WO2025169547A1 - Hot-rolled annealed sheet, method for producing same, and method for producing non-oriented electromagnetic steel sheet - Google Patents

Abstract

Provided is a hot-rolled annealing technique for an electromagnetic steel sheet having excellent cold rolling properties. The present invention provides a hot-rolled annealed sheet that has a component composition containing, in terms of mass%, 0.010% or less of C, 1.0-5.0% of Si, 0.05-5.0% of Mn, 0.10% or less of P, 0.010% or less of S, 3.0% or less of Al, 0.0080% or less of N, and 0.0050% or less of O, with the balance being Fe and unavoidable impurities, and in which the ratio Re/Rc of the recrystallized structure between a sheet width center section and an edge section is 0.95 or less. The present invention also provides a method for producing a hot-rolled annealed sheet, in which: a hot-rolled sheet is obtained by subjecting a steel material having the above component composition to hot rolling; the hot-rolled sheet is subjected to hot-rolled sheet annealing; when a sheet width center section of the hot-rolled sheet is heated from the normal temperature to holding temperature and held thereat during the hot-rolled sheet annealing, an edge section of the hot-rolled sheet reaches a maximum temperature, which is lower than the holding temperature, from the normal temperature; and the temperature rising rate Vc of the sheet width center section is increased by 1.0°C/s or more from the temperature rising rate Ve of the edge section.

Description

Hot-rolled annealed sheet, its manufacturing method, and manufacturing method of non-oriented electrical steel sheet

The present invention relates to a hot-rolled annealed steel sheet, a manufacturing method thereof, and a manufacturing method of a non-oriented electrical steel sheet.

In recent years, environmental concerns such as global warming have led to demands for reduced _CO2 emissions and energy conservation. In particular, in the automotive field, development is underway for hybrid electric vehicles (HEVs) that use both engines and motors, electric vehicles (EVs) driven solely by electric motors, and fuel cell electric vehicles (FCEVs). To improve motor efficiency, motors used in HEVs, EVs, FCEVs, and the like are generally driven in a high-frequency range, which is advantageous for high-speed rotation. Non-oriented electrical steel sheets are often used as the iron core material for these motors. To achieve high motor efficiency, there is a strong demand for these steel sheets to have low iron loss in the high-frequency range.

Traditionally, non-oriented electrical steel sheets have been designed to have low iron loss by adding alloying elements such as Si and Al to increase resistivity, or by reducing eddy current loss through thinning the sheet thickness. However, adding large amounts of alloying elements reduces the ductility and toughness of the steel sheet, resulting in frequent fractures during the cold rolling process.

As an example of a technology for preventing fractures in high-alloy steel, Patent Document 1 discloses a method for manufacturing non-oriented electrical steel sheets with high magnetic flux density, which prevents cracking during cold rolling by cold-rolling rapidly solidified cast pieces at 180°C to 350°C.

Japanese Patent Application Laid-Open No. 2004-110985

However, while the technology described in Patent Document 1 does indeed suppress cracking by performing cold rolling in the temperature range of 180 to 350°C, it has the problem that it is difficult to maintain high temperatures during rolling, and there is a high possibility of equipment wear, such as seizure of lubricating oil on the rolls.

In order to solve the aforementioned problems of the prior art, the present invention aims to provide a hot-rolled annealed sheet that is excellent in cold rolling properties in subsequent processes and does not result in a deterioration in the magnetic properties of the final product, non-oriented electrical steel sheet, and to propose an advantageous manufacturing method for it. Another aim is to propose a manufacturing method for non-oriented electrical steel sheet using this hot-rolled annealed sheet. Here, cold-rolling properties include fracture resistance and edge crack resistance.

After extensive research, the inventors discovered that in most cases, breakage due to cold rolling occurs at the edge of the steel strip. Therefore, they found that by increasing the breakage resistance of the edge of the steel strip, it is possible to significantly suppress breakage and cracking due to cold rolling, without increasing the breakage resistance of the entire steel strip. Furthermore, they discovered that a method for increasing the breakage resistance of the edge of the steel strip is to leave unrecrystallized structure in the edge of the steel strip and differentiate the ratio of recrystallized structure from the center of the steel strip. They found that this improves breakage resistance compared to when the ratio of recrystallized structure is reduced throughout the entire steel strip, and also prevents a deterioration in magnetic properties.

In other words, the hot-rolled annealed sheet of the present invention, which advantageously solves the above problems, contains, by mass%, C: 0.010% or less, Si: 1.0% or more and 5.0% or less, Mn: 0.05% or more and 5.0% or less, P: 0.10% or less, S: 0.010% or less, Al: 3.0% or less, N: 0.0080% or less, and O: 0.0050% or less, and optionally, one or more elements selected from Group A: Sn: 0.001% or more and 0.20% or less, and Sb: 0.001% or more and 0.20% or less. Group B: at least one selected from Ca: 0.0001% to 0.10%, Mg: 0.0001% to 0.10%, and REM: 0.0001% to 0.10%; Group C: one or two selected from B: 0.002% to 0.20%, and Mo: 0.002% to 0.20%; Group D: Zn: 0.0005% to 0.0050%; Group E: Ni: 0.01% to 1.0%; Group F: Cr: 0.1% to 5% .0% or less; G group: Cu: 0.005% or more and 1.0% or less; H group: Ti: 0.001% or more and 0.010% or less, V: 0.001% or more and 0.050% or less, Nb: 0.001% or more and 0.005% or less, Ta: 0.0001% or more and 0.0020% or less, W: 0.001% or more and 0.050% or less, Pb: 0.0001% or more and 0.0020% or less; I group: Co: 0.001% or more and 0.100% or less; J group: Ga: 0.0005% or more and 0.0006% or less .0300% or less, and Ge: one or two elements selected from 0.0005% to 0.0300% or less; and at least one element selected from the K group: As: 0.001% to 0.020% or less, with the balance consisting of Fe and unavoidable impurities, and characterized in that the ratio Re/Rc of the recrystallized structure at the steel sheet position Xe 10 mm widthwise away from the outermost edge of the sheet to the ratio Rc of the recrystallized structure at the sheet width center Xc is 0.95 or less.

