KR101917468B1 - Thin hot-rolled electrical steel sheets and method for manufacturing the same - Google Patents

Abstract

An aspect of the present invention is a steel sheet comprising, by weight%, at least one selected from the group consisting of 0.005% or less of C, 0.2 to 1.0% of Mn, 2.8 to 3.2% of Si, 0.025% or less of P, : 0.003% or less, Sn: 0.005% or less, Sb: 0.005% or less, N: 0.005% or less and the balance of Fe and other unavoidable impurities. The sum of Sn, Sb and P is 0.02% To 95% by area or more.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to hot rolled steel sheets,

The present invention relates to a hot rolled steel sheet and a method of manufacturing the same.

Generally, the production process of non-oriented electrical steel sheet is to manufacture a slab having a thickness of 200 mm or more in the casting process, and then, after the slab reheating, rough rolling and finish rolling as a hot rolling process, hot rolled steel coils having a thickness of 2.3 to 2.5 mm . The hot-rolled coil is then subjected to preliminary annealing, cold rolling and final annealing to produce an electric steel sheet having a thickness of 0.2 to 0.5 mmt.

These electric steel sheets are used for transformers, motors and electric appliances. Unlike ordinary carbon steels, which are important in processability such as mechanical properties, they are functional products that emphasize electrical characteristics. The required electrical properties include low iron loss, high magnetic flux density, high permeability and high throughput.

In order to improve the electrical characteristics, development is progressing generally in terms of composition adjustment, high purity, grain size adjustment through adjustment of annealing temperature, and reduction of grain size.

Among them, hot smelting is a method to suppress the grain growth during the final annealing by making the thickness as thin as possible in the hot rolled coil state, thereby reducing the reduction rate in the cold rolling.

This is known as a method of improving the electrical characteristics, which leads to reduction of eddy current loss, that is, reduction of iron loss, but there are technical problems to overcome in order to realize hot smelting in actual operation.

Typically, in order to produce a thermal laminate of 1.6 mm or less in the blast furnace, the passing speed of the coil in the finishing mill (hereinafter referred to as FM) is as high as about 1100 mpm. It is difficult to maintain the operation because the risk of sheet breakage is high because the steel sheet is required to simultaneously control the forming and calibrating while passing through a strip at such a speed.

In addition, hot rolled steel sheets can be manufactured using hot rolling mills of Pohang, which is known as hot rolling continuous rolling technique. However, the hot rolling continuous rolling technique includes not only a slab reheating process, but also basically connecting strips and strips by welding In addition, the electric steel sheet has a problem in that it can not be stably operated because there is a risk of sheet breakage due to disconnection of the joining part during the operation due to the addition of a large amount of Si.

On the other hand, the CEM (Continuous Endless Mill) process is a continuous process in which the performance process and the hot-rolling process are directly performed, and the slab immediately rolled from the performance is directly rolled Because it has process characteristics, there is no need to join strips. Even at rolling, it has a relatively low speed of 600mpm compared to blast furnace, but it has an advantage of easy control of material. In addition, the coil shape control is advantageous because the material is tensioned by applying a predetermined tension to each section of the roughing mill (RM), RM to FM and FM, Width, and longitudinal direction deviation.

However, the CEM process is a process that requires precise control. In the case of electric steel sheet, it is necessary to develop a process suitable for electric steel sheet because it has characteristics different from general low carbon steel.

Therefore, it is required to develop a new manufacturing process in order to improve electrical characteristics through hot smelting of electric steel sheets using CEM process.

Korean Patent Laid-Open Publication No. 2016-0078081

An aspect of the present invention is to provide a hot rolled steel sheet and a method of manufacturing the same.

On the other hand, the object of the present invention is not limited to the above description. It will be understood by those of ordinary skill in the art that there is no difficulty in understanding the additional problems of the present invention.

An aspect of the present invention is a steel sheet comprising, by weight%, at least one selected from the group consisting of 0.005% or less of C, 0.2 to 1.0% of Mn, 2.8 to 3.2% of Si, 0.025% or less of P, : 0.003% or less, Sn: 0.005% or less, Sb: 0.005% or less, N: 0.005% or less and the balance of Fe and other unavoidable impurities. The sum of Sn, Sb and P is 0.02% To 95% by area or more.

