Hot-rolled sheet and manufacturing method therefor

Abstract

A hot-rolled sheet according to one aspect of the present disclosure comprises: recrystallized grains which are crystal grains having a GOS value of less than 3.0º; and non-recrystallized grains which are remainders of the recrystallized grains in a metal structure, wherein the area ratio of the recrystallized grains is at least 4.0%, and the average KAM value of the recrystallized grains is at most 0.6º. Preferably, in the hot-rolled sheet according to one aspect of the present disclosure, the average KAM value of the non-recrystallized grains is at most 0.9º. Preferably, in the hot-rolled sheet according to one aspect of the present disclosure, the weighted average of the grain diameters of the recrystallized grains, with an area as a weight, is at most 100 μm. Preferably, in the hot-rolled sheet according to one aspect of the present disclosure, the area ratio of the recrystallized grains, in a region spanning from the surface to a depth corresponding to 1 / 4 of the thickness of the hot-rolled sheet, is at least 30%.

Description

Hot-rolled sheet and method for producing the same

[0001] The present disclosure relates to a hot-rolled sheet and a method for producing the same. This application claims priority based on Japanese Patent Application No. 2025-011962 filed in Japan on January 28, 2025, and the contents thereof are incorporated herein by reference.

[0002] Non-oriented electrical steel sheets are used, for example, as materials for cores of motors for electric vehicles. Non-oriented electrical steel sheets for electric vehicles are required to have low iron loss and high magnetic flux density.

[0003] Patent Documents 1 to 4 disclose various non-oriented electrical steel sheets and methods for producing the same.

[0004] Japanese Patent No. 5780013 Japanese Unexamined Patent Application Publication No. 2003-183788 Japanese Unexamined Patent Application Publication No. 2002-317254 Japanese Unexamined Patent Application Publication No. 2002-115035

[0005] The iron loss of non-oriented electrical steel sheets varies depending on the excitation frequency. When an electric vehicle runs at high speed, the efficiency of the motor depends on the iron loss at high frequencies of the non-oriented electrical steel sheet.

[0006] Examples of means for reducing the iron loss at high frequencies of non-oriented electrical steel sheets are reduction in thickness and increase in specific resistance by high alloying. However, high alloying of non-oriented electrical steel sheets embrittles the non-oriented electrical steel sheets and reduces their productivity. Non-oriented electrical steel sheets are obtained by annealing a hot-rolled steel sheet, i.e., a hot-rolled sheet, cold-rolling it, and then performing finish annealing. However, hot-rolled sheets for non-oriented electrical steel sheets contain a large amount of Si, Al, and Mn and have coarse grain sizes. Therefore, the toughness of hot-rolled sheets for non-oriented electrical steel sheets is low. Such hot-rolled sheets are extremely likely to break during pickling or cold rolling.

[0007] The cyclic bending test method for non-oriented electrical steel strips described in Annex JA of JIS C 2552:2014 "Non-oriented electrical steel strips" can be used as a method for evaluating the toughness of hot-rolled sheets for non-oriented electrical steel sheets. In this case, the test temperature shall be 60°C. In the cyclic bending test, the toughness of the test piece is evaluated by the number of bending cycles until the test piece breaks. In order to suppress breakage when unwinding the coil and during cold rolling, it is preferable to impart to the hot-rolled sheets for non-oriented electrical steel sheets a toughness such that the number of bending cycles in the cyclic bending test is four or more.

[0008] Patent documents 1 to 4 do not disclose means for improving the toughness of hot-rolled sheets for non-oriented electrical steel sheets.

[0009] In view of the above circumstances, the present disclosure aims to provide a hot-rolled sheet that can be used as a material for non-oriented electrical steel sheets and has high toughness, as well as a method for manufacturing the same.

[0010] The gist of this disclosure is as follows:

[0011] (1) A hot-rolled sheet according to one aspect of the present disclosure comprises recrystallized grains having a GOS value of less than 3.0° and unrecrystallized grains which are the remainder of the recrystallized grains in the metal structure, wherein the area ratio of the recrystallized grains is 4.0% or more, and the average KAM value, which is the arithmetic mean of the KAM values ​​of the recrystallized grains, is 0.6° or less. (2) Preferably, in the hot-rolled sheet described in (1) above, the average KAM value of the unrecrystallized grains is 0.9° or less. (3) Preferably, in the hot-rolled sheet described in (1) or (2) above, the weighted average of the grain size of the recrystallized grains, weighted by area, is 100 μm or less. (4) Preferably, in the hot-rolled sheet described in any one of (1) to (3) above, the area ratio of the recrystallized grains in the region from the surface to a depth of 1 / 4 of the thickness of the hot-rolled sheet is 30% or more. (5) Preferably, in the hot-rolled sheet described in any one of the above items (1) to (4), the chemical composition is as follows, in mass%, C: 0.0030% or less, Si: 2.00% to 7.00%, Sol. Al: 0.15% to 2.50%, Mn: 0.1% to 4.0%, Cr: 0.01% to 5.00%, P: 0.005% to 0.200%, S: 0.0004% to 0.0100%, N: 0% to 0.010%, Ti: 0.0005% to 0.0100%, Ca: 0.0005% to 0.0100%, and one or more of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: total 0.0005% to 0.0 It contains 200%, Sn: 0% to 0.10%, Sb: 0% to 0.10%, Ni: 0% to 5.0%, Cu: 0% to 5.0%, B: 0% to 0.10%, O: 0% to 0.10%, V: 0% to 0.10%, Zr: 0% to 0.10%, Bi: 0% to 0.10%, W: 0% to 0.10%, Mo: 0% to 0.10%, Nb: 0% to 0.10%, and Y: 0% to 0.10%, with the remainder being Fe and impurities. (6) Preferably, in the hot-rolled sheet described in (5) above, the chemical composition is such that, by mass%, Mn: 0.2% to 4.0%, and S: 0.0010% to 0.0100%.

[0012] (7) A method for manufacturing a hot-rolled sheet according to another aspect of the present disclosure comprises the steps of: rolling a material sheet with a thickness of 0.95 to 3.8 mm for the manufacture of a non-oriented electrical steel sheet in a temperature range of 850°C to 1150°C to a thickness of 0.75 mm to 2.1 mm; and water-cooling the rolled material sheet and then winding it in a temperature range of 550°C to 1000°C, wherein the time from the end of rolling to the start of winding is more than 6 seconds and within 15 seconds. (8) Preferably, in the method for manufacturing a hot-rolled sheet described in (7) above, the method for manufacturing a hot-rolled sheet further comprises the step of manufacturing the material sheet, wherein in the step of manufacturing the material sheet, the material hot-rolled sheet is annealed at an annealing temperature of 1050°C to 1200°C and for an annealing time of 3 minutes to 10 minutes. (9) Preferably, in the method for manufacturing a hot-rolled sheet described in (7) or (8) above, the method for manufacturing a hot-rolled sheet further comprises a step of manufacturing the base sheet, wherein in the step of manufacturing the base sheet, a base hot-rolled sheet is manufactured by a continuous casting / direct rolling method at a finishing temperature of 1050°C to 1150°C, the base hot-rolled sheet is then wound up, and the base hot-rolled sheet is then covered with a heat-insulating cover and held for one day or more. (10) Preferably, in the method for manufacturing a hot-rolled sheet described in any one of (7) to (9) above, the method for manufacturing a hot-rolled sheet further comprises a step of manufacturing the base sheet, wherein in the step of obtaining the base sheet, a cast slab with a thickness of 0.95 to 3.8 mm is manufactured by a rapid solidification method using twin rolls, and when rapidly solidifying the molten steel by the rapid solidification method, the surface temperature of the molten steel accumulated between the twin rolls is maintained at more than the solidus temperature of the molten steel + 2°C.(11) Preferably, in the method for manufacturing a hot-rolled sheet described in any one of (7) to (10) above, the material sheet has a chemical composition of, in mass%, C: 0.0030% or less, Si: 2.00% to 7.00%, Sol. Al: 0.15% to 2.50%, Mn: 0.1% to 4.0%, Cr: 0.01% to 5.00%, P: 0.005% to 0.200%, S: 0.0004% to 0.0100%, N: 0% to 0.010%, Ti: 0.0005% to 0.0100%, Ca: 0.0005% to 0.0100%, and one or more of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: total 0.0005% to 0.0 The composition contains 200%, Sn: 0% to 0.10%, Sb: 0% to 0.10%, Ni: 0% to 5.0%, Cu: 0% to 5.0%, B: 0% to 0.10%, O: 0% to 0.10%, V: 0% to 0.10%, Zr: 0% to 0.10%, Bi: 0% to 0.10%, W: 0% to 0.10%, Mo: 0% to 0.10%, Nb: 0% to 0.10%, and Y: 0% to 0.10%, with the remainder being Fe and impurities. (12) Preferably, in the method for producing a hot-rolled sheet described in (11) above, the chemical composition of the material sheet is, by mass%, Mn: 0.2% to 4.0%, and S: 0.0010% to 0.0100%.

