JP2011157603A - Non-oriented electromagnetic steel sheet and method for manufacturing non-oriented electromagnetic steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-oriented electromagnetic steel sheet in which decarburization can be easily performed and has excellent core-loss characteristic, and to provide a method for manufacturing the non-oriented electromagnetic steel sheet. <P>SOLUTION: This non-oriented electromagnetic steel sheet is composed by mass% of ≤0.006% C, 0.3-4% Cr, 1-4% Si and 0.4-3% Al at least and the balance Fe with inevitable impurities, and an oxide layer having needle-type oxides, is positioned near the surface of the steel sheet and the long-axial direction of the needle-type oxides are parallel to the thickness direction of the steel sheet. Because of the existence of such oxide layer in this non-oriented electromagnetic steel sheet, the decarburization can easily be performed and excellent core-loss characteristic is shown. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a non-oriented electrical steel sheet and a method for producing a non-oriented electrical steel sheet.

  From the viewpoint of conservation of the global environment, the harmful effects of energy-intensive civilizations in recent years are regarded as problems. In the field of electrical equipment in which non-oriented electrical steel sheets are used, further reduction in power consumption is required for motors for air conditioning equipment, drive motors for electric vehicles, and the like. Further, the motor drive control method is not a conventional current ON-OFF control, but a PWM waveform control in which harmonics by an inverter are superimposed. For this reason, electrical steel sheets excellent in high frequency characteristics have been demanded.

Conventional non-oriented electrical steel sheet manufacturing technologies include increasing specific resistance by increasing silicon (Si), aluminum (Al), chromium (Cr), etc. for the purpose of improving high-frequency iron loss. The plate thickness has been reduced as much as possible. However, the problem with Cr-added steel is the amount of carbon. Carbon in the product precipitates as Fe ₃ C (cementite), (Fe, Cr) ₇ C _3, etc. at low temperatures and deteriorates magnetically. Therefore, the carbon content is 0.006% or less, and preferably 0.003%. The following is preferable. However, with Cr-containing steel, it is difficult to decarburize in equilibrium by vacuum degassing at the steel making stage, and if it is attempted to decarburize sufficiently, a long vacuum degassing time is required, which is a serious productivity hindrance. was there.

  For this reason, conventionally, the method of decarburizing by post processes other than steelmaking has been examined. A general post-process of a high-grade non-oriented electrical steel sheet is a process of continuous hot-rolled sheet annealing at about 1000 ° C. → cold rolling → continuous recrystallization annealing at about 1000 ° C.

  For example, the following Patent Document 1 discloses a decarburization treatment technique in hot-rolled sheet annealing or recrystallization annealing, and can be said to be a technique that focuses on decarburization annealing. Specifically, this Patent Document 1 adds decarburization annealing with a hot-rolled sheet of about 750 ° C. × 2 hr prior to 860 ° C. × 3 hr of hot-rolled sheet annealing, or finish of 1000 ° C. × 1 min. It is disclosed that a decarburization annealing of 700 to 800 ° C. × 1 to 10 min is added prior to annealing (that is, recrystallization annealing). However, since the addition of these decarburization annealing is added to the normal manufacturing process, there is a problem that the cost burden is large.

  Moreover, in the following patent document 2, the method of decarburizing annealing with a hot-rolled sheet with a black skin is disclosed, and the example of the temperature x time of decarburizing annealing is 750 ° C. × 2 hr. . Also in this technique, since decarburization annealing becomes an additional process, there existed a problem that a cost burden became large.

The biggest reason why the decarburization annealing process becomes an additional process is that the temperature at which decarburization occurs is relatively low, 700 to 800 ° C. Here, although continuous recrystallization annealing is usually around 1000 ° C., it has been conventionally considered that decarburization does not occur at 1000 ° C. The reason is that when the temperature is increased to about 1000 ° C., the SiO ₂ film already covers the surface during the temperature increase, and the carbon diffusion is prevented.

JP 2002-317254 A JP 2003-247020 A

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is a non-oriented electrical steel sheet that can be easily decarburized and has excellent iron loss characteristics. And it is providing the manufacturing method of a non-oriented electrical steel sheet.

  In order to solve the above problems, according to an aspect of the present invention, in mass%, C ≦ 0.006%, Cr: 0.3 to 4%, Si: 1 to 4%, Al: 0.4 to 3% and at least the balance is made of inevitable impurities and Fe, and an oxide layer having acicular oxide is located near the surface of the steel sheet, and the acicular oxide has a major axis of the oxide. A non-oriented electrical steel sheet having a direction parallel to the thickness direction of the steel sheet is provided.

  The oxide layer preferably has a thickness of 0.2 to 4 μm.

  The non-oriented electrical steel sheet preferably further includes, by mass%, Mn ≦ 1.5%, S ≦ 0.003%, and N ≦ 0.003%.

  It is preferable that the non-oriented electrical steel sheet further includes at least one of Sn: 0.01 to 0.15% and Sb: 0.005 to 0.05% by mass.

