JP7401729B2 - Non-oriented electrical steel sheet - Google Patents

Description

The present disclosure relates to a non-oriented electrical steel sheet.

Motors and generators that operate at high speeds are increasing in response to demands for higher efficiency due to advances in drive systems. At this time, the electromagnetic steel sheet used as the material for the rotor is required to have high strength in order to withstand the centrifugal force that acts on the iron core of the rotor as well as the fatigue caused by frequent rotations and stops. On the other hand, there is a strong demand for high magnetic flux density and low iron loss for electrical steel sheets used as materials for non-rotating stators.
These rotor materials and stator materials are generally made from the same material from the viewpoint of yield. For this reason, it is desired to put into practical use electrical steel sheets that can achieve both strength and magnetic properties.

It is known that electromagnetic steel sheets usually contain Si, Mn, Al, etc. in addition to Fe for the purpose of improving magnetic properties and adjusting strength.
For example, Patent Document 1 and Patent Document 2 disclose non-oriented electrical steel sheets that each contain specific amounts of Si, Mn, Al, etc. as non-oriented electrical steel sheets that reduce iron loss.
Further, Patent Document 3 describes a non-oriented electrical steel sheet that has less anisotropy in magnetic properties depending on the magnetization direction and has a high average magnetic flux density within the steel sheet surface, which contains specific amounts of Si, Mn, Al, etc., respectively. A non-oriented electrical steel sheet that satisfies a specific crystal orientation is disclosed.

Like Si, Mn, and Al, Cr is used as an element that strengthens steel sheets and has the effect of reducing core loss. For example, Patent Documents 4 to 9 disclose techniques for further utilizing Cr in steel sheets containing Mn and Al at relatively high concentrations. In the technologies disclosed in these patent documents, in addition to regulating the upper limit of Mn and Cr contents in consideration of deterioration of rollability and punchability due to excessive increase in strength, restrictions are placed on the upper limits of Mn and Cr contents to prevent deterioration of magnetic properties due to the formation of oxides and carbides. It has been shown that consideration should be given to the content of C and O in order to avoid this.

International Publication No. 2013/046661 International Publication No. 2017/056383 Patent No. 4218077 Japanese Patent Application Publication No. 2002-115035 Japanese Patent Application Publication No. 2003-096548 Japanese Patent Application Publication No. 2002-317254 Japanese Patent Application Publication No. 2002-212689 Japanese Patent Application Publication No. 2001-303213 Japanese Patent Application Publication No. 2002-226953

The present disclosure provides a non-oriented electrical steel sheet that can produce high-strength electrical steel sheet members and electrical steel sheet members with low iron loss and high magnetic flux density in steel sheets containing relatively high concentrations of Si, Mn, and Cr. The purpose is to provide

In view of the above circumstances, the present inventors focused on the magnetic properties and strength required of non-oriented electrical steel sheets to be applied to the cores of high-speed rotating, high-efficiency motors, and in particular, proceeded with studies on steel sheets containing a high concentration of Mn. Ta. As a result, Mn has the characteristic of developing a crystal orientation that is advantageous for magnetic properties, and is an advantageous element for obtaining favorable magnetic properties while increasing strength. It has been recognized that oxides are dispersed in the steel during coil winding after rolling, hot-rolled sheet annealing, and finish annealing, which deteriorates the iron loss characteristics. Furthermore, for steel sheets in which oxides are dispersed, after punching the steel sheet to form an iron core, a heat treatment generally called "core annealing" or "strain relief annealing" is carried out for the purpose of releasing the strain caused by punching. It was also found that the adhesion of the insulation coating had deteriorated.
A detailed investigation revealed that these oxides were not caused by oxygen content in the steel resulting from the steelmaking process, but were caused by internal oxidation of the steel sheet during heat treatment, and oxides (internal oxides) formed especially near the surface of the steel sheet. ) was found to be. Therefore, in order to control the oxidation behavior in the surface layer of the steel sheet during heat treatment, we investigated the effects of various elements and found that non-oriented electrical steel sheets with Cr content adjusted within a predetermined range can avoid internal oxidation. However, it has been found that the deterioration of iron loss and the deterioration of film adhesion caused by this can be eliminated. Furthermore, internal oxides formed on the surface layer of steel sheets also act as a factor for cracks in the steel sheet base material, contributing to fractures during rolling.If internal oxidation is avoided, the content of Si, Mn, and Cr can be It has also been found that cold rollability can be ensured without such restrictions. These results led to the completion of the present invention.
That is, the gist of the present disclosure is as follows.

