JP2018178198A - Non-oriented electrical steel sheet and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-oriented electrical steel sheet having excellent magnetic characteristics and capable of suppressing the occurrence of sagging during punching. SOLUTION: The non-oriented electrical steel sheet according to the present invention has a chemical composition of mass%, C: 0.001 to 0.005%, Si: 3.0 to 5.0%, Mn: 1.0 to. It contains 3.0%, P: 0.02% or less, S: 0.005% or less, Al: 0.01% or less, and N: 0.001 to 0.005%, and the balance is Fe and impurities. Consists of. The ratio of the peak of Mn at 545 eV (Mn545) obtained by Auger electron spectroscopy to the peak of Fe at 700 eV (Fe700) at the grain boundary of the non-oriented electrical steel sheet is 0.05 to 0.15. [Selection diagram] Fig. 1

Description

  The present invention relates to a non-oriented electrical steel sheet and a method of manufacturing the same.

  Non-oriented electrical steel sheets are used as the material of the iron core of electrical equipment. In these electric devices, high energy efficiency, downsizing and high output are required. Therefore, low core loss and high magnetic density are required for non-oriented electrical steel sheets used as iron cores of electrical equipment.

Conventionally, in order to reduce the iron loss of non-oriented electrical steel sheets, the following technology is employed.
・ Si and Al etc. are contained in the non-oriented electrical steel sheet.
・ Control the grain size of non-oriented electrical steel sheet.
・ Reduce the thickness of non-oriented electrical steel sheets.

  On the other hand, in order to increase the magnetic density of non-oriented electrical steel sheets, control of texture is used. In texture control, the degree of integration of crystal planes including easy magnetization axes is increased in the steel plate plane. Specifically, the accumulation on the {111} plane not including the easy magnetization axis in the steel sheet plane is suppressed, and the accumulation on the {110} plane and the {100} plane including the easy magnetization axis is increased.

  In order to increase accumulation on {110} plane and {100} plane including easy magnetization axis, crystal rotation accompanying rolling deformation in hot rolling process and cold rolling process is controlled. In addition, in non-oriented electrical steel sheets, so-called "warm rolling" may be carried out, in particular, in which the temperature of cold rolling is carried out at a temperature higher than normal temperature (room temperature, about 25 ° C).

  In the manufacture of a non-oriented electrical steel sheet, in order to improve the magnetic properties, techniques for performing warm rolling after hot rolling are proposed in Patent Documents 1 to 5.

In the method of manufacturing a non-oriented electrical steel sheet disclosed in Patent Document 1, the Al content of the non-oriented electrical steel sheet is set to 0.02% or less by mass. In the final cold rolling step, at least one pass excluding the final pass is warm rolling at 100 to 300 ° C. Furthermore, the final pass is rolled at 100 ° C. or less at 10 to 30%. Patent Document 1 describes that this improves the iron loss W _15/50 of the non-oriented electrical steel sheet.

  In the method of manufacturing a non-oriented electrical steel sheet disclosed in Patent Document 2, Cu: 0.2% or more and 4.0% or less, Ni: 0.5% or more and 5.0% or less by mass% For the steel material, warm rolling at a rolling temperature of 100 to 300 ° C. or more is performed in one or more passes in the final cold rolling step, and the cumulative rolling reduction of warm rolling at that time is 45% or more. Patent Document 2 describes that a non-oriented electrical steel sheet excellent in the balance between strength and iron loss can be manufactured.

In the method of manufacturing a non-oriented electrical steel sheet disclosed in Patent Document 3, the hot rolling finish temperature is set to 700 ° C. or higher, which is _lower than the A _r3 transformation point. After descaling the produced hot-rolled steel sheet, the total strain applied in cold rolling is converted to logarithmic strain, and 50% or more of it is rolled at a warm temperature of 100 ° C. to 400 ° C., The final annealing is performed at 700 ° C. to 950 ° C. for 3 minutes or less. Patent Document 3 describes that a non-oriented electrical steel sheet having excellent magnetic properties can be manufactured by this.

  In warm rolling implemented by patent documents 1-3, rolling temperature is higher than cold rolling. Therefore, the crystal orientation may change due to a change in the sliding behavior of dislocations in the steel. It is considered that the interaction between the element contained in the steel and the dislocation depends on the temperature, and this temperature dependency changes the crystal orientation.

Patent Document 4 proposes a technique for controlling warm rolling conditions by paying attention to the interaction between such elements and dislocations. In the electromagnetic steel sheet manufacturing method disclosed in Patent Document 4, a steel having a solid solution (C + N) of 10 ppm or more is rolled at a reduction ratio of 20% or more in a temperature range of 200 to 500 ° C., and then recrystallization annealing is performed And develop the (110) [001] orientation component of the texture. In the method of manufacturing a non-oriented electrical steel sheet disclosed in Patent Document 5, P, S and Se in steel are suppressed to be P + 100 × S + 300 × Se ≦ 0.5, and hot-rolled sheet annealing is performed using Ac ₃ Do it in the temperature range above the point.

  Thus, warm rolling utilizes the change in crystal orientation due to the change in the sliding behavior of dislocations in steel, and aims at the formation of a favorable orientation for magnetic properties, particularly magnetic flux density. Applied to technology.

  On the other hand, non-oriented electrical steel sheets are processed into iron cores for motors by punching or the like. At this time, in the case of a hard non-oriented electrical steel sheet containing Si, the wear of the die due to punching becomes larger than that of a general processing steel sheet. When the number of times of punching increases and wear of the die increases, the punching accuracy of the steel plate decreases. Therefore, it is required to suppress the wear and tear of the mold due to punching, and there is also a demand for the development of a steel sheet which is less likely to lower the punching accuracy even if it is punched with the worn mold.

  Techniques relating to steel sheets having good punching workability are proposed in Patent Documents 6 to 14.

  In the non-oriented electrical steel sheets disclosed in Patent Documents 6 to 8, the punchability is enhanced by controlling the hardness and the yield stress. In the non-oriented electrical steel sheet disclosed in Patent Document 9, the crystal grain size of the ferrite phase is controlled to enhance the processability. In the techniques proposed in Patent Documents 6 to 9, the mechanical properties of the non-oriented electrical steel sheet are controlled to enhance the punching processability.

  In the non-oriented electrical steel sheet disclosed in Patent Document 10, the strength in the {011} <100> direction is controlled within a predetermined range, and in Patent Document 11, the influence of grain boundary strength is examined. Further, in the method of manufacturing a non-oriented electrical steel sheet disclosed in Patent Document 12, warm rolling improves punching workability in consideration of the influence of grain size control and crystal orientation control (magnetic flux density) on the occurrence of sagging. Is stated to be effective. In the non-oriented electrical steel sheet disclosed in Patent Documents 13 and 14, the punching processability is improved by adjusting the hardness and chemical composition of the surface layer of the steel sheet.

Patent No. 3888033 JP, 2005-120431, A Patent 2870818 gazette JP-A-58-84924 Unexamined-Japanese-Patent No. 2006-104530 Japanese Patent Application Publication No. 2005-60737 JP, 2005-105407, A JP-A-4-297557 JP, 2014-122405, A JP 2012-36474 A Unexamined-Japanese-Patent No. 2014-40622 JP 2003-243214 A Unexamined-Japanese-Patent No. 2-156091 JP-A-4-173940

  In the non-oriented electrical steel sheet of the above-mentioned reference, punching processability is examined. Recently, among the punching processability, particularly, the improvement of the limit number of times of punching is required.

  An object of the present invention is to provide a non-oriented electrical steel sheet capable of improving the limit number of times of punching.

  In the non-oriented electrical steel sheet according to the present invention, the chemical composition is, in mass%, C: 0.001 to 0.005%, Si: 3.0 to 5.0%, Mn: 1.0 to 3.0% P: 0.02% or less, S: 0.005% or less, Al: 0.01% or less, and N: 0.001 to 0.005%, with the balance being Fe and impurities. The ratio of the peak (grain boundary Mn 545) of Mn at 545 eV obtained by Auger electron spectroscopy at the grain boundaries of a non-oriented electrical steel sheet to the peak at 700 eV (grain boundary Fe 700) of Fe is 0.05 to 0.15. .

In the method of manufacturing a non-oriented electrical steel sheet according to the present invention, at least a hot rolling step of manufacturing a hot rolled steel sheet by performing hot rolling on a material having the above-mentioned chemical composition, and at least a hot rolled steel sheet. Warm rolling is performed in the first pass rolling, warm rolling or cold rolling is performed in the second and subsequent passes, and finishing is performed to produce a thin steel plate having a thickness of 0.10 to 0.50 mm. A rolling process and a finish annealing process for performing finish annealing on a thin steel sheet are provided. In the finish rolling step, when the rolling temperature is T (° C.), the strain rate is ε dot (s ⁻¹ ), and the rolling reduction is r (%) in the first pass rolling, formulas (1) to (5) Warm rolling is performed on the hot-rolled steel sheet under the conditions satisfying 3). Furthermore, the diameter of the work roll on which the first pass rolling is performed is set to 1000 mm or less. Furthermore, the cumulative rolling reduction in the finish rolling step is set to 75 to 95%.

