to 1% or 0.002
The range is 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.

The slab is then hot rolled and then wound.
Then, annealing is performed next, descaling is performed before or after the annealing, or both of them, and then cold rolling is performed to perform annealing.

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

Hot rolling / winding In this process, the rolling end temperature is set to a ferrite region temperature of 700 ° C or higher and the winding temperature is set to 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, it is necessary to set the rolling end temperature to a temperature within the ferrite region.

From the meaning of recrystallization and grain growth during annealing of hot-rolled sheet, the rolling end temperature is sufficient only by the upper limit to be the temperature in the ferrite region, but in reality, when the rolling end temperature falls below 700 ° C, The rolling load becomes too large, and it becomes difficult to operate with a normal rolling mill.

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

On the other hand, the reason why the winding temperature is set to 600 ° C or lower is based on the following experimental data.

FIG. 2 shows the result of investigation on the relationship between the winding temperature and the magnetic characteristics. This is C0.003%, Si0.4%, Mn0.12%, P0.08
Steel material of 5%, S0.001%, and Sol.Al0.225% is hot-rolled with the ferrite region temperature (800 ° C) as the rolling end temperature to make the plate thickness 2.1 mm, and then various values of 500-700 ° C. At 80 ° C and then pickled for descaling
The results are obtained by conducting box annealing at 0 ° C. for 30 minutes, further cold rolling to 0.5 mm, and then performing continuous annealing at 760 ° C. for 20 seconds, and investigating the magnetic properties of the thus obtained material.

In the figure, both the magnetic flux density and the iron loss are very excellent in the region where the coiling temperature is low, particularly in the temperature region of 600 ° C or lower. This is because the grain size was coarsened by annealing the hot rolled sheet. This is the reason why the upper limit of the winding temperature is set to 600 ° C. The lower limit is not specified because there is no problem in lowering the winding temperature in terms of magnetic characteristics. Recently, the winding temperature has been increased to 200 by improving the cooling capacity on the hot rolling hot run table.
Temperatures around ℃ are also possible.

Annealing to hot-rolled sheet This step is for recrystallizing and grain-growing the hot-rolled sheet that has been hot-rolled and wound as described above.

As the type of annealing, either box annealing or continuous annealing can be adopted. 650-900 ℃ for box annealing, continuous annealing
700-950 ℃ is the proper range of annealing temperature. Annealing temperature
The specifications for 650-950 ℃ are 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. Originally, it is advantageous that the annealing temperature is high from the viewpoint of the effect. However, in reality, there are equipment problems. That is, in order to set the temperature above the upper limit value, very expensive equipment is required, and in this case, improvement in performance commensurate with the equipment cost cannot be expected.

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

In principle, cold rolling is performed once, and the rolling reduction is usually about 70 to 80%.

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 900 ° C. × 5 seconds or more for the full-process product, In case of 600 ~ 800 ℃ × 5 seconds or more,
Also in the case of the present invention, conditions similar to this may be applied.

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〕

○ Example 1 Steel of each component composition shown in Table 1 was melted in a converter and formed into a slab by continuous casting, followed by hot rolling to obtain a thickness.
It was set to 2.3 mm and wound on a coil. The rolling end temperature of hot rolling was set in the range of 760 to 810 ° C. Ar of each sample steel
_One transformation point was 850 ° C or higher, and in all cases rolling was completed at temperatures within the ferrite region. The winding temperature is shown in Table 1.

Next, for No. 1 to 14 hot rolled steel strips, pickling → box annealing →
Cold rolling (23 mm → 0.5 mm) → continuous annealing was performed. Also No.
The 15, 16 hot-rolled steel strips were subjected to continuous annealing → pickling → cold rolling (2.3 mm → 0.5 mm) → continuous annealing. Table 1 shows the annealing conditions of the hot rolled sheet and the cold rolled sheet.

With respect to each of the test steel sheets thus obtained, 30 mm × 280 mm Epstein test pieces were sampled from the rolling direction of the steel strip middle portion and 8 pieces each at a right angle to the magnetic characteristics thereof.

The results are shown in the right column of Table 1.

The test results will be described.

○ No. 1 is an example of the present invention of 0.23% Si, which realizes low iron loss and high magnetic flux density.

