JP2021080496A - Method for producing non-oriented magnetic steel sheet - Google Patents

Abstract

To provide a method for producing non-oriented magnetic steel sheet in which an excellent magnetic property can be obtained for the whole circumference average (omnidirectional average).SOLUTION: The method includes: a step of performing a hot rolling on a steel material that has a chemical composition capable of causing α-γ transformation and containing, in mass%, C: 0.010% or less, Si: 1.50% to 4.00%, sol.Al: 0.0001% to 1.0%, S: 0.010% or less, N: 0.010% or less, and one or more selected from the group consisting of Mn, Ni, Co, Pt, Pb, Cu, Au: 2.50% to 5.00% in total and the balance consisting of Fe and impurities, to produce a hot-rolled steel sheet; a step of performing a cold rolling on the hot rolled steel sheet; and a step of performing an annealing after the cold rolling, and in which, the final pass of finish rolling during the hot rolling is performed at a temperature of Ar1 or more, and the cold rolling is performed at a rolling reduction of 93 to 97%.SELECTED DRAWING: None

Description

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

The non-oriented electrical steel sheet is used for the iron core of a motor, for example, and for the non-oriented electrical steel sheet, the average in all directions parallel to the plate surface (hereinafter, "overall circumference average in the plate surface (omnidirectional average)). ”), Which requires excellent magnetic properties, such as low iron loss and high magnetic flux density. Although various techniques have been proposed so far, it is difficult to obtain sufficient magnetic characteristics in all directions in the plate surface. For example, even if sufficient magnetic characteristics can be obtained in a specific direction within the plate surface, sufficient magnetic characteristics may not be obtained in other directions.

Japanese Patent No. 4029430 Japanese Patent No. 6319465

In view of the above-mentioned problems, it is an object of the present invention to provide a method for manufacturing a non-oriented electrical steel sheet capable of obtaining excellent magnetic characteristics with an all-around average (omnidirectional average).

The present inventors have made diligent studies to solve the above problems. As a result, in the production of non-oriented electrical steel sheets capable of obtaining excellent magnetic properties in all directions, the chemical composition of α-γ transformation system is premised, and austenite is transformed into ferrite during hot rolling. It usually develops by refining the structure, making the rolling reduction higher than before in cold rolling, and controlling the temperature within a predetermined range by subsequent annealing to generate overhang recrystallization (hereinafter referred to as bulging). It became clear that it is important to facilitate the development of difficult {100} crystal grains. It was also found that by setting the rolling reduction ratio of cold rolling high, it is possible to facilitate the development of {100} crystal grains without performing skin pass rolling after annealing, and it is possible to omit a part of the manufacturing process.

As a result of further diligent studies based on such findings, the present inventors have come up with various aspects of the invention shown below.

(1)
By mass%
C: 0.010% or less,
Si: 1.50% to 4.00%,
sol. Al: 0.0001% to 1.0%,
S: 0.010% or less,
N: 0.010% or less,
One or more selected from the group consisting of Mn, Ni, Co, Pt, Pb, Cu, Au: 2.50% to 5.00% in total,
Sn: 0.000% to 0.400%,
Sb: 0.000% to 0.400%,
P: 0.000% to 0.400%, and one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd: 0.0000% in total Contains 0.0100%,
Mn content (mass%) is [Mn], Ni content (mass%) is [Ni], Co content (mass%) is [Co], Pt content (mass%) is [Pt], Pb content The amount (mass%) is [Pb], the Cu content (mass%) is [Cu], the Au content (mass%) is [Au], the Si content (mass%) is [Si], sol. The Al content (% by mass) was changed to [sol. When [Al] is set, the following equation (1) is satisfied.
A process of hot-rolling a steel material having a chemical composition in which the balance is composed of Fe and impurities to obtain a hot-rolled steel sheet.
The process of cold rolling the hot-rolled steel sheet and
It has a step of annealing after the cold rolling.
A method for producing a non-oriented electrical steel sheet, characterized in that the final pass of finish rolling during hot rolling is performed at a temperature of Ar1 or higher, and the cold rolling is performed at a rolling reduction of 93% to 97%.
([Mn] + [Ni] + [Co] + [Pt] + [Pb] + [Cu] + [Au])-([Si] + [sol.Al])> 0% ... (1)

(2)
The steel material is by mass%
Sn: 0.020% to 0.400%,
Sb: 0.020% to 0.400%, and
P: The method for producing a non-oriented electrical steel sheet according to (1) above, which contains one or more selected from the group consisting of 0.020% to 0.400%.

(3)
The steel material is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd in mass%: 0.0005% to 0.0100% in total. The method for producing a non-directional electromagnetic steel sheet according to the above (1) or (2), which comprises containing the non-directional electromagnetic steel sheet.

(4)
The method for producing a non-oriented electrical steel sheet according to any one of (1) to (3) above, wherein the annealing is performed at a temperature lower than Ac1.

According to the present invention, it is possible to provide a method for manufacturing a non-oriented electrical steel sheet capable of obtaining excellent magnetic characteristics in all circumference characteristics.

Hereinafter, embodiments of the present invention will be described in detail.