In order to solve the above-mentioned problem, according to another aspect of the present invention, by mass%, C ≦ 0.007%, Cr: 0.3 to 4%, Si: 1 to 4%, Al: 0 A step of annealing a hot-rolled sheet containing at least 4 to 3%, the balance being inevitable impurities and Fe, a step of cold-rolling the annealed hot-rolled sheet to form a cold-rolled sheet, wherein the step of recrystallization annealing the rolled sheet, wherein the soaking process of recrystallization annealing, 900 to 1100 ° C., and oxidizing the water vapor partial pressure _P H2O _{/ P H2} is 0.05 to 0.8 By forming the atmosphere, there is no direction for forming an oxide layer in the vicinity of the surface of the cold-rolled plate, which has an acicular oxide, and the major axis direction of the acicular oxide is parallel to the thickness direction of the steel plate. A method for producing a conductive electrical steel sheet is provided.

Wherein in the recrystallization annealing, it is preferable to perform the heating up to 900 ° C. in an oxidizing atmosphere steam partial pressure _P H2O _{/ P H2} is 0.05 to 5.

  The oxide layer preferably has a thickness of 0.2 to 4 μm.

  The hot-rolled sheet preferably further contains, by mass%, Mn ≦ 1.5%, S ≦ 0.003%, and N ≦ 0.003%.

  The hot-rolled sheet preferably further contains at least one of Sn: 0.01 to 0.15% and Sb: 0.005 to 0.05% by mass.

  In the recrystallization annealing, the temperature raising process for raising the temperature to 900 ° C. may be an open flame atmosphere.

  In the recrystallization annealing, the cooling rate in the cooling process from 900 ° C. to 300 ° C. performed after the soaking process may be 1 to 30 ° C./s.

  As described above, the non-oriented electrical steel sheet according to the present invention includes an acicular oxide and has an internal oxide layer in which the major axis direction of the oxide is parallel to the thickness direction of the steel sheet. Therefore, it is possible to realize excellent iron loss characteristics.

It is explanatory drawing for demonstrating the structure of the non-oriented electrical steel sheet which concerns on the 1st Embodiment of this invention. It is a flowchart for demonstrating the manufacturing method of the non-oriented electrical steel plate which concerns on the same embodiment. It is explanatory drawing for demonstrating the recrystallization annealing process which concerns on the same embodiment. It is a SEM photograph for demonstrating the non-oriented electrical steel plate which concerns on the same embodiment. It is a SEM photograph for demonstrating the conventional non-oriented electrical steel sheet.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

(First embodiment)
<Structure of non-oriented electrical steel sheet>
First, the structure of the non-oriented electrical steel sheet according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is an explanatory diagram for explaining the structure of the non-oriented electrical steel sheet according to the present embodiment, and schematically shows the structure of the non-oriented electrical steel sheet according to the present embodiment.

  The non-oriented electrical steel sheet 1 according to the present embodiment is formed on a steel plate 10 that is a base material, an internal oxide layer 20 formed on the steel plate 10, and an internal oxide layer 20 as shown in FIG. The outer oxide layer 30 is mainly included. Here, the internal oxide layer 20 is an example of an oxide layer.

  The steel plate 10 which is a base material can use a cold-rolled material prepared so that each component included in the steel plate falls within a predetermined range. In addition, in order to improve the magnetic characteristic in the high frequency (frequency of about 400 Hz-1 kHz), the steel plate 10 is preferably thinner.

Next, the internal oxide layer 20 shown in FIG. 1 will be described in detail.
In the conventional non-oriented electrical steel sheet, the electrical steel sheet is manufactured so that such an internal oxide layer does not exist. However, in the non-oriented electrical steel sheet according to the present embodiment, the internal oxide layer as described below is positive. The magnetic steel sheet is manufactured so as to be formed in the following manner.

  For example, as shown in FIG. 1, the internal oxide layer 20 is a layer containing an oxide located between the outer oxide layer 30 located on the surface layer side and the steel plate 10, and is an acicular (rod-like) oxide. 21 and a portion 23 made of an Fe base material (metal). In this internal oxide layer 20, as shown in FIG. 1, the acicular oxide 21 does not cover the entire surface of the steel sheet 10, but is made of an Fe base material on which the acicular oxide 21 is not formed. The portion 23 and the portion where the needle-like oxide 21 is formed are both present.

The acicular oxide 21 is an oxide mainly composed of SiO ₂ , and includes oxides of Al ₂ O ₃ and Cr in addition to SiO ₂ . As shown in FIG. 1, the needle-like oxide 21 is formed in a bamboo forest shape on the steel plate 10, and the major axis direction of the oxide 21 is the thickness direction of the steel plate 10 (that is, FIG. 1). In the z-axis direction).

  By forming the needle-like oxide 21 as shown in FIG. 1, in the internal oxide layer 20, the portion 23 made of the Fe base material is interposed between the steel plate 10 and the external oxide layer 20. Will exist. As a result, the portion 23 made of this Fe base material functions as a passage for carbon (C) during decarburization, and the carbon contained in the steel plate 10 is transferred to the outside of the electromagnetic steel plate 1 during recrystallization annealing. It becomes possible to diffuse.

  The thickness of the internal oxide layer 20 including the needle-like oxide 21 is preferably 0.2 μm or more and 4 μm or less. By setting the thickness of the internal oxide layer 20 within the above-described range, it is possible to perform sufficient decarburization during recrystallization annealing while preventing deterioration of iron loss. In addition, when the thickness of the internal oxide layer 20 is less than 0.2 μm, it is difficult to perform sufficient decarburization during recrystallization annealing, which is not preferable. Further, when the thickness of the internal oxide layer 20 exceeds 4 μm, the deterioration of the high-frequency iron loss of the non-oriented electrical steel sheet 1 is increased, which is not preferable.

