JP2807366B2 - Method for producing oriented silicon steel sheet having uniform and good magnetic properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one-way silicon material having excellent surface properties, uniform and good magnetic properties and good productivity, particularly as a core material for transformers and other electric equipment. It is intended to propose a method for manufacturing a steel sheet.

BACKGROUND OF THE INVENTION Grain-oriented silicon steel sheets are mainly used as so-called stacked iron cores or wound iron cores as core materials for transformers and other electric equipment, and have excellent magnetic properties such as magnetic flux density and iron loss. Is basically important.

In the production of a grain-oriented silicon steel sheet, it is particularly important that secondary recrystallization is performed from primary recrystallized grains to {110} <001> oriented crystals by so-called final finish annealing. In order to effectively promote the generation of such secondary recrystallized grains, a dispersed phase called an inhibitor for suppressing the growth of primary recrystallized grains is required. Typical examples of such inhibitors include sulfides and nitrides such as MnS, MnSe, AlN and VN, which have extremely low solubility in steel. Also, Sb, Sn, A
Grain boundary segregation-type components such as s, Pb, Cu, and Mo are also used as inhibitors.

[0004] These inhibitor effects are achieved by dispersing the inhibitors in a uniform and appropriate size prior to final finish annealing. For this purpose, the slab is heated to a high temperature before hot rolling, and the inhibitor component is sufficiently dissolved, and after the hot rolling step, the precipitation and dispersion state is controlled in the steps up to the secondary recrystallization. It is important that the primary recrystallized grain structure obtained by one or more times of cold rolling and one or more times of annealing be crystallized to a suitable size throughout the thickness direction and uniformly dispersed. It is.

[0005] In the above-mentioned slab heating at a high temperature, if the solid solution of the inhibitor is insufficient, sufficient secondary recrystallization cannot be obtained and the magnetic properties deteriorate. Further, it is known that the solid solution of the inhibitor approaches a completely solid solution state as the slab heating is performed at a higher temperature for a longer time, but on the other hand, the coarsening of the crystal grains progresses.

[0006] In recent years, in the steelmaking process in recent years, the method of producing slabs has largely shifted from the ingot making / bulking rolling method to the continuous casting method. If such a continuous casting method is simply applied to a grain-oriented silicon steel sheet, the step of refining the crystal structure by slab rolling is omitted, and columnar grains develop by rapid solidification inherent in the continuous casting method. As means for suppressing the generation of columnar crystals, a method of applying electromagnetic stirring or ultrasonic vibration is known. However, although these methods have the advantage of easy operation, it is difficult to completely prevent the generation of columnar crystals to the extent that they are reduced. On the other hand, if the casting temperature is lowered to near the liquidus line, the generation of columnar crystals can be prevented. However, the levitation of inclusions is reduced and the quality is deteriorated, and casting becomes impossible due to nozzle clogging. As described above, it is difficult to prevent the generation of columnar crystals in continuous casting, and the generation is inevitable.

The columnar grains tend to cause abnormal grain growth when the slab is heated at a high temperature, and remain as coarse elongated grains after hot rolling. The coarse stretched grains are unlikely to recrystallize even after cold rolling and annealing, and that portion is {110} <0 in the final finish annealing even if the inhibitory effect of the inhibitor is sufficient.
The secondary recrystallization of the <01> orientation results in a so-called band-like fine grain structure in which the magnetic properties are deteriorated.

[0008] On the other hand, the measurement of magnetic properties of a product is usually performed according to JIS.
Based on the law (JIS C 2550), width 30mm x length 28
Approximately 500 g of 0mm size specimen (24-28 sheets with 0.30mm thickness)
Is collected in the coil width direction. For this reason,
Even if one or two strip-like fine grains with a width of 30 mm are mixed in the above-mentioned specimen, the magnetic property value does not show significant deterioration, and at present, the existence of a defective part is not noticed. In the final finish annealing, secondary recrystallization, purification and forsterite coating are performed in the same process, so that once produced, there is no apparent distinction, and there is a problem that defective parts cannot be easily removed. .

[0009] Further, the coil formed by such band-like fine particles is used for a normal product coil width of about 1000 mm to 50 mm or 100 m.
When slitting to a sheet width of about m to obtain a material for a wound core, there is a problem that the ratio of the band-like fine grains to the entire slit width is extremely increased, and the magnetic properties of the iron core are remarkably deteriorated. Therefore, it is important to prevent the generation of band-like fine grains in the production of a grain-oriented silicon steel sheet from a continuously cast slab.

