JPH08215710A - Manufacture of hot rolled silicon steel sheet excellent in surface property - Google Patents

Abstract

PURPOSE: To manufacture a hot rolled silicon steel sheet without surface crack and excellent in surface properties. CONSTITUTION: After heating a silicon containing steel slab to high temp., hot finish rolling with a tandem mill which is executed succeeding to rough rolling is executed taking the draft at a 1st stand as 20-70% and on condition that the temp. TF1 of a rolled stock on the inlet side of the 1st stand and temp. TF12 of the rolled stock between the 1st and the 2nd stands satisfy the relationship of the next inequality I. TF1 ( deg.C)-TF12 ( deg.C)<=80 ( deg.C)...I.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a hot-rolled silicon steel sheet having excellent surface properties, which is intended to prevent deterioration of magnetic properties of grain-oriented electrical steel sheets due to surface cracking or the like. Is.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are used as iron core materials for transformers and other electrical equipment, and are required to have high magnetic flux density and low iron loss. Such magnetic properties are
<110} plane parallel to the rolling surface and <
This is achieved by forming a secondary recrystallized structure composed of a texture having a so-called Goss orientation as a main orientation having a 001> axis.

For that purpose, grain-oriented electrical steel sheets include
It is known that various additive components such as silicon are added, but as a result, workability is deteriorated, and particularly surface cracks and surface defects due to hot rolling are likely to occur remarkably.

If the degree of surface cracks or surface flaws is significant, not only the defects on the appearance but also the deterioration of various characteristics such as a decrease in space factor and a decrease in interlayer insulation property, and thus surface cracks and surface flaws are generated. Prevention is one of the important issues in the manufacturing process.

Heretofore, as a method for reducing cracks in the hot rolling process of grain-oriented electrical steel sheets, for example, Japanese Patent Laid-Open No. 61-9 has been proposed.
As disclosed in Japanese Patent No. 521 (a method for manufacturing a high magnetic flux density, low iron loss unidirectional silicon steel sheet with excellent surface properties), a method of suppressing grain boundary oxidation by adding Mo or the like; Japanese Patent Application Laid-Open No. 2-182832 (method for producing grain-oriented silicon steel sheet having excellent magnetic properties and surface properties), Japanese Patent Laid-Open No. 3-115526 (method for producing unidirectional silicon steel sheet having excellent magnetic properties and surface properties) ) And JP-A-62-149815 (method for producing a low iron loss unidirectional silicon steel sheet with few surface defects) and the like, the structure is refined by recrystallization to cause cracking. There is a method of reducing it.

However, although some improvement effects are recognized by applying these methods, these methods do not provide sufficient results to meet the recent high requirements for surface properties.

Further, as disclosed in Japanese Patent Laid-Open No. 63-295044 (method for producing grain-oriented electrical steel sheet having excellent surface properties and magnetic properties), the upper limit of the in-reactor time at high temperature during slab heating is proposed. There is also a method to suppress the occurrence of slag by providing a
All of these not only lead to a decrease in productivity due to operational restrictions, but also the effects themselves are limited, and they are not at the level of satisfying the current strict quality requirements.

As described above, all of the conventional techniques aimed at reducing the occurrence of cracks are techniques relating to the improvement of the slab heating method, and their applicability and effect are limited. Therefore, the present inventors have studied each step in detail based on the assumption that there may be other factors that have a great influence, and paid particular attention to the rolling temperature of the hot rolling step.

By the way, regarding the methods for regulating the rolling temperature up to now, there are disclosed examples listed below, but all of them have different purposes from the present invention and are not effective means for preventing surface cracks. It couldn't be.

That is, Japanese Patent Application Laid-Open No. 5-9580 (method for producing thin grain silicon steel sheet having extremely excellent magnetic properties)
A technique for improving the magnetic properties by setting the hot finish rolling inlet temperature to 1000 to 1150 ° C has been proposed and disclosed. However, this technique is intended to improve the magnetic properties by controlling the precipitation size and dispersion state of the inhibitor that precipitates during the finish rolling process, and the effect of improving the surface crack aimed at by the present invention was not obtained. .

