JPH0819467B2 - Non-oriented electrical steel sheet manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a non-oriented electrical steel sheet.

[Conventional technology]

In recent years, there has been a strong demand for high magnetic flux density in electromagnetic steel sheets used as core materials, centering on high efficiency of small motors and the like.

Against this background, the so-called low grade electrical steel sheet with Si ≦ 1.0% has a feature that the magnetic flux density is high although the iron loss is relatively high, and therefore the demand thereof is increasing. In response to this, many efforts have been made to improve the properties of low-grade electrical steel sheets and reduce manufacturing costs. Among them, regarding the reduction of manufacturing costs, conventional "continuous casting → cooling to room temperature → slab reheating → hot rolling" Instead of the so-called reheating method, after continuous casting, hot rolling is performed without reheating using sensible heat of the slab or after light heating, the so-called direct-feed rolling method is a rolling method that can reduce the heating unit consumption. It is getting attention.

As is generally known, in the production of magnetic steel sheets, in order to reduce iron loss, which strongly depends on grain size, in particular, precipitation and coarsening of MnS and AlN that inhibit grain growth are required, This becomes extremely difficult when the above-mentioned direct feed rolling is performed. This is because in the reheating method, precipitation and coarsening of MnS and AlN are naturally achieved while the slab is gradually cooled to room temperature after continuous casting and during slab temperature increase during reheating. In the method, the time spent for lowering the temperature of the slab (including the temperature increase at the time of light heating) is extremely shorter than that in the reheating method, and as it is, precipitation of MnS, AlN during this period This is because coarsening cannot be expected so much. Therefore, in order to solve such a problem, the following techniques have been conventionally disclosed.

JP-A-52-108318 and JP-A-54-41219 Hold the slab for more than 40 minutes at around 900 ° C to precipitate and coarsen MnS and AlN, then reheat to around 1100 ° C and perform hot rolling. .

JP-A-58-123825 S has an extremely low S of 0.003% and is virtually free of MnS, or Ca and REM are added to facilitate precipitation and coarsening of MnS, and then the slab is 900-1150. Hold for more than 30 min at ℃,
After that, hot rolling is performed.

JP, 60-190521, A Slab is gradually cooled to 900 ° C or less, and is subjected to hot rolling after precipitation and coarsening of MnS and AlN.

[Problems to be Solved by the Invention]

As described above, various techniques for precipitation / coarsening of MnS and AlN have conventionally been disclosed, but each of them has the following problems, and it cannot be said to be sufficient.

JP-A-52-108318, JP-A-54-41219 It is necessary to maintain at a high temperature for a long time, and the surface property is deteriorated due to an increase in scale during that time. Further, when the heat retaining cover is used to prevent the scale from increasing, it takes a long time to hold the heat retaining cover itself, and it also takes time to attach and detach the heat retaining cover, resulting in a decrease in productivity. Further, since reheating is indispensable, the significance itself of direct feed rolling for the purpose of reducing the heating unit is diminished.

JP, 58-123825, A The steelmaking cost is high because of extremely low S and addition of Ca and REM.
In addition, the above-mentioned JP-A-52-108318 and JP-A-54-41219
Similar to No. 6, it requires high temperature and long-term holding, and therefore causes the same problems as those.

JP, 60-190521, A The slow cooling of the slab is insufficient for the precipitation and coarsening of MnS and AlN, which causes an increase in iron loss. Also, the start of hot rolling
Since the temperature is 900 ° C or less, the load on the mill increases significantly and it becomes difficult to secure the coiling temperature, resulting in recrystallization of the hot rolled sheet.
The magnetic properties are deteriorated due to insufficient flow growth.

As described above, the conventional techniques have problems in any of the characteristics, productivity, and cost.

In view of such circumstances, the present invention intends to provide a method for producing a non-oriented electrical steel sheet that can fully demonstrate the significance of direct rolling, which is low cost, without lowering magnetic properties and productivity. is there.

