JP5375653B2 - Method for producing non-oriented electrical steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a non-oriented silicon steel sheet with which the deterioration of pickling property can be restrained. <P>SOLUTION: The method for producing the non-oriented silicon steel sheet includes: a process for continuously annealing a hot-rolled plate composed, by mass, of &le;0.006% C, 0.3-5% Cr, 1-4% Si, 0.4-3% Al, &le;1.5% Mn, &le;0.003% S, &le;0.003% N and the balance Fe with inevitable impurities; a process for pickling the annealed hot-rolled plate; a process for making a cold-rolled sheet by cold-rolling the pickled hot-rolled plate; and a process for recrystallize-annealing the cold-rolled sheet. In the process for annealing the hot-rolled plate, the annealing temperature is controlled to be 900-1,150&deg;C, the atmosphere is controlled to be mainly N<SB>2</SB>, the dew point is controlled to be &le;50&deg;C and the O<SB>2</SB>content is controlled to be &le;1 vol.%. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to 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.

  In general, a high-grade manufacturing method for non-oriented electrical steel sheets is performed by hot rolling a continuous cast slab with adjusted components to perform hot-rolled sheet annealing and removing the surface scale of the hot-rolled sheet after annealing. The hot-rolled sheet after pickling is cold-rolled to form a cold-rolled sheet, and the cold-rolled sheet is subjected to recrystallization annealing. 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. In particular, Cr is known to be an extremely effective component for high-frequency applications because it increases the specific resistance without embrittlement of steel (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 11-229095

  However, as one of the problems with Cr-added steel, there is a problem of deterioration of pickling properties. Due to the deterioration of pickling performance, there is a need for a significant decrease in the sheeting speed in the pickling process aimed at reducing the scale remaining on the steel plate surface after pickling, or the scale remaining on the steel plate surface after pickling. In the next process (cold rolling), there were obstacles in production, such as breakage of the steel sheet due to abnormal wear of the rolls and poor shape of the steel sheet.

  Then, this invention is made | formed in view of the said problem, The place made into the objective of this invention provides the manufacturing method of the non-oriented electrical steel sheet which can suppress deterioration of pickling property. There is.

In order to solve the above problems, according to an aspect of the present invention, in mass%, C ≦ 0.006%, Cr: 0.3 to 5%, Si: 1 to 4%, Al: 0.4 to 3%, Mn ≦ 1.5%, S ≦ 0.003%, N ≦ 0.003%, the step of annealing a hot-rolled sheet of which the balance is inevitable impurities and Fe, and the annealed hot rolling A step of pickling the plate, a step of cold rolling the pickled hot-rolled plate to form a cold-rolled plate, and a step of recrystallization annealing the cold-rolled plate, In the annealing step, the annealing temperature is 1000 (not including 1000 ° C.) to 1150 ° C., the soaking time is 120 seconds to 5 minutes, the atmosphere is mainly N ₂ , the dew point is 50 ° C. or less, and the amount of O ₂ A method for producing a non-oriented electrical steel sheet with a volume% of 1% or less is provided.

  In the step of annealing the hot-rolled sheet, the dew point may be 30 ° C. or less.

In the step of annealing the hot-rolled sheet, the O ₂ amount may be 0.5% or less by volume%.

  As described above, according to the present invention, there is provided a method for producing a non-oriented electrical steel sheet capable of suppressing deterioration of pickling properties by appropriately controlling the annealing temperature and atmosphere when annealing a hot-rolled sheet. It becomes possible.

It is explanatory drawing for demonstrating the structure of the hot rolled sheet after the continuous annealing 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.

  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 hot-rolled sheet after continuous annealing>
First, the structure of the hot-rolled sheet after continuous annealing according to the first embodiment of the present invention will be described with reference to FIG. Drawing 1 is an explanatory view for explaining the structure of the hot-rolled sheet after continuous annealing concerning this embodiment, and shows the structure of the hot-rolled sheet after continuous annealing typically.