[0010] Further, an electrical insulating coating is usually applied to the surface of a silicon steel sheet used for an iron core, and when laminated and used, there is a measure to electrically insulate the layers and reduce overcurrent loss. However, when the surface of the steel sheet has flaws or has poor smoothness, not only the commercial value is reduced, but also the space factor is reduced, and the insulation property is reduced by tightening at the time of assembling the iron core. The temperature decreases, causing local heat generation, which may cause a transformer accident. Therefore, it is also important that the grain-oriented silicon steel sheet has no surface flaws and has excellent surface smoothness.

[0011]

2. Description of the Related Art In producing a grain-oriented silicon steel sheet from a continuously cast slab, as means for preventing the formation of band-like fine grains, for example, Japanese Patent Publication No. 50-37009 discloses a high magnetic flux density unidirectional silicon. Japanese Patent Publication No. 54-27820 discloses a method of producing cube-on-edge oriented silicon iron from a slab, and Japanese Patent Application Laid-Open Nos. 62-10213 and 62-130217 show a good direction of electromagnetic characteristics. Japanese Unexamined Patent Publication (Kokai) No. 3-115529 discloses a method for producing a unidirectional silicon steel sheet having uniform magnetic properties. 30-70% each, 5
A method has been proposed in which after performing rolling at 50%, 15-50%, 10-50%, and 1-10%, reheating to 1260 to 1440 ° C. and final hot rolling are performed.

In these methods, a strain is applied to the continuous cast slab in advance so that the slab is recrystallized by heating the slab to suppress the coarsening of crystal grains. However,
When a pre-strained slab is applied to an induction heating furnace, there is a problem in that secondary recrystallization does not occur in the vicinity of both ends of the sheet width even though the generation of band-like fine grains can be prevented.

Next, in the method for producing a silicon steel sheet having good magnetic properties disclosed in Japanese Patent Application Laid-Open No. 1-162725, a slab is subjected to a thickness rolling of 5% or more, and then the surface temperature is reduced to 13% by induction heating.
A method of heating the slab to 50 to 1500 ° C., applying a thickening rolling of 5% or more to the slab, and subsequently reducing the slab thickness by slab rolling, and then heating the slab surface temperature to 1350 to 1500 ° C. by induction heating, Slab surface temperature of 1350 by induction heating
There has been proposed a method in which the sheet is heated to about 1500 ° C., subjected to a thickness rolling of 5% or more, and then hot-rolled.

However, in the above method, when the thickness of the slab is increased by 5% or more by a rolling roll or a pusher, the thickness of the slab is not evenly increased, but becomes a so-called dog bone shape. When induction heating is used, there is a problem that the portion close to the induction heating coil is overheated and surface flaws are generated.
In the case of the method described above, the temperature drop near the width end is remarkable due to the slab thickening process and the slab rolling process, and it cannot be uniformly heated by the subsequent induction heating, and secondary recrystallization does not occur near the end portion. However, in the case of the above method, if the hot rolling ratio is increased by increasing the thickness by 5% or more, it is not possible to sufficiently destroy the crystal grains already remarkably coarsened by high-temperature heating and to recrystallize them. However, there are problems that band-like fine particles may be generated. In addition, in order to increase the center of the slab width by 5% or more by width pressing, the width reduction rate exceeds 25%, and surface cracks and internal cracking defects occur at the maximum pressure increasing part near the width end. There is also a problem that, when the slab surface temperature is heated to 1350 to 1500 ° C, partial melting starts at 1450 ° C or higher, and significant surface defects occur when held for 10 minutes or longer. there were.

Further, Japanese Patent Publication No. 56-18654 discloses a method for producing a grain-oriented electrical steel sheet, in which a slab is heated at a temperature of 1260 ° C. or more at a temperature range of 1250 to 1310 ° C. at an average heating rate of 150 ° C./hour or more. Heating methods have been proposed. However, this method has an effect of suppressing the crystal grain coarsening under the condition that the slab heating temperature is 1370 ° C or less.
At a high temperature of 1380 ° C, the effect of suppressing grain growth rapidly decreases, and at temperatures above 1400 ° C, significant surface oxidation and remarkable coarsening of the grains occur, making it impossible to obtain a steel sheet with expected magnetic properties and surface flaws. There was a problem.

Japanese Unexamined Patent Publication (Kokai) No. 63-109115 discloses a method for producing a grain-oriented silicon steel sheet having good electromagnetic characteristics, in which the slab is heated so that its center temperature becomes 1350 ° C. or more. Hold in the range of 1495 ° C for 5 to 60 minutes, and when the surface temperature is 1320 ° C or higher, 1420 to 1495 ° C
A method has been proposed in which the temperature is rapidly increased at a rate of 8 ° C./min or more until the crystal grain size is reached to suppress the crystal grain coarsening. In this method, the slab temperature is significantly higher than the conventional gas heating furnace alone, and the holding time is relatively short. However, when the continuous cast slab is directly heated to such a high temperature region, remarkable grain growth occurs, band-like fine grains are generated in the product, and holes and surfaces at a level where commercial value is lost due to remarkable surface oxidation and selective oxidation of grain boundaries. There were problems such as frequent wounds.

