Non-oriented electrical steel sheet and its manufacturing method

Abstract

Provided is a nonoriented electromagnetic steel sheet that achieves both fine magnetic properties and punch-out workability. Further, proposed is a method for manufacturing the nonoriented electromagnetic steel sheet. This nonoriented electromagnetic steel sheet has a component composition containing, in mass%, not more than 0.0050% of C, 2.0-5.0% of Si, 0.2-1.8% of Mn, not more than 0.020% of P, not more than 0.0050% of S, 0.25-2.00% of Al, more than 0.0030% but not more than 0.0150% of N, not more than 0.0050% of O, and 0.01-0.10% of one of or the total of the two of Sn and Sb, the remaining portion being Fe and unavoidable impurities. The number of AlN particles having a particle size not less than 0.8 μm existing in a sheet thickness cross section of the steel sheet in the rolling direction is 10 particles or more per 1 mm2. In this method for manufacturing a nonoriented electromagnetic steel sheet, the heating of a slab is performed using a heat initiation temperature of 300°C or higher and a heating temperature of 1100-1300°C. The annealing temperature of a hot-rolled sheet is set to 800-950°C and the annealing temperature for the finish annealing is set to 850-1050°C.

Description

[Technical Field]

[0001] The present invention relates to a non-oriented electrical steel sheet having excellent properties of cut surfaces after punching, and a method for producing the same. [Background technology]

[0002] In recent years, the need for energy conservation has increased, and there is a strong demand for higher efficiency in electrical equipment. As a result, there is a strong demand for improved iron loss characteristics in non-oriented electrical steel sheets, which are widely used as iron core materials in electrical equipment. To address this, iron loss has been improved by adding elements such as Si and Al that increase resistivity, or by reducing the sheet thickness.

[0003] On the other hand, when non-oriented electrical steel sheets are used as the iron core material for motors, etc., the iron core is generally made by punching out steel sheets in the shape of the iron core from the electrical steel sheet and laminating these. However, this method has the problem that the magnetic properties of the iron core deteriorate due to distortion introduced by the punching process and changes in the shape of the cut surface after punching, such as sagging and burrs.

[0004] For example, Patent Document 1 discloses a non-oriented electrical steel containing, by mass%, 1.5% or less Si, 0.4% to 1.5% Mn, 0.01% to 0.04% sol.Al, 0.0015% to 0.0015% Ti, 0.0030% to 0.0030% N, 0.0010% to 0.0040% S, and B with a B / N ratio of 0.5 to 1.5, with the remainder being Fe and unavoidable impurities, and in which 10% or more of the Mn-containing sulfides are precipitated in combination with B precipitates. This technology claims that both punchability and magnetic properties are achieved when the grain size is 30 μm or less.

[0005] Patent Document 2 discloses a non-oriented electrical steel that has excellent magnetic properties and punching workability, and that contains, by mass%, C: 0.003% or less, Si: 1.0% to 3.0%, Al: 0.1% to 3.0%, and Mn: 0.1% to 1.0%, wherein the contents of Al and Si satisfy the relationship 0.2≦Al / (Si+Al)≦0.6, with the balance being Fe and unavoidable impurities, and that has a yield ratio expressed as (yield strength / tensile strength) of 0.6 or more and a Vickers hardness of 200 or less. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2005 / 100627 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-214758 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technology disclosed in Patent Document 1 is intended for products with low-grade magnetic properties, with an Si content of 1.5% or less, and cannot be applied to high-grade products with a high Si content. Furthermore, the technology disclosed in Patent Document 2 requires the Vickers hardness of the steel sheet product to be 200 or less, but since Si is an element that increases hardness, the Si content is limited. Therefore, the above-mentioned conventional technology has the problem of being unable to obtain good magnetic properties.

[0008] In view of the above-mentioned problems of the prior art, the present invention aims to provide a non-oriented electrical steel sheet that combines good magnetic properties with punching workability, and to propose an advantageous method for producing the same. [Means for solving the problem]

[0009] To solve the above problems, the inventors conducted extensive research into the effects on magnetic properties of the steel sheet's chemical composition, manufacturing method, and the ratio of sheared surfaces to fractured surfaces on the cut surface after punching. As a result, they discovered that increasing the content of N, which has traditionally been thought to deteriorate magnetic properties, can increase the ratio of sheared surfaces on the cut surface after punching, thereby suppressing deterioration of magnetic properties, and developed the present invention.