[0013] According to this disclosure, it is possible to provide a hot-rolled sheet that can be used as a material for non-oriented electrical steel sheets and has high toughness, as well as a method for manufacturing the same.

[0014] This is a schematic diagram of an L-shaped cross-section of a hot-rolled sheet (a cross-section parallel to the rolling direction RD of the hot-rolled sheet and parallel to the thickness direction TD of the hot-rolled sheet). This is a flowchart of an example of a hot-rolled sheet manufacturing method.

[0015] A hot-rolled sheet according to one aspect of this disclosure is a hot-rolled sheet for non-oriented electrical steel sheets, comprising recrystallized grains and non-recrystallized grains, wherein the area ratio of recrystallized grains is 4.0% or more, and the average KAM value, which is the arithmetic mean of the KAM values ​​of the recrystallized grains, is 0.6° or less. Recrystallized grains and non-recrystallized grains are defined as follows: (A) Recrystallized grains are defined as crystal grains with a GOS value of less than 3.0°. (B) Non-recrystallized grains are defined as the remainder of the recrystallized grains in the metal structure. That is, grains with a GOS value greater than 3.0° are non-recrystallized grains. When determining whether a crystal grain is a recrystallized grain or a non-recrystallized grain, only the above-mentioned GOS value is considered.

[0016] The details of the hot-rolled sheet for non-oriented electrical steel according to this embodiment are described below. In this disclosure, "hot-rolled sheet for non-oriented electrical steel" may be simply referred to as "hot-rolled sheet".

[0017] The hot-rolled sheet according to this embodiment is suitable for the manufacture of non-oriented electrical steel sheets. For example, a non-oriented electrical steel sheet can be obtained by pickling, cold-rolling, and finish-rolling the hot-rolled sheet according to this embodiment. The chemical composition of the hot-rolled sheet is not particularly limited, as long as it is suitable for the manufacture of non-oriented electrical steel sheets.

[0018] A preferred example of the chemical composition of a hot-rolled sheet is shown below. However, the chemical composition listed below is not limited to the hot-rolled sheet according to this embodiment. It should be noted that known preferred embodiments of hot-rolled sheets for non-oriented electrical steel sheets are applicable to the hot-rolled sheet according to this embodiment. In the following description, the unit "%" for element content means "mass%" unless otherwise specified.

[0019] (C: Preferably 0.0030% or less) C (carbon) is an optional element that may or may not be included in the hot-rolled sheet. Therefore, the lower limit of the C content may be 0%. On the other hand, when the hot-rolled sheet contains a trace amount of C, C has the effect of slowing down grain growth during the recrystallization process. This is because the solid solution carbon segregates at the grain boundaries, exhibiting a solute dragging effect that suppresses grain boundary movement, and also exhibiting a Zener pinning effect due to the fine carbides formed by bonding with other elements such as Mn and Cr. As a result, the coarsening of recrystallized grains is suppressed, and a uniform and fine structure is obtained. Therefore, C can be positioned as a selective additive element that can act beneficially within a controllable range. Furthermore, from the viewpoint of reducing refining costs, the C content may be greater than 0%, 0.0005% or more, or 0.0010% or more.

[0020] On the other hand, by keeping the carbon content below a predetermined value, the magnetic properties of the non-oriented electrical steel sheet obtained from the hot-rolled sheet can be further enhanced. Therefore, it is preferable that the carbon content be 0.0030% or less. The lower the carbon content, the better. For example, it is even more preferable that the carbon content be 0.0025% or less, 0.0020% or less, or 0.0015% or less.

[0021] (Si: Preferably 2.00% to 7.00%) Si (silicon) increases the resistivity of non-oriented electrical steel sheets obtained from hot-rolled sheets. This reduces eddy current losses in non-oriented electrical steel sheets and improves high-frequency iron losses. Furthermore, Si improves the strength of hot-rolled sheets through solid solution strengthening. Therefore, a Si content of 2.00% or more is preferable. More preferably, the Si content is 2.50% or more, 3.00% or more, or 3.20% or more.

[0022] On the other hand, by keeping the Si content below a predetermined value, the processability of the hot-rolled sheet is further improved. Therefore, it is preferable that the Si content be 7.00% or less. More preferably, the Si content is 6.00% or less, 5.00% or less, 4.50% or less, or 4.00% or less.

[0023] (Sol. Al: preferably 0.15% to 2.50%) Sol. Al is acid-soluble aluminum. Sol. Al increases the strength of non-oriented electrical steel sheets obtained from hot-rolled sheets through solid solution strengthening. Furthermore, Sol. Al increases the resistivity of non-oriented electrical steel sheets obtained from hot-rolled sheets. As a result, eddy current losses in non-oriented electrical steel sheets obtained from hot-rolled sheets are reduced and high-frequency iron losses are improved. Therefore, the Sol. Al content is preferably 0.15% or more. More preferably, the Sol. Al content is 0.30% or more, 0.50% or more, or 1.00% or more.

[0024] On the other hand, by keeping the Sol. Al content below a predetermined value, the saturation magnetic flux density of the non-oriented electrical steel sheet obtained from the hot-rolled sheet is further improved. Therefore, it is preferable that the Sol. Al content be 2.50% or less. More preferably, the Sol. Al content is 2.40% or less, 2.00% or less, or 1.50% or less.

[0025] (Mn: Preferably 0.1% to 4.0%) Manganese (Mn) improves the strength of non-oriented electrical steel sheets obtained from hot-rolled sheets through solid solution strengthening. Furthermore, Mn increases the resistivity of non-oriented electrical steel sheets obtained from hot-rolled sheets. This reduces eddy current loss and improves high-frequency iron loss in non-oriented electrical steel sheets obtained from hot-rolled sheets. Therefore, the Mn content is preferably 0.1% or more. More preferably, the Mn content is 0.15% or more, 0.2% or more, 0.5% or more, 1.0% or more, or 1.5% or more.

[0026] On the other hand, by keeping the Mn content below a predetermined value, the development of crystal grains having the {100} orientation in the non-oriented electrical steel sheet obtained from the hot-rolled sheet is promoted. This increases the degree of accumulation of {100} orientation grains. Therefore, it is preferable that the Mn content be 4.0% or less. More preferably, the Mn content is 3.5% or less, 3.0% or less, or 2.5% or less.

[0027] (Cr: Preferably 0.01% to 5.00%) Cr (chromium) increases the resistivity of non-oriented electrical steel sheets obtained from hot-rolled sheets. This reduces eddy current losses and improves high-frequency iron losses in non-oriented electrical steel sheets obtained from hot-rolled sheets. Furthermore, Cr suppresses the generation of Kirkendal voids inside non-oriented electrical steel sheets obtained from hot-rolled sheets. Therefore, a Cr content of 0.01% or more is preferable. More preferably, a Cr content of 0.10% or more, or 0.50% or more.

[0028] On the other hand, by keeping the Cr content below a predetermined value, the saturation magnetic flux density of the non-oriented electrical steel sheet obtained from the hot-rolled sheet is improved. Therefore, it is preferable that the Cr content be 5.00% or less. More preferably, the Cr content is 4.00% or less, 3.00% or less, or 2.00% or less.

