JPH075975B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a grain-oriented electrical steel sheet having low cost and good magnetic properties in the rolling direction.

[Conventional technology]

The grain-oriented electrical steel sheet is an electromagnetic material that excels in excitation characteristics and iron loss characteristics in the rolling direction, and is widely used in various electrical equipment applications such as transformer cores.

By the way, the grain-oriented electrical steel sheet is complicated and special in the manufacturing process as compared with general cold-rolled steel sheet and non-oriented electrical steel sheet.
The cost is very high. For these reasons, cost reduction by improving the manufacturing process has become an important issue for grain-oriented electrical steel sheets.

The general manufacturing process of grain-oriented electrical steel sheets is as follows: first heat the slab to a temperature of 1300 ° C or higher, solution heat AlN and MnS and hot-roll it, and then hot-roll it once or twice with intermediate annealing. The above cold rolling is performed to obtain the final plate thickness. Then, C in steel is lowered to a low level by decarburization annealing, and primary recrystallization is adjusted. Finally 1100-1200 ℃ in batch furnace
The second step is to perform secondary annealing to produce secondary recrystallization and to purify steel (desulfurization and denitrification).

High temperature heating of slabs inhibits secondary recrystallization
Some are essential for optimizing the dispersion state of AlN and MnS.
Heating above 00 ℃ requires a special dedicated furnace, and there are problems in terms of scale loss and energy cost.

In addition, decarburization annealing uses AlN, M
This is done in order to lower the C required to optimize the dispersion state of nS to a level at which there is no problem in terms of magnetic properties, but the cost is very high.

Furthermore, high-temperature long-time annealing as finish annealing is required to remove precipitates that are harmful to the magnetic properties of the product, especially MnS, but long-time treatment at a high temperature of 1100 to 1200 ° C is costly. It is a big cause of the rise. That is, in order to reduce the cost of the grain-oriented electrical steel sheet, it is essential to reduce the cost of these heat treatments.

As an attempt to reduce the cost of heat treatment, for example, there is a method disclosed in JP-A-58-100627.

This is C0.02% or less, Si5% or less, S0.015% or less, Al0.
After slab-heating a steel material of 01 to 0.08% and N0.01% or less at 1270 ° C or less, hot rolling, hot rolled sheet annealing, cold rolling, and primary recrystallization annealing, then per 1 cm parallel to the steel sheet surface Annealing is performed to impart a temperature difference of 2 ° C. or more to cause secondary recrystallization.

In this method, since the slab heating may be performed at a temperature lower than 1300 ° C, a special dedicated furnace is not required and scale loss and energy cost are reduced. Further, since the amount of C can be lowered in advance, there is an advantage that decarburization treatment is unnecessary during the process.

[Problems to be Solved by the Invention]

However, with this method, the inhibitor effect of AlN is not sufficiently exerted, and it is difficult to stably obtain secondary recrystallization. In addition, a special annealing that imparts a temperature difference in parallel to the steel plate surface is required as the secondary recrystallization treatment, which is not a practical method.

By the way, the present inventors have been studying grain-oriented electrical steel sheets for some time, and have already proposed some useful manufacturing methods. One of them is the method disclosed in JP-A-62-83421 (hereinafter referred to as the prior application).

This is basically made of steel with extremely low carbon (C ≦ 0.010%) and a very small amount of Al (0.003 to 0.015%),
After hot rolling-cold rolling, annealing for performing primary recrystallization and finish annealing for performing secondary recrystallization are performed under required conditions. This method can effectively bring out the inhibitor effect of AlN, and further, decarburization annealing can be omitted, and in finishing annealing also secondary recrystallization can be generated by low temperature annealing in the α region, so in terms of cost. Very advantageous.

Although the method of the earlier application is highly effective,
Regarding magnetic characteristics, there are many demands for performance exceeding this,
Further improvement is desired.

It is an object of the present invention to further develop the technique of the prior application and to provide a method for producing a grain-oriented electrical steel sheet which can ensure higher and stable magnetic properties while making the most of its advantages.

[Means for Solving the Problems]

The present inventors have found an effective means for improving the secondary recrystallization behavior in the finish annealing step, that is, the Goss orientation {110} <001> integration degree of the secondary recrystallized grains when the prior application technique is applied. Therefore, as a result of repeated diligent experiments and researches, the following findings were obtained.

In addition to AlN, a small amount of MnS must be utilized as an inhibitor in order to increase the goss orientation integration of secondary recrystallized grains.

And, in order to effectively bring out the inhibitory effect of MnS under the condition that the slab heating temperature is 1270 ° C. or lower, it is important to set the ranges of Mn0.05% to 0.20% and S0.003 to 0.015%. .

