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EP-4467668-B1 - NON-ORIENTED ELECTRICAL STEEL SHEET AND METHOD OF PRODUCING SAME

EP4467668B1EP 4467668 B1EP4467668 B1EP 4467668B1EP-4467668-B1

Inventors

  • ZAIZEN, YOSHIAKI
  • NISHIYAMA, TAKESHI
  • NAKAGAWA, NOBUKO
  • OKUBO, TOMOYUKI
  • AOYAMA, TOMOHIRO

Dates

Publication Date
20260506
Application Date
20230120

Claims (3)

  1. A non-oriented electrical steel sheet comprising a chemical composition containing, in mass%, C: 0.0050 % or less, Si: 2.0 % to 6.5 %, Mn: 0.05 % to 2.0 %, P: 0.10 % or less, S: 0.0050 % or less, Al: 0.3 % to 3.0 %, N: 0.0050 % or less, Co: 0.0005 % to 0.0050 %, Ti: 0.0030 % or less, Nb: 0.0030 % or less, O: 0.0050 % or less, and, optionally, one or more groups out of the following groups A to F: group A: one or both of Sn: 0.005 % to 0.20 % and Sb: 0.005 % to 0.20 %, group B: at least one selected from the group consisting of Ca, Mg, and REM: 0.0005 % to 0.020 % in total, group C: at least one selected from the group consisting of Cu, Cr, and Ni: 0.03 % to 1.0 % in total, group D: one or both of Ge and Ga: 0.0005 % to 0.01 % in total, group E: Zn: 0.001 % to 0.05 %, and group F: one or both of Mo and W: 0.001 % to 0.05 % in total, with a balance consisting of Fe and inevitable impurities, wherein at at least one surface of the non-oriented electrical steel sheet, an amount of N existing as AlN in a range from the surface to a depth of 1/20 of a sheet thickness is 0.003 mass% or less, wherein the amount of N existing as AlN in a range from the surface to a depth of 1/20 of a sheet thickness is measured by the method set out in the description, and the surface has an oxide layer containing one or both of Al and Si and having a thickness of 10 nm or more and less than 80 nm, wherein the thickness of the oxide layer containing one or both of Al and Si is measured by the method set out in the description.
  2. The non-oriented electrical steel sheet according to claim 1, wherein a Si concentration in the oxide layer is 12 at% or more, wherein the Si concentration in the oxide layer is measured by the method set out in the description.
  3. A method of producing a non-oriented electrical steel sheet, the method comprising: subjecting a steel material to hot rolling to obtain a hot-rolled steel sheet, wherein the steel material has a chemical composition containing, in mass%, C: 0.0050 % or less, Si: 2.0 % to 6.5 %, Mn: 0.05 % to 2.0 %, P: 0.10 % or less, S: 0.0050 % or less, Al: 0.3 % to 3.0 %, N: 0.0050 % or less, Co: 0.0005 % to 0.0050 %, Ti: 0.0030 % or less, Nb: 0.0030 % or less, O: 0.0050 % or less, and, optionally, one or more groups out of the following groups A to F: group A: one or both of Sn: 0.005 % to 0.20 % and Sb: 0.005 % to 0.20 %, group B: at least one selected from the group consisting of Ca, Mg, and REM: 0.0005 % to 0.020 % in total, group C: at least one selected from the group consisting of Cu, Cr, and Ni: 0.03 % to 1.0 % in total, group D: one or both of Ge and Ga: 0.0005 % to 0.01 % in total group E: Zn: 0.001 % to 0.05 %, and group F: one or both of Mo and W: 0.001% to 0.05 % in total, with a balance consisting of Fe and inevitable impurities; subjecting the hot-rolled steel sheet to hot-rolled annealing to obtain a hot-rolled and annealed sheet; subjecting the hot-rolled and annealed sheet to cold rolling once or twice or more with intermediate annealing therebetween to obtain a cold-rolled steel sheet; subjecting the cold-rolled steel sheet to final annealing to produce a non-oriented electrical steel sheet; and subjecting, after the cold rolling and before the final annealing, a surface of the steel sheet to acidizing for 1 second to 60 seconds using an acid containing at least one selected from the group consisting of hydrochloric acid, phosphoric acid, sulfuric acid, and nitric acid at a total concentration of 3 wt% to 30 wt%.