  For example, as shown in FIG. 1, the hot-rolled sheet 1 after the continuous annealing mainly includes a steel plate 10 that is a base material and an oxide layer 20 formed on the steel plate 10.

[About hot-rolled sheet]
The steel plate 10 which is a base material is manufactured using a hot-rolled plate prepared so that each component contained in the steel plate falls within a predetermined range. The plate thickness of the steel plate 10 is preferably thinner in order to improve magnetic properties at high frequencies (frequency of about 400 Hz to 1 kHz), for example, about 0.8 mm to 3.0 mm.

  Here, the hot-rolled sheet according to the present embodiment is mass%, C ≦ 0.006%, Cr: 0.3 to 5%, Si: 1 to 4%, Al: 0.4 to 3%, Mn ≦ 1.5%, S ≦ 0.003%, N ≦ 0.003% is included at least, and the balance is a steel plate made of inevitable impurities and Fe.

  The amount of carbon (C amount) contained in the hot-rolled sheet used as the steel sheet 10 according to the present embodiment is 0.006% or less in mass%. Moreover, it is preferable that the carbon content contained in a hot-rolled sheet is 0.003% or less by mass%. If the carbon content in the hot-rolled sheet, which is the base material of a non-oriented electrical steel sheet (hereinafter abbreviated as an electrical steel sheet), exceeds 0.006%, there may be a problem in the magnetic aging of the electrical steel sheet. There is. Moreover, when the carbon content in the hot-rolled sheet is 0.003% or less, it is more preferable because excellent magnetic properties can be obtained especially after strain relief annealing.

  The amount of chromium (Cr amount) contained in the hot-rolled sheet is mass% and is 0.3% or more and 5% 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 suppress content of Si and Al added to a hot-rolled sheet to the above ranges by making Cr amount in a hot-rolled sheet into the above-mentioned range. In addition, when the amount of Cr in the hot-rolled sheet is outside the above range, the surface of the steel sheet 10 is not oxidized, which is not preferable.

  The amount of silicon (Si amount) contained in the hot-rolled sheet is 1% or more and 4% or less in mass%. It becomes possible to improve the iron loss of an electromagnetic steel sheet by containing Si in a hot-rolled sheet. By making Si amount in a hot-rolled sheet into the above-mentioned range, it becomes possible to improve the pickling property in the pickling process performed after continuous annealing while improving iron loss. When the amount of Si in the hot-rolled sheet is less than 1%, an internal oxide layer as described below is not formed, which is not preferable. Further, when the Si amount in the electromagnetic steel sheet exceeds 4%, the embrittlement increases, which is not preferable.

  The amount of aluminum (Al amount) contained in the hot-rolled sheet is 0.4% or more and 3% or less in mass%. By containing Al in the hot-rolled sheet, it is possible to improve the iron loss of the electromagnetic steel sheet. By making Al content in a hot-rolled sheet into the above-mentioned range, it becomes possible to improve the pickling property in the pickling process performed after continuous annealing while improving iron loss. When the amount of Al in the hot-rolled sheet is less than 0.4%, an internal oxide layer as described below is not formed, which is not preferable. Further, when the Al content in the hot-rolled sheet exceeds 3%, embrittlement increases, which is not preferable.

  The amount of manganese (Mn amount) contained in the hot-rolled sheet is 1.5% or less by mass%. When Mn is contained in the hot-rolled sheet at 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 a hot-rolled sheet exceeds 1.5%, since a brittle problem will arise in an electromagnetic steel plate, it is unpreferable.

  The amount of sulfur (S amount) contained in the hot-rolled sheet is 0.003% or less by mass%. Moreover, it is preferable that the sulfur amount contained in a hot-rolled sheet is 0.002% or less by mass%. When the amount of S in the hot-rolled sheet exceeds 0.003%, sulfides such as MnS increase in the magnetic steel sheet, and the movement of the domain wall in the magnetic steel sheet is hindered. Since the characteristics deteriorate, it is not preferable. If it is 0.002% or less, since the sulfide is further reduced, the iron loss is improved, which is more preferable.

