Title of invention : Steel sheet for non-oriented electrical steel sheet
Technical field
[0001]
The present invention relates to steel sheets for non-oriented electrical steel sheets.
This application claims priority based on Japanese Patent Application No. 2020-027002 filed in Japan on February 20, 2020, the content of which is hereby incorporated by reference.
Background technology
[0002]
In recent years, electrical equipment, especially in the fields of motors, rotating machines, small and medium-sized transformers, electrical equipment, etc., where non-oriented electrical steel sheets are used as iron core materials, have become global power/energy saving, CO2 reduction, etc. Demands for high efficiency and miniaturization are increasing more and more in the movement of global environment conservation represented by . Under such a social environment, it is of course an urgent task to improve the performance of non-oriented electrical steel sheets.
[0003]
In order to improve the characteristics of motors, non-oriented electrical steel sheets are required to improve magnetic properties such as iron loss and magnetic flux density. In order to improve the magnetic properties, various efforts have been made to control not only the steel composition, but also the metal structure such as grain size and crystal orientation in the steel sheet, and the control of precipitates.
[0004]
For example, Patent Document 1 discloses a non-oriented electrical steel sheet containing 0.10% to 0.30% by mass of P and having a magnetic flux density of 1.70 T or more at B50.
[0005]
Further, for example, in Patent Documents 2 to 4, by allowing P to segregate at the grain boundary of the steel sheet before cold rolling, the crystal orientation after cold rolling and recrystallization annealing is controlled to improve the magnetic properties. A technique for doing so is disclosed.
prior art documents
patent literature
[0006]
Patent Document 1: Japanese Patent Application Laid-Open No. 2002-371340
Patent Document 2: Japanese Patent Application Laid-Open No. 2012-036454
Patent Document 3: Japanese Patent Application Laid-Open No. 2005-200756
Patent Document 4: Japanese Patent Application Laid-Open No. 2016-211016
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0007]
However, with the techniques described in Patent Documents 1 to 4, the addition of the segregating element significantly deteriorates the toughness, and the problem is that the steel is broken during threading in the pickling process. That is, it has not been possible to achieve both improvement in the toughness of steel sheets for non-oriented electrical steel sheets and low iron loss and high magnetic flux density in non-oriented electrical steel sheets.
[0008]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a steel sheet for non-oriented electrical steel sheets that achieves both hot-rolled sheet toughness and magnetic properties after cold rolling and annealing. do.
Means to solve problems
[0009]
The present inventors have extensively researched methods for achieving both hot-rolled sheet toughness and magnetic properties after cold rolling and annealing in non-oriented electrical steel sheets. As a result, it was found that by controlling the soaking temperature and time during hot-rolled steel annealing within a specific range and changing the cooling rate in the width direction, a material with excellent hot-rolled steel toughness and excellent magnetic properties could be realized. I found out. That is, it was found that by annealing the hot-rolled coil after hot-rolled sheet annealing and keeping the hot-rolled coil warm during transportation, both the toughness of the hot-rolled sheet and the magnetic properties after cold rolling and annealing can be achieved. In the present invention, the toughness of a hot-rolled sheet means the toughness of a steel sheet for non-oriented electrical steel sheets that has undergone a hot-rolled sheet annealing process or a cooling process after a heat retention process and before the pickling process.
[0010]
The gist of the present invention based on the above findings is as follows.
[1] Mass %,
C: 0.0040% or less,
Si: 1.9% or more and 3.5% or less,
Al: 0.10% or more and 3.0% or less,
Mn: 0.10% or more and 2.0% or less,
P: 0.09% or less,
S: 0.005% or less,
N: 0.0040% or less,
B: 0.0060% or less
and the balance consists of Fe and impurities,
The recrystallization rate of the structure of the cross section in the plate thickness direction at each position of 10 mm from each of both ends in the plate width direction to the center of the plate width is less than 50%,
A non-oriented electrical steel sheet characterized in that, where W is the sheet width, the recrystallization rate of the structure of the cross section in the sheet thickness direction at positions 1/4 W from both ends in the sheet width direction is 50% or more. Steel plate for
[2] In addition, in mass%,
Sn: 0.01% or more and 0.50% or less,
Sb: 0.01% or more and 0.50% or less,
Cu: 0.01% or more and 0.50% or less
The steel sheet for non-oriented electrical steel sheet according to [1], characterized in that it contains one or more of
[3] Furthermore, in mass%,
　One or two or more selected from REM: 0.00050% or more and 0.040% or less,
Ca: 0.00050% or more and 0.040% or less,
　Mg: 0.00050% or more and 0.040% or less
The steel sheet for non-oriented electrical steel sheet according to claim 1 or 2, characterized in that it contains one or more of
Effect of the invention
[0011]
According to the present invention, it is possible to provide a steel sheet for non-oriented electrical steel sheets that achieves both hot-rolled toughness and magnetic properties after cold rolling and annealing.
Brief description of the drawing
[0012]
1] (A) is a schematic diagram for explaining the metal structure of a steel sheet for a non-oriented electrical steel sheet according to the present embodiment, and (B) is a schematic diagram for explaining the metal structure of a comparative material. [Fig. be.
2 is a graph showing the results of a Charpy test in Examples. FIG.
MODE FOR CARRYING OUT THE INVENTION
[0013]
A preferred embodiment of the present invention will be described in detail below. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications can be made without departing from the gist of the present invention. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present invention can be obtained. Also, each component of the following embodiments can be combined with each other.