  The non-oriented electrical steel sheet according to the present invention is excellent in punching workability.

FIG. 1 shows a peak at 545 eV of Mn (grain boundary Mn 545) and a peak at 700 eV of Fe (grain boundary Fe 700) obtained by Auger electron spectroscopy at grain boundaries in the non-oriented electrical steel sheet having the chemical composition of the present invention. It is a figure which shows the relationship between ratio (grain boundary Mn545 / grain boundary Fe700), and the limit frequency | count of punching. FIG. 2 is a view showing the relationship between the grain boundary Mn 545 / grain boundary Fe 700, the Mn content, and the limit number of times of punching in the non-oriented electrical steel sheet having the chemical composition of the present invention. FIG. 3 is a view showing the relationship among the grain boundary Mn 545 / grain boundary Fe 700, the degree of accumulation I (c), and the amount of sag in the non-oriented electrical steel sheet having the chemical composition of the present invention. FIG. 4 is a view showing the relationship between the grain boundary Mn 545 / grain boundary Fe 700, I (s) / I (c), and the punching dimensional difference in the non-oriented electrical steel sheet having the chemical composition of the present invention. FIG. 5 is a view showing the relationship between grain boundary Mn 545 / grain boundary Fe 700, strain rate and initial rolling temperature in the non-oriented electrical steel sheet having the chemical composition of the present invention. FIG. 6 is a cross-sectional view showing the end face shape of the test piece after the punching test in the example. FIG. 7 is a schematic view for explaining the method of measuring the dimensions of the test piece in the punching dimensional difference measurement test of the embodiment.

  Hereinafter, the present invention will be described in detail.

  The present inventors investigated and examined the characteristics of the non-oriented electrical steel sheet which affects the critical number of times of punching. As a result, the following findings were obtained.

  The ratio (grain boundary Mn 545 / grain boundary Fe 700) of the peak (grain boundary Mn 545) of Mn at 545 eV obtained by Auger electron spectroscopy at the grain boundary of a non-oriented electrical steel sheet to the peak (grain boundary Fe 700) of Fe , 0.05 to 0.15. This increases the number of critical punches.

  FIG. 1 shows the peak at 545 eV of Mn obtained by Auger electron spectroscopy (grain boundary Mn 545) at 700 eV of Fe (grain boundary Fe 700) at grain boundaries in a non-oriented electrical steel sheet satisfying the chemical composition of the present invention It is a figure which shows the relationship between ratio (grain boundary Mn545 / grain boundary Fe700), and the limit frequency | count of punching.

  Referring to FIG. 1, when the grain boundary Mn 545 / grain boundary Fe 700 is in the range of 0.05 to 0.15, the number of times of critical punching is remarkable as compared to the case where the grain boundary Mn 545 / grain boundary Fe 700 is in the other range. Is increasing.

  In addition, the increase in the Mn content of the steel plate basically reduces the limit number of times of punching. FIG. 2 is a view showing the relationship between the Mn content and the limit number of times of punching in a steel plate in which grain boundary Mn 545 / grain boundary Fe 700 has a specific value. Referring to FIG. 2, the critical number of times of punching increases with the increase of Mn545 / Fe700. However, when the grain boundary Mn 545 / grain boundary Fe 700 is constant, the number of critical punchings decreases due to the increase of the Mn content.

  From the above results, in the grain boundaries of non-oriented electrical steel sheets, the ratio (grain boundary Mn 545) of Mn at 545 eV obtained by Auger electron spectroscopy to the peak (grain boundary Fe 700) of Fe at 700 eV (grain boundary Mn 545 / The grain boundary Fe 700) is set to 0.05 to 0.15. In this case, the limit number of times of punching can be improved.

  By defining the grain boundary Mn 545 / grain boundary Fe 700 as described above, the mechanism for significantly increasing the number of critical punchings is not clear, but the following may be considered.

  Conventionally, it is known that the grain boundary strength decreases if an element such as P is segregated in the grain boundaries of the steel sheet. For example, Patent Document 8 discloses segregation of P and improvement in punching processability accordingly. On the other hand, in the steel of the present invention, the segregation of Mn at the grain boundaries strengthens the interaction between Fe and Mn at the grain boundaries, thereby reducing the grain boundary strength and making grain boundary fracture more likely to occur. As a result, it is considered that the limit number of times of punching increases. When the grain boundary Mn 545 / grain boundary Fe 700 does not satisfy the specified range, the interaction between Fe and Mn at the grain boundary remains weak. Therefore, the ratio of the Mn 545 to the peak at 545 eV of Mn obtained by Auger electron spectroscopy in the grain of the non-oriented electrical steel sheet (hereinafter referred to as intragranular Mn 545) (= granular Mn 545 / intragranular Mn 545) is appropriate Even if it does, an increase in the limit number of punchings can not be obtained.

  However, in general, when the Mn content is increased, the hardness of the steel plate is increased. Therefore, even if the Mn content is simply increased, the limit number of times of punching does not improve. In the present invention, as described later, Mn segregation to grain boundaries is promoted including manufacturing conditions. It is considered that Fe and Mn interact with each other at grain boundaries to exert an effect exceeding the influence of the decrease in the limit number of times of punching due to the increase in hardness of the steel sheet, and the number of times of limit punching in total increases.

  In addition, in order to segregate Mn at grain boundaries as in the steel sheet of the present invention, basically, it is necessary to increase the Mn content. As a result, low iron loss can also be achieved as a magnetic property.

  In order to increase the number of times of critical punching, it is preferable to make the average crystal grain of the non-oriented electrical steel sheet coarse. It is appropriate to consider this to be the effect of promoting Mn segregation to the grain boundaries, which is the feature of the present invention, by lowering the grain boundary density rather than simply increasing the grain size and lowering the hardness of the steel sheet. . In the steel sheet of the present invention, the ability to coarsen the average crystal grain size effectively acts on the reduction of iron loss of the steel of the present invention in combination with containing Mn at a high concentration.

The inventors examined an example of a manufacturing method for realizing the above-mentioned Mn segregation. As a result, when producing a non-oriented electrical steel sheet by rolling a hot rolled steel sheet, warm rolling is performed in at least the first pass rolling, and warm rolling or cold rolling is performed in the second and subsequent passes. Conduct (finish rolling process). Furthermore, in warm rolling in the first pass, when the rolling temperature is T (° C.), the strain rate is ε dot (s ⁻¹ ), and the rolling reduction is r (%), formulas (1) to (3) It has been found that the non-oriented electrical steel sheet having the above-described texture can be manufactured by carrying out rolling under the conditions satisfying the above and making the cumulative rolling reduction in the finish rolling step 75 to 95%.

  The non-oriented electrical steel sheet of the present invention completed based on the above findings has a chemical composition of, in mass%, C: 0.001 to 0.005%, Si: 3.0 to 5.0%, Mn: 1.0 to 3.0%, P: 0.02% or less, S: 0.005% or less, Al: 0.01% or less, and N: 0.001 to 0.005%, the balance Is composed of Fe and impurities. The ratio (grain boundary Mn 545 / grain boundary Fe 700) of the peak at 545 eV of Mn (grain boundary Mn 545) and the peak at 700 eV of Fe (grain boundary Mn 545 / grain boundary Fe 700) obtained by Auger electron spectroscopy in grain boundaries of non-oriented electrical steel sheets is It is 0.05-0.15.

  In the non-oriented electrical steel sheet described above, the peak at 545 eV of Mn obtained by Auger electron spectroscopy at the grain boundary (grain boundary Mn 545), and the peak at 545 eV of Mn obtained by Auger electron spectroscopy within the grain The ratio (intergranular Mn 545 / intragranular Mn 545) to () may be 2.0 to 10.0.

  In the non-oriented electrical steel sheet described above, when the thickness of the non-oriented electrical steel sheet is defined as t, the degree of integration of {100} <012> orientation at a depth of t / 2 from the surface of the non-oriented electrical steel sheet The ratio of the degree of integration I (s) of {100} <012> orientation to I (c) at a position t / 10 deep from the surface of the non-oriented electrical steel sheet where I (c) is 4.0 or more I (s) / I (c)) may be 0.8 to 1.2.

The above chemical composition further includes one or two selected from the group consisting of Ti: 0.01% or less, V: 0.01% or less, and Nb: 0.01% or less, instead of part of Fe. It may contain more than species. In this case, the chemical composition satisfies the formula (A).

  The above chemical composition is, in place of a part of Fe, Sn: 0.2% or less, Cu: 0.1% or less, Ni: 0.1% or less, Cr: 0.2% or less, and B: 0 It may contain one or more selected from the group consisting of .001% or less.

