Non-oriented electromagnetic steel sheet, method of manufacturing the same, and hot-rolled steel sheet

Abstract

A non-oriented electromagnetic steel sheet containing, in mass%, C: 0.0010 to 0.0050%, Si: 1.50% or less, Mn: 0.10 to 1.50%, sol. Al: 0.010 to 0.040%, Ti: 0.0030% or less, Nb: 0.0030% or less, V: 0.0030% or less, Zr: 0.0030% or less, N: 0.0030% or less, S: 0.0040% or less, B: 0.0045% or less, with the remainder being Fe and impurities, satisfies [0.0020 ≦ Ti+Nb+V+Zr ≦ 0.0120], [0.5 ≦ B / N ≦ 1.5], [sol. B ≦ 0.0005], and [N AlN ≦0.0005].

Description

Technical Field

[0001] This invention relates to non-oriented electromagnetic steel sheets and their manufacturing methods, as well as hot-rolled steel sheets as materials for the non-oriented electromagnetic steel sheets. Background Technology

[0002] In recent years, due to the increasing global demand for energy-efficient electrical equipment, higher performance characteristics are required for non-oriented electromagnetic steel sheets used as core materials in rotating machines. Specifically, for high-efficiency motors used in electrical products, advanced materials with increased Si and Al content to improve inherent resistance and larger grain size are gradually being used. On the other hand, for general-purpose motors, performance improvements are also needed; however, due to strict cost constraints, it is practically difficult to replace their materials with advanced materials as in high-efficiency motors.

[0003] The steel plate required for general-purpose models is made of materials with a Si content of less than 1.5%, and grain growth is promoted during stress-relief annealing after the stamping of the motor core, thereby significantly improving iron loss.

[0004] Furthermore, recently, there has been a growing number of users utilizing the scrap generated during iron core punching as raw material for castings. From the viewpoint of ensuring the castability of the scrap, there is a need to set the Al content of the steel plate to less than 0.05%.

[0005] As a means to improve grain growth during stress-relief annealing, for example, Patent Document 1 discloses a method for manufacturing an electrical iron sheet with excellent magnetic properties. The method is characterized in that the steel slab contains C: ≤0.065%, Si: ≤2.0%, Al: ≤0.10%, O: ≤0.020%, B / N: 0.50~2.50, and the remainder consists of Fe and unavoidable impurities. The hot-rolled sheet obtained by hot rolling the steel slab is formed into the final size by one cold rolling or two or more cold rollings including intermediate annealing, and then further annealed.

[0006] Patent document 2 discloses a non-oriented electromagnetic steel sheet containing C: less than 0.015%, Si: 0.1-1.0%, sol.Al: 0.001-0.005%, Mn: less than 1.5%, S: less than 0.008%, N: less than 0.0050%, and TO: less than 0.02%. The characteristic feature is that the weight of MnO in the steel is less than 15% relative to the total weight of the three inclusions SiO2, MnO, and Al2O3. The non-oriented electromagnetic steel sheet, after magnetic annealing, has an average grain size of more than 50 μm and low iron loss.

[0007] Patent document 3 discloses a non-oriented electromagnetic steel sheet with excellent magnetic properties, containing, by weight percent: C: 0.01% or less, Si: 0.1% to 2.0% or less, Mn: 0.1% to 1.5% or less, and, depending on the deoxidation method of the steel, Al: 0.1% or less, or Zr: 0.05% or less, with the remainder consisting of iron and unavoidable impurity elements. Its characteristic feature is that, among the oxides in the steel, oxides with a diameter of 0.5 μm to 5 μm account for a certain percentage per 1 cm. 2 The number is between 1,000 and 50,000.

[0008] Patent document 4 discloses a non-oriented electromagnetic steel sheet containing, by mass percent: C: 0.0050% or less, Si: 0.05 to 3.5%, Mn: 3.0% or less, Al: 3.0% or less, S: 0.008% or less, P: 0.15% or less, N: 0.0050% or less, and Cu: 0.2% or less, satisfying (S in Cu sulfides) / (S in steel) ≤ 0.2, or (S in Cu sulfides) / (S in Mn sulfides) ≤ 0.2, and the number density of Cu sulfides with a diameter of 0.03 to 0.20 μm in the steel sheet is 0.5 sulfides / μm. 3 the following.

[0009] Patent document 5 discloses a non-oriented electromagnetic steel sheet, characterized in that it contains, by mass percent: Si: 1.5% or less, Mn: 0.4% to 1.5% or less, Sol.Al: 0.01% to 0.04% or less, Ti: 0.0015% or less, N: 0.0030% or less, S: 0.0010% to 0.0040% or less, and B (B / N ratio) of 0.5 to 1.5. The remainder consists of Fe and unavoidable impurities. At least 10% of the Mn-containing sulfides undergo compound precipitation with B precipitates. The total distribution density of MnS, Cu2S, and their compound sulfides is 3.0 × 10⁻⁶. 5 pcs / mm 2 The distribution density of Ti precipitates with a diameter of less than 0.1 μm is 1.0 × 10⁻⁶. 3 pcs / mm 2 the following.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Application Publication No. 54-163720

[0013] Patent Document 2: Japanese Patent Application Publication No. 63-195217

[0014] Patent Document 3: Japanese Patent Application Publication No. 3-104844

[0015] Patent Document 4: Japanese Patent Application Publication No. 2004-2954

[0016] Patent Document 5: International Publication No. 2005 / 100627 Summary of the Invention

[0017] The technical problem that the invention aims to solve

[0018] However, under conditions requiring further reduction in iron loss, the aforementioned existing methods become difficult to manufacture sufficiently and stably. In particular, in techniques such as those described in Patent Documents 1 and 5, which involve adding approximately 0.002% B to Al-deoxidized steel to generate BN as a nitride and suppress the precipitation of AlN, which is detrimental to grain growth, even with low iron loss, the magnetic flux density is lower compared to Si deoxidation as described in Patent Documents 2 and 4. While Patent Document 5 discloses the effect of increasing magnetic flux density by adding Sn, this technique leads to increased costs. Furthermore, although special processes such as surface rolling have been considered to promote grain coarsening, this still results in a significant increase in manufacturing costs.