At this time, the thickness of the electrical steel sheet may be 1.6 mm or less.

In addition, the ferrite may be composed of a recrystallized structure and a recovery structure, and an area of the recrystallized structure alone may be 65% or more based on a cross section in the thickness direction of the electrical steel sheet.

Another aspect of the present invention is to provide a method of manufacturing a semiconductor device, which comprises, by wt%, 0.005% or less of C, 0.2 to 1.0% of Mn, 2.8 to 3.2% of Si, 0.025% or less of P, The molten steel containing 0.003% or less of Ti, 0.005% or less of Sn, 0.005% or less of Sb, 0.005% or less of N and 0.005% or less of other Fe and other unavoidable impurities and the sum of Sn, Sb and P is 0.02% Continuous casting in a slab;

Subjecting the continuously cast thin slab to rough rolling so as to have an outlet temperature of 900 to 950 ° C to obtain a bar plate having a thickness of 10 to 50 mm;

Heating the bar plate to a temperature of 1100 ° C or higher;

Removing the scale of the bar plate;

Finishing the bar plate from which the scale has been removed to a temperature of 750 ° C or higher to obtain a hot-rolled steel sheet having a thickness of 1.6 mm or less; And

And winding the hot-rolled steel sheet in a temperature range of 500 to 600 ° C, wherein each of the above-described steps is performed continuously.

At this time, the casting speed of the continuous casting may be 4 to 8 mpm.

The rolling speed of the rough rolling may be 20 to 50 mpm.

Further, the rough rolling is performed by three stands, the tension between the first stand and the second stand is 1.1 to 1.5, and the tension between the second stand and the third stand is controlled to 0.5 to 0.8.

In addition, the tension between the rough rolling and the finish rolling can be controlled to be 0.45 to 0.5.

The rolling speed of the finish rolling may be 200 to 600 rpm.

The finishing rolling is performed by five stands, and the difference in rolling speed between the stands can be controlled to be 10% or less.

In this case, the tension between the first stand and the second stand is 0.8 to 0.85, the tension between the second stand and the third stand is 0.8 to 1.0, the tension between the third stand and the fourth stand is 1.0 to 1.2, the tension between the fourth stand and the fifth stand is 1.2 to 1.4 Lt; / RTI >

Meanwhile, the step of removing the scale may be performed by sequentially passing the bar plate through one row for spraying the cooling water at a pressure of 200 to 400 bar and two rows for spraying the cooling water at a pressure of 100 to 200 bar.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. The various features of the present invention and the advantages and effects thereof can be understood in more detail with reference to the following specific embodiments.

According to the present invention, it is possible to provide a hot rolled steel sheet having a thickness of 1.6 mm or less, and it is possible to reduce the cold rolling reduction rate by about 8% through thinning to have a low iron loss and a high magnetic flux density, It is effective. In addition, even if the amount of expensive Sn added, which greatly affects the electrical characteristics, is reduced, electrical characteristics equal to or higher than those of conventional electric steel sheets can be obtained.

Fig. 1 shows the results of a high-temperature tensile test according to the temperature change of Inventive Example 1. Fig.
Fig. 2 is a microstructure photograph of the inventive steel 1 taken along the thickness direction of the hot-rolled steel sheet produced by varying the thickness in the CEM process.
Fig. 3 is a microstructure photograph of the inventive steel 1 observed in a thickness direction section of a hot-rolled steel sheet produced in a different thickness by a blast furnace process.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

As a result of deep research to improve electrical properties through hot smelting of an electrical steel sheet using a CEM process, the present inventors have found that the alloy composition of the conventional non-oriented electrical steel sheet has been changed and the manufacturing conditions of the performance- It has been confirmed that a hot rolled steel sheet having a grain size of 1.6 mm or less can be produced, and the present invention has been accomplished.

Hot Rolled Steel Sheet

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A hot rolled steel sheet according to one aspect of the present invention will now be described in detail.