  In FIG. 1, the needle-like oxide 21 is uniformly formed in the internal oxide layer 20. However, the present invention is not limited to this case, and the needle-like oxides 21 are adjacent to each other. The distance between the oxides 21 may not be constant. Further, the number of acicular oxides 21 present in the internal oxide layer 20 is not limited to the number shown in FIG. Moreover, although FIG. 1 illustrates the case where the major axis direction of the needle-like oxide 21 is substantially perpendicular to the steel plate plane, the present invention is not limited to this case. The major axis direction of the needle-like oxide 21 is somewhat from the direction perpendicular to the steel plate plane within the range in which the portion 23 made of the Fe base material interposed between the steel plate 10 and the outer oxide layer 30 is formed. It may be tilted.

  The internal oxide layer 20 according to this embodiment has been described above. Next, the external oxide layer 30 shown in FIG. 1 will be described.

  The outer oxide layer 30 is a layer mainly composed of iron oxide (FeO). The outer oxide layer 30 is a layer formed on the inner oxide layer 20 and positioned on the outermost surface of the non-oriented electrical steel sheet 1. The thickness of the outer oxide layer 30 is very thin compared to the thickness of the inner oxide layer 20, which is about 1% to 5% of the thickness of the inner oxide layer 20, and the thickness of the inner oxide layer 20 is, for example, about 1 to 2 μm. In this case, the thickness of the outer oxide layer 30 is about 0.04 μm.

  Here, the non-oriented electrical steel sheet 1 according to the present embodiment is in mass%, C ≦ 0.006%, Cr: 0.3-4%, Si: 1-4%, Al: 0.4-3. %, And the balance is a steel plate made of inevitable impurities and Fe. Further, the non-oriented electrical steel sheet 1 may further contain Mn ≦ 1.5%, S ≦ 0.003%, and N ≦ 0.003% by mass% in addition to the above-described components.

  In addition, there existed a problem regarding nitriding as a problem of Cr addition steel. Nitridation occurs when nitrogen (N) in the atmosphere penetrates from the surface of the steel sheet by diffusion in the recrystallization annealing, and deteriorates the iron loss characteristics. Therefore, in order to suppress this nitriding, the non-oriented electrical steel sheet 1 may further include at least one of Sn: 0.01 to 0.15% and Sb: 0.005 to 0.05%. Good.

  The amount of carbon (C amount) contained in the non-oriented electrical steel sheet (hereinafter also referred to as electrical steel sheet) 1 is 0.006% or less by mass. Moreover, it is preferable that the carbon amount contained in the steel plate 10 is 0.003% or less by mass%. If the amount of carbon in the base material of the electrical steel sheet exceeds 0.006%, there is a possibility that a problem will occur in magnetic aging. In addition, it is more preferable that the carbon content in the non-oriented electrical steel sheet is 0.003% or less because excellent magnetic properties can be obtained particularly after strain relief annealing.

  The chromium content (Cr content) contained in the electrical steel sheet 1 is mass%, and is 0.3% or more and 4% or less. When Cr is contained in the steel sheet, the specific resistance can be increased without embrittlement of the electromagnetic steel sheet. Moreover, it becomes possible to form an internal oxide layer as described below by setting the amount of Cr in the electromagnetic steel sheet within the above range. In addition, when the amount of Cr in the steel plate is out of the above range, the surface of the steel plate 10 is not oxidized, which is not preferable. In addition, it is more preferable that the amount of Cr contained in the electromagnetic steel sheet 1 is 0.5% or more and 3.5% or less by mass%. This is because, during recrystallization annealing, needle-like oxides can be observed more clearly on the surface, so that a better internal oxide layer can be formed.

  The silicon content (Si content) contained in the electrical steel sheet 1 is 1% or more and 4% or less by mass%. When Si is contained in the electromagnetic steel sheet, iron loss can be improved. By setting the amount of Si in the electromagnetic steel sheet within the above range, it is possible to improve the iron loss and form an internal oxide layer as described below. When the Si content in the electrical steel sheet is less than 1%, an internal oxide layer as described below cannot be formed. Further, when the Si amount in the electromagnetic steel sheet exceeds 4%, the embrittlement increases, which is not preferable. In addition, it is still more preferable that the amount of Si contained in the electromagnetic steel sheet 1 is 1.5% or more and 3.5% or less in mass%. This is because, during recrystallization annealing, needle-like oxides can be observed more clearly on the surface, so that a better internal oxide layer can be formed.

  The amount of aluminum (Al amount) contained in the electromagnetic steel sheet 1 is 0.4% or more and 3% or less in mass%. When Al is contained in the steel plate, iron loss can be improved. By making the amount of Al in the electrical steel sheet within the above range, it is possible to improve the iron loss and form an internal oxide layer as described below. When the Al content in the electrical steel sheet is less than 0.4%, an internal oxide layer as described below cannot be formed. Further, when the amount of Al in the electrical steel sheet exceeds 3%, embrittlement increases, which is not preferable. In addition, it is still more preferable that the amount of Al contained in the electromagnetic steel sheet 1 is 0.5% or more and 2.5% or less in mass%. This is because, during recrystallization annealing, needle-like oxides can be observed more clearly on the surface, so that a better internal oxide layer can be formed.