[Means for solving the problem]

The inventors of the present invention have conducted earnest researches on the conditions when applying direct rolling to the production of low-oriented non-oriented electrical steel sheets with Si ≦ 1.0%, and as a result, optimized the Mn, S, Al amounts and Mn / S ratio. After continuous casting of the steel slab of the specified component that was performed, when it is cooled to a specific temperature range below a specific cooling rate determined according to the component, the precipitation and coarsening of MnS and AlN are accelerated, therefore, After that, it is newly found that a non-oriented electrical steel sheet having magnetic properties equivalent to or better than that of the reheating method can be obtained simply by hot rolling immediately without holding the slab at a high temperature or reheating. Then, the method of the present invention has been completed.

The present invention is constructed based on technical recognition or elements as described below.

(1) Low grade steel with Si ≦ 1.0% is originally excellent in grain growth due to being a low Si steel, and the iron loss value required is not so severe. It can be said that it is a material suitable for the direct-rolling method in which deterioration is a concern (Si> 1.0%
High-quality materials are at the opposite end of this).

(2) Precipitation and coarsening of MnS are considered to be mainly diffusion-controlling Mn, and increase the amount of Mn to promote precipitation and coarsening of MnS.

(3) Further, by increasing the Mn / S ratio, precipitation and coarsening of MnS are further promoted, and the grain growth property is not impaired.

(4) Regarding S, the prior art is directed to MnS-free by making the S extremely low, but in the method of the present invention, the idea is completely opposite. That is, in the method of the present invention, since MnS is utilized as a nucleus for precipitation / coarsening of AlN, Sn is added in a required amount.
Secure the required number. However, needless to say, excessive S addition causes Mn / S ratio to increase, even if MnS is coarsened.
The absolute amount of nS itself increases unnecessarily and deteriorates the grain growth. Therefore, the upper limit of S is determined from this point.

(5) As described above, the coarse and sufficient amount of MnS deposited is A
Since it acts as lN precipitation nuclei, AlN precipitation and coarsening are promoted. In that case, as with MnS, the precipitation and coarsening of AlN are mainly
Since the diffusion rate of Al is limited, the required amount of Al is more than the required amount.

(6) As described in (2) above, the Mn / S ratio requires a certain value or more for MnS coarsening, but at the same time, there is an upper limit. This is because if the Mn / S ratio is excessively high, precipitation of AlN
MnS, which should be the core of coarsening, becomes too coarse. As a result, MnS
This is because the number of AlN decreases and the precipitation and coarsening of AlN is delayed. Furthermore, the upper limit of this Mn / S ratio should be determined according to the amount of Al. That is, as the amount of Al increases, the precipitation / coarsening of AlN accelerates, and the minimum required amount of MnS that serves as a nucleus that assists the precipitation / coarsening of AlN is reduced.

(7) After continuous casting, the slab whose composition has been adjusted to promote the precipitation and coarsening of MnS and AlN in this way is cooled at a specific cooling rate or lower, and during this time the precipitation and coarsening of MnS is mainly detected. Give it. Here, the specific cooling rate or less, even if the steel adjusted the composition as described above,
This is because if the cooling rate is too fast, sufficient time for precipitation and coarsening of MnS cannot be secured. The upper limit of this cooling rate is determined according to the Mn amount and the Mn / S ratio that influence the precipitation and coarsening of MnS, and the minimum amount of MnS nuclei necessary for precipitation and coarsening of AlN depends on the Al amount. Changes, so A
Needless to say, it depends on the quantity. In addition, it is necessary to consider the lower limit of the cooling rate. Of course, slower cooling is more preferable for precipitation and coarsening of MnS, but extreme slow cooling is practically equivalent to the heat retention performed by the conventional technology, resulting in deterioration of surface shape and productivity. Because.

(8) The temperature range in which the slab should be cooled is also important. That is, if this temperature is too low, cracks due to insufficient deformability of the slab will occur in the subsequent hot rolling, or the mill load will become excessive and it will be necessary to reheat the slab. on the other hand,
If the temperature is too high, the driving force for MnS precipitation / coarsening becomes small in relation to the degree of supersaturation, and even if the proper cooling described in (7) is performed, MnS precipitation / coarsening is not sufficiently achieved.
Therefore, it is essential to keep the slab at a high temperature.