A steel hot-rolled steel sheet according to one aspect of the present invention comprises, by weight, at least one of C: 0.005% or less, Mn: 0.2-1.0%, Si: 2.8-3.2% 0.2 to 0.4%, Ti: not more than 0.003%, Sn: not more than 0.005%, Sb: not more than 0.005%, N: not more than 0.005%, and the balance of Fe and other unavoidable impurities. The sum of Sn, Sb and P is not less than 0.02% And the microstructure contains at least 95% by area of ferrite.

First, the alloy composition of the present invention will be described in detail. Hereinafter, the unit of each element content means weight% unless otherwise specified.

C: 0.005% or less (excluding 0%)

Carbon (C) is generally an element that increases the strength of a steel sheet, but in the case of an electrical steel sheet it is related to electrical properties.

When the C content is more than 0.005%, it is used as a motor in the final product to generate magnetic aging by forming carbide by binding with Ti, V, Zr by heat generated during operation, and carbide migrates Thereby increasing hysteresis loss and adversely affecting electrical characteristics. C content, it is not necessary to limit the lower limit. However, the lower limit may be 0.0005% in consideration of actual operating conditions.

Mn: 0.2 to 1.0%

Manganese (Mn) is a hardening element and is a non-resistive element and serves to improve strength and electrical properties. As the addition amount increases, the resistivity increases and the iron loss can be improved. In particular, the permeability can be improved by improving the texture.

When the Mn content is less than 0.2%, the above-mentioned effect is insufficient. When the Mn content is more than 1.0%, the saturation magnetic flux density decreases and MnS or the like precipitates and the iron loss can be deteriorated.

Si: 2.8 to 3.2%

Silicon (Si) is an element that acts to lower the iron loss by increasing the resistivity of the material.

When the Si content is less than 2.8%, the above-mentioned effect is insufficient, and when the Si content is more than 3.2%, the magnetic flux density, the permeability and the rolling property are inferior.

P: not more than 0.025%, Sn: not more than 0.005%, Sb: not more than 0.005%, Sn + Sb + P? 0.02%

P (phosphorus), Sn (tin), and Sb (antimony) are segregated in the grain boundaries to inhibit the growth of harmful {111} texture, thereby lowering the iron loss and improving the magnetic flux density. When the sum of Sn, Sb and P is less than 0.02%, the above-mentioned effect is insufficient.

Sn and Sb serve to improve the iron loss and magnetic flux density. However, when the content of Sn and Sb is more than 0.005%, the hot-rolled steel sheet is manufactured by using the CEM process as in the present invention, In addition, since Sn and Sb are expensive elements, the manufacturing cost increases.

If the P content is more than 0.025%, surface defects may occur and the cold rolling property may be deteriorated.

Therefore, it is preferable to control P to 0.025% or less, Sn to 0.005% or less and Sb to 0.005% or less, and to control the sum of Sn, Sb and P to 0.02% or more.

S: not more than 0.01%

S (sulfur) forms fine MnS to increase the grain loss by suppressing grain growth and increase {111} texture structure which is detrimental to magnetism, thereby reducing the magnetic flux density. Therefore, it is desirable to suppress the content to the maximum, and it is limited to 0.01% or less.

Al: 0.2 to 0.4%

Aluminum (Al) is a non-resistive element that lowers iron loss by increasing the resistivity of the material and is added as a deoxidizer in steelmaking.

When the Al content is less than 0.2%, the above-mentioned effect is insufficient, and when the Al content exceeds 0.4%, the magnetic flux density is lowered.

Ti: not more than 0.003%

Titanium (Ti) coarsens the hot-rolled structure in hot-rolling, but forms fine TiC and TiN at the time of final annealing to increase iron loss due to grain growth inhibition, so it is limited to 0.003% or less.

N: 0.005% or less

Nitrogen (N) is an element that binds with Al, Ti or the like to form AlN or TiN, thereby suppressing grain growth and thereby increasing iron loss. Therefore, it is desirable to suppress the content to the maximum, and is limited to 0.005% or less.

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

Since the hot-rolled steel sheet of the present invention contains a large amount of Si, the microstructure contains not less than 95% by area of ferrite. More preferably, it may be composed of a ferrite single phase.

