JP2019143214A - Non-oriented electromagnetic steel sheet - Google Patents

Abstract

To provide a non-oriented electromagnetic steel sheet low in iron loss and high in fatigue strength at a high temperature (150°C).SOLUTION: There is provided a non-oriented electromagnetic steel sheet containing, by mass%, C:0.003% or less, Si:1.5 to 7.0%, Mn:0.01 to 3.0%, Al:0.020% or less, S:0.010% or less, and N:0.005 to 0.020%, and the balance Fe with inevitable impurities.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-oriented electrical steel sheet.

In recent years, in the fields of electrical machinery, especially rotating machines, medium- and small-sized transformers, electrical components, etc. in which non-oriented electrical steel sheets are used as iron core materials, they are representative of global power and energy savings, CO ₂ reduction, etc. The demand for higher efficiency and miniaturization is becoming more and more important in the global environmental conservation movement. Under such a social environment, naturally, improving the performance of non-oriented electrical steel sheets is an urgent issue.

  As is well known, in a non-oriented electrical steel sheet, many measures have been taken to improve its performance, particularly to reduce iron loss. Iron loss is roughly divided into eddy current loss and hysteresis loss. In order to reduce the eddy current loss, a method of increasing the content of Si, Al, etc. has been taken from the viewpoint of increasing the specific resistance. However, this method has a substantial upper limit because if it is added in a large amount, it easily breaks during cold rolling.

  As one of the methods for reducing the hysteresis loss, means for reducing Al to 0.01% by mass or less (hereinafter referred to as “% by mass” when the component is simply described as “%”) (hereinafter this unit) (Referred to as “Al trace”). Since Al increases the hysteresis loss more than Si, if Si and Al have the same specific resistance, a component with less Al can lower the iron loss.

  On the other hand, in recent years, fatigue strength is also required for non-oriented electrical steel sheets. There are many designs that increase the number of rotations when downsizing, and in particular, the main motor of an automobile repeats starting and stopping when driving in urban areas.Therefore, non-oriented electrical steel sheets used for rotors require materials with high fatigue strength. ing. At this time, the engine room and the motor have heat, and fatigue strength at about 100 ° C. or higher is required. It is known that fatigue strength correlates with tensile strength. Therefore, many methods for increasing fatigue strength are the same as methods for increasing tensile strength.

  As an electrical steel sheet having excellent mechanical properties, for example, Patent Document 1 includes, in addition to 3.5 to 7% Si, one or more of Ti, W, Mo, Ni, Co and Al. A steel sheet containing 20% or less is proposed. In this method, solid solution strengthening is used as a steel strengthening mechanism. However, in the case of solid solution strengthening, the cold-rolled base metal is also strengthened at the same time, so cold rolling is difficult, and in this method, a special process called warm rolling is indispensable. There is room for improvement such as improvement and yield improvement. Further, some of these alloy metals are expensive, and it is necessary to worry about an increase in cost.

  Patent Document 2 proposes a steel sheet containing B and a large amount of Ni in addition to 2.0 to 3.5% Si and 0.1 to 0.6% Mn, and having a crystal grain size of 30 μm or less. Has been. However, the refinement of crystal grains increases the strength, but has a demerit that the iron loss is greatly deteriorated.

  Patent Documents 3 and 4 propose steel sheets containing Nb, Zr, B, Ti, V, or the like in addition to 2.0 to 4.0% Si. These methods utilize precipitation strengthening by precipitates of Nb, Zr, Ti or C in addition to solid solution strengthening by Si. However, strengthening by such precipitates also has a demerit that deteriorates iron loss.

  Patent Document 5 proposes a steel sheet utilizing Cu precipitation. Unlike other precipitates, Cu precipitates can increase strength with almost no deterioration in magnetic properties. However, industrially, so-called aging heat treatment for the purpose of precipitation of Cu is required. Therefore, for example, it involves a change in the heat treatment process by the user, and there are many problems for practical use.

