JP4658840B2 - Method for producing non-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a method for producing a non-oriented electrical steel sheet used as an iron core material for electrical equipment. In particular, the present invention relates to a method for producing a non-oriented electrical steel sheet that is optimal as a material for a high-efficiency motor.

  2. Description of the Related Art In recent years, due to an increase in energy saving of electric appliances worldwide, lower iron loss has been demanded for non-oriented electrical steel sheets used as iron core materials for rotating machines.

  As is well known, increasing the Si and Al contents to increase the specific resistance and increasing the crystal grain size are the main methods for reducing the iron loss. In recent years, high-grade steel grades with Si: about 3.0% and Al: about 0.5-1.2% have been used in compressor motors and electric vehicle motors.

  The following proposals have been made as methods for improving the workability at the customer, such as punchability and caulking properties, for such steel sheets containing a large amount of Si and Al. Patent Document 1 is a method in which Al / Si is 0.7 to 1.4 and Vickers hardness is 130 to 210, and Patent Document 2 is a method in which Si ≦ 3 × Al and Vickers hardness does not exceed 200. In both cases, Al has a specific resistance substantially equal to that of Si, but pays attention to the fact that the increase in hardness is smaller than that of Si. That is, by reducing the Si amount and increasing the Al amount as compared with the conventional material, the material hardness is lowered while maintaining a high specific resistance to improve workability.

  By the way, iron loss is separated into eddy current loss and hysteresis loss. Since the eddy current loss is proportional to the square of the plate thickness and inversely proportional to the specific resistance, it is an effective method to increase the specific resistance by the above proposal. On the other hand, hysteresis loss is known to be reduced by coarsening the crystal grain size in non-oriented electrical steel sheets, and it is common to coarsen the crystal grain size to about 100 to 150 μm in high grades. . High-performance motors for air-conditioning compressors and electric vehicles are required to reduce high-frequency iron loss around 400 Hz by inverter control, and high specific resistance and thinning are progressing. However, at present, the hysteresis loss has not been sufficiently improved except for the coarsening of the crystal grain size.

  Furthermore, when Si and Al are added in a large amount, cracks and fractures are likely to occur during the production of steel sheets, and the problem of worsening productivity and yield has become apparent as demand increases.

Japanese Patent Laid-Open No. 2001-59145 JP 2001-73098 A

  The present invention provides a non-oriented electrical steel sheet that achieves both high-frequency iron loss reduction and steel sheet productivity by controlling the content ratio of Si, Al, the amount of impurities, and the ductility of the hot-rolled sheet annealed sheet. It is.

(1) By mass%, C: 0.0005% to 0.0020%, Si: 1.5% to 3.5%, Mn: 0.1% to 1.5%, Al: 0.6% to 3.0%, Ti: 0.0005% to 0.0020% In the following, As: Containing 0.0005% or more and 0.0050% or less, remaining Fe and inevitable impurities, Al / (Si + Al) is 0.3 or more and 0.5 or less, the specific resistance is 55μΩcm or more, and the high-frequency iron after strain relief annealing Non-oriented electrical steel sheet satisfying W10 / 400 ≦ 40t + 2 as steel sheet, hot-rolled, hot-rolled sheet annealing, pickling, cold-rolling, finishing, with loss W10 / 400 (W / kg) as thickness t (mm) A method for producing a non-oriented electrical steel sheet, wherein a transition temperature in an impact test of a hot-rolled sheet annealed plate is 60 ° C. or less in the method of producing in a process comprising annealing.
(2) The method for producing a non-oriented electrical steel sheet according to claim 1, further comprising Sn: 0.0050% to 0.20% by mass%.
(3) Average crystal grain of the cross section of the hot-rolled sheet annealing plate diameter D ([mu] m) and Vickers hardness H is, according to claim 1 or 2, characterized by satisfying the expression D ≦ 4.5 × (225-H ) The manufacturing method of the non-oriented electrical steel sheet described in 1.

  The present invention improves high-frequency iron loss without impairing the productivity of the steel sheet, and there are no problems of cost increase and productivity decrease.

  The inventors of the present invention have made a detailed study on the effect on hysteresis loss as well as the effect of increasing the specific resistance of Si and Al added to steel. As a result, the optimum range in which the hysteresis loss is remarkably reduced was found for the ratio of the Al addition amount to the total addition amount of Si and Al, that is, Al / (Si + Al). In addition, it was found that Ti and As precipitates were precipitated at the grain boundaries during strain relief annealing, affecting the hysteresis loss after strain relief annealing. Further, as described above, the improvement in productivity is to suppress cracking and breakage during the production of the steel sheet. In particular, the hot-rolled sheet subjected to the hot-rolled sheet annealing has grown crystal grains, and the thickness of the steel sheet is 2 Since it is about 3 mm thicker than the product plate, no effective countermeasure has been proposed so far.

  Therefore, the present inventors have conducted detailed research on the characteristics of the hot-rolled sheet annealed sheet, and by specifying the impact characteristics in the hot-rolled sheet annealed sheet and the relationship between the crystal grain size and the hardness, As a result, the present invention was completed.