(9) When the above Mn, S, Al amount and Mn / S ratio are optimized in this way and the slab is cooled in a specific temperature range at a specific cooling rate or lower, MnS precipitation / coarsening occurs. It is accelerated, and the precipitation and coarsening of AlN at each stage of slab cooling, hot rolling, and annealing of cold-rolled sheet are promoted by using this as a nucleus, and magnetic properties comparable to those of the reheating method are obtained. .

The present invention has been made on the basis of such matters, and its characteristic configuration is as follows.

(1) In weight%, C ≦ 0.0050%, 0.1% ≦ Si ≦ 1.0%,
0.5% ≦ Mn ≦ 1.5%, P ≦ 0.15%, 0.003% ≦ S ≦ 0.015
%, 0.01% ≤ Al ≤ 0.40%, N ≤ 0.0050%, balance Fe and unavoidable impurities, and 60 ≤ ([Mn] / [S]) ≤ 580 [Al] ^1/2 +17 where [Mn ]: Mn content (% by weight) [S]: S content (% by weight) [Al]: Steel having a composition satisfying the Al content (% by weight) is formed into a slab by continuous casting, and the slab is However, [Mn]: Mn content (wt%) [S]: S content (wt%) [Al]: Al content (wt%) Cooling rate CR (℃ / min) 1000 ~ 1100 Cool to a temperature range of ℃, then immediately hot-roll at a coiling temperature of 650 ℃ or higher without heat retention or reheating, and after pickling and cold rolling, at a temperature of 700 ℃ to 900 ℃. A method for manufacturing a non-oriented electrical steel sheet, which comprises annealing.

(2) In% by weight, C ≦ 0.0050%, 0.1% ≦ Si ≦ 1.0%,
0.5% ≦ Mn ≦ 1.5%, P ≦ 0.15%, 0.003% ≦ S ≦ 0.015
%, 0.01% ≤ Al ≤ 0.40%, N ≤ 0.0050, balance Fe and inevitable impurities, and 60 ≤ ([Mn] / [S]) ≤ 580 [Al] ^1/2 +17 where [Mn] : Mn content (% by weight) [S]: S content (% by weight) [Al]: Al steel (Al% (% by weight)) However, [Mn]: Mn content (wt%) [S]: S content (wt%) [Al]: Al content (wt%) Cooling rate CR (° C / min) 1000 ~ 1100 Cool to a temperature range of ℃, then immediately hot-roll at a coiling temperature of 650 ℃ or more without heat retention or reheating, after pickling and cold rolling, at a temperature of 700 ℃ to 900 ℃ A method for manufacturing a non-oriented electrical steel sheet, which comprises annealing, then applying and baking an insulating coating and the like.

[Action]

Hereinafter, the details of the present invention and the reasons for limitation thereof will be described based on test examples.

(1) Mn amount, S amount, Al amount and Mn / S ratio C: 0.0027%, Si: 0.31%, P: 0.085%, Al: 0.08%, N:
Steel with a constant 0.0029% and various Mn and S contents (steel a
Group), the slab was continuously cast, then cooled to 1070 ° C at a cooling rate of 20 ° C / min, and immediately hot-rolled under the conditions of finishing temperature 850 ° C and coiling temperature 670 ° C. (Direct-rolled material) and a hot-rolled sheet (reheated material) hot-rolled under the same conditions as the direct-rolled material after cooling the slab once to room temperature according to the ordinary method, then reheating to 1220 ° C. , After pickling, cold-rolled to a finished thickness of 0.5 mm, then annealed at 750 ° C, and measured the magnetic properties of these annealed plates by JIS Epstein method (the same measurement method was used in the following test examples). did. Fig. 1 shows the iron loss (W
_15/50 ) and the magnetic flux density (B ₅₀ ), that is, ΔW _15/50 = [W _15/50 (direct rolled material)]-[W _15/50 (reheated material)] ΔB ₅₀ = [B ₅₀ (Direct rolled material)-[B ₅₀ (reheated material)] is shown by the relationship between the amount of Mn and the amount of S.