In this case, the processing conditions include a hot rolling finishing temperature of 70
It is necessary to set the temperature in the range of 0 to 900 ° C, and it is effective to further perform the high temperature continuous annealing of 950 to 1050 ° C for the hot-rolled sheet annealing and the primary recrystallization annealing after cold rolling.

The present invention is based on the above findings, and has as its gist the following method.

C0.01% or less, Si1.8-4.0%, Mn0.05-0.20%, S0.003
~ 0.015%, Sol ・ Al0.003 ~ 0.015%, N0.0010 ~ 0.0100
%, With the balance Fe and inevitable impurities heated to 1270 ° C or lower, hot-rolled at a finishing temperature of 700 to 900 ° C, wound at a temperature of 600 ° C or lower, and then 950 ° C. A hot-rolled sheet is annealed by continuous annealing for 10 seconds or more and 10 minutes or less at a temperature of 1050 ° C or less, and then cold rolling is performed once or twice or more with intermediate annealing to obtain a final sheet thickness, and then 950
Characteristically, continuous annealing is performed at a temperature of 1050 ° C. or lower for 10 seconds or more and within 10 minutes to cause primary recrystallization, and further secondary annealing is caused by finish annealing at 800 ° C. to 1000 ° C. Method for manufacturing grain-oriented electrical steel sheet.

[Action]

Hereinafter, each constituent element of the present invention will be described specifically and in detail to clarify the operation.

○ First, the reasons for limiting the steel composition of the slab used are as follows.

C: When the C content in the steel exceeds 0.01%, unfavorable phenomena in magnetic properties such as deterioration of iron loss and deterioration of magnetic aging become remarkable. Therefore, C is set to 0.01% or less. It should be noted that the lower the C value, the more advantageous it is in terms of magnetic properties, so the lower limit is not specified.

Incidentally, the conventional grain-oriented electrical steel sheet usually contains about 0.025 to 0.085% of C at the stage of the material (hot rolled sheet), which is decarburized and annealed in the process after cold rolling. Reduced the amount to be product C. This is because the C content up to the middle of the process is considered to optimize the dispersed state of AlN and NnS as inhibitors and to improve the magnetism of the final product, but the present invention does not include such C content. In both cases, AlN and MnS can effectively act as inhibitors, and it is not necessary to include C in the material steel. Rather, it is necessary to make it extremely low in advance in order to omit the decarburization annealing.

Si: It is effective in reducing iron loss by increasing the specific resistance, and the effect is remarkable when the content is 1.8% or more. However, if the content exceeds 4%, cold rolling becomes difficult. Therefore 1.8-4.0
%.

Note that the Si amount is practically determined so that the required magnetic characteristics (iron loss, magnetic flux density) can be obtained within the specified range.

Mn: Mn produces MnS that acts as an inhibitor together with S, and plays an important role in stabilizing secondary recrystallization. However, if the Mn content exceeds 0.20%, solution heating of MnS cannot be sufficiently performed by slab heating below 1270 ° C, and the inhibitory effect of MnS may not be exhibited. If it is less than 0.05%, the brittleness during hot rolling due to FeS becomes a problem. Therefore M
The amount of n was 0.05 to 0.20%.

S: S is an important element that stabilizes the secondary recrystallization by forming MnS as an inhibitor with Mn described above.

In the range where the S addition amount is less than 0.003% and more than 0.015%, the magnetic characteristics greatly vary. This is considered to be because the amount of MnS serving as an inhibitor and the precipitation morphology become unsuitable with such an amount of S. On the other hand, the amount of S is 0.003
In the range of ~ 0.015%, the magnetic properties are always at a high level and the secondary recrystallization is stable. Therefore, the S amount is set to 0.003 to 0.015%.

Sol.Al:Al is an element required to form AlN, which is the main inhibitor of the present invention, and suppress the grain growth of primary recrystallized grains, and the definition of the addition amount thereof has an important meaning in the present invention.

The content of Al is 0.003 to 0.015% in terms of Sol.Al content,
Below the lower limit, the absolute amount of AlN as an inhibitor is insufficient and a sufficient effect cannot be expected, while above the upper limit, the distribution form as an inhibitor becomes inappropriate,
This is because stable secondary recrystallization cannot be obtained by finish annealing.

N: An element essential for the formation of AlN as an inhibitor, and in that sense, it is required to be at least 0.0010% or more. However, if the content exceeds 0.0100%, it is meaningless in terms of inhibitor effect. Therefore, N is 0.0010 to 0.0100
Defined as%.

○ Next, the manufacturing process will be described.

The method of the present invention basically uses a slab that conforms to the above component conditions, and undergoes a slab heating hot rolling hot rolling sheet annealing cold rolling continuous annealing (annealing after cold rolling) finish annealing step. A grain-oriented electrical steel sheet is manufactured.

Each step will be described below.