[0019] The present invention was made in view of the following problem, the subject of which is to provide a non-oriented electromagnetic steel sheet that suppresses the formation of AlN, reduces solid solution B, exhibits good grain growth after stress-relief annealing, and has good iron loss and magnetic flux density, as well as a method for manufacturing the same, and a hot-rolled steel sheet that can be used as a material for the non-oriented electromagnetic steel sheet.

[0020] Technical means for solving technical problems

[0021] The present invention was made to solve the above-mentioned problems, and its main purpose is to provide the following non-oriented electromagnetic steel sheet, the method for manufacturing the same, and the hot-rolled steel sheet.

[0022] (1) Chemical composition, by mass%, contains:

[0023] C: 0.0010~0.0050%

[0024] Si: below 1.50%

[0025] Mn: 0.10~1.50%

[0026] sol.Al: 0.010~0.040%

[0027] Ti: below 0.0030%

[0028] Nb: below 0.0030%

[0029] V: Below 0.0030%

[0030] Zr: below 0.0030%

[0031] N: below 0.0030%

[0032] S: below 0.0040%

[0033] B: Below 0.0045%

[0034] The remainder consists of Fe and impurities.

[0035] Satisfy the following equations (i) to (iv):

[0036] 0.0020≦Ti+Nb+V+Zr≦0.0120…(i)

[0037] 0.5≦B / N≦1.5…(ii)

[0038] sol.B≦0.0005…(iii)

[0039] N AlN ≤0.0005…(iv)

[0040] Wherein, the element symbols in equations (i) and (ii) represent the content of each element in terms of mass %; sol.B in equation (iii) represents the amount of B dissolved in solid solution in terms of mass %; and N in equation (iv) represents the amount of B dissolved in solid solution in terms of mass %; AlN The amount of N present as AlN, expressed as a percentage by mass.

[0041] (2) The non-oriented electromagnetic steel plate described in (1),

[0042] The chemical composition, in place of a portion of the Fe, contains less than 0.50% Sn by mass.

[0043] (3) The non-oriented electromagnetic steel plate described in (1) or (2),

[0044] The average grain size is less than 30 μm, and,

[0045] The average grain size after stress-relief annealing at 750℃ for 2 hours was greater than 50 μm.

[0046] (4) A method for manufacturing a non-oriented electromagnetic steel sheet, comprising:

[0047] The steelmaking process manufactures a slab having the chemical composition described in (1) or (2);

[0048] The hot rolling process involves heating the obtained slab and then hot rolling it to produce a hot-rolled steel plate.

[0049] The pickling process involves pickling the hot-rolled steel sheet.

[0050] The cold rolling process involves cold rolling the pickled hot-rolled steel sheet to produce a cold-rolled steel sheet; and

[0051] The final annealing process involves performing a final annealing on the cold-rolled steel sheet.

[0052] In the hot rolling process,

[0053] Before hot rolling, the slab is held at a temperature of 1000–1050°C for at least 30 minutes.

[0054] The cumulative reduction rate within the temperature range of 900–1000℃ is set to be above 70%.

[0055] After hot rolling, the temperature of the hot-rolled steel plate is maintained at a range of 700°C or higher and less than 780°C for at least 30 minutes.

[0056] (5) The manufacturing method of the non-oriented electromagnetic steel sheet described in (4),

[0057] In the final annealing process, the steel sheet is heated to a maximum temperature of 800°C or higher but less than 850°C at an average heating rate of 20°C or higher, and the time for the cold-rolled steel sheet to reach a temperature of 800°C or higher is set to less than 15 seconds.

[0058] (6) A hot-rolled steel sheet, which is a hot-rolled steel sheet used as the material for the non-oriented electromagnetic steel sheet described in any one of (1) to (3),

[0059] The chemical composition, expressed as a percentage by mass, contains:

[0060] C: 0.0010~0.0050%

[0061] Si: below 1.50%

[0062] Mn: 0.10~1.50%

[0063] sol.Al: 0.010~0.040%

[0064] Ti: below 0.0030%

[0065] Nb: below 0.0030%

[0066] V: Below 0.0030%

[0067] Zr: below 0.0030%

[0068] N: below 0.0030%

[0069] S: below 0.0040%

[0070] B: Below 0.0045%,

[0071] The remainder consists of Fe and impurities.

[0072] Satisfy the following equations (i) to (iv):

[0073] 0.0020≦Ti+Nb+V+Zr≦0.0120…(i)

[0074] 0.5≦B / N≦1.5…(ii)

[0075] sol.B≦0.0005…(iii)

[0076] N AlN ≤0.0005…(iv)

[0077] Wherein, the element symbols in equations (i) and (ii) represent the content of each element in terms of mass %; sol.B in equation (iii) represents the amount of B dissolved in solid solution in terms of mass %; and N in equation (iv) represents the amount of B dissolved in solid solution in terms of mass %; AlN The amount of N present as AlN, expressed as a percentage by mass.