Also, C: 0.0034%, Si: 0.80%, P: 0.051%, Al: 0.27
%, N: 0.0033% is constant, and Mn content and S content are variously changed (steel b group).
Cool to 1020 ℃ at a cooling rate of in, and immediately finish at 820
℃, the hot rolled plate obtained by hot rolling under the conditions of the coiling temperature 700 ℃ (directly rolled material), the slab is cooled to room temperature according to a conventional method, then reheated to 1250 ℃, The hot-rolled sheet (reheated sheet) obtained by hot rolling under the same conditions as the direct-rolled sheet was pickled, cold-rolled to a finished thickness of 0.5 mm, and then purified at 850 ° C. The magnetic properties of the pure plate were measured. FIG. 2 shows the above ΔW _15/50 and ΔB ₅₀ of the direct-rolled material and the reheated material in the relationship between the amount of Mn and the amount of S.

From the results shown in FIGS. 1 and 2 above, the iron loss value (ΔW _15/50 <0.3
W / kg) and higher magnetic flux density than reheated material (ΔB ₅₀ ＞ 0.01
T) has Mn ≥ 0.5%, 0.003% ≤ S ≤ 0.015%, [Mn / S] ≥ 6 regardless of the steel types of steel group a and steel group b.
It can be seen that the area is 0. The upper limit of Mn / S is 181 in the steel group a and 318 in the steel group b, which varies depending on the Al amount as described in (6) above. This will be described later.

Further, in the above description of (1) to (9) regarding the present invention, the description has been made only from the viewpoint of promoting precipitation / coarsening of MnS and AlN, and improving grain growth and iron loss by this.
As for the magnetic flux density, in the component range where the upper limit is limited, the directly rolled material is higher than the reheated material,
The present invention can also improve the magnetic flux density. Although the details of this reason are not always clear, the following reasons can be considered. That is, from the viewpoint of grain growth property, although there is no difference in the precipitation state of MnS, AlN between the direct-feed rolled material and the reheated material, due to the difference in the process, the direct-feed rolled material is more preferable than the reheated material. The precipitates are fine and large in number, and most of the AlN in the directly rolled material precipitates with MnS as the nuclei, etc. There is a difference in the distribution state and properties of the precipitates on the fine side. And, based on such a difference, in the direct-rolled material, the way of entering strain during cold rolling, the distribution is different from the reheated material,
It is considered that this affects the texture formation after the subsequent annealing and brings about the improvement of the magnetic velocity density as described above.

It should be noted that this magnetic flux density is 0.003% ≤ through the precipitation amount of MnS.
When S <0.005%, ΔB ₅₀ = 0.01 to 0.02T, 0.005% ≦ S ≦ 0.
At 015%, ΔB ₅₀ > 0.02T, which differs depending on the amount of S. Therefore, 0.003% ≦ S from the viewpoint of iron loss value only
≦ 0.015% is sufficient, but from the viewpoint of considering the magnetic flux density, 0.005% ≦ S ≦ 0.015% is preferable.

C: 0.0027%, Si: 0.31%, P: 0.085%, N: 0.0029% are constant (same as steel a group), Mn amount, S amount and Mn / S ratio are Mn ≧
Steels with different amounts of Al (0.5%, 0.003% ≤ S ≤ 0.015%, Mn / S ≥ 60)
And C: 0.0034%, Si: 0.80%, P: 0.051%, N: 0.0033% are constant (same as steel b group), and Mn amount, S amount and Mn / S ratio are the same as those of the steel c group. For steels (steel d group) in which the Al content was changed variously in the range, and for steel c group, steel a described above was used.
In the same manufacturing process as the group (Fig. 1) and for the steel d group, the same manufacturing process as the above-mentioned steel group b (Fig. 2),
The annealed plates of the direct rolled material and the reheated material were manufactured, and their magnetic properties were measured. FIG. 3 shows the ΔW _15/50 and ΔB ₅₀ of these direct-rolled material and reheated material by the relationship between the Mn / S ratio and the Al content. According to this, as described in (6) above, the upper limit of the Mn / S ratio of the straight rolled material is given as a function of the amount of Al, and (Mn / S) ≤ (580 [Al] ^1/2 +17) Only if
It can be seen that ΔW _15/50 <0.3 W / kg and ΔB ₅₀ > 0.01 T have the same iron loss as the reheated material and a higher magnetic flux density than the reheated material.