  The reason for limiting the numerical values of the component composition of the steel sheet defined in the present invention will be described below. In addition, content of a component composition is the mass%.

  C is defined as 0.0020% or less because Ti carbide is generated during stress relief annealing and iron loss after stress relief annealing is deteriorated. The lower limit is set to 0.0005% in consideration of the productivity of degassing treatment.

  Si is an effective element for increasing the electric resistance, but if added excessively, the cold rolling property is remarkably deteriorated, so the upper limit was made 3.5%. From the viewpoint of reducing iron loss, the lower limit was set to 1.5%.

  Mn is an element effective for increasing electrical resistance like Si, but is added in excess of 1.5%, and the lower limit is set to 0.1% from the viewpoint of detoxifying S (MnS).

  Al, like Si, is an element effective for increasing electrical resistance. However, if the added amount exceeds 3.0%, the castability deteriorates. Therefore, considering the productivity, the upper limit was set to 3.0%. From the viewpoint of reducing iron loss, the lower limit was made 0.6%. In this case, the saturation magnetic flux density is significantly reduced and the magnetic properties are deteriorated.

  Al / (Si + Al) is the ratio of the amount of Al added to the total amount of Si and Al added. The range in which the hysteresis loss is minimized is defined as 0.3 or more and 0.5 or less.

  Ti is defined as 0.0020% or less because it generates carbides during strain relief annealing and reduces the cost of iron loss improvement by strain relief annealing. The lower limit was set to 0.0005% in consideration of the productivity of the steelmaking process.

  As is generally an element that does not produce precipitates and is dissolved in the steel sheet, but precipitates together with Ti carbide during strain relief annealing, reducing the cost of iron loss improvement by strain relief annealing. I found out that it was new. The range not affected by this is defined as 0.0050% or less. The lower limit was set to 0.0005% in consideration of the productivity of the steelmaking process.

  Sn is known to improve the texture and to prevent nitriding and oxidation during annealing, and may be positively added for these purposes. In that case, 0.0050% at which the effect was obtained was defined as the lower limit, and 0.20% at which the effect was saturated was defined as the upper limit.

  The specific resistance was specified to be 55 μΩcm or more in order to reduce high-frequency iron loss.

  The high-frequency iron loss (W10 / 400) after strain relief annealing must be a value corresponding to the plate thickness. This is because eddy current loss, which accounts for about half of high-frequency iron loss, is reduced by thinning. Therefore, W10 / 400 ≦ 40t + 2 was specified as iron loss improvement considering the plate thickness.

  Next, the reasons for limiting the manufacturing conditions in the present invention will be described.

  It is the transition temperature in the impact test of hot-rolled sheet annealed plate, but the transition temperature is high in the steel plate with cracks and fractures, the manufacturing itself was a brittle region, and further in the ductile region by adjusting the components and annealing conditions As a result of production, it was found that no cracks or breaks occur. In the manufacturing process of pickling, cold rolling, and finish annealing that may cause cracking and breaking, a steel plate temperature of 70 ° C can be secured, so there is no problem if the transition temperature is lower than this, so the upper limit of the transition temperature is defined as 60 ° C . Of course, the transition temperature is preferably room temperature in order to pass the plate more stably. The transition temperature specified here is a temperature that can be interpolated with a ductile fracture surface ratio of 50% in the transition curve showing the relationship between the test temperature and the ductile fracture surface ratio, as defined in JIS. Alternatively, an average value of absorbed energy at a temperature at which the ductile fracture surface ratio is 0% and 100% may be calculated. The test piece is basically the size specified by JIS, but the width of the test piece is the thickness of the hot-rolled sheet. Accordingly, the size is 55 mm in length in the rolling direction, the height is 10 mm, and the width is about 1.5 to 3.0 mm depending on the thickness of the hot-rolled sheet. Further, in the test, it is preferable to stack a plurality of test pieces and bring them closer to a normal test condition of 10 mm in thickness.

  Regarding the crystal grain size and Vickers hardness of the hot-rolled sheet annealing plate, it was found that ductility can be ensured by reducing the crystal grain size even if the Vickers hardness is high. As a relational expression indicating the threshold value, D ≦ 4.5 × (225−H) was defined.

  Here, the hot-rolled sheet annealed plate is a hot-rolled sheet that has been subjected to hot-rolled sheet annealing, but may be a steel sheet that has been pickled after hot-rolled sheet annealing.