[0010] Based on the above findings, the present invention is configured as follows. [1]In mass%, C: 0.0050% or less, Si: 2.0~5.0%, Mn: 0.2~1.8%, P: 0.020% or less, S: 0.0050% or less, Al: 0.25~2.00% N: more than 0.0030% and not more than 0.0150%, O: not more than 0.0050%, one or both of Sn and Sb: 0.01 to 0.10% in total, with the balance being Fe and unavoidable impurities. 2 It is a non-oriented electrical steel sheet with 10 or more grains per square inch. [2] In the above [1], the steel sheet is a non-oriented electrical steel sheet containing, in addition to the above chemical composition, at least one component selected from the following groups A to I: Note In mass%, Group A: one or more selected from Ca, Mg, and REM: 0.0010 to 0.0080% in total Group B: one or more selected from Ti, Nb, and V: 0.0005 to 0.0030% in total C group: one or more selected from Cr, Mo, Cu, and Ni: 0.005 to 0.40% in total D group: one or more selected from Co, W, and Ta: 0.0005 to 0.0200% in total ·E group; B:0.0003~0.0040% F group: one or more selected from Ge and Ga: 0.0005 to 0.0100% in total Group G: one or more selected from Zn and As: 0.001 to 0.010% in total ·Group I; Pb:0.0001~0.0015% [3] In the above [1] or [2], the non-oriented electrical steel sheet has a shear surface ratio of 60% or more in the cut surface punched from the steel sheet. Here, the shear surface ratio (%) refers to the value of (area of ​​shear surface) / (area of ​​shear surface+area of ​​fracture surface)×100. [4] A steel slab having a composition containing, by mass%, C: 0.0050% or less, Si: 2.0 to 5.0%, Mn: 0.2 to 1.8%, P: 0.020% or less, S: 0.0050% or less, Al: 0.25 to 2.00%, N: more than 0.0030% and 0.0150% or less, O: 0.0050% or less, one or two of Sn and Sb: 0.01 to 0.10% in total, and the balance being Fe and unavoidable impurities, is heated and hot-rolled to form a hot-rolled sheet, A method for producing a non-oriented electrical steel sheet includes the steps of subjecting a hot-rolled sheet to hot-rolled sheet annealing, followed by cold rolling once or by cold rolling two or more times with intermediate annealing in between to form a cold-rolled sheet, and then subjecting the cold-rolled sheet to finish annealing, wherein the slab is heated at a heating start temperature of 300°C or higher and a heating temperature of 1100 to 1300°C, the hot-rolled sheet is annealed at a temperature of 800 to 950°C, and the cold-rolled sheet is finish annealed at a temperature of 850 to 1050°C. [5] In the above [4], the method for producing a non-oriented electrical steel sheet is such that the steel slab further contains, in addition to the above chemical composition, at least one component selected from the following groups A to I: Note In mass%, Group A: one or more selected from Ca, Mg, and REM: 0.0010 to 0.0080% in total Group B: one or more selected from Ti, Nb, and V: 0.0005 to 0.0030% in total C group: one or more selected from Cr, Mo, Cu, and Ni: 0.005 to 0.40% in total D group: one or more selected from Co, W, and Ta: 0.0005 to 0.0200% in total ·E group; B:0.0003~0.0040% F group: one or more selected from Ge and Ga: 0.0005 to 0.0100% in total Group G: one or more selected from Zn and As: 0.001 to 0.010% in total ·Group I; Pb:0.0001~0.0015% [Effects of the Invention]

[0011] According to the present invention, it is possible to produce a non-oriented electrical steel sheet that has both good magnetic properties and punching workability, and therefore it is possible to provide a material that is suitable for manufacturing motors that use iron cores produced by punching. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a sheared end portion. [Figure 2] 1 is a graph showing the relationship between the number density of AlN particles and the shear plane ratio. [Figure 3] 1 is a graph showing the relationship between the shear surface ratio and iron loss. DETAILED DESCRIPTION OF THE INVENTION