Slab heating Slough heating is 1300 to 14
It was customary to carry out at an ultrahigh temperature of 00 ° C. This is because AlN and MnS must be sufficiently solution-treated at the slab heat stage in order to precipitate AlN and MnS in an effective state (size and dispersion state) as an inhibitor in the process after hot rolling. It is from the recognition that there is. However, such high temperature heating of the slab has many problems such as yield reduction due to slag generation, increase in energy cost, troubles in the heating furnace, etc. Very expensive.

One of the aims of the present invention is to reduce the heating temperature of the slab heating to reduce the cost. For this purpose, the amount of AlN and MnS in steel is made smaller than usual, and a small amount of AlN and MnS is efficiently used as an inhibitor.

According to such a method, it is sufficient that the heating temperature of the slab is 1270 ° C. or lower, which is equivalent to that of a cold rolled steel sheet, and the inhibitor effect is sufficiently exhibited by heating at this low temperature, and secondary recrystallization is stable in the finish annealing step. Will be ensured.
Therefore, in the present invention, the heating temperature of the slab is limited to 1270 ° C or lower.

At such a low temperature, direct charge (roll), which has been actively used in recent years from the viewpoint of energy saving, that is, the slab is directly charged into a heating furnace without being cooled, and immediately heated and reheated. It is also possible to adopt the method of applying hot rolling.

The lower limit of the slab heating temperature is not particularly limited, but it is preferable to heat the slab at 1000 ° C or higher in consideration of the actual operation such as the ability of the rolling mill.

Finishing temperature of hot rolling This is an important manufacturing condition for stabilizing secondary recrystallization. When the finishing temperature exceeds 900 ° C, the secondary recrystallization becomes unstable and the magnetic properties vary. This is during hot rolling
It is considered that the precipitation state of AlN or MnS or the texture of the hot-rolled sheet becomes unsuitable for Goss-oriented ({110} <001>) secondary recrystallization, but the details have not been clarified yet.

On the other hand, if the finishing temperature is 700 ° C or lower, problems will occur in shape control etc. in the current hot rolling equipment. Therefore, the temperature of hot rolling or higher is set in the range of 700 to 900 ° C.

Winding Temperature In the present invention, AlN precipitated in the hot-rolled sheet annealing and subsequent steps plays an important role as an inhibitor. Therefore, the winding temperature exceeds 600 ° C, the amount of AlN in the wound state decreases, and the secondary recrystallization becomes unstable. Therefore, the winding temperature was set to 600 ° C or lower. The lower limit is not set because it does not cause a problem in terms of magnetic properties.

Hot-rolled sheet annealing Hot-rolled sheet annealing is necessary to prevent ridging and to disperse AlN. Ridging means high Si like steel of the present invention.
This is a surface undulation that linearly extends in the rolling direction that occurs when cold rolling is performed on steel while leaving an unrecrystallized portion on the hot-rolled sheet. To prevent this, it is necessary to completely recrystallize the hot-rolled sheet, which requires continuous annealing at 800 ° C for 10 seconds or longer.
Also, AlN precipitated during hot-rolled sheet annealing is important as an inhibitor for secondary recrystallization, and in order to realize this proper dispersed precipitation state and increase the degree of integration of Goss-oriented grains, 950 ° C is used for rapid heating. Exceeding annealing is suitable. Also, hot rolled sheet annealing exceeding 1050 is not suitable for AlN dispersion.
It should be noted that even if the soaking time for hot-rolled sheet annealing exceeds 10 minutes, there is no practical meaning. Therefore, it was set to 10 seconds or more and 10 minutes or more at 950 ° C or higher and 1050 ° C or lower.

Cold rolling Cold rolling is one cold rolling, but it does not matter whether it is cold rolling twice or more with intermediate annealing. As the condition of the intermediate annealing, continuous annealing at 800 to 950 ° C is desirable, but it is not particularly specified.

Continuous annealing after cold rolling In order to generate secondary recrystallization with a high degree of integration in the Goss orientation, the primary recrystallization texture and grain size and the precipitation state (distribution and morphology) of AlN and MnS as inhibitors are appropriate. Must be a combination. This is achieved by continuous annealing after the final plate thickness. This annealing requires rapid heating and continuous annealing is suitable. As the annealing condition, the heating rate is preferably 5 ° C./S or more.

If the annealing temperature is below 950 ° C or around 1050 ° C, the above-mentioned texture, ferrite grain size, precipitation of inhibitors, etc. are not appropriate, and the Goss orientation integration degree in secondary recrystallization becomes low. If the annealing time is less than 10 seconds, the effect of annealing cannot be obtained, and soaking for more than 10 minutes is actually unnecessary.

From the above, the continuous annealing condition after cold rolling was set to 950 ° C to 1050 ° C and 10 seconds to 10 minutes.