<1> Chemical composition is Si: 1.95 to 4.10% by mass%,
Mn: 2.50-5.00%,
Cr: 0.02 to 5.00%, and the balance: Fe and impurity elements, or Fe, arbitrary elements and impurity elements,
Non-oriented electrical steel sheet.
<2> The chemical composition further includes Al: 0.95% or less in mass %,
Ni: 1.0% or less,
Cu: 4.0% or less,
Total of one or more selected from Ca, Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: 0.05% or less,
The non-oriented electrical steel sheet according to <1>, which satisfies at least one of B: 0.02% or less, and the sum of one or two selected from Sn and Sb: 0.2% or less.
<3> The chemical composition further includes C: 0.0050% or less in mass %,
N: 0.0040% or less,
S+Se: 0.0030% or less,
P: 0.03% or less,
<1> or <2> that satisfies at least one of O: 0.0040% or less, and the total of one or more selected from Ti, V, W, Nb, Zr, and Mo: 0.05% or less Non-oriented electrical steel sheet as described.

According to the present disclosure, non-directional steel sheets containing relatively high concentrations of Si, Mn, and Cr can be used to produce high-strength electrical steel sheet members and electrical steel sheet members with low iron loss and high magnetic flux density. A magnetic steel sheet is provided.

Hereinafter, a non-oriented electrical steel sheet according to an embodiment of the present disclosure will be described in detail.
Note that in this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower limit and upper limit.
Moreover, in this specification, "%" of element content represents "mass %."

[Non-oriented electrical steel sheet]
A non-oriented electrical steel sheet that is an embodiment of the present disclosure has a chemical composition in mass % of Si: 2.0 to 4.0%, Mn: 2.5 to 5.0%, and Cr: 0.02. ~5.0%, and the remainder: Fe and impurity elements, or Fe, arbitrary elements, and impurity elements.

The non-oriented electrical steel sheet according to this embodiment has high magnetic flux density, low iron loss, and high strength. Therefore, for example, when members constituting the stator and rotor of a drive motor are punched out of the non-oriented electrical steel sheet according to the present embodiment, the punched members as the rotor, which requires high strength to withstand high-speed rotation, are particularly strained. It can be used as an electromagnetic steel sheet member constituting a rotor without being subjected to annealing.
On the other hand, since the stator does not rotate and does not require as much strength as the rotor, the stamped parts used as the stator do not have any particular problems even if the strength decreases due to strain relief annealing, and they are even better in terms of low iron loss and high magnetic flux density. You can get a stator with
That is, the non-oriented electrical steel sheet according to the present embodiment makes it possible to manufacture a high-strength electromagnetic steel sheet member for a rotor and an electromagnetic steel sheet member with low iron loss and high magnetic flux density for a stator.

The reason why the non-oriented electrical steel sheet according to the present embodiment can preferably achieve high magnetic flux density, low iron loss, and high strength is not clear, but it is thought to be as follows.
In conventional steel sheets containing a high concentration of Mn, internal oxidation occurs during heat treatment during the manufacturing process of the steel sheet, and oxides formed on the surface layer of the steel sheet deteriorate the magnetic properties. This oxide is considered to be a composite oxide of not only Mn but also Si, which is contained at the same time, and Al, which is contained as necessary. When such a steel sheet contains Cr in an appropriate range, the intrusion of oxygen from the heat treatment atmosphere into the steel is suppressed, and/or the diffusion of the intruded oxygen into the interior of the steel sheet is suppressed, although the reason is not clear. , internal oxides are less likely to form. This phenomenon is thought to be influenced by the concentration of Cr in the surface layer of the steel sheet during oxidation, the preferential formation of an external oxide film by Cr, and the like.
Furthermore, it has been reported that when Cr is contained, Cr oxides and Cr carbides are formed and the magnetic properties are inhibited, so it is necessary to control the content of O and C. These problems do not occur in steel sheets containing O and C at a high concentration, and no special control is required for O and C. The reason for this is not clear, but it is thought that the coexistence of Mn and Cr within an appropriate concentration range, as well as the coexistence of Si and Al, suppresses the formation of Cr oxides and carbides inside the steel sheet. . It is hoped that the details of the phenomenon will be clarified in the future.

Hereinafter, a non-oriented electrical steel sheet, a method for manufacturing the same, etc. according to the present embodiment will be described in detail.

(chemical composition)
The non-oriented electrical steel sheet according to the present embodiment essentially contains Si: 1.95 to 4.10%, Mn: 2.50 to 5.00%, and Cr: 0.02 to 5.00% in mass %. element, and the remainder: Fe and impurity elements, or Fe, arbitrary elements, and impurity elements.
First, essential elements will be explained. In the present disclosure, an "essential element" is an element that is essential to be included in order to obtain the effects of the present disclosure.