[0014]

[Chemical composition]
First, the chemical composition of the steel sheet for non-oriented electrical steel sheet according to the present embodiment (hereafter, the steel sheet for non-oriented electrical steel sheet will be simply referred to as steel sheet) will be described. In addition, below, the notation of "%" shall represent "mass %" unless there is a notice in particular. Moreover, the lower limit value and the upper limit value are included in the range of numerical limits described below. Any numerical value indicated as "greater than" or "less than" is not included in the numerical range.
[0015]
(C: 0.0040% or less)
C increases the iron loss of the final product, the non-oriented electrical steel sheet, and causes magnetic aging. The C content of the steel sheet according to this embodiment is 0.0040% or less. The C content is preferably 0.0030% or less, more preferably 0.0020% or less. The lower limit of the C content includes 0%, but it is difficult to make the C content 0% in terms of production technology, and 0.0001% is the practical lower limit.
[0016]
(Si: 1.9% or more and 3.5% or less)
Si has the effect of reducing iron loss by increasing the electrical resistance of the non-oriented electrical steel sheet and reducing eddy current loss. Si also has the effect of improving the punching accuracy of the core by increasing the yield ratio. If the Si content of the steel sheet is 1.9% or more, the above effect can be obtained. The Si content of the steel sheet is preferably 2.0% or more, more preferably 2.1% or more. On the other hand, if the Si content is excessive, the magnetic flux density of the non-oriented electrical steel sheet decreases, and in the manufacturing process of the non-oriented electrical steel sheet itself, the yield ratio increases, resulting in a decrease in workability such as cold rolling. , the Si content is 3.5% or less because of the high cost. The Si content of the steel sheet is preferably 3.0% or less, more preferably 2.5% or less.
[0017]
(Al: 0.10% or more and 3.0% or less)
Al, like Si, has the effect of increasing the electrical resistance of the non-oriented electrical steel sheet and reducing the eddy current loss, thereby reducing iron loss, but the increase in yield strength is smaller than that of Si. If the Al content is 0.10% or more, the iron loss is reduced, the yield strength is increased, the yield ratio is increased, and the punching workability of the iron core is improved. The Al content of the steel sheet is preferably 0.20% or more. On the other hand, when the Al content of the steel sheet is excessive, the saturation magnetic flux density is lowered, leading to a decrease in the magnetic flux density. Furthermore, when the Al content of the steel sheet is excessive, the yield ratio decreases and the punching accuracy of the non-oriented electrical steel sheet decreases. Therefore, the Al content of the steel sheet is 3.0% or less. The Al content of the steel sheet is preferably 2.5% or less. In addition, Al content may be 0.1% or more, and may be 0.2% or more.
[0018]
(Mn: 0.10% or more and 2.0% or less)
Mn has the effect of increasing the electrical resistance and reducing the eddy current loss, as well as improving the primary recrystallization texture and developing the {110}<001> crystal orientation desirable for improving rolling direction magnetic properties. Furthermore, Mn suppresses precipitation of fine sulfides such as MnS that are harmful to grain growth. For these purposes, the Mn content of the steel sheet is 0.10% or more. The Mn content of the steel sheet is preferably 0.20% or more. On the other hand, if the Mn content is excessive, the crystal grain growth itself during annealing deteriorates and iron loss increases. Therefore, the Mn content of the steel sheet is 2.0% or less. The Mn content of the steel sheet is preferably 1.5% or less. In addition, the Mn content may be 0.1% or more, or may be 0.2% or more.
[0019]
(P: 0.09% or less)
　P has the effect of increasing the punching accuracy of the non-oriented electrical steel sheet, but when the P content increases, it becomes very brittle. This tendency is remarkable in steel sheets with Si≧2%. Therefore, the P content of the steel sheet is 0.09% or less. The P content of the steel sheet is preferably 0.05% or less. Although the lower limit of the P content is not particularly limited, it is preferably 0.005% or more from the viewpoint of magnetic flux density deterioration due to P reduction.
[0020]
(S: 0.005% or less)
S finely precipitates as sulfides such as MnS and inhibits recrystallization and grain growth during final annealing. Therefore, the S content of the steel sheet is 0.005% or less. The S content of the steel sheet is preferably 0.004% or less. Although the lower limit of the S content is not particularly limited, it is preferably 0.0005% or more from the viewpoint of cost increase due to desulfurization.
[0021]
(N: 0.0040% or less)
N reduces the coverage of the internal oxide layer formed on the surface side of the hot-rolled sheet due to the fine precipitation of nitrides such as AlN formed during hot-rolled sheet annealing and finish annealing. Inhibits grain growth. Therefore, the N content of the steel sheet is 0.0040% or less. The N content of the steel sheet is preferably 0.0030% or less. Although the lower limit of the N content is not particularly limited, it is preferably 0.0005% or more from the viewpoint of cost increase for reducing N.
[0022]
(B: 0.0060% or less)
B inhibits recrystallization and grain growth during final annealing due to fine precipitation of nitrides such as BN. Therefore, the B content of the steel sheet is 0.0060% or less. The B content of the steel sheet is preferably 0.0040% or less. Although the lower limit of the B content is not particularly limited, it is preferably 0.0001% or more from the viewpoint of cost increase for reducing B.