  When the magnetic steel sheet 1 further contains manganese, the manganese amount (Mn amount) contained in the magnetic steel sheet 1 is preferably 1.5% or less by mass%. When Mn is contained in the electromagnetic steel sheet in the above-described content, it is possible to increase the specific resistance of the electromagnetic steel sheet and improve the iron loss. In addition, when the amount of Mn in an electromagnetic steel plate exceeds 1.5%, since the problem of a brittleness will arise in an electromagnetic steel plate, it is unpreferable.

  When the magnetic steel sheet 1 further contains sulfur, the sulfur amount (S amount) contained in the magnetic steel sheet 1 is preferably 0.003% or less, and more preferably 0.002% or less in mass%. When the amount of S in the electrical steel sheet exceeds 0.003%, sulfides such as MnS increase in the electrical steel sheet, and the movement of the domain wall in the electrical steel sheet is inhibited, and the magnetic properties of the electrical steel sheet. Is not preferable because it deteriorates. If it is 0.002% or less, since the sulfide is further reduced, the iron loss is improved, which is more preferable.

  When the magnetic steel sheet 1 further contains nitrogen, the amount of nitrogen (N amount) contained in the magnetic steel sheet 1 is preferably 0.003% or less by mass%. If the N content in the electrical steel sheet is more than 0.003%, a bulge-shaped surface defect called a blister occurs in the electrical steel sheet, which is not preferable.

  When the electromagnetic steel sheet 1 further contains tin, the tin amount (Sn amount) contained in the electromagnetic steel sheet 1 is preferably 0.01% or more and 0.15% or less by mass%. When Sn is contained in the electromagnetic steel sheet in the above-described content, nitriding of the steel sheet during recrystallization annealing can be prevented. In addition, when the Sn content in the electrical steel sheet is less than 0.01%, it is not preferable because nitriding of the steel sheet during recrystallization annealing cannot be sufficiently prevented. In addition, when the Sn content in the electrical steel sheet exceeds 0.15%, the effect of preventing nitriding during recrystallization annealing is saturated, which is not preferable from the viewpoint of cost.

  When the magnetic steel sheet 1 further contains antimony, the antimony amount (Sb amount) contained in the magnetic steel sheet 1 is preferably 0.005% or more and 0.05% or less by mass%. When Sb is contained in the electromagnetic steel sheet in the above-described content, nitriding of the steel sheet during recrystallization annealing can be prevented. In addition, when the amount of Sb in the magnetic steel sheet is less than 0.005%, it is not preferable because nitriding of the steel sheet during recrystallization annealing cannot be sufficiently prevented. Moreover, when the amount of Sb in the magnetic steel sheet exceeds 0.05%, the effect of preventing nitriding during recrystallization annealing is saturated, which is not preferable from the viewpoint of cost.

  When tin or antimony is contained in the steel plate, a thin oxide layer of tin or antimony is formed from the steel plate 10 and the internal oxide layer 20 as a base material in the final stage in which an internal oxide layer as described below is formed. 2 is formed in a two-dimensional film shape (that is, in parallel with the xy plane in FIG. 1). This thin oxide layer is thought to block nitrogen penetration and prevent nitriding of the electrical steel sheet.

  Note that tin or antimony is an element that exhibits an anti-nitriding effect even when contained alone in the steel sheet, but recrystallization occurs even when both tin and antimony are contained in the steel sheet. It is possible to effectively prevent nitriding of the steel sheet during annealing.

  Further, the non-oriented electrical steel sheet according to the present embodiment is likely to be nitrided during recrystallization annealing by forming an internal oxide layer as described below. Therefore, by including at least one of tin and antimony in the steel sheet 10, not only can it effectively prevent nitriding of the steel sheet during recrystallization annealing, but also improve the iron loss of the electromagnetic steel sheet. It becomes possible.

  The electromagnetic steel sheet 1 may contain unavoidable impurities that cannot be reduced to zero ppm industrially. Examples of such inevitable impurities include elements such as copper (Cu), nickel (Ni), phosphorus (P), titanium (Ti), niobium (Nb), vanadium (V), zirconium (Zr), and oxygen (O). Can be mentioned. Among these inevitable impurities, especially Ti, Nb, V, Zr, O, etc., even if the content is very small, it forms fine precipitates and degrades the iron loss of the steel sheet. The content is preferably 0.005% or less.

  Thus, the non-oriented electrical steel sheet 1 according to the present embodiment mainly has a three-layer structure of the steel sheet 10, the internal oxide layer 20, and the external oxide layer 30 as the base material. The needle-shaped oxide 21 is formed so that the major axis direction of the oxide is parallel to the thickness direction of the steel plate. By having such a structure, the non-oriented electrical steel sheet 1 according to the present embodiment can easily perform decarburization during recrystallization annealing, and can realize excellent iron loss characteristics.

<Method for producing non-oriented electrical steel sheet>
Then, the manufacturing method of the non-oriented electrical steel sheet which concerns on this embodiment is demonstrated in detail, referring FIG. 2 and FIG. FIG. 2 is a flowchart for explaining a method of manufacturing a non-oriented electrical steel sheet according to the present embodiment, and FIG. 3 is an explanatory diagram for explaining a recrystallization annealing process according to the present embodiment.

[Outline of manufacturing method]
Prior to the detailed description of the method for manufacturing a non-oriented electrical steel sheet according to this embodiment, an outline of the method for manufacturing a non-oriented electrical steel sheet according to this embodiment will be described first.