<Example 1>
In a laboratory vacuum melting furnace, by mass%, C: 0.0015%, Si: 2.1-3.0%, Mn: 0.25%, Al: 0.6-2.5%, S: 0.0010%, Ti: 0.0013%, As: 0.0038 Steel pieces containing 0.05% Sn and 0.05% were prepared. These steel slabs were heated at 1100 ° C for 60 minutes, then immediately hot rolled to a thickness of 2.0mm, annealed at 900 ° C for 60 seconds, and then cold-rolled once. The plate thickness was 0.30 mm. The cold-rolled sheet thus obtained was subjected to finish annealing at 1050 ° C. for 30 seconds and then subjected to strain relief annealing at 750 ° C. for 2 hours. As shown in Table 1, in Samples 1, 5, and 6 that satisfy the conditions of the present invention, good high-frequency iron loss was obtained, and productivity problems such as cracking and fracture did not occur. Samples 2 and 3 have poor iron loss because Al / (Si + Al) exceeds 0.5, and sample 7 has a high transition temperature of 70 ° C., which causes cracking due to cold rolling. Sample 8 whose particle size did not meet the requirements was broken by pickling. Further, in Samples 9 and 10, Al / (Si + Al) was less than 0.3 and the iron loss was poor, and in Samples 11 and 12, the transition temperature and grain size were not specified, and fractured by cold rolling.

<Example 2>
In a laboratory vacuum melting furnace, in mass%, C: 0.0010-0.0025%, Si: 2.4%, Mn: 0.25%, Al: 1.8%, S: 0.0015%, Ti: 0.0011-0.0034%, As: 0.0024 Steel pieces containing% were prepared. These steel slabs were heated at 1100 ° C for 60 minutes, then immediately hot rolled to a thickness of 2.0mm, annealed at 900 ° C for 60 seconds, and then cold-rolled once. The plate thickness was 0.35 mm. The cold-rolled sheet thus obtained was subjected to finish annealing at 1025 ° C. for 30 seconds and then subjected to strain relief annealing at 750 ° C. for 2 hours. As shown in Table 2, good high-frequency iron loss was obtained in samples 1, 2, 4, and 5 with C: 0.0020% or less and Ti: 0.0020% or less satisfying the conditions of the present invention.

<Example 3>
In the laboratory vacuum melting furnace, by mass%, C: 0.0016%, Si: 2.2%, Mn: 0.2%, Al: 1.5%, S: 0.0017%, Ti: 0.0018%, As: 0.0024-0.0089% The contained steel pieces were produced. These steel slabs were heated at 1050 ° C for 60 minutes, then immediately hot rolled to a sheet thickness of 2.3 mm, hot rolled at 1000 ° C for 60 seconds, and cold-rolled once. The plate thickness was 0.35 mm. The cold-rolled sheet thus obtained was subjected to finish annealing at 1000 ° C. for 30 seconds and then subjected to strain relief annealing at 750 ° C. for 2 hours. As shown in Table 3, good high-frequency iron loss was obtained in Samples 1 to 3 with As: 0.0050% or less satisfying the conditions of the present invention.

<Example 4>
In a laboratory vacuum melting furnace, by mass%, C: 0.0015%, Si: 2.7%, Mn: 0.5%, Al: 1.4%, S: 0.0014%, Ti: 0.0016%, As: 0.0023% A steel piece was prepared. These steel slabs were heated at 1120 ° C for 60 minutes, then immediately hot rolled to a sheet thickness of 2.3 mm, subjected to hot rolled sheet annealing at 850-1100 ° C for 60 seconds, and then cold-rolled once. The plate thickness was 0.50 mm. The cold-rolled sheet thus obtained was subjected to finish annealing at 1030 ° C. for 40 seconds and then subjected to strain relief annealing at 750 ° C. for 2 hours. As shown in Table 4, in Samples 1 to 4 that satisfy the conditions of the present invention, good high-frequency iron loss was obtained, and productivity problems such as cracking and fracture did not occur. Samples 5 and 6 were fractured by cold rolling because the transition temperature of hot-rolled sheet annealing was as high as 70 ° C or higher.

Claims (3)

In mass%, C: 0.0005% to 0.0020%, Si: 1.5% to 3.5%, Mn: 0.1% to 1.5%, Al: 0.6% to 3.0%, Ti: 0.0005% to 0.0020%, As : Containing 0.0005% or more and 0.0050% or less, consisting of remaining Fe and inevitable impurities, Al / (Si + Al) being 0.3 or more and 0.5 or less, specific resistance being 55μΩcm or more, and high-frequency iron loss after strain relief annealing W10 / Non-oriented electrical steel sheet satisfying W10 / 400 ≦ 40t + 2 as steel sheet, hot-rolled, hot-rolled sheet annealing, pickling, cold-rolling, and finish-annealing, where 400 (W / kg) is the thickness t (mm) formula In the method manufactured in a process, the transition temperature in the impact test of a hot-rolled sheet annealing board is 60 degrees C or less, The manufacturing method of the non-oriented electrical steel sheet characterized by the above-mentioned. 2. The method for producing a non-oriented electrical steel sheet according to claim 1, further comprising Sn: 0.0050% or more and 0.20% or less by mass%. Hot-rolled sheet the mean grain diameter D of the cross section of the annealed sheet ([mu] m) and Vickers hardness H is, according to claim 1 or 2, characterized by satisfying the expression D ≦ 4.5 × (225-H ) A method for producing a non-oriented electrical steel sheet.