Non-oriented electrical steel sheet with excellent magnetic properties and its manufacturing method

Abstract

To provide a manufacturing method of a novel and improved non-oriented electromagnetic steel sheet capable of manufacturing a non-oriented magnetic steel sheet excellent in magnetic characteristics while improving productivity by improving cold fragility, and a non-oriented electromagnetic steel sheet obtained thereby.SOLUTION: A non-oriented magnetic steel sheet characterized by containing by mass%, C: over 0% to 0.0050% or smaller, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: over 0% to smaller than 0.030%, S: over 0% to 0.0050% or smaller, Sol. Al: over 0% to 0.0040% or smaller; N: over 0% to 0.0040%; Cu: 0.00% to 1.0% or smaller, Sn: 0.000% to 0.10%, Sb: 0.000% to 0.10%, Ca: 0.0000% to 0.0050%, and the remainder is Fe and impurity, Mn2SiO4 complex precipitated with SiO2 in the surface layer of base steel is 0.000001 piece / μm2 or larger, and 10.000 pieces / μm2, and its manufacturing method..SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a non-oriented electrical steel sheet having excellent magnetic properties and a method for producing the same. [Background technology]

[0002] Recently, global environmental issues have been attracting attention, and the demand for energy conservation efforts has been increasing. In particular, there has been a strong demand in recent years for high efficiency electrical equipment. For this reason, there has been an increasing demand for improved magnetic properties in non-oriented electrical steel sheets, which are widely used as iron core materials for motors, transformers, etc. In recent years, this trend is particularly evident in motors for electric and hybrid vehicles, where the efficiency of motors has been increasing, and in motors for compressors.

[0003] In order to improve the magnetic properties of non-oriented electrical steel sheets, it is effective to increase the electrical resistance of the steel sheets and reduce eddy current loss by adding alloy elements to the steel. For this reason, as disclosed in the following Patent Documents 1 and 2, for example, elements that have the effect of increasing electrical resistance, such as Si, Al, Mn, or P, are added to improve the magnetic properties. Furthermore, Patent Documents 3 and 4 disclose that the combined addition of Mn and Si improves cold rolling properties in addition to improving the magnetic properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-129409 A [Patent Document 2] JP 2015-131993 A [Patent Document 3] JP 2018-66033 A [Patent Document 4] JP 2019-99854 A Summary of the Invention [Problem to be solved by the invention]

[0005] High alloying (increasing the Si concentration or Al concentration) is effective for improving the magnetic properties of non-oriented electrical steel sheets (NO). However, increasing the Si concentration or Al concentration significantly deteriorates cold brittleness, so it is generally difficult to achieve both productivity and magnetic properties. In response to this, various approaches have been proposed, such as those disclosed in Patent Documents 3 and 4, but further improvements in the compatibility of productivity and magnetic properties are still required.

[0006] Therefore, an object of the present invention is to provide a new and improved method for producing non-oriented electrical steel sheet that can improve cold brittleness to increase productivity while producing non-oriented electrical steel sheet with excellent magnetic properties, and a non-oriented electrical steel sheet obtained thereby. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors have conducted extensive research and have found that by setting the Al content to a predetermined value or less, adding Mn, which has little effect on the deterioration of cold rolling property, together with Si, and controlling the pickling conditions, The inventors have found that it is possible to improve both the cold rolling properties and the magnetic properties, and have completed the present invention.

[0008] The present invention, which was obtained based on the above findings, provides the following aspects. [1] The steel sheet contains, by mass%, C: more than 0% to 0.0050%, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% to less than 0.030%, S: more than 0% to 0.0050%, Sol.Al: more than 0% to 0.0040%, N: more than 0% to 0.0040%, Cu: 0.00% to 1.0%, Sn: 0.000% to 0.10%, Sb: 0.000% to 0.10%, Ca: 0.0000% to 0.0050%, and the balance is Fe and impurities. 2 and Mn precipitated 2SiO 4 0.000001 pieces / μm 2 More than 10.000 pieces / μm 2 A non-oriented electrical steel sheet comprising: [2] a hot rolling process in which a steel slab containing, by mass%, C: more than 0% and not more than 0.0050%, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% and less than 0.030%, S: more than 0% and not more than 0.0050%, Sol.Al: more than 0% and not more than 0.0040%, N: more than 0% and 0.0040%, Ca: 0.0000% to 0.0050%, with the balance being Fe and impurities, is heated and then hot rolled to obtain a hot rolled steel sheet; a hot-rolled sheet annealing process for annealing the hot-rolled sheet; A pickling process for pickling the hot-rolled annealed sheet; A cold rolling process in which, after the pickling, a single cold rolling or multiple cold rolling processes with intermediate annealing are performed to obtain a cold-rolled steel sheet; A finish annealing process for performing finish annealing on the cold-rolled steel sheet; and an insulating coating step of applying an insulating coating. a liquid temperature of the pickling solution is from 15°C to 100°C, the time for which the steel sheet is immersed in the pickling solution is from 5 to 200 seconds, the pH is from -1.5 to less than 7, and the pickling solution contains Mn in an amount of from 0.01 g / L to 2.00 g / L. [3] The method for producing a non-oriented electrical steel sheet according to [2], wherein the steel slab contains, by mass%, REM: 0.0001 to 0.0100%. [4] The method for producing a non-oriented electrical steel sheet according to [3], characterized in that the pickling solution has Cu and Mn contents of 0.01 g / L or more and 5.00 g / L or less. [5] The method for producing a non-oriented electrical steel sheet according to [3] or [4], characterized in that the final annealing is performed at a soaking annealing temperature of 800°C or higher, and the heating rate from 500 to 800°C in the heating step is 100°C / sec to 2000°C / sec. [6] The method for producing a non-oriented electrical steel sheet according to any one of [3] to [5], characterized in that the final annealing is performed at a soaking annealing temperature of 800°C or higher, and the atmospheric dew point at 500 to 800°C in the temperature increasing step is set to be -50°C or higher and 10°C or lower. [7] The method for producing a non-oriented electrical steel sheet according to any one of [3] to [6], characterized in that the final annealing is performed at a soaking annealing temperature of 800°C or higher, and an oxygen potential at the soaking annealing temperature of the final annealing is set to 0.2 or lower. [8] The method for producing a non-oriented electrical steel sheet according to any one of [3] to [7], wherein the steel slab further contains, in mass%, at least one selected from Sn: 0.005% to 0.10% and Sb: 0.005% to 0.10%, in place of a part of the remaining Fe. Effect of the Invention