In addition, a more preferable solution to the problem for the hot-rolled annealed sheet according to the present invention is that the ratio Rc of recrystallized structure in the sheet width center portion Xc is 80% or more, and/or the ratio Re of recrystallized structure at the steel sheet position Xe is in the range of 5% to 95%.

Furthermore, a method for producing a hot-rolled annealed sheet according to the present invention, which advantageously solves the above-mentioned problems, is a method for producing any of the above-mentioned hot-rolled annealed sheets, and includes a hot rolling step of hot-rolling a steel material having the above-mentioned chemical composition to obtain a hot-rolled sheet, and a hot-rolled sheet annealing step of annealing the hot-rolled sheet, wherein in the hot-rolled sheet annealing step, when a widthwise center portion Xc of the hot-rolled sheet is heated from room temperature to a holding temperature _T1 and held there, a steel sheet position Xe 10 mm away in the width direction from an outermost widthwise portion of the hot-rolled sheet reaches a maximum temperature _T2 that is lower than the holding temperature _T1 from room temperature, and a temperature rise rate Vc of the widthwise center portion Xc is made 1.0°C/s or more higher than a temperature rise rate Ve of the steel sheet position Xe.

The method for producing a hot-rolled annealed sheet according to the present invention is as follows:
(a) In the hot-rolled sheet annealing step, at least one of the following (1) to (4) is satisfied:
(b) When a hot-rolled sheet having a sheet width W in the range of 900 mm or more and 1100 mm or less is subjected to the hot-rolled sheet annealing process, a heat suppression region is provided in a range from 20 mm or more in the sheet width direction from the edge of the sheet width to 0.250 × W or less in the sheet width direction from the edge of the sheet width,
This would be a more preferable solution to the problem.
(1) The holding temperature _T1 of the width center portion Xc of the hot-rolled sheet is set to 900 ° C. or higher,
(2) The holding time _t1 at the holding temperature _T1 of the width center portion Xc of the hot-rolled sheet is set to a range of 2 seconds to 120 seconds,
(3) The maximum temperature _T2 at the steel plate position Xe is set in the range of 750 ° C. or more and 1000 ° C. or less; and
(4) The time _t2 during which the temperature is equal to or higher than the maximum temperature _T2 -50°C is set to a range of 5 seconds to 20 seconds.

The method for manufacturing a non-oriented electrical steel sheet according to the present invention, which advantageously solves the above-mentioned problems, is characterized by cold-rolling any of the above-mentioned hot-rolled annealed sheets to form a cold-rolled sheet, and then finish-annealing the cold-rolled sheet to form a cold-rolled annealed sheet.

In this invention, the edge portion refers to both edges on either side of the width, but it does not necessarily have to be applied to both sides; applying this technology to just one side is also effective in reducing breakage. For example, if the characteristics of the rolling mill cause edge cracks or breakage to occur unevenly on one edge, applying this technology to just one side will have a breakage reduction effect.

The present invention makes it possible to provide hot-rolled annealed steel sheets with excellent cold rolling properties. Furthermore, these hot-rolled annealed steel sheets can be used to produce non-oriented electrical steel sheets with high magnetic flux density, high frequency, and low iron loss.

Hereinafter, embodiments of the present invention will be described together with the reasons for limitations.
[Hot-rolled annealed sheet]
<Composition of steel plate>
A preferred composition of the hot-rolled annealed steel sheet according to one embodiment of the present invention will now be described. The unit of the content of elements in the composition is "mass%", and hereinafter, unless otherwise specified, will be simply referred to as "%".

<Basic component composition>
C: 0.010% or less C is a harmful element that causes magnetic aging in the finished non-oriented electrical steel sheet, forming carbides and increasing iron loss. Therefore, since the adverse effects become particularly pronounced when the C content exceeds 0.010%, the C content in the steel sheet is set to 0.010% or less. Preferably, it is set to 0.004% or less. While there is no particular lower limit for the C content, a steel sheet with an excessively reduced C content is very expensive, so it is preferably set to about 0.0001%.

Si: 1.0% or more and 5.0% or less Si has the effect of increasing the resistivity of steel and reducing iron loss, and also has the effect of increasing the strength of steel through solid solution strengthening. To achieve these effects, the Si content should be 1.0% or more. On the other hand, if the Si content exceeds 5.0%, the magnetic flux density decreases significantly due to a decrease in the saturation magnetic flux density, so the upper limit is set to 5.0% or less. Therefore, the Si content is set to be in the range of 1.0% or more and 5.0% or less. Preferably, it is 1.5% or more, and preferably less than 4.5%. More preferably, it is 2.0% or more, and more preferably less than 4.0%.

Mn: 0.05% or more and 5.0% or less Like Si, Mn is a useful element for increasing the resistivity and strength of steel. To achieve this effect, the Mn content must be 0.05% or more. On the other hand, a content exceeding 5.0% may promote the precipitation of MnC, deteriorating the magnetic properties. Therefore, the upper limit of the Mn content is set to 5.0%. Therefore, the Mn content is set to the range of 0.05% or more and 5.0% or less. Preferably, it is 0.1% or more and preferably 3.0% or less.

P: 0.10% or less P is a useful element used to adjust the strength (hardness) of steel. However, if the P content exceeds 0.10%, toughness decreases and cracks tend to occur during processing. Therefore, the upper limit of the P content is set to 0.10%. Although there is no particular lower limit, since steel sheets with excessively reduced P content are very expensive, it is preferable that the P content be 0.001% or more. The P content is preferably 0.08% or less, and more preferably 0.003% or more.