[0013] The inventors, assuming the manufacture of motors by punching non-oriented electrical steel sheets, conducted experiments to investigate the influence of AlN precipitates on the characteristics of the cut surface after punching, and the influence of the characteristics of the cut surface on the magnetic properties. Specifically, first, test specimens were prepared in which the N content in the material was varied to vary the size and number density of AlN precipitate particles in the steel sheet. Next, the effects of the size and number density of AlN precipitate particles on the ratio of sheared surfaces in the punched cut surface were investigated, and the following experiments were conducted to investigate the effect of the ratio of sheared surfaces on the magnetic properties. Here, a schematic diagram of a punched cut surface S is shown in Figure 1. Generally, a punched shear surface S is composed of a sag 1, a shear surface 2, a fracture surface 3, and a burr 4. Sag 1 is the area of ​​small deformation from the top surface of a steel plate with thickness t to the top end of shear surface 2. Burr 4 is the area that protrudes downward from the bottom surface of a steel plate with thickness t. For normal electrical steel plate thicknesses, neither of these areas need to be taken into consideration when calculating the shear surface ratio, as they are sufficiently small compared to the shear surface and fracture surface. Therefore, the ratio of the shear plane 2 is calculated as the ratio of the area of ​​the shear plane 2 to the total area of ​​the shear plane 2 and the fracture plane 3.

[0014] Steel slabs were manufactured based on a chemical composition containing, by mass%, 0.0033% C, 2.8% Si, 0.30% Mn, 0.010% P, 0.003% S, 0.64% Al, 0.025% Sn, and 0.0013% O, with N added at various levels ranging from 0.0020 to 0.010%. The steel slabs were then heated starting at 500°C and heated to 1150°C, hot-rolled to a 1.8 mm thick hot-rolled sheet, and annealed at 930°C for 30 seconds. The hot-rolled and annealed sheet was then pickled and cold-rolled to a 0.25 mm thick cold-rolled sheet, which was then finish-annealed at 980°C for 15 seconds to produce a non-oriented electrical steel sheet.

[0015] To evaluate the punching workability and magnetic properties of the non-oriented electrical steel sheet thus obtained, test pieces of 280 mm long x 30 mm wide were punched from the L direction (rolling direction) and C direction (direction perpendicular to the rolling direction) of the steel sheet with a clearance of 5%. The iron loss W of these test pieces was measured in accordance with JIS C 2550-1. 15 / 50 was measured.

[0016] Furthermore, test pieces measuring 280 mm in length and 10 mm in width were taken from the L and C directions of the obtained non-oriented electrical steel sheets by punching, also with a clearance set to 5%. Next, the punched cut surfaces were observed under an optical microscope, and the ratios of the shear surfaces on the cut surfaces in the L and C directions were measured and the average values ​​were calculated.

[0017] In addition, test pieces were cut out from the obtained non-oriented electrical steel sheets, polished, and the cross section of the sheet thickness in the rolling direction was observed using FE-SEM. 2 The number of AlN particles with a particle size of 0.8 μm or more observed per unit area was measured. The reason for selecting 0.8 μm or more is that a prior investigation showed that particle sizes of 0.8 μm or more have an effect on fracture.

[0018] Figure 2 shows the effect of the number of coarse AlN particles (particle diameter 0.8 μm or more) on the shear surface ratio. In Figure 2, the AlN particles (particles / mm2) on the X axis are AlN particles with a particle diameter of 0.8 μm or more. From Figure 2, it can be seen that the number of coarse AlN particles is 1 mm 2 When the number of sheared surfaces is 10 or more per wire, the sheared surface ratio is 60% or more. Figure 3 shows the effect of the sheared surface ratio on iron loss. Figure 3 shows that when the sheared surface ratio is 60% or more, iron loss is improved.

[0019] From the above results, we discovered that the shear surface ratio on the punched cut surface S is a new evaluation factor for iron loss after punching, and that increasing this evaluation factor, the shear surface ratio, can suppress the deterioration of iron loss due to punching. We also discovered that an effective way to increase the shear surface ratio is to increase the number of coarse AlN precipitate particles with a particle size of 0.8 μm or more, and that an effective way to achieve this is to increase the amount of N in the steel, leading to the development of this invention.

[0020] <Non-oriented electrical steel sheet> The non-oriented electrical steel sheet according to this embodiment will be described. First, the reasons for limiting the chemical composition of the non-oriented electrical steel sheet will be explained. Note that "%" in the chemical composition means "% by mass" unless otherwise specified.

[0021] C: 0.0050% or less C is a harmful element that forms carbides and deteriorates iron loss. Therefore, the C content is set to 0.0050% or less. Preferably, the C content is 0.0035% or less, and more preferably, 0.0030% or less. There is no particular lower limit for the C content, but from the viewpoint of reducing the decarburization cost in the steelmaking process, it is preferably 0.0003% or more.

