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

Abstract

The present invention provides a hot-rolled annealed sheet for an electrical steel sheet, the hot-rolled annealed sheet being excellent in terms of cold rolling properties (fracture resistance and edge cracking resistance) in a post-process. Provided is a hot-rolled annealed sheet for an electrical steel sheet, the hot-rolled annealed sheet having a component composition that contains, in mass%, 0.010% or less of C, 1.0% to 5.0% inclusive of Si, 0.05% to 5.0% inclusive of Mn, 0.1% or less of P, 0.01% or less of S, 3.0% or less of Al, and 0.0080% or less of N, with the balance being made up of Fe and inevitable impurities. At least at one of the plate width edge parts of the hot-rolled annealed sheet for an electrical steel sheet, the ratio dC / dE of the average crystal grain size dC at the plate width center part to the average crystal grain size dE at a position of 10 mm from the plate width edge part is 1.2 or more.

Description

Hot-rolled annealed sheet for electrical steel sheet and manufacturing method thereof, and manufacturing method of non-oriented electrical steel sheet

[0001] The present invention relates to a hot-rolled annealed sheet for electrical steel sheet and a manufacturing method thereof, and a manufacturing method of a non-oriented electrical steel sheet.

[0002] In recent years, due to concerns about the environment such as global warming, CO ２ In response to the demand for reduced emissions and energy conservation, the automotive field is seeing the development of hybrid electric vehicles (HEVs) that use both engines and motors, electric vehicles (EVs) that are driven solely by electric motors, and fuel cell electric vehicles (FCEVs). To improve motor efficiency, motors used in HEVs, EVs, FCEVs, and the like are generally driven in a high-frequency range that is advantageous for high-speed rotation. Non-oriented electrical steel sheets are often used as the iron core material for these motors, and there is a strong demand for these steel sheets to have low iron loss in the high-frequency range in order to achieve high motor efficiency.

[0003] Conventionally, attempts have been made to reduce iron loss in non-oriented electrical steel sheets by adding alloying elements such as Si and Al to increase resistivity or by reducing sheet thickness to reduce eddy current loss. However, adding large amounts of alloying elements reduces the ductility and toughness of the steel sheet, resulting in frequent fractures during the cold rolling process. Patent documents 1 and 2, for example, disclose methods for producing non-oriented electrical steel sheets with high magnetic flux density, which suppress cracking during cold rolling by cold rolling rapidly solidified slabs at 180°C to 350°C.

[0004] JP 2004-323972 A JP 2005-298876 A

[0005] However, in the techniques described in Patent Documents 1 and 2, although cracking can be suppressed by performing cold rolling in a temperature range of 180°C to 350°C, there are problems in that it is difficult to maintain a high temperature of the steel sheet during rolling, and in that there is a high possibility of causing equipment wear, such as seizure of lubricating oil on the rolls.

[0006] The present invention has been made in consideration of the above-mentioned problems of the conventional technology, and an object of the present invention is to provide a hot-rolled annealed sheet for electrical steel sheet that has excellent cold rolling properties (fracture resistance and edge crack resistance) in subsequent processes, together with an advantageous manufacturing method thereof.

[0007] The present inventors have conducted extensive research into solving the above problems and have found that in most cases, the origin of fracture due to cold rolling is located in a region near the edge of the hot-rolled annealed sheet (steel strip), and that increasing the fracture resistance of this region can significantly suppress fractures and cracks without increasing the fracture resistance of the entire hot-rolled annealed sheet. Furthermore, they have found that by refining the crystal grains in this region and creating a difference in crystal grain size from the center, the fracture resistance is improved compared to when the crystal grains in the entire hot-rolled annealed sheet are refined, and deterioration of magnetic properties can be prevented.

[0008] The present invention was made based on this finding and has the following configuration: [1] A steel sheet having a chemical composition containing, in mass%, C: 0.010% or less, Si: 1.0% to 5.0%, Mn: 0.05% to 5.0%, P: 0.1% or less, S: 0.01% or less, Al: 3.0% or less, and N: 0.0080% or less, with the balance consisting of Fe and inevitable impurities, and at least one of the sheet width edge portions, an average crystal grain size d C The average grain size d at the position 10 mm from the edge of the sheet width E Ratio to d C / d EHot-rolled and annealed electrical steel sheet with a modulus of 1.2 or more. [2] The composition further comprises, in mass%, Zn: 0.0005% or more and 0.020% or less, Mo: 0.002% or more and 0.20% or less, Ni: 0.01% or more and 1.0% or less, Cr: 0.01% or more and 5.0% or less, Cu: 0.005% or more and 1.0% or less, Ca: 0.0001% or more and 0.10% or less, Mg: 0.0001% or more and 0.10% or less, REM: 0.0001% or more and 0.10% or less, Sn: 0.001% or more and 0.20% or less, Sb: 0.001% or more and 0.20% or less, B: 0.0020% or less, Ti: 0.010% or less, Nb: 0.0050% or less, V: 0.0050% or less, Pb: 0.0050% or less, Zr: 0.0050% or less, [3] The hot-rolled annealed sheet for electrical steel sheet according to [1], containing one or more elements selected from the group consisting of Ta: 0.0020% or less, W: 0.0050% or less, Se: 0.0050% or less, Bi: 0.0050% or less, As: 0.020% or less, Co: 0.10% or less, Ge: 0.030% and Ga: 0.030% or less. C is 70 μm or more and 300 μm or less, and the average grain size d E [4] A hot-rolled annealed sheet for electrical steel sheet according to any one of [1] to [3], wherein the maximum value of the average grain size gradient in the sheet width direction is 0.2 μm / mm or more and 1.5 μm / mm or less. [5] A hot-rolled annealed sheet for electrical steel sheet according to any one of [1] to [4], wherein the position where the average grain size gradient in the sheet width direction is maximum is within 200 mm from the sheet width edge portion. [6] At both sheet width edge portions, the average grain size d C The average grain size d at the position 10 mm from the edge of the sheet E Ratio to d C / d E[7] A method for producing a hot-rolled annealed sheet for electrical steel sheet according to any one of [1] to [6], comprising a hot rolling step of hot-rolling a steel material having the composition according to [1] or [2] to obtain a hot-rolled sheet, and a hot-rolled sheet annealing step of hot-rolling the hot-rolled sheet, wherein in the hot-rolled sheet annealing step, when holding a widthwise center portion of the hot-rolled sheet at a holding temperature T1, a maximum temperature T2 reached at a position 10 mm from the widthwise edge portion of at least one of the widthwise edges of the hot-rolled sheet satisfies T1-T2 ≧ 20°C. [8] The method for producing a hot-rolled annealed sheet for electrical steel sheet according to [7], wherein, in the hot-rolled sheet annealing step, the holding temperature T1 at the width center of the hot-rolled sheet is 900°C or higher and 1150°C or lower, and the holding time t1 at T1 is 1 second or higher and 120 seconds or lower. [9] The method for producing a hot-rolled annealed sheet for electrical steel sheet according to [7] or [8], wherein, in the hot-rolled sheet annealing step, the maximum temperature reached T2 is 750°C or higher and 1000°C or lower.

