Hot rolled steel sheet for non-oriented electrical steel sheet, non-oriented electrical steel sheet and method for producing the same

Abstract

A hot-rolled steel sheet for non-oriented electromagnetic steel sheet according to one embodiment of the present invention contains, in mass %, the following: C: less than 0.0050%, Si: more than 0.5% and less than 3.5%, Mn: more than 0.1% and less than 1.5%, Al: more than 0.1% and less than 1.5%, Cu: more than 0.01% and less than 0.10%, Sn: more than 0.01% and less than 0.20%; the remainder is composed of Fe and impurities; and within the range from the surface to a depth of 10 μm, it has a Cu concentration peak of more than 0.12%.

Description

Technical Field

[0001] The present invention relates to a hot-rolled steel sheet for a non-oriented electrical steel sheet, a non-oriented electrical steel sheet and a method for producing the same.

[0002] This application claims priority based on Japanese Patent Application No. 2020-027000 filed in Japan on February 20, 2020, the contents of which are incorporated herein by reference. Background Art

[0003] In recent years, due to the increasing demand for energy saving in electrical equipment worldwide, there has been a demand for higher performance characteristics for non-oriented electromagnetic steel sheets used as core materials for rotating machines. Specifically, for motors called high-efficiency models in electrical products, advanced materials that increase the Si and Al content to increase resistivity and increase the grain size have gradually begun to be used. However, these measures will increase the manufacturing cost of non-oriented electromagnetic steel sheets. Therefore, from the perspective of reducing costs, it is very important to simplify the manufacturing process.

[0004] Self-annealing during hot rolling is a technology that is expected to simplify the annealing of hot-rolled sheets. The purpose of hot-rolled sheet annealing is to promote recrystallization and grain growth of hot-rolled steel sheets (hot-rolled sheets), thereby eliminating the shape defect problem called wrinkles and improving magnetic properties. The following is a technology for achieving this effect by annealing the hot-rolled steel sheet at the temperature of the hot-rolled coil itself, that is, by so-called self-annealing.

[0005] For example, Patent Document 1 discloses the following self-annealing technology: in a non-oriented electromagnetic steel sheet having a good magnetic flux density and containing, by mass%, the following: C: ≤ 0.005%, Si: 0.1-2.0%, Mn: 0.05-0.6%, Al: ≤ 0.5%, and a number density of AlN with an average diameter of 10-200 nm, the coiling temperature of hot rolling is set to 780°C or above.

[0006] Patent document 2 discloses the following simplified technology for hot-rolled plate annealing: in terms of mass %, it contains: C: ≦0.008%, 2% ≦Si+Al ≦3%, 0.02 ≦Mn ≦1.0%, satisfying the relationship of 0.3% ≦Al / (Si+Al) ≦0.5%, the hot rolling finishing temperature is set to above 1050°C, the subsequent water injection-free time is set to above 1 second and below 7 seconds, and the steel is coiled at below 700°C by water injection cooling.

[0007] Patent document 3 discloses a method for manufacturing the following non-oriented electromagnetic steel sheet: containing, in weight %, the following: C: less than 0.010%, Si: more than 0.1% and less than 2.0%, Mn: more than 0.1% and less than 1.5%, Al: more than 0.1% and less than 1.0%, Sn: more than 0.02% and less than 0.20%, Cu: more than 0.1% and less than 1.0%; hot-rolled sheet annealing or self-annealing is performed at a temperature below the Ac1 phase transformation point; the magnetic flux density is high and the iron loss is low.

[0008] These methods are intended to promote the grain growth of hot-rolled steel sheets and improve the magnetic properties while omitting the annealing of the hot-rolled steel sheets. However, these methods have the problem that the amount of scale generated in the hot-rolled steel sheets increases, the pickling property deteriorates, the pickling efficiency decreases, or the surface quality of the finished steel sheets deteriorates. Therefore, these methods have the problem that the advantages of simply omitting the annealing of the hot-rolled steel sheets cannot be obtained.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: International Publication No. 2013 / 069754

[0012] Patent Document 2: Japanese Patent Application Publication No. 2010-242186

[0013] Patent Document 3: Japanese Patent Application Laid-Open No. 4-6220 Summary of the invention

[0014] Technical problem to be solved by the invention

[0015] The present invention has been made in view of these problems, and provides a hot rolled steel sheet for non-oriented electrical steel sheet and a method for producing the same, and a non-oriented electrical steel sheet and a method for producing the same, in which residual scale during pickling is reduced and the surface quality of the finished steel sheet is good.