[0023]
The steel sheet according to the present embodiment further has, in mass%, Sn: 0.01% or more and 0.50% or less, Sb: 0.01% or more and 0.50% or less, Cu: 0.01% or more and 0.50% % or less is preferably contained. The content of each element is described below. Since Sn, Sb and Cu are not essential in the steel sheet, the lower limit of their content is 0%. Moreover, even if these elements are contained as impurities, the above effects are not impaired.
[0024]
Sn, Sb and Cu improve the primary recrystallization texture of the base steel sheet, further develop the texture into a {110}<001> texture desirable for improving the rolling direction magnetic properties, and improve the magnetic properties. It has the effect of further suppressing undesirable {111}<112> texture and the like. On the other hand, even if the Sn content, the Sb content, or the Cu content is increased, the above effect is saturated, and rather the toughness of the steel sheet may be lowered. Therefore, the base material steel plate has Sn: 0.01% or more and 0.50% or less, Sb: 0.01% or more and 0.50% or less Lower, Cu: It is preferable to contain one or more of 0.01% or more and 0.50% or less.
[0025]
The steel sheet according to the present embodiment further includes, in mass%, one or more selected from REM: 0.00050% or more and 0.040% or less, Ca: 0.00050% or more and 0.040% or less, Mg: It is preferable to contain one or more of 0.00050% or more and 0.040% or less. If the content of one or more selected from REM, one or more of Ca and Mg is 0.00050% or more, grain growth is further promoted. The content of one or more selected from REM and one or more of Ca and Mg is preferably 0.0010% or more, more preferably 0.0050% or more. On the other hand, if the content of one or more selected from REM, one or more of Ca and Mg is 0.0400% or less, the magnetic properties of the non-oriented electrical steel sheet are further reduced. more suppressed. The content of one or more selected from REM and one or more of Ca and Mg is preferably 0.0300% or less, more preferably 0.0200% or less. Since REM, Ca and Mg are not essential in the steel sheet, the lower limit of their content is 0%. Note that REM is an abbreviation for Rare Earth Metal, and refers to elements belonging to the Sc, Y, and lanthanide series. In the case of lanthanides, they are industrially added in the form of misch metals.
[0026]
The above steel components can be measured by a general steel analysis method. For example, the steel composition may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Incidentally, C and S can be measured using a combustion-infrared absorption method, N can be measured using an inert gas fusion-thermal conductivity method, and O can be measured using an inert gas fusion-nondispersive infrared absorption method.
[0027]
[Metal structure]
Next, the metal structure of the steel sheet according to this embodiment will be described with reference to FIG. FIG. 1A is a schematic diagram for explaining the metal structure of the steel sheet according to this embodiment. FIG. 1B is a schematic diagram for explaining the metal structure of the comparative material. The steel sheet shown in FIG. 1(A) and the steel sheet shown in FIG. 1(B) have the same chemical composition, but the steel sheet shown in FIG. 1(A) and the steel sheet shown in FIG. Manufacturing conditions are different.
In FIG. 1, WS refers to one widthwise end of the hot-rolled steel sheet, C refers to the center of the hot-rolled steel sheet in the widthwise direction, and DS refers to the other widthwise end of the hot-rolled steel sheet. . In addition, RD indicates the rolling direction, and ND indicates the direction normal to the rolling surface (thickness direction).
[0028]
The metal structure of the steel sheet according to the present embodiment has a recrystallization rate of less than 50% in the structure of the cross section in the thickness direction at each position of 10 mm from each of both ends in the width direction to the center direction of the width of the plate. When W is assumed, the recrystallization rate of the structure of the cross section in the plate thickness direction at the position of 1/4 W from each end in the plate width direction is 50% or more. Here, W is 800 mm or more. Therefore, the position of 1/4W from the end in the width direction is positioned closer to the center of the width than the position of 10 mm in the width center direction from both ends of the width bar. Here, the thickness direction cross section means a cross section parallel to the thickness direction and the longitudinal direction (or rolling direction) of the steel sheet.
[0029]
As shown in FIG. 1A, the steel sheet according to the present embodiment has recrystallized crystal grains on the front and back surfaces (ends in the ND direction), but the center in the thickness direction is in the rolling direction. A processed structure that extends and is layered in the plate thickness direction is confirmed. On the other hand, in the case of the conventional steel sheet as shown in FIG. 1B, no layered structure in the rolling direction is observed at the center in the thickness direction. Thus, a recrystallized structure refers to a structure with an aspect ratio of 2.5 or less, and a processed structure refers to a structure with an aspect ratio of more than 2.5. The aspect ratio can be calculated by measuring the length of the major axis and the length of the minor axis using a SEM (Scanning Electron Microscope).