Si: 1.95-4.10%
Si has the effect of increasing the electrical resistance of the steel plate, reducing eddy current loss, and reducing iron loss. Furthermore, Si improves the magnetic flux density by making the texture of the steel sheet favorable for electrical steel sheets. It is also included to increase the strength of the steel plate. In order to obtain these effects, the Si content is set to 1.95% or more.
On the other hand, if the content of Si is too high, the saturation magnetic flux density of the steel plate will decrease. Furthermore, cracks are likely to occur in the steel sheet during cold rolling. Therefore, the Si content is set to 4.10% or less. The content of Si is preferably 3.50% or less, more preferably 3.00% or less.

Mn: 2.50-5.00%
Mn is an important element in the present disclosure, and is an essential element in order to exhibit the effects of the present disclosure by coexisting with Cr, which will be described later. Therefore, the Mn content in the non-oriented electrical steel sheet according to this embodiment is set to 2.50% or more. The Mn content is preferably 3.00% or more, more preferably 3.50% or more.
Further, like Si, Mn has the effect of increasing the electrical resistance of steel and reducing iron loss. Furthermore, the texture of the steel sheet is made preferable for electrical steel sheets to improve magnetic flux density. Moreover, Mn is also advantageous in that the amount of decrease in the saturation magnetic flux density of the steel sheet is small. It is also used to increase the strength of steel plates.
On the other hand, if the Mn content is too high, the alloy cost increases, so the Mn content is set to 5.00% or less. The Mn content is preferably 4.50% or less, more preferably 4.00% or less.

Cr:0.02~5.00%
Cr is an important element in the present disclosure, and is made to coexist with the above-mentioned Mn for the purpose of controlling oxidation behavior near the surface of the steel sheet during heat treatment, and is an essential element in order to exhibit the effects of the present disclosure. The content for this purpose is 0.02% or more and 5.00% or less. Further, Cr has the effect of improving strength adjustment, corrosion resistance, and especially high frequency characteristics. Therefore, the Cr content is preferably 0.05% or more, more preferably 0.11% or more, and still more preferably 0.21% or more.
On the other hand, excessive content of Cr not only saturates the effect but also increases raw material cost. Therefore, the Cr content is preferably 4.50% or less, more preferably 2.90% or less, even more preferably 1.00% or less, even more preferably 0.50% or less, and 0.45% or less. But that's fine.

Remaining portion: Fe and impurity elements, or Fe, arbitrary elements, and impurity elements The remaining portion of the non-oriented electrical steel sheet according to the present embodiment is substantially Fe. However, for the purpose of improving various properties including magnetic properties, an arbitrary element may be contained in place of a part of Fe. Furthermore, it is also permissible to contain impurity elements.

First, arbitrary elements will be explained. In the present disclosure, the term "arbitrary element" does not eliminate the effects of the present disclosure even if it is contained within an appropriate range, and from the perspective of obtaining the effects of the present disclosure, the content may be zero; Or, it refers to an element that can be intentionally left or actively added because it can be included for other effects, regardless of whether it is known or not.

Al: 0.95% or less In the non-oriented electrical steel sheet according to the present embodiment, Al is an optional element, and from the viewpoint of the effects of the present disclosure, the Al content may be zero.
On the other hand, Al is an oxide-forming element, and if the Al content exceeds 0.95%, coarse oxides may be formed during the casting process, which may become a starting point for fracture during the manufacturing process. Moreover, if Al is contained excessively, alumina-based oxides will be formed on the surface of the steel material, which will accelerate wear and tear on rolling rolls during rolling. Therefore, the Al content is preferably 0.95% or less. It is more preferably 0.90% or less, and still more preferably 0.80% or less.
From the viewpoint of reducing oxide inclusions by deoxidation, the Al content is preferably 0.001% or more.

Ni: 1.0% or less When Ni is contained, like Mn, Ni increases the electrical resistance of the steel sheet and reduces iron loss. However, since Ni is expensive and increases product cost, the upper limit of the amount added is preferably 1.0% or less unless there is a special reason.

Cu: 4.0% or less When Cu is contained, like Mn, Cu increases the electrical resistance of the steel sheet and reduces iron loss. Further, by containing 1.5% or more of Cu, it is possible to form fine Cu precipitates through heat treatment, thereby increasing the strength of the steel sheet. However, if the Cu content is too high, the steel material becomes brittle and processing becomes difficult, so the upper limit is preferably about 4%.

Examples of optional elements other than those mentioned above include Ca, Mg, Sr, Ba, Ce, La, Nd, Pr, Zn, Cd, B, Sn, and Sb.

