JPS60128210A - Heating method of grain oriented silicon steel slab - Google Patents

Abstract

PURPOSE:To obtain the titled steel sheet with less variance in magnetic characterstic by heating electrically a grain oriented silicone steel slab prior to hot rolling in at least the high-temp. region to the prescribed rolling temp. to heat uniformly the slab without generating molten scale and subjecting such slab to hot rolling. CONSTITUTION:A grain oriented silicon steel slab 1 is heated in a heating furnace and in succession thereto, the slab 1 is electrically heated by electrodes 2, 2 to increase the temp. thereof. The temp. region where the slab 1 is heated in the heating furnace is made up to 1,250 deg.C at the max. in ths case and the heating in the succeeding temp. region exceeding said region is accomplished by the conduction of electricity through the electrodes 2, 2. More specifically, the heating to >=1,250 deg.C at which the molten scale consisting essentially of FeO, Fe2O3. SiO2, etc. is liable to be generated is accomplished by conduction of electricity and therefore the deposition of the scale in the heating furnace is prevented. The cost for repairing the furnace is consequently reduced and relatively shorter time is required for heating up on account of the use of electricity. The method is thus advantageous in terms of cost and production efficiency. In the figure, 3, 6 denote cylinders 4 a heat insulating material and 5 a member for holding the heat insulating material, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention provides crystal orientation with Miller index (20)<001>.
The present invention relates to a method for manufacturing a grain-oriented silicon steel sheet that is aligned in orientation, and particularly to a heating method prior to hot rolling of a slab for a grain-oriented silicon steel sheet.

As is well known, grain-oriented silicon steel sheets contain Si of 2.5 to 4.0.
It is manufactured by hot-rolling a slab containing about 1.5% to form a hot coil, followed by cold rolling, decarburization annealing, and then final finishing annealing, and the process: jl 1 (l)
A secondary recrystallized structure is formed in which crystals with a <0.01> orientation are highly concentrated, resulting in excellent magnetic properties with high magnetic flux density and low core loss.For this reason, it has been widely used as iron core material, etc. has been done.

In the manufacturing process of grain-oriented silicon steel sheets, it is necessary to suppress the growth of crystal grains in the annealed Shisen orientation and selectively grow crystal grains in the (110) <001> orientation. Mn sometimes has the function of suppressing the growth of crystal grains.
Elements that form inhibitors such as S, MnSe, and AlN are added. In order for these inhibitors to be fully effective, it is necessary to form a sufficient solid solution of inhibitor-forming elements in the base metal in advance. Prior to rolling, it is necessary to heat the slab to a temperature at which the inhibitor-forming elements are completely dissolved in the base metal.

Conventionally, heating furnaces such as pusher type and walking beam type have been used to heat the slab. However, when heating a slab for the above-mentioned purpose using these heating furnaces, the following problems commonly occur.

As is well known, various conventional heating furnaces are equipped with skids to hold the slab, but when heating the slab in these heating furnaces, the heat is removed from the water-cooled skid, so the slab is heated uniformly. It is very difficult to heat the slab to a high temperature, resulting in so-called skid marks on the slab. Therefore, as mentioned above, in order to completely dissolve the inhibitor-forming elements in the base metal of the slab, the lowest temperature part must be higher than the solid solution temperature of the inhibitor, based on the lowest temperature part where heat is removed from the skid of the slab. It was necessary to heat the entire slab until the temperature was reached, and other parts were overheated, and specifically, the sieve temperature sometimes reached 1400° C. or higher.

As a result, the conventional heating method described above not only has the disadvantage that the magnetic properties of the product obtained after a series of treatments vary due to the occurrence of skid marks, but also
Due to excessive heating of the slab, molten scales such as FeOtFe203 and Sr02 are generated on the slab during the heating process of the slab, which deteriorates the product yield, and the molten scales accumulate in the furnace, resulting in low furnace efficiency. At the same time, the life of the furnace is shortened, and in order to deal with this, the furnace has to be repaired frequently to remove the accumulated molten scale, which causes the inconvenience of incurring excessive costs. Ta.

As a way to deal with such problems,
No. 291 or Japanese Unexamined Patent Publication No. 58-25429 proposes a method in which an antioxidant is applied to the surface of a slab to suppress the formation of scale. . However, these methods require the formation of a fractured M layer in order to coat the surface of the slab with an antioxidant, and as a result, heating at a higher temperature and longer time is required, which is disadvantageous in terms of cost and requires no fundamental solution. It's not.