[10] The method for producing a hot-rolled annealed sheet for electrical steel sheet according to any of [7] to [9], wherein, in the hot-rolled sheet annealing step, the time t2 during which the temperature at a position 10 mm from the width edge of the hot-rolled sheet is equal to or higher than the maximum temperature reached T2 - 50°C is 5 seconds or higher and 50 seconds or lower.

[11] A method for producing a hot-rolled annealed sheet for electrical steel sheet according to any of [7] to

[10] , wherein in the hot-rolled sheet annealing step, a heating suppression region is between a sheet width edge portion and a position X1 mm from the sheet width edge portion, X1 being 20 mm or more and 250 mm or less.

[12] A method for producing a hot-rolled annealed sheet for electrical steel sheet according to any of [7] to

[11] , wherein, in both sheet width edge portions of the hot-rolled sheet, a maximum temperature T2 at a position 10 mm from the sheet width edge portion satisfies T1 - T2 ≧ 20°C.

[13] A method for producing a non-oriented electrical steel sheet, comprising: a cold-rolling step of cold-rolling the hot-rolled annealed sheet for electrical steel sheet according to any of [1] to [6] to obtain a cold-rolled sheet; and an annealing step of annealing the cold-rolled sheet.

[0009] In the present invention, the width edge portion refers to the edge in the width direction of the plate, and may be either the left or right edge.

[0010] According to the present invention, a hot-rolled annealed sheet for electrical steel sheet, which has excellent cold rolling properties (fracture resistance and edge crack resistance) in subsequent processes, is provided, along with an advantageous manufacturing method thereof. An electrical steel sheet manufactured using the hot-rolled annealed sheet of the present invention is sufficiently free from deterioration in magnetic properties. In particular, by using the hot-rolled annealed sheet of the present invention in the manufacture of a non-oriented electrical steel sheet, a non-oriented electrical steel sheet with high magnetic flux density and low iron loss at high frequency can be provided, and the use of this non-oriented electrical steel sheet can achieve high motor efficiency. Furthermore, even if the non-oriented electrical steel sheet is subjected to strain relief annealing in order to reduce the increase in iron loss due to strain during punching, the above-mentioned effects are not affected in any way.

[0011] The details of the present invention will be explained below together with the reasons for the limitations.

[0012] [Hot-rolled annealed sheet] <Composition> The composition of the hot-rolled annealed sheet of the present invention will be described. The unit of the content of elements in the composition is "mass%", but hereinafter, unless otherwise specified, it will be simply expressed as "%".

[0013] C: 0.010% or less C is an element that forms carbides and adversely affects iron loss characteristics. In particular, if the C content exceeds 0.010%, the adverse effects become significant, so the C content is set to 0.010% or less. Preferably, it is set to 0.004% or less. While there is no particular lower limit for C, excessive reduction of C leads to increased costs, so it is preferably set to about 0.0001%.

[0014] Si: 1.0% to 5.0% Si has the effect of increasing the resistivity of steel, reducing iron loss, and increasing the strength of steel through solid solution strengthening. To achieve these effects, the Si content should be 1.0% or more. On the other hand, if the Si content exceeds 5.0%, the magnetic flux density decreases significantly, so the upper limit is set to 5.0% or less. Therefore, the Si content is set to the range of 1.0% to 5.0%. Preferably, the Si content is in the range of 1.5% to less than 4.5%, and more preferably, in the range of 2.0% to less than 4.0%.

[0015] Mn: 0.05% to 5.0% Like Si, Mn is a useful element for increasing the resistivity and strength of steel. To achieve this effect, the Mn content should be 0.05% or more. However, if it exceeds 5.0%, it may promote the precipitation of MnC, deteriorating the magnetic properties, so the upper limit is set to 5.0%. Therefore, the Mn content is set to 0.05% to 5.0%. The preferred range is 0.1% to 3.0%.

[0016] P: 0.1% or less P is a useful element used to adjust the strength (hardness) of steel. However, if it exceeds 0.1%, toughness decreases and cracks tend to occur during processing, so the upper limit is set to 0.1%. There is no particular lower limit, but since excessive reduction of P leads to increased costs, it is preferable to set it to 0.001%. A more preferable range is 0.003% or more and 0.08% or less.

[0017] S: 0.01% or less S is an element that forms fine precipitates and adversely affects iron loss characteristics. In particular, if the content exceeds 0.01%, the adverse effects become significant, so the content is set to 0.01% or less. More preferably, it is set to 0.005% or less. Although there is no particular lower limit, excessive reduction of S leads to increased costs, so it is preferably set to 0.0001%. More preferably, it is set to a range of 0.0003% or more and 0.0080% or less.

[0018] Al: 3.0% or less Like Si, Al is a useful element that increases the resistivity of steel and reduces iron loss. To achieve this effect, it is preferable to add 0.005% or more. More preferably, it is 0.010% or more, and even more preferably, it is 0.015% or more. On the other hand, if it exceeds 3.0%, it promotes nitriding of the steel sheet surface and may deteriorate the magnetic properties, so the upper limit is set to 3.0%. More preferably, it is 2.0% or less.