Ca, Mg, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd particularly coarsen sulfides, and B particularly coarsens nitrides, thereby improving the growth of crystal grains in the heat treatment process. Contributes to lower iron loss.
On the other hand, if the content of each of the elements Ca, Mg, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd is too high, the magnetic properties will deteriorate, so the content of each of these elements is 0.05%. The total content is preferably 0.05% or less.
Further, if the B content is too high, the magnetic properties will deteriorate, so the B content is preferably 0.02% or less.
Furthermore, it is known that Sn and Sb develop crystal orientations favorable for magnetic properties. On the other hand, if the content of each element Sn and Sb is too high, the magnetic properties will deteriorate, so the content of each of these elements is preferably 0.2% or less, and the total content is also 0.2%. It is preferable that it is below.
Each of the above arbitrary elements can be added within a known range, but the preferable content in the steel sheet according to this embodiment is 5% or less in total of the arbitrary elements.

Next, impurity elements will be explained. In the present disclosure, "impurity elements" do not eliminate the effects of the present disclosure even if they are contained within an appropriate range, and from the perspective of obtaining the effects of the present disclosure, the content may be zero; Basically, it is an element that is preferably zero (close to) because there is almost no merit in using it, and regardless of whether it is publicly known or not, it has an adverse effect on the manufacturing process or usage environment of electrical steel sheets. Note that impurity elements include elements that are unavoidably mixed in from ores used as raw materials, scraps, or the manufacturing environment when industrially manufacturing electrical steel sheets, and elements that are difficult to remove.

C: 0.0050% or less C may form carbides and deteriorate magnetic properties in high magnetic fields. Further, since magnetic properties in a high magnetic field deteriorate when magnetic aging occurs, it is preferable to keep the C content low. Therefore, the C content is preferably 0.0050% or less.
From the viewpoint of manufacturing costs, it is advantageous to reduce the C content using degassing equipment (for example, RH vacuum degassing equipment) at the molten steel stage, and if the C content is 0.0050% or less, magnetic aging can be suppressed. is large. In the non-oriented electrical steel sheet according to the present embodiment, since non-metallic precipitates such as carbides are not used as a main means of increasing strength, there is no advantage of intentionally including C, and it is preferable that the C content is small. Therefore, the C content is preferably 0.0040% or less, more preferably 0.0030% or less. If techniques such as electrodeposition are used, it is possible to reduce the C content to 0.0010% or less, which is below the limit of chemical analysis, and the C content may even be 0%. On the other hand, considering industrial costs, the lower limit may be set to 0.0003%.
On the other hand, it has been reported that C forms fine carbides in Cr-containing steel and has an adverse effect on magnetic properties, but in this embodiment, which contains a relatively large amount of Mn, it is not necessary to consider this effect. Almost no, it may be contained in an amount of 0.001% or more. Furthermore, since no particular problem occurs even when the content is 0.002% or more, it is possible to enjoy the advantage of reducing decarburization costs in general practical steel manufacturing methods.

N: 0.0040% or less Like C, N deteriorates the magnetic properties in a high magnetic field due to the formation of nitrides and magnetic aging. Therefore, the N content is preferably 0.0040% or less. In order to avoid deterioration of magnetic properties in high magnetic fields, the lower the N content, the better; setting it to 0.0027% or less will sufficiently avoid negative effects on magnetic properties in high magnetic fields due to magnetic aging and nitride formation. can. The N content is more preferably 0.0022% or less, particularly preferably 0.0015% or less. By using techniques such as electrodeposition, it is possible to reduce the N content to 0.0001% or less, which is below the limit of chemical analysis, and the N content may even be 0%. On the other hand, considering industrial costs, the lower limit may be set to 0.0003%.

S+Se: 0.0030% or less S and Se may form sulfides and deteriorate magnetic properties in a high magnetic field, so the content is preferably low. The total content of S and Se is limited to 0.0030% or less, preferably 0.0020% or less, and more preferably 0.0010% or less. The total content of S and Se may be 0%.

P: 0.03% or less P makes steel brittle and reduces cold rollability and product workability, so the P content is limited to 0.03% or less. The P content is preferably 0.02% or less, more preferably 0.01% or less.
On the other hand, the content of P is controlled for the purpose of adjusting strength and suppressing nitriding and carburization during manufacturing, and when it is segregated at grain boundaries before cold rolling, it improves the texture and increases the magnetic flux density. It is known that the content of 0.001% or more is improved. In general practical steel manufacturing methods, P may be contained as an impurity in an amount of about 0.002% or more.

O: 0.0300% or less O forms coarse inclusions, causes embrittlement starting from these, and reduces cold rollability and product workability, so the O content should be 0.0300% or less. Preferably limited. The O content is more preferably 0.0200% or less, further preferably 0.0100% or less, particularly preferably 0.0040% or less.
The above O content includes the amount of O that increases due to internal oxidation during the heat treatment process of the steel sheet manufacturing process, in addition to the control in molten steel in the steel manufacturing process. However, in this embodiment, internal oxidation during the heat treatment process is effectively avoided, so that an inadvertent increase in O content is suppressed. Therefore, it is relatively easy to keep the O content low.
On the other hand, it has been reported that O forms fine oxides in Cr-containing steel and has an adverse effect on magnetic properties; however, in this embodiment containing a relatively large amount of Mn, it is necessary to consider this effect. There is almost no content, and the content may exceed 0.0010%. Furthermore, since no particular problem occurs even if the content exceeds 0.0020%, it is also possible to enjoy the advantage of reducing deoxidation costs in general practical steel manufacturing methods.