In Japanese Patent Publication No. 62-48725 (method for producing thin high magnetic flux density grain-oriented electrical steel sheet), the hot finish front temperature is controlled to 1150 to 1250 ° C. to cause precipitation in the finish rolling process. Precipitating the inhibitor uniformly and finely, and then controlling the surface temperature after hot finishing to 950 to 1100 ℃ to suppress the precipitation of MnS in the finishing stand, and to control the coil winding temperature to 500 to 600 ℃. Thus, a technique has been proposed and disclosed in which the precipitation of AlN from the finishing stand to the winding is controlled and the precipitation of Sn to the grain boundaries is positively performed. However, this method is also aimed at improving the magnetic properties by finely and uniformly precipitating the inhibitor, and the effect of suppressing the surface crack aimed at by the present invention was not recognized at all.

Further, Japanese Patent Laid-Open No. 4-362137 (a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties) first rolls from the center to a 2/5 thick layer at a temperature of 1350 ° C. or higher during rough rolling. And 1350 ° C from the center to the 2 / 5th thickness in the final pass.
Above, a method of rolling from the surface layer to 1/5 layer thickness at 1200 ° C. or lower has been proposed and disclosed. This method also aims at making the precipitation of the inhibitor uniform in the plate thickness direction, and is not effective at all in preventing the surface cracks aimed at by the present invention.

In addition, in Japanese Unexamined Patent Publication No. 4-124218 (method for producing a grain-oriented silicon steel sheet having excellent magnetic properties), the final pass of the hot rough rolling is performed from the outermost surface of the steel sheet to 1/5 of the sheet thickness. Temperature up to the depth of 1200 to 1250 ° C and a reduction rate of 50
A method is proposed and disclosed which is carried out under a condition of not less than%.
This method is intended to improve the magnetic properties by controlling the temperature and the structure in the plate thickness direction and making the structure fine and appropriately dispersing the inhibitor. The desired effect was difficult to obtain.

On the other hand, in Japanese Patent Laid-Open No. 55-62124 (hot rolling method for unidirectional silicon steel sheet), the finish rolling start temperature and the finish rolling end temperature are defined for the purpose of preventing the occurrence of edge cracks. A hot rolling method for unidirectional silicon steel sheets, which makes the difference within 220 ° C, is proposed and disclosed. Certainly, this method can achieve the desired reduction of edge cracks in the hot rolled sheet. However, since the generation mechanism is different between the ear crack and the surface crack, this method has no effect on the prevention of the surface crack aimed at by the present invention.

As described above, in the heretofore known methods in which the rolling temperature in the hot rolling is regulated, the hot rough rolling temperature, the hot finish rolling start temperature and the hot finish rolling are mainly used for the purpose of improving the magnetic properties. Often, the end temperature, coil winding temperature, etc. are specified individually or in combination, and as a matter of course, these methods do not provide sufficient effect of preventing surface cracks. Even the ones in which the rolling start temperature and the hot finish rolling end temperature were regulated could not prevent surface cracking.

[0016]

As described above, in the hot rolling in the manufacturing process of silicon steel, there is no sufficiently satisfactory conventional technique to prevent the occurrence of surface cracks. It was

Therefore, the applicant company of this invention first
According to JP / 9301901 specification, at the time of hot finish rolling, the rolling at the first stand is performed by the entrance side plate thickness t _F1 (mm), the exit side plate thickness t _F2 (mm), and the surface temperature at the time of biting. T _F0
(° C) and from the steel plate surface at the time of biting (t _F1 −
t _F2 ) / 2 (mm) In relation to the temperature T _F1 (° C.) at the depth, the following equation (T _F1 −T _F0 ) / {(t _F1 −t _F2 ) / 2} ≦ 10 + t _F1 /
We propose a method for producing hot-rolled silicon steel sheets with excellent surface properties by setting the conditions to satisfy 10 (° C / mm). According to this method, the surface quality can certainly be improved. However, in actual operation, although the temperature of the steel plate surface is measured, it is not possible to directly measure the temperature inside the thickness direction with the current technology, so the temperature inside the thickness direction is monitored online.・ It is not easy to control. Therefore, this method has a problem in applicability to actual operation.