[0016] Technical means for solving technical problems

[0017] The gist of the present invention is as follows.

[0018] (1) A hot-rolled steel sheet for non-oriented electrical steel sheet according to one embodiment of the present invention contains, by mass%, C: less than 0.0050%, Si: more than 0.5% and less than 3.5%, Mn: more than 0.1% and less than 1.5%, Al: more than 0.1% and less than 1.5%, Cu: more than 0.01% and less than 0.10%, Sn: more than 0.01% and less than 0.20%, with the remainder being Fe and impurities, and having a Cu concentration peak of more than 0.12% in a range from the surface to a depth of 10 μm.

[0019] (2) A non-oriented electrical steel sheet according to another embodiment of the present invention contains, in terms of mass%, C: not more than 0.0050%, Si: not less than 0.5% and not more than 3.5%, Mn: not less than 0.1% and not more than 1.5%, Al: not less than 0.1% and not more than 1.5%, Cu: not less than 0.01% and not more than 0.10%, Sn: not less than 0.01% and not more than 0.20%, with the remainder being Fe and impurities, and having a Cu concentration peak of not less than 0.12% in a range from the surface to a depth of 5 μm.

[0020] (3) A method for manufacturing a hot-rolled steel sheet for a non-oriented electromagnetic steel sheet according to another embodiment of the present invention is the method for manufacturing the hot-rolled steel sheet for a non-oriented electromagnetic steel sheet described in (1), comprising a steelmaking step and a hot rolling step, wherein the hot rolling step comprises: billet heating, rough rolling, finish rolling and coiling, wherein the air ratio in the billet heating of the hot rolling step is set to be greater than 1.0 and less than 1.2, the temperature of the rough-rolled steel sheet before the finish rolling of the hot rolling step is set to be greater than 1000°C and less than 1050°C, the finish rolling temperature in the finish rolling of the hot rolling step is set to be greater than 930°C and less than 970°C, and the coiling temperature in the coiling of the hot rolling step is set to be greater than 750°C and less than 800°C.

[0021] (4) Another embodiment of the present invention is a method for producing a non-oriented electrical steel sheet according to the method for producing a non-oriented electrical steel sheet as described in (2), comprising a pickling step, a cold rolling step and a finishing annealing step, wherein in the cold rolling step, the hot-rolled steel sheet for the non-oriented electrical steel sheet as described in (1) is cold rolled.

[0022] (5) In the method for producing a non-oriented electrical steel sheet according to (4), the pickling solution used in the pickling step may contain thiosulfate.

[0023] Effects of the Invention

[0024] According to the present invention, a hot-rolled steel sheet for non-oriented electrical steel sheet and a non-oriented electrical steel sheet having less scale remaining during pickling and good surface quality of the finished steel sheet can be provided stably at low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is an example of a Cu concentration map of the surface layer of the hot-rolled steel sheet according to the present embodiment. DETAILED DESCRIPTION

[0026] The present inventors focused on the surface oxide scale of hot-rolled steel sheets after self-annealing, and investigated the reasons why the efficiency of removing oxide scale during pickling was poor, oxide scale remained in the product, and the surface quality deteriorated in the non-oriented electrical steel sheets that were self-annealed during the hot rolling process and the hot-rolled sheet annealing was omitted. As a result, it was found that the oxide scale on the surface of the hot-rolled steel sheet that was self-annealed during the hot rolling process was very thick compared to the hot-rolled steel sheet that was passed through the hot-rolled sheet annealing process. This is because, compared to the hot-rolled sheet annealing that was performed in a furnace with a controlled atmosphere, the hot-rolled steel sheet was continuously oxidized by oxygen in the atmosphere because the self-annealing in the hot rolling process was performed in the atmosphere.

[0027] The present inventors have conducted intensive research on methods for suppressing the progress of oxidation in such atmospheric annealing. The considerations are as follows.