[0029] (P: Preferably 0.005% to 0.200%) Phosphorus (P) increases the strength of non-oriented electrical steel sheets obtained from hot-rolled sheets. Furthermore, during annealing of the hot-rolled sheets, P suppresses recrystallization starting from grain boundaries. As a result, P suppresses the growth of {111} oriented grains and the like that impair magnetic properties. Therefore, the P content is preferably 0.005% or more. More preferably, the P content is 0.010% or more, 0.020% or more, or 0.050% or more.

[0030] On the other hand, by keeping the P content below a predetermined value, the embrittlement of the hot-rolled sheet is further suppressed. Therefore, it is preferable that the P content be 0.200% or less. More preferably, the P content is 0.150% or less, 0.120% or less, or 0.100% or less.

[0031] (S: Preferably 0.0004% to 0.0100%) S (sulfur) forms fine sulfides such as MnS. By keeping the S content below a predetermined value, the formation of fine sulfides can be suppressed, reducing iron loss in the non-oriented electrical steel sheet obtained from the hot-rolled sheet and improving its magnetic properties. Furthermore, by suppressing the formation of fine sulfides by keeping the S content below a predetermined value, recrystallization and grain growth are promoted during annealing of the hot-rolled sheet. Therefore, the S content is preferably 0.0100% or less. More preferably, the S content is 0.0080% or less, 0.0060% or less, or 0.0050% or less.

[0032] On the other hand, increasing the sulfur content above a predetermined value reduces the manufacturing cost of the hot-rolled sheet. Therefore, it is preferable that the sulfur content be 0.0004% or higher. More preferably, the sulfur content is 0.0010% or higher, 0.0020% or higher, 0.0030% or higher, or 0.0040% or higher.

[0033] (N: Preferably 0% to 0.010%) N (nitrogen) is an optional element. N combines with Al to form fine AlN, which inhibits the growth of crystal grains during annealing. Therefore, by keeping the N content below a predetermined value, the magnetic properties of the non-oriented electrical steel sheet obtained from the hot-rolled sheet are improved. For this reason, it is preferable to have an N content of 0.010% or less. It is even more preferable that the N content be 0.0050% or less, and even more preferable that it be 0.0030% or less.

[0034] Since a low N content is preferable, there is no need to limit the lower limit, and the lower limit may be 0%. However, since it is not easy to achieve a 0% content industrially, the lower limit may be greater than 0%, greater than 0.00010%, greater than 0.00150%, or greater than 0.00250%.

[0035] (Ti: Preferably 0.0005% to 0.0100%) Ti forms finely precipitated carbonitrides, which have the effect of increasing the strength of the steel through precipitation strengthening and grain refinement strengthening. On the other hand, the finely precipitated carbonitrides inhibit the growth of crystal grains during annealing. By setting the Ti content to below a predetermined value, the amount of Ti carbonitrides is reduced, and the magnetic properties of the non-oriented electrical steel sheet obtained from the hot-rolled sheet are improved. For this reason, it is preferable to set the Ti content to 0.0100% or less. It is even more preferable that the Ti content be 0.0050% or less, and even more preferable that be 0.0030% or less.

[0036] Since a low Ti content is preferable, there is no need to limit the lower limit, and the lower limit may be 0%. However, since it is not easy to achieve a Ti content of 0% industrially, the Ti content may be greater than 0%, greater than 0.00010%, greater than 0.00150%, or greater than 0.00250%.

[0037] (Ca: Preferably 0.0005% to 0.0100%) Ca (calcium) forms sulfides and / or oxysulfides. Ca fixes sulfur and suppresses the precipitation of fine sulfides such as MnS. This facilitates the movement of magnetic domain walls in non-oriented electrical steel sheets obtained from hot-rolled sheets, and reduces iron loss. Therefore, a Ca content of 0.0005% or more is preferable. More preferably, the Ca content is 0.0010% or more, 0.0015% or more, or 0.0020% or more.

[0038] On the other hand, by keeping the Ca content below a predetermined value, the iron loss characteristics of the non-oriented electrical steel sheet obtained from the hot-rolled sheet are improved. Therefore, it is preferable that the Ca content be 0.0100% or less. More preferably, the Ca content is 0.0090% or less, 0.0080% or less, or 0.0060% or less.

[0039] (One or more of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd: total 0.0005% to 0.0200%) In this disclosure, Mg, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd are referred to as the "specified element group". The specified element group forms sulfides and / or oxysulfides. The specified element group fixes S and suppresses the precipitation of fine sulfides such as MnS. This facilitates the movement of magnetic domain walls in the non-oriented electrical steel sheet obtained from the hot-rolled sheet, and reduces iron loss. Therefore, the hot-rolled sheet according to this disclosure contains one or more elements selected from the specified element group. Preferably, the total content of the specified element group is 0.0005% or more. More preferably, the total content of the specified element group is 0.0010% or more, 0.0015% or more, or 0.0020% or more.

[0040] On the other hand, by keeping the content of specific elements below a predetermined value, the iron loss of non-oriented electrical steel sheets obtained from hot-rolled sheets is improved. Therefore, it is preferable that the total content of specific elements be 0.0200% or less. More preferably, the total content of specific elements is 0.0180% or less, 0.0160% or less, or 0.0120% or less.

[0041] (Sn: 0% to 0.10%) (Sb: 0% to 0.10%) Sn (tin) and Sb (antimony) are optional elements that do not need to be included in the hot-rolled sheet. There is no need to limit the lower limit of Sn and Sb, and the lower limit may be 0%. However, Sn and Sb have the effect of improving the texture of the non-oriented electrical steel sheet obtained from the hot-rolled sheet, thereby improving magnetic properties such as magnetic flux density. To obtain this effect more reliably, the Sn content is preferably greater than 0%, preferably 0.0010% or more, and more preferably 0.010% or more. Similarly, the Sb content is preferably greater than 0%, preferably 0.0010% or more, preferably 0.0020% or more, more preferably 0.010% or more, and more preferably greater than 0.0250%.

[0042] Also, when the contents of Sn and Sb are set to be not more than a predetermined value, embrittlement of the steel and cold rolling fracture are further suppressed. Further, when the contents of Sn and Sb are set to be not more than a predetermined value, the magnetic properties of the non-oriented electromagnetic steel sheet obtained from the hot rolled sheet are improved. Therefore, the contents of Sn and Sb are each set to be 0.10% or less. Further, in order to refine the average crystal grain size of the surface region, it is preferable that the content of each of Sn and Sb is less than 0.030%.

[0043] (Ni: 0% to 5.0%) Ni (nickel) is a selective element. Ni has an effect of improving magnetic properties such as saturation magnetic flux density, for example. On the other hand, when the Ni content is set to be not more than a predetermined value, the workability of the hot rolled sheet is further improved. Further, when the Ni content is set to be not more than a predetermined value, the manufacturing cost of the hot rolled sheet is suppressed. Therefore, the Ni content is set to be 5.0% or less. The Ni content is preferably 0.50% or less, and more preferably 0.10% or less.

[0044] There is no need to limit the lower limit value of Ni, and the lower limit value may be 0%. However, in order to more surely obtain the above effects, the Ni content is preferably more than 0%, and preferably 0.0010% or more.

[0045] (Cu: 0% to 5.0%) Cu (copper) is a selective element. Cu has an effect of improving the strength of the steel sheet. On the other hand, when the Cu content is set to be not more than a predetermined value, the workability of the hot rolled sheet is further improved. Further, when the Cu content is set to be not more than a predetermined value, the saturation magnetic flux density of the non-oriented electromagnetic steel sheet obtained from the hot rolled sheet is improved. Also, when the Cu content is set to be not more than a predetermined value, the manufacturing cost of the hot rolled sheet is suppressed. Therefore, the Cu content is set to be 5.0% or less. The Cu content is preferably 0.10% or less.