  The amount of nitrogen (N amount) contained in the hot-rolled sheet is 0.003% or less by mass%. When the amount of N in the hot-rolled sheet exceeds 0.003%, it is not preferable because a bulge-shaped surface defect called a blister occurs in the magnetic steel sheet.

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

  In the above, the steel plate 10 which concerns on this embodiment, and the hot-rolled sheet used when manufacturing this steel plate 10 were demonstrated. Next, the oxide layer 20 according to this embodiment will be described.

[About oxide layer]
For example, as illustrated in FIG. 1, the oxide layer 20 is a layer containing an oxide formed on the steel plate 10. Examples of the oxide contained in the oxide layer 20 include iron oxide (FeO), silicon dioxide (SiO ₂ ), and aluminum oxide (Al ₂ O ₃ ). In addition to these oxides, for example, an oxide of Cr may be included.

  The steel plate surface of the hot-rolled sheet after continuous annealing with the scale attached was analyzed by glow discharge emission spectroscopy (GDS) while sputtering from the outermost surface. Thereby, about the oxide layer 20 which concerns on this embodiment, the state of what kind of component is contained in the part of which thickness can be grasped | ascertained.

As a result of analysis, in the hot-rolled sheet after continuous annealing according to the present embodiment, an oxide layer mainly composed of FeO, an oxide layer mainly composed of SiO ₂ and Al ₂ from the outermost surface of the steel sheet toward the base material. It has been found that it has three types of oxide layers called oxide layers mainly composed of O ₃ . Therefore, in the following description, an oxide layer mainly composed of FeO is referred to as an outer oxide layer, and an oxide layer mainly composed of SiO ₂ and an oxide layer mainly composed of Al ₂ O ₃ are collectively arranged. It will be referred to as an oxide layer.

  This result is schematically shown in FIG. That is, in the hot-rolled sheet after continuous annealing according to the present embodiment, the internal oxide layer 21 is formed on the steel plate 10 serving as a base material, and the external oxide layer 23 is formed on the internal oxide layer 21.

<Relationship between oxide layer and pickling properties>
As a result of the above-mentioned analysis using GDS, when the component balance of the Cr component, the Si component and the Al component is in the above range in the so-called Cr-added steel, a large amount of SiO ₂ or Al ₂ O ₃ remains. I understood. In particular, when the amount of Al increases, the thickness of the oxide layer mainly composed of Al ₂ O ₃ becomes thicker after hot-rolled sheet annealing, and a deep concentration of Al ₂ O ₃ penetrates into the steel sheet very deeply. There was found.

As a result of studying the relationship with the pickling property by the present inventors based on these findings obtained, the deterioration of the pickling property is caused by abnormal development of Al ₂ O _{3 due} to abnormal oxidation that occurs during annealing of the hot-rolled sheet. It was concluded that this was the case.

That is, since the oxide layer mainly composed of Al ₂ O ₃ developed by annealing becomes thick, it becomes difficult to remove the oxide layer in the pickling process, and Al ₂ O ₃ itself is a hard oxide. For this reason, the rolling roll is significantly worn.

  The reason why such abnormal oxidation occurs is not clear at present, but the following reasons are conceivable. That is, when the Cr—Si—Al component balance is in the specific range as described above, the outermost layer oxide having a high Cr concentration is distributed in a mottled manner (in an island shape). As a result, on the steel sheet surface, there are a portion covered with the outermost layer oxide with a high Cr concentration and a portion not covered, and diffusion of oxygen in the atmosphere into the steel plate becomes easy. It is considered a thing.