[0030]
In general, when the recrystallization rate of the steel sheet is small, the iron loss of the non-oriented electrical steel sheet, which is the final product, increases and the magnetic flux density decreases. The steel sheet according to the present embodiment has a recrystallization rate of less than 50% in the structure of the cross section in the thickness direction at each position 10 mm from each of both ends in the width direction in the width center direction, and both ends in the width direction , to each position of 10 mm in the sheet width center direction, the recrystallization rate is even smaller, and this is a portion that can cause an increase in iron loss. However, when manufacturing a non-oriented electrical steel sheet using the steel sheet according to the present embodiment, the relevant portion is finally cut off, and the remaining portion other than the relevant portion becomes the final non-oriented electrical steel sheet. Therefore, even if the recrystallization rate of the portion from each of both ends in the width direction of the steel plate according to the present embodiment to each position of 10 mm in the width center direction is less than 50%, the portion is non-directional electromagnetic It does not degrade the magnetic properties of the steel sheet. On the other hand, if the recrystallization rate of the structure of the cross section in the plate thickness direction at each position 10 mm from each of the both ends in the plate width direction in the plate width center direction is 50% or more, the toughness is reduced, and the subsequent pickling step. It cannot withstand the stress applied by the bending treatment by a leveler or the like in the above, and breakage or the like occurs, making it impossible to stably thread the sheet. The recrystallization rate of the structure of the cross section in the plate thickness direction at each position of 10 mm in the plate width center direction from each of both ends in the plate width direction is preferably 45% or less, more preferably 40% or less.
[0031]
On the other hand, if the recrystallization rate of the structure in the cross section in the plate thickness direction at the position of 1/4W from each end in the plate width direction is 50% or more, the crystal orientation {111} strength that deteriorates the magnetic properties of the product plate decreases. do. As a result, core loss is reduced and a high magnetic flux density is obtained. The recrystallization rate of the structure of the cross-section in the sheet thickness direction at positions 1/4W from both ends in the sheet width direction is preferably 55% or more, more preferably 60% or more.
[0032]
The recrystallization rate according to the present invention refers to the area of ​​the portion excluding the processed structure with respect to the area of ​​the cross section in the plate thickness direction of the steel plate. The recrystallization rate can be calculated by observing the cross section of the steel sheet before cold rolling (before pickling) using an optical microscope. Specifically, the cross section in the thickness direction at each position of 10 mm from each of both ends in the width direction of the steel plate before cold rolling to the center of the width is polished using a nital corrosive solution and polished using an optical microscope. Obtain post-cross-sectional photographs. A plurality of straight lines were drawn in the plate thickness direction and the rolling direction at a pitch of 200 μm on the structure photograph, and the ratio of the intersections located in the recrystallized phase to the total number of intersections of the straight lines in the plate thickness direction and the straight lines in the rolling direction was taken as the recrystallization rate. .
[0033]
As described above, according to the steel sheet of the present invention, it is possible to provide a non-oriented electrical steel sheet that achieves both improved hot-rolled sheet toughness, low core loss, and high magnetic flux density. INDUSTRIAL APPLICABILITY The present invention stably produces and provides non-oriented electrical steel sheets with low core loss and high magnetic flux density, which are desirable as iron core materials for electrical equipment, particularly for rotating machines, small and medium-sized transformers, and electrical equipment. can. Therefore, it can sufficiently respond to urgent mass production in the field of electrical equipment in which non-oriented electrical steel sheets are used as iron core materials, and its industrial value is extremely high.
[0034]

Next, a method for manufacturing a steel sheet for non-oriented electrical steel sheets according to the present embodiment (hereinafter, the method for manufacturing a steel sheet for non-oriented electrical steel sheets is also simply referred to as a steel sheet manufacturing method) will be described. The method for manufacturing a steel sheet according to the present embodiment includes a hot rolling process of hot rolling a slab having the above chemical composition, a hot rolled sheet annealing process and a cooling process of annealing the steel sheet after the hot rolling process, or a hot rolling process A heat retention process is provided in place of the plate annealing process. In the steel sheet manufacturing method according to the present embodiment, the cooling step is particularly important because the steel sheet has the metal structure described above. Below, when the method for manufacturing a steel sheet according to the present embodiment includes a hot rolling annealing step and a cooling step (first manufacturing method), and when the method for manufacturing a steel plate according to the present embodiment includes a heat retention step and a cooling step. Each of the cases (second manufacturing method) will be described.
[0035]
When the steel sheet according to the present embodiment is manufactured by the first manufacturing method, the method for manufacturing the non-oriented electrical steel sheet includes a hot rolling step of hot rolling a slab having the chemical composition described above, and a hot rolling step. It has a hot-rolled sheet annealing process for annealing the subsequent steel sheet, a cooling process, a pickling process, a cold rolling process, a finish annealing process, and an insulating coating forming process. Further, when the steel sheet according to the present embodiment is manufactured by the second manufacturing method, the method for manufacturing the non-oriented electrical steel sheet includes a hot rolling step of hot rolling a slab having the chemical composition, a heat retention step, It has a cooling process, a pickling process, a cold rolling process, a final annealing process, and an insulating coating forming process.
[0036]
In addition, in the present embodiment, the steel sheet for non-oriented electrical steel sheet means a steel sheet before the pickling process that has undergone the cooling process after the hot-rolled sheet annealing process or the heat retention process. The steel sheet for non-oriented electrical steel sheet according to the present invention can also be rephrased as "hot-rolled sheet annealed sheet used for non-oriented electrical steel sheet", for example, when obtained by the first manufacturing method described below. In addition, when obtained by the second manufacturing method described below, it can be rephrased as "a hot-rolled sheet used for a non-oriented electrical steel sheet".