[0022] Si: 2.0 to 5.0% Si has the effect of increasing the resistivity of steel and reducing iron loss. To achieve this effect, the Si content is set to 2.0% or more. Preferably, the Si content is set to 2.8% or more. When applied to high-grade materials that require even lower iron loss, it is more preferable that the Si content be greater than 3.0%. On the other hand, if the Si content exceeds 5.0%, punching workability decreases and rolling becomes difficult. Therefore, the Si content is set to 5.0% or less. From the viewpoint of suppressing a decrease in magnetic flux density, the Si content is preferably set to 3.8% or less.

[0023] Mn: 0.2 to 1.8% Like Si, Mn is an element that is effective in reducing iron loss. Therefore, the Mn content is set to 0.2% or more. Preferably, the Mn content is 0.3% or more. On the other hand, if the Mn content exceeds 1.8%, the iron loss will deteriorate due to the precipitation of fine Mn carbides. Therefore, the Mn content is set to 1.8% or less.

[0024] P:0.020% or less P segregates at grain boundaries, embrittling the steel sheet and reducing punching workability and rollability. Therefore, the P content is set to 0.020% or less. Preferably, the P content is 0.015% or less, and more preferably, 0.010% or less. There is no particular lower limit for the P content, but from the viewpoint of reducing the cost of reducing P in the steelmaking process, it is preferably 0.003% or more.

[0025] S: 0.0050% or less S is a harmful element that impairs hot workability and forms fine sulfides, deteriorating iron loss. Therefore, the S content is set to 0.0050% or less. The S content is preferably 0.0030% or less. Less than 0.0020% is more preferable.

[0026] Al: 0.25 to 2.00% Like Si, Al has the effect of increasing the resistivity of steel sheet and reducing iron loss. Furthermore, in the present invention, Al combines with N to form coarse AlN, which are dispersed in the steel, thereby improving punching workability. Therefore, the Al content is set to 0.25% or more. Preferably, the Al content is set to 0.6% or more. On the other hand, excessive addition of Al generates a large amount of alumina, which reduces punching workability and induces surface defects. Therefore, the Al content is set to 2.00% or less. Preferably, the Al content is set to 1.80% or less.

[0027] N: Over 0.0030% and up to 0.0150% N forms AlN, which precipitates and disperses in steel, thereby improving punching workability. The larger the size and number of AlN particles, the greater the effect. Therefore, the N content is set to more than 0.0030%. Note that by increasing the size of AlN particles and dispersing a larger number of AlN particles, punching workability is further improved. Therefore, the N content is preferably more than 0.0050%, and more preferably more than 0.0080%. On the other hand, adding too much N may cause bubbles to form in the steel slab, which may reduce manufacturability. In addition, punching workability is reduced. Therefore, the N content is set to 0.0150% or less.

[0028] O: 0.0050% or less O forms oxides, inhibits grain growth, and deteriorates core loss. Therefore, the O content is set to 0.0050% or less, and preferably, the O content is set to 0.0030% or less.

[0029] Sn and Sb type 1 or 2: 0.01 to 0.10% in total Sn and Sb are elements effective in improving texture and magnetic properties. Therefore, the total content of Sn and Sb is set to 0.01% or more. However, even if one or both of Sn and Sb are added in excess, the above effects are saturated, so the total content of Sn and Sb is set to 0.10% or less.

[0030] The non-oriented electrical steel sheet according to the present invention preferably contains, in addition to the above-mentioned composition of the non-oriented electrical steel sheet, Fe and unavoidable impurities as the remainder, and in order to improve the magnetic properties, the non-oriented electrical steel sheet preferably further contains at least one group of elements selected from the following groups A to I:

[0031] Group A: 0.0010 to 0.0080% in total of one or more selected from Ca, Mg, and REM Ca, Mg, and REM have the effect of fixing S as sulfides and improving iron loss. In addition, since sulfides of Ca, Mg, and REM are formed at a higher temperature than MnS, the sulfide particles become coarse, which also has the effect of improving punching workability. Therefore, the total content of one or more of Ca, Mg, and REM is preferably 0.0010% or more. On the other hand, excessive Ca, Mg, and REM contents form inclusions, reducing manufacturability. Therefore, the total content of one or more of Ca, Mg, and REM is preferably 0.0080% or less. More preferably, the total content of one or more of Ca, Mg, and REM is 0.0050% or less.