  In order to remove the scales generated in this way, the scale breakage due to the leveler and shot blasting normally performed prior to the pickling process was strengthened, and surface grinding with a normal wire brush after the pickling process was strongly performed. . However, even when such treatment was performed, there was no significant effect on descaling.

Therefore, as a result of intensive studies conducted by the inventors to suppress the deterioration of the pickling property, as described below, by controlling the annealing atmosphere during annealing of the hot-rolled sheet, It was conceived that the Al ₂ O ₃ content can be suppressed and the pickling property can be improved. Below, the manufacturing method of the non-oriented electrical steel sheet which can suppress deterioration of pickling property is demonstrated in detail.

<About the manufacturing method of non-oriented electrical steel sheet>
[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 pickling process S17. The method mainly includes a cold rolling step S19 and a recrystallization annealing step S21.

  Steelmaking process S11 is a process of manufacturing the steel material containing a desired component. By passing through this steelmaking process, C ≦ 0.006%, Cr: 0.3-5%, Si: 1-4%, Al: 0.4-3%, Mn ≦ 1.5% by mass% , S ≦ 0.003%, N ≦ 0.003% at least, and the balance is made of a steel material composed of inevitable impurities and Fe.

  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.

  After the hot-rolled sheet annealing step S15, the pickling step S17 is performed to wash away the oxide scale formed on the hot-rolled plate using acid.

  In addition, the above-mentioned annealing process and pickling process are demonstrated in detail anew later.

  Cold rolling process S19 implemented after pickling process S17 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 S21 performed after the cold rolling step S19 is a step of removing work strain generated in the steel sheet during rolling by recrystallizing the crystal structure by annealing.

  Through such a procedure, a non-oriented electrical steel sheet is manufactured. In addition, after recrystallization annealing process S21, 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 used as a motor core, or used after the laminated motor core is subjected to strain relief annealing at about 700 to 800 ° C. To do.

[About annealing process]
Then, the annealing process of the manufacturing method of the non-oriented electrical steel sheet which concerns on this embodiment is demonstrated in detail.

  As described above, the annealing process is a process aimed at improving the magnetic flux density and reducing the hysteresis loss. There are two methods for annealing steel sheets: batch annealing, in which coiled steel is put into an annealing furnace, and continuous annealing, in which coiled steel is rewound, but from the point of heat uniformity of the coil, continuous annealing is used. It is preferable to anneal the hot rolled sheet.

In the annealing process according to the present embodiment, the temperature at which the hot-rolled sheet is annealed (hereinafter referred to as the annealing temperature) is set to 900 ° C to 1150 ° C. By setting the annealing temperature to 900 ° C. to 1150 ° C., the magnetic flux density required for the non-oriented electrical steel sheet can be realized without damaging various facilities used in the annealing process. When the annealing temperature is less than 900 ° C., the magnetic flux density required for the non-oriented electrical steel sheet cannot be obtained. In addition, when the annealing temperature is less than 900 ° C., the development of Al ₂ O ₃ is small, so that there is little problem that the pickling property is deteriorated. On the other hand, when the annealing temperature exceeds 1150 ° C., the hearth roll provided in the furnace, the damage to the furnace wall, and the like are increased, which is not preferable. The soaking time in the annealing step according to the present embodiment is preferably about 10 seconds to 5 minutes.

In the annealing process according to the present embodiment, the atmosphere in the furnace is an atmosphere mainly composed of nitrogen (N ₂ ), the dew point is 50 ° C. or less, and the oxygen (O ₂ ) amount is 1% or less by volume%. Use a weakly oxidizing atmosphere. The dew point of 50 ° C. is about 19.4% by volume. For example, when the dew point is 50 ° C. and the amount of oxygen is 1% by volume, assuming that the balance is nitrogen, the volume% of nitrogen is about 80%. In addition to nitrogen and oxygen, the furnace may contain CO, CO ₂ , H _2, etc., but the volume of nitrogen is preferably 60% or more from the viewpoint of cost.