[0037]
[First manufacturing method]
(Hot rolling process)
In the hot rolling process, the slab containing the above chemical components is hot rolled into a hot rolled steel sheet. The heating temperature of the slab is 1080°C or higher and 1200°C or lower. If the heating temperature of the slab is 1200° C. or less, solid solution or fine precipitation of sulfides and the like is suppressed, and an increase in iron loss is suppressed. The upper limit of the slab heating temperature is preferably 1180°C. On the other hand, if the heating temperature of the slab is 1080° C. or higher, high hot workability can be obtained. The lower limit of the slab heating temperature is preferably 1100°C.
[0038]
The finishing temperature is 850°C or higher and 1000°C or lower. If the finishing temperature is less than 850° C., the hot workability deteriorates and the plate thickness accuracy in the plate width direction decreases. The lower finishing temperature is preferably 860°C. On the other hand, if the finishing temperature exceeds 1000° C., the recrystallization rate of the steel sheet after hot rolling becomes high, and the toughness decreases. The upper limit of finishing temperature is preferably 990°C.
[0039]
(Hot-rolled sheet annealing process)
In the hot-rolled sheet annealing process, the steel sheet after the hot rolling process is annealed, and the annealed steel sheet is coiled into a coil. The annealing temperature is 900° C. or more and 950° C. or less, and the annealing time is 30 seconds or more and 100 seconds or less. If the annealing temperature is less than 900° C., sufficient recrystallization does not occur, and when an electrical steel sheet is produced using a steel sheet with insufficient recrystallization, crystal grains of {111} orientation develop and the magnetic properties deteriorate. descend. The lower limit of the annealing temperature is preferably 910°C. On the other hand, if the annealing temperature is higher than 950° C., the recrystallization rate increases, and the effect of structure control in the subsequent cooling step cannot be obtained sufficiently. The upper limit of the annealing temperature is preferably 940°C.
[0040]
The annealing atmosphere is not particularly limited as long as it is an atmosphere in which general hot-rolled sheet annealing is performed. The annealing atmosphere may be, for example, an inert atmosphere or an oxidizing atmosphere, and specific examples include a nitrogen atmosphere, an argon atmosphere, a vacuum atmosphere, an air atmosphere, an oxygen atmosphere, and the like.
[0041]
(Cooling process)
In the cooling step, the coil after hot-rolled sheet annealing is cooled at a cooling rate of 0.5°C/min or more and 2.0°C/min or less. Specifically, air of about 15 to 20 ° C. is blown with a blower, for example, toward the side surface of the coil formed by winding the hot-rolled sheet at a high temperature (the side surface of the steel sheet after hot-rolled sheet annealing is laminated). Cool the coil from the side.
[0042]
In the cooling process, the cooling rate at each position of 10 mm in the width center direction from each of both ends in the width direction is the cooling rate at each position of 1/4 W in the width center direction from each of both ends in the width direction. Cool so that it becomes larger than It is preferable that the cooling rate at each position of 10 mm from each of the both ends in the sheet width direction to the sheet width center direction is 0.5° C./min or more and 2.0° C./min or less. At each position 10 mm from each of the widthwise ends of the widthwise direction to the widthwise center direction When the cooling rate is 0.5 ° C./min or more and 2.0 ° C./min or less, the cooling rate at each position of 1/4 W from each of both ends in the width direction to the center direction of the width is More preferably, the cooling rate is less than 0.5°C/min, and even more preferably 0.4°C/min or less. In the cooling process according to the present embodiment, as described above, air is blown by a blower to cool the side surface of the coil formed by winding the hot-rolled sheet at a high temperature. Therefore, the cooling rate at each position of 10 mm in the width center direction from each of both ends in the width direction is larger than the cooling rate at each position of 1/4 W in the width direction from each of both ends in the width direction. Become. If the cooling rate is not controlled by an operation such as blowing with a blower, it is difficult to achieve the cooling rate conditions of the present application.
[0043]
The cooling rate at each position in the width direction of the plate was obtained by measuring the surface temperature at each position in the width direction of the plate. The cooling time in the cooling process is defined as the time during which the blower blows air to the sides of the coil.
[0044]
It is preferable that the cooling rate is fast in order to reduce the recrystallization rate, but if the cooling rate is more than 2.0 ° C./min, the structure of the cross section in the thickness direction at the position of 1/4 W from each end in the width direction The recrystallization rate of the steel sheet is lowered, and the magnetic properties of the non-oriented electrical steel sheet manufactured using this steel sheet are lowered. The upper limit of the cooling rate is preferably 1.8°C/min. On the other hand, when the cooling rate is less than 0.5° C./min, elements such as P and Sn segregate at grain boundaries during cooling, resulting in deterioration of toughness. The lower limit of the cooling rate is preferably 0.6°C/min.
[0045]
The cooling process may be carried out, for example, during the transportation of the coil to the pickling device used in the pickling process before cold rolling the steel sheet in the method for manufacturing a non-oriented electrical steel sheet. In this case, the coil is preferably transported with its axial direction substantially horizontal. Since the coil is conveyed with its axial direction substantially horizontal, the cooling rate is substantially the same at both ends of the coil edge, and substantially the same metal structure is obtained.
[0046]
According to the first manufacturing method, since the coil is cooled from its side surfaces, the cooling rate of the ends of the coil is higher than that of the central portion in the width direction, and the amount of heat applied to the ends of the coil is reduced. As a result, the recrystallization rate of the structure of the cross section in the plate thickness direction at each position of 10 mm from each of the both end portions in the plate width direction in the plate width center direction is less than 50%. On the other hand, the cooling rate of the central portion of the coil is low, and the recrystallization rate of the structure of the cross section in the plate thickness direction is 50% or more at the positions of 1/4W from both ends in the plate width direction. So far, the first manufacturing method has been described.