In the method of manufacturing a non-oriented electrical steel sheet according to the present invention, at least a hot rolling step of manufacturing a hot rolled steel sheet by performing hot rolling on a material having the above-mentioned chemical composition, and at least a hot rolled steel sheet. Warm rolling is performed in the first pass rolling, warm rolling or cold rolling is performed in the second and subsequent passes, and finishing is performed to produce a thin steel plate having a thickness of 0.10 to 0.50 mm. A rolling process and a finish annealing process for performing finish annealing on a thin steel sheet are provided. In the finish rolling step, when the rolling temperature is T (° C.), the strain rate is ε dot (s ⁻¹ ), and the rolling reduction is r (%) in the first pass rolling, formulas (1) to (5) Warm rolling is performed on the hot-rolled steel sheet under the conditions satisfying 3). Furthermore, the diameter of the work roll on which the first pass rolling is performed is set to 1000 mm or less. Furthermore, the cumulative rolling reduction in the finish rolling step is set to 75 to 95%.

  In the cold rolling, for example, the rolling temperature is set to 150 ° C. or less.

  In the finish rolling step, a tandem rolling mill may be used, each having a pair of work rolls and including a plurality of rolling stands arranged in a row. In this case, warm rolling is performed at least on the rolling stand for performing the first pass rolling, or on a rolling stand and a rolling stand arranged downstream of the rolling stand, and the rolling stand is arranged downstream of the warm rolling. It is carried out by cold rolling at the above-mentioned rolling stand.

  In the finish annealing step, the highest temperature may be 900 to 1200 ° C.

  Hereinafter, the non-oriented electrical steel sheet according to the present invention will be described in detail.

[Chemical composition]
The chemical composition of the non-oriented electrical steel sheet according to the present invention contains the following elements. In addition, "%" in the chemical composition of a non-oriented electrical steel sheet means mass% unless otherwise noted.

C: 0.001 to 0.005%
Carbon (C) is present as solid solution C in the steel and improves the texture due to dynamic strain aging during warm rolling. This increases the magnetic flux density of the non-oriented electrical steel sheet. If the C content is less than 0.001%, this effect can not be obtained. On the other hand, if the C content exceeds 0.005%, fine carbides are precipitated in the steel and the magnetic properties are degraded. Therefore, the C content is 0.001 to 0.005%. The lower limit of the C content is preferably 0.0015%, more preferably 0.002%. The upper limit of the C content is preferably 0.004%, more preferably 0.003%.

Si: 3.0 to 5.0%
Silicon (Si) increases the specific resistance of the steel plate and reduces the eddy current loss. Si further reduces the hysteresis loss. If the Si content is less than 3.0%, the above effect can not be obtained. If the Si content is less than 3.0%, phase transformation may occur during finish annealing, and the effects of the present invention may be impaired. On the other hand, if the Si content exceeds 5.0%, the rollability in warm rolling described later and the punching processability of the non-oriented electrical steel sheet decrease. Therefore, the Si content is 3.0 to 5.0%. The preferred lower limit of the Si content is 3.5%. The upper limit of the Si content is preferably 4.5%, more preferably 4.0%.

Mn: 1.0 to 3.0%
Manganese (Mn) increases the resistivity of the steel. Mn further coarsens sulfides and renders them harmless. In addition, segregation of Mn at grain boundaries can increase the limit number of times of punching. If the Mn content is less than 1.0%, these effects can not be obtained. On the other hand, if the Mn content exceeds 3.0%, the magnetic flux density of the steel decreases. Furthermore, phase transformation occurs during annealing, and the effect of the present invention is lost. Therefore, the Mn content is 1.0 to 3.0%. The preferable lower limit of the Mn content is 1.5%, more preferably 2.0%. The upper limit of the Mn content is preferably 2.8%, more preferably 2.5%.

P: 0.02% or less Phosphorus (P) is an impurity. P lowers the workability of the steel and can cause cracking in the steel sheet during cold rolling. Therefore, the P content is 0.02% or less. The P content is preferably as low as possible. The lower limit of the P content is not particularly limited. From the viewpoint of cost and productivity of dephosphorization, a preferable lower limit of P content is 0.01%.

S: 0.005% or less Sulfur (S) is an impurity. S generates MnS to increase iron loss. Therefore, the S content is 0.005% or less. The S content is preferably as low as possible. The lower limit of the S content is not particularly limited. From the viewpoint of the cost and productivity of desulfurization, the preferable lower limit of the S content is 0.001%.

Al: 0.01% or less Aluminum (Al) deoxidizes the steel. Al further coarsens nitrides to render them harmless. However, if the Al content exceeds 0.01%, grain boundary segregation of Mn is suppressed, and the effect of the present invention is lost. Therefore, the Al content is 0.01% or less.

N: 0.001 to 0.005%
Nitrogen (N), like C, is present as solid solution N in the steel, and improves texture by dynamic strain aging during warm rolling. This increases the magnetic flux density of the non-oriented electrical steel sheet. If the N content is less than 0.001%, this effect can not be obtained. On the other hand, if the N content exceeds 0.005%, fine AlN precipitates and the magnetic properties deteriorate. Therefore, the N content is 0.001 to 0.005%. The preferred lower limit of the N content is 0.0015%, and more preferably 0.002%. The upper limit of the N content is preferably 0.004%, more preferably 0.003%.

  The balance of the chemical composition of the non-oriented electrical steel sheet according to the present invention consists of Fe and impurities. Here, when the non-oriented electrical steel sheet is manufactured industrially, the impurities are mixed from ore as a raw material, scrap, or manufacturing environment. The content of these impurities is acceptable as long as the non-oriented electrical steel sheet of the present embodiment is not adversely affected.

[Arbitrary element]
The chemical composition of the non-oriented electrical steel sheet of the present invention may further contain one or more selected from the group consisting of Ti, V and Nb instead of part of Fe. When these elements are contained, the chemical composition satisfies the formula (A).
Here, the content (mass%) of the element in the non-oriented electrical steel sheet is substituted for the element symbol in the formula (A). In addition, "0" is substituted about the thing whose content of the corresponding element is less than a detection limit among the elemental symbols in Formula (A).

Ti: 0.01% or less V: 0.01% or less Nb: 0.01% or less Titanium (Ti), vanadium (V) and niobium (Nb) are optional elements. These elements form carbonitrides to fix C and N. If these carbonitrides exist before cold rolling, dynamic strain aging due to solid solution C and solid solution N can not be obtained. The Ti content is 0.01% or less, the V content is 0.01% or less, the Nb content is 0.01% or less, and the total content of Ti, V and Nb satisfies the formula (A). For example, dynamic strain aging by solid solution C and solid solution N can be used.

  The preferred lower limit of the Ti content is 0.005%. The preferable lower limit of V content is 0.005%. The preferred lower limit of the Nb content is 0.005%.

  In the present specification, when the Ti content is 0.004% or less, the Ti content is interpreted as the impurity level. Similarly, when the V content is 0.004% or less, the V content is interpreted as the impurity level. When the Nb content is 0.004% or less, the Nb content is interpreted as the impurity level.

  The chemical composition of the non-oriented electrical steel sheet of the present invention may further contain one or more selected from the group consisting of Sn, Cu, Ni, Cr and B in place of part of Fe. .

Sn: 0.2% or less Tin (Sn) is an optional element and may not be contained. When contained, Sn improves the texture of the steel sheet and increases the magnetic flux density. Sn further suppresses nitriding at the time of finish annealing and suppresses deterioration of the magnetic properties. On the other hand, if the Sn content exceeds 0.2%, the workability of the steel sheet may be reduced to cause cracks in the steel sheet during cold rolling. Therefore, the Sn content is 0.2% or less. The preferred lower limit of the Sn content is 0.01%, and more preferably 0.02%. The preferable upper limit of the Sn content is 0.15%, and more preferably 0.1%.

Cu: 0.1% or less Copper (Cu) is an optional element and may not be contained. If excessively contained, Cu lowers the saturation magnetic flux density, lowering the magnetic flux density B _50. Cu further forms CuS and degrades iron loss. Furthermore, when Cu is contained together with Ni, an internal oxide layer is easily formed on the surface of the steel sheet, and as a result, high frequency iron loss is deteriorated. Therefore, the Cu content is 0.1% or less. The lower limit of the Cu content is not particularly limited, but is preferably 0.01% or more from the viewpoint of being mixed from iron scrap.

Ni: 0.1% or less Nickel (Ni) is an optional element and may not be contained. When it is contained, Ni increases the magnetic flux density B ₅₀ and further enhances the steel plate strength. However, if the Ni content is too high, the raw material cost becomes high. When Ni is further contained together with Cu, an internal oxide layer is easily formed on the surface of the steel sheet, and as a result, high frequency iron loss is deteriorated. Therefore, the Ni content is 0.1% or less. The lower limit value of the Ni content is not particularly limited, but is preferably 0.01% or more from the viewpoint of the magnetic flux density B ₅₀ and the steel plate strength.

Cr: 0.2% or less Chromium (Cr) is an optional element and may not be contained. If excessively contained, Cr lowers the saturation magnetic flux density, thereby decreasing the magnetic flux density B _50. Therefore, the Cr content is 0.2% or less. The lower limit of the Cr content is not particularly limited, but is preferably 0.01% or more from the viewpoint of being mixed from iron scrap.

B: 0.001% or less Boron (B) is an optional element and may not be contained. If excessively contained, B lowers the saturation magnetic flux density, thereby decreasing the magnetic flux density B _50. Therefore, the B content is 0.001% or less. The lower limit value of the B content is not particularly limited, but is preferably 0.0001% or more from the viewpoint of being mixed from iron scrap.