[0032] B group: one or more selected from Ti, Nb and V, 0.0005 to 0.0030% in total Ti, Nb, and V form precipitates, which have the effect of improving punching workability by refining the structure and dispersing the precipitates. Therefore, the total content of one or more of Ti, Nb, and V is preferably 0.0005% or more. On the other hand, excessive Ti, Nb, and V content significantly inhibits grain growth and deteriorates iron loss. Therefore, the total content of one or more of Ti, Nb, and V is preferably 0.0030% or less.

[0033] C group: 0.005 to 0.40% in total of one or more selected from Cr, Mo, Cu, and Ni Cr, Mo, Cu, and Ni have the effect of increasing the resistivity of steel and improving iron loss. Therefore, the total content of one or more of Cr, Mo, Cu, and Ni is preferably 0.005% or more. On the other hand, excessive Cr, Mo, Cu, and Ni contents deteriorate the surface properties. Therefore, the total content of one or more of Cr, Mo, Cu, and Ni is preferably 0.40% or less.

[0034] D group: one or more selected from Co, W and Ta, 0.0005 to 0.0200% in total Co, W, and Ta form precipitates, which have the effect of improving punching workability by refining the structure and dispersing the precipitates. Therefore, the total content of one or more of Co, W, and Ta is preferably 0.0005% or more. More preferably, the total content of one or more of Co, W, and Ta is 0.0010% or more. On the other hand, excessive Co, W, and Ta content significantly inhibits grain growth and deteriorates iron loss. Therefore, the total content of one or more of Co, W, and Ta is preferably 0.0200% or less.

[0035] ·E group; B:0.0003~0.0040% B has the effect of refining the grain structure and improving punching workability. To obtain this effect, the B content is preferably 0.0003% or more. On the other hand, if the B content is excessive, not only will the above effect saturate, but excessive borides will be generated, deteriorating iron loss. Therefore, the B content is preferably 0.0040% or less.

[0036] F group: one or more selected from Ge and Ga, 0.0005 to 0.0100% in total Ge and Ga segregate on the steel sheet surface and at grain boundaries, suppressing oxidation and nitriding during annealing and thereby improving iron loss. To achieve this effect, it is preferable that the steel sheet contains at least one element selected from Ge and Ga in a total amount of 0.0005% or more. The Ge and Ga contents are more preferably 0.0008% or more. On the other hand, excessive Ge and Ga contents cause significant segregation and deteriorate punching workability. Therefore, the Ge and Ga contents are preferably 0.0100% or less.

[0037] G group: Zn, As, and one or more selected from 0.001 to 0.010% in total Zn and As have the effect of refining the grain structure and improving punching workability. To achieve this effect, it is preferable that the total content of one or more elements selected from Zn and As be 0.001% or more. On the other hand, if the Zn and As contents are excessive, the oxides become excessive and iron loss deteriorates. Therefore, it is preferable that the Zn and As contents be 0.010% or less.

[0038] ·Group I; Pb:0.0001~0.0015% Pb has the effect of refining the structure and improving punching workability. To obtain this effect, the Pb content is preferably 0.0001% or more. On the other hand, if the Pb content is excessive, the iron loss will deteriorate due to finely dispersed Pb particles, so the Pb content is preferably 0.0015% or less.

[0039] Next, the morphology of AlN particles present in the non-oriented electrical steel sheet according to this embodiment will be described. AlN particles with a particle diameter of 0.8 μm or more present in the plate thickness cross section in the rolling direction are 2 10 or more per prize The punching workability of steel sheets is largely dependent on the dispersion state of AlN particles in the steel sheet. Specifically, if the particle size of the AlN particles is small, it does not have a significant effect on the fracture behavior during punching. However, in the cross section of the thickness of non-oriented electrical steel sheets in the rolling direction, AlN particles with a particle size of 0.8 μm or more are dispersed within 1 mm. 2By dispersing 10 or more particles per mm, the ratio of sheared surfaces in the punched cut surface increases, improving punching workability. 2 More preferably, 18 or more per mm 2 20 or more per 1 mm. 2 There are 50 or fewer per item. If excessively coarse AlN particles exist, the number density of the AlN particles decreases, so AlN particles with particle diameters of 0.8 μm to 6.0 μm are formed within 1 mm 2 Preferably, there are 10 or more per unit.

[0040] The dispersion state of AlN is determined by, for example, observing the thickness cross section of the steel sheet in the rolling direction using FE-SEM-EDX or FE-EPMA, calculating the particle size from the square root of the product of the major axis and minor axis of the AlN particle, and measuring the number of AlN particles per unit area with a particle size of 0.8 μm or more.