[0047]
[Second manufacturing method]
Next, the second manufacturing method will be explained. The second manufacturing method includes a hot rolling step of hot rolling a slab having the above chemical composition, and a heat retaining step. The hot rolling process in the second manufacturing method is the same as the hot rolling process in the first manufacturing method, and thus the description is omitted here. The heat retention step will be described in detail below.
[0048]
(Heat retention process)
The heat retention process is a process for retaining the heat of the steel sheet in a high temperature state after the hot rolling process. In the heat retention process, this heat is used to control the metallographic structure. Specifically, in the heat retaining step, a coil formed by winding a hot-rolled steel sheet is covered with a heat retaining cover for retaining the heat of the coil, thereby retaining the heat of the coil. The method of winding the steel sheet after the hot rolling process into a coil is the same as the method of winding the steel sheet in the hot-rolled sheet annealing process of the first manufacturing method, and thus the description thereof is omitted here.
[0049]
The heat retention temperature, which is the temperature of the coil during heat retention, is 600°C or higher and 850°C or lower. If the heat retention temperature exceeds 850° C., the recrystallization rate of the coil side surface increases. The upper limit of the heat retention temperature is preferably 840°C. On the other hand, if the heat retention temperature is less than 600° C., the central portion in the width direction (plate width direction) of the coil is not sufficiently recrystallized, resulting in an increase in iron loss and a decrease in magnetic flux density. The lower limit of the heat retention temperature is preferably 650°C or higher, more preferably 700°C or higher. Note that the heat retention time in the heat retention step is the time from when the cover is put on the coil to when it is removed. The heating time is preferably 1 minute to 2 hours.
[0050]
It should be noted that when the heat retention temperature is high, the heat retention step may be performed without the above-described cover. In this case, the heat retention step means the process from the time the hot-rolled steel sheet is wound into a coil to the time the temperature of the coil starts to drop. The time point at which the coil is formed is the time point at which one turn of the coil is finished from the hot-rolled steel sheet in one zone. The point at which the temperature of the coil begins to fall is the point at which the cooling rate of the coil changes, in other words, the point of inflection on the cooling rate curve. Depending on the heat retention temperature, the temperature change in the coil may be extremely small for a predetermined period of time after winding the coil, and after the predetermined period of time, the temperature of the coil begins to drop rapidly.
[0051]
A group in which the slab used for the manufacture of the steel sheet contains Sn: 0.01% or more and 0.50% or less, Sb: 0.01% or more and 0.50% or less, and Cu: 0.01% or more and 0.50% or less When one or more selected elements are contained, these elements contribute to low iron loss and high magnetic flux density, so that the heat retention temperature can be lowered, so that the toughness of the steel sheet is further improved. can be improved. Therefore, 1 selected from the group consisting of Sn: 0.01% or more and 0.50% or less, Sb: 0.01% or more and 0.50% or less, and Cu: 0.01% or more and 0.50% or less When the seed or two or more are contained, by setting the temperature of the heat retention process to 850° C. or less, it is possible to achieve both appropriate toughness, low core loss, and high magnetic flux density.
[0052]
Of course, the slab is selected from the group consisting of Sn: 0.01% or more and 0.50% or less, Sb: 0.01% or more and 0.50% or less, and Cu: 0.01% or more and 0.50% or less. When the heating temperature or finishing temperature in the hot rolling process is increased, the recrystallization rate increases and the magnetic properties improve, but the toughness may decrease. In that case, for example, it is possible to adjust the recrystallization rate by controlling the winding temperature.
[0053]
The slab is selected from the group consisting of Sn: 0.01% or more and 0.50% or less, Sb: 0.01% or more and 0.50% or less, and Cu: 0.01% or more and 0.50% or less. Although it is not necessarily clear about the mechanism of low iron loss and high magnetic flux density by containing one or more of these elements, the growth of {111} oriented grains that adversely affect the magnetic properties This is thought to be for the purpose of suppressing
[0054]
From the viewpoint of recrystallization, the heat retention time, which is the time during which the coil temperature is maintained at the above temperature, is preferably 1 minute or longer. The lower limit of heat retention time is more preferably 15 minutes. On the other hand, if the heat retention time is longer than 2 hours, the recrystallization rate near the sides of the coil increases, and breakage is likely to occur in the pickling process or cold rolling process in manufacturing the non-oriented electrical steel sheet. Therefore, the heat retention time is preferably 2 hours or less. The heat retention time is more preferably 1.5 hours or less.
[0055]
The heat retention atmosphere is not particularly limited, and may be performed in an atmosphere in which general hot-rolled sheet annealing is performed. The heat retaining atmosphere may be, for example, an inert atmosphere or an oxidizing atmosphere, and specific examples include a nitrogen atmosphere, an argon atmosphere, a vacuum atmosphere, an air atmosphere, an oxygen atmosphere, and the like.
[0056]
Through the heat retention process as described above, elements are segregated at the grain boundaries, and there is an effect of suppressing recrystallization of {111} oriented grains appearing from the grain boundaries after cold rolling and annealing. Therefore, the non-oriented electrical steel sheet manufactured by the second manufacturing method including the heat retention process has better magnetic properties than the non-oriented electrical steel sheet manufactured by the first manufacturing method including the annealing process.
