JPH02263921A - Production of grain-oriented silicon steel plate - Google Patents

Abstract

PURPOSE:To produce a grain-oriented silicon steel plate excellent in magnetic properties by applying preliminary hot rolling to a slab prior to electrification and heating at the time of producing a grain-oriented silicon steel plate from a continuously cast slab of silicon steel. CONSTITUTION:A continuously cast slab having a composition consisting of 0.02-0.12% C, 2.0-4.0% Si, 0.04-0.20% Mn, 0.01-0.05% S and/or 0.005-0.05% Se, and the balance iron with inevitable impurities is subjected, with of without heating up to 900-1200 deg.C by means of a gas heating furnace, to preliminary hot rolling at 5-50% draft at >=900 deg.C average temp. in cross section of slab in a temp. region between 900 and 1200 deg.C. Successively, the above slab is subjected to heating up to 1300-1450 deg.C under the condition of >=20A/cm<2> current density by means of direct electrification and heating regarding the slab itself as a resistor and then to hot rolling. By this method, the grain-oriented silicon steel plate having superior magnetic properties can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing grain-oriented electrical steel sheets having excellent magnetic properties.

(Prior art) A unidirectional electrical steel sheet has a so-called Goss orientation (1
10) It is generally well known that crystals are manufactured by accumulating secondary recrystallized grains with <001> orientation. For magnetic properties, it is important that the accumulated crystal grains are close to the Goss orientation, and in order to generate such secondary recrystallized grains, fine inhibitors such as A, QN, MnSMnSe, etc. must be added before finishing annealing. It needs to be evenly distributed.

In order to obtain such fine and uniformly dispersed inhibitors, the slab must be heated to 1,300°C or higher, including the center of the slab, to form a solid solution of the inhibitor before hot rolling. An important requirement is to control inhibitors during rolling and post-rolling quenching. The above heating was usually done by gas heating the continuously cast slab, so if the inside of the slab was heated to 1300℃ or higher, the surface
The temperature becomes 350° C. or higher, and the atmosphere in the furnace inevitably becomes an oxidizing atmosphere. As a result, a large amount of slag, surface defects, and edge cracks occur, resulting in lower yields, higher costs, and shorter heating furnace life. In addition, even in a normal walking beam (WB) type gas heating furnace, heating from 1250°C to 1350°C is at most 1.5°C.
Because the heating rate is only ℃/min, the heating time is long (the difference between the coldest point in the slab and the surface temperature of the slab is more than 50℃ during the heating process. Heating tends to coarsen the crystal grains within the slab, forming band-shaped secondary recrystallization defects called linear fine grains in the final product, which is a major factor in deteriorating properties or reducing yield. If the crystal grains in the slab become coarser due to high-temperature and long-term heating, the grain boundaries will become significantly weaker.
Problems with slab breakage may occur in the heating furnace.

In order to satisfy the recent demand for lower iron loss in unidirectional electrical steel sheets, it is necessary to increase the Si content and make the finished product thinner (although increasing the Si content lowers the γ ratio at high temperatures and reduces the crystal grains within the slab). It promotes growth and increases the solid solution temperature of MnS etc.
Furthermore, as the product becomes thinner, a stronger inhibitor is required, and a more complete solid solution of MnS etc. is required by heating at a higher temperature and for a longer period of time.

As mentioned above, the appropriate temperature range for slab heating during hot rolling of unidirectional electrical steel sheets has a lower limit temperature determined from the standpoint of solid solution of the inhibitor, and an upper limit temperature determined from the standpoint of slab grain growth. In order to satisfy the iron loss requirement, the upper limit temperature falls and the lower limit temperature rises, creating a contradictory situation.]0 To overcome this problem, recently the slab heating of grain-oriented electrical steel sheets has been changed from gas heating to heating. , a technique of heating to a predetermined temperature by induction heating in a non-oxidizing atmosphere and a technique of heating to a predetermined temperature by direct current heating have been developed. Both of these technologies are heated to about 1000°C in a normal gas heating furnace and then heated to 1000°C by one of the following methods from the viewpoint of thermal efficiency and work efficiency.
A method of heating to a predetermined temperature of 300°C to 1450°C is adopted. The reason for using a non-oxidizing atmosphere is to suppress the generation of slag to improve yield and to reduce surface defects caused by slag.