In view of these circumstances, the present invention makes it possible to produce grain-oriented silicon steel sheets with less variation in magnetic properties at low cost by uniformly heating a slab without generating molten scale and subjecting it to hot rolling. An object of the present invention is to provide a method for heating a grain-oriented silicon steel slab.

That is, the method for heating a grain-oriented silicon steel slab of the present invention involves, in order to heat the grain-oriented silicon steel slab to a predetermined rolling temperature before hot rolling, to conduct electricity in at least a temperature range up to the predetermined rolling temperature. It is characterized by heating.

The present invention will be explained in more detail below.

FIG. 1 and FIG. 2 schematically show an example of an electrical heating device used for carrying out the present invention.

The electrodes 2 arranged so as to come into contact with both ends of the slab 1 in the longitudinal direction are movable in the longitudinal direction of the slab 1 by a cylinder 3, and a heat insulating material 4 is attached to a heat insulating material holding member 5 on the west side of the slab 1. and are arranged along the longitudinal direction of the slab 1. Each of the heat insulating material holding members 5 is movable by a cylinder 6 in a direction perpendicular to the longitudinal direction of the slab 1, so that the heat insulating material 4 can be brought into close contact with the slab 1. be done. Note that the electrode 2 is provided with a cooling water supply pipe 7.

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, cylinder 3, heat insulating material 4, heat insulating material holding member 5, cylinder 6 The energization heating device of i# is supplied from a heating furnace (not shown).
This is also arranged near a table roller 8 that feeds the slab 1 to a hot rolling device (not shown).

In the present invention, using the rolling line as described above, heating of the slab 1 before hot rolling is performed as follows.

That is, the ingot, material, or continuous cast material slab 1 heated to the required temperature and discharged from the heating furnace is assembled into the multiple U-2
8 and is separated from the table roller 8, the west side is covered by the heat insulating material 4, and the electrodes 2 are brought into contact with both ends. Thereafter, in this state, electricity is applied to the slab 1 through the electrode 2, and the slab 1 generates heat due to the specific resistance of the slab 1 itself, and is heated to the point of being heated.

In the above process, it is preferable to heat the slab l in a heating furnace, and then raise the temperature of the slab l by an electric heating device to F h 15 and a half 1 for each furnace.

In other words, the heat source in the current heating device is electricity, and electricity is generally more expensive than heat sources such as gas, so heating each slab only with the current heating device from the beginning will reduce production efficiency and This is not appropriate from both cost standpoints. However, as mentioned above, the scales generated when grain-oriented silicon steel is heated are FeO, Fe2O, ・S +
The main component is 02, etc., and it starts flowing out as molten scale at around 1200°C. Therefore, in the heating furnace, slab 1
If the heating temperature range is set to a maximum of 1250°C, and then the heating in the temperature range exceeding that temperature range is performed using an electric heating device, it is possible to prevent scale accumulation in the heating furnace, thereby reducing the cost of the furnace repair mentioned above. Moreover, since the heat source is switched to electricity after preheating the slab, the heating time due to the use of electricity is relatively short, so there are no problems with cost or production efficiency.

For example, when using a continuously cast material slab, it is not necessarily necessary to heat it in a conventional heating furnace. It may also be heated to a required temperature using an electrical heating device. In addition, in particular, continuous casting materials have the disadvantage that they are more prone to abnormal grain growth when heated than agglomerated materials, but by heating with electricity as performed in this invention, the slab is uniformly heated. By doing so, such abnormal grain growth can be prevented.

Next, examples of this invention will be described.

Example The atmosphere in the walking beam heating furnace was adjusted to be constant at 1,320°C, and a silicon steel slab of 140 t x 1,050 w x 5,000 mm was heated in the walking beam heating furnace to 1,230°C, and then taken out from the heating furnace. The slab was heated to 1300°C using an electrical heating device. .

Comparative Example As in the above example, the atmosphere of the walking beam heating furnace was adjusted to be constant at 1320°C, and the walking beam heating furnace was used to generate 140t x 1050w x 5OO0
1 silicon steel was heated to 97° and 1,300°.