In addition, as a method of inductively heating a slab, Japanese Patent Application Laid-Open No. 63-100128 discloses a method for producing a grain oriented silicon steel sheet having good magnetic properties and surface properties, and Japanese Patent Application Laid-Open No. 63-109115 discloses a method having good electromagnetic properties. Japanese Patent Application Laid-Open No. 2-138418 describes a method for producing a grain-oriented silicon steel sheet having a slab center temperature of 1300 to 1450 ° C. and a temperature of 1350 ° C. or more (surface temperature). Is 1420-1495
° C), and a method of controlling the temperature to 1400 to 1470 ° C. However, these methods do not take measures to prevent coarsening of crystal grains, and there is a problem in that strip-shaped fine grains are generated by slab heating at 1380 ° C. or higher.

[0018]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and inhibits productivity of a grain-oriented silicon steel sheet having excellent surface properties and uniform magnetic properties as an iron core material. It is intended to propose a method of manufacturing without performing.

[0019]

SUMMARY OF THE INVENTION The present invention relates to a slab heating method, hot rolling conditions, and the like for obtaining a product having excellent surface properties, uniform magnetic properties and good magnetic properties from a continuous cast slab for oriented silicon steel sheets. The results of intensive studies have been achieved. First, the experimental results on which the present invention is based are described below.

[0020] The present inventors have previously considered that if the slab crystal grains are 20 mm or less, a microstructure will be formed in the hot rolling (rough rolling, finish rolling), cold rolling and annealing steps, and no band-like fine grains will be generated on the product sheet. He perceived and began experimenting with this recognition.

Experiment 1 First, since the generation of the band-like fine grains of the product was caused by the coarse crystal grains after slab heating, a measure for miniaturizing the slab structure was examined.

C: 0.035 wt%, Si: 3.15 wt%, Mn: 0.07
After slowly cooling a 215 mm thick continuous cast large slab containing 5 wt% and S: 0.018 wt%, 215 (thickness) × 200 × 2
Cut out a test piece with a size of 00mm and use a small electric furnace to 900 ~ 13
After heating to a temperature range of 50 ° C. and performing preliminary hot rolling in a rolling reduction range of 0 to 50%, a solid solution treatment was performed in a heating furnace at 1380 ° C. for 50 minutes to investigate the crystal grain size. FIG. 1 summarizes the results of these investigations.

FIG. 1 shows the relationship between the preliminary hot rolling reduction and the crystal grain size with the preliminary hot rolling temperature as a parameter. As is clear from FIG. Preliminary hot rolling in the temperature range of 900 to 1300 ° C is necessary to reduce the grain size to 20 mm or less, where the temperature is low and the preliminary hot rolling reduction rate is high, so that the grain size is 20 mm or less, which does not generate band-like fine grains. It was often found that the rolling reduction required 2% or more.

Experiment 2 Next, a test piece cut into a size of 215 (thickness) × 200 × 200 from the continuous cast slab similar to the above-mentioned experiment 1 was used.
℃ × 30 minutes of heating, followed by preliminary hot rolling at a reduction rate of 0 to 50%, followed by heating at 1430 ℃ × 30 minutes, 5 passes of rough rolling into sheet bars of 25 and 40 mm thickness, Immediately after splitting into two, half of the hot rolled sheet was subjected to finish rolling to form a 2.4 mm thick hot rolled sheet.

These hot-rolled sheets were further subjected to primary cold rolling to obtain 0.1%.
After having a thickness of 72 mm, it is subjected to intermediate annealing at 930 ° C for 2 minutes,
Further, secondary cold rolling is performed to a final thickness of 0.30 mm, and thereafter, decarburizing annealing is performed at 820 ° C. for 3 minutes in wet hydrogen, and then an annealing separator mainly containing MgO is applied. In hydrogen
Finish annealing was performed at 1180 ° C. for 5 hours to obtain a product plate.

In the above-mentioned material examination, samples are taken from each sheet bar after rough rolling, the state of destruction and recrystallization of crystal grains in the slab stage is investigated, and the magnetic characteristics and crystal structure of each product sheet are examined. investigated.

Based on the results of these investigations, FIG. 2 shows the relationship between the unrecrystallized stretched grain generation rate and the rough rolling reduction rate in the cross section of the sheet bar. From this experiment, it was recognized that the residual ratio of the stretched grains tended to be lower as the preliminary hot rolling reduction ratio was higher and the rough rolling reduction ratio was higher.