[0009] The method for producing a non-oriented electrical steel sheet according to the present invention is a new and improved method for producing a non-oriented electrical steel sheet that can improve cold brittleness to increase productivity and can produce a non-oriented electrical steel sheet with excellent magnetic properties, and the non-oriented electrical steel sheet obtained by the above-mentioned production method is a non-oriented electrical steel sheet with excellent magnetic properties. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a flow chart showing an example of the flow of the method for producing a non-oriented electrical steel sheet according to this embodiment. [Diagram 2] FIG. 2 is a schematic diagram for explaining the surface layer portion of the steel plate base material. [Diagram 3] FIG. 3 is a schematic diagram for explaining composite precipitates of SiO2 and Mn2SiO4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] First, the gist of the present invention will be described.

[0012] (Production method) In order to improve the magnetic properties of non-oriented electrical steel sheets, as disclosed in Patent Documents 1 and 2, elements that have the effect of increasing electrical resistance, such as Si, Al, Mn, or P, are added to improve the magnetic properties. In particular, Al, like Si, has the effect of increasing electrical resistance and reduces eddy current loss, which is one of the causes of iron loss, but on the other hand, it significantly deteriorates cold brittleness. Therefore, the present inventors have investigated the possibility of adding Mn, which causes little deterioration in cold rolling property, together with Si while setting the Al content at a predetermined value or less, and have recognized the adverse effects caused by Mn. The drawback is that the oxide film becomes porous during final annealing. If the oxide film is porous, gases in the annealing atmosphere (especially N) can easily penetrate into the surface layer of the steel sheet and react with the constituent elements in the steel sheet to form nitrides (sometimes called inclusions, such as (Si,Mn)N or MnSiN). 2 When Al (rather than Mn) is added, a relatively tight coating is formed, so gases in the annealing atmosphere (especially N) are less likely to penetrate to the surface layer of the steel sheet, and (Si,Mn)N or MnSiN are precipitated. 2 This can prevent the formation of precipitates such as AlN (which are factors that deteriorate magnetic properties). In order to prevent gases (especially N) in the annealing atmosphere from penetrating into the surface layer of the steel sheet, there are measures such as lowering the dew point of the atmosphere during heating and soaking in the final annealing process (drying), but these alone are insufficient to prevent the oxide film from becoming porous. In response to this, the present inventors came up with the idea that it would be possible to form a tight coating by controlling the Mn concentration in the pickling solution. Specifically, when the Mn concentration in the pickling solution is equal to or higher than a certain level, a Mn segregation layer is formed on the surface of the steel sheet after pickling. The Mn segregation layer is a tight coating, which helps to prevent the formation of precipitates during final annealing, thus resulting in good magnetic properties. Although Mn is added to the pickling solution in the above, the same effect can be obtained if any substance other than Mn forms a segregation layer. For example, the Cu concentration in the pickling solution may be set to a certain level or higher. Furthermore, by controlling the temperature rise rate and annealing atmosphere in the final annealing, the magnetic properties can be improved in a more favorable direction. On the other hand, in the embodiment of the present invention, since the Al content is limited, it is possible to avoid deterioration of cold brittleness caused by Al.

[0013] (About the product) The non-oriented electrical steel sheet obtained by the manufacturing method of the present invention has the following characteristic structure: A part of the Mn segregation layer formed on the surface layer of the steel sheet originating from the pickling solution is converted into SiO 2 Mn 2 SiO 4 Specifically, spherical SiO 2 The surrounding area is Mn 2 SiO 4 The structure is surrounded by a core / shell structure. Note that, since an insulating coating is applied to normal non-oriented electrical steel sheets after final annealing, no traces of this technology remain on the product surface. However, by removing the insulating coating and observing the surface layer of the steel sheet, the above characteristic structure can be confirmed. Therefore, the core / shell type Mn 2 SiO 4 By counting the number, it is possible to determine whether the effect of the present invention is achieved, that is, it is possible to certify that the non-oriented electrical steel sheet is according to an embodiment of the present invention.

[0014] The present inventors have taken the above findings into consideration and arrived at the present invention. One embodiment of the present invention is a method for producing a non-oriented electrical steel sheet having the following configuration.

[0015] The present invention relates to a hot rolling process for obtaining a hot rolled steel sheet by heating and hot rolling a steel slab containing, by mass%, C: more than 0% and 0.0050% or less, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% and less than 0.030%, S: more than 0% and 0.0050% or less, Sol.Al: more than 0% and 0.0040% or less, N: more than 0% and 0.0040%, Ca: 0.0000% to 0.0050%, and the balance being Fe and impurities; a hot rolling process for annealing the hot rolled sheet; a pickling process for pickling the hot rolled annealed sheet; and a cold rolling process in which a single cold rolling or multiple cold rolling processes with intermediate annealing are performed to obtain a cold-rolled steel sheet after the above-mentioned step, a finish annealing process in which the cold-rolled steel sheet is finish-annealed, and an insulating coating process in which an insulating coating is applied, wherein the temperature of the pickling solution is from 15°C to 100°C, the steel sheet is immersed in the pickling solution for from 5 seconds to 200 seconds, the pH is from -1.5 to less than 7, and the pickling solution contains Mn at a concentration of from 0.01 g / L to 2.00 g / L.