The characteristics of this reheating method are that, unlike the conventional gas heating method, it is possible to perform arbitrary rapid heating according to the input current, and the temperature can be easily controlled, and the temperature deviation within the slab can be sufficiently small, suppressing slab grain growth. Compared to conventional gas heating, the temperature of the coldest spot in the slab can be maintained at a higher temperature for a longer period of time, and the thinner height is 81 mm.
It is possible to obtain hot-rolled sheets necessary for ultra-low iron loss grain-oriented electrical steel sheets.

However, in the induction heating method, heat generation is most likely to occur in the surface layer of the slab as an effect unique to the heating method. Therefore,
In order to generate enough heat in the center of the slab, it is possible to lower the induction frequency, but this will reduce thermal efficiency. In the case of continuously cast slabs, the center of the slab suffers from center segregation and requires high-temperature and long-term heating, especially for solid solution of MnS and the like, but induction heating is disadvantageous in heating the center of the slab as described above. In other words, in order to raise the temperature at the center of the slab, it is necessary to either input a huge amount of power and heat it at a low frequency, or rely on heat conduction from near the surface, which can also cause grain growth within the slab. Become. To avoid this, a method has been proposed in JP-A-62-103322 in which the heating conditions are accurately controlled by controlling the frequency during heating. On the other hand, the direct current heating method requires simpler and lower cost equipment than induction heating, and does not require the troublesome handling of inserting a slab into the induction heating coil, which is required with the induction heating method. , it can be as simple as simply pressing the electrodes against each end of the slab. In the hot rolling of grain-oriented electrical steel sheets, it is desirable to shorten the time from the time when the slab is heated and when it is extracted from the furnace to the completion of hot rolling, from the viewpoint of reducing the size of inhibitor precipitation. For this reason, the fact that slab heating requires less handling, shortens handling time, and shortens the time from extraction to completion of hot rolling is as important as the heating temperature. The law is favorable.

The direct current heating method enables uniform and rapid heating over the entire cross section of the slab, which is extremely advantageous for slab grain growth, and is also explained in JP-A-83-19570. In addition, the slab heating temperature can be easily controlled simply by controlling the current density, and it is possible to obtain the necessary solid solution conditions for the inhibitor without increasing the slab surface temperature more than necessary.

(Problems to be Solved by the Invention) However, according to repeated experiments by the present inventors, simply adopting the energization heating method does not produce sufficiently satisfactory results for the dramatically improved properties that were initially expected. I couldn't get it.

In order to stably produce thin (0.17 mo+ or less) products using direct current heating, the slab heating temperature must be set to 1300°C or higher, preferably 1350°C or higher, to promote the solid solution of inhibitors such as MnS. Although holding conditions for 10 minutes or more are required, grain growth in the slab begins to occur even under such conditions. Particularly different from gas heating, the internal temperature of the slab is uniform with a deviation of about 10°C, but a temperature difference of about 30°C occurs at about 10 degrees from the slab surface. This is because in direct a-electric heating, the slab itself acts as a heater and heats the furnace, and heat is radiated from the slab surface.

Therefore, crystal grain growth progresses at about 10III11 on the slab surface, weakening the grain boundaries, and cracking defects at the edges called edge cracks are likely to occur during hot rolling.

One possible solution to this problem is to add alternating current to the current flowing through the slab, but this would result in a significant increase in equipment costs.

Further, when the temperature reaches 1350° C. or higher, crystal grain growth progresses even inside the slab unless the current density of electrical heating is significantly increased (to 40 A/cd or higher) and rapid heating is performed.

Furthermore, when holding at temperatures above 1400°C, the current density is reduced to 8OA.
If rapid heating is not carried out to a temperature of /c- or higher, crystal grain growth will proceed and the product will likely be defective. In order to increase the current density, a further significant increase in equipment costs is unavoidable.

The present invention advantageously solves the above-mentioned problems, and aims to propose a method for more stably manufacturing thin grain-oriented electrical steel sheets by direct current heating.

(Means for Solving the Problems) Now, as a result of intensive research by the present inventors in order to solve the above problems, MnS, MnSe, and A11N.