  As described above, the non-oriented electrical steel sheet according to the present embodiment is characterized in that it includes an internal oxide layer in which needle-like oxides are erected. By forming the internal oxide layer having such a structure on the cold-rolled plate, the cold-rolled plate can be decarburized even at a high temperature of about 1000 ° C.

This internal oxide layer includes a portion in which an oxide such as SiO _{2 as} a main component grows in a needle shape in the plate thickness direction and a portion made of an Fe base material existing between adjacent oxides. The internal oxide layer in which such needle-shaped oxides are forestated is subjected to recrystallization annealing under a predetermined condition for a system containing at least four elements of Fe, Si, Al, and Cr in a predetermined content. Is formed. That is, the internal oxide layer described above is formed by performing a soaking process of recrystallization annealing in an oxidizing atmosphere on a steel sheet in which the amount of each element of Si—Al—Cr belongs to a specific region. When a soaking process is performed on such a steel sheet in an oxidizing atmosphere, explosive oxide formation occurs. At this time, an oxide mainly composed of SiO ₂ moves from the surface of the steel sheet toward the inner layer. Grows rapidly.

Carbon contained in the cold-rolled sheet, which is the base material, is diffused to the outside of the steel sheet by using the portion made of the Fe base material as a passage, and is removed from the inside of the steel sheet by reacting with H ₂ O in the external atmosphere. . As a result, in the method for manufacturing a non-oriented electrical steel sheet according to the present embodiment, decarburization at a high temperature is possible.

  Moreover, in the manufacturing method of the non-oriented electrical steel sheet according to the present embodiment, the conventional non-oriented electrical steel sheet can be used as a heat history cycle regarding the temperature and time of the recrystallization annealing process by enabling decarburization at a high temperature. The thermal history cycle in the manufacturing process can be applied without changing anything except the atmosphere. As a result, in the method for manufacturing the non-oriented electrical steel sheet according to the present embodiment, it is possible to perform a recrystallization annealing step for obtaining desired magnetic characteristics while performing decarburization. Thereby, in the manufacturing method of the non-oriented electrical steel sheet according to the present embodiment, the decarburization annealing process at 700 ° C. to 800 ° C. which is essential in the conventional manufacturing method of the non-oriented electrical steel sheet becomes unnecessary.

  The outline of the method for manufacturing the non-oriented electrical steel sheet according to the present embodiment has been described above. Below, the manufacturing method of the non-oriented electrical steel sheet which concerns on this embodiment is demonstrated in order later in detail.

[Overall flow of manufacturing method]
The non-oriented electrical steel sheet manufacturing method according to the present embodiment includes, for example, as shown in FIG. 2, a steelmaking process S11, a hot rolling process S13, a hot rolled sheet annealing process S15, and a cold rolling process S17. And a recrystallization annealing step S19.

  Steelmaking process S11 is a process of manufacturing the steel material containing a desired component. In order to manufacture the non-oriented electrical steel sheet according to the present embodiment, in mass%, C ≦ 0.007%, Cr: 0.3 to 4%, Si: 1 to 4%, Al: 0.4 to It is necessary that it contains at least 3% and the balance is inevitable impurities and Fe. Here, when the carbon content is more than 0.007% in mass%, even if decarburization is performed in the recrystallization annealing process described later, the final carbon content is 0.006% or less in mass%. This is not preferable because there is a possibility that a problem may arise in the magnetic aging of the non-oriented electrical steel sheet. The reason why the Cr amount, the Si amount, and the Al amount are within the above-described ranges is as described above.

  In addition, as described above, the steel material after the component adjustment may include mass Mn ≦ 1.5%, S ≦ 0.003%, and N ≦ 0.003%. Moreover, the steel material after component adjustment is the mass%, and may contain at least any one of Sn: 0.01-0.15% and Sb: 0.005-0.05%.

  Hot rolling process S13 implemented after steelmaking process S11 is a process which hot-rolls the steel materials after a component adjustment, and makes it a hot rolled material. In the hot rolling, the heating of the steel material (for example, slab) is not particularly limited, but is preferably a low temperature of about 950 to 1200 ° C. in order to prevent generation of fine precipitates. Further, the thickness of the hot-rolled sheet to be manufactured is not particularly limited, but is about 0.8 to 3.0 mm.

  The hot-rolled sheet annealing step S15 performed after the hot-rolling step S13 is a step of annealing the hot-rolled plate manufactured in the hot-rolling step. By annealing the hot-rolled sheet, it is possible to improve the magnetic flux density of the steel sheet and reduce the hysteresis loss. This hot-rolled sheet can be annealed by, for example, continuous annealing. The annealing temperature of the hot-rolled sheet is preferably set to, for example, 800 to 1100 ° C. in consideration of the heat uniformity of the coil.

  In addition, you may perform the pickling process which wash | cleans the oxide scale produced | generated on the hot-rolling original sheet or the hot-rolled sheet using acids, such as hydrochloric acid, before or after implementation of this annealing process S15 of a hot-rolled sheet.