[0016] The method for producing a non-oriented electrical steel sheet according to this embodiment will be specifically described below.

[0017] <Composition of Steel Billets> First, the composition of the steel billet (slab) of the non-oriented electrical steel sheet according to this embodiment will be described. In the following, unless otherwise specified, the notation "%" will represent "mass %". The remainder other than the elements described below is Fe and impurities. Here, impurities refer to components contained in raw materials or components mixed in during the manufacturing process, and components that are not intentionally contained in the steel sheet. In addition, the chemical composition of the steel billet, which is the material of the non-oriented electrical steel sheet, is basically similar to the composition of the non-oriented electrical steel sheet. However, in the manufacture of general non-oriented electrical steel sheets, some of the contained elements are discharged outside the system during the finish annealing process and the insulating film formation process during the manufacturing process, so that the chemical composition of the steel billet, which is the material, and the non-oriented electrical steel sheet, which is the final product, differ. In order to obtain the desired characteristics of the non-oriented electrical steel sheet, the composition of the steel billet can be appropriately adjusted taking into account the effects of the finish annealing process and the insulating film formation process during the manufacturing process. In addition, unless otherwise specified, the expression "electromagnetic steel sheet" in the present invention refers to an electromagnetic steel sheet at any step in the manufacturing process of an electromagnetic steel sheet from the steel billet to the final product. In other words, unless otherwise specified, the expression "electromagnetic steel sheet" in the manufacturing process of a non-oriented electrical steel sheet in the present invention refers to an electromagnetic steel sheet at any step in the manufacturing process of an electromagnetic steel sheet from the steel billet to before the insulating coating application step.

[0018] [C: More than 0%~0.0050% or less] C (carbon) is an element that is inevitably contained and causes iron loss deterioration. If the C content exceeds 0.0050%, magnetic aging (a phenomenon in which carbides precipitate over time and magnetic properties deteriorate) occurs in the non-oriented electrical steel sheet, and good magnetic properties cannot be obtained. Therefore, in the non-oriented electrical steel sheet according to this embodiment, the C content is set to 0.0050% or less. The C content is preferably 0.0040% or less, and more preferably 0.0030% or less. The lower the C content, the better, but if the C content is reduced below 0.0005%, it will only lead to unnecessary cost increases. Therefore, the C content is preferably 0.0005% or more.

[0019] [Si:2.5%~5.0%] Si (silicon) is an element that increases the electrical resistance of steel, reduces eddy current loss, and improves iron loss. In addition, Si is an element that is effective in increasing the strength of non-oriented electrical steel sheets because of its high solid solution strengthening ability. Increasing strength is important from the viewpoints of suppressing deformation during high-speed rotation of a motor and suppressing fatigue failure due to variable stress accompanying start and stop. In order to fully exert such effects, it is necessary to contain 2.5% or more of Si. On the other hand, if the Si content exceeds 5.0%, the workability is significantly deteriorated and it becomes difficult to perform cold rolling (i.e., the cold rolling property is reduced). Therefore, the Si content is set to 5.0% or less. The Si content is preferably 3.0% or more and 4.5% or less, and more preferably 3.2% or more and 3.8% or less.

[0020] [Mn: 0.05%~4.0%] Mn (manganese) is an element that is effective in reducing eddy current loss and improving iron loss by increasing electrical resistance without deteriorating the workability of steel. In addition, although Mn has a lower solid solution strengthening ability than Si, it is an element that can contribute to high strength without deteriorating the workability. In order to fully exert such effects, it is necessary to contain 0.05% or more of Mn. On the other hand, if the Mn content exceeds 4.0%, the decrease in magnetic flux density becomes significant. Therefore, the Mn content is set to 4.0% or less. The Mn content is preferably 0.07% or more and 3.0% or less, and more preferably 0.1% or more and 2.0% or less.

[0021] [P: More than 0%~0.030% or less] P (phosphorus) is an element that is inevitably contained (i.e., the content exceeds 0%), and in the high alloy steel with a high content of Si and Mn that is the subject of this embodiment, it is an element that significantly deteriorates the workability and makes cold rolling difficult. Such deterioration of the workability becomes significant when the content of P exceeds 0.030%. Therefore, the content of P is set to 0.030% or less. The content of P is preferably 0.001% or more and 0.020% or less, and more preferably 0.002% or more and 0.010% or less.

[0022] [S: More than 0%~0.0050% or less] S (sulfur) is an element that is inevitably contained, and also increases core loss by forming fine precipitates of MnS, thereby degrading the magnetic properties of the non-oriented electrical steel sheet. Therefore, the S content needs to be 0.0050% or less. The lower the S content, the better, but reducing the S content below 0.0001% will only lead to unnecessary increases in costs. Therefore, the S content is preferably 0.0001% or more. The S content is preferably 0.0040% or less, and more preferably 0.0030% or less.

[0023] [Sol.Al: More than 0%~0.0040% or less] When dissolved in steel, aluminum (Al) is an element that increases the electrical resistance of the non-oriented electrical steel sheet, thereby reducing eddy current loss and improving iron loss. However, in this embodiment, aluminum is not actively contained because Mn, an element that increases electrical resistance without deteriorating workability more than Al, is actively contained. In this case, if the content of Al exceeds 0.0040%, fine nitrides are precipitated in the steel, inhibiting grain growth during hot-rolled sheet annealing and finish annealing, and deteriorating magnetic properties. Therefore, the content of Al is set to 0.0040% or less. On the other hand, if the content of Al is reduced to less than 0.0001%, it will only lead to unnecessary cost increases. Therefore, the content of Al is preferably 0.0001% or more and 0.0030% or less, and more preferably 0.0001% or more and 0.0020% or less. Since Al is limited within the above range, deterioration of cold brittleness due to Al can be avoided.