Examples of impurity elements other than those mentioned above include Ti, V, W, Nb, Zr, and Mo. Any of these elements may inhibit grain growth. The preferred content of each of the above elements is 0.05% or less, and the total content of these elements is also preferably 0.05% or less.

The above chemical composition is a numerical value of the chemical composition constituting the steel plate. If the steel plate serving as the measurement sample has an insulating coating or the like on its surface, it is necessary to remove this before performing the measurement.
Examples of methods for removing the insulation coating etc. of electrical steel sheets include the following. First, an electrical steel sheet having an insulating coating and the like is immersed in a sodium hydroxide aqueous solution containing 10% by mass of NaOH and 90% by mass of H ₂ O at 80° C. for 15 minutes. Next, it is immersed in an aqueous sulfuric acid solution containing 10% by mass of H ₂ SO ₄ and 90% by mass of H ₂ O at 80° C. for 3 minutes. Thereafter, it is washed by immersion in a nitric acid aqueous solution containing 10% by mass of HNO ₃ and 90% by mass of H ₂ O at room temperature for a little less than 1 minute. Finally, dry it with a hot air blower for less than 1 minute. Thereby, a steel plate from which an insulating coating, which will be described later, has been removed can be obtained.

The content of each element in the electrical steel sheet can be measured, for example, by inductively coupled plasma mass spectrometry (ICP-MS method). Specifically, first, an electrical steel sheet to be measured is prepared. A part of the electromagnetic steel sheet is faceted and weighed, and this is used as a measurement sample. The measurement sample is dissolved in an acid to obtain an acid solution, the residue is collected from a filter paper and separately melted in an alkali, etc., and the melt is extracted with an acid to form a solution. By mixing the solution and the acid solution and diluting as necessary, a solution for ICP-MS measurement can be obtained.

(Average grain size)
The average grain size of the non-oriented electrical steel sheet according to this embodiment is not particularly limited. Although the non-oriented electrical steel sheet according to the present embodiment has a certain degree of strength due to solid solution strengthening, it is possible to further increase the strength by utilizing the strengthening ability due to grain refinement. In order to further increase the strength of the rotor member and to improve the magnetic properties of the stator member, it is preferable to control as follows.
First, from the viewpoint of a rotor member, higher strength can be imparted by preferably having an average crystal grain size of 60 μm or less. From this viewpoint, the average crystal grain size is more preferably 50 μm or less, and even more preferably 30 μm or less.
On the other hand, from the viewpoint of stator members that do not require strength, it is assumed that a steel plate with a controlled average grain size is subjected to additional heat treatment from the viewpoint of rotor members, and after punching as a stator member, for example, strain relief is applied. Magnetic properties can be made more preferable by causing sufficient grain growth during annealing. The average grain size after strain relief annealing is, for example, 100 to 250 μm.
Of course, if it is not used as a rotor member, or if it is used as a rotor member but does not require such high strength, the average grain size of the non-oriented electrical steel sheet to be manufactured as a coil should be 100 to 250 μm. It may be manufactured as such.
The average crystal grain size can be determined by the line segment method. Specifically, the cross-sectional microstructure of a steel plate is photographed at three or more locations at around 100x magnification using an optical microscope, the average intercept length L is determined by the line segment method, and the average crystal grain is calculated by multiplying it by 1.12. diameter.

(Tensile strength)
As described above, the non-oriented electrical steel sheet according to the present embodiment becomes an electrical steel sheet having high strength due to solid solution strengthening by the contained elements and grain refinement strengthening in consideration of heat treatment conditions. Considering application to applications requiring strength, the tensile strength (TS) is preferably 500 MPa or more, more preferably 550 MPa or more, and even more preferably 680 MPa or more. If the TS of the non-oriented electrical steel sheet according to this embodiment is 500 MPa or more, for example, when used as a rotor of a drive motor, damage can be effectively prevented even if the sheet rotates at high speed. In addition, the TS of the non-oriented electrical steel sheet according to this embodiment is determined by the crystal grain size obtained by controlling the manufacturing conditions such as rolling and annealing when manufacturing the non-oriented electrical steel sheet according to this embodiment, in addition to the components. The things that can be adjusted through control are as described above.
Note that the upper limit of the TS of the non-oriented electrical steel sheet according to the present embodiment is not particularly limited, but from the viewpoint of ease of manufacture, it may be 1100 MPa or less, or 1000 MPa or less.
Here, TS is a value based on a measurement method in Examples described later.