[0078] (7) The hot-rolled steel plate described in (6),

[0079] The chemical composition contains, in place of a portion of the Fe, Sn, in a mass percentage of less than 0.50%.

[0080] Invention Effects

[0081] According to the present invention, non-oriented electromagnetic steel sheets with good grain growth after stress-relief annealing and good iron loss and magnetic flux density after stress-relief annealing can be provided stably at low cost. Attached Figure Description

[0082] Figure 1 This is a graph showing the relationship between the remaining B quantity and the magnetic flux density. Detailed Implementation

[0083] The inventors investigated the reason why the magnetic flux density of Al deoxidized steel containing approximately 0.002% B is lower than that of Si deoxidized steel, focusing on the form in which B exists. B has the effect of suppressing the precipitation of AlN, which is extremely detrimental to grain growth. This is because B is more likely to form nitrides than Al. However, the inventors recognized that in the case of excess B in non-oriented electromagnetic steel sheets, B exists in a solid solution state, which causes a decrease in magnetic flux density (see reference). Figure 1 ).

[0084] Reducing the boron (B) content avoids an increase in dissolved B due to excess B; however, excess nitrogen (N) leads to AlN formation, thus worsening grain growth. Therefore, it is preferable to increase the B content as much as possible without causing dissolved B formation. However, precise control of the B content is difficult to achieve industrially. This is because, in addition to Al and B, nitride-forming elements include Ti, Nb, V, and Zr. The presence of these elements must be considered when controlling the B content. However, since these elements are usually impurities mixed into non-oriented electromagnetic steel sheets, their amounts are difficult to accurately determine. Furthermore, the nitrogen (N) content of the non-oriented electromagnetic steel sheet may vary during the steelmaking process, making it difficult to precisely determine the amount of B to be added. Thus, ensuring that the non-oriented electromagnetic steel sheet contains the exact amount of B needed to suppress AlN formation is extremely difficult industrially.

[0085] In view of this situation, the inventors focused on studying a method that allows for both more and less B relative to N while simultaneously obtaining good magnetic properties, and as a result, the following understanding was obtained.

[0086] First, a method for generating B precipitates other than BN during hot rolling was investigated when the amount of B was excessively high relative to the amount of N. The results showed that by setting the hot rolling temperature and cumulative reduction rate within appropriate ranges, the amount of B precipitates other than BN could be increased. Specifically, it was desirable to perform hot rolling at a temperature range of 900–1000 °C with a cumulative reduction rate of 70% or higher. This effect is presumably due to hot rolling promoting B precipitation.

[0087] Furthermore, by subjecting the hot-rolled steel sheet to heat treatment at a temperature range of 700°C to 780°C for at least 30 minutes, the aforementioned B precipitates other than BN generated during processing can be allowed to grow. As a result, in the final annealing of the cold-rolled steel sheet, or in the stress-relief annealing of the final annealed steel sheet (non-oriented electromagnetic steel sheet), good grain growth is achieved, resulting in low iron loss and high magnetic flux density.

[0088] Next, a method was investigated to prevent the formation of AlN, which is detrimental to grain growth, when the amount of boron (B) is insufficient relative to the amount of nitrogen (N). The results showed that if the slab before hot rolling is subjected to heat treatment at a temperature range of 1000–1050 °C for at least 30 minutes, and the hot-rolled steel sheet is subjected to heat treatment at a temperature range of 700 °C or higher but less than 780 °C for at least 30 minutes, AlN formation can be avoided. In the final annealing of the cold-rolled steel sheet, or in the stress-relief annealing of the non-oriented electromagnetic steel sheet after final annealing, good grain growth is achieved, resulting in low iron loss and high magnetic flux density.

[0089] Based on the above understanding, in Al deoxidized steel with approximately 0.002% B added, it was found that even without additional special processes to promote grain coarsening, it is possible to achieve both low iron loss and high magnetic flux density, thus completing this invention.

[0090] This invention is based on the above understanding. The elements of this invention will be described below.

[0091] 1. Chemical composition

[0092] The chemical composition of the non-oriented electromagnetic steel sheet and hot-rolled steel sheet according to one embodiment of the present invention is described below. The reasons for the limitation of each element are as follows. In addition, in the following description, "%" for content means "mass %".

[0093] C: 0.0010~0.0050%

[0094] C has the effect of fixing the solid-solidified B as a carbide. However, when the amount of C exceeds 0.0050%, magnetic aging will degrade iron losses. Therefore, the C content is set to 0.0010 to 0.0050%. The C content is preferably 0.0015% or more, 0.0020% or more, or 0.0025% or more. In addition, the C content is preferably 0.0045% or less, 0.0040% or less, or 0.0035% or less.

[0095] Si: below 1.50%

[0096] Si is an effective element for increasing electrical resistance. However, when the Si content exceeds 1.50%, it leads to increased hardness, decreased magnetic flux density, and increased manufacturing costs. Therefore, the Si content is set to 1.50% or less. The Si content is preferably 1.30% or less, 1.00% or less, or 0.80% or less. The lower limit for Si content is 0%, but to obtain the aforementioned effects, the Si content is preferably 0.10% or more, 0.20% or more, or 0.50% or more.