As a result, it was found that in order to keep the residual ratio of the stretched grains at 2% or less, it is necessary to perform preliminary hot rolling to keep the slab grains at 20 mm or less and to have a rough rolling reduction of 80% or more. did. It was also found that the recrystallized grain size tended to be finer as the rolling reduction was higher.

Next, FIG. 3 shows the relationship between the measurement results obtained by measuring the magnetic properties of the product plate for each 30 × 280 mm test piece in accordance with the JIS method and the rolling reduction ratio. Magnetic properties are better when the preliminary hot rolling reduction is higher and the rough rolling reduction is higher. In addition, it was confirmed from the crystal structure investigation that band-like fine grains were generated when the preliminary hot rolling was not performed or when the rough rolling reduction was less than 80%.

Experiment 3 Based on the above experimental results, an experiment was further conducted with a large slab. C: 0.037 wt%, Si: 3.18 wt%, Mn: 0.072 wt%,
S: 190mm, 215mm, 250m containing 0.017 wt%
m and 300mm continuous cast slabs were
After heating at 00 ° C for 30 minutes, pre-rolling with 5% reduction was performed, then it was placed in an induction heating furnace, heated at 1420 ° C for 20 minutes, and finished by rough rolling to form a 30 mm thick sheet bar. Rolled into a 2.4 mm thick hot rolled sheet. Further, the hot-rolled sheet was subjected to primary cold rolling, intermediate annealing and secondary cold rolling under the same conditions as in Experiment 2 to a final thickness of 0.30 mm, and decarburizing annealing under the same conditions as in Experiment 2; The product sheet was subjected to the application of an annealing separator and finish annealing, and the magnetic properties and crystal structure were investigated. After removing 15mm from both ends of the board width 1030mm,
FIG. 4 shows the relationship between magnetic properties and slab thickness measured by cutting out a test piece having a width of 100 mm and a length of 400 mm.

As is apparent from this figure, the magnetic characteristics are slab thicknesses of 250 mm, 215 mm, 190 mm, and 300 mm in the order of good quality, and the magnetic characteristics of the 300 mm thick slab are remarkably deteriorated. As a result of investigating the cause, it is considered that the inhibitor dissolution was insufficient in the 300 mm thick slab because the segregation index of the inhibitor component S (the ratio of the maximum segregation S amount of molten slab to the amount of molten steel S) was abnormally high at 1.95. Was done. Therefore, it was found that simply increasing the initial slab thickness and increasing the rough rolling reduction ratio did not solve the problem, and it was found that it was important to select a slab thickness that could prevent segregation and sufficiently dissolve the inhibitor.

The slab thickness is limited to 250 mm at which a segregation index of less than 1.50 is obtained in order to sufficiently dissolve the inhibitor by heating in a temperature range of 1380 to 1440 ° C. for a short time in a range of 5 to 50 minutes. Preferably, the lower limit is 180 mm, at which a predetermined preliminary hot rolling reduction and a rough rolling reduction can be secured.

Further, it was found that all of the above four types of slabs did not undergo secondary recrystallization at a width of about 50 mm near the edge of the plate width, and the magnetic characteristics were significantly deteriorated. The cause of this was investigated using a decarburized annealed plate before secondary recrystallization. As a result, it was found that the inhibitor size was as large as 0.5 μm, and the inhibitor function was significantly reduced.

Experiment 4 In order to find a solution to the above-mentioned secondary recrystallization failure at both ends of the sheet width, a continuously cast slab having a slab thickness of 215 mm having the same composition as in Experiment 3 was heated in a gas heating furnace at 1230 ° C. for 30 minutes. After heating for 10 minutes and performing preliminary hot rolling at a rolling reduction of 10% in a rough rolling mill, the following treatments were performed before heating in an induction heating furnace.

Slab 1: Immediately charged into an induction heating furnace.
The temperature at a position 15 mm from the end of the slab width was -120 ° C compared to the temperature at the center of the width. Slab 2: Heat from both sides on the table until it is charged into the induction heating furnace, and make the temperature at the position of 15 mm from the end of the slab width -50 ° C compared to the temperature at the center of the width, and then into the induction heating furnace Charged. Slab 3: Heated in the same manner as described above, the temperature at a position 15 mm from the end of the slab width was set to -5 ° C compared to the temperature at the center of the slab, and then the slab was charged into the induction heating furnace. Slab 4: Heated in the same manner as in Slab 2, and the temperature at the position 15 mm from the end of the slab width is +30 compared to the temperature at the center of the width.
C. and then charged into an induction heating furnace.