[Auger electron spectroscopy peak]
In the grain boundaries of the non-oriented electrical steel sheet of the present invention, the ratio (grain boundary Mn 545) of Mn at 545 eV obtained by Auger electron spectroscopy to the peak at 700 eV of Fe (grain boundary Fe 700) (grain boundary Mn 545 / grain boundary Fe 700) is 0.05 to 0.15.

  In the non-oriented electrical steel sheet described above, the peak at 545 eV of Mn obtained by Auger electron spectroscopy at the grain boundary (grain boundary Mn 545), the peak at 545 eV of Mn obtained by Auger electron spectroscopy within the grain The ratio of the inner Mn 545) (grain boundary Mn 545 / intragranular Mn 545) is preferably 2.0 to 10.0.

  If the grain boundary Mn 545 / grain boundary Fe 700 is less than 0.05, grain boundary fracture due to Mn segregated in the grain boundary does not occur sufficiently. As a result, the number of critical punchings is reduced. On the other hand, if Mn 545 / Fe 700 exceeds 0.15, the brittleness of the steel plate is increased, and fracture tends to occur during handling of the steel plate. Therefore, the grain boundary Mn 545 / grain boundary Fe 700 is 0.05 to 0.15. The lower limit of grain boundary Mn 545 / grain boundary Fe 700 is preferably 0.07, and more preferably 0.09. The upper limit of grain boundary Mn 545 / grain boundary Fe 700 is preferably 0.14, and more preferably 0.13.

  If the grain boundary Mn 545 / grain boundary Fe 700 is out of the range, the effect of the invention can not be obtained even if the grain boundary Mn 545 / intragranular Mn 545 is 2.0 to 10.0.

[Method of measuring Auger electron spectroscopy peak]
Intergranular Mn 545, intragranular Mn 545, and intergranular Fe 700 are measured by the following method. The non-oriented electrical steel sheet is cut at a cross section perpendicular to the rolling direction, and a plurality of coarse sample pieces of 18 mm L × 4 mm W (L: length in the rolling direction, W: sheet width) are collected. The rough sample piece is cut at the center in the lengthwise direction to prepare a test piece for measuring an Auger electron spectral peak.

  The prepared test piece for measuring Auger electron spectroscopy peak is placed in an Auger electron spectroscopy device, the sample is cooled with liquid nitrogen, and the sample is broken. The intergranular fracture surface of the sample is found out, and analysis is made at 10 places using the amount of Mn and the amount of Fe at the grain interface as a standard. Then, at each measurement point, the ratio (grain boundary Mn 545 / grain boundary Fe 700) of the Mn peak “grain boundary Mn 545” at 545 eV to the Fe peak “grain boundary Fe 700” at 700 eV is determined, and the average value is calculated.

  Similarly, the fractured surface within the grain of the sample is found out, and analysis is made at 10 places using the amount of Mn in the grain as a standard. Then, at each measurement point, the ratio (grain boundary Mn 545 / intra-grain Mn 545) of the Mn peak “grain boundary Mn 545” at 545 eV to “in-grain Mn 545” is determined, and the average value is calculated.

[Group organization]
Preferably, when the thickness of the non-oriented electrical steel sheet of the present invention is defined as t (mm), the texture of the non-oriented electrical steel sheet has the following (feature I) and (feature II).
(I) In the texture at the t / 2 depth position (plate thickness central layer) from the steel sheet surface, the degree of integration I (c) of {100} <012> direction is 4.0 or more.
(II) The {100} <012> orientation density I (s) at the t / 10 depth position (surface layer) from the surface of the steel sheet {100} <012> at the t / 2 depth position from the surface The ratio (I (s) / I (c)) to the density I (c) of orientation is 0.8 to 1.2.

[I: Texture of central thickness layer]
If the degree of integration I (c) in the {100} <012> direction in the thickness center layer is 4.0 or more, the amount of sag decreases. The upper limit of the degree of accumulation I (c) is preferably 4.5, more preferably 5.0.

  FIG. 3 is a view showing the relationship between the degree of accumulation I (c), the grain boundary Mn 545 / grain boundary Fe 700, and the amount of sag. Referring to FIG. 3, when the degree of accumulation I (c) is less than 4.0 (indicated by x in the figure), the amount of sag does not change so much even if the grain boundary Mn 545 / grain boundary Fe 700 increases. On the other hand, when the degree of accumulation I (c) is 4.0 or more (○ in the drawing), the amount of sagging decreases with the increase of the grain boundary Mn 545 / grain boundary Fe 700. And if the degree of integration I (c) is 4.0 or more and the grain boundary Mn 545 / grain boundary Fe 700 is 0.05 to 0.15, the amount of sag is 15 μm or less.

[II: About the ratio of the degree of integration of the surface layer and the thickness center layer]
The ratio of the degree of integration of the surface layer and the thickness center layer in the {100} <012> orientation improves the punching dimensional accuracy at the time of punching. This effect is effectively obtained when I (s) / I (c) is 0.8 to 1.2. The preferred range of I (s) / I (c) is 0.85 to 1.15, and more preferably 0.9 to 1.1.

  FIG. 4 is a view showing the relationship between I (s) / I (c), grain boundary Mn 545 / grain boundary Fe 700, and a punching dimension difference. The smaller the punching dimensional difference, the higher the punching dimensional accuracy. Referring to FIG. 4, when I (s) / I (c) is 0.8 to 1.2 (○ in the figure), I (s) / I (c) is less than 0.8 ( The punching dimension difference is smaller than in the case where x marks in the drawing and I (s) / I (c) are larger than 1.2 (* marks in the drawing). And, when I (s) / I (c) is 0.8 to 1.2, and the grain boundary Mn 545 / grain boundary Fe 700 is 0.05 to 0.15, the punching dimension difference is 10 μm or less Thus, excellent punching dimensional accuracy can be obtained.

[Measuring method of density]
The degree of integration I (s) and the degree of integration I (c) can be measured by the following method. The non-oriented electrical steel sheet is cut at a cross section perpendicular to the rolling direction, and a plurality of rough sample pieces having a thickness t are collected. Chemical polishing is performed on the rough sample piece to prepare a test piece for I (s) measurement in which the plate thickness is reduced by t / 10 from the surface. In addition, chemical polishing is performed on the rough test specimen to prepare a test specimen for measurement of I (c) whose thickness is reduced by t / 2 from the surface.

A pole figure of {200}, {110} and {211} planes is measured by the X-ray diffractometer for the produced measurement test piece, and a crystal orientation distribution function ODF (Orientation Determination Function) is created. Do. The densities I (c) and I (s) are determined using the generated ODF. The {111} <112> orientation indicates an integration degree of φ ₁ = 55 ° and Φ = 30 ° in the φ ₂ = 45 ° cross section in the ODF. The {100} <012> orientation indicates an integration degree of φ ₁ = 20 ° and Φ = 0 ° in the φ ₂ = 45 ° cross section in the ODF.

[About average grain size]
In the present invention, the average crystal grain size is not particularly limited, but preferably 100 μm or more. In the steel sheet of the present invention, Mn is segregated at grain boundaries in the recrystallization and grain growth processes in the finish annealing step after finish rolling including warm rolling as described later. Therefore, as grain growth progresses, Mn segregation in grain boundaries tends to become stronger, and it is a preferable form to increase the average grain size. Generally from the viewpoint of punching processability, when the grain size is increased, the ductility of the steel plate is increased, resulting in deformation such as being stretched at the time of breaking of punching, which may cause generation of burrs and problems of shape accuracy is there. However, in the steel of the present invention, intergranular fracture easily occurs because of Mn segregation, and the fracture progresses rapidly from the intergranular fracture. Therefore, even if the crystal grain size is coarsened, the above problem hardly occurs. Furthermore, it is preferable to increase the particle size also from the viewpoint of reducing iron loss. Therefore, the preferable average grain size is 100 μm or more. A further preferable average grain size is 120 μm or more. The preferred average crystal grain size is 250 μm or less, more preferably 200 μm or less.

  The average grain size of the non-oriented electrical steel sheet can be measured by the following method. The metal structure in the cross section in the longitudinal direction and the thickness direction is photographed at six fields of view at 100 times to obtain a photographic image (7000 μm × 1000 μm) in total. A line is drawn in the longitudinal direction on the obtained photographic image, the number of intersections of grain boundaries is counted, and the length of the longitudinal line is divided by the number of intersections. The average grain size can be obtained by the above method.

[Method of manufacturing non-oriented electrical steel sheet]
An example of the manufacturing method of the non-oriented electrical steel sheet of the present invention will be described. The method for producing a non-oriented electrical steel sheet according to the present invention comprises warm rolling the step of hot rolling a slab to produce a hot rolled steel sheet (hot rolling step) and at least first pass rolling, 2 In warm rolling or cold rolling by rolling after the pass, and further, warm rolling in the first pass is performed under specific conditions to produce a thin steel plate (finish rolling step); And a step of performing finish annealing to recrystallize (finish annealing step). Each step will be described in detail below.