[0019] N: 0.0080% or less N is an element that forms fine precipitates and adversely affects iron loss characteristics. In particular, if the N content exceeds 0.0080%, the adverse effects become significant, so the N content is set to 0.0080% or less. Preferably, the N content is set to 0.003% or less. Although there is no particular lower limit, excessive reduction of N leads to increased costs, so the N content is preferably set to 0.0005%. More preferably, the N content is set to a range of 0.0008% or more and 0.0030% or less.

[0020] The component composition of the present invention may further contain one or more elements selected from Zn, Mo, Ni, Cr, Cu, Ca, Mg, REM, Sn, and Sb within the following ranges depending on the required properties.

[0021] Zn: 0.0005% to 0.020% Zn is an element that is effective in improving texture, thereby increasing magnetic flux density and reducing iron loss. To achieve this effect, the Zn content should be 0.0005% or more. However, if the Zn content exceeds 0.020%, the effect saturates and costs increase unnecessarily, so the upper limit is set to 0.020%. Therefore, if Zn is contained, the Zn content is preferably in the range of 0.0005% to 0.020%, more preferably 0.0005% to 0.0050%.

[0022] Mo: 0.002% or more and 0.20% or less Mo has the effect of forming fine carbides in steel and increasing the strength of the steel sheet. To obtain this effect, the Mo content should be 0.01% or more. On the other hand, if the Mo content exceeds 0.20%, excessive carbides are formed and iron loss deteriorates, so the upper limit is set to 0.20%. Therefore, when Mn is contained, the Mo content is preferably in the range of 0.01% or more and 0.20% or less.

[0023] Ni: 0.01% or more and 1.0% or less Ni is an element that improves the toughness of steel and can be added as needed. To achieve this effect, the Ni content should be 0.01% or more. However, the effect of Ni saturates when the Ni content exceeds 1.0%, so the upper limit is set to 1.0%. Therefore, when Ni is added, the Ni content is preferably in the range of 0.01% or more and 0.01% or less.

[0024] Cr: 0.01% to 5.0% Cr has the effect of increasing the resistivity of steel and reducing iron loss. To achieve this effect, the Cr content should be 0.05% or more. However, if the Cr content exceeds 5.0%, the magnetic flux density decreases significantly due to a decrease in the saturation magnetic flux density, so the upper limit is set to 5.0%. Therefore, if Cr is contained, the Cr content is preferably in the range of 0.01% to 5.0%, and more preferably 0.05% to 5.0%.

[0025] Cu: 0.01% or more and 1.0% or less Cu is an element that improves the toughness of steel and can be added as needed. To achieve this effect, the Cu content should be 0.01% or more. However, the effect saturates when Cu exceeds 1.0%, so the upper limit is set to 1.0%. Therefore, when Cu is added, the Cu content is preferably in the range of 0.01% or more and 1.0% or less.

[0026] Ca: 0.0001% or more and 0.10% or less Ca is an element that fixes S as sulfides and contributes to reducing iron loss. To obtain this effect, the Ca content should be 0.0001% or more. On the other hand, if the Ca content exceeds 0.10%, the effect saturates and costs increase unnecessarily, so the upper limit is set to 0.10%. Therefore, when Ca is contained, the Ca content is preferably in the range of 0.0001% or more and 0.10% or less.

[0027] Mg: 0.0001% or more and 0.10% or less Mg is an element that fixes S as sulfides and contributes to reducing iron loss. To obtain this effect, the Mg content should be 0.0001% or more. On the other hand, if the Mg content exceeds 0.10%, the effect saturates and costs increase unnecessarily, so the upper limit is set to 0.10%. Therefore, when Mg is contained, the Mg content is preferably in the range of 0.0001% or more and 0.10% or less.

[0028] REM: 0.0001% or more and 0.10% or less REM is a group of elements that fix S as sulfides and contribute to reducing iron loss. To obtain this effect, the REM content should be 0.0001% or more. On the other hand, if the REM content exceeds 0.10%, the effect saturates and costs increase unnecessarily, so the upper limit is set to 0.10%. Therefore, when REM is contained, it is preferable that the REM content be in the range of 0.0001% or more and 0.10% or less.

[0029] Sn: 0.001% or more and 0.20% or less Sn is an element that is effective in improving the texture, thereby increasing magnetic flux density and reducing iron loss. To achieve this effect, the Sn content should be 0.001% or more. However, if the Sn content exceeds 0.20%, the effect saturates and costs increase unnecessarily, so the upper limit is set to 0.20%. Therefore, if Sn is contained, the Sn content is preferably in the range of 0.001% or more and 0.20% or less.

[0030] Sb: 0.001% or more and 0.20% or less Sb is an element that is effective in improving the texture, thereby increasing the magnetic flux density and reducing iron loss. To achieve this effect, the Sb content should be 0.001% or more. However, if the Sb content exceeds 0.20%, the effect saturates and costs increase unnecessarily, so the upper limit is set to 0.20%. Therefore, if Sb is contained, the Sb content is preferably in the range of 0.001% or more and 0.20% or less.

[0031] The component composition of the present invention may further contain one or more elements selected from B, Ti, Nb, V, Pb, Zr, Ta, W, Se, Bi, As, Co, Ge, and Ga.

[0032] B: 0.0020% or less B is an element that contributes to improving the strength of steel sheet by refining the grain structure of the steel sheet, but if added in an amount exceeding 0.0020%, nitrides precipitate in the steel during operation, increasing iron loss. For this reason, when B is contained, the upper limit of the B content is set to 0.0020%. The B content may be 0%.

[0033] Ti: 0.010% or less Ti is an element that contributes to improving the strength of steel sheet by refining the grain structure of the steel sheet, but if added in excess of 0.010%, excessive carbides will precipitate in the steel, increasing iron loss. Therefore, if Ti is contained, the upper limit of the Ti content is set to 0.010%. The Ti content may be 0%.