[0057]
(Cooling process)
In the cooling process, the coil that has undergone the heat retention process is cooled at a cooling rate of 0.5°C/min or more and 2.0°C/min or less. Specifically, air of about 15 to 20° C. is blown by, for example, a blower toward the side surface of the coil that has undergone the heat retention process (the surface on which the side surfaces of the steel sheets after the heat retention process are laminated) to cool the coil from the side surface.
[0058]
In the cooling process, the cooling rate at each position of 10 mm in the width center direction from each of both ends in the width direction is the cooling rate at each position of 1/4 W in the width center direction from each of both ends in the width direction. Cool so that it becomes larger than It is preferable that the cooling rate at each position of 10 mm from each of the both ends in the sheet width direction to the sheet width center direction is 0.5° C./min or more and 2.0° C./min or less. If the cooling rate at each position 10 mm from each of the width direction ends to the width center direction is 0.5 ° C / min or more and 2.0 ° C / min or less, It is more preferable that the cooling rate at each position of 1/4 W from each to the width center direction is less than 0.5° C./min, more preferably 0.4° C./min or less. In the cooling process according to the present embodiment, as described above, air is blown by a blower to cool the side surface of the coil formed by winding the hot-rolled sheet at a high temperature. Therefore, the cooling rate at each position of 10 mm in the width center direction from each of both ends in the width direction is larger than the cooling rate at each position of 1/4 W in the width direction from each of both ends in the width direction. Become.
[0059]
The cooling rate at each position in the width direction of the plate was obtained by measuring the surface temperature at each position in the width direction of the plate. The cooling time in the cooling process is defined as the time during which the blower blows air to the sides of the coil.
[0060]
It is preferable that the cooling rate is fast in order to reduce the recrystallization rate, but if the cooling rate is more than 2.0 ° C./min, the structure of the cross section in the thickness direction at the position of 1/4 W from each end in the width direction The recrystallization rate of the steel sheet is lowered, and the magnetic properties of the non-oriented electrical steel sheet manufactured using this steel sheet are lowered. The upper limit of the cooling rate is preferably 1.8°C/min. On the other hand, when the cooling rate is less than 0.5° C./min, elements such as P and Sn segregate at grain boundaries during cooling, resulting in deterioration of toughness. The lower limit of the cooling rate is preferably 0.6°C/min.
[0061]
The cooling process may be carried out, for example, during the transportation of the coil to the pickling device used in the pickling process before cold rolling the steel sheet in the method for manufacturing a non-oriented electrical steel sheet. In this case, the coil is preferably transported with its axial direction substantially horizontal. Since the coil is conveyed with its axial direction substantially horizontal, the cooling rate is substantially the same at both ends of the coil edge, and substantially the same metal structure is obtained.
[0062]
It should be noted that the cooling process is more preferably started immediately after removing the cover described above. Alternatively, the cooling process is more preferably initiated by the time the temperature of the coil begins to drop.
[0063]
According to the second manufacturing method, as in the first manufacturing method, the coil is cooled from its side surfaces. less heat is given to As a result, the recrystallization rate of the structure of the cross section in the plate thickness direction at each position of 10 mm from each of the both end portions in the plate width direction in the plate width center direction is less than 50%. On the other hand, the cooling rate of the central portion of the coil is low, and the recrystallization rate of the structure of the cross section in the plate thickness direction is 50% or more at the positions of 1/4W from both ends in the plate width direction. The second manufacturing method is a manufacturing method that can omit the hot-rolled sheet annealing step, and therefore is a more preferable steel sheet manufacturing method than the first manufacturing method. So far, the second manufacturing method has been described.
[0064]
In both the first manufacturing method and the second manufacturing method, the steel sheet after the hot rolling process is subjected to high temperature finishing treatment in order to control the grain size to an extent that can suppress the increase in iron loss. may be implemented. A high temperature finishing treatment is, for example, a treatment for recrystallization of a hot-rolled sheet.
Example
[0065]
Next, an embodiment of the present invention will be described. The conditions in this example are examples of one condition adopted for confirming the feasibility and effects of the present invention, and the present invention is not limited to these examples. The present invention achieves the objects of the present invention without departing from the gist of the present invention. Various conditions can be adopted as long as the desired results are achieved.
[0066]

A steel having the chemical composition shown in Table 1 was cast and hot-rolled under the conditions shown in Tables 2 and 3 to produce a hot-rolled sheet with a thickness of 2.0 mm and a width of 1000 mm. After that, a heat treatment (atmosphere: nitrogen 100%) (hot-rolled sheet annealing step) for 1 second to 100 seconds at the hot-rolled sheet annealing temperature shown in Table 2 or a heat retention step shown in Table 3 is performed. A steel plate was produced by cooling at the cooling rate shown in . The content of REM is the total amount of one or more selected from the group consisting of Sc, Y and rare earth elements.
[0067]
The cooling process was performed using a blower. The cooling rate is the cooling rate at each position of 10 mm from each of both ends in the width direction to the width center direction, and the cooling rate at each position of 1/4 W from each of both ends in the width direction to the width center direction. and the surface temperature was measured respectively.