[0028] The hot rolling process includes: heating of the steel slab, hot rolling (rough rolling and finishing rolling), and coiling. First, the surface of the steel slab is oxidized during the steel slab heating stage to form oxide scale. However, the oxide scale in the steel slab heating stage is removed during hot rolling and does not remain in the hot rolled steel sheet. The oxide scale remaining in the hot rolled steel sheet is the oxide scale generated from finishing rolling to coiling and after coiling.

[0029] The generation of these scales is an unavoidable problem if you want to enjoy the effect of self-annealing. In order to make the grains grow, the steel sheet temperature must be above a predetermined value, but the atmosphere cannot be controlled during hot rolling. Therefore, an attempt is made to make the chemical composition of the outermost surface of the hot-rolled steel sheet after the hot rolling is completed to be a composition that is difficult to be oxidized.

[0030] As a result, it is known that by making the steel contain an appropriate amount of Cu and enriching Cu just below the surface oxide scale in advance during the slab heating stage of hot rolling, the Cu-enriched region is exposed on the outermost surface of the hot-rolled steel sheet after finish rolling. The present inventors have found that by exposing the Cu-enriched region to the outermost surface of the hot-rolled steel sheet, the oxidation resistance of Cu is brought into play, and oxidation during self-annealing can be suppressed.

[0031] Furthermore, in the pickling process after the self-annealing, by adding a pickling accelerator mainly composed of thiosulfate to the pickling solution, the removal of the oxide scale generated during the self-annealing can be promoted. In addition, the inventors have found that by doing so, the effect on other steel types passing through the same pickling line can be avoided by utilizing the fact that the steel is more easily decomposed in the pickling solution containing thiosulfate.

[0032] Based on the above findings, the inventors have found conditions for achieving good surface quality of products in hot rolled steel sheets for non-oriented electrical steel sheets and non-oriented electrical steel sheets subjected to self-annealing during hot rolling, thereby completing the present invention.

[0033] Furthermore, the composition of the hot-rolled steel sheet for non-oriented electrical steel sheet and the non-oriented electrical steel sheet of the present embodiment and the reasons for the numerical limitations of the products are described. It should be noted that the description of the chemical composition shown below applies to both the hot-rolled steel sheet and the non-oriented electrical steel sheet of the present embodiment unless otherwise specified. In addition, the unit "%" of the content of each element in the chemical composition represents mass % unless otherwise specified.

[0034] <Chemical composition>

[0035] The components of the hot-rolled steel sheet and the non-oriented electrical steel sheet will be described below.

[0036] C deteriorates the iron loss of the non-oriented electrical steel sheet due to magnetic aging. Therefore, the C content is 0.0050% or less. The lower limit of the C content is 0%. On the other hand, from the viewpoint of avoiding the formation of solid solution B, the C content may be 0.0010% or more. The C content may be 0.0045% or less, 0.0040% or less, or 0.0035% or less. The C content may be 0.0015% or more, 0.0020% or more, or 0.0025% or more.

[0037] Si is an effective element for increasing the resistance of non-oriented electromagnetic steel sheets, and its content can be appropriately adjusted according to the required characteristics such as iron loss, magnetic flux density, and strength. However, when the Si content is less than 0.5%, the effect of reducing iron loss is small. On the other hand, if the Si content exceeds 3.5%, the toughness of the hot-rolled steel sheet and the non-oriented electromagnetic steel sheet will decrease, and manufacturing becomes difficult. Therefore, the above values ​​are the upper and lower limits of the Si content. The Si content can also be less than 3.2%, less than 3.0%, or less than 2.5%. The Si content can also be more than 0.6%, more than 0.8%, or more than 1.0%.

[0038] Mn acts as a sulfide-generating element and promotes the grain growth of the non-oriented electrical steel sheet. From the purpose of obtaining this effect, the lower limit of the Mn content is 0.1%. Furthermore, from the purpose of adjusting the phase transformation temperature to increase the resistance, it is preferred to make the Mn content appropriate. 1.5%, at which these effects are saturated, is the upper limit of the Mn content. The Mn content may also be less than 1.2%, less than 1.0%, or less than 0.8%. The Mn content may also be more than 0.2%, more than 0.4%, or more than 0.6%.