[0034] Nb: 0.0050% or less Nb is an element that contributes to improving the strength of steel sheet by refining the grain structure of the steel sheet, but if added in excess of 0.0050%, excessive carbides will precipitate in the steel, increasing iron loss. Therefore, when Nb is contained, the upper limit of the Nb content is set to 0.0050%. The Nb content may be 0%.

[0035] V: 0.0050% or less V is an element that contributes to improving the strength of steel sheet by refining the grain structure of the steel sheet, but if added in excess of 0.0050%, excessive carbides precipitate in the steel, increasing iron loss. Therefore, when V is contained, the upper limit of the V content is set to 0.0050%. The V content may be 0%.

[0036] Pb: 0.0050% or less Pb is an element that contributes to improving the strength of steel sheets by refining the grain structure of the steel sheet, but if added in excess of 0.0050%, excessive precipitation in the steel increases iron loss. Therefore, if Pb is contained, the upper limit of the Pb content is set to 0.0050%. The Pb content may be 0%.

[0037] Zr: 0.0050% or less Zr is an element that contributes to improving the strength of steel sheet by refining the grain structure of the steel sheet, but if added in excess of 0.0050%, excessive carbides will precipitate in the steel, increasing iron loss. Therefore, if Zr is contained, the upper limit of the Zr content is set to 0.0050%. The Zr content may be 0%.

[0038] Ta: 0.0020% or less Ta is an element that contributes to improving the strength of steel sheet by refining the grain structure of the steel sheet, but if added in excess of 0.0020%, excessive carbides will precipitate in the steel, increasing iron loss. Therefore, if Ta is contained, the upper limit of the Ta content is set to 0.0020%. The Ta content may be 0%.

[0039] W: 0.0050% or less W is an element that contributes to improving the strength of steel sheets by refining the grain structure of the steel sheet, but if added in excess of 0.0050%, excessive carbides will precipitate in the steel, increasing iron loss. Therefore, if W is contained, the upper limit of the W content is set to 0.0050%. The W content may be 0%.

[0040] Se: 0.0050% or less Se is an element that contributes to improving the strength of steel sheet by refining the grain structure of the steel sheet, but if added in an amount exceeding 0.0050%, excessive MnSe precipitates in the steel, increasing iron loss. Therefore, when Se is contained, the upper limit of the Se content is set to 0.0050%. The Se content may be 0%.

[0041] Bi: 0.0050% or less Bi is an element that contributes to improving the strength of steel sheet by refining the grain structure of the steel sheet, but if added in an amount exceeding 0.0050%, excessive precipitation in the steel increases iron loss. Therefore, when Bi is contained, the upper limit of the Bi content is set to 0.0050%. The Bi content may be 0%.

[0042] As: 0.020% or less As contributes to improving the magnetic flux density of steel sheets by improving the texture. However, the effect saturates at 0.030% or more. Therefore, when As is contained, the upper limit of the As content is set to 0.10%. The As content may be 0%.

[0043] Co: 0.10% or less Co contributes to improving the magnetic flux density of steel sheets by increasing the saturation magnetic flux density. However, adding more than 0.10% of Co makes the cost excessively high. Therefore, when Co is contained, the upper limit of the Co content is set to 0.10%. The Co content may be 0%.

[0044] Ge: 0.030% or less Ge contributes to improving the magnetic flux density of steel sheet by improving the texture. However, the effect saturates at 0.030% or more. Therefore, when Ge is contained, the upper limit of the Ge content is set to 0.10%. The Ge content may be 0%.

[0045] Ga: 0.030% or less Ga contributes to improving the magnetic flux density of steel sheets by improving the texture. However, the effect saturates at 0.030% or more. Therefore, when Ga is contained, the upper limit of the Ga content is set to 0.10%. The Ga content may be 0%.

[0046] In the above composition, the balance other than the above components is Fe and unavoidable impurities.

[0047] <Microstructure> Next, the microstructure of the hot-rolled annealed steel sheet of the present invention will be described.

[0048] (Average grain size at the center of the sheet width d C The grain size d at the position 10 mm from the edge of the sheet width E Ratio to d C / d E (The difference is 1.2 or more.) According to the study by the present inventors, it was found that by providing a difference in the grain size between the width center and the region near the width edge, fractures and edge cracks during the cold rolling process are significantly suppressed compared to simply making the grain size of the entire hot-rolled annealed sheet finer. The reason for this is presumed to be as follows: Generally, the work hardening rate with respect to plastic deformation decreases as the grain size decreases. When the grain size in the region near the width edge is smaller than that in the width center, the work hardening rate in the region near the width edge is smaller than that in the width center, and stress acts to reduce the tension in the region near the width edge during rolling. This is presumed to significantly suppress the initiation of cracks in the region near the width edge, thereby reducing fractures and edge cracks.

[0049] Furthermore, the inventors' investigations revealed that the difference in grain size between the center of the sheet width and the region near the edge of the sheet width is the average grain size d E Average grain size d at the width center of the hot-rolled and annealed sheet C The ratio d C / d E It has been found that by making the ratio d 1.2 or more, it is possible to obtain a hot-rolled annealed sheet in which breakage and edge cracking during cold rolling are sufficiently suppressed. C / d E is preferably 1.4 or more, more preferably 1.6 or more. C / d E The upper limit of the ratio d C / d E The average grain size d at the center of the width of the hot-rolled and annealed sheet is usually 10 or less. C and the average grain size d at a position 10 mm from the edge of the sheet width E can be measured by the methods described in the Examples.

[0050] The hot-rolled annealed sheet of the present invention has a ratio d C / d E is 1.2 or more, but at both width edges, the ratio d C / d E However, if the edge cracks or breaks occur unevenly on one side due to the rolling mill's habit, the ratio d C / d E A sufficient effect of reducing breakage may be obtained by making the value of the cross section satisfy 1.2 or more.