In the above Examples and Comparative Examples, the weight of the slab was first measured before heating, and the weight of the baked-out slab was measured again after heating to calculate the weight loss during the heating process. The results are shown in Table 1 and FIG.

Furthermore, the slab heating efficiency from the temperature at which electrical heating was started was measured for the example, and the slab heating efficiency in the walking beam heating furnace from the same temperature was measured for the comparative example. The results are shown in Table 1.

Furthermore, both Examples and Comparative Examples were repeated,
After hot rolling a portion of each slab, the magnetic properties were examined along the longitudinal direction of the slab. The results are shown in FIGS. 6 and 7.

It can be seen from Table 1 and FIG. 5 that the weight loss in the Examples is much smaller than that in the Comparative Examples.

The decrease in slab volume during this heating process is due to the generation and loss of molten scale, and from the results shown in Table 1 and Figure 5, the generation and loss of molten scale in the example was greater than that in the comparative example. It turns out that there are far fewer. This is because when electrical heating is performed as in the example, the slab is heated uniformly, so there is no relatively low-temperature area, and the entire slab is heated excessively to bring the low-temperature area to the required temperature. This is because there is no need to heat it.

In addition, since the slab is heated from the inside with electrical heating, there is no need to bring the outer surface of the slab into contact with the heating atmosphere and make it higher in temperature than the inside. This is because it can prevent Furthermore, from Table 1, it can be seen that the examples are more advantageous in terms of heating efficiency.

Furthermore, referring to FIGS. 6 and 7, it can be seen that the products obtained in the examples have more uniform magnetic properties in the longitudinal direction than those of the comparative examples.

This is because in the example, the entire slab is heated uniformly by electrical heating, and skid marks do not occur and the heating becomes uneven, unlike when heating in a heating furnace.

As described above, according to the method for heating a grain-oriented silicon steel slab of the present invention, Mn
, S, Se, etc. are heated to a predetermined rolling temperature in order to form a solid solution in the base metal of the slab.The entire slab can be uniformly heated by electrically heating at least the high temperature range up to the rolling temperature. , it is possible to produce a grain-oriented silicon steel sheet with uniform and good magnetic properties.

In addition, since the entire slab can be heated uniformly, the inhibitor can be completely dissolved in the slab base metal without overheating the slab, and according to the present invention, the inhibitor can be melted into the slab during the slab heating process. No scale occurs. As a result, it not only improves product run-through in the production of grain-oriented silicon steel sheets, but also prevents molten scale from accumulating in the heating furnace used for slab heating, thereby shortening the furnace life and reducing furnace efficiency. to prevent
Furthermore, it is possible to eliminate the need for furnace repair to remove deposits, and as a result, the manufacturing cost of grain-oriented silicon steel can be reduced.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a plan view showing an example of a slab energization heating device used for carrying out the present invention, Fig. 2 is a side view of the same, and Fig. 3 is shown in Figs. 1 and 2. A schematic diagram showing an example of a rolling/annealing line for grain-oriented silicon steel sheets configured with an electrical heating device, FIG. 4 is a view in the direction of arrow A in FIG. 3, and FIG. 8 is a slab weight of an example and a comparative example. The sixth figure is a diagram showing the loss rate, and the sixth figure is a diagram showing the results of examining changes in magnetic properties along the longitudinal direction of the grain-oriented silicon steel plate obtained by the example of the present invention.
FIG. 7 is a diagram showing the results of examining changes in magnetic properties along the longitudinal direction of grain-oriented silicon steel sheets obtained by the conventional method. l...Slab 4.2...Electrode, 3...Cylinder, 4...Insulating material, 5: ]-Insulating material holding member, 6...
cylinder,. 8...Table roller. Applicant Kawasaki Steel Co., Ltd. Agent Patent attorney Takehito Toyota (and 1 other person) Figure 5 Missing Φφ main phase --- ↓ - 1-νhi, Chinese, Irami 8 Figure 6 Slab length, 8-sided bacteria Figure 7 Slab length direction

Claims (1)

[Claims] A method for heating a grain-oriented silicon steel slab, which comprises heating the grain-oriented silicon steel slab to a predetermined rolling temperature before hot rolling, by electrically heating the grain-oriented silicon steel slab at least in a high temperature range up to the predetermined rolling temperature. .