[0097] Mn: 0.10~1.50%

[0098] Mn is a sulfide-forming element, and from the viewpoint of promoting grain growth, it is preferable to contain an appropriate amount. However, when the Mn content exceeds 1.50%, the phase transformation temperature decreases, making it difficult to control the microstructure of hot-rolled steel sheets, hindering grain growth, and deteriorating iron losses. Furthermore, the decrease in saturation magnetic flux density becomes significant. Therefore, the Mn content is set to 0.10–1.50%. The Mn content is preferably 0.30% or more, 0.50% or more, or 0.70% or more. Additionally, the Mn content is preferably 1.20% or less, 1.00% or less, or 0.80% or less.

[0099] sol.Al: 0.010~0.040%

[0100] Al is an essential element for deoxidation of steel. When the content of sol.Al (Al existing in a solid solution state) is less than 0.010%, a stable deoxidation effect cannot be obtained, leading to problems such as nozzle clogging. On the other hand, from the user's viewpoint of waste utilization, a lower Al content is preferable. Therefore, the sol.Al content is set to 0.010–0.040%. The sol.Al content is preferably 0.015% or more, 0.020% or more, or 0.025% or more. Furthermore, the sol.Al content is preferably 0.035% or less, 0.030% or less, or 0.028% or less.

[0101] Ti: below 0.0030%

[0102] Ti forms nitrides, which significantly deteriorates grain growth. However, Ti is an element that is mixed into steel as an impurity, so it is difficult to achieve a Ti content of 0% industrially. Furthermore, trace amounts of Ti have the effect of inhibiting AlN formation. On the other hand, when its content is excessive, it deteriorates grain growth. Therefore, the Ti content is set to 0.0030% or less. The Ti content is preferably 0.0025% or less, 0.0020% or less, or 0.0015% or less. On the other hand, to obtain the above-mentioned effects, the Ti content is preferably 0.0005% or more, 0.0008% or more, 0.0010% or more, or 0.0012% or more.

[0103] Nb: below 0.0030%

[0104] Nb forms nitrides, which significantly deteriorates grain growth. However, Nb is an element that is mixed into steel as an impurity, so it is difficult to set the Nb content to 0 in industrial applications. Furthermore, even trace amounts of Nb have the effect of inhibiting AlN formation. On the other hand, when its content is excessive, it deteriorates grain growth. Therefore, the Nb content is set to 0.0030% or less. The Nb content is preferably 0.0025% or less, 0.0020% or less, or 0.0015% or less. On the other hand, to obtain the above-mentioned effects, the Nb content is preferably 0.0005% or more, 0.0008% or more, 0.0010% or more, or 0.0012% or more.

[0105] V: below 0.0030%

[0106] V forms nitrides, which significantly deteriorates grain growth. However, V is an element that is mixed into steel as an impurity, so it is difficult to set the V content to 0 in industrial applications. In addition, even trace amounts of V have the effect of inhibiting the formation of AlN. On the other hand, when its content is excessive, it deteriorates grain growth. Therefore, the V content is set to 0.0030% or less. The V content is preferably 0.0025% or less, 0.0020% or less, or 0.0015% or less. On the other hand, if the above-mentioned effects are desired, the V content is preferably 0.0005% or more, 0.0008% or more, 0.0010% or more, or 0.0012% or more.

[0107] Zr: below 0.0030%

[0108] Zr forms nitrides, which significantly deteriorates grain growth. However, Zr is an element that is mixed into steel as an impurity, so it is difficult to set the Zr content to 0 in industrial applications. In addition, even trace amounts of Zr have the effect of inhibiting AlN formation. On the other hand, when its content is excessive, it deteriorates grain growth. Therefore, the Zr content is set to 0.0030% or less. The Zr content is preferably 0.0025% or less, 0.0020% or less, or 0.0015% or less. On the other hand, if the above-mentioned effects are desired, the Zr content is preferably 0.0005% or more, 0.0008% or more, 0.0010% or more, or 0.0012% or more.

[0109] Regarding Ti, Nb, V, and Zr, each element can be present individually or in combination with two or more. However, when the total content of these elements is too low, the effect of inhibiting AlN formation cannot be achieved; on the other hand, when there is an excess, grain growth is deteriorated. Therefore, the total content of these elements needs to satisfy the following equation (i).

[0110] 0.0020≦Ti+Nb+V+Zr≦0.0120…(i)

[0111] In equation (i) above, the element symbols represent the content (mass%) of each element.

[0112] N: below 0.0030%

[0113] Nitrogen (N) forms nitrides that are detrimental to grain growth. To prevent this deterioration, the upper limit of the N content is set to 0.0030%. The N content is preferably 0.0025%, 0.0020%, or 0.0015% or less. Furthermore, the N content is preferably minimized; however, since N is an element that mixes into steel as an impurity, it is difficult to set the N content to 0% industrially. In this invention, the lower limit of the N content is defined based on the premise that N is present to a certain extent, using the relationship with the B content described later. Alternatively, the lower limit of the N content can be determined separately. For example, the N content can be set to 0.0008% or more, 0.0010% or more, or 0.0012% or more. Furthermore, the term "N content" means including the N that constitutes the N described later. AlN The content of all forms of N, including N in BN, etc.

[0114] S: below 0.0040%

[0115] Sulfide (S) forms sulfides, significantly hindering grain growth. In particular, when the S content exceeds 0.0040%, the precipitation of sulfides increases, impeding grain growth. Therefore, the S content is set to 0.0040% or less. The preferred S content is 0.0035% or less, 0.0030% or less, or 0.0025% or less. The lower limit for S content is 0%, but considering refining costs, the S content can also be set to 0.0008% or more, 0.0010% or more, or 0.0012% or more.