Description

TECHNICAL FIELD The present disclosure relates to a non-oriented electrical steel sheet and a method of producing the same. BACKGROUND In recent years, energy saving is required due to consideration for the environment such as global warming. In the automotive field, hybrid electric vehicles (HEVs) that use both an engine and a motor, electric vehicles (EVs) driven only by an electric motor, fuel cell electric vehicles (FCEVs), etc. are being developed. The motors used in these vehicles are typically driven in a high frequency range which is advantageous for high speed rotation, in order to enhance efficiency. Non-oriented electrical steel sheets are often used as an iron core material for such drive motors of HEVs and EVs. In order to achieve high motor efficiency, non-oriented electrical steel sheets are strongly required to have lower iron loss in the high frequency range. Conventionally, the iron loss of non-oriented electrical steel sheets is reduced mainly by adding alloying elements such as Si and Al to enhance specific resistance or by reducing the sheet thickness to reduce eddy current loss. However, when a large amount of alloying elements are added for iron loss reduction, saturation magnetic flux density decreases. A decrease in magnetic flux density causes an increase in copper loss in the motor, leading to lower motor efficiency. Moreover, in order to reduce the thickness of the non-oriented electrical steel sheet, it is necessary to reduce the thickness of the hot-rolled steel sheet or increase the cold rolling reduction in the production process. This lowers productivity. Accordingly, if a non-oriented electrical steel sheet that has both high magnetic flux density and low iron loss in the high frequency range and also has excellent productivity can be developed, it will greatly contribute to higher efficiency of electric devices. As a method of achieving low iron loss in the high frequency range, for example, JP H11-343544 A (PTL 1) discloses a method in which 1.5 mass% to 20 mass% of Cr is added to enhance the specific resistance of steel and achieve low iron loss in the high frequency range. KR 2021 0080657A (PTL 2) describes a non-oriented electrical steel sheet and method for manufacturing the same. EP 3916113A1 (PTL 3) describes the production of a non-oriented electrical steel sheet. CITATION LIST Patent Literature PTL 1: JP H11-343544 APTL 2: KR 2021 0080657APTL 3: EP 3916113A1 SUMMARY (Technical Problem) However, since Cr is an element that decreases saturation magnetic flux density, the technique disclosed in PTL 1, which requires the addition of a large amount of Cr, cannot achieve both high magnetic flux density and low high-frequency iron loss. It could therefore be helpful to provide a non-oriented electrical steel sheet with reduced iron loss in a high frequency range without addition of a large amount of alloying elements such as Cr, which causes a decrease in magnetic flux density, and without reduction of the sheet thickness, which causes a decrease in productivity. (Solution to Problem) Upon careful examination focusing on the influence of the surface state of a non-oriented electrical steel sheet on its magnetic properties, we discovered that, by limiting the Co content in the steel to a certain range and subjecting the steel sheet after cold rolling and before final annealing to acidizing to limit the nitrogen amount in the surface layer to a certain range, iron loss can be reduced without causing a decrease in magnetic flux density. The present disclosure is based on these discoveries. The present invention is defined by the independent claims. An advantageous embodiment is described in the dependent claim. (Advantageous Effect) It is thus possible to provide a non-oriented electrical steel sheet with reduced iron loss in a high frequency range without causing a decrease in magnetic flux density or productivity. In detail, since low high-frequency iron loss can be achieved by adding a small amount of Co and controlling the nitrogen amount in the surface layer by acidizing, addition of a large amount of alloying elements such as Cr, which causes a decrease in magnetic flux density, is unnecessary. Moreover, excellent magnetic properties can be achieved without reduction of the sheet thickness, which causes a decrease in productivity. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: FIG. 1 is a graph illustrating the correlation between Co content and high-frequency iron loss (W10/400);FIG. 2 is a graph illustrating the correlation between surface layer nitridation amount and high-frequency iron loss (W10/400);FIG. 3 is a graph illustrating the correlation between acid concentration and high-frequency iron loss (W10/400);FIG. 4 is a graph illustrating the correlation between acid concentration and surface layer nitridation amount;FIG. 5 is a graph illustrating the correlation between acidizing time and high-frequency iron loss (W10/400); andFIG. 6 is a grap