Next, each slab charged into the induction heating furnace as described above was heated at 1410 ° C. for 25 minutes by induction heating, then roughly rolled into a 30 mm-thick sheet bar, followed by finish rolling to a 2.4 mm-thick sheet bar. A hot rolled sheet was used.

These hot-rolled sheets were subjected to primary cold rolling, intermediate annealing, and secondary cold rolling under the same conditions as in Experiment 2 to obtain 0.30 mm
, And subjected to decarburizing annealing, application of an annealing separator, and finish annealing under the same conditions as in Experiment 2 to obtain a product sheet.
The magnetic properties and crystal structure of each product sheet thus obtained were investigated. After removing 15 mm from both ends of the plate width of 1030 mm, an average value of the measured values of the magnetic properties (n = 1) was cut out from a test piece having a width of 100 mm and a length of 400 mm.
Table 1 shows the observation results of 0), the range thereof, and the crystal structure.

[0038]

[Table 1]

As is clear from Table 1, before the slab is introduced into the induction heating furnace, the slab end is heated, and the temperature near the slab end is in the range of -50 to + 30 ° C. with respect to the temperature at the center of the slab width. By doing so, it was found that secondary recrystallization progressed to the end of the sheet width, and the above-mentioned problem of secondary recrystallization failure could be solved.

The reason for this is not clear, but it is considered that when a large temperature difference occurs in the slab width direction, the induction heating does not raise the temperature to the temperature necessary for solid solution of the inhibitor, and the temperature is not sufficiently uniform. Can be The above temperature difference is + 30 ° C
When the end of the slab is heated so as to exceed the range, surface defects due to overheating occur.

Experiment 5 In order to make the magnetic properties uniform in the width direction and to easily obtain high magnetic properties, it is important to select the slab thickness. However, the range of slab thickness applicable for this purpose is narrow, and the size of the continuous casting mold must be changed frequently, and the productivity of the continuous casting operation including other steel types due to the change of the mold size is significantly reduced. Newly occurred.

Therefore, as a means for suppressing segregation, increasing the rough rolling ratio and improving the magnetic properties and improving the productivity, the segregation of the inhibitor component is small, and it is used relatively frequently in other steel types. A solution to the above problem was studied by using a 215 mm thick continuous cast slab and increasing the thickness with a width press.

C: 0.041 wt%, Si: 3.35 wt%, Mn: 0.
073 wt%, Se: 0.019 wt%, Sb: 0.025 wt%, Mo: 0.01
Six 215mm thick continuous cast slabs containing 2 wt% were heated to 1100 ° C in a gas heating furnace, and then reduced by 2% by a width press.
%, 8%, 15%, 25% and 35% were applied under a width reduction, flattened and rolled immediately to a thickness of 215 mm, and subsequently heated at 1430 ° C. for 15 minutes in an induction heating furnace.

The slab was heated from both sides by a burner on the table from the gas heating furnace until it was extracted and subjected to the width pressing, and from the width pressing to the operation into the induction heating furnace. The temperature difference between the position 15 mm from the center and the central part was kept within 0 to -20 ° C.

The slab extracted from the induction heating furnace was rough-rolled into a 35 mm-thick sheet bar, followed by finish rolling into a 2.7 mm-thick hot-rolled sheet. These hot plates are further cold-rolled to a thickness of 0.82 mm, subjected to intermediate annealing at 950 ° C. for 1 minute, further cold-rolled to a final plate thickness of 0.30 mm, and then wet-hydrogen After decarburizing annealing at 820 ° C. for 2 minutes in the atmosphere, an annealing separator containing MgO as a main component was applied thereto, and subjected to finish annealing at 1180 ° C. for 5 hours in hydrogen to obtain a product plate. The product sheets thus obtained were investigated for magnetic properties, crystal structure and occurrence of surface defects. Table 2 shows the results.

[0046]

[Table 2]

As can be seen from Table 2, no band-like fine particles were generated at a width reduction ratio of 8 to 25%, and the magnetic properties were improved. on the other hand,
At a width reduction ratio of 4% or less, only a small increase in pressure at the center is obtained, and the effect of preventing band-like fine particles is small. At a width reduction ratio of 35% or more, a so-called dog bone is remarkably generated near the end. At this portion, cracks occurred on the surface and inside.

From the results of a series of experiments described above, in order to prevent surface flaws and to obtain a oriented silicon steel sheet having good and uniform magnetic properties without impairing the productivity, the following,,, and It turned out that we needed to follow.