S: 0.010% or less S is an element that forms fine precipitates and adversely affects iron loss characteristics. In particular, if the S content exceeds 0.010%, the adverse effects become significant. Therefore, the S content is set to 0.010% or less, and more preferably 0.008% or less. Although there is no particular lower limit, since steel sheets with excessively reduced S content are very expensive, it is preferable that the S content be 0.0001% or more. More preferably, it is 0.0003% or more, and even more preferably 0.005% or less.

Al: 3.0% or less Excessive addition of Al can promote nitriding of the steel sheet surface and degrade magnetic properties. Therefore, the Al content is set to 3.0% or less, and more preferably 2.0% or less. Similarly to Si, Al is a useful element that has the effect of increasing the resistivity of steel and reducing iron loss. To achieve this effect, it is preferable to add 0.005% or more, more preferably 0.010% or more, and even more preferably 0.015% or more.

N: 0.0080% or less N is an element that forms fine precipitates and adversely affects iron loss characteristics. In particular, if the N content exceeds 0.0080%, the adverse effects become significant, so the N content is set to 0.0080% or less. Preferably, the N content is set to 0.0030% or less. Although there is no particular lower limit, steel sheets with excessively reduced N content are very expensive, so the N content is preferably set to 0.0005% or more. More preferably, the N content is set to 0.0008% or more.

O: 0.0050% or less O (oxygen) is an element that forms non-metallic inclusions in molten steel and adversely affects iron loss characteristics. In particular, if the O content exceeds 0.0050%, the adverse effects become significant. Therefore, the O content is set to 0.0050% or less, and preferably 0.0030% or less. Although there is no particular lower limit, since steel sheets with excessively reduced O content are very expensive, the O content is preferably set to 0.0005% or more, and more preferably 0.0008% or more.

The hot-rolled annealed sheet according to this embodiment has C: 0.010% or less, Si: 1.0% or more and 5.0% or less, Mn: 0.05% or more and 5.0% or less, P: 0.10% or less, S: 0.010% or less,
The alloy contains 3.0% or less Al, 0.0080% or less N, and 0.0050% or less O, with the balance being Fe and unavoidable impurities. Furthermore, in addition to the above basic component composition, at least one arbitrary element selected from the following groups A to K may be contained depending on the required properties.

Group A: Sn: 0.001% or more and 0.20% or less, and one or two selected from Sb: 0.001% or more and 0.20% or less. Sn: 0.001% or more and 0.20% or less. Sn is an element that is effective in improving magnetic flux density and reducing iron loss by improving texture. To achieve this effect, the Sn content should be 0.001% or more. On the other hand, if the Sn content exceeds 0.20%, the effect saturates and costs increase unnecessarily. Therefore, it is preferable to set the upper limit of the Sn content to 0.20%. Therefore, the Sn content is preferably in the range of 0.001% or more and 0.20% or less.

Sb: 0.001% or more and 0.20% or less Sb is an element that is effective in improving the texture, thereby increasing the magnetic flux density and reducing iron loss. To obtain this effect, the Sb content should be 0.001% or more. On the other hand, if the Sb content exceeds 0.20%, the effect saturates, resulting in an unnecessary increase in costs. Therefore, it is preferable to set the upper limit of the Sb content to 0.20%. Therefore, it is preferable that the Sb content be in the range of 0.001% or more and 0.20% or less.

Group B: at least one selected from Ca: 0.0001% to 0.10%, Mg: 0.0001% to 0.10%, and REM: 0.0001% to 0.10%. Ca: 0.0001% to 0.10%. Ca is an element that fixes S as sulfides and contributes to reducing iron loss. To achieve this effect, the Ca content should be 0.0001% or more. On the other hand, if the Ca content exceeds 0.10%, the effect saturates and costs increase unnecessarily. Therefore, it is preferable to set the upper limit of the Ca content to 0.10%. Therefore, it is preferable that the Ca content be in the range of 0.0001% to 0.10%.

Mg: 0.0001% or more and 0.10% or less Mg is an element that fixes S as sulfides and contributes to reducing iron loss. To obtain this effect, the Mg content should be 0.0001% or more. On the other hand, if the Mg content exceeds 0.10%, the effect saturates and costs increase unnecessarily. Therefore, it is preferable to set the upper limit of the Mg content to 0.10%. Therefore, it is preferable to contain Mg in the range of 0.0001% or more and 0.10% or less.

REM: 0.0001% or more and 0.10% or less REM (rare earth metal elements) are a group of elements that fix S as sulfides and contribute to reducing iron loss. To obtain this effect, the REM content should be 0.0001% or more. On the other hand, if the REM content exceeds 0.10%, the effect saturates and costs increase unnecessarily, so the upper limit is set to 0.10%. Therefore, the REM content is preferably in the range of 0.0001% or more and 0.10% or less.

Group C: B: 0.002% or more and 0.20% or less, and Mo: 0.002% or more and 0.20% or less. B: 0.002% or more and 0.20% or less. B has the effect of forming fine carbides in steel and increasing the strength of the steel sheet. To achieve this effect, the B content should be 0.002% or more. On the other hand, if the B content exceeds 0.20%, excessive carbides are formed and iron loss increases. Therefore, it is preferable to set the upper limit of the B content to 0.20%. Therefore, the B content is preferably in the range of 0.002% or more and 0.20% or less.

Mo: 0.002% or more and 0.20% or less Mo has the effect of forming fine carbides in steel and increasing the strength of the steel sheet. To obtain this effect, the Mo content should be 0.01% or more. On the other hand, if the Mo content exceeds 0.20%, excessive carbides are formed and iron loss increases. Therefore, it is preferable to set the upper limit of the Mo content to 0.20%. Therefore, the Mo content is preferably in the range of 0.01% or more and 0.20% or less.