[0046] There is no need to limit the lower limit value of Cu, and the lower limit value may be 0%. However, in order to more surely obtain the above effects, the Cu content is preferably more than 0%, and preferably 0.0010% or more.

[0047] Furthermore, the chemical composition of the hot-rolled sheet according to this embodiment is preferably as follows: B: 0% to 0.10%, O: 0% to 0.10%, V: 0% to 0.10%, Zr: 0% to 0.10%, Bi: 0% to 0.10%, W: 0% to 0.10%, Mo: 0% to 0.10%, Nb: 0% to 0.10%, Y: 0% to 0.10%. The B content is preferably 0.010% or less. The O content is preferably 0.010% or less. The V content is preferably 0.0020% or less. The Zr content is preferably 0.0020% or less. The Bi content is preferably 0.010% or less. The W content is preferably 0.010% or less. The Mo content is preferably 0.01% or less. The Nb content is preferably 0.0020% or less. The Y content is preferably 0.010% or less. The V content is preferably 0.0020% or more. The Nb content is preferably 0.0020% or more. The B content may be 0.0040% or more. The O content may be 0.0050% or more. The Zr content may be 0.0500% or more. The Bi content may be 0.0500% or more. The W content may be 0.0500% or more. The Mo content may be 0.0500% or more. The Y content may be 0.0500% or more.

[0048] (Remainder: Fe and impurities) The remainder of the chemical composition of the hot-rolled sheet contains iron and impurities. The impurities are components that are mixed in, for example, due to raw materials such as ore or scrap, or various factors in the manufacturing process when industrially manufacturing steel materials, and are those that are allowed within a range that does not adversely affect the hot-rolled sheet according to this embodiment. As impurities, for example, As, Se, Te, Pb, Co, Cd, Pt, Au, In, Ga, Ge, O, Sc, Hf, and rare earth elements (REM) may each be contained at 0.10% or less within a range that does not eliminate the effects of the non-oriented electrical steel sheet. Note that the term "REM" may be understood by those skilled in the art to be a total of 17 elements consisting of Sc, Y, and lanthanoids. However, in this disclosure, the term "REM" means a total of 14 elements consisting of Sc and lanthanoids (excluding La and Ce). In this disclosure, the "content of REM" means the total content of these 15 elements. When using lanthanoids as REM, industrially, REM is added in the form of mischmetal. The contents of Y, La, and Ce are defined as described above.

[0049] (Recrystallized grains and non-recrystallized grains) The hot-rolled sheet has crystal grains. The crystal grains are either recrystallized grains or non-recrystallized grains. The recrystallized grains and non-recrystallized grains are defined as follows. (A) Recrystallized grains are defined as crystal grains with a GOS value of less than 3.0°. (B) Non-recrystallized grains are defined as the remainder of the recrystallized grains in the metal structure. That is, grains with a GOS value exceeding 3.0° are non-recrystallized grains. Note that when determining whether a crystal grain corresponds to recrystallized grains or non-recrystallized grains, only the above-mentioned GOS value is considered. The hot-rolled sheet for non-oriented electrical steel sheets according to this embodiment has recrystallized grains and non-recrystallized grains.

[0050] (Area ratio of recrystallized grains: 4.0% or more) In the hot-rolled sheet according to this embodiment, the area ratio of recrystallized grains, that is, the recrystallization rate, is 4.0% or more. The measurement method of the area ratio of recrystallized grains will be described later.

[0051] The area percentage of recrystallized grains may be 5.0% or more, 8.0% or more, or 10.0% or more. The upper limit of the area percentage of recrystallized grains can be any value less than 100%. For example, the area percentage of recrystallized grains may be 40% or less, 35% or less, or 30%.

[0052] In conventional non-oriented hot-rolled sheets for electrical steel that are not subjected to hot-rolled sheet annealing, the area ratio of the recrystallized structure is substantially 0%. On the other hand, in conventional non-oriented hot-rolled sheets for electrical steel that are subjected to hot-rolled sheet annealing, the area ratio of the recrystallized structure is substantially 100%. In the non-oriented hot-rolled sheets for electrical steel according to this embodiment, unlike the prior art, the above-mentioned recrystallization rate is achieved by partially inducing recrystallization by means other than hot-rolled sheet annealing.

[0053] (Average KAM value of recrystallized grains: 0.6° or less) The average KAM value of recrystallized grains contained in hot-rolled sheets is set to 0.6° or less. The KAM value is an index value of the magnitude of local strain in a crystal grain. The closer the KAM value is to 0°, the smaller the local strain. The average KAM value of recrystallized grains is the arithmetic mean of the KAM values ​​of recrystallized grains contained in a predetermined observation field. The method for measuring the average KAM value of recrystallized grains will be described later.

[0054] The average KAM value of the recrystallized grains is preferably 0.5° or less, 0.4° or less, or 0.3.0° or less. The lower limit of the average KAM value of the recrystallized grains is not particularly limited. For example, the average KAM value of the recrystallized grains may be greater than 0°, 0.1° or more, or 0.2° or more.

[0055] (Effects) The inventors focused on the correlation between the state of recrystallized grains in a hot-rolled sheet and the results of repeated bending tests of the hot-rolled sheet. They found that the larger the area ratio of recrystallized grains, the better the results of repeated bending tests. This is presumed to be because the particle size of the recrystallized grains is finer than that of the unrecrystallized grains. The finer the crystal grains, the greater the toughness of the hot-rolled sheet tends to be.

[0056] Furthermore, the inventors discovered that the average KAM value of the recrystallized grains also affects the results of repeated bending tests on the hot-rolled sheet. By reducing the average KAM value of the recrystallized grains to 0.6° or less, the toughness of the hot-rolled sheet was further improved, resulting in even better results in repeated bending tests.

[0057] Generally, to improve the magnetic properties of non-oriented electrical steel sheets, the alloying component of the hot-rolled sheet material is sometimes increased. However, increasing the alloying component worsens the mechanical properties of the hot-rolled sheet. Nevertheless, in hot-rolled sheets that have undergone the aforementioned measures, the toughness is improved, making the increase in alloying component permissible.

[0058] The most basic embodiment of the hot-rolled sheet for non-oriented electrical steel according to this embodiment has been described above. A more preferred embodiment will be described below.

[0059] (Average KAM value of unrecrystallized grains: preferably 0.9° or less) Preferably, the average KAM value of unrecrystallized grains is 0.9° or less. The average KAM value of unrecrystallized grains is the arithmetic mean of the KAM values ​​of unrecrystallized grains included in a predetermined observation field. The method for measuring the average KAM value of unrecrystallized grains will be described later.

[0060] Similar to recrystallized grains, the average KAM value of unrecrystallized grains also affects the toughness of the hot-rolled sheet. The smaller the average KAM value of unrecrystallized grains, the higher the toughness of the hot-rolled sheet. By reducing the average KAM value of unrecrystallized grains to 0.9° or less, the toughness of the hot-rolled sheet can be further improved.

[0061] The average KAM value of the unrecrystallized grains is more preferably 0.8° or less, 0.7° or less, or 0.6° or less. The lower limit of the average KAM value of the unrecrystallized grains is not particularly limited. For example, the average KAM value of the unrecrystallized grains may be greater than 0°, 0.1° or more, or 0.2° or more.

[0062] (Weighted average of recrystallized grain size, weighted by area: preferably 100 μm or less) The average grain size of the recrystallized grains is preferably 100 μm. The average grain size of the recrystallized grains is the weighted average of the area of ​​the equivalent circular diameter of the recrystallized grains included in the measurement field. The average value of the equivalent circular diameter of the recrystallized grains is a weighted average calculated from the average value obtained by multiplying each area value by the ratio of the area of ​​each crystal grain to the total area. The method for measuring the average grain size of the recrystallized grains will be described later.

[0063] The finer the recrystallized grains, the higher the toughness of the hot-rolled sheet. By reducing the average particle size of the recrystallized grains to 100 μm or less, the toughness of the hot-rolled sheet can be further improved.