○ Nos. 2 to 11 are examples in which the composition conditions or the manufacturing conditions were changed for the ultra-low Al steel type of about 0.5% Si.

No. 2 and No. 3 of the present invention having a winding temperature of 600 ° C. or less have excellent iron loss and magnetic flux density as compared with No. 6 in which the temperature exceeds the range of the present invention.

Inventive Example N in which the annealing temperature of the hot rolled sheet is in the range of 650 to 950 ° C
In o.5, both the iron loss and the magnetic flux density are remarkably superior to those of No. 4 in which the annealing temperature falls below the range of the present invention.

No. 7 ~ No. 9 steel composition is substantially the same except for the amount of Mn, Mn amount of the present invention example No. 7 of 0.20% or less, Mn amount exceeds the present invention No. 8 Compared with No.9 and No.9, the iron loss and magnetic flux density are also good.

Nos. 10 and 11 are substantially different only in terms of the amount of S in the steel composition, and in Example No. 10 of the present invention in which the amount of S is 0.006% or less, the amount of S exceeds the range of the present invention. A marked improvement is observed in both of the above characteristics.

○ No. 12 to 14 is an example in which the amount of Sol.Al is changed in a steel type of about 0.5% Si, and the present invention examples No. 12 and 13 in which the amount of Sol.Al is within the range of 0.150 to 1.0% are Sol. .Al content is 0.033% and both properties are better than No.14 which does not meet the conditions of the present invention, and especially remarkable improvement in iron loss is observed.

○ Nos. 15 and 16 are steel types of about 0.8% Si and are examples of the present invention. Compared with the examples of the present invention described above, the magnetic flux density is low due to the high Si content, but the iron loss is remarkably low and the iron loss / magnetic flux density balance is high.

Example 2 Example 1 is the result of magnetically measuring the Epstein test piece after cutting and sampling, and here, No. 1 of Example 1 is used.
The Epstein test pieces taken from 2, 5, 8, 13, and 14 were further subjected to strain relief annealing for 750 × 2 h, and then the magnetic properties were evaluated. This shows the magnetic properties as a semi-processed material.

The results are shown in Table 2.

Nos. 2, 5, and 13 are examples of the present invention, but these showed good magnetic characteristics of low iron loss and high magnetic flux density even after stress relief annealing.

〔The invention's effect〕

As is clear from the above description, the method of the present invention is capable of producing a non-oriented electrical steel sheet having a low iron loss and a high magnetic flux density and excellent magnetic properties, and moreover, as in the prior art, It does not require hot rolling at low temperature, which is very difficult, and does not cause any problems in normal equipment for operation.

Therefore, the present invention can be said to be an extremely significant invention in practice as a measure for improving the performance of the non-oriented electrical steel sheet.

[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, and FIG. 2 is a plot diagram showing the relationship between winding temperature and magnetic properties.

Claims (2)

[Claims] 1. A steel material comprising C0.010% or less, Si0.1 to 1.0%, Mn0.20% or less, S0.006% or less, and Sol.Al0.002% or less, with the balance being Fe and inevitable impurities. Or, a steel material containing P0.050 to 0.200% in this steel material,
Hot rolling is performed at a rolling end temperature of 700 ° C. or higher and a temperature in the ferrite region, followed by winding at a temperature of 600 ° C. or lower, and then annealing at a temperature of 650 to 950 ° C.,
A method for producing a non-oriented electrical steel sheet having a high magnetic flux density, which comprises performing descaling before or after or both, followed by cold rolling and annealing. 2. A steel comprising C0.010% or less, Si0.1 to 1.0%, Mn0.20% or less, S0.006% or less, and Sol.Al0.150 to 1.0% with the balance being Fe and inevitable impurities. Material, or steel material containing P0.050-0.200% in addition to this steel material,
Hot rolling is performed at a rolling end temperature of 700 ° C. or higher and a temperature in the ferrite region, followed by winding at a temperature of 600 ° C. or lower, and then annealing at a temperature of 650 to 950 ° C.,
A method for producing a non-oriented electrical steel sheet having a high magnetic flux density, which comprises performing descaling before or after or both, and then performing cold rolling and annealing.