At this time, the ferrite is composed of a recrystallized structure and a recovery structure, and the recrystallized structure may be 60% or more by area based on the cross-section in the thickness direction of the electrical steel sheet.

Similar to the hot-rolled electrical steel sheet produced by the conventional blast furnace process, a recrystallized structure is formed on the surface side, a recovered structure is formed on the surface side, and a recrystallized structure and a recovered structure are mixed therebetween Respectively.

FIGS. 2 and 3 are photographs of microstructures in which the inventive steel 1 is observed by a CEM process and a blast furnace process, respectively, in cross-section in the thickness direction of the hot-rolled steel sheet with different thicknesses. As can be seen from Figs. 2 and 3, it can be seen that the recrystallized structure increases as the thickness of the steel sheet decreases. As the recrystallized structure increases, it becomes easier to obtain a uniform structure after homogenization and annealing, and electrical characteristics are improved. When the recrystallized structure is less than 60% by area, the above-mentioned effect is insufficient.

Meanwhile, the thickness of the electrical steel sheet may be 1.6 mm or less. As can be seen from FIGS. 2 and 3, the recrystallized structure increases as the thickness of the steel sheet decreases. When the thickness exceeds 1.6 mmt, it is difficult to secure a recrystallized structure of 60% or more by area.

In addition, the cold reduction ratio can be reduced by about 8% through thinning, which has a lower iron loss and electric flux density than conventional electric steel sheets, and thus has an excellent electrical characteristic. In addition, even if the amount of expensive Sn or Sb added, which greatly affects the electrical characteristics, is reduced, electrical characteristics equal to or higher than those of the conventional electric steel sheet can be secured.

Meanwhile, in the present invention, the hot-rolled electrical steel sheet refers to a hot-rolled steel sheet for use in an electric steel sheet, and the hot-rolled steel sheet of the present invention is cold rolled and annealed to produce an electrical steel sheet.

Method of manufacturing hot rolled steel sheet

Hereinafter, a method for manufacturing a hot rolled steel sheet according to another aspect of the present invention will be described in detail.

In another aspect of the present invention, there is provided a method for manufacturing a hot rolled steel product, comprising the steps of: continuously casting a molten steel having the alloy composition described above in a thin slab of 90 mm or more; Subjecting the continuously cast thin slab to rough rolling so as to have an outlet temperature of 900 to 950 ° C to obtain a bar plate having a thickness of 10 to 50 mm; Heating the bar plate to a temperature of 1100 ° C or higher; Removing the scale of the bar plate; Finishing the bar plate from which the scale has been removed to a temperature of 750 ° C or higher to obtain a hot-rolled steel sheet having a thickness of 1.6 mm or less; And winding the hot-rolled steel sheet in a temperature range of 500 to 600 DEG C, wherein each of the steps is performed continuously.

Continuous casting step

The molten steel having the above-described alloy composition is continuously cast in a thin slab of 90 mm or more.

When the thickness is less than 90 mm, the uniformity of the texture and rolling becomes difficult due to the temperature drop. In order to solve this problem, it is possible to solve the problem by the additional heating equipment. However, it is desirable to exclude it because it causes cost increase.

At this time, the casting speed of the continuous casting may be 4 to 8 mpm.

This is because a casting speed of 4mpm or more is required in order to secure the target rolling temperature. On the other hand, when the casting speed exceeds 8mpm, the electric steel sheet contains a large amount of Si, so that the lubrication between the cast steel and the mold in the performance mold may not be performed properly, so that the molten steel bath surface becomes unstable and the operation success rate may be lowered.

Rough rolling  step

The continuously cast thin slab is subjected to rough rolling so that the rough rolling inlet temperature is 1000 to 1200 ° C to obtain a bar plate having a thickness of 10 to 50 mm.

If the rough rolling inlet temperature is less than 1000 ° C, an increase in the rough rolling load and a crack may occur in the edge portion of the bar plate. On the other hand, if it is higher than 1200 ° C, the hot-rolled scale remains and the quality of the hot-rolled surface may deteriorate.

When the thickness of the bar plate is more than 50 mm, the rolling load during the finish rolling increases. When the bar plate thickness is less than 10 mm, the rolling deformation resistance becomes large, which may cause difficulty in operation.