[0051] Hereinafter, preferred embodiments of the hot-rolled annealed sheet of the present invention will be further described. Unless otherwise specified, the description of the "sheet width edge portion" refers to the ratio d C / d E The width edge portion of the plate satisfies the condition of 1.2 or more.

[0052] (Average grain size at the center of the sheet width d C is 70 μm or more and 300 μm or less, and the average grain size d at the position 10 mm from the edge of the plate width E The hot rolled annealed sheet of the present invention has an average grain size d E Average grain size d at the center of the sheet width C The ratio d C / d E The effect of the present invention is not limited by the value of the average grain size at each position. However, in order to make the effect of the present invention more remarkable, it is necessary to control d C and dE are preferably in the following ranges, respectively:

[0053] Average grain size at the center of the sheet width d C is preferably 70 μm or more and 300 μm or less. C If d is 70 μm or more, the effect of suppressing deterioration of the magnetic properties of the electrical steel sheet manufactured using the hot-rolled annealed sheet of the present invention is higher, C If is 300 μm or less, the ratio d C / d E The effect of suppressing breakage by controlling the temperature can be more effectively exhibited.

[0054] Average grain size d at 10 mm from the edge of the plate E is preferably 10 μm or more and 200 μm or less. E If d is 10 μm or more, it is easy to avoid the situation where the edge of the sheet width becomes excessively hard due to the strengthening of the crystal grain refinement, which in turn promotes the generation of fracture origins. E If is 200 μm or less, the ratio d C / d E The effect of suppressing breakage by controlling the temperature can be more effectively exhibited.

[0055] (Maximum value of average grain size gradient in the sheet width direction Δd max The inventors' investigations have revealed that in order to prevent fracture, it is effective to avoid excessively large changes in the structure in the sheet width direction. In order to avoid the occurrence of stress concentration sites during rolling that promote fracture originating from the inside of the steel sheet, the maximum value of the average grain size gradient in the sheet width direction is preferably 5.0 μm / mm or less, more preferably 4.0 μm / mm or less, and even more preferably 3.0 μm / mm or less. On the other hand, the ratio d C / d E In order to fully obtain the fracture suppression effect achieved by controlling the grain size, the maximum value of the average grain size gradient in the sheet width direction is preferably 0.2 μm / mm or more. The maximum value of the average grain size gradient in the sheet width direction can be determined by the method described in the Examples.

[0056] (Position X2 where the gradient of the average grain size in the sheet width direction is maximum is within 200 mm from the sheet width edge) The inventors' studies have found that by controlling the distance between the position where the gradient of the average grain size in the sheet width direction is maximum and the sheet width edge, the effect of reducing tension at the sheet width edge can be used to sufficiently suppress fracture. For this reason, it is preferable that the position where the gradient of the average grain size in the sheet width direction is maximum is within 200 mm from the sheet width edge. It is more preferable that it is within 100 mm, and even more preferable that it is within 50 mm. The position where the gradient of the average grain size in the sheet width direction is maximum can be determined by the method described in the Examples.

[0057] The hot-rolled and annealed steel sheet of the present invention is used to produce electrical steel sheets, which include non-oriented electrical steel sheets and grain-oriented electrical steel sheets.

[0058] [Method for Producing Hot-Rolled Annealed Sheet] Next, the method for producing a hot-rolled annealed sheet of the present invention will be described.

[0059] The method for producing a hot-rolled annealed sheet of the present invention is, in outline, a method for obtaining the above-mentioned hot-rolled annealed sheet of the present invention by successively subjecting a steel material having the above-mentioned chemical composition to hot rolling and hot-rolled annealing. In the method for producing a hot-rolled annealed sheet of the present invention, as long as the steel material satisfies the chemical composition specified in the present invention and the hot-rolled annealing conditions are within the range of the present invention, there are no other particular limitations, and known techniques can be applied.

[0060] <Steel Material> The steel material is not particularly limited as long as it has the chemical composition described for the hot-rolled annealed steel sheet. The method for producing the steel material is not particularly limited, and known methods using a converter, electric furnace, or the like can be used. From the viewpoint of productivity and the like, it is preferable to produce a slab (steel material) by continuous casting after the smelting, but the slab may also be produced by known casting methods such as ingot casting-blooming rolling or thin slab continuous casting.

[0061] <Hot rolling step> The hot rolling step is a step of hot rolling a steel material having the above-mentioned composition to obtain a hot-rolled sheet. The hot rolling step is not particularly limited as long as it is a step of heating a steel material having the above-mentioned composition and hot-rolling it to obtain a hot-rolled sheet of a predetermined size, and any known hot rolling step can be applied.

[0062] An example of a hot rolling process is a hot rolling process in which a steel material is heated to a temperature of 1000°C to 1200°C, the heated steel material is hot rolled at a finish rolling outlet temperature of 800°C to 950°C, and after hot rolling is completed, the steel material is subjected to appropriate post-rolling cooling (for example, cooling in a temperature range of 450°C to 950°C at an average cooling rate of 20°C / s to 100°C / s), and then coiled at a coiling temperature of 400°C to 700°C to form a hot-rolled sheet of a predetermined size and shape. The width of the obtained hot-rolled sheet can be adjusted by slitting or edge trimming at the inlet side of the hot-rolled sheet annealing process. In the hot-rolled annealing process, the width of the hot-rolled sheet when it enters the annealing furnace is usually 600mm to 2000mm, and the same applies to the hot-rolled annealed sheet.

[0063] <Hot-rolled sheet annealing process> The hot-rolled sheet annealing process is a process in which the hot-rolled sheet is heated and held at a high temperature to normalize the hot-rolled sheet, thereby obtaining a hot-rolled annealed sheet. In the method for producing a hot-rolled annealed sheet of the present invention, the hot-rolled sheet that has been subjected to the hot rolling process is heated and held at a suitable holding temperature T1 required for recrystallization of the hot-rolled sheet at the widthwise center portion of the hot-rolled sheet, and then cooled. At the same time, the maximum temperature T2 at a position 10 mm from the widthwise edge of at least one of the widthwise edges of the hot-rolled sheet satisfies the condition T1 - T2 ≧ 20°C. The maximum temperature T2 at a position 10 mm from the widthwise edge of both widthwise edges may also satisfy the condition T1 - T2 ≧ 20°C.