[Hot rolling process]
In the hot rolling step, the slab is hot rolled to produce a hot rolled steel sheet. The slab has the chemical composition described above. The slabs are manufactured in a known manner. For example, a molten metal having the above-described chemical composition is used to produce a slab by a continuous casting method. The melt having the above-described chemical composition may be used to produce an ingot by the ingot method, and the ingot may be rolled to produce a slab. Slab rolling may be performed on a slab manufactured by a continuous casting method.

  Hot rolling is performed on the prepared slab. The various conditions in hot rolling are not specifically limited. The slab heating temperature at the time of hot rolling is not particularly limited. Preferably, the slab heating temperature is 1000 ° C. to 1300 ° C. from the viewpoint of cost and hot rollability. A further preferable lower limit of the slab heating temperature is 1050 ° C. A further preferable upper limit of the slab heating temperature is 1250 ° C.

  In the manufacturing method of the present invention, hot-rolled sheet annealing may or may not be performed on the hot-rolled steel sheet. When hot-rolled sheet annealing is performed, for example, the finishing temperature is 700 ° C. to 950 ° C., and the winding temperature is 750 ° C. or less. When hot-rolled sheet annealing is not performed, the finishing temperature is 850 to 900 ° C., and the winding temperature is 850 ° C. or less.

  When hot-rolled sheet annealing is performed, for example, the maximum temperature reached is 950 to 1050 ° C., and the holding time is 1 to 180 seconds. Hot-rolled sheet annealing is performed, for example, by a continuous annealing furnace. If the maximum ultimate temperature and the holding time are within the above ranges, the load on the equipment can be suppressed and productivity can also be enhanced. Furthermore, the magnetic properties of the non-oriented electrical steel sheet are also enhanced.

[About Mn segregation in finish rolling process and finish annealing process]
The finish rolling process and the finish annealing process carried out after producing the hot rolled steel sheet by the hot rolling process are closely related to the Mn segregation to the grain boundary which is a feature of the present invention, and the constraint conditions of each process are It is determined in consideration of the influence of Mn segregation on grain boundaries. For this reason, first, a phenomenon relating to Mn segregation which occurs from the finish rolling process to the finish annealing process will be described. It should be noted that this phenomenon is not completely elucidated, and it is noted in advance that the explanation here includes the assumption based on the examination result.

[Condition from rolling to after rolling]
In order to sufficiently concentrate Mn into grain boundaries, it is necessary to roll a steel material containing a considerable amount of Mn and C in a temperature range of T1 (° C.) or more. This is considered to be due to the high dislocation density state in the machined structure due to the special deformation behavior during rolling. T1 is expressed by the following equation.

  Generally, in high Si steels, the slip system of dislocations during deformation is limited, and twins are generated in deformation in a temperature range of about 200 ° C. or less (twin deformation). Since twin deformation is deformation without dislocation movement, dislocation density does not increase. In the temperature range of about 200 ° C. or higher, twin deformation is suppressed, and furthermore, the C movement by diffusion and the dislocation movement speed by deformation become comparable, and the interaction becomes strong. As a result, dislocations are less likely to move (so-called blue hot brittleness, dynamic strain aging), and dislocation density is increased. However, when the temperature is higher than about 400 ° C., the movement speed of C becomes faster, so the interaction becomes smaller.

  On the other hand, in the steel of the present invention containing a large amount of Mn, a considerable portion of C forms an Mn-C dipole, and the moving speed is slow. For this reason, the temperature range where the above-mentioned action works strongly rises, and the lower limit of the temperature range where the dislocation density rises is about 400 ° C. or more. However, since the amount of strain and strain rate affect this temperature, the temperature taking this into consideration becomes T1 (° C.). The upper limit rises to 600 ° C. It is believed that these temperatures also depend on the steel components, in particular, the amounts of Mn and C, but since the analysis becomes complicated, in the present invention, one pass in the finish rolling process is considered as a range where the invention effect is obtained. The rolling temperature T of the eye is defined as T1 to 600.degree.

  The same situation of high dislocation density seems to be achievable with "high Mn" + "cold rolling at high cold rolling rate". However, in the studies so far, the invention effect has not been obtained by rolling at a temperature of T1 or lower including general cold rolling. Although the reason for this is unknown, it is considered that the difference in dislocation structure and the like is affecting.

[The state from during recrystallization to after recrystallization]
As described above, in the temperature range of T 1 to 600 ° C., Mn and C have strong interactions with dislocations in the form of Mn—C dipoles. In the process of recrystallization, the grain boundaries are moved because the recrystallized grain boundaries driven by the high dislocation density in the machined structure move under the interaction with the Mn-C dipole, particularly in the initial stage of the final annealing. It moves in such a manner as to sweep the Mn-C dipole and Mn is concentrated in the grain boundaries. It is thought that the interaction between Mn and C becomes weak at the later stage of annealing which is at a higher temperature. However, Mn once concentrated in grain boundaries moves together with grain boundaries while being segregated in grain boundary movement accompanying grain growth. Therefore, it is possible to concentrate a sufficient amount of Mn in the grain boundary of the final structure.

  After that, the process returns to the description of the manufacturing process.

[Finish rolling process]
In the finish rolling step, at least the first pass rolling in warm rolling is performed on the hot-rolled steel sheet manufactured by the hot rolling step. And rolling after 2nd pass is implemented by warm rolling or cold rolling, and a thin steel plate is manufactured. Here, "pass" means that a steel plate passes through one rolling stand which has a pair of work rolls, and receives pressure.

  In the finish rolling step, tandem rolling may be performed using a tandem rolling mill including a plurality of rolling stands arranged in a row (each rolling stand has a pair of work rolls) to perform a plurality of passes. A plurality of passes may be performed by performing reverse rolling with a Sendzimir rolling mill or the like having a pair of work rolls. From the viewpoint of productivity, it is preferable to carry out a plurality of rolling passes using a tandem rolling mill.

  When the cold rolling process is performed, heat treatment may be performed on the steel plate during the cold rolling. That is, in the cold rolling step in the present invention, a plurality of passes may be performed by sandwiching the heat treatment halfway.

  Hereinafter, the conditions in the finish rolling process will be described.

[Cumulative rolling reduction in finish rolling process]
The cumulative rolling reduction in the finish rolling step is 75 to 95%. The cumulative rolling reduction (%) is defined as follows.
Cumulative rolling reduction = (1-Thickness of thin steel sheet after final pass of finish rolling process / thickness of hot rolled steel sheet before warm rolling in 1st pass) × 100

  The cumulative rolling reduction is defined based on the product thickness limitations. For example, when the thickness of the heat-rolled steel plate is 2.0 mm and the final thickness of the non-oriented electrical steel plate is 0.10 to 0.50 mm, the cumulative rolling reduction is 75 to 95%. From the above viewpoints, the cumulative rolling reduction in the finish rolling step in the present invention is 75 to 95%. The preferable lower limit of the cumulative rolling reduction is 85%. The preferred upper limit of the cumulative rolling reduction is 92.5%.

[First pass warm rolling process]
As described above, the first pass rolling on the heat-rolled steel plate is performed by warm rolling. The conditions for warm rolling in the first pass are as follows.

[Regarding Formula (1) to Formula (3)]
In warm rolling in the first pass, rolling is further performed under the conditions satisfying formulas (1) to (3).
Here, T (° C.) is the rolling temperature at the first pass rolling (unit: ° C., hereinafter referred to as initial rolling temperature), and more specifically, the rolling stand entry side where the first pass rolling is performed Steel plate temperature in ° C. The ε dot (epsilon dot) is a strain rate (the unit is s ^-1 , hereinafter referred to as an initial strain rate) of the first pass rolling. r is the rolling reduction of the first pass rolling (unit:%, hereinafter, referred to as initial rolling reduction).

  That is, in the first pass rolling in the finish rolling step, warm rolling is performed at an initial strain rate satisfying the formula (2), an initial reduction ratio satisfying the formula (3), and a rolling temperature satisfying the formula (1) .

[About formula (1)]
The initial rolling temperature T is an important factor to control the degree of Mn segregation to grain boundaries as described above.

  If the initial rolling temperature T (° C.) does not satisfy the equation (1), strain is less likely to be accumulated. Therefore, Mn segregation to the crystal grain boundary after recrystallization is not promoted, and the grain boundary Mn 545 / grain boundary Fe 700 becomes less than 0.05.

  If the initial rolling temperature T is less than T1, I (s) / I (c) is less than 0.80. Therefore, the punching dimensional difference is reduced.

  Furthermore, if the initial rolling temperature T exceeds 600 ° C., the degree of integration I (c) becomes less than 4.0, and I (s) / I (c) becomes 1.20 or more. Therefore, the punching dimensional accuracy is reduced.

FIG. 5: is in the manufacturing process of the non-oriented electrical steel sheet of the chemical composition of this invention. It is a figure which shows the relationship between the initial stage strain rate (s- ¹ ) and the initial stage rolling temperature (degreeC) in warm rolling of the 1st pass, and grain boundary Mn545 / grain boundary Fe700. In FIG. 5, as an example, the initial rolling reduction r is 30% (satisfying equation (3)). Therefore, the left side of Formula (1) is T1 = 223.2 × (ε dot) ^0.1159 .