At this time, the rough rolling out temperature may be 900 ° C or higher. When the temperature is lower than 900 DEG C, it is difficult to secure the temperature of the bar plate at 1100 DEG C or higher even after heating after rough rolling.

At this time, the rolling speed of the rough rolling may be 20 to 50 mpm.

If the rolling speed of the rough rolling is more than 50mpm, the performance is lowered because the performance-rolling is directly connected and problems occur in the performance process. On the other hand, in the case of less than 20 mpm, it is difficult to secure the temperature during finish rolling, and it is difficult to obtain rolling load and uniform structure.

Further, the rough rolling is performed by three stands, the tension between the first stand and the second stand is 1.1 to 1.5, and the tension between the second stand and the third stand is controlled to 0.5 to 0.8.

This is to maintain the proper tension for stable rolling and shipping in the process where the performance-rolling is directly connected. Since electric steel sheet has excellent high temperature ductility, when the tension is set to the general low carbon steel standard (RM 1 ~ 2: 2.0 ~ 2.4, RM 2 ~ 3: 1.5 ~ 1.9), poor width and plate rupture may occur.

Bar plate heating step

The bar plate is heated to 1100 DEG C or higher.

Fig. 1 shows the results of a high-temperature tensile test according to the temperature change of Inventive Example 1. Fig. It can be seen that the stress increase between 750 ° C / 700 ° C / 600 ° C is abruptly changed with respect to the stress increase between 850 ° C / 800 ° C / 750 ° C. Therefore, the electric steel sheet has a high temperature strength rapidly changed around 750 ° C due to the addition of a large amount of Si, and since the strength is rapidly increased at a temperature lower than 750 ° C, the finish rolling temperature must be 750 ° C or more, It is preferable to heat it to 1100 占 폚 or more in consideration of the drop.

Scale removal step

The scale of the bar plate is removed. It is desirable to remove the surface scale thickness to 50 탆 or less, and if the surface scale is not sufficiently removed, a large number of spindle-shaped and scale-shaped scales can be formed.

At this time, the step of removing the scale may be performed by sequentially passing the bar plate through one row for spraying the cooling water at a pressure of 200 to 400 bar and two rows for spraying the cooling water at a pressure of 100 to 200 bar.

Finishing rolling step

The bar plate on which the scale has been removed is finely rolled to a temperature of 750 DEG C or higher to obtain a hot-rolled steel sheet having a thickness of 1.6 mm or less. When the finishing rolling temperature is lower than 750 캜, the high temperature strength sharply increases.

At this time, the tension between the rough rolling and the finish rolling can be controlled to be 0.45 to 0.5.

This is to maintain the proper tension for stable rolling and shipping in the process where the performance-rolling is directly connected. Since electric steel sheet has excellent high temperature ductility, when the tension is set to the general low carbon steel standard (RM ~ FM: 0.61 ~ 0.66), poor width and plate rupture may occur.

The rolling speed of the finish rolling may be 200 to 600 rpm.

If the rolling speed of the finish rolling exceeds 600 mPm, there may be a case of operating failure such as plate breakage, and because isothermal and constant speed rolling is difficult, uniform temperature can not be ensured and material deviation may occur. On the other hand, in the case of less than 200 mpm, the rolling speed is too slow and it is difficult to secure the finishing rolling temperature to 750 캜 or more.

The finishing rolling is performed by five stands, and the difference in rolling speed between the stands can be controlled to be 10% or less.

If the difference in rolling speed between stands is more than 10%, uniform cooling may be difficult in the subsequent cooling process, which may cause material variations.

In this case, the tension between the first stand and the second stand is 0.8 to 0.85, the tension between the second stand and the third stand is 0.8 to 1.0, the tension between the third stand and the fourth stand is 1.0 to 1.2, the tension between the fourth stand and the fifth stand is 1.2 to 1.4 Lt; / RTI >

This is to maintain the proper tension for stable rolling and shipping in the process where the performance-rolling is directly connected. Since electric steel sheet is excellent in high temperature ductility, tension is set to general low carbon steel standard (FM1 ~ 2: 0.90 ~ 0.10, FM2 ~ 3: 1.00 ~ 1.2, FM3 ~ 4: 1.3 ~ 1.5, FM4 ~ 5: 1.3 ~ 1.5) Width problems and sheet breakage may occur.