[0064] (The maximum temperature T2 at the position 10 mm from the width edge is T1-T2≧20°C) In the hot-rolled sheet annealing process, the maximum temperature T2 at the position 10 mm from the width edge is limited to T1-T2≧20°C. When T1-T2<20°C, the difference in grain size between the width center and the region near the width edge becomes small, and the average grain size d C The average grain size d at the position 10 mm from the edge of the sheet width E The ratio d C / d E The temperature T1-T2 ratio cannot be set to 1.2 or more. Preferably, T1-T2≧35°C, and more preferably, T1-T2≧50°C.

[0065] A preferred embodiment of the hot-rolled sheet annealing step in the method for producing a hot-rolled annealed sheet according to the present invention will be further described below. Unless otherwise specified, the term "sheet width edge portion" refers to the sheet width edge portion in which the maximum temperature T2 is controlled to satisfy T1-T2≧20°C.

[0066] (Holding temperature T1 at the sheet width center is 900°C or higher and 1100°C or lower) In the hot-rolled sheet annealing process, the holding temperature T1 at the sheet width center is preferably 900°C or higher and 1100°C or lower. If T1 is 900°C or higher, it is possible to easily prevent the grain size at the sheet width center from becoming excessively fine, and if T1 is 1100°C or lower, it is possible to easily prevent the grain size from becoming excessively coarse. Therefore, by setting T1 in the above range, the average grain size d at the sheet width center can be reduced. C can be easily set to 70 μm or more and 300 μm or less.

[0067] (Holding time t1 at holding temperature T1 in the width center portion is 2 seconds or more and 120 seconds or less) In the hot-rolled sheet annealing process, the holding time t1 at holding temperature T1 in the width center portion is preferably 2 seconds or more and 120 seconds or less. If t1 is 2 seconds or more, recrystallization and grain growth by hot-rolled sheet annealing are sufficient, and the average grain size d C can be easily set to 70 μm or more, and if t1 is 120 seconds or less, the temperature profile in the sheet width direction does not become excessively flat, and the average crystal grain size gradient in the sheet width direction can be easily set to 0.2 μm / mm or more.

[0068] (Maximum temperature T2 at 10 mm from the sheet width edge is 750°C or higher and 1000°C or lower) In the hot-rolled sheet annealing process, the maximum temperature T2 at 10 mm from the sheet width edge is preferably 750°C or higher and 1000°C or lower. If T2 is 750°C or higher, it is easy to prevent the grain size in the region near the sheet width edge from becoming excessively fine, and the average grain size d at 10 mm from the sheet width edge can be reduced. E can be easily made 10 μm or more, and if T2 is 1000 °C or less, d E can be easily reduced to 200 μm or less.

[0069] (Time t2 during which the temperature 10 mm from the width edge is equal to or higher than the maximum temperature T2-50°C is 5 seconds or more and 50 seconds or less) In the hot-rolled sheet annealing process, it is preferable to limit the time t2 during which the temperature 10 mm from the width edge is equal to or higher than the maximum temperature T2-50°C to 5 seconds or less. If t2 is 5 seconds or more, cooling after the temperature 10 mm from the width edge reaches the maximum temperature T2 can be appropriately controlled, and the temperature profile in the width direction does not become excessively steep, and the average grain size gradient in the width direction can easily be set to 1.5 μm / mm or less. Furthermore, if t2 is 50 seconds or less, the temperature profile in the width direction does not become excessively flat, and the average grain size gradient in the width direction can easily be set to 0.2 μm / mm or more.

[0070] (The heating suppression region is between the sheet width edge and the X1 mm position from the sheet width edge) In the hot-rolled sheet annealing process, a heating suppression region can be set to intentionally change the temperature in the sheet width direction. Specific examples of such methods include reducing burner heating only in the region near the sheet width edge to prevent overheating, using an edge cover to prevent overheating, applying a temperature rise prevention material with low emissivity that can suppress radiant heating, and removing black scale only in the region near the sheet width edge to reduce emissivity and prevent temperature rise. Any method that can intentionally change the temperature can be used, and is not limited to these. It is preferable to set the heating suppression region between the sheet width edge and the X1 mm position from this sheet width edge, where X1 is in the range of 20 mm to 250 mm. If X1 is 20 mm or more, the temperature rise due to heat conduction at a position 10 mm from the sheet width edge is appropriate, and the T1-T2 can easily be set to 20°C or more. Furthermore, if X1 is 250 mm or less, the position at which the average grain size gradient in the sheet width direction is maximum can be easily controlled to within 200 mm from the sheet width edge. X1 is more preferably 40 mm or more and 150 mm or less. The heat suppression zone is preferably provided near at least one sheet width edge, and more preferably near both sheet width edges.

[0071] <Pickling Step> The method for producing a hot-rolled annealed sheet of the present invention can include a pickling step. Here, the pickling step is a step of pickling the hot-rolled sheet after the hot-rolled sheet annealing step. The pickling step is not particularly limited as long as it is a step that can pickle the pickled steel sheet to an extent that cold rolling can be performed on it, and a known pickling step using, for example, hydrochloric acid or sulfuric acid can be applied. When the hot-rolled sheet annealing step is performed, this pickling step may be performed continuously in the same line as the hot-rolled sheet annealing step, or may be performed in a separate line. The hot-rolled annealed sheet of the present invention includes both a state that has not been pickled (black skin) and a state that has been pickled (white skin).

[0072] [Method for producing non-oriented electrical steel sheet] The method for producing a non-oriented electrical steel sheet of the present invention is generally a method comprising sequentially subjecting the hot-rolled annealed sheet of the present invention to cold rolling and cold-rolled annealing. The method for producing a non-oriented electrical steel sheet of the present invention is not particularly limited as long as the hot-rolled annealed sheet of the present invention is used, and known techniques can be applied.