Referring to FIG. 5, when the initial strain rate is 10 to 1000 (s ⁻¹ ), the grain boundary Mn 545 / grain boundary if the initial rolling temperature is equal to or higher than the curve of T 1 = 222.3 × (ε dot) ^0.1159. Fe 700 becomes 0.05 or more. If the initial rolling temperature is lower than the curve of T1 = 222.3 × (ε dot) ^0.1159 , Mn545 / Fe700 becomes less than 0.05.

[About formula (2)]
The initial strain rate ε dot (Epsilon dot), in conjunction with the initial rolling temperature T, is a factor that affects the occurrence of dynamic strain aging. The initial strain rate ε dot is also a factor that controls the frequency of occurrence of an inhomogeneously deformed structure due to the sliding deformation of the crystal. If the initial strain rate ε dot is high, the dislocation moving speed can not follow deformation, and nonuniform deformation such as a deformation zone occurs. Such non-uniform deformation is not preferable for Mn segregation to grain boundaries in subsequent recrystallization annealing.

If the initial strain rate ε dot is less than 10 s ⁻¹ , the grain boundary Mn 545 / grain boundary Fe 700 becomes less than 0.05. Also, I (c) is less than 4.0 and the magnetic flux density B ₅₀ is low. On the other hand, even if the initial strain rate ε dot exceeds 1000 s ⁻¹ , the grain boundary Mn 545 / grain boundary Fe 700 becomes less than 0.05. If the initial strain rate ε dot satisfies the equation (2), the grain boundary Mn 545 / grain boundary Fe 700 becomes 0.05 to 0.15, provided that the equations (1) and (3) are satisfied. The preferred lower limit of the initial strain rate ε dot is 10 s ⁻¹ . The preferred upper limit of the initial strain rate ε dot is 100 s ⁻¹ .

[Formula (3)]
The initial rolling reduction r, in conjunction with the initial rolling temperature T, is a factor that affects the accumulation of strain. The initial rolling reduction r is also a factor that controls the frequency of occurrence of an inhomogeneously deformed structure due to the sliding deformation of the crystal.

If the initial draft r is less than 10%, the accumulation of strain becomes insufficient and the magnetic flux density B ₅₀ becomes low. Moreover, although grain boundary Mn 545 / grain boundary Fe 700 is satisfied, grain boundary Mn 545 / intra-grain Mn 545 may be low. On the other hand, if the initial rolling reduction r exceeds 50%, the amount of Mn segregation to the grain boundaries in the recrystallized structure increases, and the grain boundary Mn545 / grain boundary Fe 700 becomes more than 0.15. Therefore, the number of limit punchings is reduced. If the initial rolling reduction r satisfies the formula (3), the grain boundary Mn 545 / grain boundary Fe 700 can be made 0.05 to 0.15, provided that the formula (1) and the formula (2) are satisfied. The upper limit of the initial draft r is preferably 30%, more preferably 20%.

  In order to increase the limit number of times of punching, it is preferable that the initial draft r be 50% or less, and the lower limit of the initial draft r is preferably 10% or more.

[About work roll diameter]
The diameter of the work roll of the rolling stand for performing the first pass rolling in the finish rolling process is 1000 mm or less, preferably 400 to 1000 mm. When the diameter of the work roll is 1000 mm or less, the grain boundary Mn 545 / grain boundary Fe 700 becomes 0.05 or more, and a sufficient limit number of times of punching can be obtained. If the work roll diameter is 400 mm or more, the degree of integration I (c) will be 4.0 or more, I (s) / I (c) will be in the range of 0.80 to 1.20, and the amount of sag will be suppressed And the punching accuracy is also increased. Furthermore, since the grain boundary Mn545 / intragranular Mn 545 is increased, the number of critical punchings is also increased.

[About pass schedule]
From the viewpoint of effectively accumulating the strain, it is preferable to carry out warm rolling from the first pass rolling. Since the plate thickness is thin in rolling after the second pass (rolling on a rolling stand placed downstream of the initial rolling stand), a sufficient rolling shape ratio (roll contact arc length / average plate thickness) It is difficult to take. For this reason, it is difficult to set the deformation state required for the present invention, and significant improvement of the effects of the present invention can not be expected. Further, even if warm rolling is performed after the rolling process, the Mn segregation effect may be saturated and the number of critical punchings may be reduced.

  In the present invention, when warm rolling or cold rolling is performed at such a small rolling shape ratio, the deformation state necessary for the present invention introduced in the first pass partially disappears, and recrystallization and grain growth In the process, Mn segregation to grain boundaries is excessive, which may inhibit the effects of the invention. Therefore, in the present invention, the manufacturing method is defined under the conditions of the first pass rolling. However, it goes without saying that warm rolling after the second pass is not excluded unless the invention effect is completely lost.

  Further, also from the viewpoint of avoiding brittle fracture, it is advantageous to use warm rolling for the first pass rolling with a high rolling shape ratio.

  Furthermore, from the viewpoint of avoiding over-tension failure, when the rolling reduction per pass is increased or when the strain rate per pass is increased, the rolling load may increase and the tension may become too large. In this case, the steel plate during rolling may break. As a result of the investigation, excessive tension is likely to occur at the outlet side of the rolling stand (initial rolling stand) where the first pass rolling is performed and at the outlet side of the rolling stand where the second pass rolling is performed. Performing warm rolling in the first pass rolling is also advantageous in order to suppress excess tension being applied to the steel sheet.

  From the viewpoint of the work rolls used for warm rolling, the roll life by warm rolling is lower than the roll life by cold rolling. In warm rolling, work rolls are more easily worn than cold rolling, and tempering occurs. In the present invention, the rolling rate can be increased by setting only the first pass to warm rolling.

  For the above reasons, it is a preferable embodiment of the present invention to use warm rolling as the former stage including the first pass of rolling and cold rolling as the latter stage. In the latter stage cold rolling, the rolling temperature (the steel plate temperature) is 150 ° C. or less. As a result, while improving the magnetic characteristics, it is possible to reduce the thickness variation and to avoid the concern that the preferred working texture state formed in the first pass warm rolling may be destroyed.

  In the case of using a tandem rolling mill, warm rolling is performed at a rolling stand for performing at least first pass rolling, and a rolling stand arranged downstream of the rolling stand, and warm rolling is performed at the rolling stand. Cold rolling may be performed at one or more rolling stands located downstream.

[Control of rolling temperature]
The hot rolled steel sheet is heated for warm rolling in the previous stage including the first pass of rolling. As a heating method in the warm rolling process, a known heating method can be applied, including electromagnetic induction heating, electric current heating, heater heating, heating in an atmosphere gas, and the like.

  When applying cold rolling in order to obtain the above merits in post-warm rolling after warm rolling, contact with a cooling roll or the like, cooling gas, etc., before warm-rolling and before a pass to be cold-rolled, or cooling gas The steel plate may be cooled to a required temperature by a known method such as spraying.

[Finish annealing process]
The cold rolled steel sheet manufactured by carrying out the finish rolling process is subjected to finish annealing to manufacture a non-oriented electrical steel sheet. In the finish annealing, the cold rolled steel sheet finished to the final thickness is annealed and recrystallized.

  The maximum temperature and holding time of the final annealing are not particularly limited. The highest reaching temperature and the holding time are appropriately set according to the chemical composition of the non-oriented electrical steel sheet, the conditions of the hot rolling process and the finish rolling process. As described above, it is preferable to adopt the condition that the average grain size of the non-oriented electrical steel sheet after finish annealing is 100 μm or more. The setting of the maximum attainable temperature and the retention time is easy for those skilled in the art. The highest temperature reached in the preferred finish annealing is 900-1100 ° C. In this case, the degree of integration I (c) becomes 4.0 or more, and the amount of sagging can be suppressed. The holding time at the highest temperature (i.e., the holding time at 900-1100 [deg.] C.) is, for example, 10-90 seconds. Heat treatment and structure observation are performed using sample cold-rolled steel plates rolled by the same chemical composition, the same hot rolling process conditions, and the same finish rolling process conditions, and the conditions of the finish rolling annealing (maximum achieved temperature and retention in advance) Time) may be determined. In this case, more appropriate conditions for making the average crystal grain size 100 μm or more can be determined.

[Other process]
In the manufacturing method described above, the coating step may be performed after the finish annealing step. In the coating process, an insulating coating is applied to the surface of the non-oriented electrical steel sheet after finish annealing. The type of insulating coating is not particularly limited. The insulating coating may be an organic component or an inorganic component. The insulating coating may contain an organic component and an inorganic component. The inorganic component is, for example, a dichromic acid-boric acid type, a phosphoric acid type, a silica type or the like. The organic component is, for example, a general acrylic resin, acrylic styrene resin, acrylic silicon resin, silicon resin, polyester resin, epoxy resin, or fluorine resin. In consideration of paintability, preferred resins are emulsion type resins. An insulating coating may be provided which exhibits adhesive ability by heating and / or pressing. The insulating coating having adhesion is, for example, acrylic resin, phenol resin, epoxy resin, melamine resin.