[0024] [N: More than 0%~0.0040% or less] N (nitrogen) is an element that is inevitably contained, and also causes magnetic aging, increases iron loss, and deteriorates the magnetic properties of non-oriented electrical steel sheets. The N content must be 0.0040% or less. The lower the N content, the better, but attempting to reduce the N content below 0.0001% will only lead to unnecessary increases in costs. Therefore, the N content is preferably 0.0001% or more. The N content is preferably 0.0001% or more and 0.0030% or less, and more preferably 0.0001% or more and 0.0020% or less.

[0025] [Cu:0.00%~1.0%] Cu (copper) is an optional element useful for improving magnetic flux density. Therefore, in the non-oriented electrical steel sheet according to this embodiment, in order to obtain such an effect, Cu may be contained in the base steel as an optional element in place of a part of the remaining Fe. In order to fully exert such an effect, the Cu content is preferably 0.05% or more. On the other hand, if the Cu content exceeds 1.0%, the effect of adding Cu becomes saturated, and only an unnecessary increase in costs is caused. Therefore, the Cu content is preferably 1.0% or less. When Cu is contained in the base steel, the Cu content is preferably 0.05% or more and 0.25% or less, more preferably 0.07% or more and 0.20% or less.

[0026] [Sn: 0.000%~0.10%] [Sb: 0.000%~0.10%] Sn (tin) and Sb (antimony) are optional elements that are useful for ensuring low iron loss by segregating to the surface and suppressing oxidation and nitridation during annealing. In addition to this effect, they also have a texture improving effect (magnetic property improving effect). Therefore, in the non-oriented electrical steel sheet according to this embodiment, in order to obtain such an effect, at least one of Sn and Sb may be contained in the base steel as an optional added element in place of a part of the remaining Fe. In order to fully exert such an effect, it is preferable that the content of Sn or Sb is 0.005% or more. On the other hand, if the content of Sn or Sb exceeds 0.10%, the ductility of the base steel may decrease, making cold rolling difficult. Therefore, it is preferable that the content of Sn or Sb is 0.10% or less. When Sn or Sb is contained in the base steel, the content of Sn or Sb is more preferably 0.01% or more and 0.05% or less, respectively.

[0027] [Ca: 0.0000%~0.0050%] Ca (calcium) is an element that inhibits the precipitation of fine MnS by combining with S to form coarse compounds, and promotes the growth of crystal grains during annealing. Furthermore, Ca is an element that is effective in avoiding nozzle clogging caused by oxides during continuous casting when combined with one or more REMs such as La, Ce, Pr, and Nd. In order to obtain such effects, the Ca content is preferably 0.0001% or more, and more preferably 0.0002% or more. On the other hand, if the Ca content exceeds 0.0050%, the effect of improving the grain growth and the effect of suppressing nozzle clogging as described above are saturated, which is economically disadvantageous. Therefore, the Ca content is set to 0.0050% or less. The Ca content is preferably 0.0040% or less, and more preferably 0.0030% or less. [REM: 0.0001%~0.0100% in total] REM is an abbreviation for Rare Earth Metal, and includes La, Ce, Pr, Nd, etc. REM is an element that inhibits the precipitation of fine MnS by combining with S to form coarse sulfides, sulfates, or both, and promotes grain growth during annealing. Furthermore, when combined with Ca, it is an effective element for avoiding nozzle clogging caused by oxides during continuous casting. In order to obtain such effects, the total content of one or more REMs is preferably 0.0001% or more. On the other hand, if the total content of one or more REMs exceeds 0.0100%, the coarsening effect of the fine precipitates as described above is saturated and it is economically disadvantageous, which is not preferable. Therefore, the total content of one or more REMs is preferably 0.0100% or less. The total content of one or more REMs is preferably 0.0010% or more and 0.0090% or less.

[0028] In the non-oriented electrical steel sheet according to the present embodiment, the contents of elements other than the above-mentioned elements, such as Ni (nickel) and Cr (chromium), are not particularly specified. In the non-oriented electrical steel sheet according to the present embodiment, even if these elements are contained in an amount of 0.5% or less, there is no particular effect on the effects of the present invention. In addition, even if Mg (magnesium) is contained in a range of 0.002% or less, there is no particular effect on the effects of the present invention.

[0029] Furthermore, even if elements such as B (boron) are contained in the range of 0.0001% to 0.0050% in addition to the above elements, the effects of the present invention are not impaired.

[0030] The chemical components of the non-oriented electrical steel sheet according to this embodiment have been described in detail above. Next, in the manufacturing method of the non-oriented electrical steel sheet according to this embodiment, hot rolling, hot-rolled sheet annealing, pickling, cold rolling, finish annealing, and insulation coating steps are sequentially performed on a steel slab having the predetermined chemical composition as described above. Fig. 1 is a flow chart showing an example of the flow of the manufacturing method of the non-oriented electrical steel sheet according to this embodiment. Hereinafter, each step performed in the manufacturing method of the non-oriented electrical steel sheet according to this embodiment will be described in detail with reference to Fig. 1.

[0031] <Hot rolling process> In the manufacturing method of the non-oriented electrical steel sheet according to the present embodiment, first, a steel slab having the above-mentioned chemical composition is heated, and the heated steel slab is hot-rolled to obtain a hot-rolled sheet (step S101). The heating temperature of the steel slab when subjected to hot rolling is not particularly specified, but is preferably, for example, 1050°C to 1250°C. The thickness of the hot-rolled sheet after hot rolling is also not particularly specified, but is preferably, for example, about 1.6 mm to 3.5 mm, taking into account the final thickness of the base steel. The hot rolling process is preferably completed while the temperature of the steel sheet is in the range of 700°C to 1000°C. The heating temperature of the steel slab is more preferably 1050°C to 1150°C, and the end temperature of the hot rolling is more preferably 750°C to 950°C.