Group D: Zn: 0.0005% or more and 0.0050% or less Zn is an element that is effective in improving the magnetic flux density and reducing iron loss by improving the texture. To obtain this effect, the Zn content should be 0.0005% or more. On the other hand, if the Zn content exceeds 0.0050%, the effect saturates and costs increase unnecessarily. Therefore, it is preferable to set the upper limit of the Zn content to 0.0050%. Therefore, it is preferable to contain the Zn content in the range of 0.0005% or more and 0.0050% or less.

Group E: Ni: 0.01% or more and 1.0% or less Ni is an element that improves the toughness of steel and can be added as needed. To obtain this effect, the Ni content should be 0.01% or more. However, if the Ni content exceeds 1.0%, the effect saturates, so the upper limit of the Ni content is set to 1.0%. Therefore, the Ni content is preferably in the range of 0.01% or more and 1.0% or less.

Group F: Cr: 0.1% or more and 5.0% or less Cr has the effect of increasing the resistivity of steel and reducing iron loss. To obtain this effect, the Cr content should be 0.05% or more. On the other hand, if the Cr content exceeds 5.0%, the magnetic flux density decreases significantly due to a decrease in the saturation magnetic flux density, so the upper limit is set to 5.0%. Therefore, the Cr content is preferably in the range of 0.05% or more and 5.0% or less.

Group G: Cu: 0.005% or more and 1.0% or less Cu is an element that improves the toughness of steel and can be added as needed. To achieve this effect, the Cu content should be 0.01% or more. However, if the Cu content exceeds 1.0%, the effect saturates, so when Cu is added, the upper limit of the Cu content is set to 1.0%. Therefore, the Cu content is preferably in the range of 0.005% or more and 1.0% or less.

H group: at least one selected from Ti: 0.001% to 0.010%, V: 0.001% to 0.050%, Nb: 0.001% to 0.005%, Ta: 0.0001% to 0.0020%, W: 0.001% to 0.050%, and Pb: 0.0001% to 0.0020%. Ti is an element that has the effect of increasing the strength of the steel sheet and can be added appropriately. To achieve this effect, the Ti content should be 0.001% or more. However, if the Ti content exceeds 0.010%, fine precipitates will form in the steel sheet, increasing iron loss, so the upper limit of the Ti content is preferably 0.010%.

V: 0.001% or more and 0.050% or less V is an element that has the effect of increasing the strength of the steel sheet and can be added as needed. To obtain this effect, the V content should be 0.001% or more. However, if the V content exceeds 0.050%, fine precipitates will form in the steel sheet, increasing iron loss, so it is preferable to set the upper limit of the V content to 0.050%.

Nb: 0.001% or more and 0.005% or less Nb is an element that has the effect of increasing the strength of steel sheet and can be added as needed. To obtain this effect, the Nb content should be 0.001% or more. However, if the Nb content exceeds 0.005%, fine precipitates will form in the steel sheet, increasing iron loss. Therefore, it is preferable to set the upper limit of the V content to 0.005%.

Ta: 0.0001% or more and 0.0020% or less Ta is an element that has the effect of increasing the strength of the steel sheet and can be added as needed. To obtain this effect, the Ta content should be 0.0001% or more. However, if the Ta content exceeds 0.0020%, fine precipitates will form in the steel sheet, increasing iron loss, so it is preferable to set the upper limit of the Ta content to 0.0020%.

W: 0.001% or more and 0.050% or less W is an element that has the effect of increasing the strength of the steel sheet and can be added as needed. To obtain this effect, the W content should be 0.001% or more. However, if the W content exceeds 0.050%, fine precipitates will form in the steel sheet, increasing iron loss, so it is preferable to set the upper limit of the W content to 0.050%.

Pb: 0.0001% or more and 0.0020% or less Pb is an element that has the effect of increasing the strength of the steel sheet and can be added as needed. To obtain this effect, the Pb content should be 0.0001% or more. However, if the Pb content exceeds 0.0020%, fine precipitates will form in the steel sheet, increasing iron loss. Therefore, it is preferable to set the upper limit of the Pb content to 0.0020%.

Group I: Co: 0.001% or more and 0.100% or less Co is an element that has the effect of increasing the magnetic flux density of the steel sheet and can be added as needed. To achieve this effect, the Co content should be 0.001% or more. However, since a large amount of Co increases the alloy cost, it is preferable to set the upper limit of the Co content to 0.100%.

J group: one or two elements selected from Ga: 0.0005% to 0.0300% and Ge: 0.0005% to 0.0300% Ga: 0.0005% to 0.0300% Ga is an element that improves the texture of the steel sheet and increases the magnetic flux density, and can be added as needed. To achieve this effect, the Ga content should be 0.0005% or more. However, adding a large amount of Ga saturates the effect and increases the alloy cost, so it is preferable to set the upper limit of the Ga content to 0.0300%.

Ge: 0.0005% or more and 0.0300% or less Ge is an element that has the effect of improving the texture of the steel sheet and increasing the magnetic flux density, and can be added as needed. To obtain such effects, the Ge content should be 0.0005% or more. However, if a large amount of Ge is added, the effect saturates and the alloy cost increases, so it is preferable to set the upper limit of the Ge content to 0.0300%.

K group: As: 0.001% or more and 0.020% or less As is an element that has the effect of increasing the strength of steel sheets and can be added appropriately. To obtain this effect, the As content should be 0.001% or more. However, if the As content exceeds 0.020%, the risk of fracture during cold rolling increases. Therefore, it is preferable to set the upper limit of the As content to 0.020%.

Among the optional elements listed above, contents below the preferred range for effective function are permitted as unavoidable impurities, as they do not affect the cold rolling properties or magnetic properties of electrical steel sheet products.

<Steel plate microstructure>
Next, the microstructure of the hot-rolled annealed sheet according to this embodiment will be described. Here, recrystallization refers to the generation and growth of crystal grains with extremely low dislocation density by holding the material at high temperature. The recrystallized structure and the non-recrystallized structure can be distinguished by observation with an optical microscope.