JP 60-238421 A JP-A-1-162748 Japanese Patent Laid-Open No. 2-8346 JP-A-6-330255 JP 2004-84053 A

  Patent Documents 1 and 5 have a problem that productivity and cost are poor, and Patent Documents 2 to 4 have a problem that iron loss is bad. In view of the above problems, an object of the present invention is to provide a non-oriented electrical steel sheet that has little influence on iron loss, does not impair productivity, is less costly, and has high fatigue strength.

  The inventors of the present invention focused on increasing the fatigue strength in the temperature range where the motor for driving the automobile is actually used. A motor for driving an automobile may have a temperature of 100 ° C. or more when in use. In iron, this temperature is the range in which interstitial solid solution elements diffuse through the steel and age harden.

  Therefore, the present inventors have intensively studied whether the above problem can be solved by using solute N having little interaction with iron. As a result, when there is a large amount of N in the aluminum traces and steel sheets, it manufactures electrical steel sheets that have high fatigue strength, low iron loss, good productivity, and little increase in costs at the motor use temperature. Investigated what can be done.

  The present invention has been made based on the above findings, and the gist thereof is as follows.

  (1) By mass%, C: 0.003% or less, Si: 1.5 to 7.0%, Mn: 0.01 to 3.0%, Al: 0.020% or less, S: 0.010 %, N: 0.005 to 0.020%, the balance being Fe and inevitable impurities, a non-oriented electrical steel sheet.

  (2) The non-oriented electrical steel sheet according to (1), wherein the difference between the fatigue strength at 23 ° C. and the fatigue strength at 150 ° C. is 60 MPa or more.

  (3) The non-oriented electrical steel sheet according to (1), wherein the difference between the fatigue strength at 23 ° C. and the fatigue strength at 150 ° C. is 80 MPa or more.

  (4) The non-oriented electrical steel sheet according to any one of (1) to (3), wherein the thickness is 0.10 to 0.70 mm.

  (5) Furthermore, by mass%, Sn: 0 to 0.40%, Cu: 0 to 1.0%, Sb: 0 to 0.40%, and P: 0 to 0.40%, or 1 or 2 The non-oriented electrical steel sheet according to any one of (1) to (4), which contains seeds or more.

  (6) Further, in mass%, one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd are contained in a total amount of 0 to 0.0100%. The non-oriented electrical steel sheet according to any one of claims 1 to 5.

  According to the present invention, a non-oriented electrical steel sheet with low iron loss, high productivity, low cost, and high fatigue strength can be provided.

It is a figure which shows the relationship between the amount of N in Example, and the difference of the fatigue strength of 23 degreeC and 150 degreeC.

  Hereinafter, the present invention will be described in detail.

<Non-oriented electrical steel sheet>
The non-oriented electrical steel sheet of the present invention is in mass%, C: 0.003% or less, Si: 1.5 to 7.0%, Mn: 0.01 to 3.0%, Al: 0.020% Hereinafter, it is characterized by containing S: 0.010% or less and N: 0.005-0.020%, with the balance being Fe and inevitable impurities. The non-oriented electrical steel sheet of the present invention also includes a steel sheet having an aspect that does not contain C and S elements.

  Hereinafter, the reasons for limiting the steel components of the non-oriented electrical steel sheet of the present invention will be described.

(C: 0.003% or less)
C is a harmful component that increases iron loss, and also causes deterioration of magnetic properties. For this reason, C content is made into 0.003% or less. The C content is preferably 0.003% or less. On the other hand, the lower limit of the C content is not particularly limited, and the content may be 0, but is preferably 0.001% or more from the viewpoint of cost in steelmaking.

(Si: 1.5% to 7.0%)
Si is a component that has the effect of reducing iron loss by increasing eddy current loss by increasing electrical resistance, and also by improving the punchability to the iron core by increasing the yield ratio. Also have. In order to achieve these effects, the Si content is 1.5% or more.

  As the Si content increases, the fatigue strength increases, but the magnetic flux density decreases and the hardness increases, resulting in deterioration of punching workability. Also in the manufacturing process of the non-oriented electrical steel sheet itself, The workability such as rolling is reduced and the cost is high. For this reason, Si content shall be 7.0% or less. The Si content is preferably 2.5% or more and 4.5% or less.