[0073] <Cold Rolling Step> The cold rolling step is a step of cold rolling the hot-rolled annealed sheet (pickled sheet) that has been subjected to the pickling. In the cold rolling step, the hot-rolled annealed sheet that has been subjected to the pickling is cold-rolled to obtain a cold-rolled sheet. There are no particular limitations on the cold rolling step as long as it is a step that obtains a cold-rolled sheet of predetermined dimensions by cold rolling, and any known cold rolling step can be applied.

[0074] An example of the cold rolling step is a cold rolling step in which a pickled sheet is rolled using a four-stand tandem mill under conditions of a total rolling reduction of 80% or more and less than 95% to form a cold-rolled sheet of a predetermined size and shape.

[0075] <Annealing step> The annealing step is a step of annealing the cold-rolled sheet that has been subjected to the cold-rolling step to obtain a cold-rolled annealed sheet. The annealing step is not particularly limited as long as it is a step of heating, holding, and cooling the cold-rolled sheet to obtain a cold-rolled annealed sheet, and any known annealing step can be applied. Note that, usually, an insulating coating is applied to the surface after the annealing step, but the method and type of coating are not particularly limited, and any known insulating coating step can be applied.

[0076] An example of the annealing step is to heat the cold-rolled sheet to a temperature of 800° C. or higher and 1200° C. or lower in a non-oxidizing atmosphere, hold the temperature for 5 to 60 seconds, and then cool the sheet.

[0077] Although the above description has been given of the case where the hot-rolled annealed steel sheet of the present invention is applied to the production of a non-oriented electrical steel sheet, the hot-rolled annealed steel sheet of the present invention can also be applied to the production of a grain-oriented electrical steel sheet.

[0078] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0079] <Production of Hot-Rolled Annealed Sheet> Molten steel having the chemical composition shown in Tables 1 and 2 was produced by a commonly known method and continuously cast into a 230 mm thick slab (steel material). The obtained slab was hot-rolled to obtain a 2.0 mm thick hot-rolled sheet (1200 mm wide). The obtained hot-rolled sheet was subjected to hot-rolled annealing and pickling under the conditions shown in Tables 3 and 4 to obtain a hot-rolled annealed sheet (pickled sheet). Heat suppression zones were provided near both widthwise edges, and similar control was performed.

[0080] <Production of Cold-Rolled Sheet> The hot-rolled annealed sheet (pickled sheet) was subjected to cold rolling at room temperature using a reverse rolling mill to obtain a cold-rolled sheet (non-oriented electrical steel sheet) having a sheet thickness of 0.25 mm.

[0081] <Production of Cold-Rolled Annealed Sheet> The cold-rolled sheet was annealed by a known method in which it was held at 1000°C for 10 seconds in a non-oxidizing atmosphere, and then an insulating coating was applied by a known method to obtain a cold-rolled annealed sheet (non-oriented electrical steel sheet).

[0082]

[0083]

[0084]

[0085]

[0086] <Evaluation> (Structural Observation) A test piece for structural observation was taken from the center of the sheet width from the obtained hot-rolled annealed sheet. In addition, test pieces for structural observation were taken continuously at 20 mm intervals near one of the sheet width edges, from a position 10 mm from the sheet width edge to a position 410 mm from the sheet width edge. Next, the taken test piece was embedded in resin with the surface perpendicular to the rolling direction (RD surface) as the observation surface, and was polished to a mirror finish by colloidal silica polishing. Electron backscatter diffraction (EBSD) measurement was performed on the mirror-finished observation surface to obtain local orientation data. At this time, the step size was 2 μm and the measurement area was 10 mm. 2 The above was the case. Measurements can be performed in a single scan of the entire area, or the results of multiple scans can be combined using the Combo Scan function. The obtained local orientation data was analyzed using analysis software: OIM Analysis 8. Prior to data analysis, coordinate rotation was performed so that the sample coordinate system had the A1 axis / / rolling direction, the A2 axis / / perpendicular to the rolling direction, and the A3 axis / / sheet surface direction. Furthermore, in the Partition Properties of the analysis software, grain average data points were selected using the formula: GCI[&;5.000,2,0.000,0,0,8.0,1,1,1.0,0;]>0.1, and data points unsuitable for analysis were excluded. At this time, more than 98% of the data points were valid.

[0087] The following analysis was performed on the data adjusted as described above, with the grain boundary definitions set to Grain Tolerance Angle = 5°, Minimum Grain Size = 2, Minimum Anti-Grain Size = 2, and Multiple Rows Requirement and Anti-Grain Multiple Rows Requirement both set to OFF. The Area Average value calculated using the Grain Size (diameter) function on the preprocessed data was used as the average grain size. If the average grain size at a position X1 mm from the sheet width edge is D1 μm and the average grain size at the adjacent measurement point X1 + 20 mm from the sheet width edge is D2 μm, the average grain gradient at a position X1 + 10 mm from the edge is defined as (D2 - D1) / 10 [μm / mm], and the maximum value in the sheet width direction was used as the maximum average grain gradient.

[0088] (Evaluation of Rollability) The number of edge cracks per 1000 m of the obtained cold-rolled sheet was investigated. Edge cracks with a crack length of 2 mm or more were counted as the number N. When the number of edge cracks per 1000 m was 2 or less, the cold-rollability was considered to be good.

[0089] (Evaluation of magnetic properties) A ​​test piece for magnetic measurement having a width of 30 mm and a length of 280 mm, with the length direction being the rolling direction and the direction perpendicular to the rolling direction, was taken from the obtained cold-rolled annealed sheet, and the magnetic flux density B of the cold-rolled annealed sheet was measured by the Epstein method in accordance with JIS C2550-1:2011. 50 and iron loss W 10 / 400 was measured. 50 ≧1.50(T) and B50 / Bs≧0.81, the magnetic flux density is evaluated as good, and W 10 / 400 When the value was ≦15.0 (W / kg), the iron loss characteristics were evaluated as good.