It has been found that the above two problems can be solved by performing preliminary hot rolling to give 5 to 50% deformation in the preliminary hot rolling before heating the continuously cast slab of grain oriented electrical steel sheet using sb as an inhibitor. Invented it.

Conventionally, there is a method known in Japanese Patent Publication No. 54-27820, in which a continuously cast slab is deformed by 5 to 50% by pre-hot rolling, and then heated with gas to a temperature of 1800°C or higher to produce grain-oriented electrical steel sheets. As long as the method uses gas heating, it is not suitable for thin materials due to the various problems caused by heating the high-temperature slab mentioned above.
．． Up to 17 mm is the limit of industrial production.

Therefore, it has been experimentally confirmed that it is possible to achieve both more complete solid solution of the inhibitor and suppression of crystal grain growth within the slab by introducing pre-hot rolling at the same time as conducting electrical heating. That is, the present invention has C: 0.02 to 0,
12%, Si: 2.0-4.0%, Mn: 0.
04 to 0.20%, S: 0.01 to 0.05% and Se: 0.005 to 0.05%, and the remainder is iron and inevitable impurities. In a unidirectional electrical steel sheet manufacturing method that includes hot rolling, one-time cold rolling or intermediate annealing, a continuous casting slab is heated to 900 to 125 [] ° C. in a gas heating furnace, or Average cross-sectional temperature of slab 900℃ without heating
5 to 5 in the temperature range of 900 to 1200℃
A method for producing a unidirectional electrical steel sheet, which involves preliminary hot rolling at 0%, followed by heating to 1,300 to 1,450°C under conditions of a current density of 20 A/c- or more by direct current heating in which the slab itself is regarded as a resistor, and then hot rolling. is the first invention, and the first invention further includes AD:O, [105 to 0.040%, N: 0.003
The second invention uses steel with ~0.015% of 81-7, and the third invention uses steel with S
b: o, steel containing 002 to 0.05% is used, and both the second and third inventions produce unidirectional electrical steel sheets by performing the same treatment as the first invention. The main points are as follows.

(for production) The reasons for limiting the steel composition in the present invention will be described below.

Regarding the C content regulated in the present invention, if it is less than 0.020%, it causes a mixed grain structure, unstable secondary recrystallization, and deterioration of magnetic properties. On the other hand, if it exceeds (1, (112%), the time required for decarburization in the subsequent process will be longer.
The content was set at 0 to 0.12%.

Si has the effect of increasing specific resistance and reducing iron loss, but if it is less than 2.0%, its effect is small.

On the other hand, if the content increases, the steel becomes brittle and cold rolling becomes difficult, so the content should be 4.0% or less.

Mn combines with S or Se, respectively, to form the inhibitor M
It is a component that forms nS and MnSe and contributes to the development of secondary recrystallization. To enable this effect, Mn is 0.
04-0.209δ, S is 0. O1 to 0.05% and/or Se 0.005 to 0.05% are required.

Furthermore, when Al1N is used as an inhibitor, 8Ω: 0.00 is required to make AgN act self-effectively.
5 to 0.04%, and N: 0.003 to 0.015%. Further, when adding sb, 0.002 to 0.05% is required to exhibit its effect.

Pre-rolling must be carried out at 5% or more in order to prevent edge cracking. Further, in order to enhance the effect of suppressing crystal grain growth inside the slab, it is preferable that the content is 15% or more. On the other hand, 5
If it exceeds 0%, the shape of the slab becomes unstable, making it difficult to charge it into an energized heating furnace and to press the electrode. Therefore 5
The deformation was ~50%. The temperature of preliminary hot rolling is set at a lower limit of 900° C. due to the load on the rolling mill, and on the other hand, as the temperature increases, crystal grains become larger, so the upper limit is set at 1250° C. Further, when the continuously cast slab was electrically heated without being heated immediately after casting, the lower limit was similarly set to 900°C.

If the current density is below 20 A/cd, it takes a long time to raise the temperature to 8 degrees, which is over 1300 degrees Celsius, so 2 OA/cd is required.
The lower limit was c+#.

The lower limit of the heating temperature for electrical heating is 1300℃, which is inhibitor M.
Due to the solid solution of nS, the upper limit of 1450°C was set to prevent melting of the slab.