(Al: 0.020% or less)
Al is contained in a conventional non-oriented electrical steel sheet in order to increase electrical resistance and reduce eddy current loss (one type of iron loss) in the same manner as Si. However, in the present invention, since the fatigue strength is increased by the solute N, it is necessary to reduce the amount of Al highly reactive with the solute N.

  Since Al is usually used for deoxidation, it remains somewhat in the steel sheet. Even if Al remains in the steel sheet as an oxide, there is no problem. However, when the amount of solute Al is large, it reacts with solute N to produce AlN. AlN not only reduces the solid solution N, but also AlN itself makes the crystal grains finer, so that the iron loss also deteriorates.

  Therefore, the total Al amount is limited to 0.020% or less. The amount of Al may be 0, but if it is attempted to reduce Al too much, the cost of steelmaking will increase, so it may be 0.0001% or more.

(Mn: 0.01-3.0%)
Mn has the effect of increasing the electrical resistance and decreasing the eddy current loss, improving the primary recrystallization texture, and developing the desired {110} <001> crystal orientation for improving the magnetic properties in the rolling direction. . Furthermore, Mn suppresses the precipitation of fine sulfides such as MnS that are harmful to crystal grain growth. In order to achieve these effects, the Mn content is 0.01% or more. On the other hand, when the Mn content increases, the crystal grain growth itself during annealing decreases, and the iron loss increases. For this reason, Mn content shall be 3.0% or less. The Mn content is preferably 0.1% or more and 0.5% or less.

(S: 0.010% or less)
S inhibits recrystallization and grain growth during finish annealing due to fine precipitation of sulfides such as MnS. For this reason, S content shall be 0.010% or less. However, the S content when there is no element for fixing S such as REM is preferably 0.001% or less. On the other hand, the lower limit value of the S content is not particularly limited, and the content may be 0, but is preferably 0.0003% or more from the viewpoint of the cost of removing S and productivity.

(N: 0.005-0.020%)
In conventional non-oriented electrical steel sheets, it has been considered preferable that N is less because it inhibits recrystallization and crystal grain growth during finish annealing due to fine precipitation of nitrides such as AlN. However, if the total Al content is 0.020% or less, the pinning effect of AlN can be reduced. As a result, N can be present in the steel as an interstitial solid solution element, and fatigue strength at high temperatures can be reduced. To rise.

  And the increase amount of the fatigue strength in 100 degreeC or more can be enlarged by making N content 0.005% or more. Therefore, the N content is 0.005% or more. From the viewpoint of securing the allowance for increasing the fatigue strength, it is preferably 0.008% or more, more preferably 0.010% or more, and still more preferably 0.018% or more. On the other hand, when the N content exceeds 0.020%, the material is easily cracked, and productivity is reduced. Therefore, the upper limit is made 0.020%.

(Other elements)
For steel sheets, one or more of Sn: 0 to 0.40%, Cu: 0 to 1.0%, Sb: 0 to 0.40%, P: 0 to 0.40% in mass%. It may contain. These elements are not essential, and the content may be zero.

  Sn, Cu, Sb, and P have an effect of suppressing recrystallization from the grain boundary during annealing and suppressing a texture of {111} <112> crystal orientation, which is undesirable for magnetic properties. In order to achieve these effects, it is preferable that the Sn content, the Sb content, and the P content are 0.02% or more and the Cu content is 0.1% or more.

  On the other hand, even if the content of Sn, Cu, Sb, and P is increased, the above action is saturated and the steel sheet may be embrittled. For this reason, it is preferable that Sn content, Sb content, and P content are 0.40% or less, and Cu content is 1.0% or less.

  Further, the steel sheet contains, in mass%, one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd, and 0 to 0.0100% in total. May be. These elements are not essential, and the content may be zero.

  Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd fix S as sulfide or oxysulfide, avoid fine precipitation of MnS, etc., smooth the domain wall movement, and iron It has the effect of reducing the loss. In order to achieve these effects, the total amount of the above elements is preferably 0.0010% or more.

  On the other hand, when the content of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd is increased, the sulfide or oxysulfide itself becomes excessive and the iron loss is deteriorated. For this reason, the total of the above elements is preferably 0.0100% or less.