[0041] Next, the magnetic properties and punching workability of the non-oriented electrical steel sheet according to this embodiment will be described.

[0042] Magnetic properties Evaluate the magnetic properties of the steel sheet after punching. For example, for a sheet thickness of 0.25 mm, the iron loss W 15 / 50 If the magnetic flux density is 2.40 W / kg or less, the magnetic properties are considered to be good and the material is considered to be effective in improving the efficiency of motors, etc.

[0043] Punching processability The punchability of a steel sheet is evaluated by the shear surface ratio of the punched cut surface S. When the shear surface ratio is 60% or more, good magnetic properties can be obtained even in the as-punched state. Here, the shear surface ratio (%) refers to the value of (area of ​​shear surface 2) / (area of ​​shear surface 2 + area of ​​fracture surface 3) × 100, as shown in Figure 1. We have newly discovered that in the punched cut surface S, the shear surface 2 and fracture surface 3 affect punching workability, and that the proportion of shear surface 2 in particular has a significant impact, so we have defined the shear surface ratio as above. The areas of the shear surface 2 and the fracture surface 3 are determined by observing the punched cut surface S with an optical microscope.

[0044] <Method of manufacturing non-oriented electrical steel sheets> Next, a method for manufacturing a non-oriented electrical steel sheet according to this embodiment will be described. Steel slab The composition of the steel slab used to manufacture the non-oriented electrical steel sheet of this embodiment is adjusted to fall within the above-mentioned range of composition. The method for producing the steel is not particularly limited and may be a known refining process using a converter, an electric furnace, a vacuum degasser, or the like. Furthermore, the steel slab is preferably produced by a continuous casting method, but may also be produced by an ingot casting-blooming rolling method or a thin slab continuous casting method. Furthermore, iron scrap or direct reduced iron may also be used as the raw material.

[0045] hot rolling Steel slab heating start temperature: 300°C or higher, heating temperature: 1100-1300°C Hot rolling is a process in which a steel slab having the above-mentioned chemical composition is reheated to a predetermined temperature and then hot-rolled to obtain a hot-rolled sheet of a predetermined thickness. However, if the manufactured steel slab is cooled to a low temperature below 300°C, the AlN in the slab becomes excessively coarse and the number of AlN particles decreases, making it impossible to obtain a sufficient number density in the product sheet. For this reason, it is necessary to maintain the surface temperature of the steel slab at 300°C or higher using a heat-retaining cover or the like, and to set the heating start temperature of the steel slab at 300°C or higher. From the viewpoint of increasing the number density of AlN, the heating start temperature of the steel slab is preferably 450°C or higher, more preferably 550°C or higher.

[0046] Furthermore, as described above, the AlN in the steel slab before heating has a large particle size and a small particle count. Therefore, it is necessary to partially melt the AlN and properly disperse the AlN during or after hot rolling. Therefore, the heating temperature of the steel slab is set to 1100°C or higher. To partially melt the AlN and sufficiently increase the number density of AlN, the heating temperature of the steel slab is preferably 1150°C or higher, more preferably 1220°C or higher. On the other hand, if the heating temperature of the steel slab is too high, excessive remelting of AlN occurs, resulting in fine precipitation of AlN during cooling after hot rolling, making it impossible to obtain large AlN particles in the product sheet. Therefore, the heating temperature of the steel slab is set to 1300°C or lower.

[0047] The time for which the steel slab is held at the above heating temperature is preferably 10 minutes or more, but is more preferably 15 minutes or more in order to make the temperature inside the steel slab more uniform.

[0048] Furthermore, the hot rolling following the slab heating may be carried out under ordinary known conditions.

[0049] The coiling temperature of the hot-rolled steel sheet is preferably 500°C or higher and 700°C or lower.

[0050] Hot-rolled sheet annealing Annealing temperature for hot-rolled sheets: 800-950°C Next, the hot-rolled steel sheet is subjected to hot-rolled sheet annealing to promote recrystallization and coarsening of the rolled structure of the hot-rolled sheet and to coarsen the AlN particles to an appropriate size in order to improve punching workability. For this reason, the annealing temperature of the hot-rolled sheet is set to 800°C or higher. The annealing temperature of the hot-rolled sheet is preferably 850°C or higher. On the other hand, if the annealing temperature of the hot-rolled sheet is too high, the AlN will partially melt, reducing the number of coarse AlN particles and degrading punching workability, so the annealing temperature of the hot-rolled sheet is set to 950°C or lower. The annealing temperature of the hot-rolled sheet is preferably 930°C or lower. The soaking time in the hot-rolled sheet annealing should be a time that allows the hot-rolled sheet to be uniformly heated, and is preferably 5 to 200 seconds.