After hot-rolling, the coil is electrically heated, held at a predetermined temperature for a predetermined time, and then quickly hot-rolled and rapidly cooled to produce a hot-rolled coil.

Thereafter, the finished product is manufactured by performing known cold rolling once or by cold rolling with intermediate annealing.

Edge cracking at high temperatures also occurs when recrystallization progresses using the strain imparted during pre-hot rolling during electrical heating as a driving force, which suppresses coarsening of crystal grains and does not weaken grain boundaries, resulting in cracks near the surface. The occurrence of ear cracking is extremely reduced.

At the same time, grain growth within the slab hardly occurs 0.27
In manufacturing a product of mm+4, conventional weight rolling is not necessary and the tandem rolling method improves the conventional properties by 1.

(Examples) Examples of the present invention are shown in Table 1. Table 2 shows the components after steel making.

The conditions are that the amount of current is 110A/eJ, the average hot-rolling finish rolling temperature is 1000 to 1100°C, and the hot-rolling thickness is 2.3.
It's a dragon. O, 17m+* product has an intermediate thickness of 1.301+
A plate of No. 1 was produced by cold rolling on a scale with intervening annealing. Other finished products are produced by cold rolling.

(Effects of the Invention) As explained above, according to the present invention, it is possible to minimize the incidence of edge cracking, and also to almost eliminate the incidence of linear fine grains, and to easily manufacture thin products. is possible.

sub-agent

Claims (1)

[Claims] 1. C: 0.02-0.12%, Si: 2.0-4.0
%, Mn: 0.04-0.20%, S: 0.01-0.
05% and Se: 0.005 to 0.05%, and the remainder is iron and unavoidable impurities. Hot rolling is performed, and cold rolling is carried out once or twice with intermediate annealing in between. In the unidirectional electrical steel sheet manufacturing method that includes the above cold rolling process, continuous casting slabs are heated to 900 to 1250°C in a gas heating furnace.
Preliminary hot rolling of 5 to 50% in the temperature range of 900 to 1,200 degrees Celsius with or without heating at an average cross-sectional temperature of 900 degrees Celsius or higher, followed by direct energization in which the slab itself is regarded as a resistor. Current density 20A/cm^2 by heating
A method for producing a grain-oriented electrical steel sheet, which is heated to 1300 to 1450°C and then hot rolled under the above conditions. 2, C: 0.02-0.12%, Si: 2.0-4.0
%, Mn: 0.04-0.20%, S: 0.01-0.
05% and Se: 0.005-0.05%, Al: 0.005-0.040%, N: 0.0
Production of unidirectional electrical steel sheets, which involves hot rolling an electrical steel slab containing 0.03 to 0.015%, with the balance consisting of iron and unavoidable impurities, and cold rolling once or two or more times with intermediate annealing in between. In the method, continuous casting slabs are heated in a gas heating furnace for 900 m
The average cross-sectional temperature of the slab is 900°C or higher, either by heating to ~1250°C or without heating, and from 900 to 1200°C.
Preliminary hot rolling of 5 to 50% in the temperature range of ℃, followed by direct current heating, which treats the slab itself as a resistor, to a current density of 20
A method for producing a unidirectional electrical steel sheet, which comprises heating to 1300 to 1450°C and then hot rolling under conditions of A/cm^2 or more. 3, C: 0.02-0.12%, Si: 2.0-4.0
%, Mn: 0.04-0.20%, S: 0.01-0.
05% and one or two of Se: 0.005 to 0.05%, Sb: 0.002 to 0.05%, and the balance is iron and inevitable impurities.
In a unidirectional electrical steel sheet manufacturing method that includes one cold rolling or two or more cold rolling steps with intermediate annealing, a continuously cast slab is heated to 900 to 1250°C in a gas heating furnace, or the slab cross section is processed without heating. Average temperature 90
5 in the temperature range of 0℃ or higher and 900 to 1200℃
A unidirectional electrical steel sheet that is pre-hot-rolled to ~50%, then heated to 1300-1450°C at a current density of 20A/cm^2 or more by direct current heating, which treats the slab itself as a resistor, and then hot-rolled. Production method.