[0068]
[table 1]

[0069]
[Table 2]

[0070]
[Table 3]

[0071]
For steel sheets manufactured under each condition, the recrystallization rate of the structure of the cross section in the thickness direction at each position of 10 mm from each of both ends in the width direction to the center of the width, and the position of 500 mm from each end in the width direction The recrystallization rate of the structure of the plate thickness direction cross section was measured. The recrystallization rate was calculated by the following method. First, the cross section in the plate thickness direction at each of the above positions was polished using alumina, etched with a nital corrosive solution, and then a photograph of the cross section after etching was obtained using an optical microscope. Then, a plurality of straight lines are drawn at intervals of 200 μm in the sheet thickness direction and the rolling direction on the microstructure photograph, and the ratio of the intersections located in the recrystallized phase to the total number of intersections of the straight lines in the sheet thickness direction and the straight lines in the rolling direction is calculated as the recrystallization rate. and
[0072]
In addition, the toughness of the manufactured steel plate was evaluated by the following method. A Charpy impact test was performed according to JIS Z 2242:2018 to confirm the ductile fracture surface ratio of the fracture surface. When the ductile brittle transition temperature (DBTT) was 0°C or lower, the evaluation result was good (A), and when it was 0°C or higher, the evaluation result was bad (B).
[0073]
In addition, the manufactured steel plate was pickled by immersing it in hydrochloric acid (7.5% by mass) at 85°C for 30 seconds. Then, it was cold-rolled to a thickness of 0.3 mm at a cold-rolling rate of 75%, and subjected to finish annealing at 1050°C for 30 seconds.
[0074]
A 55 mm square sample was taken from each of the finish-annealed steel sheets, and W 15/50 (iron loss when the steel sheet was magnetized to a magnetic flux density of 1.5 T at 50 Hz) was measured by a Single Sheet Tester (SST) according to JIS C 2556:2015. It was measured.
With respect to iron loss W 15/50, the evaluation result is judged to be good (A) in the case of less than 2.60 W/kg, and the evaluation result is bad (B) in the case of 2.60 W/kg or more. It was determined that there is.
For the magnetic flux density, the magnetic flux density value B50 (T) was measured when a magnetizing force of 5000 A/m was applied. Examples with a B50 of 1.60 T or more were judged to have a good evaluation result (A), and examples with a B50 of less than 1.60 were judged to have a poor evaluation result (B).
Tables 4 and 5 show the recrystallization rate, toughness, and magnetic flux density, and Fig. 2 shows the results of the Charpy test.
[0075]
[Table 4]

[0076]
[Table 5]

[0077]
As shown in Tables 4 and 5, in mass%, C: 0.0040% or less, Si: 1.9% or more and 3.5% or less, Al: 0.10% or more and 3.0% or less, Mn: 0.10% or more and 2.0% or less, P: 0.09% or less, S: 0.005% or less, N: 0.0040% or less, B: 0.0060% or less, the balance being Fe and Consists of impurities, the recrystallization rate of the structure of the cross section in the thickness direction at each position of 10 mm from each of the both ends in the width direction to the center of the width is less than 50%, and when the width is W, the width direction is A steel sheet having a recrystallization rate of 50% or more in the structure of the cross section in the thickness direction at the position of 1/4W from each end has good hot-rolled toughness and magnetic properties after cold rolling and annealing was good. The steel sheets of D31 to D34 had good hot-rolled toughness and good magnetic properties after cold rolling and annealing, but some of them were not subjected to the desired hot rolling. . It is believed that this is because the conditions of the hot rolling process were not favorable.
In addition, as can be seen from FIG. 2, in the examples of the present invention, the ductile fracture surface ratio is high even at 0°C, while in the comparative example, the temperature at which the ductile fracture surface ratio starts to increase is above 0°C. In the inventive example, the hot-rolled sheet toughness was good.
Industrial applicability
[0078]
According to the present invention, it is possible to provide a steel sheet for non-oriented electrical steel sheets that achieves both hot-rolled toughness and magnetic properties after cold rolling and annealing, and is therefore industrially extremely useful.
The scope of the claims
[Claim 1]
in % by mass,
C: 0.0040% or less,
Si: 1.9% or more and 3.5% or less,
Al: 0.10% or more and 3.0% or less,
Mn: 0.10% or more and 2.0% or less,
P: 0.09% or less,
S: 0.005% or less,
N: 0.0040% or less,
B: 0.0060% or less
and the balance consists of Fe and impurities,
The recrystallization rate of the structure of the cross section in the plate thickness direction at each position of 10 mm from each of both ends in the plate width direction to the center of the plate width is less than 50%,
A non-oriented electrical steel sheet characterized in that, where W is the sheet width, the recrystallization rate of the structure of the cross section in the sheet thickness direction at positions 1/4 W from both ends in the sheet width direction is 50% or more. Steel plate for
[Claim 2]
Furthermore, in mass%,
Sn: 0.01% or more and 0.50% or less,
Sb: 0.01% or more and 0.50% or less,
Cu: 0.01% or more and 0.50% or less
The steel sheet for non-oriented electrical steel sheet according to claim 1, characterized in that it contains one or more of
[Claim 3]
Furthermore, in mass%,
　One or two or more selected from REM: 0.00050% or more and 0.040% or less,
Ca: 0.00050% or more and 0.040% or less,
　Mg: 0.00050% or more and 0.040% or less
The steel sheet for non-oriented electrical steel sheet according to claim 1 or 2, characterized in that it contains one or more of