[0039] Al is an element necessary for deoxidation of steel. From the viewpoint of ensuring a stable deoxidation effect and suppressing the formation of fine AlN, the Al content is set to be above 0.1%. Furthermore, an appropriate amount of Al may be contained to increase electrical resistance. On the other hand, excess Al may deteriorate castability during steelmaking. From this point of view, 1.5% is set as the upper limit of the Al content. The Al content may also be below 1.2%, below 1.0%, or below 0.8%. The Al content may also be above 0.2%, above 0.4%, or above 0.6%.

[0040] Cu is an important element of the hot-rolled steel sheet and non-oriented electromagnetic steel sheet of the present embodiment. By making use of the characteristics of Cu that is more difficult to oxidize than iron or silicon, by making the steel billet contain an appropriate amount of Cu, Cu is enriched in the surface layer of the hot-rolled steel sheet, thereby inhibiting the formation of oxide scale. In order to obtain the above effect, the Cu content is made above 0.01%. Cu may also be preferably above 0.010%, above 0.02%, above 0.020%, above 0.05%, or above 0.050%. However, if the Cu content exceeds 0.10%, scaly folding defects will occur more easily. Therefore, 0.10% is used as the upper limit of the Cu content. The Cu content may also be below 0.100%, below 0.08%, below 0.080%, below 0.07%, below 0.070%, below 0.06%, or below 0.060%.

[0041] Sn is an important element of the hot-rolled steel sheet and non-oriented electromagnetic steel sheet of the present embodiment. By making use of the characteristics of Sn that is more difficult to oxidize than iron or silicon, the formation of oxide scale during hot rolling can be suppressed by making the steel billet contain an appropriate amount of Sn. In order to obtain the above effect, the Sn content is made to be above 0.01%. The Sn content is more preferably above 0.010%, above 0.02%, above 0.020%, above 0.05%, or above 0.050%. However, if the Sn content exceeds 0.20%, the effect will be saturated. Therefore, 0.20% is used as the upper limit of the Sn content. The Sn content can also be below 0.200%, below 0.15%, below 0.150%, below 0.10%, below 0.100%, below 0.08%, or below 0.080%.

[0042] The remainder of the chemical composition of the hot-rolled steel sheet and the non-oriented electrical steel sheet of the present embodiment is Fe and impurities. Impurities refer to trace elements allowed within a range that does not adversely affect the hot-rolled steel sheet and the non-oriented electrical steel sheet of the present embodiment.

[0043] <Cu concentration peak value of hot-rolled steel sheet for non-oriented electrical steel sheet>

[0044] In the hot-rolled steel sheet for non-oriented electromagnetic steel sheet of the present embodiment, the Cu-rich layer of its surface layer is specified. First, it is necessary to have a peak value of Cu concentration between the surface of the hot-rolled steel sheet and a depth of 10 μm. Furthermore, if the Cu concentration peak value does not meet 0.12%, the oxidation of the hot-rolled steel sheet will be aggravated, and a good surface quality as a finished plate cannot be obtained. Therefore, the hot-rolled steel sheet of the present embodiment has a Cu concentration peak value of more than 0.12% in the range from its surface to a depth of 10 μm. The Cu concentration peak value in the range from the surface of the hot-rolled steel sheet to a depth of 10 μm may also be 0.13% or more, 0.14% or more, 0.15% or more, or 0.20% or more. The upper limit value of the Cu concentration peak value in the range from the surface of the hot-rolled steel sheet to a depth of 10 μm is not particularly limited, for example, the Cu concentration peak value may be less than 1.00%, less than 0.90%, less than 0.70%, or less than 0.65%.

[0045] <Cu concentration peak value of non-oriented electrical steel sheet>

[0046] In the non-oriented electrical steel sheet of the present embodiment, the Cu-rich layer of the surface layer is defined in the same manner as the hot-rolled steel sheet. However, the non-oriented electrical steel sheet is obtained by cold-rolling the hot-rolled steel sheet. In the non-oriented electrical steel sheet obtained by cold-rolling the hot-rolled steel sheet having the Cu peak position within the preferred range, there is usually a peak in the Cu concentration from the surface to a depth of 5 μm. Therefore, in the non-oriented electrical steel sheet of the present embodiment, the range from the surface to a depth of 5 μm has a Cu concentration peak of 0.12% or more. If the Cu concentration peak does not meet 0.12%, oxidation will occur at the stage of the hot-rolled steel sheet, and good surface quality as a finished plate cannot be obtained. The Cu concentration peak from the surface of the non-oriented electrical steel sheet to a depth of 5 μm may also be 0.13% or more, 0.14% or more, 0.15% or more, or 0.20% or more. The upper limit of the Cu concentration peak in the range from the surface of the non-oriented electrical steel sheet to a depth of 5 μm is not particularly limited, and for example, the Cu concentration peak may be 1.00% or less, 0.90% or less, 0.70% or less, or 0.65% or less.