[0064] The average particle size of the recrystallized grains is more preferably 90 μm or less, 80 μm or less, or 70 μm or less. The lower limit of the average particle size of the recrystallized grains is not particularly limited. For example, the average particle size of the recrystallized grains may be 40 μm or more, 50 μm or more, or 60 μm or more.

[0065] (Area ratio of recrystallized grains in the surface region: 30% or more) In this disclosure, as illustrated in Figure 1, the region from the surface 11 of the hot-rolled sheet 1 to a depth of 1 / 4 of the thickness t of the hot-rolled sheet 1 is defined as the surface region 12. Preferably, in the hot-rolled sheet 1 for non-oriented electrical steel sheets according to this embodiment, the area ratio of recrystallized grains in the surface region 12 is 30% or more. In Figure 1, RD is the rolling direction of the hot-rolled sheet 1, and TD is the thickness direction of the hot-rolled sheet 1. Furthermore, "area ratio of recrystallized grains in the surface region 12" means the area ratio measured in the surface region 12. The method for measuring the area ratio of recrystallized grains in the surface region 12 will be described later.

[0066] It is even more preferable that the recrystallized grains are arranged near the surface 11 of the hot-rolled sheet 1. Fracture of the hot-rolled sheet 1 often originates from the surface 11 and its vicinity. By arranging many recrystallized grains in the surface region 12, which is a region that is likely to be the starting point of fracture, the toughness of the hot-rolled sheet 1 can be further enhanced.

[0067] The area ratio of recrystallized grains in the surface region 12 is more preferably 35% or more, 40% or more, or 50% or more. The upper limit of the area ratio of recrystallized grains in the surface region 12 is not particularly limited. For example, the area ratio of recrystallized grains in the surface region 12 may be 100% or less, 90% or less, 80% or less, or 70% or less.

[0068] (2. Method for Manufacturing Non-Oriented Electrical Steel Sheets) Next, a method for manufacturing hot-rolled non-oriented electrical steel sheets according to another aspect of the present disclosure will be described. However, the manufacturing method described below is not limited to the hot-rolled non-oriented electrical steel sheets according to this embodiment. Any hot-rolled non-oriented electrical steel sheet that satisfies the above requirements shall be considered a hot-rolled non-oriented electrical steel sheet according to this embodiment, regardless of its manufacturing method.

[0069] The method for manufacturing a hot-rolled sheet for non-oriented electrical steel according to this embodiment, as illustrated in the flowchart of Figure 2, comprises the steps of rolling a material sheet with a thickness of 0.95 to 3.8 mm for the manufacture of non-oriented electrical steel in a temperature range of 850°C to 1150°C to a thickness of 0.75 mm to 2.1 mm, and winding the rolled material sheet in a temperature range of 550°C to 1000°C.

[0070] (Hot-rolled annealed sheet) In the method for manufacturing non-oriented electrical steel sheets according to this embodiment, a hot-rolled annealed sheet for manufacturing non-oriented electrical steel sheets is used as the starting material. Hereinafter, the "hot-rolled annealed sheet for manufacturing non-oriented electrical steel sheets" will simply be referred to as the "raw material sheet".

[0071] The chemical composition of the base plate is not particularly limited. The chemical composition of the base plate can be, for example, within the range of the chemical composition of the hot-rolled sheet according to this embodiment described above. That is, the hot-rolled annealed sheet (base plate) has a chemical composition of C: 0.0030% or less, Si: 2.00% to 7.00%, Sol. Al: 0.15%–2.50%, Mn: 0.2%–4.0%, Cr: 0.01%–5.00%, P: 0.005%–0.200%, S: 0.0010%–0.0100%, N: 0%–0.010%, Ti: 0.0005%–0.0100%, Ca: 0.0005%–0.0100%, Mg, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd: Total 0.0005%–0.0200% The composition may include %, Sn: 0% to 0.10%, Sb: 0% to 0.10%, Ni: 0% to 5.0%, Cu: 0% to 5.0%, B: 0% to 0.10%, O: 0% to 0.10%, V: 0% to 0.10%, Zr: 0% to 0.10%, Bi: 0% to 0.10%, W: 0% to 0.10%, Mo: 0% to 0.10%, Nb: 0% to 0.10%, and Y: 0% to 0.10%, with the remainder being Fe and impurities. Naturally, the above-mentioned preferred chemical composition of the hot-rolled sheet can also be applied to the base sheet.

[0072] The thickness of the material plate shall be 0.95 to 3.8 mm. Preferably, the thickness of the material plate is 1.0 mm or more, 1.2 mm or more, or 1.5 mm or more. Preferably, the thickness of the material plate is 3.0 mm or less, 2.5 mm or less, or 2.0 mm or less. The thickness of the material plate can be measured using a micrometer.

[0073] The metal structure and manufacturing method of the base sheet are not limited. For example, a base sheet can be obtained by hot-rolling and annealing a slab having a predetermined chemical composition under known conditions suitable for the manufacture of hot-rolled sheets for non-oriented electrical steel sheets. Alternatively, a cast slab obtained by the twin-roll method can also be used as the base sheet.

[0074] Particularly preferred examples of means for obtaining a base sheet are shown below. (A) A hot-rolled sheet (base hot-rolled sheet) manufactured under known hot-rolling conditions is annealed at an annealing temperature of 1050°C to 1200°C and an annealing time of 3 to 10 minutes. A preferred example of the annealing temperature is 1100°C, and a preferred example of the annealing time is 5 minutes. The resulting hot-rolled and annealed sheet is used as the base sheet. (B) A hot-rolled sheet (base hot-rolled sheet) is manufactured at a finishing temperature of 1050°C or higher by the continuous casting and direct rolling method (CC-DR method). The hot-rolled sheet is rolled up, covered with a heat-retaining cover, and held for one day or more. The resulting hot-rolled sheet is used as the base sheet. The upper limit of the finishing temperature is not particularly limited, but it can be 1150°C or lower. (C) A cast slab with a thickness of 0.95 to 3.8 mm is manufactured by a rapid solidification method using twin rolls. When rapidly solidifying molten steel using the rapid solidification method, the molten steel temperature is maintained above the solidus temperature + 2°C. The "molten steel temperature immediately before solidification" refers to the surface temperature of the molten steel accumulated between the twin rolls. The surface temperature of the molten steel can be measured using a radiation thermometer or thermocouple. The resulting slab is used as the base plate. Rapidly cooling the molten steel according to the above temperature conditions is preferable to promote the development of columnar crystals in the slab. It is more preferable that the molten steel temperature immediately before solidification be above the solidus temperature + 10°C. It should be noted that the hot-rolled sheet used as a raw material in the process of manufacturing the base plate, and the hot-rolled sheet manufactured in the process of manufacturing the base plate, are naturally different concepts from the final hot-rolled sheet, i.e., the hot-rolled sheet according to this embodiment. The hot-rolled sheet manufactured under known hot-rolling conditions and subjected to annealing in method (A) is different from the hot-rolled sheet according to this embodiment. Furthermore, the hot-rolled sheet manufactured by the continuous casting / direct rolling method in means (B) is, naturally, a different concept from the hot-rolled sheet according to this embodiment. In this disclosure, the hot-rolled sheet used as a raw material in the process of manufacturing the base sheet, and the hot-rolled sheet manufactured in the process of manufacturing the base sheet, may be referred to as "base hot-rolled sheet." Also in this disclosure, the hot rolling used to manufacture the base sheet is referred to as "first hot rolling." The hot rolling included in means (A) and means (B) is the first hot rolling.Furthermore, the hot-rolled sheet obtained by means (B) may be subjected to the second rolling described later after the heat-insulating cover has been removed and it has been allowed to cool to room temperature, or it may be subjected to the second rolling described later without cooling to room temperature.