[Method for manufacturing non-oriented electrical steel sheet]
The method for manufacturing the non-oriented electrical steel sheet according to the present embodiment is not particularly limited as long as the non-oriented electrical steel sheet according to the present embodiment having the above-mentioned chemical composition and structure can be manufactured. For example, a heating step of heating a slab having the chemical composition of the non-oriented electrical steel sheet according to the present embodiment, a hot rolling step of hot rolling the heated slab, and a step of heating the slab having the chemical composition of the non-oriented electrical steel sheet according to the present embodiment; It can be manufactured through a cold rolling process of cold rolling a steel plate and a final annealing process of finally annealing the cold rolled steel plate.
In addition, if necessary, after the hot rolling process and before the cold rolling process, a hot rolled plate annealing process in which a hot rolled steel plate (hot rolled plate) is annealed, and a cold rolling process when cold rolling is performed multiple times. An intermediate annealing process in which a steel plate (cold rolled plate) is annealed during the inter-rolling process, a skin pass rolling process with a small rolling reduction for the purpose of improving strength, etc., and a magnetic rolling process to improve magnetic properties. An annealing process or the like may also be performed.
Each step will be explained below. Note that the composition of the slab (ingot) is the same as that of the non-oriented electrical steel sheet described above, so a description thereof will be omitted.

(Heating process)
In the heating step, the slab having the above chemical composition is heated to 1000-1250°C. Specifically, the slab is placed in a heating furnace or soaking furnace and heated in the furnace. The holding time at the above heating temperature in the heating furnace or soaking furnace is, for example, 30 to 200 minutes.

Slabs are manufactured in a known manner. For example, molten steel is produced in a converter or electric furnace. The produced molten steel is subjected to secondary refining using a degassing facility or the like to obtain molten steel having the above chemical composition. Slabs are cast using molten steel by continuous casting or ingot forming. The cast slab may be subjected to blooming rolling.

(Hot rolling process)
In the hot rolling process, a steel plate is manufactured by hot rolling a slab that satisfies the above-mentioned chemical composition.
In the hot rolling process, the slab heated in the heating process is rolled in multiple passes to produce a steel plate. Here, "pass" means that the steel plate passes through one rolling stand having a pair of work rolls and is rolled down. Hot rolling is performed, for example, by performing tandem rolling 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 rolling in multiple passes. Alternatively, reverse rolling with a pair of work rolls may be performed to perform multiple passes of rolling. From the viewpoint of productivity, it is preferable to perform multiple rolling passes using a tandem rolling mill.

(Hot rolled plate annealing process)
In the method for manufacturing an electrical steel sheet according to the present embodiment, an annealing process (generally referred to as a hot-rolled plate annealing process) may be performed after the hot rolling process and before the cold rolling process. The term "annealing" used herein means, for example, heat treatment at a heating temperature of not higher than the A _c1 transformation point and not lower than 300°C. However, the chemical composition of the electrical steel sheet according to this embodiment has a high Mn content as described above. Therefore, when hot-rolled sheet annealing is performed, Mn segregates at grain boundaries, which may reduce the workability of the steel sheet (hot-rolled steel sheet) after the hot rolling process. Therefore, in this embodiment, after the hot rolling process is completed, it is preferable to omit the hot rolled sheet annealing process and perform the cold rolling process.

(cold rolling process)
After the hot rolling process, a hot rolled plate annealing process is performed as needed, and then a cold rolling process is performed. Cold rolling is performed, for example, by performing tandem rolling 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 rolling in multiple passes. It's okay. Further, reverse rolling may be performed using a Sendzimir rolling mill or the like having a pair of work rolls to perform rolling in one pass or multiple passes. From the viewpoint of productivity, it is preferable to perform rolling in multiple passes using a tandem rolling mill.

In the cold rolling process, when rolling is performed by multiple passes, annealing treatment (intermediate annealing) may be performed during cold rolling. From the viewpoint of improving the average magnetic properties in three directions (direction D: 45° rolling direction), it is preferable to perform cold rolling without performing intermediate annealing. For example, when reverse rolling is performed and cold rolling is performed in multiple passes, cold rolling is performed in multiple passes without annealing treatment between the cold rolling passes. . Note that cold rolling may be performed in only one pass using a reverse rolling mill. Further, when cold rolling is performed using a tandem rolling mill, cold rolling is performed continuously in multiple passes (passes at each rolling stand).
In addition, when intermediate annealing is performed, it is preferable that the intermediate annealing temperature T1 is, for example, 500° C. to less than the A _c1 transformation point.