<The ratio Re/Rc of the recrystallized structure ratio Re at a position Xe 10 mm away from the outermost edge in the width direction of the sheet to the recrystallized structure ratio Rc at the center Xc of the sheet width is 0.95 or less>
According to the inventors' investigations, by providing a difference in the recrystallized structure ratio between the width center and the width edge, fractures and edge cracks during the cold rolling process were significantly suppressed compared to simply reducing the recrystallized structure ratio of the entire hot-rolled annealed sheet. The inventors believe the reason for this is as follows: Generally, the work-hardening rate for plastic deformation decreases as the recrystallized structure ratio decreases. It is presumed that the work-hardening rate at the width edge is lower than that at the width center, which causes stress to act to reduce tension at the width edge during rolling. This significantly suppresses the initiation of cracks at the steel sheet edge, thereby reducing fractures and edge cracks. That is, by setting the ratio Re/Rc (the recrystallized structure ratio Re at the width center Xc of the hot-rolled annealed sheet, Rc, to the recrystallized structure ratio Re at the position Xe 10 mm away from the width edge in the width direction) to 0.95 or less, a hot-rolled annealed sheet can be obtained that sufficiently suppresses fractures and edge cracks during cold rolling. The ratio is preferably 0.8 or less, and more preferably 0.7 or less. There is no particular need to set a lower limit, but it is usually 0.05 or more in a hot-rolled and annealed sheet produced using the method described below.

<<The ratio Rc of recrystallized structure at the center Xc of the sheet width is 80% or more>>
The hot-rolled annealed sheet of this embodiment controls the ratio of the recrystallized structure ratio Rc in the sheet width center to the recrystallized structure ratio Re at the steel sheet position Xe on the sheet width edge side, and the effects of the present invention are not limited by the value of the recrystallized structure ratio at the sheet width center itself. On the other hand, there is a suitable range for the recrystallized structure ratio at the sheet width center, and the effects of the present invention are even more pronounced when it is within that range. When the recrystallized structure ratio at the sheet width center Xc is 80% or more, the magnetic properties of the final product are less likely to deteriorate. For the above reasons, it is more preferable that the recrystallized structure ratio Rc at the sheet width center Xc is 80% or more.

<The ratio Re of the recrystallized structure at the position Xe on the sheet width edge side is in the range of 5% or more and 95% or less>
The hot-rolled annealed steel sheet of this embodiment controls the ratio of the recrystallized structure ratio Rc at the width center to the recrystallized structure ratio Re at the width edge of the steel sheet at position Xe. The effects of the present invention are not limited by the value of the recrystallized structure ratio at position Xe itself. However, there is a preferred range for the recrystallized structure ratio at position Xe, and the effects of the present invention are more pronounced when the ratio is within that range. When the recrystallized structure ratio Re at position Xe on the width edge of the hot-rolled annealed steel sheet of this embodiment is 5% or more, the width edge does not become excessively hard, and the generation of fracture initiation points is suppressed. On the other hand, when the recrystallized structure ratio Re at position Xe on the width edge of the steel sheet is 95% or less, the fracture suppression effect achieved by controlling the Re/Rc ratio is more likely to be significantly achieved. For these reasons, it is preferable that the recrystallized structure ratio Re at position Xe on the width edge of the steel sheet be in the range of 5% to 95%.

[Manufacturing conditions for hot-rolled annealed sheets]
Next, a method for producing a hot-rolled annealed sheet according to this embodiment will be described.
In summary, the hot-rolled annealed steel sheet according to the present embodiment is obtained by successively hot-rolling and hot-rolled annealing a steel material having the above-described chemical composition. In this embodiment, as long as the chemical composition and hot-rolled annealing conditions are within the ranges specified in the claims, any commonly known method may be used.

<Steel material>
The steel material is not particularly limited as long as it has the above-mentioned component composition.
The method for producing the steel material and the method for adjusting the composition are not particularly limited, and known methods for producing the steel material using a converter or an electric furnace, a vacuum degassing device, or other devices and methods can be used. From the viewpoint of productivity and other factors, it is preferable to produce a slab (steel material) by continuous casting after the production. On the other hand, a slab or thin slab may also be produced by known casting methods such as ingot making-blooming rolling or thin slab continuous casting.

<Hot rolling process>
The hot rolling step is a step of hot rolling a steel material having the above-mentioned composition to obtain a hot-rolled sheet. The hot rolling step is not particularly limited as long as it is a step of heating a steel material having the above-mentioned composition, hot rolling it, and obtaining a hot-rolled sheet of a predetermined size, and any conventional hot rolling step can be applied.

The following hot rolling process is an example of a commonly used hot rolling process. For example, the steel material is heated to a temperature in the range of 1000°C to 1200°C. The heated steel material is hot rolled at a finish rolling outlet temperature in the range of 800°C to 950°C. After hot rolling is completed, appropriate post-rolling cooling is performed, for example, in the temperature range of 450°C to 950°C at an average cooling rate in the range of 20°C/s to 100°C/s. The steel is then coiled at a coiling temperature in the range of 400°C to 700°C to produce a hot-rolled sheet of the specified dimensions and shape.