Also, according to the figure, it is understood that the lower limit of the Al amount described in (5) above is 0.01%.

From the above results, in the present invention, as shown in FIG.
The amount, the amount of S, the amount of Al, and the Mn / S ratio were defined as follows.

0.5% ≦ Mn ≦ 1.5% 0.003% ≦ S ≦ 0.015% (preferably 0.005% ≦ S ≦ 0.015%) 0.01% ≦ Al ≦ 0.40% 60 ≦ ([Mn] / [S]) ≦ 580 [Al] ^{1 / 2} ＋17 Here, the upper limit of the amount of Mn is set to 1.5% because Mn is 1.5%.
This is because the magnetic characteristics are not improved even if added in excess of the above, and rather the cost is increased. Similarly, Al exceeding 0.40%
The addition of Al causes an unnecessary increase in cost, and also causes a drastic deterioration of the magnetic flux density. Therefore, the upper limit of the Al content is set to 0.40%.

(2) Other components C: If contained in excess of 0.0050%, deterioration of magnetic properties and increase in magnetic aging are caused. Therefore, in the present invention, C ≦ 0.0050%.
The target is ultra low carbon steel.

Si: An element that causes a decrease in iron loss through an increase in specific resistance, but it is necessary to add 0.1% or more to fully exhibit this effect. However, addition of Si in excess of 1.0% causes a rapid decrease in magnetic flux density, so the upper limit is made 1.0%.

P: An element that increases hardness and improves punchability without significantly impairing magnetic properties. However, addition of more than 0.15% not only saturates these effects but also leads to rapid deterioration of magnetic properties, so the upper limit is made 0.15%.

N: As described in (5) above, precipitation and coarsening of AlN is caused by MnS
Since it strongly depends on the number of nuclei and the amount of Al, it is not necessary to specify the amount of N in this sense. However, if N exceeds 0.0050%, the magnetic properties deteriorate due to an increase in solid solution N itself, so the upper limit is made 0.0050%.

(3) Slab cooling conditions after continuous casting C: 0.0027%, Si: 0.31%, P: 0.085%, N: 0.0029% are constant (same as steel a group), Mn content, S content, Al content and Mn Steel with various A / S ratios within the range of the present invention (Steel a group) and C: 0.0034
%, Si: 0.80%, P: 0.051%, N: 0.0033% are constant (same as steel b group), and steels having various Mn content, S content, Al content and Mn / S ratio within the scope of the present invention ( For steel group f), for the straight rolled material, the manufacturing process with various slab cooling rate CR after continuous casting was adopted, and the straightened rolled material and the reheated material were manufactured and their magnetic properties were evaluated. It was measured. The manufacturing process is the same as the above-described steel group a (steel group a (first group) except that the slab cooling rate is changed for the straight rolled material).
Fig.), And the steel f group, the steel b group described above (second
(Fig.). The above slab cooling rate
CR was defined as the average cooling rate (℃ / min) from 1400 ℃ at 1/4 width of slab and 1/4 thickness.

Fig. 5 shows the ΔW _15/50 between these directly rolled materials and reheated materials.
And ΔB ₅₀ are shown by the relationship between the Mn amount, the Al amount and the Mn / S ratio and the slab cooling rate CR. According to this, as described in (7) above, the upper limit of the slab cooling rate CR is
Amount, Al amount, Mn / S ratio As is different for each steel type, ΔW _15/50 <0.3W / only when the slab is continuously cast and then cooled at the above cooling rate or less.
Good magnetic properties such as kg and ΔB ₅₀ > 0.01T are obtained. Further, as described in (7) above, extreme slow cooling is substantially equivalent to keeping the slab at a high temperature, which leads to deterioration of surface quality and productivity, and in order to prevent this, the lower limit of the cooling rate CR is It should be 5 ° C / min.