Before the slab is heated, a width reduction of 8% or more, preferably 25% or less is applied. Next, flattening preliminary rolling with a rolling reduction of 2 to 30% is performed. The slab after the pre-rolling is heated so that the difference ΔT between the end portion temperature and the width center portion temperature is in the range of −50 ° C. ≦ ΔT ≦ + 30 ° C., and then charged into an induction heating furnace and heated. The slab extracted from the heating furnace is subjected to rough rolling with a total draft of 80% or more.

The present invention has been made based on the above findings, and the gist is as follows.

Si: A silicon steel slab containing 2.5 wt% or more and 4.0 wt% or less is subjected to hot rolling by heating at a high temperature, and then to cold rolling once or twice with intermediate annealing. After finishing to the final sheet thickness, decarburizing annealing, then applying an annealing separator and performing finish annealing to produce a unidirectional silicon steel sheet, prior to heating the slab to high temperature, hot slab Width reduction of 8% or more and reduction of 2
% Or more and 30% or less and then flattening preliminary rolling, and then adjusting the temperature difference ΔT between the slab end surface temperature and the slab center surface temperature to within a range of −50 ° C. <ΔT <+ 30 ° C. It is heated to a temperature range of 1380 ° C or higher and 1440 ° C or lower by induction heating, and is subjected to hot rolling in which rough rolling with a rolling reduction of 80% or more is performed followed by finish rolling. This is a method for producing a grain-oriented silicon steel sheet having excellent magnetic properties. Here, flattening pre-rolling is rolling in which the cross-section of a dockbone shape is reduced by width reduction into a generally rectangular shape using flat rolls, etc., and the pre-rolling reduction rate increases under width pressure for the purpose of suppressing grain growth. Expressed by the median width at which the thickness becomes minimum. Preliminary rolling includes rolling to a thickness smaller than the initial slab thickness using a flat roll or the like within a range where the rough rolling reduction is not insufficient.

[0052]

The silicon-containing steel used as the material of the present invention has well-known conventional component compositions. Among them, preferred representative compositions are as follows.

C: 0.01 to 0.10 wt% C is a component useful not only for uniform micronization of the structure during hot rolling and cold rolling but also for development of the Goss orientation.
It is preferable to contain 0.01 wt% or more. However, if the content exceeds 0.10 wt%, the Goss orientation will be disturbed, so the upper limit is preferably set to 0.10 wt%.

Si: 2.5 to 4.0 wt% Si increases the specific resistance of the steel sheet and effectively contributes to the reduction of iron loss. However, if it exceeds 4.0 wt%, the cold rolling property is impaired.
If it is less than 5 wt%, not only the specific resistance decreases, but also α-γ during final high-temperature annealing performed for secondary recrystallization and purification.
The transformation causes randomization of the crystal orientation, and a sufficient iron loss improvement effect cannot be obtained. Therefore, its content is 2.5
wt% and 4.0 wt% or less.

Mn: 0.02 to 0.12 wt% Mn is preferably contained at least 0.02 wt% or more in order to prevent hot embrittlement, but if it is too much, the magnetic properties are deteriorated. It is preferable that

One or more selected from S and Se: 0.00
5 to 0.06 wt% S and Se are both effective components as inhibitors for controlling secondary recrystallization of grain-oriented silicon steel sheets. From the viewpoint of suppressing power, the content is preferably 0.005 wt% or more, but if it exceeds 0.06 wt%, the effect is impaired. Therefore, the lower and upper limits of the content are 0.005 wt
% And about 0.06 wt%.

Al: 0.005 to 0.10 wt%, N: 0.004 to 0.
015 wt% Al and N become AlN and act as inhibitors. To act as an inhibitor, Al is 0.005--0.
Preferably, 10 wt% and N are contained in the range of 0.004 to 0.015 wt%. That is, if the content is less than the lower limit, the suppressing power is insufficient, and if it exceeds the upper limit, the crystal grains are coarsened and the suppressing power is impaired.

Here, the above-mentioned MnS, MnSe-based and AlN-based can be used in combination. In addition, as the inhibitor component, in addition to the above-mentioned S, Se and Al, Cu, Sn, Sb, Mo
And P, etc., are advantageously compatible, so that they can be contained together in small amounts, respectively. The preferred content ranges of these components are Cu and Sn: 0.01 to 0.15 wt% each, and Sb and Mo: 0.005 to 0.005 each.
0.1 wt%, P: 0.01 to 0.2 wt%. In addition, about each of these inhibitor components, both independent use and combined use are suitable.