[0075] Furthermore, the hot-rolled sheet obtained by (B) and the cast slab obtained by (C) may also be referred to as "hot-rolled annealed sheet" in this disclosure. That is, the term "hot-rolled annealed sheet" is a concept that includes not only annealed hot-rolled sheets but also steel sheets that are considered to be metallurgically equivalent thereto. In method (B), heating and cooling for annealing are not performed. However, in the hot-rolled sheet obtained by method (B), a phenomenon called self-annealing occurs by covering and holding it with a heat-retaining cover. Therefore, the hot-rolled sheet obtained by method (B) is considered to be metallurgically equivalent to the hot-rolled annealed sheet. In method (C), hot rolling is not performed, but it has the same thickness and coarse recrystallized structure as the hot-rolled annealed sheet obtained by method (A). Therefore, the hot-rolled sheet obtained by method (C) is also considered to be metallurgically equivalent to the hot-rolled annealed sheet.

[0076] (Second Hot Rolling) The base sheet is hot-rolled. During hot rolling, the base sheet is brought to a temperature range of 850°C to 1150°C at the entrance of the first pass. In this disclosure, the hot rolling performed on the base sheet is referred to as the second hot rolling. The base sheet that has undergone the second hot rolling is the hot-rolled sheet for non-oriented electrical steel according to this embodiment. Note that if the base sheet is manufactured by means (C) above, hot rolling is performed only once in the manufacturing process of the hot-rolled sheet for non-oriented electrical steel. This is because means (C) above does not include hot rolling. However, even in this case, the rolling performed on the base sheet is conveniently referred to as the "second hot rolling".

[0077] The thickness of the hot-rolled sheet is 0.75 mm to 2.1 mm. Preferably, the thickness of the hot-rolled sheet is 0.9 mm or more, 0.95 mm or more, or 1.0 mm or more. Preferably, the thickness of the hot-rolled sheet is 1.8 mm or less, 1.5 mm or less, or 1.25 mm or less.

[0078] The second hot rolling is a type of hot rolling because it is carried out at a high temperature. However, in this disclosure, a distinction is made between the hot rolling performed during the manufacturing of the base sheet and the second hot rolling performed on the said base sheet. For example, the hot rolling performed in example (A) of the means for obtaining the base sheet described above is not the second hot rolling.

[0079] The second hot rolling is performed to bring the area ratio of recrystallized grains and the average KAM value of the hot-rolled sheet within a predetermined range. The second hot rolling reduces the thickness of the base sheet, resulting in a hot-rolled sheet. Dislocations are introduced into the base sheet during this process. The dislocations promote recrystallization, resulting in an area ratio of recrystallized grains of 4.0% or more. Furthermore, the average KAM value of the recrystallized grains formed by the second hot rolling is set to 0.6° or less.

[0080] In the conventional manufacturing of non-oriented electrical steel sheets, one of the purposes of annealing a hot-rolled sheet is to remove dislocations from the sheet. Therefore, a person skilled in the art would not reintroduce dislocations to a hot-rolled sheet annealed by manufacturing method A. The hot-rolled sheet manufactured by manufacturing method B and the cast slab manufactured by manufacturing method C are metallurgically equivalent to the hot-rolled and annealed sheet, so a person skilled in the art would not hot-roll them. However, in the manufacturing method according to this embodiment, a second hot-rolling is performed on the base sheet before cold-rolling.

[0081] The second hot rolling is carried out within a temperature range of 850 to 1150°C. Preferably, the second hot rolling is carried out within a temperature range of 950 to 1050°C. If the rolling temperature is too high, the dislocation density in the surface layer of the hot-rolled sheet will be insufficient, and recrystallization will not proceed. On the other hand, if the rolling temperature is too low, iron atoms will not be able to diffuse, and recrystallization will not proceed.

[0082] The material sheet subjected to the second hot rolling is then water-cooled and further wound up. The winding after the second hot rolling is carried out within a temperature range of 550 to 1000°C. Water cooling is performed until the temperature of the material sheet reaches the winding temperature. The winding temperature is preferably 600°C or higher. The winding temperature after the second hot rolling may be 900°C or lower, or 800°C or lower. If the winding temperature is too high, the dislocation density in the surface layer of the hot-rolled sheet will be insufficient and recrystallization will not proceed. On the other hand, if the winding temperature is too low, iron atoms cannot diffuse and recrystallization will not proceed. In addition, the time from the end of rolling to the start of winding should be between 6 seconds and 15 seconds.

[0083] The reduction ratio in the second hot rolling process is preferably, for example, 20 to 45%.

[0084] While not particularly limited, after the completion of the second hot rolling, cooling may be carried out to a temperature range near the coiling temperature as needed. The cooling conditions are not particularly limited. For example, the coiled hot-rolled sheet can be left in a room temperature environment to lower its temperature to room temperature. In other words, the coiled hot-rolled sheet can be allowed to cool naturally. However, no heat treatment such as annealing or high-temperature holding should be performed on the hot-rolled sheet. This is because these heat treatments may change the recrystallized structure of the hot-rolled sheet controlled by the second hot rolling. For example, after the completion of the second hot rolling, the hot-rolled sheet can be coiled and left at room temperature.

[0085] (Parameter Evaluation Method) The following describes the evaluation methods for various parameters that define the hot-rolled sheet for non-oriented electrical steel sheets according to this embodiment. For the sake of convenience, the specific names of measuring instruments used to evaluate parameters are shown below as examples. However, the measurement results are not essentially dependent on the measuring instruments. The parameters of the hot-rolled sheet for non-oriented electrical steel sheets according to this embodiment can be evaluated using instruments equivalent to the measuring instruments exemplified below.

[0086] (Method for identifying recrystallized and unrecrystallized grains based on GOS value) The method for identifying recrystallized and unrecrystallized grains based on GOS value is described below. The GOS value is the average of the orientation differences between all measurement points within the same crystal grain. Crystal grains with large strain will have a high GOS value. First, an L-shaped section is formed of the hot-rolled sheet 1. An L-shaped section is a section that is parallel to the rolling direction RD of the hot-rolled sheet 1 and also parallel to the thickness direction TD of the hot-rolled sheet 1. The L-shaped section is polished to a mirror finish by mechanical polishing. After that, electrolytic polishing is performed on the L-shaped section to remove the strain layer created by mechanical polishing.

[0087] Next, the crystal orientation of the L-section is analyzed at an accelerating voltage of 20 kV using electron backscatter diffraction (EBD) by FE-SEM. As shown in Figure 1, the analysis field A includes the region from one surface 11 to the other surface 11 of the hot-rolled sheet 1. The dimension of the analysis field A along the rolling direction RD is set to 500 μm or more. The spacing between the crystal orientation measurement points is set to 1 μm. This provides a crystal orientation map of bcc iron in the analysis field A of the L-section. The crystal orientation data obtained by EBD measurement is composed of hexagonal or square pixels as the basic unit. If a pixel partially overlaps the region boundary, pixels whose centroid is within the region are included in that region, while pixels whose centroid is outside the region are excluded from that region.

[0088] The crystal orientation map data mentioned above includes data that should be ignored when analyzing the sample, such as the vacuum region outside the sample. Therefore, in analyzing the crystal orientation map data, only measurement points with a CI value > 0.1 and an IQ value greater than or equal to the median of the measurement data are used for the analysis. The CI value is an indexed reliability index. The IQ value is a value that represents the image quality of the electron diffraction pattern used in EBSD measurements.

[0089] In the crystal orientation map of analysis field A, grain boundaries with a crystal orientation difference of 5.0° or more are considered crystal grain boundaries. Regions enclosed by these grain boundaries are considered crystal grains. These crystal grains are either recrystallized grains or unrecrystallized grains.

[0090] Then, for each crystal grain identified by the procedure described above, the geodesic orientation (GOS) within it is determined. Crystal grains with a GOS of less than 3.0° are considered recrystallized grains. Crystal grains other than recrystallized grains are considered unrecrystallized grains. Unrecrystallized grains are those with a GOS of 3.0° or greater. For crystal orientation analysis, for example, TSL's EBSD crystal orientation analysis software, OIM Data Collection and OIM Data Analysis, can be used.

[0091] (Method for measuring the area fraction of recrystallized grains) The method for measuring the area fraction of recrystallized grains is as follows. First, the recrystallized grains included in the analysis field A described above are identified using the procedure described above. The recrystallized grains are identified based on the GOS value. Next, the total area of ​​all recrystallized grains included in the analysis field A is divided by the area of ​​the analysis field A. The value obtained is considered to be the area fraction of recrystallized grains.