[0047] In both the hot-rolled steel sheet and the non-oriented electrical steel sheet, the Cu concentration peak was determined using GDS (glow discharge luminescence analyzer). Specific means are as follows.

[0048] Pretreatment: Clean the surface of the hot-rolled steel sheet or non-oriented electrical steel sheet. If the non-oriented electrical steel sheet has an insulating film, remove the insulating film and then clean it. Furthermore, remove a few nm of the surface layer of the hot-rolled steel sheet or non-oriented electrical steel sheet by argon sputtering.

[0049] Measurement: GDS was used to measure the depth distribution of Cu concentration. Figure 1 Based on the position and height of the Cu concentration peak shown in the concentration map, it is determined whether the Cu concentration peak is included in a predetermined position and whether its concentration is within a predetermined range.

[0050] <Manufacturing method>

[0051] Next, the hot-rolled steel sheet for non-oriented electrical steel sheet and the method for producing the non-oriented electrical steel sheet according to the present embodiment will be described.

[0052] The method for manufacturing a hot-rolled steel sheet of the present embodiment comprises a steelmaking process and a hot rolling process, wherein the hot rolling process includes heating of a steel slab, rough rolling, finish rolling, and coiling, and the air ratio in heating of the steel slab in the hot rolling process is set to 1.0 or more and 1.2 or less, the temperature of the rough-rolled steel sheet (steel sheet obtained by rough rolling the steel slab) before finish rolling in the hot rolling process is set to 1000° C. or more and 1050° C. or less, the finishing temperature in finish rolling in the hot rolling process is set to 930° C. or more and 970° C. or less, and the coiling temperature in coiling in the hot rolling process is set to 750° C. or more and 800° C. or less. The reasons for limiting the manufacturing conditions of the manufacturing method of the present embodiment are described below.

[0053] The steelmaking process is not particularly limited. Here, the composition of the steel slab may be appropriately adjusted by a known method so that the chemical composition of the hot-rolled steel sheet and the non-oriented electrical steel sheet falls within the above range.

[0054] In the hot rolling process, after heating the steel slab, the steel slab is subjected to rough rolling and finish rolling to obtain a hot-rolled steel sheet, and the hot-rolled steel sheet is coiled.

[0055] In the manufacturing method of the present embodiment, it is necessary to sufficiently generate scale on the steel billet in advance during the stage of heating the steel billet, so that Cu is enriched just below the scale. By descaling before finish rolling in this way, a sufficient Cu-enriched layer can be exposed on the surface of the steel plate. For this reason, the air ratio during heating of the steel billet is set in the range of 1.0 to 1.2. When the air ratio is less than 1.0, the enrichment of Cu cannot be fully carried out, and there is a possibility that the Cu-enriched layer cannot be obtained. When the air ratio exceeds 1.2, the amount of scale increases significantly, and even by a variety of descaling methods, the scale cannot be fully removed, and the surface properties of the hot-rolled steel plate or non-oriented electromagnetic steel plate will deteriorate.

[0056] Furthermore, the temperature of the rough rolled steel sheet before the subsequent finish rolling is set to 1000° C. to 1050° C., and the finish rolling temperature is set to 930° C. to 970° C. In this way, Cu can be further enriched.

[0057] Then, by setting the coiling temperature to 750° C. or higher, self-annealing occurs on the hot-rolled steel sheet, thereby promoting grain growth. Also, by setting the coiling temperature to 800° C. or lower, internal oxidation of the hot-rolled steel sheet can be suppressed.

[0058] The method for manufacturing the non-oriented electrical steel sheet of the present embodiment includes: a process for manufacturing the hot-rolled steel sheet of the present embodiment (i.e., the method for manufacturing the hot-rolled steel sheet of the present embodiment), a pickling process, a cold rolling process, and a finishing annealing process. The cold rolling process and the finishing annealing process are not particularly limited, and known conditions can be appropriately adopted.