By making the atmosphere mainly nitrogen, dew point is 50 ° C. or less, and oxygen amount is 1% by volume or less, abnormal growth of Al ₂ O ₃ can be prevented, and hot-rolled sheet with improved pickling properties Can be manufactured. When the dew point exceeds 50 ° C. or the oxygen amount exceeds 1% by volume, the internal oxide layer grows explosively, and the pickling performance in the pickling process performed after annealing is remarkable. Since it deteriorates, it is not preferable.

In addition, when the dew point is 30 ° C. or less or the oxygen amount is 0.5% by volume or less, abnormal growth of Al ₂ O ₃ can be further prevented, and further pickling performance can be further improved. This is more preferable because it can be achieved.

In the annealing process according to the present embodiment, CO, CO ₂ , H _{2 and the} like may be included as the furnace atmosphere in addition to the gas components listed above.

[About pickling process]
Then, the pickling process of the manufacturing method of the non-oriented electrical steel sheet which concerns on this embodiment is demonstrated in detail.

  As described above, the pickling step is a step of washing away the oxide scale formed on the hot-rolled sheet using an acid. As the acid used in the pickling step, any acid can be used as long as it can react with the oxide scale and remove the oxide scale from the steel sheet surface of the hot-rolled sheet. Examples of the acid include nitric acid, hydrofluoric acid, hydrochloric acid and the like. In consideration of maintenance management of equipment such as tanks and piping, hydrochloric acid is preferably used among the acids exemplified above.

  Moreover, you may perform the process of destroying a scale with a leveler or shot blasting prior to this pickling process. Moreover, you may perform the process of grinding the surface of a hot-rolled board using a wire brush etc. after a pickling process. These mechanical treatments are effective for removing scale existing on the surface of the hot-rolled sheet.

In addition, by setting a large amount of grinding in mechanical grinding using a wire brush or the like and using a method of scraping off Al ₂ O ₃ located in the deep part of the internal oxide layer 23, Al ₂ O ₃ can be more reliably removed. It is also possible to do. However, if the oxide layer is to be ground deeply, the tip of the wire brush becomes extremely worn, and costs are increased, which is not realistic. Therefore, the actual grinding amount is preferably about ² to 15 g / m ² , for example.

(Example)
Below, the manufacturing method of the non-oriented electrical steel sheet which concerns on embodiment of this invention is demonstrated in detail, showing an Example. In addition, the Example shown below is an example of the manufacturing method of the non-oriented electrical steel plate which concerns on embodiment of this invention to the last, Comprising: The manufacturing method of the non-oriented electrical steel plate concerning this invention is limited to the following examples. It is not done.

<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 3 mm. Subsequently, hot-rolled sheet annealing was performed at an annealing temperature of 1120 ° C. The soaking time was 2 minutes. After annealing, a shot blast treatment with a 0.5 mmφ steel ball was performed for 15 seconds, immersed in a 25% HCl, 85 ° C. solution for 40 seconds, and then the surface was ground with a wire brush by 7 g / m ² .

The atmosphere was set to the following two levels.
(1) A mixed air stream containing N ₂ -based water vapor with a dew point of 65 ° C. and 1.5% by volume of O ₂ (2) An air stream composed of 100% dry N ₂

Before shot blasting after annealing, the film thickness of the generated oxide layer was measured by observing a cross section of the steel sheet with a scanning electron microscope (SEM). The average thickness of the outer oxide layer mainly composed of FeO and the inner oxide layer mainly composed of SiO ₂ and Al ₂ O ₃ was determined. The outer oxide layer and the inner oxide layer are easily distinguishable because they have different color tones due to the difference in the main compound.

  The steel plate surface after pickling and wire brush treatment was observed with the naked eye to determine whether or not the scale remained. The amount of the remaining scale was expressed as a ratio of the area of the scale that occupies the steel sheet surface. If the entire surface has a silvery metallic luster, the remaining scale is 0%. For example, if a dark brown scale remains in half of the surface of the steel sheet, the remaining ratio is 50%.