In view of the above, the present invention controls the reduction ratio of the finishing first stand in hot rolling, the rolled material temperature on the entry side of the finishing first stand, and the temperature of each rolled material between the finishing first stand and the second stand. The purpose is to propose a method for manufacturing hot-rolled silicon steel sheets with excellent surface properties that is easy to apply to actual operations, based on a completely new viewpoint of relaxing the stress generated on the surface and preventing the occurrence of surface cracks. And

[0019]

[Means for Solving the Problems]
Temperature of rolled material on the first stand side during finish rolling (Table
Surface temperature) T_F1And between the first stand and the second stand
Rolled material temperature (surface temperature) T_F12Is the surface ratio of hot rolled sheet
New finding that it has a special relationship with the frequency of occurrence
Was. Thus, the pressure on the first stand during finish rolling is
Rolling reduction rate and T _F1And T_F12To identify the relationship with
It came to the light. That is, based on the above findings
The gist of the present invention is as follows.

A method for producing a hot-rolled silicon steel sheet, comprising heating a steel slab containing Si: 2.0 to 4.5 wt% at a high temperature, then performing rough rolling in a hot state and then finish rolling with a tandem rolling mill, In the finish rolling, the rolling reduction rate in the first stand is set in the range of 20 to 70%, and the rolling material temperature T _F1 between the first stand and the rolling material temperature T _F12 between the first stand and the second stand. Is a method for manufacturing a hot-rolled sheet of silicon steel having excellent surface properties, which is characterized in that it is carried out under conditions satisfying the following formula (1) (first invention). Further, in the method described in the first aspect of the invention, the temperature T _F1 of the rolled material on the first stand-in side in finish rolling is set in the range of 1000 to 1200 ° C (second).
invention).

Here, the rolling material temperature T _F12 between the first stand and the second stand is the rolling material temperature between the strip coolant on the exit side of the first stand and the strip coolant on the entrance side of the second stand, and is T _F1 and T _F12. Both are the surface temperature of the rolled material.

[0022]

OPERATION The process and operation of the present invention will be described below, including experimental examples. The inventors repeated earnest experiments in order to prevent surface cracks and surface defects of the rolled material during hot rolling, and between the finishing first stand and the second stand, which had not been noticed so far. As noted above, the occurrence of surface cracks has a deep relationship with the temperature difference between the rolling material temperature on the entry side of the finishing first stand and the rolling material temperature between the finishing first stand and the second stand. Found. The reason for this is not clear, but it can be considered as follows.

That is, in hot finish rolling, finish
Gage No. 1 stand side rolled material temperature T _F1And the first stand-
Second stand rolling material temperature T_F12When the temperature difference between
Temperature difference between the surface and the center of the rolled material is small,
The tensile stress generated on the material surface is small, but T_F1And T_F12When
If the temperature difference between the
The difference in degree is also large, and therefore the pulling that occurs on the surface of the rolled material
It is assumed that the tensile stress increases and leads to cracking.
I can guess.

When the rolling reduction is relatively large,
Is insensitive to the occurrence of cracks.
The stress caused by the temperature difference between the surface temperature and the center temperature of
Cracks are less likely to occur. In addition, the reduction rate is large.
Inevitably, the temperature difference between the steel plate surface and the center will inevitably be small.
Therefore, the limited range T of the present invention_F1(℃) -T_F12(℃) ≦ 8
Easy to meet 0 (℃) and prevent surface cracks
Is all T_F1(℃) -T _F12(℃) ≦ 80 (℃) can be arranged
It is considered to be.

Experimental examples will be described below. Experimental Example 1 Using four types of steels with different composition shown in Table 1, T _F1 −
A rolling experiment was carried out while changing T _F12, and the number of cracks in the hot-rolled sheet obtained was investigated.

[Table 1]

The results of these investigations are summarized in FIG.
FIG. 1 is a graph showing the relationship between T _F1 -T _F12 and the number of cracks generated.

As is apparent from FIG. 1, T _F1 is 1000 to 12
It can be seen that, when T _F1 -T _F12 is 80 ° C. or less in the range of 00 ° C., cracking does not occur, but when it exceeds 80 ° C., cracking occurs. Further, when T _F1 exceeds 1200 ° C. or less than 1000 ° C., cracking becomes remarkable.