Next, C: 0.0041%, Si: 0.12%, Mn: 0.52%, P: 0.111
%, S: 0.008%, Al: 0.03%, N: 0.0033%, steel having a composition of Mn / S = 65, that is, Mn, Al in the steel of the present invention,
A steel with a relatively low Mn / S ratio and a compositionally disadvantageous to the precipitation and coarsening of MnS and AlN (steel g: The upper limit of the slab cooling rate of this steel is 52 ° C / min), C: 0.0023%, Si: 0.85%, Mn: 1.47%, P: 0.051
%, S: 0.006%, Al: 0.37%, N: 0.0017%, steel having a composition of Mn / S = 245, that is, Mn, A in the steel of the present invention.
l, Mn / S ratio are both high, and the composition is considerably advantageous for precipitation and coarsening of MnS and AlN (Steel h: The upper limit of the slab cooling rate of this steel is 138 ℃ / mi
(for n), annealed sheets of the straight rolled material and the reheated material were manufactured by the manufacturing process under the following conditions, and their magnetic properties were measured. During the manufacturing process, the slab cooling rate CR after continuous casting is 7 ° C./min (less than or equal to the upper limit of the present invention), 45 ° C./min (less than or equal to the upper limit of the present invention), and 55 ° C. / min (exceeding the same upper limit), steel h has 3 levels of 20 ° C / min (below the same upper limit), 130 ° C / min (below the same upper limit) and 145 ° C / min (over the same upper limit) After the slab was cooled to various temperatures at these cooling rates, hot rolling was immediately started. On the other hand, with respect to the reheated material as a comparative material, the reheating temperature was 1220 ° C. for steel g and 1250 ° C. for steel h, and hot rolling was performed. In addition, in the process after the hot rolling, for the steel g, the above-described steel a group (first
Fig.), And also for steel h, the steel b group described above (Fig. 2)
Is the same as

FIG. 6 shows the ΔW _15/50 of the direct rolled material and the reheated material in relation to the slab cooling temperature for each of steel g and steel h. According to this, both steel g and steel h, that is,
If the cooling rate of the slab is within the range of the present invention regardless of whether or not it is an advantageous component for precipitation and coarsening of MnS and AlN (for steel g, 7 ° C / min, 45 ° C / min, for steel h, 20 ℃ / min,
At 130 ° C / min), in the slab cooling temperature range of 1000 to 1100 ° C, the directly rolled material exhibits ΔW _15/50 <0.3W / kg, which is comparable to the reheated material in iron loss. On the other hand, if the slab cooling temperature exceeds 1100 ° C, even if the present invention steel is cooled at the slab cooling rate specified by the present invention, ΔW _15/50
> 0.7 W / kg, so excellent iron loss cannot be obtained.

The existence of such a critical temperature can be explained in terms of the driving force for precipitation and coarsening of MnS, as described in (8) above.
That is, when the slab is cooled at a predetermined cooling rate after continuous casting, the lower the temperature, the higher the degree of supersaturation of MnS,
As the driving force for precipitation / coarsening increases, the precipitation / coarsening of MnS follows an exponential change. In other words, the precipitation and coarsening of MnS rapidly progresses only when the slab temperature is below a certain temperature. Therefore, in order to achieve sufficient precipitation / coarsening of MnS and further promote precipitation / coarsening of AlN using MnS as a nucleus, it is necessary to set the slab cooling temperature to a certain temperature or lower. In the method of the present invention, this temperature corresponds to 1100 ° C.

On the other hand, when the cooling temperature of the slab is lower than 1000 ° C, as described in (8) above, edge cracking occurs in the hot rolled sheet due to insufficient deformability of the slab, or when the temperature is lower than 950 ° C, the mill load increases. Therefore, hot rolling itself becomes impossible.

When the cooling rate of the slab exceeds the range specified by the present invention (55 g / min for steel g and 145 ° C./min for steel h),
Even with the steel of the present invention, ΔW _15/50 > 0.7 W / kg, regardless of the cooling temperature of the slab, and it can be confirmed that excellent iron loss cannot be obtained.

Regarding ΔB ₅₀ , when the slab cooling rate was within the range of the present invention and the slab cooling temperature was 1100 ° C. or less, both exceeded 0.02T, but the slab cooling temperature was 1100.
When the temperature was higher than 0 ° C or the slab cooling rate was out of the range of the present invention, the result was less than 0.02T.