[0092] (Method for measuring the average KAM value of recrystallized grains) The average KAM value of recrystallized grains is determined by the following procedure. First, the recrystallized grains included in the analysis field A described above are identified using the procedure described above. The recrystallized grains are identified based on the GOS value. Next, the KAM value of all recrystallized grains included in the analysis field A is measured. The arithmetic mean of the KAM values ​​of the recrystallized grains is taken as the average KAM value of the recrystallized grains.

[0093] (Method for measuring the average KAM value of unrecrystallized grains) The average KAM value of unrecrystallized grains is determined by the following procedure. First, the unrecrystallized grains included in the analysis field A described above are identified using the procedure described above. Unrecrystallized grains are identified based on the GOS value. Next, the KAM value is measured for all unrecrystallized grains included in the analysis field A. The crystal orientation data obtained by EBSD measurement is entered into the analysis software and the Kernel Average Misorientation (KAM) is calculated. The KAM value is defined as the average value of the crystal orientation at each measurement point and the orientation difference with the surrounding adjacent measurement points. If adjacent points are separated by a grain boundary of 5.0° or more, that point is excluded from the KAM calculation. This limits the KAM value to the evaluation of local strain within the grain. The arithmetic mean of the KAM values ​​of the unrecrystallized grains is taken as the average KAM value of the unrecrystallized grains.

[0094] (Method for measuring the average particle size of recrystallized grains) The method for measuring the average particle size of recrystallized grains is as follows. First, the recrystallized grains included in the analysis field A described above are identified using the procedure described above. The recrystallized grains are identified based on the GOS value. Next, a weighted average value is calculated from the average value obtained by multiplying the area of ​​each recrystallized grain by the ratio of the area of ​​each crystal grain to the total area.

[0095] (Method for measuring the area ratio of recrystallized grains in the surface region) The method for measuring the area ratio of recrystallized grains in the surface region 12 is as follows. First, the recrystallized grains included in the analysis field A described above are identified using the procedure described above. Next, the area of ​​the recrystallized grains included in the surface region 12 is measured. Then, the total area of ​​the recrystallized grains included in the surface region 12 is divided by the area of ​​the surface region 12. The value obtained is considered to be the area ratio of recrystallized grains in the surface region 12.

[0096] The effects of one aspect of this disclosure will be further illustrated by the examples. However, the conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effectiveness of this disclosure. This disclosure is not limited to these examples of conditions. This disclosure may adopt various conditions as long as they do not depart from its gist and achieve its objectives.

[0097] First, various hot-rolled annealed sheets (base sheets), which are the raw materials for hot-rolled sheets for non-oriented electrical steel sheets, were manufactured. Next, the hot-rolled annealed sheets were hot-rolled and wound up. The time from the end of rolling to the start of winding was set to more than 6 seconds and within 15 seconds. The chemical composition of the hot-rolled annealed sheets is shown in Tables 1 to 3. Note that the chemical composition of the hot-rolled annealed sheet in Example No. a1 was the same as that of Example No. 12. The chemical composition of the hot-rolled annealed sheet in Example No. a2 was the same as that of Example No. 16. The thickness of the hot-rolled annealed sheets is shown in Tables 4 to 7. The manufacturing conditions for the hot-rolled annealed sheets were one of the following: - Manufacturing condition A: A hot-rolled sheet manufactured under known hot-rolling conditions is annealed at 1100°C for 5 minutes. - Manufacturing condition A1: A hot-rolled sheet manufactured under known hot-rolling conditions is annealed at 1000°C for 1 minute. - Manufacturing condition A2: Hot-rolled sheets manufactured under known hot-rolling conditions are annealed at 1230°C for 5 minutes. - Manufacturing condition B: Hot-rolled sheets are manufactured by continuous casting and direct rolling (CC-DR method) at a finishing temperature of 1050°C or higher. The hot-rolled sheets are then wound up in a temperature range of 900°C to 1000°C, covered with a heat-insulating cover, and held for one day. - Manufacturing condition B1: Hot-rolled sheets are manufactured by continuous casting and direct rolling (CC-DR method) at a finishing temperature of 950°C. The hot-rolled sheets are wound up, covered with a heat-insulating cover, and held for one day. - Manufacturing condition C: Cast slabs are manufactured by a rapid solidification method using twin rolls. The temperature of the molten steel is maintained above the solidus temperature + 2°C. The thickness of the cast slabs is 0.95 to 3.8 mm. These cast slabs are used as the base sheet. • Manufacturing condition C1: A cast slab was produced by a rapid solidification method using twin rolls. The temperature of the molten steel was maintained at or below the solidus temperature + 2°C. This cast slab was used as the base plate.

[0098] Manufacturing conditions A, B, and C are appropriate conditions for manufacturing hot-rolled annealed sheets (raw material sheets). The grain size of the hot-rolled annealed sheet obtained under manufacturing condition A1 was smaller than that obtained under manufacturing condition A. The grain size of the hot-rolled annealed sheet obtained under manufacturing condition A2 was larger than that obtained under manufacturing condition A. The grain size of the hot-rolled annealed sheet obtained under manufacturing condition B1 was smaller than that obtained under manufacturing condition B. The grain size of the hot-rolled annealed sheet obtained under manufacturing condition C1 was smaller than that obtained under manufacturing condition C. In conditions C and C1, the temperature of the molten steel was measured using an infrared thermometer. The "molten steel temperature" refers to the temperature of the molten steel when manufacturing a cast slab using the rapid solidification method with twin rolls, and is the temperature of the molten steel accumulated between two cooled rotating rolls. The grain size of the raw material sheets obtained under these manufacturing conditions can be evaluated using an optical microscope or EBSD.

[0099] The manufacturing conditions for hot-rolled annealed sheets are described in Tables 4 to 7. The rolling temperature of the hot-rolled annealed sheets is described in Tables 4 to 7. The thickness and coiling temperature of the hot-rolled sheets are described in Tables 4 to 7.

[0100] The recrystallized and non-recrystallized grains of the hot-rolled sheets for non-oriented electrical steel obtained using the procedure described above were analyzed. All hot-rolled sheets contained both recrystallized and non-recrystallized grains. The area percentage of recrystallized grains is shown in Tables 8 to 11. Since the sum of the area percentages of non-recrystallized and recrystallized grains is 100%, the area percentage of non-recrystallized grains is not listed in the table. Furthermore, the average KAM values ​​of the recrystallized grains are shown in Tables 8 to 11. These values ​​were measured using the method described above.

[0101] Furthermore, repeated bending tests were conducted on hot-rolled sheets for non-oriented electrical steel. The results of the repeated bending tests are shown in Tables 8 to 11. Hot-rolled sheets that passed the repeated bending test four or more times were considered to be hot-rolled sheets for non-oriented electrical steel with high toughness.

[0102] The repeated bending test was, in principle, carried out in accordance with Annex JA "Repeated Bending Test Method and Test Equipment Specifications" of JIS C2552:2014 "Non-Oriented Electrical Steel Strip". The test method for evaluating non-oriented electrical steel sheets was adapted for the evaluation of hot-rolled sheets for non-oriented electrical steel sheets. ・Specimen shape: Rectangle with a width of 29 mm and a length of 250 to 320 mm ・Specimen sampling method: Cut from the hot-rolled sheet with the longitudinal direction of the specimen aligned with the rolling direction ・Sample temperature during testing: 60°C The length of the specimens varied within the above range for convenience in the preparation process. Since the length of the specimens does not affect the results of the repeated bending test, it was judged that the variation in specimen length was acceptable. The procedure was as follows: The specimen was placed in a metal repeated bending tester with a radius of 3.5 mm. The specimen was bent 90 degrees to one side and returned to its initial position. This was considered one bending cycle. Next, the specimen was bent 90 degrees to the other side in the same manner, returning it to its initial position. This was considered the second bending cycle. The test was repeated until a crack appeared in the specimen, and the number of bending cycles was recorded. Three tests were performed on each type of specimen. The values ​​listed in Tables 8 to 11 are the average values ​​of the three tests. The repeated bending test machine was the same type as the one exemplified in Figure JA. 2 of Annex JA of JIS C2552:2014. However, the radius of curvature of the test machine described in that standard is 5 mm. The test machine used in this experiment differed from the test machine described in that standard only in terms of the size of the curvature.