(Remainder)
The balance of the steel sheet is Fe and impurities. Here, the impurity refers to a component contained in the raw material or a component mixed in the manufacturing process and not intentionally included in the steel plate.

  Next, the characteristics of the non-oriented electrical steel sheet of the present invention will be described.

  Generally, the fatigue strength of a non-oriented electrical steel sheet increases at a temperature higher than room temperature. This is considered to be an influence of the interstitial solid solution element.

  The non-oriented electrical steel sheet of the present invention has a higher fatigue strength at high temperatures than that of conventional non-oriented electrical steel sheets due to solute N. Note that the fatigue strength at room temperature is comparable to that of a conventional non-oriented electrical steel sheet.

  In the non-oriented electrical steel sheet of the present invention, the difference between the fatigue strength at 23 ° C. and the fatigue strength at 150 ° C. is preferably 60 MPa or more, more preferably 80 MPa or more. The difference in fatigue strength tends to increase as the solute N increases (FIG. 1). Therefore, the difference between the fatigue strength at 23 ° C. and the fatigue strength at 150 ° C. may be set to a desired value by adjusting the amount of solute N based on FIG.

  In the present invention, the fatigue strength is measured at a stress ratio of 0.05 using a 100 kN fatigue tester manufactured by MTS, heating the parallel part of the test piece and its periphery. The fatigue strength is defined as a stress amplitude that is not destroyed after 2 million cycles.

  The temperature is changed so that only the parallel part of the test piece and the periphery thereof become a tubular furnace. In the present invention, the fatigue strength at 23 ° C. and 150 ° C. is measured, and the improvement in characteristics due to temperature change is measured.

  Hereinafter, an example of the manufacturing method of the non-oriented electrical steel sheet of this invention is demonstrated.

-Steelmaking process-
A feature of the present invention is the Al trace. Since Al is a good deoxidizer, the dissolved oxygen in the molten steel becomes high when Al is not added. As a result, when a desulfurizing agent (for example, Ca flux) is added, there is a concern that the desulfurizing agent reacts with oxygen prior to sulfur and a large amount of sulfur remains in the slab after casting. Sulfur remaining in the slab may change to fine MnS in the subsequent hot rolling, and may deteriorate the magnetic properties. Therefore, it is necessary to examine desulfurization strengthening (increase in desulfurization time, etc.) by a known method so that such a situation does not occur.

  Another special process in the present invention is high N. This can be done by adding any nitride into the steel. N can also be increased by exposing the molten steel to the atmosphere, but it is difficult to uniformly add the desired amount. Since excessive addition tends to cause cracks in the subsequent process, the N amount needs to be 0.020% or less.

-Hot rolling process-
In the hot rolling process, it is necessary to process the slab to a plate thickness that is easy to cold-roll by rolling it hot. The conditions in the hot rolling are not particularly limited. For example, the steel strip can be hot-rolled under conditions where the finish rolling completion temperature is 800 to 1100 ° C. and the winding temperature is 400 to 700 ° C.

-Cold rolling process-
In the cold rolling step, the hot-rolled sheet or hot-rolled annealed sheet is cold-rolled to obtain the final sheet thickness (product sheet thickness). In the cold rolling process, rolling becomes difficult if the alloy becomes high. Therefore, rolling may be performed at a plate temperature of 80 ° C. or higher.

  In the cold rolling process, conditions other than the cold rolling reduction ratio are not particularly limited. For example, the temperature can be 100 to 300 ° C., and the number of times of cold rolling and finish annealing can be 2 to 10 times.

  In the cold rolling process, the steel strip may be cold-rolled once, or the steel strip may be cold-rolled a plurality of times. When performing multiple times of cold rolling, it is good to give an intermediate annealing to a steel plate between multiple times of intermediate cold rolling. From the point of making it easy to obtain a non-oriented electrical steel sheet having a target thickness, it is preferable to perform cold rolling a plurality of times through intermediate annealing in the cold rolling step.

  The product plate thickness can be, for example, 0.10 to 0.70 mm.

-Annealing process-
In the annealing step, after cold rolling, the steel strip is annealed under the condition that the entire surface recrystallization is completed and the grains grow. As a result, a non-oriented electrical steel sheet with low iron loss and high magnetic flux density can be manufactured.