Coiling  step

The hot-rolled steel sheet is wound in a temperature range of 500 to 600 ° C. If the coiling temperature is less than 500 캜, the crystal grain size becomes small, and the iron loss increases as the hysteresis loss increases. If the coiling temperature exceeds 600 캜, the crystal grain size becomes large and the iron loss may increase as the eddy current loss increases.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

( Example  One)

Hot-rolled steel sheets having the thicknesses shown in the following Table 3 were prepared using the blast furnace process or CEM process (performance-rolling direct process) shown in Table 2 below.

The hot-rolled steel sheet was cold-rolled to a thickness of 0.35 mm, and its iron loss and magnetic flux density were measured.

division Alloy element (% by weight) C Mn Si P S Al Ti Sn Sb N P + Sn + Sb Inventive Steel 1 0.0049 0.50 3.04 0.02 0.004 0.32 0.0025 0.003 0.002 0.0016 0.025 Comparative River 1 0.0017 0.04 3.02 0.05 0.0016 0.22 0.001 0.03 0.0015 0.0012 0.08 Comparative River 2 0.0014 0.18 3.20 0.010 0.0014 0.08 0.0010 0.025 0.0010 0.0010 0.036 Comparative Steel 3 0.0018 0.22 0.7 0.037 0.004 0.025 0.0002 0.002 0 0.0020 0.039 Comparative Steel 4 0.0015 0.15 3.0 0.055 0.0045 0.003 0.001 0.060 0 0.0010 0.114 Comparative Steel 5 0.0049 0.50 3.04 0.02 0.004 0.32 0.0025 0.003 0.055 0.0016 0.078

fair
division Speed
(mpm) Slab
thickness
(mm) Slab
Reheat temperature
(° C) Rough rolling
Output temperature
(° C) Bar plate
Heating temperature
(° C) Wrap-up
Rolling temperature
(° C) Coiling
Temperature
(° C) CEM 5.0 96 X 940 1130 750 580 blast furnace 1.2 230 1190 970 X 850 620

division Steel grade fair Hot-rolled steel sheet
Thickness (mm) Iron loss
(W15 / 50, W / kg) Magnetic flux density
(B50, Tesla) Operation possible
Whether Inventory 1 Inventive Steel 1 CEM 1.4 2.18 1.68 O Comparative Example 1 blast furnace 2.3 2.47 1.69 O Comparative Example 2 Comparative River 1 blast furnace 2.3 2.26 1.67 O Comparative Example 3 Comparative River 2 blast furnace 2.3 2.08 1.66 O Comparative Example 4 Comparative Steel 3 blast furnace 2.3 5.55 1.74 O Comparative Example 5 Comparative Steel 4 blast furnace 2.3 2.05 1.63 O Comparative Example 6 Comparative River 1 CEM 1.4 - - X Comparative Example 7 Comparative River 2 CEM 1.4 - - X Comparative Example 8 Comparative Steel 4 CEM 1.4 - - X Comparative Example 9 Comparative Steel 5 CEM 1.4 - - X Comparative Example 10 Comparative Steel 4 blast furnace 1.4 - - X

Comparative Examples 2 to 4 are electrical steel sheets produced using the blast furnace process. As shown in Comparative Example 4, when the Sn content is as low as 0.002%, it can be confirmed that the iron loss is high.

However, in Inventive Example 1, which satisfies the alloy composition and manufacturing conditions proposed in the present invention, the Sn content is 0.003%, which is much lower than that of Comparative Examples 2, 3 and 5, 5).

In Comparative Examples 6 to 9, when the Sn or Sb content was excessive, vertical cracks occurred at the edges of the cement when the CEM process was used, so that it was impossible to operate due to a high risk of operating accidents.

In Comparative Example 10, when an attempt was made to manufacture a hot-rolled steel sheet having a thickness of 1.4 mm by using a conventional blast furnace process, plate breakage and plate twist occurred, and a load was generated due to a high rolling rate.