[0116] B: Below 0.0045%

[0117] Boron (B) is an essential element for suppressing the formation of AlN, which is detrimental to grain growth. Therefore, the B content is in the range of 0.0045% or less, and is determined according to the N content mentioned above. Specifically, the B content is controlled in a manner that satisfies formula (ii) below. Furthermore, the so-called B content means the content of all forms of B, including B that forms solid solution B (sol.B) and precipitates such as BN. Setting the B / N value to 0.5 to 1.5 is one of the important means to achieve both the reduction of solid solution B and the suppression of AlN formation. In addition, the B / N value is preferably 0.6 or more, 0.7 or more, or 0.8 or more. Furthermore, the B / N value is preferably 1.4 or less, 1.3 or less, or 1.0 or less.

[0118] 0.5≦B / N≦1.5…(ii)

[0119] In equation (ii) above, the element symbols represent the content (mass%) of each element.

[0120] In addition, in this invention, besides the content of B, the content of sol.B is also specified. Regarding the content of sol.B, as an upper limit that will not affect the magnetic flux density, it is set to 0.0005% or less. That is, the content of sol.B needs to satisfy the following equation (iii).

[0121] sol.B≦0.0005…(iii)

[0122] The content of sol.B is preferably 0.0004% or less, or 0.0003% or less. Furthermore, the content of sol.B is preferably reduced as much as possible, and therefore, its lower limit is 0%. On the other hand, the content of sol.B may also be specified as 0.00005% or more, 0.00010% or more, or 0.00015% or more.

[0123] In this invention, the content of sol.B is determined in the following order. First, test pieces are cut from non-oriented electromagnetic steel sheets or hot-rolled steel sheets, and then, in 10% acetylacetone-1% tetramethylammonium chloride / methanol, at 20 mA / cm², the content of sol.B is determined. 2 The current density for electrolysis was approximately 0.4 g. The solution used in this electrolysis was filtered through a 0.2 μm filter, and the extraction residue collected on the filter was analyzed by ICP-N (Inductively Coupled Phosphorus) to determine the boron (B) content. The B content in the extraction residue was then obtained by subtracting the B content in the extraction residue from the B content in the steel.

[0124] Sn: below 0.50%

[0125] In this invention, Sn is not essential; therefore, its content is limited to 0%. From the viewpoint of reducing alloy costs, the Sn content is preferably minimized. However, Sn has the effect of increasing magnetic flux density. In addition, Sn is effective in suppressing nitriding and oxidation of the steel sheet surface during annealing. Furthermore, Sn is particularly easy to nitrid when it contains 0.010 to 0.040% sol.Al. Therefore, Sn can be included as needed. Specifically, the Sn content is preferably 0.01% or more, 0.02% or more, or 0.05% or more. On the other hand, even if the Sn content is too high, its effect will saturate; therefore, the Sn content can also be set to 0.40% or less, 0.30% or less, 0.20% or less, 0.10% or less, 0.09% or less, or 0.08% or less.

[0126] 2. Precipitates

[0127] Regarding N (hereinafter referred to as "N") that constitutes AlN AlNThe content of N is set below 0.0005%, as an upper limit that will not affect grain growth. AlN The content of needs to satisfy the following formula (iv).

[0128] N AlN ≤0.0005…(iv)

[0129] N AlN The content of N is preferably less than 0.0004% or less, or less than 0.0003%. Furthermore, N... AlN The content of N is preferably reduced as much as possible; therefore, its lower limit is 0%. Alternatively, N can be... AlN The content is specified as 0.00005% or more, 0.00010% or more, or 0.00015% or more.

[0130] In this invention, N AlN The content was determined in the following order. First, test pieces were cut from non-oriented electromagnetic steel sheets or hot-rolled steel sheets, and then dissolved in 10% acetylacetone-1% tetramethylammonium chloride / methanol at 20 mA / cm². 2 The current density for electrolysis was approximately 0.4 g. The solution used in this electrolysis was filtered through a 0.2 μm filter. The Al content in the extraction residue collected on the filter was determined using ICP-N spectrophotometry. Then, assuming that all the Al in the extraction residue existed as AlN, the N content in the extraction residue was calculated by multiplying the Al content by 14 / 27, and this N content was taken as the N content. AlN The content of.

[0131] Furthermore, as mentioned above, the state of the precipitate is very important in this invention; however, the state of the precipitate is not specifically defined. This is because the precipitate is extremely fine, making it technically difficult to define its state. Additionally, it has been confirmed that by using N... AlN The amount of precipitates is set within the range mentioned above, thereby the precipitates are well controlled and the magnetic properties of the non-oriented electromagnetic steel sheet are improved.

[0132] 3. Grain size

[0133] The average grain size of the non-oriented electromagnetic steel sheet in this embodiment is not specifically defined. As described above, the non-oriented electromagnetic steel sheet is used after machining and stress-relief annealing; therefore, the average grain size varies depending on the stress-relief annealing conditions. Considering the actual usage conditions described above, as long as the grain growth during stress-relief annealing is good, it is not necessary to specify the average grain size during the non-oriented electromagnetic steel sheet stage. On the other hand, from the viewpoint of improving punching workability, the average grain size is an important factor. In non-oriented electromagnetic steel sheets provided for punching, punching workability is improved when the average grain size is 30 μm or less. Therefore, the average grain size of the final annealed non-oriented electromagnetic steel sheet can also be set to 30 μm or less. Known techniques can be appropriately used as a means to set the average grain size to 30 μm or less.