  By the above manufacturing process, the non-oriented electrical steel sheet according to the present invention can be manufactured. The non-oriented electrical steel sheet of the present invention is excellent in magnetic properties. Furthermore, the occurrence of sagging in punching can be suppressed.

  Hereinafter, the present invention will be specifically described by way of examples.

  Hot rolling was performed on a slab (slab) having a chemical composition shown in Table 1 to produce a hot-rolled steel plate having a thickness of 2.0 mm. "-" In Table 1 shows that content was less than a detection limit.

  With respect to the hot-rolled steel sheet, hot-rolled sheet annealing was carried out soaking at 1000 ° C for one minute. Thereafter, using a tandem rolling mill in which five rolling stands were arranged in a row, rolling under the first pass was carried out by warm rolling under the conditions shown in Table 2. Furthermore, the 2nd-5th pass rolling was implemented by cold rolling at 100 degrees C or less, and the thin steel plate of 0.25 mm of plate | board thickness was manufactured. The cumulative rolling reduction in the finish rolling step was 88% in any test number. The steel sheet after finish rolling was held at the finish annealing temperature (maximum ultimate temperature) shown in Table 2 for 14 seconds. A non-oriented electrical steel sheet was manufactured by the above manufacturing process.

In addition, T1 in Table 2 was made into the left side of Formula (1), and T2 was made into the right side of Formula (1). Specifically, T1 was as follows.
An Auger electron spectral peak was measured on the non-oriented electrical steel sheet manufactured in the above steps, and the following evaluation test was performed.

[Magnetic property evaluation test]
Relative to the non-oriented electrical steel sheet of each test number, the 55mm angle magnetic measurement test, the magnetic flux density was measured _{B 50} in 5000A / m. The magnetic flux density B ₅₀ is obtained as an average of L direction (rolling direction) and C direction (the direction perpendicular to the rolling direction).

[Limit punching frequency measurement test]
A punching test was carried out on the manufactured non-oriented electrical steel sheet by punching a 55 mm × 55 mm square magnetic measurement sample. The non-oriented electrical steel sheet was cut so as to have a cross section parallel to the punching direction and perpendicular to the punching blade. And the edge part of the nondirectional electromagnetic steel plate was embedded in resin among the cut surfaces, and it grind | polished. The edge of the non-oriented electrical steel sheet after polishing was photographed with an optical microscope to generate a photographic image. Using the photographic image, the height of the burr formed at the end of the steel plate by punching was measured. FIG. 6 is a schematic view of a photographic image of an end of a steel plate in a punching test. Referring to FIG. 6, in the steel plate end portion 100, a sagging portion 101, a sheared surface 102, a fractured surface 103, and a burr 104 are formed in order from the punching direction PU.

  The limit number of times of punching was measured by the number of times of punching until the height D104 of "barrier" at punching a 55 mm square magnetic measurement sample from a product plate exceeds 25 μm (that is, the maximum D104 becomes 25 μm or less). .

[Punching dimensional difference measurement test]
The punching test was performed in the following manner. Punching was performed using a 55 mm square mold to prepare a 55 mm × 55 mm test piece shown in FIGS. 7A and 7B. The clearance was 8% of the plate thickness.

  As shown to FIG. 7 (A), three places (L1-L3) measured the length of the rolling direction of a square-shaped test piece. Specifically, referring to FIG. 7A, the length in the rolling direction at the position of 5 mm in the width direction from the left side parallel to the rolling direction among the test pieces was defined as L1. Similarly, the rolling direction length at the widthwise center position is defined as L2. The rolling direction length at a position of 5 mm in the width direction from the right side parallel to the rolling direction was defined as L3.

  Furthermore, as shown to FIG. 7 (B), the length of the square-like width direction was measured at three places (C1-C3). Specifically, referring to FIG. 7B, the length in the width direction at a position of 5 mm in the rolling direction from the upper side parallel to the width direction among the test pieces is defined as C1. Similarly, the widthwise length at the center position in the rolling direction is defined as C2. The length in the width direction at a position of 5 mm in the rolling direction from the lower side parallel to the width direction was defined as C3.

The lengths L1 to L3 and the lengths C1 to C3 described above were measured. The punching dimension accuracy A (μm) defined by the following equation was evaluated using each of the measured lengths L1 to L3 and C1 to C3.

[Dare measurement test]
A punching test was carried out on the manufactured non-oriented electrical steel sheet by punching a 55 mm × 55 mm square magnetic measurement sample. The non-oriented electrical steel sheet was cut so as to have a cross section parallel to the punching direction and perpendicular to the punching blade. And the edge part of the nondirectional electromagnetic steel plate was embedded in resin among the cut surfaces, and it grind | polished. The edge of the non-oriented electrical steel sheet after polishing was photographed with an optical microscope to generate a photographic image. The amount of dripping D101 (see FIG. 6) formed at the end of the steel plate by punching was determined using the photographic image. Specifically, the amount of dripping D101 of the dripping portion 101 is measured at arbitrary five steel plate end portions after punching. The average of the measured dripping amount D101 was defined as the dripping amount.

[result]
The evaluation results are shown in Table 2. Referring to Table 2, in test numbers 2 to 12, 16, 17, 27, 32, 37, 39, 40, 41, 43 to 46, the chemical composition was appropriate, and the production conditions were also appropriate. Therefore, the Auger peak ratio grain boundary Mn 545 / grain boundary Fe 700 was between 0.05 and 0.15. As a result, the limit number of times of punching was 43 × 10 ⁴ or more, which was good.

  Furthermore, in the test numbers 2 to 12, 16, 17, 27, 32, 41, 44 to 46, among the manufacturing conditions, the initial rolling reduction r is 10% or more, and the work roll diameter is less than 1100 mm, And the highest achieved temperature in finish annealing was in the range of 900-1100 ° C. Therefore, the degree of integration I (c) is 4.0 or more, and I (s) / I (c) is between 0.8 and 1.2. As a result, the amount of sagging was as small as 15 μm or less, and the occurrence of sagging during punching could be sufficiently suppressed. The punching dimensional difference was as small as 10 μm or less.

On the other hand, the test No. 1, 13-15, 22-24, and 47-49 had inadequate chemical composition. Therefore, the Auger peak ratio grain boundary Mn 545 / grain boundary Fe 700 did not fall within a range of 0.05 to 0.15 even under appropriate manufacturing conditions, and the limit number of times of punching was as low as 43 × 10 ⁴ times.

In Test No. 18, since the initial rolling temperature T was too low, I (s) / I (c) was too low. Furthermore, since the initial strain rate was too low, the density I (c) was less than 4.0, and the grain boundary Mn 545 / grain boundary Fe 700 did not fall within the range of 0.05 to 0.15. Therefore, the magnetic flux density _{B 50} is less than 1.65 T, magnetic properties were low. Furthermore, the amount of dripping also exceeded 15 μm. Furthermore, the punching dimensional difference also exceeded 10 μm. In addition, the limit number of punches was low.

In the test numbers 19 and 20, the initial strain rate was too low. Therefore, the integration degree I (c) was less than 4.0, and the grain boundary Mn 545 / grain boundary Fe 700 did not fall within the range of 0.05 to 0.15. As a result, the amount of dripping exceeded 15 μm, and the limit number of times of punching was as low as less than 43 × 10 ⁴ times.

In Test No. 21, the initial strain rate was too low. Furthermore, the initial rolling temperature T was too high. Therefore, the integration degree I (c) was less than 4.0, and the grain boundary Mn 545 / grain boundary Fe 700 did not fall within the range of 0.05 to 0.15. As a result, the amount of dripping exceeded 15 μm, and the limit number of times of punching was as low as less than 43 × 10 ⁴ times. Moreover, since I (s) / I (c) exceeded 1.2, the punching dimensional difference exceeded 10 μm.

  The initial rolling temperature was too low in test numbers 25, 26, 29-31. Therefore, I (s) / I (c) was too low. As a result, the punching dimensional difference exceeded 10 μm. Since the initial rolling temperature of test No. 25 was too low, the grain boundary Mn 545 / grain boundary Fe 700 did not fall between 0.05 and 0.15. As a result, I (c) was less than 4.0, and the amount of sag exceeded 15 μm. Moreover, since the grain boundary Mn 545 / grain boundary Fe 700 did not enter between 0.05 and 0.15, even if the grain boundary Mn 545 / intragranular Mn 545 was in 2.0 to 10.0, the limit number of times of punching was low. . In the test numbers 26 and 29 to 31, the grain boundary Mn 545 / grain boundary Fe 700 did not enter between 0.05 and 0.15 because the initial rolling temperature was deviated. As a result, I (c) was 4.0 or more, but the amount of sag exceeded 15 μm. In addition, since the grain boundary Mn 545 / grain boundary Fe 700 did not enter between 0.05 and 0.15, the limit number of times of punching was low even if the grain boundary Mn 545 / intragranular Mn 545 was 2.0 to 10.0.