  Here, in the annealing step, “annealing” refers to well-known annealing (for example, finish annealing, decarburization annealing to reduce solute C, finish annealing, strain relief annealing, etc.) performed after cold rolling. .

  In the decarburization annealing, if there is a certain amount or more of carbon in the steel sheet, the temperature of the iron core may rise to 150-200 ° C during actual electrical equipment operation. This is done to prevent the problem of deterioration.

The finish annealing is performed for the purpose of reducing the dislocation density in the steel plate as long as it is not recrystallized.
The strain relief annealing is performed for the purpose of removing the distortion of the non-oriented electrical steel sheet.

  In the annealing process, all of the well-known annealing may be performed, or any one or more of the well-known annealing may be performed (for example, only finishing annealing is performed, decarburization annealing, finishing annealing is performed, etc.) Good.

  However, in the annealing step, at least finish annealing is preferably performed from the viewpoint of reducing the dislocation density in the steel sheet and improving the iron loss. In particular, when recrystallization is performed, iron loss is greatly improved. Therefore, it is desirable to perform final annealing at 800 ° C. or higher for recrystallization.

  The non-oriented electrical steel sheet and the manufacturing method thereof according to the present invention can be applied to iron core materials for electrical equipment (particularly iron core materials for rotating machines, small and medium-sized transformers, electrical components, etc.). The non-oriented electrical steel sheet and the manufacturing method thereof according to the present invention can sufficiently meet the urgent demand for high efficiency and miniaturization in the field of electrical equipment, and its industrial value is extremely high.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, these examples do not limit the present invention.

(Example 1)
The ingredients listed in Table 1 were tested using the cast material.

  Casting was performed by pouring molten steel into a 150 mm square mold and lowering to room temperature at a solidification rate of about 0.1 ° C./second. Then, after reheating to 1150 degreeC, it rolled to 2.0 mm and implemented annealing 1000 degreeC x 1 minute after that. However, no. Only the samples 17 and 18 (Si: 6.5%) were reheated before the slab fell to 200 ° C. or lower.

  Next, it was cold-rolled at a cold rolling temperature of 50 ° C. and a cold rolling reduction of 90% to obtain a steel strip having a thickness of 0.35 mm. At this time, no. Only samples 17 and 18 were performed at a cold rolling temperature of 150 ° C. Next, the obtained steel strip was finish-annealed. In the finish annealing, the steel strip was heated at a temperature rising rate of 20 ° C./second, and after reaching 1000 ° C., it was air-cooled after 15 seconds of soaking. Through these steps, a non-oriented electrical steel sheet was obtained.

  The fatigue strength of the obtained non-oriented electrical steel sheet was measured by the method described above, and the difference between the fatigue strength at 23 ° C. and the fatigue strength at 150 ° C. was determined.

  Moreover, the iron loss W10 / 400 of the obtained non-oriented electrical steel sheet was measured. The iron loss W10 / 400 is an energy loss (W / kg) generated in iron when an alternating magnetic field of 1.0 T is applied at 400 Hz. A steel plate was cut into a 55 mm square from the base material (one side is the rolling direction), and the average value in the rolling direction and its 90 ° direction was taken as the measured value.

  No. 1-6 are the conditions which changed N mainly. When N is within the range of the invention, the fatigue strength increase when the temperature is set to 150 ° C. is larger than when N is less than the lower limit of the range of the present invention (No. 2 and 3). If too much was added, it could not be investigated because it cracked during casting.

  No. 8 and 9 are cases where Al is outside the scope of the invention. The fatigue strength increase margin at 150 ° C. was not large compared to the case where N was less than the lower limit of the present invention range (No. 2, 3). It is presumed that this is because Al is bonded to N and precipitates to prevent aging of solid solution N.

  No. FIG. 1 summarizes the results of 1-9. From this, it was found that controlling the amounts of Al and N leads to an increase in fatigue strength at a practical temperature (150 ° C.).

  No. 15 and 16 are cases where C is outside the scope of the invention. The increase in fatigue strength is good, but the iron loss is worse, so it is not suitable for practical use. No. 17 and 18 are when the amount of Si is changed. When exceeding the scope of the invention, cracking occurred by cold rolling.