[0134] Typically, non-oriented electromagnetic steel sheets are supplied for machining and stress-relief annealing after leaving the factory. When the average grain size after stress-relief annealing is 50 μm or more, the iron loss characteristics are greatly improved. In this embodiment, the non-oriented electromagnetic steel sheet has a well-controlled chemical composition and oxide state, resulting in an average grain size of 50 μm or more after stress-relief annealing at 750°C for 2 hours. Furthermore, in actual products, the stress-relief annealing conditions are not limited to the above conditions; considering both equipment limitations and grain growth promotion, the annealing temperature and time can be appropriately varied.

[0135] The average grain size of non-oriented electromagnetic steel sheets can be determined using the following method: The L-section (parallel to the rolling direction) of the non-oriented electromagnetic steel sheet is ground and etched, and observed using an optical microscope. The magnification is set to 100x, and the field of view area is set to 0.5 mm². 2 The number of observation positions was set to 3. For these optical microscope images, the average grain size of the non-oriented electromagnetic steel sheet was determined by applying JIS G 0551:2013 "Microscopic test method for steel – grain size".

[0136] 4. Manufacturing method

[0137] The manufacturing method of the non-oriented electromagnetic steel sheet in this embodiment includes a steelmaking process, a hot rolling process, a pickling process, a cold rolling process, and a final annealing process.

[0138] (a) Steelmaking process

[0139] In the steelmaking process, slabs with the aforementioned chemical composition are produced through appropriate refining and casting. The manufacturing conditions are not particularly limited in the steelmaking process, and known conditions can be appropriately employed.

[0140] (b) Hot rolling process

[0141] In the hot rolling process, after heating the slab obtained through the continuous casting process, hot rolling is performed to produce a hot-rolled steel sheet. This process manufactures a hot-rolled steel sheet according to one embodiment of the present invention. Furthermore, subsequent processes do not substantially affect the chemical composition and the state of the oxides. Therefore, as described above, the chemical composition and the state of the precipitates in the hot-rolled steel sheet are the same as those in the non-oriented electromagnetic steel sheet of this embodiment.

[0142] Hot rolling is a crucial process for controlling precipitates and ensuring magnetic properties. In hot rolling, the slab is held at a temperature of 1000–1050°C for at least 30 minutes before hot rolling. Next, hot rolling is performed with a cumulative reduction of at least 70% within a temperature range of 900–1000°C. Then, after hot rolling, the hot-rolled steel sheet is held at a temperature of 700°C to 780°C for at least 30 minutes.

[0143] As mentioned above, determining whether the B content is excessive or insufficient relative to the N content during the steelmaking process is technically extremely difficult. However, in the hot rolling process, by meeting the aforementioned manufacturing conditions, it is possible to address both cases of excessive and insufficient B content relative to N content. These cases are explained in detail below.

[0144] First, when the B content is in excess relative to the N content, the amount of AlN can be suppressed by using B to fix N. Therefore, N can be reduced. AlN The content is set to 0.0005% or less. On the other hand, due to the generation of excess B, the sol.B content may exceed 0.0005%. Therefore, it is necessary to suppress the solid-solution B content by generating B precipitates other than BN. Although B can form carbides, the precipitation temperature of B carbides is relatively low. Therefore, by setting the cumulative reduction rate in the temperature range of 900–1000 °C to 70% or more, the precipitation of B carbides can be promoted.

[0145] Furthermore, hot rolling under the aforementioned conditions promotes the precipitation of boron carbides; however, some boron may remain in a solid solution state in the hot-rolled steel sheet. However, by maintaining the hot-rolled steel sheet at a temperature between 700°C and 780°C for at least 30 minutes after hot rolling, this solid solution boron can be precipitated. This is because boron carbides do not precipitate even at temperatures below 700°C, but melt at temperatures above 780°C.

[0146] Next, when the B content is insufficient relative to the N content, sol.B can be set to 0.0005% or less; however, it is necessary to suppress the formation of AlN. In this invention, the formation of AlN, which is detrimental to grain growth, is suppressed by generating nitrides of Ti, Nb, V, and Zr. These nitrides are relatively fine, therefore, they need to be sufficiently grown in this process. Therefore, before hot rolling, the slab temperature is maintained at a range of 1000–1050°C for at least 30 minutes, and after hot rolling, the hot-rolled steel plate temperature is maintained at a range of 700°C or higher and less than 780°C for at least 30 minutes. Thus, by using Ti, Nb, V, and Zr to fix N and suppress the AlN content, it is possible to reduce the N content. AlN The content is set to below 0.0005%.

[0147] Furthermore, there are no particular restrictions on the reduction rate in the hot rolling process, but it is preferable to set it to 90% or more. Additionally, there are no particular restrictions on the thickness of the resulting hot-rolled steel sheet, but it is preferably 1.0 to 4.0 mm, more preferably 2.0 to 3.0 mm.

[0148] (c) Pickling process

[0149] In the pickling process, hot-rolled steel sheets obtained through the hot rolling process are pickled. The pickling conditions are not particularly limited and can be set within the usual range of the manufacturing conditions for non-oriented electromagnetic steel sheets.

[0150] (d) Cold rolling process

[0151] In the cold rolling process, hot-rolled steel sheets that have been pickled are cold-rolled to produce cold-rolled steel sheets. The cold rolling conditions are not particularly limited and can be set within the typical range for manufacturing non-oriented electromagnetic steel sheets. For example, the reduction rate in the cold rolling process is preferably set to 50–95%, more preferably 75–85%.