  Cold rolling process S17 implemented after hot-rolled sheet annealing process S15 is a process of cold-rolling a hot-rolled sheet and manufacturing a cold-rolled sheet having a desired thickness. Although cold rolling can be performed by normal reverse rolling or tandem rolling, reverse rolling using a Sendzimer mill or the like is preferable because a cold rolled sheet having a high magnetic flux density can be produced. Moreover, in order to prevent a brittle fracture | rupture, it is also preferable to warm-roll at 40-200 degreeC. The thickness of the cold-rolled plate is preferably thin in order to improve the high-frequency magnetic characteristics, and is preferably 0.1 to 0.5 mm, for example.

  The recrystallization annealing step S19 performed after the cold rolling step S17 is a step of removing work distortion generated in the steel sheet during rolling by recrystallizing the crystal structure by annealing. This recrystallization annealing step will be described in detail below again with reference to FIG.

  By passing through such a procedure, the non-oriented electrical steel sheet according to the present embodiment is manufactured. In addition, after this recrystallization annealing process S19, the application | coating and baking process of an insulating film are normally performed. This insulating film may be an organic material, an inorganic material, or a mixture of an organic material and an inorganic material.

  The non-oriented electrical steel sheet manufactured in this way is laminated after being punched into a desired shape, and is used as a motor core, or is used after the laminated motor core is subjected to strain relief annealing at about 700 to 800 ° C. To do.

[Recrystallization annealing process]
Next, the recrystallization annealing process performed in the method for manufacturing a non-oriented electrical steel sheet according to the present embodiment will be described in detail with reference to FIG.

  As shown in FIG. 3, for example, the recrystallization annealing process is divided into three processes: i) heating process, ii) soaking process, and iii) cooling process.

  The heating process is a process of heating a cold-rolled sheet for performing recrystallization annealing to a desired temperature. In this heating process, the cold-rolled sheet at room temperature is heated to about 900 ° C. using a radiant tube heating method or a non-oxidation furnace (NOF). The heating time can be appropriately adjusted according to the target temperature.

The atmosphere in the furnace during the heating process is a mixed gas composed of hydrogen (H ₂ ) + nitrogen (N ₂ ) + water vapor (H ₂ O), and is preferably an oxidizing atmosphere. By making the oxidizing atmosphere from the heating process, the carbon contained in the steel sheet can be decarburized more easily. In addition, when using a non-oxidation furnace for the heating of a steel plate, it is also possible to utilize the direct flame burner combustion gas of a non-oxidation furnace for the heating of a steel plate. A non-oxidizing furnace is usually used for heating up to about 900 ° C., but this combustion gas is a gas containing many components such as CO, CO ₂ , H ₂ O, H ₂ , O ₂ , and N _2. . Therefore, a desired oxidizing atmosphere can be easily realized by using this combustion gas. In addition, it is preferable that the dew point in a heating process is at least 30 degreeC or more.

Further, when the temperature rises to a predetermined temperature or higher in the heating process, the oxidation starts and the internal oxide layer 20 starts to be formed. However, the internal oxide layer having a needle-like oxide can be formed by setting a strong oxidizing atmosphere in the initial process of oxidation. 20 becomes easy to develop. Therefore, the atmosphere in the furnace during _heating, it is preferable that the water vapor partial pressure represented by _P H2O _/ P _H2 is the oxidizing atmosphere is from 0.05 to 5. Note that P _H2O is the partial pressure of the water vapor component (H ₂ O), and P _H2 is the partial pressure of the hydrogen component (H ₂ ). If the water vapor partial pressure is less than 0.05, decarburization cannot be performed, which is not preferable. Further, when the water vapor partial pressure is more than 5, oxidation unevenness called a gas mark occurs on the surface of the steel sheet, which is not preferable because the appearance as a product is impaired.

  The soaking process is a process of mainly performing decarburization of the steel sheet and recrystallization of the crystal structure in the steel sheet while maintaining the temperature in the furnace within a predetermined range.

  Here, in order to form the internal oxide layer 20 according to the present embodiment, it is necessary to perform annealing at 900 to 1100 ° C. in the soaking process. Here, when the annealing temperature is less than 900 ° C., the time required for decarburization becomes long, which is not preferable. In addition, when the annealing temperature is 1100 ° C. or higher, the damage to the refractories and hearth rolls of the annealing furnace that performs recrystallization annealing is not preferable.

Moreover, in order to form the internal oxide layer 20 according to the present embodiment, it is necessary to make the atmosphere in the furnace in the soaking process an oxidizing atmosphere. More specifically, the atmosphere in the soaking process is a mixed gas composed of hydrogen (H ₂ ) + nitrogen (N ₂ ) + water vapor (H ₂ O), and the water vapor partial pressure represented by P _H2O / PH ₂ is set. 0.05 to 0.8. Here, when the water vapor partial pressure is less than 0.05, decarburization cannot be performed, which is not preferable. In addition, when the water vapor partial pressure is more than 0.8, the thickness of the formed internal oxide layer 20 becomes too thick and the high frequency iron loss is deteriorated, which is not preferable. By adjusting the water vapor partial pressure, the amount of oxygen combined with silicon in the steel sheet can be adjusted, and the thickness of the formed internal oxide layer 20 can be limited. Therefore, in this embodiment, by setting the water vapor partial pressure in the soaking process to 0.05 to 0.8, it is possible to limit the thickness of the formed internal oxide layer 20 to 0.2 μm or more and 4 μm or less. It becomes.