The rolling reduction ratio RR1 in the cold rolling step is, for example, 85 to 95%. Here, the rolling reduction ratio RR1 in the cold rolling process is defined as follows.
Rolling ratio RR1 (%) = (1 - Thickness of steel plate after final pass rolling in cold rolling process/Thickness of steel plate before cold rolling in first pass in cold rolling process) x 100

The plate thickness after cold rolling may be adjusted as appropriate depending on the use of the non-oriented electrical steel sheet according to the present disclosure, and is not particularly limited. From the perspective of reducing the weight of the motor, a thinner plate is preferable, but the thinner the plate, the more difficult mass production tends to be.Also, when punching the steel plate into the desired shape, the steel plate is more likely to deform, reducing yield. There is a possibility that it will decrease. Therefore, the plate thickness after cold rolling is preferably 0.05 to 0.50 mm, and from the viewpoint of balance between magnetic properties and productivity, 0.15 to 0.35 mm is preferable, and 0.20 to 0.20 mm. 0.30 mm is more preferable.

(Final annealing process)
After completing cold rolling, finish annealing is performed. By final annealing, 10% or more of the processed structure formed by cold rolling is recrystallized in terms of area ratio, and the crystal grain size is adjusted to 60 μm or less. These conditions are appropriately set in consideration of the components of the steel according to the present embodiment, particularly the Mn and Cr contents.
If special consideration is required, the steel according to this embodiment also has a special composition in that it contains relatively larger amounts of Mn and Cr than conventional steels, and therefore is more effective than ordinary steel sheets. (Recrystallization and) grain growth is likely to be delayed. However, this specification can be easily determined by a person skilled in the art having ordinary knowledge by appropriately processing and heat-treating a steel having the relevant composition and observing its recrystallization behavior. Although it depends on the steel composition and the manufacturing conditions before cold rolling, for example, in the case of continuous annealing, the annealing temperature (T2) is about 700 to 900°C and the annealing time (t1) is about 1 to 300 seconds. It is not something that deviates greatly from the standard conditions. During final annealing between 600 and 700°C, it is preferable to slowly heat and increase the temperature over 25 seconds or more.

(Coating process)
Further, a coating process for forming the above-mentioned insulating film may be performed. The coating process can be performed, for example, after a cold rolling process, after a finish annealing process, after a temper rolling process, after a magnetic annealing process, or after a punching process.
The insulating film can be appropriately selected and used depending on the purpose and the like, and may be either an organic film or an inorganic film. Examples of organic films include polyamine resins, acrylic resins, acrylic styrene resins, alkyd resins, polyester resins, silicone resins, fluororesins, polyolefin resins, styrene resins, vinyl acetate resins, epoxy resins, phenolic resins, urethane resins, and melamine. Examples include resin. Further, examples of the inorganic film include a phosphate film, an aluminum phosphate film, and an organic-inorganic composite film containing the above-mentioned resin.
Although the thickness of the insulating film is not particularly limited, it is preferable that the film thickness is 0.05 μm or more and 2 μm or less.

According to the above manufacturing method, it is possible to manufacture the non-oriented electrical steel sheet according to the present embodiment, which has high magnetic flux density, low core loss in a high frequency region, and also has high strength.

(Other processes)
The method for manufacturing a non-oriented electrical steel sheet according to the present embodiment is not limited to the above manufacturing steps, and may further include other steps. For example, after final annealing and coating, additional cold working may be performed at a reduction rate of approximately 20% or less to obtain a so-called semi-processed non-oriented electrical steel sheet. Although the properties change considerably due to additional cold working and subsequent user heat treatment, the effect of the present disclosure, which appropriately suppresses internal oxidation due to the Mn and Cr contents, can be enjoyed in the steel sheet manufacturing process and product use. can do.

Although the non-oriented electrical steel sheet according to the present embodiment has been described above, the present disclosure is not limited to the above. The above is an example, and any technology of the present disclosure may have substantially the same configuration as the technical idea stated in the claims of the present disclosure and produce similar effects. covered within the scope.

Hereinafter, the non-oriented electrical steel sheet of the present disclosure will be specifically described with reference to Examples, but the non-oriented electrical steel sheet of the present disclosure is not limited thereto. The non-oriented electrical steel sheet of the present disclosure may adopt various conditions as long as the purpose of the present disclosure is achieved without departing from the gist of the present disclosure.

(Example: Manufacture of electrical steel sheet)
Slabs (ingots) each having a composition (steel composition) shown in the steel types shown in Table 1 were produced in a vacuum melting furnace. In addition, the underlined content of the components shown in Table 1 means that it is outside the scope of the present disclosure, and "-" means that the component (element) is not intentionally added. .