[0152] (e) Final annealing process

[0153] In the final annealing process, the cold-rolled steel sheet obtained through the cold rolling process is subjected to final annealing. There are no particular limitations on the conditions in the final annealing process, and known conditions can be appropriately used. However, increasing the heating rate of the cold-rolled steel sheet can increase the magnetic flux density, which is therefore preferable. Therefore, it is preferable to set the heating rate in the final annealing process to 20°C / s or more. Here, the heating rate refers to the value obtained by dividing the difference between the heating start temperature and the soaking temperature of the cold-rolled steel sheet by the time from the heating start temperature to the soaking temperature, and the average heating rate from the heating start temperature to the soaking temperature.

[0154] Furthermore, in the final annealing process, when the maximum reached temperature (temperature of the cold-rolled steel sheet) is above 850°C, the grain size becomes too large, which may cause defects in the blanking process performed before stress-relief annealing. To avoid this defect, it is preferable to set the maximum reached temperature to be less than 850°C. On the other hand, when the maximum reached temperature is below 800°C, recrystallization becomes insufficient, which may also cause defects in the blanking process. To avoid this defect, it is preferable to set the maximum reached temperature to be above 800°C. In addition, to avoid the grain size becoming too large and causing defects in the blanking process performed before stress-relief annealing, it is preferable to set the time when the temperature of the cold-rolled steel sheet is above 800°C to be less than 15 seconds.

[0155] There are no particular limitations on the thickness of the non-oriented electromagnetic steel sheet manufactured through the above processes, but it is preferably 0.1 to 1.0 mm, and more preferably 0.2 to 0.7 mm.

[0156] The present invention will now be described in more detail by way of examples, but the present invention is not limited to these examples.

[0157] Example

[0158] Non-oriented electromagnetic steel sheets were manufactured by sequentially performing steelmaking, hot rolling, pickling, cold rolling, and final annealing processes. The chemical composition of the non-oriented electromagnetic steel sheets is shown in Table 1, and the manufacturing conditions are shown in Table 2. Furthermore, each steel sheet was manufactured five times under the same conditions.

[0159] [Table 1]

[0160]

[0161] [Table 2]

[0162]

[0163] For the obtained non-oriented electromagnetic steel sheet, sol.B and N were measured using the following method. AlN The content of.

[0164] First, test pieces were cut from non-oriented electromagnetic steel sheets and placed in a solution of 10% acetylacetone-1% tetramethylammonium chloride / methanol at 20 mA / cm². 2 The current density for electrolysis was approximately 0.4 g. The solution used in this electrolysis was filtered through a 0.2 μm filter, and the boron content in the extraction residue collected on the filter was determined using ICP-N (Inductively Coupled Phosphorus) spectrophotometry. The content of sol.B was then obtained by subtracting the boron content in the extraction residue from the boron content in the steel.

[0165] Similarly, test pieces were cut from non-oriented electromagnetic steel sheets and subjected to an atmosphere of 20 mA / cm² in 10% acetylacetone-1% tetramethylammonium chloride / methanol. 2 The current density for electrolysis was approximately 0.4 g. The solution used in this electrolysis was filtered through a 0.2 μm filter. The Al content in the extraction residue collected on the filter was determined using ICP-ELISA. The N content in the extraction residue was then calculated by multiplying the Al content by 14 / 27, and this N content was taken as the N2 content. AlN The content of.

[0166] Regarding sol.B and N AlN The content was averaged from the measured values ​​obtained from 5 steel plates, and the average was taken as the result of each measurement.

[0167] Next, the obtained non-oriented electromagnetic steel sheet was subjected to stress-relief annealing at 750°C for 2 hours. The following characteristics of the stress-relief annealed non-oriented electromagnetic steel sheet were evaluated.

[0168] (A) Iron loss after stress-relief annealing

[0169] The iron loss (W15 / 50) of the stress-relief annealed steel sheet was measured in accordance with JIS C 2552:2014 "Non-oriented electromagnetic steel strip". Non-oriented electromagnetic steel sheets with a W15 / 50 of less than 5.0 W / kg after stress relief annealing were judged to have excellent iron loss characteristics after stress relief annealing.

[0170] (B) Magnetic flux density after stress-relief annealing

[0171] The magnetic flux density (B0.05) of the stress-relieved annealed steel sheet was measured in accordance with JIS C 2552:2014 "Non-oriented electromagnetic steel strip". 50 B) of the stress-relief annealed steel sheet 50 Non-oriented electromagnetic steel sheets with a strength of 1.70T or higher are judged to have excellent magnetic flux density after stress-relief annealing.

[0172] (C) Grain growth during stress-relief annealing

[0173] The average grain size of the stress-relief annealed steel sheet was determined using the same method as that used for determining the average grain size of the non-oriented electromagnetic steel sheet described above. Non-oriented electromagnetic steel sheets with an average grain size of 50 μm or more after stress-relief annealing were considered to have good grain growth during stress-relief annealing.

[0174] (D) Stamping processability

[0175] The workability of non-oriented electromagnetic steel sheets before stress-relief annealing and after final annealing was evaluated. Specifically, the steel sheets were punched with a clearance of 7% to 12% of the sheet thickness. The burr height in the punched section was measured. For specimens with a burr height of 30 μm or less, the workability was judged as "good" (mark A). For specimens with a burr height greater than 30 μm but less than 100 μm, the workability was judged as "acceptable" (mark B).