  The soaking time (the time represented by t2-t1 in FIG. 3) is preferably, for example, 1 second to 100 seconds. If the soaking time is lengthened, the amount of decarburization increases, but the productivity is hindered. The decarburization amount is preferably 10 ppm (0.0010% by mass) or more, but such decarburization amount can be sufficiently achieved by forming an internal oxide layer having acicular oxides. The amount of decarburization.

  Moreover, it is preferable that the particle size of the crystal | crystallization produced | generated by recrystallization annealing is 30 micrometers-130 micrometers, for example. This crystal grain size can be measured, for example, by observing the structure with an optical microscope of about 100 times. The crystal grain size is an average grain size, and can be determined by a normal line segment method (a method of counting the number of crystal grain boundaries and intersections crossing a straight line).

  The cooling process is a process of cooling the steel plate that has undergone the soaking process to a desired temperature. Here, in the electrical steel sheet containing Cr like the non-oriented electrical steel sheet according to this embodiment, the strain sensitivity of iron loss is stronger than the steel containing only Si, and in particular, high frequency and low magnetic field iron. It was found that the residual stress in the steel sheet after recrystallization annealing was effective for the loss. This residual stress is compression in the width direction of the steel sheet, and the iron loss deterioration in the width direction is large. Therefore, it is desirable to reduce the stress remaining on the non-oriented electrical steel sheet after recrystallization annealing. By reducing the residual stress, the residual magnetic flux density can be improved.

  In order to reduce the residual stress in the recrystallization annealing, it was found that the cooling rate in the recrystallization annealing can be improved by gradually cooling. More specifically, it was found that residual stress in recrystallization annealing can be reduced by setting the cooling rate from 900 ° C. to 300 ° C. to 30 ° C./sec or less. Further, the cooling rate is preferably 1 ° C./sec or more from the viewpoint of productivity. Further, the in-furnace tension is preferably 0.5 to 6 MPa, which is a slightly low value. Note that since the residual strain hardly occurs at a temperature of 300 ° C. or lower, the cooling rate may not be controlled.

The recrystallization annealing process according to the present embodiment has been described in detail above.
The conventional atmosphere in the general recrystallization annealing process is a reducing atmosphere using a gas in which hydrogen and nitrogen are mixed. In this reducing atmosphere, carbon contained in the steel sheet is decarburized. I can't. Therefore, in the recrystallization annealing step according to this embodiment, as described above, at least the soaking atmosphere is an oxidizing atmosphere. As a result, the carbon in the steel sheet can be dispersed in the atmosphere using the portion 23 made of the Fe base material in the formed internal oxide layer 20 as a passage, and the carbon contained in the steel sheet can be decarburized. It becomes possible.

(Example)
Below, the manufacturing method of the non-oriented electrical steel sheet and the non-oriented electrical steel sheet according to the embodiment of the present invention will be described in detail with reference to examples. In addition, the Example shown below is an example of the manufacturing method of the non-oriented electrical steel sheet and the non-oriented electrical steel sheet according to the embodiment of the present invention to the last, and the non-oriented electrical steel sheet and the non-oriented property according to the present invention. The manufacturing method of the electrical steel sheet is not limited to the following example.

<Example 1>
The components shown in Table 1 were melt-cast by a vacuum melting test in a laboratory and hot-rolled to a thickness of 2 mm. Hot rolled sheet annealing was performed in N ₂ at 1000 ° C. for 1 minute, and then pickling and cold rolling to obtain 0.30 mm. Subsequently, recrystallization annealing including a soaking process for 15 seconds at 1000 ° C. was performed with an atmosphere of 80% H ₂ + 20% N ₂ and water vapor at 20 ° C. dew point. The water vapor partial pressure P _H2O / P _H2 was 0.14.

After the recrystallization annealing, the carbon (C) component and the nitrogen (N) component were subjected to chemical analysis, and the internal oxide layer was observed with a scanning electron microscope (SEM). The thickness of the internal oxide layer was measured by measuring the width of 10 mm at the center of the steel sheet with SEM and averaging the obtained measurement values. The recrystallized and annealed steel sheet is punched to 100 mm square, and then subjected to strain relief annealing at 750 ° C. for 2 hours in an N ₂ atmosphere, and the magnetic properties at 400 Hz are measured according to a single plate magnetic property measuring device (according to JIS C 2550). ). Further, in the SEM observation of the internal oxide layer, the steel sheet cross section after recrystallization annealing was polished and then subjected to night corrosion for observing the metal structure under a normal optical microscope, and then the steel sheet cross section was observed by SEM. The obtained results are shown in Table 2 and FIGS. 4A and 4B.

  As shown in Tables 1 and 2, when the Cr-Si-Al content is within the range according to the present invention, a needle-like internal oxide layer is formed and decarburization is possible. It was. Moreover, although the tendency of nitriding is recognized when a needle-like oxide is formed, the effect of suppressing nitriding was recognized by the addition of Sn or Sb.

  FIG. 12 shows that the internal oxidation progresses in a needle shape in the thickness direction of the steel sheet. On the other hand, FIG. 1 shows that the internal oxide layer has developed as a two-dimensional film in the direction of the steel sheet as in the prior art.