The obtained slab was charged into a heating furnace and heated at 1200°C, and the finishing temperature was set at 800°C to obtain a 2.3 mm hot rolled steel plate. Thereafter, a 0.25 mm cold rolled steel plate was obtained by cold rolling. Thereafter, finish annealing was performed in a continuous annealing furnace, and an acrylic insulation film was further coated to produce a non-oriented electrical steel sheet. At this time, the finish annealing conditions were adjusted so that the average crystal grain size of the steel plate was about 30 μm. Although these conditions are not particularly specified, it is only a matter of adjusting the degree of recrystallization and grain growth depending on the components, and is an easy operation for those skilled in the art.

<Evaluation>
The following measurements and evaluations were performed on the obtained non-oriented electrical steel sheet.
The average crystal grain size was determined by the line segment method described above.
The magnetic flux density can be measured according to the method for testing the magnetic properties of a single magnetic steel sheet described in JIS C 2556 (2011), and the magnetic flux density B ₅₀ in a magnetic field of 5000 A/m was measured.
The iron loss was measured as iron loss W _10/400 under the conditions of a maximum magnetic flux density of 1.0 T and a frequency of 400 Hz according to the method specified in JIS-C-2550 (2011).
Regarding the tensile strength, a No. 5 tensile test piece described in JIS Z2241 (2011) was taken in the rolling direction, and a tensile test was conducted according to the test method described in JIS Z2241 (2011) to evaluate the tensile strength.

Further, the above-mentioned non-oriented electrical steel sheet was subjected to an additional heat treatment in a nitrogen atmosphere at 750° C. for 2 hours in a box furnace, and the film adhesion was evaluated. Film adhesion was evaluated by peeling area ratio in a tape peeling test. Note that the additional heat treatment described above simulates strain relief annealing that is generally practiced. In addition, the above additional heat treatment causes grain growth, slightly changes the magnetic flux density, and reduces iron loss, but since this change in magnetic properties is not something special and is a phenomenon within the normal range, the magnetic properties are not displayed intentionally. .
The evaluation results are shown in Table 2.

From the evaluation results shown in Table 2, the effects of the present disclosure can be confirmed. The points to be noted regarding this will be explained.
It is known that the magnetic properties of electrical steel sheets vary greatly depending on the components. In the present disclosure, the effects are particularly exhibited by the addition of Cr, but when evaluating the effects, comparison should be made between steel plates in which components other than Cr are basically the same.
In this embodiment, S05 to S08 to S01 to S04, S10 to S09, S12 to S11, S17 to S20 to S13 to S16, S22 to S21, S24 to S23, S39 to S43 to S34 to S38, S44 to S47 to In S56 to S59 for S48 to S51 and S52 to S55, the components are adjusted so that the effects of the present disclosure can be confirmed.
In addition, in S25 to S33, the components are adjusted to check the change in characteristics when the Cr content is simply changed in a specific steel type.
Comparison of properties in consideration of this point shows that the steel sheet of the invention example is a non-oriented electrical steel sheet that has excellent tensile strength and magnetic properties (core loss, magnetic flux density), and has both tensile strength and magnetic properties. Furthermore, it can be seen that the film has excellent adhesion after additional heat treatment.

Claims (4)

The chemical composition is Si: 2.00 to 4.10% by mass,
Mn: 2.50 to 3.50%,
Cr: 0.02-2.90%,
Al: 0.95% or less,
and the remainder: Fe and impurity elements, or Fe, arbitrary elements and impurity elements ,
The arbitrary element is
Ni: 1.0% or less,
Cu: 4.0% or less,
Total of one or more selected from Ca, Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: 0.05% or less,
B: 0.02% or less,
Total of one or two selected from Sn and Sb: 0.2% or less,
C: 0.0050% or less,
N: 0.0040% or less,
S+Se: 0.0030% or less,
P: 0.03% or less,
O: 0.0040% or less, and
Total of one or more selected from Ti, V, W, Nb, Zr and Mo: 0.05% or less
at least one of
The average crystal grain size is 60 μm or less ,
Non-oriented electrical steel sheet. The chemical composition is Ni: 1.0% or less in mass %,
Cu: 4.0% or less,
Total of one or more selected from Ca, Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: 0.05% or less,
The non-oriented electrical steel sheet according to claim 1, containing at least one of B: 0.02% or less and a total of one or two selected from Sn and Sb: 0.2% or less. The chemical composition is C: 0.0050% or less in mass %,
N: 0.0040% or less,
S+Se: 0.0030% or less,
P: 0.03% or less,
O: 0.0040% or less, and the total of one or more selected from Ti, V, W, Nb, Zr, and Mo: 0.05% or less
The non-oriented electrical steel sheet according to claim 1 or 2, comprising at least one of the following . The non-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the average grain size is 50 μm or less.