Also, pickling, were also measured the thickness of the _Al 2 _{O 3} after wire brushing. The thickness of Al ₂ O ₃ can be grasped by GDS on the steel sheet surface. The depth from the profile in the depth direction of the measurement result of GDS to the point showing the Al value that is half of the maximum concentrated Al amount of the outermost layer was defined as the thickness of Al ₂ O ₃ . Here, the irradiation area of GDS is 4 mmφ, and the GDS apparatus used for the analysis is JY5000RF-PSS type manufactured by Joban Yvon.

  The results obtained are shown in Table 2. In Table 2, the result in the atmosphere (1) is displayed as wet, and the result in the atmosphere (2) is displayed as dry.

  As is clear from the results shown in Tables 1 and 2, the drop in scale deteriorates in the component range of the hot-rolled sheet according to the present invention, however, the problem of remaining scale is solved by the hot-rolled sheet annealing atmosphere control. I understand that.

When attention is paid to the thickness of the internal oxide layer, the thickness of the internal oxide layer in the dry atmosphere is thinner than that in the wet atmosphere. It can be seen that it is not proportional to the thickness. Since the remaining scale is proportional to the amount of remaining Al ₂ O ₃ , it is considered that not only the depth of Al ₂ O ₃ in the internal oxide layer but also the degree of concentration is related to the remaining scale.

Further, as the remaining scale area%, less than 5% is a level that causes no industrial problems, and the thickness of the corresponding remaining Al ₂ O ₃ is 0.2 μm or less. Therefore, in Table 2, the acceptable levels of residual scale and residual Al ₂ O ₃ thickness were set to less than 5% and 0.2 μm or less, respectively. As is apparent from Table 2, it can be seen that the hot-rolled sheet according to the present invention satisfies this acceptable level. In the dry atmosphere, since the thickness of the outer oxide layer is rather increased, it is assumed that the oxidation process is a rather complicated process.

<Example 2>
In mass%, C: 0.001%, Cr: 0.8%, Si: 2.5%, Al: 1.4%, Mn: 0.2%, S: 0.002%, N: 0.00. Molten steel containing 001% was continuously cast and heated at 1150 ° C. to form a 1.8 mm thick hot rolled coil. Subsequently, hot-rolled sheet annealing was performed in the laboratory, the annealing temperature was 930 ° C., and the soaking time was 100 seconds. At this time, the main body of the annealing atmosphere was N _2, and the dew point of water vapor and the amount of O ₂ were variously changed as shown in Table 3.

After annealing, a shot blast treatment with a steel ball of 0.5 mmφ was performed for 40 seconds, immersed in an 18% HCl, 95 ° C. solution for 20 seconds, and then the surface was ground by 8 g / m ² with a wire brush. In the same manner as in Example 1, the remaining scale was investigated, and the results are shown in Table 3.

  As is apparent from the results in Table 3, by setting the water vapor dew point and the oxygen amount according to the present invention, a steel sheet with less scale remaining after pickling could be obtained. This result has shown that the deterioration of the pickling property of the hot-rolled sheet after annealing could be suppressed by controlling the annealing temperature and atmosphere by the method for producing the non-oriented electrical steel sheet according to the present invention.

In addition, the experiment No. shown in Table 3 Under the same conditions as in No. 9, hot-rolled sheets were manufactured using equipment used in actual operations. As a result, the remaining scale was 5% and the remaining Al ₂ O ₃ thickness was 0.05 μm. This was identical to the result obtained in Table 3. As is clear from this result, when the hot-rolled sheet was manufactured using the equipment used for actual operation, the same result as when the hot-rolled sheet was manufactured in the laboratory was obtained.