  In the test numbers 28 and 33, the initial rolling temperature T was too high. Therefore, I (s) / I (c) was too high. As a result, the punching dimensional accuracy exceeded 10 μm. Furthermore, the degree of accumulation I (c) was less than 4.0. Therefore, the amount of dripping exceeded 15 μm. Furthermore, the Auger peak specific grain boundary Mn 545 / grain boundary Fe 700 did not enter between 0.05 and 0.15. Therefore, the limit number of times of punching was low.

  In the test numbers 34 to 36, the initial strain rate was too fast. Therefore, Auger peak specific grain boundary Mn 545 / grain boundary Fe 700 did not enter between 0.05 and 0.15. As a result, even if the grain boundary Mn545 / intragranular Mn 545 was in the range of 2.0 to 10.0, the critical number of times of punching was low.

  Further, in the test No. 34, the initial rolling temperature T was too low. Therefore, the integration degree I (c) was less than 4.0, and I (s) / I (c) was less than 0.80. As a result, the sag amount exceeded 15 μm, and the punching dimensional difference exceeded 10 μm. Furthermore, the Auger peak specific grain boundary Mn 545 / grain boundary Fe 700 did not enter between 0.05 and 0.15.

  Furthermore, in the test No. 36, the initial rolling temperature T was too high. Therefore, the degree of integration I (c) was less than 4.0, and I (s) / I (c) exceeded 1.20. As a result, the sag amount exceeded 15 μm, and the punching dimensional difference exceeded 10 μm.

  In test No. 38, the initial draft r was too high. Therefore, the grain boundary Mn 545 / grain boundary Fe 700 did not enter between 0.05 and 0.15, and the punching dimensional difference exceeded 10 μm. In addition, even when the grain boundary Mn545 / intragranular Mn 545 was in the range of 2.0 to 10.0, the limit number of times of punching was low.

  In Test No. 42, the work roll diameter was too large. The Auger peak specific grain boundary Mn 545 / grain boundary Fe 700 did not enter between 0.05 and 0.15, and the punching dimensional difference exceeded 10 μm. In addition, even when the grain boundary Mn545 / intragranular Mn 545 was in the range of 2.0 to 10.0, the limit number of times of punching was low.

  In mass%, Si: 3.3%, Al: 0.005%, Mn: 2.2%, P: 0.01%, C: 0.003%, N: 0.0021%, S: 0. Hot rolling was performed on a slag (slab) containing 0005% and the balance being Fe and an impurity element to obtain a hot-rolled steel plate having a thickness of 2.0 mm. Hot-rolled sheet annealing was performed on this hot-rolled steel sheet, which was heated at 1000 ° C. for one minute.

After hot-rolled sheet annealing, the finish rolling process was performed using a tandem rolling mill in which five rolling stands were arranged in a line. Specifically, in the first pass rolling, the initial strain rate was 31 s ⁻¹ and the initial rolling reduction was 30%. The cumulative rolling reduction in the finish rolling step was 85%. The rolling temperature at each stand from the first pass to the fifth pass was as shown in Table 3. The steel sheet after finish rolling was held at a finish annealing temperature of 1000 ° C. for 14 seconds. A non-oriented electrical steel sheet was manufactured by the above manufacturing process.

For non-oriented electrical steel sheets of each test number, in the same manner as in Example 1, the degree of integration I (s), the degree of integration I (c), I (s) / I (c), average grain size Auger peak ratio Mn 545 / Fe 700, sag amount (μm), magnetic flux density B ₅₀ (T), punching dimensional accuracy, limit punching number was determined.

[result]
The results are shown in Table 3. In Test Nos. 1 and 2, the chemical composition was appropriate, and the production conditions were also appropriate. Therefore, the degree of integration I (c) is 4.0 or more, and I (s) / I (c) is between 0.8 and 1.2. Moreover, Mn545 / Fe700 was between 0.05 and 0.15. As a result, the amount of sag was as small as 15 μm or less, and the punching dimensional accuracy was as small as 10 μm or less. Furthermore, it was excellent also in the limit number of times of punching.

  On the other hand, in the test numbers 3 to 5, the rolling temperature in the 3rd to 5th passes was high, and the grain boundary Mn 545 / grain boundary Fe 700 exceeded 0.15. As a result, the punching dimensional accuracy exceeded 10 μm, and the number of critical punchings was small.

In the test numbers 6 to 13, the initial rolling temperature in the first pass was too low to satisfy the formula (1). Therefore, I (c), I (s) / I (c) were too low, and the grain boundary Mn 545 / grain boundary Fe 700 was less than 0.05. As a result, even if the droop amount exceeds 15 μm, the punching dimensional accuracy exceeds 10 μm, and the grain boundary Mn545 / intragranular Mn 545 is in the range of 2.0 to 10.0, the limit number of times of punching is low. Further, the magnetic flux density _{B 50} is also low.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these examples. It is obvious that those skilled in the art can conceive of various modifications or alterations within the scope of the idea described in the claims, and they are naturally within the technical scope of the present invention. It is understood that.

Claims (9)

Non-oriented electrical steel sheet,
The chemical composition is
In mass%,
C: 0.001 to 0.005%,
Si: 3.0 to 5.0%,
Mn: 1.0 to 3.0%,
P: 0.02% or less,
S: 0.005% or less,
Al: 0.01% or less, and
N: 0.001 to 0.005%,
And the balance consists of Fe and impurities,
The non-oriented electrical steel sheet having a ratio of a peak Mn 545 at 545 eV of Mn obtained by Auger electron spectroscopy to a peak Fe 700 at 700 eV of Fe obtained at Auger electron spectroscopy in a grain boundary of the non-oriented electrical steel sheet is 0.05 to 0.15. The non-oriented electrical steel sheet according to claim 1, further comprising:
The ratio of the peak at 545 eV of Mn obtained by Auger electron spectroscopy at the grain boundaries of the non-oriented electrical steel sheet to the peak at 545 eV of Mn obtained by Auger electron spectroscopy in the grains of the non-oriented electrical steel sheet is 2 Non-oriented electrical steel sheet which is from 0 to 10.0. The non-oriented electrical steel sheet according to claim 1 or 2, further comprising:
When the thickness of the non-oriented electrical steel sheet is defined as t, the degree of integration I (c) of {100} <012> orientation at the depth position t / 2 from the surface of the non-oriented electrical steel sheet is 4.0. That's it,
The ratio of the degree of integration I (s) of {100} <012> orientation at the t / 10 depth position from the surface of the non-oriented electrical steel sheet to the degree I (c) of the integration is 0.8 to 1.2 Non-oriented electrical steel sheet that is. The non-oriented electrical steel sheet according to any one of claims 1 to 3, wherein
The chemical composition is further substituted for part of Fe,
Ti: 0.01% or less,
V: 0.01% or less, and
Nb: contains one or more selected from the group consisting of 0.01% or less,
The non-oriented electrical steel sheet, wherein the chemical composition satisfies the formula (A).
The non-oriented electrical steel sheet according to any one of claims 1 to 4, wherein
The chemical composition is further substituted for part of Fe,
Sn: 0.2% or less,
Cu: 0.1% or less
Ni: 0.1% or less,
Cr: 0.2% or less, and
B: 0.001% or less,
Non-oriented electrical steel sheet containing one or more selected from the group consisting of The hot rolling process which hot-rolls with respect to the raw material which has a chemical composition in any one of Claims 1-5, and manufactures a hot rolled sheet steel,
Warm rolling is performed in at least the first pass rolling on the heat-rolled steel plate, and warm rolling or cold rolling is performed in second and subsequent rolling, and a plate of 0.10 to 0.50 mm A finish rolling process for producing a thin steel plate having a thickness;
And a finish annealing step of performing finish annealing on the thin steel plate,
In the finish rolling process,
In the first-pass rolling, when the rolling temperature is T (° C.), the strain rate is ε dot (s ⁻¹ ), and the rolling reduction is r (%), formulas (1) to (3) are satisfied. Warm rolling is performed on the hot rolled steel sheet under the conditions;
The diameter of the work roll that carries out the first pass rolling shall be 1000 mm or less,
The manufacturing method of a non-oriented electrical steel sheet which makes a cumulative rolling reduction in the above-mentioned finish rolling process 75 to 95%.
A method of manufacturing a non-oriented electrical steel sheet according to claim 6,
In the cold rolling,
The manufacturing method of a non-oriented electrical steel sheet which makes the above-mentioned rolling temperature in the 3rd pass or less 150 ° C or less. A method of manufacturing a non-oriented electrical steel sheet according to claim 6 or 7,
In the finish rolling process,
Using a tandem rolling mill, each having a pair of work rolls, comprising a plurality of rolling stands arranged in a row,
The warm rolling is performed at the rolling stand which carries out at least the first pass rolling, or at the rolling stand and a rolling stand arranged downstream thereof.
The manufacturing method of a non-oriented electrical steel sheet implemented by cold rolling with the rolling stand arranged downstream of the said rolling stand which implements the said warm rolling. A method of manufacturing a non-oriented electrical steel sheet according to any one of claims 6 to 8, wherein
In the finish annealing step,
The manufacturing method of a non-oriented electrical steel sheet which makes the highest reach | attainment temperature 900-1200 degreeC.