From the above results, in the present invention, after continuous casting, in addition to cooling the slab at a predetermined cooling rate or less determined depending on the steel composition, the cooling temperature range of the slab at that time is specified to be 1000 ° C or more and 1100 ° C or less. There is a need to.

However, the above cooling temperature range specifications are based on the assumption of minimum cost and maximum productivity, and there is some margin in terms of cost or productivity, and if reheating of the slab is allowed, reheating is recommended. Slab cooling temperature may be lower than 1000 ° C., since it acts rather favorably for precipitation and coarsening of MnS. However, according to the calculation by the present inventors, when the temperature is lower than 600 ° C., the cost and time required for reheating exponentially increase, and therefore the temperature decrease of the slab below 600 ° C. should be avoided. Regarding the reheating temperature,
Needless to say, the temperature should be 1000 ° C or higher to secure hot rolling property, but if it exceeds 1150 ° C, MnS once precipitated / coarsed is redissolved, so the upper limit of reheating temperature is 1150 ° C.
It is desirable to set the temperature to ° C. The reheating time is considered to be 10 minutes or more and 30 minutes or less in order to ensure the uniform heating of the slab and prevent scale increase.

(4) Other manufacturing conditions Hot rolling conditions: When the coiling temperature is lower than 650 ° C, precipitation and coarsening of MnS and AlN are insufficient, and progress of recrystallization and coarsening of the hot rolled sheet Is also delayed, and as a result, the absolute values of the magnetic properties themselves of both the straight-rolled material and the reheated material deteriorate. Therefore, the winding temperature must be 650 ° C or higher.

The finishing temperature does not need to be specified because it has little effect on the progress of precipitation and coarsening of MnS and AlN, but it is preferably 750 ° C or higher from the viewpoint of ensuring the winding temperature.

Pickling and cold rolling conditions: There is no particular requirement, and it can be carried out by a conventional method.

Annealing conditions: If the annealing temperature is less than 700 ° C, the absolute value of the magnetic properties itself deteriorates as with the hot rolling temperature above, so the lower limit is
Set to 700 ° C. On the other hand, if the annealing temperature exceeds 900 ° C, not only will the cost be unnecessarily increased, but excessive coarsening of the ferrite grains will develop an unfavorable texture in terms of magnetic properties, which will lower the magnetic flux density. Therefore, the upper limit is 90
Set to 0 ° C.

〔Example〕

Using the steels shown in Table 1, the slabs were continuously cast, cooled to various temperatures at various cooling rates, and immediately hot-rolled. For the hot rolled sheet (reheated material) obtained by cooling the slab as a material once to room temperature, then reheating it to a prescribed temperature, and then hot rolling it under the same conditions as the straight rolled material After that, it was cold-rolled to a finished thickness of 0.5 mm and subsequently annealed for 3 minutes. The Epstein magnetic properties (the magnetic properties of the straight-rolled material and the reheated material, and the difference between the magnetic characteristics of the two) obtained in this manner are shown in Tables 2-a to 2-c together with specific manufacturing conditions. And Tables 3-a to 3-c.

Tables 2-a to 2-c show the effects of the steel components, and the comparative materials all satisfy the conditions of the present invention except for the components. According to the table, the directly rolled material according to the method of the present invention has ΔW _15/50 <0.3 W / kg, ΔB ₅₀ > 0.01 T, which is comparable to the reheated material, and the iron loss value is higher than that of the reheated material. Also shows a high magnetic flux density, whereas some comparative steels show the same ΔB ₅₀ as the invention steel, but the iron loss is ΔW _15/50 > 0.7 W / kg. It can be seen that the direct loss rolling significantly deteriorates the iron loss.