[0059] The pickling process is not particularly limited. Here, in order to further promote the removal of the internal oxide layer (scale) generated during self-annealing, it is preferred to add a pickling accelerator to the pickling solution. It should be noted that the pickling solution sometimes remains in the manufacturing process, which may have a bad influence on the manufacturing of other steel grades. As a pickling accelerator that has no bad influence on other steel grades without an internal oxide layer, for example, a thiosulfate system is used.

[0060] Example

[0061] (A) Hot rolled steel plate

[0062] The steel slabs having the chemical components shown in Table 1 were hot rolled under the steel slab heating conditions and finish rolling conditions shown in Table 2 to obtain the hot rolled steel sheets shown in Table 3. In these tables, values ​​outside the scope of the invention are underlined. These hot rolled steel sheets were evaluated by the following method.

[0063] (1) Determination of Cu concentration peak

[0064] Pretreatment: The surface of the hot-rolled steel sheet was cleaned and then several nm of the surface layer of the hot-rolled steel sheet was removed by argon sputtering.

[0065] Measurement: GDS was used to measure the distribution of Cu concentration in the depth direction to obtain a Cu concentration map. Based on the position and height of the Cu concentration peak shown in the concentration map, it was determined whether the Cu concentration peak was included in the predetermined position and whether its concentration was within the predetermined range. The height of the Cu concentration peak (Cu concentration peak) is recorded in Table 3.

[0066] (2) Evaluation of residual scale during pickling (evaluation of scale after pickling)

[0067] After the hot-rolled steel sheet is immersed in a 6% hydrochloric acid solution for 60 seconds, the cross section is mirror-polished and the thickness of the internal oxide layer (i.e., the thickness of the oxide scale) is measured using an optical microscope. The oxide scale thickness obtained by the measurement is less than 1 μm and is judged as a hot-rolled steel sheet with a good oxide scale evaluation. It should be noted that the oxide scale thickness can also be measured using a scanning electron microscope.

[0068] Table 1

[0069]

[0070] Table 2

[0071]

[0072] Table 3

[0073]

[0074] Hot rolled steel sheets C1 to C13 obtained by hot rolling steel slabs having chemical components within the scope of the invention under manufacturing conditions within the scope of the invention have a Cu concentration peak of 0.12% or more in the range from the surface to a depth of 10 μm. Furthermore, hot rolled steel sheets C1 to C13 have less scale remaining during pickling.

[0075] On the other hand, in Comparative Examples c1 to c8, much scale remained during pickling.

[0076] Specifically, in Comparative Example c1, it was confirmed that oxide scale with a thickness of 5 μm remained.

[0077] In Comparative Example c2, it was confirmed that oxide scale with a thickness of 6 μm remained.

[0078] In Comparative Example c3, it was confirmed that oxide scale with a thickness of 8 μm remained.

[0079] In Comparative Example c4, it was confirmed that oxide scale with a thickness of 15 μm remained.

[0080] In Comparative Example c5, it was confirmed that oxide scale with a thickness of 13 μm remained.

[0081] In Comparative Example c6, it was confirmed that oxide scale with a thickness of 11 μm remained.

[0082] In Comparative Example c7, it was confirmed that oxide scale with a thickness of 10 μm remained.

[0083] In Comparative Example c8, it was confirmed that oxide scale with a thickness of 18 μm remained.

[0084] (B) Non-oriented electrical steel sheet

[0085] The steel slabs having the chemical composition described in Table 1 were hot rolled under the steel slab heating conditions and finish rolling conditions described in Table 2 to obtain hot rolled steel sheets. These hot rolled steel sheets were pickled, hot rolled, and finish annealed to obtain the non-oriented electromagnetic steel sheets shown in Table 4. In Table 4, the values ​​outside the scope of the invention are underlined. It should be noted that the pickling conditions were immersion in 8% hydrochloric acid for 90 seconds. The Cu concentration peaks of these non-oriented electromagnetic steel sheets were evaluated in the same manner as the hot rolled steel sheets. Furthermore, the surface quality of these non-oriented electromagnetic steel sheets was evaluated by cross-sectional observation under an optical microscope. Specifically, the cross-section of the non-oriented electromagnetic steel sheet after mirror polishing and finish annealing was measured with an optical microscope for the thickness of the oxide scale. Products with an oxide scale thickness of less than 1 μm obtained by observation were judged as non-oriented electromagnetic steel sheets with good product surface quality. It should be noted that the non-oriented electromagnetic steel sheet coated with an insulating film after finish annealing can also be immersed in a high-temperature alkaline solution to remove the insulating film, and the thickness of the oxide scale can be evaluated after washing with water. Alternatively, the thickness of the oxide scale may be measured using a scanning electron microscope.