[0176] The evaluation results are shown in Table 3. Furthermore, the characteristic evaluation was conducted using five steel plates. Additionally, Table 3 shows the average and maximum values ​​for iron loss, and the average and minimum values ​​for magnetic flux density.

[0177] [Table 3]

[0178]

[0179] As shown in Table 3, in tests No. 1 to 8, 29 and 30 that meet the requirements of this invention, it can be seen that excellent magnetic properties are consistently exhibited. On the other hand, in tests No. 9 to 18 where the chemical composition does not meet the requirements of this invention, it is the result of at least one deterioration in iron loss and magnetic properties.

[0180] Furthermore, in experiments No. 19–24, steel with insufficient B content relative to N content was used, and the manufacturing conditions were inappropriate; therefore, N… AlN Exceeding the upper limit of the content resulted in deterioration of iron loss. Furthermore, in experiments No. 25–28, steel with an excess of B content relative to N content was used, and the manufacturing conditions were inappropriate. Therefore, the solid solution B content exceeded the upper limit, resulting in deterioration of magnetic flux density.

[0181] Industrial applicability

[0182] According to the present invention, non-oriented electromagnetic steel sheets with good grain growth after stress-relief annealing and good iron loss and magnetic flux density can be stably provided at low cost. Therefore, the present invention has extremely high industrial applicability.

Claims

1. A non-oriented electromagnetic steel sheet, comprising, in mass%: Si: 1.50% or less, Mn: 0.10 to 1.50%, sol. Al: 0.010 to 0.040%, Ti: 0.0030% or less, Nb: 0.0030% or less, V: 0.0030% or less, Zr: 0.0030% or less, N: 0.0030% or less, S: 0.0040% or less, B: 0.0045% or less, and the balance being Fe and impurities, satisfying the following (i) to (iv): 0.0020 ≦ Ti + Nb + V + Zr ≦ 0.0120 (i) 0.5 ≦ B / N ≦ 1.5 (ii) sol. B ≦ 0.0005 (iii) 0.0005 ≦ sol. Al ≦ 0.040 (iv) C：0.0010～0.0050％、 2. The non-oriented electromagnetic steel sheet according to claim 1, comprising, in mass%, instead of a part of the Fe, Sn: 0.50% or less, in the chemical composition.

3. The non-oriented electromagnetic steel sheet according to claim 1 or claim 2, having an average grain size of 30 μm or less, and having an average grain size of 50 μm or more after a stress relief annealing performed at 750°C for 2 hours.

4. A method of manufacturing a non-oriented electromagnetic steel sheet, which is a method of manufacturing the non-oriented electromagnetic steel sheet according to any one of claims 1 to 3, comprising: a steel manufacturing step of manufacturing a slab having the chemical composition according to claim 1 or claim 2; a hot rolling step of performing hot rolling after heating the obtained slab to manufacture a hot-rolled steel sheet; an acid pickling step of performing acid pickling on the hot-rolled steel sheet; a cold rolling step of performing cold rolling on the hot-rolled steel sheet after the acid pickling to manufacture a cold-rolled steel sheet; and a final annealing step of performing final annealing on the cold-rolled steel sheet, wherein, in the hot rolling step, the slab is held for 30 minutes or more in a temperature range of 1000 to 1050°C before the hot rolling is performed, a cumulative reduction rate in a temperature range of 900 to 1000°C is set to 70% or more, and the hot-rolled steel sheet is held for 30 minutes or more in a temperature range of 700°C or more and less than 780°C after the hot rolling is performed.

5. The method of manufacturing a non-oriented electromagnetic steel sheet according to claim 4, wherein, in the final annealing step, the cold-rolled steel sheet is heated to a maximum reaching temperature of 800°C or more and less than 850°C at an average heating rate of 20°C / s or more, and a time period in which the temperature of the cold-rolled steel sheet is 800°C or more is set to 15 seconds or less.

6. A hot-rolled steel sheet, which is a hot-rolled steel sheet serving as a material for the non-oriented electromagnetic steel sheet according to any one of claims 1 to 3, comprising, in mass%: Si: 1.50% or less, Mn: 0.10 to 1.50%, sol. Al: 0.010 to 0.040%, Ti: 0.0030% or less, Nb: 0.0030% or less, V: 0.0030% or less, Zr: 0.0030% or less, N: 0.0030% or less, S: 0.0040% or less, B: 0.0045% or less, and the balance being Fe and impurities. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ N AlN ≦0.0005…(iv) wherein The element symbols in the formulae (i) and (ii) represent the content of each element in mass%, sol.B in the formula (iii) is the solid-solved B amount in mass%, and N in the formula (iv) is the N amount existing as AlN in mass%. AlN as AlN in mass%. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ C：0.0010～0.0050％、 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The remainder is Fe and impurities, satisfies the following (i) to (iv) formulae: 0.0020 ≦ Ti + Nb + V + Zr ≦ 0.0120... (i) 0.5 ≦ B / N ≦ 1.5... (ii) sol.B ≦ 0.0005... (iii) N AlN ≦0.0005…(iv) wherein, The element symbols in the formulae (i) and (ii) represent the content of each element in mass%, sol.B in the formula (iii) is the solid-solved B amount in mass%, and N in the formula (iv) is the N amount existing as AlN in mass%. AlN as AlN in mass%.

7. The hot-rolled steel sheet according to claim 6, contains, instead of a part of the Fe in the chemical composition, Sn: 0.50% or less in mass%.

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