[0032] <Hot-rolled sheet annealing process> After the hot rolling, hot-rolled steel sheet annealing is optionally performed (step S103). In the case of continuous annealing, the hot-rolled steel sheet may be annealed by soaking at, for example, 750°C to 1200°C for 10 seconds to 10 minutes. In the case of box annealing, the hot-rolled steel sheet may be annealed by soaking at, for example, 650°C to 950°C for 30 minutes to 24 hours. Although the magnetic properties will be inferior to those in the case of performing the hot-rolled steel sheet annealing process, in order to reduce costs, the hot-rolled steel sheet may be subjected to self-annealing or the like, or the hot-rolled steel sheet annealing process may be omitted.

[0033] <Acid washing process> After the hot rolling or hot-rolled sheet annealing, pickling is performed (step S105). This removes a scale layer mainly composed of oxides formed on the surface of the steel sheet by hot rolling or hot-rolled sheet annealing. When the hot-rolled sheet annealing is box annealing, the pickling step is preferably performed before the hot-rolled sheet annealing from the viewpoint of descaling properties.

[0034] The pickling process of the non-oriented electrical steel sheet according to this embodiment is carried out under the following pickling conditions: the temperature of the pickling solution is 15°C or higher and 100°C or lower, the time for which the steel sheet is immersed in the pickling solution is 5 seconds or higher and 200 seconds or lower, the pH is -1.5 or higher and lower than 7, and the pickling solution contains Mn at 0.01 g / L or higher and 2.00 g / L or lower.

[0035] In this embodiment, the temperature of the pickling solution is 15°C or more and 100°C or less. If the temperature of the pickling solution is less than 15°C, the effect of removing scale by pickling becomes insufficient, which is not preferable. If the temperature of the pickling solution exceeds 100°C, the handling of the pickling solution becomes difficult, which is not preferable. The temperature of the pickling solution is 15°C or more and 100°C or less, which is advantageous in that Mn contained in the pickling solution can satisfactorily form a Mn segregation layer on the steel sheet surface. The temperature of the solution is preferably 50°C or more and 90°C or less, more preferably 60°C or more and 90°C or less.

[0036] In this embodiment, the time for which the steel sheet is immersed in the pickling solution is 5 seconds or more and 200 seconds or less. If the time for which the steel sheet is immersed in the pickling solution is less than 5 seconds, the effect of removing scale by pickling becomes insufficient, which is not preferable. If the time for which the steel sheet is immersed in the pickling solution exceeds 200 seconds, the equipment becomes long and large, which is not preferable. The immersion time is preferably 10 seconds or more and 150 seconds or less, more preferably 20 seconds or more and 150 seconds or less.

[0037] In this embodiment, the pH of the pickling solution is -1.5 or more and less than 7.0. If it is 7.0 or more, the scale removal effect becomes insufficient, which is not preferable. On the other hand, a solution that can be actually prepared has a pH of -1.5 or more. The pH is preferably less than 2.0, more preferably less than 1.0. Examples of acid components contained in the pickling solution include sulfuric acid, hydrochloric acid, and nitric acid.

[0038] In this embodiment, the pickling solution contains Mn at 0.01 g / L or more and 2.00 g / L or less. By pickling the steel sheet with the pickling solution containing this predetermined concentration of Mn, a Mn segregation layer is formed on the surface of the steel sheet after pickling. Since the Mn segregation layer is a tight coating, it is possible to avoid the formation of precipitates in the subsequent finish annealing. Since precipitates are a factor that deteriorates magnetic properties, good magnetic properties can be obtained by avoiding the formation of such precipitates. In order to fully exert such effects, it is necessary to contain Mn at 0.01 g / L or more. On the other hand, if the content of Mn exceeds 2.00 g / L, the effect is saturated, and the magnetic properties may decrease, and the scale removal effect may also decrease. Therefore, the upper limit of Mn in the pickling solution is set to 2.00 g / L or less. The Mn content in the pickling solution is preferably 0.05 g / L or more and 1.00 g / L or less, more preferably 0.1 g / L or more and 0.50 g / L or less.

[0039] In addition, when Cu is contained in the pickling solution, a Cu segregation layer is formed on the steel sheet surface after pickling, similar to Mn. This Cu segregation layer is also a tight coating, so that the formation of precipitates can be avoided in the subsequent finish annealing. In other words, by containing Cu in the pickling solution, the formation of precipitates that cause deterioration of magnetic properties can be avoided, and good magnetic properties can be obtained. Therefore, Cu may be added to the pickling solution as an optional addition. In order to fully exert such effects, it is preferable that the total content of Cu and Mn is 0.01 g / L or more. On the other hand, if the content of Cu is excessive, the effect may be saturated and the scale removal effect may be reduced. Therefore, it is preferable that the total content of Cu and Mn is 5.00 g / L or less. The total content of Mn and Cu in the pickling solution is preferably 0.02 g / L or more and 4.00 g / L or less, more preferably 0.03 g / L or more and 2.00 g / L or less.

[0040] <Cold rolling process> After the above pickling (when the hot-rolled sheet annealing is performed by box annealing, this may be after the hot-rolled sheet annealing step), cold rolling is performed (step S107). In this cold rolling, the pickled sheet from which the scale has been removed is rolled at a rolling reduction rate such that the final sheet thickness of the base steel is 0.10 mm or more and 0.50 mm or less.

[0041] <Finishing annealing process> After the cold rolling, a finish annealing is performed (step S109). The conditions of the finish annealing are not particularly specified, and known conditions (e.g., continuous annealing) used in the finish annealing of non-oriented electrical steel sheets can be adopted. Note that the soaking temperature, heating rate, atmospheric dew point, oxygen potential of the atmosphere, etc. may be appropriately adjusted so that a recrystallized texture advantageous for magnetic properties is formed.