[0086] Table 4

[0087]

[0088] Non-oriented electrical steel sheets D1 to D13 obtained by hot rolling steel slabs having chemical components within the scope of the invention under manufacturing conditions within the scope of the invention have a Cu concentration peak of 0.12% or more in the range from the surface to a depth of 5 μm. The hot-rolled steel sheets D1 to D13 have good surface quality.

[0089] On the other hand, in Comparative Examples d1 to d8, much scale remained during pickling.

[0090] Specifically, in Comparative Example d1, it was confirmed that oxide scale with a thickness of 5 μm remained.

[0091] In Comparative Example d2, it was confirmed that oxide scale with a thickness of 6 μm remained.

[0092] In Comparative Example d3, it was confirmed that oxide scale with a thickness of 8 μm remained.

[0093] In Comparative Example d4, it was confirmed that oxide scale with a thickness of 9 μm remained.

[0094] In Comparative Example d5, it was confirmed that oxide scale with a thickness of 12 μm remained.

[0095] In Comparative Example d6, it was confirmed that oxide scale with a thickness of 10 μm remained.

[0096] In Comparative Example d7, it was confirmed that oxide scale with a thickness of 7 μm remained.

[0097] In Comparative Example d8, it was confirmed that oxide scale with a thickness of 11 μm remained.

[0098] Industrial Availability

[0099] According to the present invention, a hot-rolled steel sheet for non-oriented electrical steel sheet and a non-oriented electrical steel sheet having less scale residue during pickling and good surface quality of the finished steel sheet can be stably provided at low cost. Therefore, the present invention has high industrial applicability.

Claims

1. A hot-rolled steel sheet for non-oriented electromagnetic steel sheet, characterized in that: Contains by mass %: C: 0.0050% or less, Si: 0.5% to 3.5% Mn: 0.1% or more and 1.5% or less, Al: 0.1% to 1.5%, Cu: 0.01% to 0.09% Sn: 0.01% to 0.20%; The remainder consists of Fe and impurities; In the range from the surface to a depth of 10 μm, there is a Cu concentration peak of 0.12% or more.

2. A non-oriented electromagnetic steel sheet, characterized in that: Contains by mass %: C: 0.0050% or less, Si: 0.5% to 3.5% Mn: 0.1% or more and 1.5% or less, Al: 0.1% to 1.5%, Cu: 0.01% to 0.09%, Sn: 0.01% to 0.20%; The remainder consists of Fe and impurities; In the range from the surface to a depth of 5 μm, there is a Cu concentration peak of 0.12% or more.

3. A method for producing the hot-rolled steel sheet for non-oriented electromagnetic steel sheet according to claim 1, characterized in that: Equipped with steel making process and hot rolling process; The hot rolling process includes billet heating, rough rolling, finish rolling and coiling; The air ratio in the heating of the steel slab in the hot rolling step is set to be 1.0 or more and 1.2 or less; The temperature of the rough rolled steel sheet before the finish rolling in the hot rolling step is set to 1000° C. to 1050° C. The finishing rolling temperature in the finishing rolling of the hot rolling step is set to 930° C. or higher and 970° C. or lower; The coiling temperature in the coiling in the hot rolling step is set to 750° C. or higher and 800° C. or lower.

4. A method for manufacturing the non-oriented electromagnetic steel sheet according to claim 2, characterized in that: It has pickling process, cold rolling process and finishing annealing process; In the cold rolling step, the hot-rolled steel sheet for non-oriented electrical steel sheet according to claim 1 is cold rolled.

5. The method for producing a non-oriented electrical steel sheet according to claim 4, wherein: The pickling solution used in the pickling step contains thiosulfate.

Images