[0051] Pickling Pickling is a process in which a steel sheet after hot-rolled annealing is pickled to remove scale from the steel sheet. The pickling conditions may be any conditions that remove scale to an extent that allows for cold rolling in the subsequent process, and conventional pickling conditions using, for example, hydrochloric acid or sulfuric acid may be applied. In order to accelerate scale removal, cracks may be generated in the scale before or during the pickling process by a mechanical method such as shot blasting or light reduction rolling.

[0052] cold rolling Cold rolling is a process in which a hot-rolled annealed sheet that has been pickled is cold-rolled to a product sheet thickness (final sheet thickness). There are no particular limitations on the cold rolling as long as the final sheet thickness can be achieved. However, if the reduction in cold rolling is too low, the strength of the steel sheet after finish annealing may be significantly reduced, so the reduction in cold rolling is preferably 50% or more, and more preferably 70% or more. Furthermore, cold rolling is not limited to one pass, and two or more passes with intermediate annealing in between may be performed as needed. The intermediate annealing conditions in this case may also be commonly used conditions and are not particularly limited.

[0053] Finishing annealing Finishing annealing temperature: 850~1050℃ Finish annealing of cold-rolled sheets is a process in which the cold-rolled sheets, which have been cold-rolled to their final thickness, are annealed to impart desired magnetic and strength properties. The finish annealing temperature of cold-rolled sheets is 850°C or higher to sufficiently eliminate the strain introduced by cold rolling through recrystallization and obtain good magnetic properties. Furthermore, to obtain good magnetic properties, the finish annealing temperature of cold-rolled sheets is preferably 880°C or higher. On the other hand, if the finish annealing temperature of cold-rolled sheets is too high, the recrystallized structure becomes too coarse, resulting in a decrease in magnetic properties. Therefore, the finish annealing temperature of cold-rolled sheets is 1050°C or lower. Preferably, the finish annealing temperature of cold-rolled sheets is 1030°C or lower.

[0054] The steel sheet that has been subjected to the above-mentioned finish annealing is then coated with an insulating coating as necessary to obtain a finished sheet. The insulating coating may be inorganic, organic, or a mixture of inorganic and organic, and there is no particular limitation. [Example]

[0055] Steel having the chemical composition shown in Table 1 was melted using a conventional refining process and then formed into a slab using a continuous casting method. The slab was then heated in a gas furnace to a temperature of 1120°C for 45 minutes, and then hot-rolled, consisting of rough rolling and finish rolling, to produce a hot-rolled sheet with a thickness of 1.8 mm. This hot-rolled sheet was then subjected to hot-rolled sheet annealing, pickled, and cold-rolled to a cold-rolled sheet with a final thickness of 0.25 mm, and this cold-rolled sheet was then finish-annealed to produce the product sheet. The conditions for the hot rolling, hot-rolled sheet annealing, and cold-rolled sheet finish annealing are shown in Table 2.

[0056] Next, samples were taken from the product plates and subjected to the following evaluation tests. [Magnetic properties] Test pieces with a width of 30 mm and a length of 280 mm were taken from the L direction (rolling direction) and C direction (direction perpendicular to the rolling direction) of the above sample by punching with a clearance set to 5%, and the iron loss W 15 / 50 was measured. [Punching processability] The cross section of the above sample in the rolling direction was polished and observed using FE-SEM. Using the method described above, 1 mm of AlN particles with a particle diameter of 0.8 μm or more was identified. 2 The number of hits was measured. In addition, test pieces 280 mm long x 10 mm wide were punched from the L and C directions of the above sample using a punching process with a clearance set to 5%, and the cut surfaces in the L and C directions were observed using an optical microscope to measure the ratio of sheared surfaces and calculate the average value for the L and C directions. As a result, a sheared surface ratio of over 65% was designated as excellent punchability and marked with a "◎", a sheared surface ratio of 60% to 65% was designated as good punchability and marked with a "〇", and a sheared surface ratio of less than 60% was designated as poor punchability and marked with an "×".

[0057] The results of the above evaluation are shown in Table 2. From these results, it can be seen that the number density of AlN particles with a particle diameter of 0.8 μm or more is 10 particles / mm 2 As a result, the ratio of sheared surfaces was 60% or more, and the iron loss was 2.40 W / kg or less, providing good magnetic properties. Furthermore, the number density of AlN particles with a particle diameter of 0.8 μm or more was 18 particles / mm2 When the amount of the sheared surface was increased, the ratio of the sheared surface was higher than 65%, and the iron loss was 2.10 W / kg or less, indicating better magnetic properties.