Experimental Example 2 Using steel having the composition shown in Table 2, T _F1 = 1175 under the conditions in which the occurrence of cracks was small in Experimental Example 1.
℃, T _F1 −T _F12 = 0,40,80 ℃ under each condition, after changing the reduction ratio at the finishing 1st stand and performing hot rolling respectively, the grain-oriented silicon steel plate was subjected to the normal process. After manufacturing, the number of cracks generated in the hot rolled sheet and the magnetic characteristics (magnetic flux density) of the product were investigated.

[Table 2]

The results of these investigations are shown in FIGS. FIG. 2 is a graph showing the relationship between the rolling reduction in the first stand and the number of cracks generated, and FIG. 3 is a graph showing the relationship between the rolling reduction in the first stand and the magnetic flux density (B ₈ ) in the product.

As is clear from FIG. 2 and FIG. 3, it is understood that the reduction ratio in the first stand is in the range of 20 to 70% under the condition that no crack is generated and the magnetic characteristics are good.

From the results of Experimental Examples 1 and 2 described above, the preferable condition range for preventing the occurrence of cracks and obtaining a product having excellent magnetic characteristics is that the rolling reduction at the finishing first stand is 20 to 70%. It is also found that T _F1 -T _F12 is 80 ° C. or lower. Furthermore, it can be seen that setting T _F1 in the temperature range of 1000 to 1200 ° C. is advantageous for preventing the occurrence of cracks.

Note that the rolling reduction rate at the finishing first stand is 20.
When it is less than 70% and more than 70%, the cause of deterioration of the magnetic properties of the product is not always clear, but when the rolling reduction is too low, sufficient dislocations cannot be introduced to obtain a fine dispersion of the inhibitor. It is considered that the inhibitory power of the inhibitor decreases, and if the reduction ratio at the first stand is too high, the reduction ratio at the post-finish rolling stage will be low, resulting in insufficient formation of texture. To be

When the surface temperature of the rolled material entering the finishing first stand exceeds 1200 ° C., the temperature is too high and recrystallization after the completion of rough rolling is not sufficiently achieved, so that surface cracking of the rolled material becomes remarkable. On the other hand, if the temperature is less than 1000 ° C, grain boundary embrittlement, which is thought to be caused by the grain boundary precipitation of precipitates, occurs and surface cracking of the rolled material becomes prominent.

Next, the reasons for limiting the component composition of the present invention will be described. Si: 2.0 wt% to 4.5 wt% Si is a component that increases the specific resistance of the steel sheet used as a product and contributes to the reduction of iron loss. If the content is less than 2.0 wt%, the iron loss reducing effect is weakened, and In the final finish annealing at high temperature for purification and secondary recrystallization, the α-γ transformation causes randomization of the crystal orientation and sufficient magnetic properties cannot be obtained. Interrollability is impaired. Therefore, its content should be 2.0 wt% or more and 4.5 wt% or less.

The other components are not particularly limited, but the typical preferable component composition as a hot-rolled sheet for grain-oriented electrical steel sheets is as follows. C: 0.01 wt% to 0.1 wt%, Si: 2.0 wt% to 4.5 wt%, M
n: 0.02 wt% to 0.12 wt%, and as an inhibitor component system, one or two kinds of S and Se in the case of MnS, MnSe system are 0.01 wt% to 0.1 wt%, and Al in the case of AlN system. :
A component composition containing 0.01 wt% to 0.06 wt% and N: 0.03 wt% to 0.015 wt%. The above-mentioned MnS, MnSe and AlN
The systems may be used in combination.

On the other hand, specific means for hot rolling to achieve the present invention include (1) controlling the amount of cooling water on the exit side of the finishing first stand, and (2) between the finishing first and second stands. To prevent heat removal due to radiation at
(3) Prevent unnecessary cooling water from splashing on the billet,
(4) It is advisable to use a single means or a combination of means such as increasing the rolling speed to reduce heat removal from the surface of the rolled material.

After heating the slab, a hot-rolled steel strip (hot-rolled sheet) having a thickness of 1.4 mm to 3.5 mm is formed by ordinary hot rolling. The thickness of the sheet bar after rough rolling in hot rolling is not particularly limited, but about 25 to 60 mm is suitable.