<Hot-rolled sheet annealing process>
The hot-rolled sheet annealing process is a process of annealing the hot-rolled sheet by heating the hot-rolled sheet and holding it at a high temperature. More specifically, when the widthwise center portion Xc of the hot-rolled sheet is heated to and held at an appropriate holding temperature _T1 required for recrystallization of the hot-rolled sheet, a steel sheet position Xe 10 mm away from the widthwise edge portion of the hot-rolled sheet reaches a maximum temperature _T2 lower than the holding temperature _T1 from room temperature. The hot-rolled sheet annealing process is a process in which the temperature rise rate Vc at the widthwise center portion Xc is 1.0°C/s or more higher than the temperature rise rate Ve at the steel sheet position Xe. Preferably, the holding temperature _T1 is 900°C or higher. Preferably, the holding time _t1 at the holding temperature _T1 is in the range of 2 seconds to 120 seconds. Preferably, the maximum temperature _T2 at the steel sheet position Xe is in the range of 750°C to 1000°C. Preferably, the time _t2 during which the steel sheet temperature at position Xe is equal to or higher than the maximum temperature _T2 -50°C is set to a range of 5 seconds to 20 seconds. Preferably, when a hot-rolled sheet having a sheet width W in the range of 900 mm to 1100 mm is subjected to the hot-rolled sheet annealing process, a heating suppression region is provided in a range from 20 mm or more in the sheet width direction from the outermost edge of the sheet width to 0.250 × W or less in the sheet width direction from the outermost edge of the sheet width.

Following the hot-rolled sheet annealing process, a pickling process is usually carried out. There are no particular restrictions on the pickling process, as long as it is a process that can pickle the steel sheet to the extent that it can be cold-rolled after pickling; for example, a conventional pickling process using hydrochloric acid or sulfuric acid can be applied. This pickling process may be carried out continuously in the same line as the hot-rolled sheet annealing process, or it may be carried out in a separate line. The hot-rolled sheet annealed in this invention includes both a state that has not been pickled (black skin) and a state that has been pickled (white skin).

<<Making the temperature rise rate Vc at the sheet width center portion Xc greater than the temperature rise rate Ve at the steel sheet position Xe by 1.0°C/s or more>>
In the hot-rolled sheet annealing process, the heating rate when heating the sheet width center Xc from room temperature to the holding temperature _T1 is defined as Vc. Furthermore, the heating rate when the steel sheet position Xe, 10 mm away from the outermost edge in the sheet width direction, reaches the maximum temperature _T2 from room temperature is defined as Ve. Vc-Ve is limited to 1.0°C/s. If Vc-Ve<1.0°C/s, the difference in the proportion of recrystallized structure between the sheet width center and the sheet width edge becomes small, and the ratio Re/Rc of the proportion Rc of recrystallized structure at the sheet width center to the proportion Re of recrystallized structure at the sheet width edge cannot be set to 0.95 or less. Preferably, Vc-Ve≧3°C/s, and more preferably, Vc-Ve≧5°C/s.

<<Holding temperature _T1 at width center Xc is 900°C or higher>>
In the hot-rolled sheet annealing process, the holding temperature _T1 of the sheet width center portion Xc is preferably 900°C or higher. By setting _T1 to 900°C or higher, the ratio Rc of the recrystallized structure in the sheet width center portion Xc can be set to 80% or higher. Although no upper limit is particularly specified, if _T1 is higher than 1100°C, the sheet width edge portion may be heated by heat conduction, and the ratio of the recrystallized structure in the sheet width edge portion may become excessively high. Therefore, it is preferable to control the holding temperature _T1 of the sheet width center portion Xc to 900°C or higher and 1100°C or lower.

<<The holding time _t1 at the holding temperature _T1 of the sheet width center portion Xc is set to 2 seconds or more and 120 seconds or less>>
In the hot-rolled sheet annealing process, the holding time _t1 at the holding temperature _T1 of the sheet width center Xc is preferably 2 seconds or more and 120 seconds or less. If _t1 is 120 seconds or less, the ratio Re/Rc of the recrystallized structure ratio between the sheet width center and the sheet width edge can be set to 0.95 or less, which is preferable because it improves cold rolling properties. Furthermore, by setting the lower limit of the holding time _t1 to 2 seconds, recrystallization and grain growth due to hot-rolled sheet annealing are sufficient, resulting in good magnetic properties. Therefore, the holding time _t1 at the holding temperature _T1 of the sheet width center Xc is preferably 2 seconds or more and 120 seconds or less.

<<Maximum temperature _T2 at steel plate position Xe is set in the range of 750°C or higher and 1000°C or lower>>
In the hot-rolled sheet annealing process, the maximum temperature _T2 at the steel sheet position Xe, which is 10 mm away from the outermost edge of the hot-rolled sheet in the width direction, is preferably set to 750°C or higher and 1000°C or lower. When the maximum temperature _T2 is 750°C or higher, recrystallization at the steel sheet position Xe is sufficient, and the recrystallized structure ratio Re satisfies 5% or higher. On the other hand, when the maximum reached temperature _T2 is 1000°C or lower, the recrystallized structure ratio Re satisfies 95% or lower. Therefore, the maximum reached temperature _T2 at the steel sheet position Xe is preferably set to 750°C or higher and 1000°C or lower. The maximum reached temperature _T2 at the steel sheet position Xe needs to be lower than the holding temperature _T1 at the sheet width center Xc. Otherwise, the recrystallized structure ratio Re at the steel sheet position Xe will be higher than the recrystallized structure ratio Rc at the sheet width center Xc.

<<The time _t2 during which the steel plate temperature at the position Xe is equal to or higher than the maximum temperature _T2 -50°C is set to a range of 5 seconds to 20 seconds>>
In the hot-rolled sheet annealing process, it is preferable that the time _t2 during which the steel sheet position Xe is at or above the maximum temperature _T2 -50°C is in the range of 5 seconds to 20 seconds. Note that _t2 is the sum of the time to heat the steel sheet to _the maximum temperature _T2 and the time to cool it from the maximum temperature _T2 . When _t2 is 5 seconds or more, a sufficient time can be secured for the steel sheet position Xe to cool after reaching the maximum temperature T2, recrystallization can proceed moderately, and the ratio Re of the recrystallized structure can be made 5% or more. When _t2 is 20 seconds or less, recrystallization proceeds moderately, and the ratio Re of the recrystallized structure can be made 95% or less.