[0058] [Table 1-1]

[0059] [Table 1-2]

[0060] [Table 2-1]

[0061] [Table 2-2] [Industrial Applicability]

[0062] The technique of the present invention can also be applied to shearing of a plurality of stacked electromagnetic steel sheets. [Explanation of symbols]

[0063] S: Sheared end 1: Who 2: Shear plane 3: Fractured surface 4: Return t: plate thickness

Claims

1. In mass%, C: 0.0050% or less, Si: 2.0 to 5.0%, Mn: 0.2-1.8%, P: 0.020% or less, S: 0.0050% or less, Al: 0.25-2.00%, N: more than 0.0030% and not more than 0.0150%; O: 0.0050% or less, One or both of Sn and Sb: containing 0.01 to 0.10% in total, The balance has a composition consisting of Fe and unavoidable impurities, The number of AlN particles with a particle diameter of 0.8 μm or more present in the plate thickness section in the rolling direction is 1 mm ２ 10 or more per one non-oriented electrical steel sheet.

2. 2. The non-oriented electrical steel sheet according to claim 1, wherein the steel sheet further contains, in addition to the above-mentioned chemical composition, at least one component selected from the following groups A to I: Note In mass%, Group A: one or more selected from Ca, Mg, and REM: 0.0010 to 0.0080% in total Group B: one or more selected from Ti, Nb, and V: 0.0005 to 0.0030% in total C group: one or more selected from Cr, Mo, Cu, and Ni: 0.005 to 0.40% in total Group D: one or more selected from Co, W, and Ta: 0.0005 to 0.0200% in total ・Group E; B: 0.0003-0.0040% F group: one or more selected from Ge and Ga: 0.0005 to 0.0100% in total Group G: one or more selected from Zn and As: 0.001 to 0.010% in total ・Group I; Pb: 0.0001-0.0015%

3. 3. The non-oriented electrical steel sheet according to claim 1, wherein a shear surface ratio in a cut surface punched from the steel sheet is 60% or more. Here, the shear surface ratio (%) refers to the value of (area of ​​shear surface) / (area of ​​shear surface+area of ​​fracture surface)×100.

4. In mass%, C: 0.0050% or less, Si: 2.0 to 5.0%, Mn: 0.2-1.8%, P: 0.020% or less, S: 0.0050% or less, Al: 0.25-2.00%, N: more than 0.0030% and not more than 0.0150%; O: 0.0050% or less, One or both of Sn and Sb: containing 0.01 to 0.10% in total, A method for producing a non-oriented electrical steel sheet, comprising the steps of heating a steel slab having a component composition with the balance being Fe and unavoidable impurities, hot-rolling the slab to form a hot-rolled sheet, annealing the hot-rolled sheet, and then cold-rolling the slab once or two or more times with intermediate annealing therebetween to form a cold-rolled sheet, and then finish-annealing the cold-rolled sheet, The slab is heated at a heating start temperature of 300°C or higher and a heating temperature of 1100 to 1300°C, The annealing temperature of the hot-rolled sheet is 800 to 950°C, The finish annealing temperature of the cold-rolled sheet is 850 to 1050 ° C., A method for producing a non-oriented electrical steel sheet, characterized in that the number of AlN particles having a particle diameter of 0.8 μm or more present in a cross section of the steel sheet in the rolling direction after finish annealing is 10 or more per mm 2 .

5. 5. The method for producing a non-oriented electrical steel sheet according to claim 4, wherein the steel slab further contains, in addition to the above-mentioned chemical composition, at least one component selected from the following groups A to I: Note In mass%, Group A: one or more selected from Ca, Mg, and REM: 0.0010 to 0.0080% in total Group B: one or more selected from Ti, Nb, and V: 0.0005 to 0.0030% in total C group: one or more selected from Cr, Mo, Cu, and Ni: 0.005 to 0.40% in total Group D: one or more selected from Co, W, and Ta: 0.0005 to 0.0200% in total ・Group E; B: 0.0003-0.0040% F group: one or more selected from Ge and Ga: 0.0005 to 0.0100% in total Group G: one or more selected from Zn and As: 0.001 to 0.010% in total ・Group I; Pb: 0.0001-0.0015%

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