[0103]

[0104]

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[0116]

[0117] In hot-rolled non-oriented electrical steel sheets obtained under appropriate manufacturing conditions, the area ratio of recrystallized grains and the average KAM value of the recrystallized grains were suitably controlled. These hot-rolled non-oriented electrical steel sheets possessed high toughness.

[0118] On the other hand, the hot-rolled sheets for non-oriented electrical steel sheets in Examples 47 to 54 were judged to have insufficient toughness because the repeated bending test results were less than four times.

[0119] In the hot-rolled sheet for non-oriented electrical steel in Example 47, the area ratio of recrystallized grains was insufficient, and the average KAM value of the recrystallized grains was inappropriate. This is presumed to be because the rolling temperature was too high when rolling the hot-rolled annealed sheet in Example 47 to make a hot-rolled sheet. The rolling temperature is the temperature of the base sheet at the entrance side of the first pass of the second hot rolling process.

[0120] In the hot-rolled sheet for non-oriented electrical steel sheet of Example 48, the area ratio of recrystallized grains was insufficient, and the average KAM value of the recrystallized grains was inappropriate. This is presumed to be because the rolling temperature when rolling the hot-rolled annealed sheet of Example 48 into a hot-rolled sheet was too low.

[0121] In the hot-rolled sheet for non-oriented electrical steel in Example 49, the area ratio of recrystallized grains was insufficient, and the average KAM value of the recrystallized grains was inappropriate. This is presumed to be because the hot-rolled sheet in Example 49 was made too thin.

[0122] In the hot-rolled sheet for non-oriented electrical steel in Example 50, the area ratio of recrystallized grains was insufficient. This is presumed to be because the hot-rolled sheet in Example 50 was too thick.

[0123] In the hot-rolled sheet for non-oriented electrical steel in Example 51, the average KAM value of the recrystallized grains was inappropriate. This is presumed to be because the manufacturing conditions for the hot-rolled and annealed sheet in Example 51 were inappropriate.

[0124] In the hot-rolled sheet for non-oriented electrical steel in Example 52, the area ratio of recrystallized grains was insufficient. This is presumed to be because the manufacturing conditions for the hot-rolled and annealed sheet in Example 52 were inappropriate.

[0125] In the hot-rolled sheet for non-oriented electrical steel sheet of Example 53, the area ratio of recrystallized grains was insufficient, and the average KAM value of the recrystallized grains was inappropriate. This is presumed to be because the manufacturing conditions for the hot-rolled and annealed sheet of Example 53 were inappropriate.

[0126] In the hot-rolled sheet for non-oriented electrical steel in Example 54, the average KAM value of the recrystallized grains was inappropriate. This is presumed to be because the manufacturing conditions for the hot-rolled and annealed sheet in Example 54 were inappropriate.

[0127] 1 Hot rolled plate 11 Surface 12 Surface layer area t Thickness A Analysis field

Claims

1. A hot-rolled sheet comprising: recrystallized grains having a GOS value of less than 3.0°; and unrecrystallized grains which are the remainder of the recrystallized grains in the metal structure, wherein the area ratio of the recrystallized grains is 4.0% or more, and the average KAM value, which is the arithmetic mean of the KAM values ​​of the recrystallized grains, is 0.6° or less.

2. The hot-rolled sheet according to claim 1, characterized in that the average KAM value of the unrecrystallized grains is 0.9° or less.

3. The hot-rolled sheet according to claim 1 or 2, characterized in that the weighted average of the particle size of the recrystallized grains, weighted by area, is 100 μm or less.

4. The hot-rolled sheet according to claim 1 or 2, characterized in that the area ratio of the recrystallized grains in the region from the surface to a depth of 1 / 4 of the thickness of the hot-rolled sheet is 30% or more.

5. Chemical composition, in mass%, C: 0.0030% or less, Si: 2.00% to 7.00%, Sol. Al: 0.15%–2.50%, Mn: 0.1%–4.0%, Cr: 0.01%–5.00%, P: 0.005%–0.200%, S: 0.0004%–0.0100%, N: 0%–0.010%, Ti: 0.0005%–0.0100%, Ca: 0.0005%–0.0100%, One or more of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: Total 0.0005%–0.0200%, Sn: 0%–0.10%, Sb: 0%–0.10%, Ni: 0%–5.0%, Cu: 0%–5.0%, B A hot-rolled sheet according to claim 1 or 2, characterized in that it contains 0% to 0.10% of , , , , , , , , , , , , , , , , , , , , , , , , , , , and , with the remainder being Fe and impurities.

6. The hot-rolled sheet according to claim 5, characterized in that, in the above chemical composition, Mn: 0.2% to 4.0% and S: 0.0010% to 0.0100% by mass.

7. A method for manufacturing a hot-rolled sheet, comprising the steps of: rolling a material sheet with a thickness of 0.95 to 3.8 mm for the manufacture of a non-oriented electrical steel sheet at a temperature range of 850°C to 1150°C to a thickness of 0.75 mm to 2.1 mm; and water-cooling the rolled material sheet, and then winding it at a temperature range of 550°C to 1000°C, wherein the time from the end of rolling to the start of winding is between 6 seconds and 15 seconds.

8. The method for manufacturing a hot-rolled sheet according to claim 7, wherein the method for manufacturing the hot-rolled sheet further comprises a step of manufacturing the base sheet, and in the step of manufacturing the base sheet, the base hot-rolled sheet is annealed at an annealing temperature of 1050°C to 1200°C and for an annealing time of 3 minutes to 10 minutes.

9. The method for manufacturing a hot-rolled sheet according to claim 7, further comprising a step of manufacturing a base sheet, wherein in the step of manufacturing the base sheet, a base hot-rolled sheet is manufactured by a continuous casting / direct rolling method at a finishing temperature of 1050°C to 1150°C, the base hot-rolled sheet is then wound up, and the base hot-rolled sheet is then covered with a heat-insulating cover and held for one day or more.

10. The method for manufacturing a hot-rolled sheet according to claim 7, further comprising a step of manufacturing a base sheet, wherein in the step of obtaining the base sheet, a cast slab with a thickness of 0.95 to 3.8 mm is manufactured by a rapid solidification method using twin rolls, and when rapidly solidifying the molten steel by the rapid solidification method, the surface temperature of the molten steel accumulated between the twin rolls is maintained at more than the solidus temperature of the molten steel + 2°C.

11. The material plate has a chemical composition of, in mass%, C: 0.0030% or less, Si: 2.00% to 7.00%, Sol. Al: 0.15%–2.50%, Mn: 0.1%–4.0%, Cr: 0.01%–5.00%, P: 0.005%–0.200%, S: 0.0004%–0.0100%, N: 0%–0.010%, Ti: 0.0005%–0.0100%, Ca: 0.0005%–0.0100%, One or more of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: Total 0.0005%–0.0200%, Sn: 0%–0.10%, Sb: 0%–0.10%, Ni: 0%–5.0%, Cu: 0%–5.0%, B: 0%–0.10% A method for producing a hot-rolled sheet according to any one of claims 7 to 10, characterized in that it contains O: 0% to 0.10%, V: 0% to 0.10%, Zr: 0% to 0.10%, Bi: 0% to 0.10%, W: 0% to 0.10%, Mo: 0% to 0.10%, Nb: 0% to 0.10%, and Y: 0% to 0.10%, with the remainder being Fe and impurities.

12. The method for manufacturing a hot-rolled sheet according to claim 11, characterized in that the chemical composition of the material sheet is, in mass%, Mn: 0.2% to 4.0% and S: 0.0010% to 0.0100%.

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