Next, the manufacturing process conditions of the present invention will be described. 180 having the above component composition melted by an ordinary method
First, the continuous casting slab of ~ 250mm thickness is preheated. When the preheating temperature exceeds 1300 ° C., the strain imparted by the pre-rolling is quickly recovered, the effect of refining the crystal grains is weakened, and
If it is less than 10, the hot strength of the steel increases and the energy for deformation becomes too large. Therefore, it is preferable that the temperature range is 900 ° C. or higher and 1300 ° C. or lower as a temperature range in which the effect of refining crystal grains can be obtained and hot working is easy.

The pre-heated slab is subjected to a width reduction of 8% or more. If the rolling reduction is less than 8%, a sufficient thickening at the center in the width direction cannot be obtained, and the effect of preventing band-like fine particles is small. When the content exceeds 25%, a so-called dog bone is remarkably generated in the vicinity of the end portion, and cracks easily occur on the surface or inside. Therefore, the width reduction is preferably 8% or more, and the upper limit thereof is preferably 25% or less.

Here, the width reduction may be not only the above-mentioned press but also a vertical roll, an edger or any other suitable for this purpose.

Following the width reduction, flattening preliminary rolling is performed at a reduction ratio of 2 to 30%. The flattening pre-rolling is necessary for flattening the slab surface, but is also necessary for reducing the slab crystal grains. If the rolling reduction is less than 2%, the slab crystal grains cannot be refined to 20 mm or less. On the other hand, if it exceeds 30%, the rolling reduction in the rough rolling in hot rolling decreases, and the stretched grains remain in the sheet bar. Rate is higher. Therefore, the rolling reduction is 2% or more and 30% or less.

The slab after the preliminary rolling is heated so that the temperature difference ΔT between the width end and the width center satisfies −50 ° C. ≦ ΔT ≦ + 30 ° C., and then charged into the induction heating furnace. This ΔT is −50 ° C.
If the temperature falls below a lower level, sufficient induction heating cannot be obtained by subsequent induction heating, the temperature required for the solid solution of the inhibitor does not reach at the width end, and if the temperature rises higher than + 30 ° C., surface defects due to overheating occur. Therefore, ΔT is −50 ° C. ≦ ΔT ≦ +
Keep in the range of 30 ° C.

As a method of controlling the temperature of the slab width end portion, a method using a gas burner is preferable. It is also effective to prevent the increase.

The slab charged in the induction heating furnace is heated here until the inhibitor is dissolved. Usually, the solid solution treatment of the inhibitor is carried out at 1250 ° C. or higher, and for a long time at a low temperature, and for a short time at a high temperature. In the present invention, in order to prevent slab crystal grains from coarsening and to prevent surface flaws, the heating temperature is 1380 ° C. or more and 1440 ° C. or less, and in this heating, an inert gas atmosphere is used, and the heating time is 5 minutes. It is desirable that the heating be performed for a short time within 50 minutes or more.

Hot rolling is performed after heating in the induction heating furnace. In this case, the rolling reduction in the rough rolling needs to be 80% or more in order to break down the slab crystal grains and make them finer. After this rough rolling, a hot rolled steel strip having a thickness of 1.4 to 3.5 mm is formed by finish rolling.

Further, after pickling this hot-rolled steel strip, cold rolling is performed once or two or more times with intermediate annealing, and decarburizing annealing is performed.
Although a directional silicon steel strip is formed by applying an annealing separator and finish annealing, these steps may be performed according to a conventional method.

[0068]

EXAMPLES Example 1 C: 0.042 wt%, Si: 3.35 wt%, Mn: 0.072 wt%, S
e: a 250 mm thick slab containing 0.019 wt% of Sb, 0.025 wt% of Sb, and 0.012 wt% of Mo, and the balance substantially consisting of iron, was preheated in a gas heating furnace under the conditions shown in Table 3; Subsequently, after flattening preliminary rolling was performed under the width pressure, the temperature difference ΔT between the end and the center of the slab was adjusted. Following this,
It was charged in an induction heating furnace and heated at 1430 ° C. for 15 minutes.

[0069]

[Table 3]

Next, these slabs extracted from the induction heating furnace were each converted into a sheet bar having a thickness of 40 mm by rough rolling, and then a hot-rolled sheet having a thickness of 2.0 mm by finish rolling. Next, these hot-rolled sheets were annealed at 950 ° C. for 1 minute, and the first cold-rolling was performed to a sheet thickness of 0.60 mm.
And then subjected to secondary cold rolling to a final thickness of 0.23 mm. Next, after decarburizing annealing at 820 ° C. for 3 minutes in wet hydrogen, an annealing separator containing MgO as a main component is applied, and then subjected to finish annealing at 1200 ° C. for 5 hours in hydrogen to perform directional quenching. An element steel plate was used.