<<Providing a heat suppression region in a range of 20 mm or more in the width direction from the edge of the plate>>
In the hot-rolled sheet annealing process, the following methods can be used to provide a heat suppression region that intentionally changes the temperature in the sheet width direction: (a) preventing overheating by weakening burner heating only at the edge, (b) preventing overheating by applying an edge cover, (c) applying a temperature rise prevention material with low emissivity that can suppress radiant heating, and (d) preventing temperature rise by removing black scale only at the edge. Any method that can intentionally change the temperature is acceptable and does not limit the scope of the invention. It is preferable to provide a heat suppression region in a range of 20 mm or more in the sheet width direction from the outermost edge of the sheet. If the heat suppression region is in a range of 20 mm or more from the outermost edge of the sheet width, the temperature at the steel sheet position Xe, 10 mm from the outermost edge, is less likely to rise due to thermal conduction of the steel sheet. Therefore, the temperature rise rate Vc at the sheet width center Xc can be made 1.0°C/s or more higher than the temperature rise rate Ve at the steel sheet position Xe. On the other hand, with regard to the upper limit of the heat suppression region, when a hot-rolled sheet having a sheet width W in the range of 900 mm to 1100 mm is subjected to the above-mentioned hot-rolled sheet annealing process, it is preferable to provide the heat suppression region in a range from the outermost width portion to 0.250 × W or less in the sheet width direction. Within this range, the proportion of recrystallized structures in the entire steel sheet is sufficient, and deterioration of magnetic properties can be suppressed. Therefore, preferably, the heat suppression region is set to a range of 20 mm or more in the sheet width direction from the outermost width portion. Preferably, when a hot-rolled sheet having a sheet width W in the range of 900 mm to 1100 mm is subjected to the hot-rolled sheet annealing process, the heat suppression region is set to a range from the outermost width portion to 0.250 × W or less in the sheet width direction.

<Acid washing process>
The pickling process is a process of pickling the hot-rolled annealed sheet after the hot-rolled sheet annealing process. The pickling process is not particularly limited as long as it is a process that can pickle the steel sheet after pickling to an extent that cold rolling can be performed, and for example, a conventional pickling process using hydrochloric acid or sulfuric acid can be applied. When the hot-rolled sheet annealing process is performed, this pickling process may be performed continuously in the same line as the hot-rolled sheet annealing process, or may be performed in a separate line.

<Cold rolling process>
The cold rolling process is a process of cold rolling the hot-rolled annealed sheet (pickled sheet) that has been subjected to the pickling. In the cold rolling process, the hot-rolled annealed sheet that has been subjected to the pickling is cold-rolled to obtain a cold-rolled sheet. There are no particular limitations on the process as long as a cold-rolled sheet of predetermined dimensions can be obtained by cold rolling, and any conventional cold rolling process can be applied.

An example of a commonly used cold rolling process is a cold rolling process in which a pickled sheet is rolled using a five-stand tandem mill under conditions of a total reduction of 80% or more but less than 95% to produce a cold-rolled sheet of the specified dimensions and shape. The number of stands may be four or less, or six or more.

<Finishing annealing process>
The final annealing step is a step in which the cold-rolled sheet that has been subjected to the cold rolling step is annealed to obtain a cold-rolled annealed sheet. The final annealing step is not particularly limited as long as it is a step in which the cold-rolled sheet is heated, held, and cooled to obtain a cold-rolled annealed sheet, and a conventional annealing step can be applied. Note that an insulating coating may be applied to the surface after the final annealing step. The method and type of insulating coating are not particularly limited, and a conventional insulating coating step can be applied.

An example of a commonly used annealing process is a finish annealing process in which cold-rolled sheet is heated to a temperature of 800°C or higher and 1200°C or lower in a non-oxidizing atmosphere, held at that temperature for 5 to 60 seconds, and then cooled.

The present invention will be explained in detail below using examples. However, the present invention is not limited to these examples.

<Manufacturing of hot-rolled annealed sheets>
Molten steel having the chemical composition shown in Table 1 was produced by a commonly known method and continuously cast into a 230 mm thick slab (steel material). The obtained slab was hot rolled to obtain a hot rolled sheet having a thickness of 2.0 mm. The obtained hot rolled sheet was subjected to hot rolled sheet annealing and pickling under the conditions shown in Tables 2-1 and 2-2 to obtain a hot rolled annealed sheet (pickled sheet).

<Production of cold-rolled sheets>
The hot-rolled and annealed sheet (pickled sheet) was then cold-rolled at room temperature using a tandem mill to a sheet thickness of 0.25 mm to obtain a cold-rolled sheet.

<Production of cold-rolled annealed sheet>
The cold-rolled sheet was then subjected to finish annealing by a known method in which it was held at 1000°C for 10 seconds in a non-oxidizing atmosphere, and then coated by a known method to obtain a cold-rolled annealed sheet (non-oriented electrical steel sheet).

<Evaluation>
<Tissue Observation>
For the obtained hot-rolled annealed sheet, test pieces for microstructure observation were taken from the sheet width center and from a position 10 mm from the sheet width outermost edge. Next, the taken test pieces were embedded in resin with the cross section in the sheet thickness direction as the observation surface, and observed with an optical microscope to measure the proportion of recrystallized structure.

<Rollability evaluation>
The number of edge cracks per 1000 m of the obtained cold-rolled sheet was investigated. Edge cracks with a crack length of 2 mm or more were counted as the number N. When the number of edge cracks per 1000 m of the cold-rolled sheet was 2.0 or less, the cold-rollability was considered to be good.

<Magnetic property evaluation>
From the obtained cold-rolled annealed sheet, a magnetic measurement test piece having a width of 30 mm and a length of 280 mm, with the length direction being the rolling direction and the direction perpendicular to the rolling direction, was taken, and the magnetic flux density B50 and iron loss W10 _/400 of the cold-rolled annealed sheet were measured by the Epstein method in accordance with JIS C2550-1: 2011. The magnetic flux density was evaluated as good when B50 ≧ 1.55 T, and the iron loss characteristics were evaluated as good when W10 _/400 ≦ 14.0 W/kg after annealing.