Fig. 2 is a microstructure photograph of a hot rolled steel sheet produced by varying the thickness of Inventive Steel 1 in a thickness direction in a CEM process. Fig. 3 is a graph showing the thickness of the hot rolled steel sheet Fig.

2 corresponds to Inventive Example 1 when the thickness is 1.4 mm, and corresponds to Comparative Example 1 when the thickness is 2.3 mm in Fig. In the case of Inventive Example 1, the recrystallized structure was 68 area%, and in Comparative Example 1, the recrystallized structure was 51 area%.

Comparative Example 1 and Inventive Example 1 were compared with iron loss and magnetic flux density measured by cold rolling to the same thickness to confirm that the iron loss of Comparative Example 1 was high and the electrical properties were improved. The thickness of the hot rolled steel sheet or the recrystallized grain fraction This is important.

( Example  2)

After preparing molten steel having the composition of Inventive Steel 1 in Table 1 above, a hot-rolled steel sheet was produced using the CEM process under the manufacturing conditions shown in Table 4 below.

division Steel grade Speed
(mpm) Slab
thickness
(mm) Rough rolling
Output temperature
(° C) Bar plate
Heating temperature
(° C) Wrap-up
Rolling temperature
(° C) Coiling
Temperature
(° C) Hot-rolled steel sheet
thickness
mm work
possible
Whether Inventory 1 Inventive Steel 1 5.0 96 940 1130 750 580 1.4 O Comparative Example 11 5.0 96 940 1130 700 580 1.4 X

In the case of Comparative Example 11, when the finish rolling temperature was lower than 750 占 폚, edge cracking occurred due to a rapid increase in high temperature strength, and the operation was impossible.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims (12)

delete delete delete The steel sheet according to any one of claims 1 to 3, wherein the content of C is 0.005% or less, the content of Mn is 0.2 to 1.0%, the content of Si is 2.8 to 3.2%, the content of P is 0.025% or less, the content of S is 0.01% : 0.005% or less, Sb: 0.005% or less, N: 0.005% or less, remaining Fe and other unavoidable impurities, the sum of Sn, Sb and P being 0.02% or more;
Rolling the continuously cast thin slab to a rough rolling inlet temperature of 900 to 950 ° C to obtain a bar plate having a thickness of 10 to 50 mm;
Heating the bar plate to a temperature of 1100 ° C or higher;
Removing the scale of the bar plate;
Finishing the bar plate from which the scale has been removed to a temperature of 750 ° C or higher to obtain a hot-rolled steel sheet having a thickness of 1.6 mm or less; And
And a step of winding the hot-rolled steel sheet at a temperature in the range of 500 to 600 ° C, wherein each of the steps is carried out continuously, and the casting speed of the continuous casting is 4 to 8 mpm.
delete 5. The method of claim 4,
Wherein the rolling speed of the rough rolling is 20 to 50 mpm.
5. The method of claim 4,
Wherein the rough rolling is performed by three stands, wherein the tension between the first stand and the second stand is controlled to be 1.1 to 1.5, and the tension between the second stand and the third stand is controlled to be 0.5 to 0.8.
5. The method of claim 4,
Wherein the tension between the rough rolling and the finish rolling is controlled to be 0.45 to 0.5.
5. The method of claim 4,
Wherein the rolling speed of the finish rolling is 200 to 600 rpm.
5. The method of claim 4,
The finish rolling is performed by five stands,
And the difference in rolling speed between the stands is controlled to be 10% or less.
11. The method of claim 10,
The tension between the first stand and the second stand is 0.8-0.85, the tension between the second stand and the third stand is 0.8-1.0, the tension between the third stand and the fourth stand is 1.0-1.2, and the tension between the fourth stand and the fifth stand is 1.2-1.4 Wherein the hot-rolled steel sheet has a thickness of 10 mm or less.
5. The method of claim 4,
Wherein the step of removing the scale is performed by sequentially passing the bar plate through one row for spraying cooling water at a pressure of 200 to 400 bar and two rows for spraying cooling water at a pressure of 100 to 200 bar. Gt;

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