After removing 15 mm from both ends of the coil having a width of 960 to 1200 mm thus obtained, samples were taken from the front and rear ends and the center of the coil, and the magnetic characteristics based on the JIS method were measured and the surface flaw was measured. And the state of secondary recrystallization were investigated. The results of these surveys are shown in Table 3 above.

As is evident from Table 3, the application of the present invention does not cause surface flaws or band-like fine particles even with a thin product, and improves the magnetic characteristics.

Example 2 C: 0.075 wt%, Si: 3.20 wt%, Mn: 0.075 wt%, S
e: 0.020 wt%, Sb: 0.025 wt%, Cu: 0.04 wt%, Sn:
A 215 mm thick continuously cast slab containing 0.03 wt%, Mo: 0.012 wt% and N: 0.0085 wt%, the balance being substantially iron, was preheated in a gas heating furnace under the conditions shown in Table 4, Subsequently, after flattening preliminary rolling was performed under the width pressure, the temperature difference ΔT between the end and the center of the slab was adjusted. Subsequently, it was charged into an induction heating furnace and heated at 1420 ° C. for 20 minutes.

[0074]

[Table 4]

Next, these slabs extracted from the induction heating furnace were each subjected to rough rolling to form a 35 mm-thick sheet bar, and then to finish rolling to obtain a 2.8 mm-thick hot-rolled sheet. Next, these hot-rolled sheets were subjected to primary cold rolling to a sheet thickness of 1.8 mm, then subjected to intermediate annealing at 1100 ° C. for 2 minutes, and subjected to secondary cold rolling to a final sheet thickness of 0.30 mm. Next, in wet hydrogen at 840 ° C,
After decarburizing annealing for 3 minutes, an annealing separator containing MgO as a main component was applied, and finish annealing was performed in hydrogen at 1200 ° C. for 20 hours to obtain a grain-oriented silicon steel sheet.

After removing 15 mm from both ends of the coil having a width of 960 to 1200 mm thus obtained, samples were taken from the front and rear ends and the center of the coil, and the magnetic characteristics based on the JIS method were measured and the surface flaw was measured. And the state of secondary recrystallization were investigated. The results of these surveys are shown in Table 4 above.

As is clear from Table 4, application of the present invention makes it possible to prevent surface flaws and band-like fine grains from occurring even in a high magnetic flux density oriented silicon steel sheet, and to improve the magnetic properties. Has been removed.

[0078]

According to the present invention, the continuous casting slab is pre-heated, subjected to flattening pre-rolling under a width reduction, and the temperature difference in the slab width direction is controlled, and the slab is charged into an induction heating furnace to sufficiently solidify the inhibitor. By optimizing the processing conditions of each step of applying heating to melt, and further optimizing the draft in the subsequent rough rolling,
Produces a grain-oriented silicon steel sheet that prevents surface flaws and generates a uniform secondary recrystallized structure without band-like fine grains, and that has uniform and excellent magnetic properties without impairing productivity. And

The grain-oriented silicon steel sheet obtained by the present invention has excellent magnetic properties and excellent safety against transformer accidents and the like, and can be advantageously used as an iron core of electrical equipment.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a preliminary hot rolling reduction and a crystal grain size.

FIG. 2 is a graph showing a relationship between a rough rolling reduction ratio and a residual ratio of stretched grains in a sheet bar.

FIG. 3 is a graph showing a relationship between a rolling reduction and a magnetic flux density B8 of a grain-oriented silicon steel sheet product.

FIG. 4 is a graph showing the relationship between the thickness of a continuous cast slab and the magnetic flux density B8 of a grain-oriented silicon steel sheet product.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Shimomu 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. Kawasaki Steel Corporation Mizushima Works (56) References JP-A-3-133501 (JP) , A) JP-B-52-47179 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) C21D 8/12

Claims (1)

(57) [Claims] 1. A silicon steel slab containing not less than 2.5 wt% and not more than 4.0 wt% of Si is subjected to hot rolling by heating at a high temperature, and then cold rolling is performed once or twice or more with intermediate annealing. After finishing to a final sheet thickness, decarburizing annealing, and then applying an annealing separator and performing finish annealing to produce a unidirectional silicon steel sheet, prior to high-temperature heating of the slab, the slab Width reduction with hot reduction of 8% or more, flattening pre-rolling with a reduction of 2% or more and 30% or less, and then the temperature of the slab end surface temperature and the slab center surface temperature The difference ΔT is -50
After adjusting the temperature within the range of ℃ ≤ ΔT ≤ + 30 ° C, heat it to a temperature range of 1380 ° C or more and 1440 ° C or less by induction heating,
A method for producing a grain-oriented silicon steel sheet having excellent surface properties and uniform and excellent magnetic properties, characterized by performing hot rolling in which finish rolling is performed after rough rolling of 80% or more.