[0042] Specifically, it is preferable that the soaking temperature of the finish annealing is 800°C or higher, and the heating rate from 500 to 800°C in the heating step is 100°C / sec to 2000°C / sec. The lower limit of the heating rate is more preferably 200°C / sec or higher, and even more preferably 400°C / sec or higher. The upper limit of the heating rate is not limited, but is set to 2000°C / sec because if the heating rate is too high, distortion is introduced and the magnetic properties may deteriorate. The above-mentioned temperature rise rate can be achieved, for example, by using direct heating or indirect heating using a radiant tube in the case of heating by gas combustion, or by using other known heating methods such as electrical heating or induction heating.

[0043] It is also preferred that the soaking annealing temperature is 800° C. or higher, and the atmospheric dew point during the temperature increase step from 500 to 800° C. is −50° C. to 10° C. The lower limit of the atmospheric dew point is more preferably −40° C. or higher, and even more preferably −30° C. or higher. The upper limit of the atmospheric dew point is more preferably 5° C. or lower, and even more preferably 1° C. or lower.

[0044] It is also preferable that the soaking annealing temperature is 800° C. or higher, and the oxygen potential at the soaking annealing temperature is 0.2 or lower. The oxygen potential is defined as the ratio of the water vapor partial pressure to the hydrogen partial pressure in the annealing atmosphere (PH 2 O / PH 2 The upper limit of the oxygen potential is more preferably 0.1 or less, and further preferably 0.01 or less.

[0045] In the temperature increasing step in the finish annealing step, the average temperature increasing rate may be set to 1° C. / sec to 2000° C. / sec. The lower limit of the soaking temperature is preferably 700°C or higher, more preferably 800°C or higher, and even more preferably 900°C or higher, and the upper limit of the soaking temperature is preferably 1200°C or lower, more preferably 1100°C or lower, and even more preferably 1050°C or lower. Furthermore, in the cooling process after the soaking process, the average cooling rate may be 1° C. / sec to 100° C. / sec to 200° C. or less. The average cooling rate is more preferably 5° C. / sec to 50° C. / sec, and further preferably 5° C. / sec to 30° C. / sec.

[0046] <Insulating film formation process> After the finish annealing, an insulating coating is formed (step S111). The insulating coating according to the present embodiment is not particularly limited as long as it is used as an insulating coating for a non-oriented electrical steel sheet, and a known insulating coating can be used. The insulating coating forming step is also not particularly limited, and a known insulating coating treatment liquid may be used, and the treatment liquid may be applied and dried by a known method.

[0047] The insulating coating may be, for example, a composite insulating coating that is mainly made of an inorganic material and further contains an organic material. Here, the composite insulating coating is, for example, an insulating coating that is mainly made of at least one of inorganic materials such as metal chromate salts, metal phosphate salts, colloidal silica, Zr compounds, and Ti compounds, and has fine organic resin particles dispersed therein. In particular, from the viewpoint of reducing the environmental load during production, which has become increasingly necessary in recent years, an insulating coating that uses a metal phosphate salt, a coupling agent of Zr or Ti, or a carbonate or ammonium salt thereof as a starting material is preferably used.

[0048] Here, the amount of the insulating coating as described above is not particularly limited, but is, for example, 0.1 g / m per side. 2 More than 2.0g / m 2 It is preferable to keep the thickness to about 0.3 g / m or less per side. 2 More than 1.5g / m 2It is even more preferable that the adhesion amount of the insulating coating is set to be as follows. By forming the insulating coating so as to achieve such an adhesion amount, it is possible to maintain excellent uniformity. When the adhesion amount of the insulating coating is measured afterwards, various known measurement methods can be used. The adhesion amount of the insulating coating can be calculated, for example, by immersing the non-oriented electrical steel sheet on which the insulating coating has been formed in a hot alkaline solution to remove only the insulating coating, and then calculating it from the difference in mass before and after removal of the insulating coating.

[0049] In addition, the surface of the base steel on which the insulating coating is formed may be subjected to any pretreatment before the treatment liquid is applied, such as a degreasing treatment with an alkali or an acid pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid, or the like, or the surface may be left as it is after finish annealing without being subjected to these pretreatments.

[0050] By going through the steps as described above, the non-oriented electrical steel sheet according to this embodiment can be manufactured.

[0051] One embodiment of the present invention is a non-oriented electrical steel sheet having the following configuration.

[0052] The steel sheet contains, by mass%, C: more than 0% to 0.0050%, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% to less than 0.030%, S: more than 0% to 0.0050%, Sol.Al: more than 0% to 0.0040%, N: more than 0% to 0.0040%, Cu: 0.00% to 1.0%, Sn: 0.000% to 0.10%, Sb: 0.000% to 0.10%, Ca: 0.0000% to 0.0050%, and the balance is Fe and impurities. 2 and Mn precipitated 2 SiO 4 0.000001 pieces / μm 2 More than 10.000 pieces / μm 2 A non-oriented electrical steel sheet comprising:

[0053] The non-oriented electrical steel sheet according to this embodiment will be specifically described below.

[0054] <Steel plate composition> The non-oriented electrical steel sheet according to this embodiment can be manufactured by the above-mentioned manufacturing method, and its chemical composition corresponds to the chemical composition of the steel billet (slab) of the non-oriented electrical steel sheet used in the manufacturing method.

[0055] <SiO 2 and Mn 2 SiO 4 Complex precipitates with The non-oriented electrical steel sheet according to the present embodiment has a surface layer of a base steel sheet containing SiO 2 and Mn precipitated 2 SiO 4 0.000001 pieces / μm 2 More than 10.000 pieces / μm 2 Contains the following:

[0056] SiO 2 This is due to the internal oxidation of Si in the steel sheet composition. 2 SiO 4 This indicates that part of the Mn segregated layer formed on the surface of the steel sheet, which originates from Mn in the pickling solution, is converted into SiO 2 Therefore, this SiO 2 and Mn precipitated 2 SiO 4 As shown in the schematic diagram of Figure 2, the composite precipitates are formed in the surface layer of the steel sheet base material. The surface layer of the steel sheet refers to a region extending from the interface between the steel sheet base material (base metal) and the insulating coating to a depth of 1 μm toward the inside of the steel sheet. The composite precipitates are spherical SiO 2 The surrounding area is Mn 2 SiO 4 It is a structure surrounded by (Core / Shell structure).