Tables 3-a to 3-c show the effects of the slab cooling rate and the slab cooling temperature in the manufacturing conditions. Also in this case, ΔW _15/50 <0.3 W / kg, ΔB ₅₀ > for direct _feed rolling in which the slab cooling rate and the slab cooling temperature satisfy the conditions of the present invention.
An iron loss value of 0.01T, which is comparable to that of the reheated material, and a magnetic flux density higher than that of the reheated material were obtained. On the other hand, in Comparative Examples in which the slab cooling rate and the slab cooling temperature are out of the range of the present invention, ΔB ₅₀ is the same as that of the present invention material, but the iron loss is ΔW _15/50 > 0.7 W / kg. However, the core loss of the straight-rolled material is significantly higher than that of the reheated material.

[Advantages of the Invention] According to the present invention described above, in applying the direct rolling to the production of the non-oriented electrical steel sheet, the special adjustment of the steel composition, which was indispensable in the prior art, and the high temperature / long time of the slab were required. It does not require steps such as holding and reheating that increase costs and decreases productivity, and realizes the minimum cost and productivity maximum that are the original advantages of direct-feed rolling, and has magnetic properties equivalent to or better than those of reheated materials. A non-oriented electrical steel sheet can be manufactured.

[Brief description of drawings]

FIGS. 1 and 2 is, Mn ratios for differences in the magnetic characteristics of the hot direct rolling material and reheating material _{(ΔW 15/50, ΔB 50),} S amount and
6 is a graph showing the influence of the Mn / S ratio and its appropriate range. Third
The figure shows Al against the difference in the magnetic properties of the straight rolled material and the reheated material.
6 is a graph showing the influence of the amount and Mn / S ratio and its appropriate range.
FIG. 4 is a graph showing the range of the present invention regarding the amount of Mn, the amount of S, the amount of Al, and the Mn / S ratio. FIG. 5 is a graph showing the influence of the slab cooling rate of the straight-rolled material on the difference in magnetic characteristics between the straight-rolled material and the reheated material, and its appropriate range. FIG. 6 is a graph showing the influence of the slab cooling temperature of the straight-rolled material on the difference in iron loss W _15/50 between the straight-rolled material and the reheated material and its appropriate range.

Claims (2)

[Claims] 1. In weight%, C ≦ 0.0050%, 0.1% ≦ Si ≦
1.0%, 0.5% ≦ Mn ≦ 1.5%, P ≦ 0.15%, 0.003% ≦ S ≦
0.015%, 0.01% ≦ Al ≦ 0.40%, N ≦ 0.0050%, balance Fe
And unavoidable impurities, and 60 ≦ ([Mn] / [S]) ≦ 580 [Al] ^1/2 +17 where [Mn]: Mn content (wt%) [S]: S content ( Wt%) [Al]: A steel having a composition satisfying the Al content (wt%) is formed into a slab by continuous casting, and the slab is However, [Mn]: Mn content (wt%) [S]: S content (wt%) [Al]: Al content (wt%) Cooling rate CR (℃ / min) 1000 ~ 1100 Cool to a temperature range of ℃, then immediately hot-roll at a coiling temperature of 650 ℃ or more without heat retention or reheating, after pickling and cold rolling, at a temperature of 700 ℃ to 900 ℃ A method for manufacturing a non-oriented electrical steel sheet, which comprises annealing. 2. In% by weight, C ≦ 0.0050%, 0.1% ≦ Si ≦
1.0%, 0.5% ≦ Mn ≦ 1.5%, P ≦ 0.15%, 0.003% ≦ S ≦
0.015%, 0.01% ≤ Al ≤ 0.40%, N ≤ 0.0050, balance Fe and inevitable impurities, and 60 ≤ ([Mn] / [S]) ≤ 580 [Al] ^1/2 +17 where [Mn ]: Mn content (% by weight) [S]: S content (% by weight) [Al]: Steel having a composition satisfying the Al content (% by weight) is formed into a slab by continuous casting, and the slab is However, [Mn]: Mn content (wt%) [S]: S content (wt%) [Al]: Al content (wt%) Cooling rate CR (℃ / min) 1000 ~ 1100 Cool to a temperature range of ℃, then immediately hot-roll at a coiling temperature of 650 ℃ or higher without heat retention or reheating, and after pickling and cold rolling, at a temperature of 700 ℃ to 900 ℃. A method for manufacturing a non-oriented electrical steel sheet, which comprises annealing, followed by application of an insulating film and baking.