<Example 2>
Continuous molten steel containing 0.0040% C, 1% Cr, 3% Si, 1% Al, 0.2% Mn, 0.001% S, 0.001% N, 0.02% Sn by mass% It was cast and heated at 1100 ° C. to obtain a hot rolled coil having a thickness of 1.5 mm. Next, annealing was performed at 1100 ° C. for 2 minutes in N ₂ , pickling, and cold rolling to a thickness of 0.25 mm. This cold-rolled sheet was tested in a laboratory to change the soaking temperature and soaking time of recrystallization annealing, the atmosphere in heating and soaking, and the like. The soaking time was all 10 seconds. The cooling atmosphere was N ₂ and the cooling rate was constant at 20 ° C./second. After recrystallization annealing, analysis, structure observation, and magnetic measurement were performed in the same manner as in Example 1 to obtain Table 3. In Example 2, strain relief annealing was not performed.

  As shown in Table 3, it is understood that a needle-like internal oxide layer is obtained by the temperature and atmosphere included in the range according to the present invention, the target decarburization amount is ensured, and excellent high-frequency iron loss is obtained. It was.

  In addition, Experiment No. 3, the non-oriented electrical steel sheet was manufactured using the equipment used for actual operation under the same conditions as shown in FIG. 3, and the manufactured non-oriented electrical steel sheet was analyzed in the same manner as in Example 1. Tissue observation and magnetic measurements were performed. As a result, a 1.6 μm-thick internal oxide layer having needle-like oxide was formed, and W10 / 800 was 31.4 W / kg. As is clear from this result, even when non-oriented electrical steel sheets are manufactured using equipment used in actual operation, the same results as when non-oriented electrical steel sheets are manufactured in the laboratory are obtained. It was.

<Example 3>
Experiment No. 2 of Example 2 The experiment was conducted by controlling the cooling speed from 900 ° C. to 300 ° C. in the recrystallization annealing temperature and atmosphere of No. 8. Table 4 shows the obtained iron loss results.

  As shown in Table 4, excellent high frequency iron loss was obtained by cooling at a cooling rate included in the range according to the present invention. In addition, especially about this high frequency iron loss, iron loss deterioration when exciting in the steel plate width direction was remarkable. Here, the L direction is the rolling direction, and the C direction is the width direction perpendicular to the rolling direction. Regarding the amount of C, the internal oxide layer structure, and the thickness, Experiment No. The result obtained in 8 was exactly the same.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Non-oriented electrical steel sheet 10 Steel sheet 20 Internal oxide layer 21 Oxide 23 Part which consists of Fe base material 30 External oxide layer

Claims (11)

% By mass, C ≦ 0.006%, Cr: 0.3-4%, Si: 1-4%, Al: 0.4-3% at least, and the balance consists of inevitable impurities and Fe,
The oxide layer with acicular oxide is located near the surface of the steel sheet,
The acicular oxide is a non-oriented electrical steel sheet, characterized in that the major axis direction of the oxide is parallel to the thickness direction of the steel sheet.   The non-oriented electrical steel sheet according to claim 1, wherein the oxide layer has a thickness of 0.2 to 4 μm.   3. The non-oriented electrical steel sheet according to claim 1, further comprising, by mass%, Mn ≦ 1.5%, S ≦ 0.003%, and N ≦ 0.003%. Non-oriented electrical steel sheet.   The non-oriented electrical steel sheet further includes at least one of Sn: 0.01 to 0.15% and Sb: 0.005 to 0.05% by mass. The non-oriented electrical steel sheet according to any one of 1 to 3. Hot rolling comprising at least C ≦ 0.007%, Cr: 0.3 to 4%, Si: 1 to 4%, Al: 0.4 to 3% with the balance being inevitable impurities and Fe Annealing the plate;
Cold rolling the hot-rolled sheet that has been annealed into a cold-rolled sheet; and
Recrystallizing the cold-rolled sheet; and
Including
The soaking process of recrystallization annealing, 900 to 1100 ° C., and that the steam partial pressure _P H2O _{/ P H2} is the oxidizing atmosphere is 0.05 to 0.8, have a needle-like oxide And the manufacturing method of the non-oriented electrical steel sheet characterized by forming the oxide layer in which the major axis direction of the said acicular oxide is parallel to the thickness direction of a steel plate in the surface vicinity of the said cold rolled sheet. Wherein in the recrystallization annealing, the water vapor partial pressure P _{H2O /} P _H2 is and performing heated to 900 ° C. in an oxidizing atmosphere is from 0.05 to 5, non-oriented electrical steel sheet according to claim 5 Manufacturing method.   The method for manufacturing a non-oriented electrical steel sheet according to claim 5 or 6, wherein the oxide layer has a thickness of 0.2 to 4 µm.   The hot rolled sheet according to any one of claims 5 to 6, further comprising, by mass%, Mn ≦ 1.5%, S ≦ 0.003%, and N ≦ 0.003%. The manufacturing method of the non-oriented electrical steel sheet described in 1.   The hot-rolled sheet further includes at least one of Sn: 0.01 to 0.15% and Sb: 0.005 to 0.05% by mass%. The manufacturing method of the non-oriented electrical steel sheet according to any one of 8.   The method for producing a non-oriented electrical steel sheet according to any one of claims 5 to 9, wherein in the recrystallization annealing, a temperature raising process for raising the temperature to 900 ° C is an open flame atmosphere. .   11. The recrystallization annealing, wherein a cooling rate in a cooling process from 900 ° C. to 300 ° C. performed after the soaking process is 1 to 30 ° C./s. The manufacturing method of the non-oriented electrical steel sheet as described in a term.