[0057] Tracing the origin of the above-mentioned composite precipitates, the composite precipitates confirmed in the surface layer of the finished non-oriented electrical steel sheet are evidence of the presence of a Mn segregated layer on the steel sheet surface after pickling. As described above, the Mn segregated layer after pickling is a tight coating, which prevents the formation of precipitates that deteriorate the magnetic properties during final annealing, thereby providing good magnetic properties. Therefore, SiO 2 and Mn precipitated 2 SiO 4 By observing the number density of the particles, it is possible to determine whether the above-mentioned effect is present. 2 and Mn precipitated 2 SiO 4 0.000001 pieces / μm 2 On the other hand, if the composite precipitates are less than 10,000 particles / μm 2 If the number of complex precipitates exceeds this limit, the effect of the complex precipitates will saturate and the magnetic properties may deteriorate. Therefore, the upper limit of the number density of complex precipitates is 10,000 particles / μm 2 The number density of the composite precipitates is preferably 0.000005 particles / μm 2 More than 1.000 pieces / μm 2 Less than or equal to 0.000010 particles / μm 2 More than 0.100 pieces / μm 2 The following is the result.

[0058] Here, SiO 2 and Mn 2 SiO 4 The number density of the composite precipitates with can be controlled by appropriately adjusting the component composition of the steel billet and the pickling conditions when producing the non-oriented electrical steel sheet according to this embodiment.

[0059] The precipitates present in the surface layer of the steel sheet can be verified by using the following measurement method. That is, in a cross section (L cross section) parallel to the rolling direction of a product sheet (finish annealed sheet) that has been subjected to Focused Ion Beam (FIB) processing, morphological observation and dimensional measurement are performed using a transmission electron microscope (TEM) in accordance with known methods, and composition analysis or crystal structure analysis by electron beam diffraction is performed using an energy dispersive X-ray analyzer (EDS) attached to the TEM, thereby enabling the evaluation of the precipitates present in the surface layer of the base steel sheet.

[0060] In addition, the SiO 2 and Mn 2 SiO 4 The number of composite precipitates with ZnO per a given area can be measured as follows. That is, during the above TEM observation, 2 The number of complex precipitates in any visual field having an area of ​​1 mm or more is counted. 2 The number of composite precipitates per unit area may be taken as the number of composite precipitates per unit area.

[0061] In EDS analysis of the precipitate, SiO 2 Part and Mn 2 SiO 4 The element contents obtained by EDS analysis are different between the SiO 2 The part may be a precipitate in which the peak height of the Si Kα ray and the peak height of the Mn Kα ray of the EDS are 1.0 times or more and 0.5 times or less than the peak height of the O Kα ray, respectively. 2 Since the Mn portion is amorphous, it is not possible to obtain an electron diffraction pattern, so a more accurate analysis can be performed by combining EDS and electron diffraction patterns. 2 SiO 4 The part has a crystal structure. By comparing the electron diffraction pattern with the JCPDS card, Mn 2 SiO 4 For example, JCPDS No. 35-048 can be used. 2 SiO 4When EDS analysis is performed on this material, an EDS spectrum is obtained in which the peak heights of Si Kα radiation and Mn Kα radiation are 0.5 times or more and 1.0 times or more, respectively, the peak height of O Kα radiation.

[0062] <About the insulation coating> Next, a brief description will be given of the insulating coating that the non-oriented electrical steel sheet according to this embodiment preferably has.

[0063] Here, the insulating coating according to this embodiment can be obtained by the insulating coating formation step of the above-mentioned method for producing a non-oriented electrical steel sheet. In order to improve the magnetic properties of non-oriented electrical steel sheets, it is important to reduce iron loss, which is composed of eddy current loss and hysteresis loss. By providing an insulating coating on the surface of the steel sheet base material, it is possible to suppress the conduction between the laminated electrical steel sheets forming the iron core and reduce the eddy current loss of the iron core, thereby making it possible to further improve the practical magnetic properties of the non-oriented electrical steel sheet.

[0064] <Method of measuring the magnetic properties of non-oriented electrical steel sheets> The non-oriented electrical steel sheet according to the present embodiment has the above-mentioned structure and exhibits excellent magnetic properties. Here, the various magnetic properties exhibited by the non-oriented electrical steel sheet according to the present embodiment can be measured by the Epstein method defined in JIS C2550. EXAMPLES

[0065] The non-oriented electrical steel sheet according to the present invention will be specifically described below with reference to examples and comparative examples. Note that the examples shown below are merely examples of the non-oriented electrical steel sheet according to the present invention, and the non-oriented electrical steel sheet according to the present invention is not limited to the examples below.

[0066] Example 1 A steel slab containing the composition shown in Table 1, with the balance being Fe and impurities, was heated to 1150°C and then hot-rolled to a thickness of 2.0 mm. Then, the hot-rolled sheets of test numbers 1 to 14 and 27 to 34 were subjected to continuous annealing-type hot-rolled sheet annealing at 1000°C for 40 seconds. The hot-rolled sheets of test numbers 15 to 26 were not subjected to hot-rolled sheet annealing. Next, the hot-rolled sheets and the hot-rolled sheet annealed sheets were immersed in an 80°C pickling solution (pH<1) containing 0.25±0.05 g / L of Mn for 30 seconds. Then, the sheets were cold-rolled to a thickness of 0.25 mm and finish-annealed at 1000°C for 15 seconds. Then, a solution containing an emulsion of acrylic resin and mainly composed of metal phosphate was applied and baked on both sides of the steel sheet to form a composite insulating coating, thereby producing a non-oriented electrical steel sheet. Here, the temperature rise rate from 500 to 800° C. in the temperature rise step of the above-mentioned finish annealing was 400° C. / s, and the atmospheric dew point was −30° C. The oxygen potential at the soaking annealing temperature was 0.01. In Table 1 below, "Tr" indicates that the corresponding element was not added intentionally. After that, the magnetic flux density B of each non-oriented electrical steel sheet was measured by the Epstein method specified in JIS C2550. 50 and iron loss W 10 / 400 The results are shown in Table 1 below. In addition, the cross section of the obtained non-oriented electrical steel sheet was observed by a transmission electron microscope (TEM), and 10 fields of view were measured at a magnification of 10,000. 2 SiO 4 and SiO 2 The average number density of the composite precipitates was counted. The results are shown in Table 1. In the evaluation column, iron loss of 11.5 or less is categorized as VG (Very Good), iron loss of 11.5 or more and 12.5 or less is G (Good), iron loss of 12.5 or more and 13.0 or less is F (Fine), and iron loss of 13.0 or more or which could not be rated due to breakage or other reasons is NG (Not Good).