Finishing Annealing The present invention is intended to cause stable secondary recrystallization by finishing annealing at a low temperature mainly by optimizing the components, and in the finishing annealing, so-called annealing annealing at a high temperature of 1000 ° C. or higher is not performed.
This leads to cost reduction.

If the temperature of finish annealing is less than 800 ° C, secondary recrystallization does not occur, and good magnetic properties cannot be expected. In addition, the present invention uses a relatively small amount of 1N and MnS as inhibitors, and secondary recrystallization at 1000 ° C. or lower is sufficient. Therefore 800-1000
Annealed at ℃.

The atmosphere for finish annealing is not particularly limited, but it is desirable to set the atmosphere containing nitrogen until the secondary recrystallization is completed in order to enhance the inhibitor effect of AlN.

Before the finish annealing, a step of surface-treating an annealing separator or the like is generally performed to prevent seizure.

〔Example〕

Continuously cast slabs of various components shown in Table 1 were directly charged into a slab heating furnace without cooling to room temperature, and hot rolling → hot rolled sheet annealing → cold rolling → continuous under the conditions shown in the table. Annealing →
Subjected to finish annealing was measured rolling direction of the iron loss W17 / 50 and magnetic flux density B _8. In addition, descaling is performed on each test material before or after annealing the hot-rolled sheet. Also, an annealing separator was applied before the finish annealing. The magnetic measurement was carried out by JIS C2550, after cutting and sampling an Epstein test piece having a width of 30 mm and a length of 280 mm from the rolling direction and after strain relief annealing at 800 ° C. for 2 hours.

The test results will be described.

Nos. 1 to 6 are examples in which the amount of S is variously changed under the same hot rolling finishing and winding conditions with substantially the same composition except for the amount of S. The hot rolling conditions are all within the scope of the present invention, and all steel types except the S content have compositions within the scope of the present invention.

The amount of S deviates from the present invention to the low and high levels (hereinafter, “deviation”).
Means "outside the scope of the invention") No. 1,6
Is within the scope of the present invention after the hot rolled sheet annealing, but the S content was within the scope of the present invention, but after the hot rolled sheet annealing, compared with Nos. 3 and 5 under the same conditions, the core loss and the magnetic flux density were significantly inferior. There is. Also, No.
Even if the composition is within the range of the present invention as in Nos. 2 and 4, good magnetic properties are not obtained even when the temperature of the continuous annealing deviates from the lower or higher values.

No. 7 to 11 are the same steel grades of the composition of the present invention range, while good magnetic properties are obtained in No. 9 and 11 satisfying the conditions of the present invention even after hot rolling, whereas hot rolling is performed. No. 7 with a higher finishing temperature, No. 8 with a lower continuous annealing temperature and No. 10 with a higher annealing temperature did not have good magnetic properties.

Nos. 12 to 17 are examples of the same steel type having the composition within the range of the present invention, and the hot-rolled sheet annealing conditions were variously changed. No. 1 of the scope of the present invention
Nos. 5 and 16 have good ridging properties and magnetic properties. On the other hand, all of the conditions other than the hot rolled sheet annealing conditions are within the scope of the present invention, but even if the hot rolled sheet annealing is continuous annealing, the temperature deviates to a low level.
Nos. 12 to 14 are inferior in ridging property and magnetic property.
Further, No. 17 which was subjected to hot-rolled sheet annealing by batch annealing has good ridging property, but secondary recrystallization is not stable and magnetic properties are poor.

〔The invention's effect〕

As is clear from the above description, the method of the present invention stabilizes a grain-oriented electrical steel sheet having a high level of magnetic properties without performing costly heat treatment such as slab high temperature heating, decarburizing annealing, high temperature finishing annealing, etc. Can be manufactured.

Claims (1)

[Claims] 1. By weight%, C0.01% or less, Si1.8-4.0%, M
n0.05 to 0.20%, S0.003 to 0.015%, Sol.Al0.003 to 0.015%
%, N 0.0010 to 0.0100%, with the balance being Fe and unavoidable impurities, the slab is heated to 1270 ° C or lower and the finishing temperature 70
Hot rolling is performed at 0 to 900 ° C, wound at a temperature of 600 ° C or less, and then hot-rolled sheet is annealed by continuous annealing at a temperature of 950 ° C or 1050 ° C for 10 seconds or more and 10 minutes or less, Then, cold rolling is performed once or twice or more with intermediate annealing to obtain the final plate thickness, and then at a temperature of 950 ° C or less than 1050 ° C for 10 seconds or more 1
A method for producing a grain-oriented electrical steel sheet, which comprises performing continuous annealing within 0 minutes to cause primary recrystallization, and further performing secondary annealing at 800 to 1000 ° C for finish annealing.