In the evaluation column, for cold rolling property, those that broke during rolling and those that had more than 2.0 edge cracks per 1000 m of cold-rolled sheet length were marked "bad." Furthermore, those whose composition was outside the scope of the present invention and whose magnetic flux density B50 was less than 1.55 T or whose iron loss W10 _/400 was more than 14.0 W/kg, regardless of the hot-rolled sheet annealing conditions, were marked "bad." Of the remaining samples, those whose magnetic flux density B50 was 1.55 T or more and whose iron loss W10 _/400 was 14.0 W/kg or less were marked "excellent," and the rest were marked "good."

The results in Tables 3-1 and 3-2 show that all hot-rolled and annealed sheets according to the present invention have excellent cold rolling properties, and furthermore, cold-rolled and annealed sheets obtained by cold-rolling and annealing the hot-rolled and annealed sheets according to the present invention also have excellent magnetic properties.

Claims (7)

In mass%,
C: 0.010% or less,
Si: 1.0% or more and 5.0% or less,
Mn: 0.05% or more and 5.0% or less,
P: 0.10% or less,
S: 0.010% or less,
Al: 3.0% or less,
Contains N: 0.0080% or less and O: 0.0050% or less,
Further, optionally,
Group A: one or two selected from Sn: 0.001% or more and 0.20% or less, and Sb: 0.001% or more and 0.20% or less;
Group B: at least one selected from Ca: 0.0001% or more and 0.10% or less, Mg: 0.0001% or more and 0.10% or less, and REM: 0.0001% or more and 0.10% or less;
Group C: one or two selected from B: 0.002% or more and 0.20% or less, and Mo: 0.002% or more and 0.20% or less;
Group D: Zn: 0.0005% or more and 0.0050% or less;
Group E: Ni: 0.01% or more and 1.0% or less;
Group F: Cr: 0.1% or more and 5.0% or less;
Group G: Cu: 0.005% or more and 1.0% or less;
H group: at least one selected from Ti: 0.001% or more and 0.010% or less, V: 0.001% or more and 0.050% or less, Nb: 0.001% or more and 0.005% or less, Ta: 0.0001% or more and 0.0020% or less, W: 0.001% or more and 0.050% or less, and Pb: 0.0001% or more and 0.0020% or less;
Group I: Co: 0.001% or more and 0.100% or less;
J group: one or two elements selected from Ga: 0.0005% or more and 0.0300% or less, and Ge: 0.0005% or more and 0.0300% or less; and K group: As: 0.001% or more and 0.020% or less,
The balance is Fe and unavoidable impurities,
A hot-rolled annealed sheet, wherein the ratio Re/Rc of the recrystallized structure at the steel sheet position Xe 10 mm away from the edge portion in the width direction to the ratio Rc of the recrystallized structure at the center portion Xc of the sheet width is 0.95 or less. The hot-rolled annealed sheet according to claim 1 further satisfies either or both of the following: the ratio Rc of recrystallized structure in the sheet width center portion Xc is 80% or more, and the ratio Re of recrystallized structure in the steel sheet position Xe is in the range of 5% or more and 95% or less. A method for producing the hot-rolled annealed sheet according to claim 1 or 2,
The method includes a hot rolling step of hot rolling a steel material having the above-mentioned component composition to obtain a hot-rolled sheet, and a hot-rolled sheet annealing step of hot-rolling the hot-rolled sheet,
In the hot-rolled sheet annealing process, when the sheet width central portion Xc of the hot-rolled sheet is heated from room temperature to a holding temperature _T1 and held, a steel sheet position Xe 10 mm away in the width direction from the sheet width outermost edge portion of the hot-rolled sheet reaches a maximum temperature _T2 that is lower than the holding temperature _T1 from room temperature,
a temperature rise rate Vc at the sheet width center portion Xc being greater than a temperature rise rate Ve at the steel sheet position Xe by 1.0°C/s or more. The method for manufacturing a hot-rolled annealed sheet according to claim 3, wherein the hot-rolled sheet annealing step satisfies at least one of the following (1) to (4).
(1) The holding temperature _T1 of the width center portion Xc of the hot-rolled sheet is set to 900 ° C. or higher,
(2) The holding time _t1 at the holding temperature _T1 of the width center portion Xc of the hot-rolled sheet is set to a range of 2 seconds to 120 seconds,
(3) The maximum temperature _T2 at the steel plate position Xe is set in the range of 750 ° C. or more and 1000 ° C. or less; and
(4) The time _t2 during which the maximum temperature is equal to or higher than _T2 -50°C is set to be in the range of 5 seconds to 20 seconds. When a hot-rolled sheet having a sheet width W in the range of 900 mm or more and 1100 mm or less is subjected to the hot-rolled sheet annealing process,
The method for manufacturing a hot-rolled annealed sheet according to claim 3, wherein a heat suppression region is provided in a range from 20 mm or more in the sheet width direction from the outermost edge portion of the sheet width to 0.250 × W or less in the sheet width direction from the outermost edge portion of the sheet width. When a hot-rolled sheet having a sheet width W in the range of 900 mm or more and 1100 mm or less is subjected to the hot-rolled sheet annealing process,
The method for manufacturing a hot-rolled annealed sheet according to claim 4, wherein a heat suppression region is provided in a range from 20 mm or more in the sheet width direction from the outermost edge portion of the sheet width to 0.250 × W or less in the sheet width direction from the outermost edge portion of the sheet width. A method for producing a non-oriented electrical steel sheet, comprising cold rolling the hot-rolled annealed sheet according to claim 1 or 2 to obtain a cold-rolled sheet, and then finish-annealing the cold-rolled sheet to obtain a cold-rolled annealed sheet.