<Example 3>
Experiment No. 1 of Example 1 1 and Experiment No. Using the 12 hot-rolled sheets, hot-rolled sheet annealing was performed at the temperatures shown in Table 4, and the soaking time was 140 seconds. The shot blasting, pickling and wire brush were made the same conditions as in Example 1. After cold rolling to a thickness of 0.25 mm and degreasing the steel sheet surface, annealing was performed at 1000 ° C. for 3 seconds in a 30% H ₂ + 70% N ₂ atmosphere. The magnetic properties were measured with a 100 mm square single plate magnetometer (conforming to JIS C 2550) and shown in Table 4 below.

  As shown in Table 4, those within the scope of the present invention exhibited excellent high-frequency iron loss W10 / 800 (W / kg). In addition, when comparing the low-frequency and high-frequency iron loss, Table 1 Experiment No. outside the scope of the present invention. 1 and Table 1 Experiment No. of the scope of the present invention. Although there was almost no difference in W15 / 50 from the 12 materials, a large significant difference was observed in iron loss at a high frequency of 800 Hz. Moreover, the outstanding magnetic flux density and the iron loss characteristic were obtained by the high temperature hot rolled sheet annealing of 900 degreeC or more of this invention.

  The embodiment of the method for manufacturing the non-oriented electrical steel sheet according to the present invention has been described above.

In the conventional idea for the hot-rolled sheet annealing atmosphere, oxidation by water vapor, O ₂ or the like has never been considered. This is because, in normal hot-rolled sheet annealing, annealing is performed with the hot-rolled sheet scale attached to the surface of the steel sheet regardless of the atmosphere, so that the idea of making a non-oxidizing atmosphere has not occurred. In other words, even if additional oxidation was performed somewhat during annealing, it was thought that there was no problem because the pickling process was performed after annealing. Therefore, conventionally, the phenomenon of abnormal development of Al ₂ O ₃ oxide in a specific Cr—Si—Al component system as described so far has been overlooked, and the pickling property by this Al ₂ O ₃ oxide is overlooked. No knowledge has been obtained that the damage will occur.

However, the present inventor has not only conceived that the phenomenon of abnormal development of Al ₂ O ₃ oxide in a specific Cr—Si—Al component system affects the deterioration of pickling properties, but also the Al The inventors have conceived that the abnormal development of ₂ O ₃ oxide can be suppressed by controlling the atmosphere in the annealing process, and have reached the present invention.

  The non-oriented electrical steel sheet manufactured by the manufacturing method according to the present invention has excellent specific resistance, and is used as a material for a motor core used at high frequency by being laminated after being punched into a desired shape. Is possible.

  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.

1 Hot-rolled sheet after annealing 10 Steel sheet 20 Oxide layer 21 Internal oxide layer 23 External oxide layer

Claims (3)

% By mass, C ≦ 0.006%, Cr: 0.3-5%, Si: 1-4%, Al: 0.4-3%, Mn ≦ 1.5%, S ≦ 0.003%, A step of continuously annealing a hot-rolled sheet containing N ≦ 0.003% and the balance being inevitable impurities and Fe;
Pickling the hot-rolled sheet that has been annealed; and
Cold-rolling the hot-rolled sheet that has been pickled into a cold-rolled sheet,
Recrystallizing the cold-rolled sheet; and
Including
In the step of annealing the hot-rolled sheet, the annealing temperature is 1000 (not including 1000 ° C.) to 1150 ° C., the soaking time is 120 seconds to 5 minutes, the atmosphere is mainly N ₂ , and the dew point is 50 ° C. or less. And a method for producing a non-oriented electrical steel sheet, wherein the amount of O ₂ is 1% or less by volume.   The method for producing a non-oriented electrical steel sheet according to claim 1, wherein in the step of annealing the hot-rolled sheet, the dew point is set to 30 ° C. or less. The method for producing a non-oriented electrical steel sheet according to claim 1 or 2, wherein, in the step of annealing the hot-rolled sheet, the amount of O ₂ is 0.5% or less by volume.

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