[0090]

[0091]

[0092] From the results of Tables 5 and 6, it can be seen that all of the hot-rolled annealed sheets according to the present invention have excellent cold rolling properties, and further, the cold-rolled annealed sheets obtained by cold-rolling and annealing the hot-rolled annealed sheets according to the present invention also have excellent magnetic properties.

[0093] According to the present invention, a hot-rolled annealed sheet for electrical steel sheet, which has excellent cold rolling properties (fracture resistance and edge crack resistance) in subsequent processes, is provided, along with an advantageous manufacturing method thereof. An electrical steel sheet manufactured using the hot-rolled annealed sheet of the present invention sufficiently avoids deterioration in magnetic properties. In particular, by using the hot-rolled annealed sheet of the present invention in the manufacture of a non-oriented electrical steel sheet, a non-oriented electrical steel sheet with high magnetic flux density and low iron loss at high frequency can be provided, and by using this non-oriented electrical steel sheet, high efficiency of motors can be achieved. As such, the present invention is highly useful industrially.

Claims

1. A steel sheet having a chemical composition containing, by mass%, C: 0.010% or less, Si: 1.0% to 5.0%, Mn: 0.05% to 5.0%, P: 0.1% or less, S: 0.01% or less, Al: 3.0% or less, and N: 0.0080% or less, with the balance consisting of Fe and unavoidable impurities, and at least one of the widthwise edges, the average grain size d at the widthwise center C The average grain size d at the position 10 mm from the edge of the sheet width E Ratio to d C / d E Hot-rolled and annealed electrical steel sheet with a modulus of 1.2 or more.

2. The above-mentioned chemical composition further includes, in mass%, Zn: 0.0005% or more and 0.020% or less, Mo: 0.002% or more and 0.20% or less, Ni: 0.01% or more and 1.0% or less, Cr: 0.01% or more and 5.0% or less, Cu: 0.005% or more and 1.0% or less, Ca: 0.0001% or more and 0.10% or less, Mg: 0.0001% or more and 0.10% or less, REM: 0.0001% or more and 0.10% or less, Sn: 0.001% or more and 0.20% or less, Sb: 0.001% or more and 0.20% or less, B: 0.0020% or less, Ti: 0.010% or less, Nb: 0.0050% or less, V: 0.0050% or less, Pb: 0.0050% or less, 2. The hot-rolled annealed sheet for electrical steel sheet according to claim 1, comprising one or more selected from the group consisting of Zr: 0.0050% or less, Ta: 0.0020% or less, W: 0.0050% or less, Se: 0.0050% or less, Bi: 0.0050% or less, As: 0.020% or less, Co: 0.10% or less, Ge: 0.030% and Ga: 0.030% or less.

3. The average grain size d at the center of the sheet width C is 70 μm or more and 300 μm or less, and the average grain size d E The hot-rolled annealed sheet for electrical steel sheet according to claim 1 or 2, wherein the grain size is 10 μm or more and 200 μm or less.

4. A hot-rolled and annealed sheet for electrical steel according to any one of claims 1 to 3, wherein the maximum value of the average grain size gradient in the sheet width direction is 0.2 μm / mm or more and 1.5 μm / mm or less.

5. A hot-rolled annealed sheet for electrical steel according to any one of claims 1 to 4, wherein the position at which the gradient of the average grain size in the sheet width direction is maximum is within 200 mm from the sheet width edge.

6. The average grain size d at the center of the strip width at both strip width edges C The average grain size d at the position 10 mm from the edge of the sheet width E Ratio to d C / d E The hot-rolled annealed sheet for electrical steel sheet according to any one of claims 1 to 5, wherein the value satisfies 1.2 or more.

7. A method for producing a hot-rolled annealed sheet for use as an electromagnetic steel sheet according to any one of claims 1 to 6, comprising a hot rolling step of hot-rolling a steel material having the composition according to claim 1 or 2 to obtain a hot-rolled sheet, and a hot-rolled sheet annealing step of annealing the hot-rolled sheet, wherein in the hot-rolled sheet annealing step, when the widthwise center of the hot-rolled sheet is held at a holding temperature T1, the maximum temperature T2 reached at a position 10 mm from the widthwise edge of at least one of the widthwise edges of the hot-rolled sheet satisfies T1-T2 ≧ 20°C.

8. A method for manufacturing a hot-rolled annealed sheet for electrical steel sheet according to claim 7, wherein in the hot-rolled sheet annealing step, the holding temperature T1 at the center of the width of the hot-rolled sheet is 900°C or higher and 1150°C or lower, and the holding time t1 at T1 is 1 second or higher and 120 seconds or lower.

9. The method for producing a hot-rolled annealed sheet for electrical steel according to claim 7 or 8, wherein the maximum temperature T2 reached in the hot-rolled sheet annealing step is 750°C or higher and 1000°C or lower.

10. A method for manufacturing a hot-rolled annealed sheet for electrical steel sheet according to any one of claims 7 to 9, wherein, in the hot-rolled sheet annealing step, the time t2 during which the temperature at a position 10 mm from the edge of the hot-rolled sheet width is equal to or higher than the maximum temperature T2-50°C is 5 seconds or more and 50 seconds or less.

11. A method for manufacturing a hot-rolled annealed sheet for electrical steel sheet according to any one of claims 7 to 10, wherein in the hot-rolled sheet annealing step, the heating suppression region is between the sheet width edge and a position X1 mm from the sheet width edge, and X1 is 20 mm or more and 250 mm or less.

12. A method for producing a hot-rolled annealed sheet for electrical steel according to any one of claims 7 to 11, wherein the maximum temperature T2 reached at a position 10 mm from the widthwise edge of the hot-rolled sheet satisfies T1-T2 ≧ 20°C at both widthwise edges of the hot-rolled sheet.

13. A method for producing a non-oriented electrical steel sheet, comprising: a cold rolling step of cold rolling the hot-rolled annealed sheet for electrical steel sheet according to any one of claims 1 to 6 to produce a cold-rolled sheet; and an annealing step of annealing the cold-rolled sheet.

Images