[0067] [Table 1]

[0068] Example 2 The steel slabs shown in Table 1, the balance of which is Fe and impurities, were heated to 1160°C, and then hot-rolled to a thickness of 2.0 mm. Then, the hot-rolled sheets of test numbers A1 to 15 and a1 to 2 were annealed at 1000°C for 40 seconds by continuous annealing. The hot-rolled sheets of test numbers A16 to A20 were not annealed. Next, the hot-rolled sheets and the hot-rolled annealed sheets were pickled under the conditions shown in Table 2. Then, the sheets were cold-rolled to a thickness of 0.25 mm, and were finish-annealed for 15 seconds under the conditions shown in Table 2. Then, a solution mainly containing a metal phosphate and an acrylic resin emulsion was applied and baked on both sides of the steel sheet to form a composite insulating coating, thereby producing a non-oriented electrical steel sheet. Then, the magnetic flux density B of each of the produced non-oriented electrical steel sheets was measured by the Epstein method specified in JIS C2550. 50 and iron loss W 10 / 400 The results are shown in Table 2 below. In addition, the cross section of the obtained non-oriented electrical steel sheet was observed by a transmission electron microscope (TEM), and 10 fields of view were measured at a magnification of 10,000. 2 SiO 4 and SiO 2 The average number density of the composite precipitates was counted. The results are shown in Table 2 below. In the evaluation column, as in Table 1, iron loss of 11.5 or less is categorized as VG (Very Good), between 11.5 and 12.5 as G (Good), between 12.5 and 13.0 as F (Fine), and over 13.0 or less or unable to be rated due to breakage or other reasons as NG (Not Good).

[0069] [Table 2]

Claims

1. The steel sheet contains, by mass%, C: more than 0% and not more than 0.0050%, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% and less than 0.030%, S: more than 0% and not more than 0.0050%, Sol. Al: more than 0% and not more than 0.0040%, N: more than 0% and not more than 0.0040%, Cu: 0.00% to 1.0%, Sn: 0.000% to 0.10%, Sb: 0.000% to 0.10%, Ca: 0.0000% to 0.0050%, and the balance being Fe and impurities. ２ and Mn precipitated ２ SiO ４ 0.000001 pieces / μm ２ Above, 10,000 pieces / μm ２ A non-oriented electrical steel sheet comprising:

2. A method for producing the non-oriented electrical steel sheet according to claim 1, comprising: The present invention relates to a hot rolling process in which a steel slab containing, by mass%, C: more than 0% to 0.0050%, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% to less than 0.030%, S: more than 0% to 0.0050%, Sol.Al: more than 0% to 0.0040%, N: more than 0% to 0.0040%, Ca: 0.0000% to 0.0050%, and the balance being Fe and impurities is heated and then hot rolled to obtain a hot rolled steel sheet, a hot rolled sheet annealing process optionally annealing the hot rolled sheet, a pickling process pickling the hot rolled sheet or the hot rolled sheet annealed sheet, and a single cold rolling or multiple cold rollings with intermediate annealing therebetween after the pickling. a finish annealing process for subjecting the cold-rolled steel sheet to finish annealing; and an insulating coating process for providing an insulating coating, wherein the pickling solution has a liquid temperature of 15°C or higher and 100°C or lower, the steel sheet is immersed in the pickling solution for 5 seconds or higher and 200 seconds or lower, the pH of the pickling solution is -1.5 or higher and lower than 7, and the pickling solution contains Mn in an amount of 0.01 g / L or higher and 2.00 g / L or lower.

3. The method for producing a non-oriented electrical steel sheet according to claim 2, characterized in that the steel slab contains, by mass%, REM: 0.0001 to 0.0100%.

4. The method for producing a non-oriented electrical steel sheet according to claim 3, wherein the pickling solution contains Cu and Mn in a total amount of 0.01 g / L or more and 5.00 g / L or less.

5. The method for producing a non-oriented electrical steel sheet according to claim 3 or 4, characterized in that the final annealing is carried out at a soaking annealing temperature of 800°C or higher, and the heating rate from 500 to 800°C in the heating step is 100°C / sec to 2000°C / sec.

6. The method for producing a non-oriented electrical steel sheet according to any one of claims 3 to 5, characterized in that the final annealing is performed at a soaking annealing temperature of 800°C or higher, and the atmospheric dew point at 500 to 800°C in the temperature increasing step is set to -50°C or higher and 10°C or lower.

7. The method for producing a non-oriented electrical steel sheet according to any one of claims 3 to 6, characterized in that the final annealing is performed at a soaking annealing temperature of 800°C or higher, and an oxygen potential at the soaking annealing temperature of the final annealing is set to 0.2 or lower.

8. The method for producing a non-oriented electrical steel sheet according to any one of claims 3 to 7, wherein the steel slab further contains, in mass%, at least one selected from Sn: 0.005% to 0.10% and Sb: 0.005% to 0.10% in place of a part of the remaining Fe.

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