(Example 2)
The ingredients listed in Table 2 were tested using the cast material.

  Casting was performed by pouring molten steel into a 150 mm square mold and lowering to room temperature at a solidification rate of about 0.1 ° C./second. Then, after reheating to 1150 degreeC, it rolled to 2.0 mm and implemented annealing 1000 degreeC x 1 minute after that.

  Next, it was cold-rolled at a cold rolling temperature of 50 ° C. and a cold rolling reduction of 90% to obtain a steel strip having a thickness of 0.35 mm. Furthermore, the obtained steel strip was finish-annealed. In the finish annealing, the steel strip was heated at a temperature rising rate of 20 ° C./second, and after reaching 1000 ° C., it was air-cooled after 15 seconds of soaking. Through these steps, a non-oriented electrical steel sheet was obtained.

  The fatigue strength of the obtained non-oriented electrical steel sheet was measured by the method described above, and the difference between the fatigue strength at 23 ° C. and the fatigue strength at 150 ° C. was determined.

  Moreover, magnetic flux density B50 of the obtained non-oriented electrical steel sheet was measured. The magnetic flux density B50 is a magnetic flux density (T) generated in iron when an alternating magnetic field of 5000 A / m is applied at 50 Hz. A steel plate was cut into a 55 mm square from the base material (one side is the rolling direction), and the average value in the rolling direction and its 90 ° direction was taken as the measured value.

  No. 2 to 5 are conditions in which an optional additive element (Sn, Cu, Sb, P) is added. No. 1 is an electrical steel sheet containing only essential elements, and the properties are good as it is, but it can be seen that B50 is further improved by adding the above elements.

(Example 3)
The ingredients listed in Table 3 were tested using the cast material.

  Casting was performed by pouring molten steel into a 150 mm square mold and lowering to room temperature at a solidification rate of about 0.1 ° C./second. Then, after reheating to 1150 degreeC, it rolled to 2.0 mm and implemented annealing 1000 degreeC x 1 minute after that.

  Next, it was cold-rolled at a cold rolling temperature of 50 ° C. and a cold rolling reduction of 90% to obtain a steel strip having a thickness of 0.35 mm. Furthermore, the obtained steel strip was finish-annealed. In the finish annealing, the steel strip was heated at a temperature rising rate of 20 ° C./second, and after reaching 1000 ° C., it was air-cooled after 15 seconds of soaking. Through these steps, a non-oriented electrical steel sheet was obtained.

  The fatigue strength of the obtained non-oriented electrical steel sheet was measured by the above-described method, and the difference between the fatigue strength at 23 ° C. and the fatigue strength at 150 ° C. and the iron loss W10 / 400 were determined.

  No. 2-11 are the conditions which added arbitrary addition elements (Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, Cd). No. 1 is an electrical steel sheet containing only essential elements, and the characteristics are good as it is, but it is understood that W10 / 400 can be further reduced by adding the above elements.

Claims (6)

% By mass
C: 0.003% or less,
Si: 1.5 to 7.0%,
Mn: 0.01 to 3.0%,
Al: 0.020% or less,
S: 0.010% or less, and N: 0.005-0.020%
A non-oriented electrical steel sheet characterized in that the balance is Fe and inevitable impurities.   The non-oriented electrical steel sheet according to claim 1, wherein the difference between the fatigue strength at 23 ° C and the fatigue strength at 150 ° C is 60 MPa or more.   The non-oriented electrical steel sheet according to claim 1, wherein the difference between the fatigue strength at 23 ° C and the fatigue strength at 150 ° C is 80 MPa or more.   The non-oriented electrical steel sheet according to any one of claims 1 to 3, wherein a plate thickness is 0.10 to 0.70 mm.   Furthermore, by mass%, Sn: 0 to 0.40%, Cu: 0 to 1.0%, Sb: 0 to 0.40%, and P: 0 to 0.40%. The non-oriented electrical steel sheet according to any one of claims 1 to 4.   Furthermore, it contains 0 to 0.0100% in total of one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd by mass%. The non-oriented electrical steel sheet according to any one of -5.

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