Subsequent normal process of the hot rolled steel strip, pickling process, cold rolling process of one time or more than two times with intermediate annealing, followed by decarburizing annealing, annealing separating material application and final finishing annealing process, etc. Any known means can be used.

[0039]

【Example】

Example 1 C: 0.03 wt%, Si: 2.9 wt%, Mn: 0.065 wt%, Se:
A silicon steel slab containing 0.022 wt% and N: 0.005 wt%, the balance of which is 220 mm in thickness and consisting essentially of Fe, was heated to 1400 ° C and then rough-rolled to a plate thickness of 50 mm, followed by finish rolling. A hot-rolled sheet having a plate thickness of 2.0 mm was obtained by rolling down 7 stands with a rolling reduction of 50% on 1 stand.

At this time, the surface temperature of each hot-rolled sheet obtained by variously changing the temperature T _F1 of the rolled material on the entry side to the finishing first stand and the temperature T _F12 of the rolled material between the first and second stands. The cracks were observed.

The results are shown in Table 3 together with the rolling temperature conditions.
Are shown together.

[Table 3]

As is apparent from Table 3, the comparative examples of Samples Nos. 5 and 6 in which T _F1 -T _F12 were out of the limited range of the present invention were found to have many cracks, but were suitable for the present invention. The conforming example has no cracks.

Example 2 C: 0.07 wt%, Si: 3.1 wt%, Mn: 0.080 wt%, Se: 0.
03wt%, Al: 0.02wt% and N: 0.001wt%,
The balance consists of 220 mm thick silicon steel slab heated to 1380 ° C and then rough-rolled to a plate thickness of 50 mm. The hot rolled sheet with a plate thickness of 3.0 mm was obtained by rolling down the sheet.

At this time, the surface temperature of each hot-rolled sheet obtained by variously changing the temperature T _F1 of the rolled material entering the finishing first stand and the temperature T _F12 of the rolled material between the first stand and the second stand. The cracks were observed.

The results are shown in Table 4 together with the rolling temperature conditions.
Are shown together.

[Table 4]

As is clear from Table 4, T _F1 and T _F1 −T
_A large number of cracks were found in the comparative examples of Sample Nos. 11 to 15 in which _F12 was out of the limited range of the present invention, whereas no cracks were generated in the comparative examples of Samples No. 7 to 10 conforming to the present invention. .

[0047]

INDUSTRIAL APPLICABILITY According to the present invention, the reduction ratio at the finishing first stand in hot rolling of silicon steel, the entering side of the finishing first stand, and the temperature of the rolled material between the finishing first stand and the second stand are suitable. By setting the range, it is intended to produce a silicon steel hot-rolled sheet having good surface properties based on a completely new viewpoint of relaxing the stress generated on the sheet surface and preventing the occurrence of surface cracks. According to the improvement of yield,
It can contribute extremely advantageously to the prevention of quality deterioration of silicon steel sheet products.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between T _F1 −T _F12 and the number of cracks generated.

FIG. 2 is a graph showing the relationship between the rolling reduction and the number of cracks generated in the first stand.

FIG. 3 is a graph showing the relationship between the rolling reduction in the first stand and the magnetic flux density (B ₈ ) in the product.

Claims (2)

[Claims] 1. A method for producing a hot-rolled silicon steel sheet, comprising heating a steel slab containing Si: 2.0 to 4.5 wt% at a high temperature, and then performing rough rolling in a hot state and then finish rolling with a tandem rolling mill. The above-mentioned finish rolling,
20 to 70% of the range, the temperature T of the rolled material on the first stand side
Manufacture of a hot-rolled silicon steel sheet having excellent surface properties, which is performed under the condition that _F1 and the rolling material temperature T _F12 between the first stand and the second stand satisfy the relationship of the following formula (1). Method. [Note] T _F1 (° C) -T _F12 (° C) ≤ 80 (° C) ------ (1) 2. The method for producing a hot-rolled silicon steel sheet having excellent surface properties according to claim 1, wherein the temperature T _{F1 of the} rolled material on the first stand side in finish rolling is in the range of 1000 ° C. or higher and 1200 ° C. or lower. .