First, the chemical composition of the non-oriented electrical steel sheet according to the embodiment of the present invention and the steel material used in the manufacturing method thereof will be described. In the following description, "%", which is a unit of the content of each element contained in non-oriented electrical steel sheets or steel materials, means "mass%" unless otherwise specified. The non-oriented electrical steel sheet and steel material according to the present embodiment have a chemical composition capable of causing a ferrite-austenite transformation (hereinafter, α-γ transformation), and have a C: 0.010% or less and Si: 1.50% to. 4.00%, sol. Al: 0.0001% to 1.0%, S: 0.010% or less, N: 0.010% or less, Mn, Ni, Co, Pt, Pb, Cu, Au One or more selected from the group : Total 2.50% to 5.00%, Sn: 0.000% to 0.400%, Sb: 0.000% to 0.400%, P: 0.000% to 0.400%, and One or more selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd: Containing a total of 0.0000% to 0.0100%, the balance being Fe and impurities. It has a chemical composition consisting of. Furthermore, Mn, Ni, Co, Pt, Pb, Cu, Au, Si and sol. The Al content satisfies a predetermined condition described later. Examples of impurities include those contained in raw materials such as ore and scrap, and those contained in the manufacturing process.

(C: 0.010% or less)
C increases iron loss and causes magnetic aging. Therefore, the lower the C content, the better. Such a phenomenon is remarkable when the C content exceeds 0.010%. Therefore, the C content is set to 0.010% or less. The reduction of the C content also contributes to the uniform improvement of the magnetic properties in all directions in the plate surface. Although the lower limit of the C content is not particularly limited, it is preferably 0.0005% or more in consideration of the cost of decarburization treatment at the time of refining.

(Si: 1.50% to 4.00%)
Si increases the electrical resistance, reduces the eddy current loss, reduces the iron loss, increases the yield ratio, and improves the punching workability to the iron core. If the Si content is less than 1.50%, these effects cannot be sufficiently obtained. Therefore, the Si content is 1.50% or more. On the other hand, when the Si content exceeds 4.00%, the magnetic flux density decreases, the punching workability decreases due to an excessive increase in hardness, and cold rolling becomes difficult. Therefore, the Si content is set to 4.00% or less.

(Sol.Al: 0.0001% to 1.0%)
sol. Al increases electrical resistance, reduces eddy current loss, and reduces iron loss. sol. Al also contributes to the improvement of the relative magnitude of the magnetic flux density B50 with respect to the saturation magnetic flux density. Here, the magnetic flux density B50 is the magnetic flux density in a magnetic field of 5000 A / m. sol. If the Al content is less than 0.0001%, these effects cannot be sufficiently obtained. Al also has a desulfurization promoting effect in steelmaking. Therefore, sol. The Al content is 0.0001% or more. On the other hand, sol. When the Al content exceeds 1.0%, the magnetic flux density is lowered, the yield ratio is lowered, and the punching workability is lowered. Therefore, sol. The Al content is 1.0% or less.

(S: 0.010% or less)
S is not an essential element and is contained as an impurity in steel, for example. S inhibits recrystallization and grain growth during annealing due to the precipitation of fine MnS. Therefore, the lower the S content, the better. The increase in iron loss and the decrease in magnetic flux density due to the inhibition of recrystallization and grain growth are remarkable when the S content exceeds 0.010%. Therefore, the S content is set to 0.010% or less. Although the lower limit of the S content is not particularly limited, it is preferably 0.0003% or more in consideration of the cost of desulfurization treatment at the time of refining.

(N: 0.010% or less)
Since N deteriorates the magnetic properties as in C, the lower the N content, the better. Therefore, the N content is 0.010% or less. Although the lower limit of the N content is not particularly limited, it is preferably 0.0010% or more in consideration of the cost of denitrification treatment at the time of refining.

(One or more selected from the group consisting of Mn, Ni, Co, Pt, Pb, Cu, Au: 2.50% to 5.00% in total)
Since these elements are elements necessary for causing α-γ transformation, it is necessary to contain at least one of these elements in a total of 2.50% or more. On the other hand, if the total exceeds 5.00%, the cost becomes high and the magnetic flux density may decrease. Therefore, at least one of these elements should be 5.00% or less in total.

Further, it is assumed that the following conditions are further satisfied as the conditions under which the α-γ transformation can occur. That is, the Mn content (mass%) is [Mn], the Ni content (mass%) is [Ni], the Co content (mass%) is [Co], and the Pt content (mass%) is [Pt]. Pb content (mass%) is [Pb], Cu content (mass%) is [Cu], Au content (mass%) is [Au], Si content (mass%) is [Si], sol. The Al content (% by mass) was changed to [sol. When it is set to [Al], it is assumed that the following equation (1) is satisfied in terms of mass%.
([Mn] + [Ni] + [Co] + [Pt] + [Pb] + [Cu] + [Au])-([Si] + [sol.Al])> 0% ... (1)

If the above equation (1) is not satisfied, the α-γ transformation does not occur, so that the magnetic flux density becomes low.

(Sn: 0.000% to 0.400%, Sb: 0.000% to 0.400%, P: 0.000% to 0.400%)
Sn and Sb improve the texture after cold rolling and recrystallization, and improve the magnetic flux density thereof. Therefore, these elements may be contained if necessary, but if they are contained in an excessive amount, the steel is embrittled. Therefore, both the Sn content and the Sb content are set to 0.400% or less. Further, P may be contained in order to secure the hardness of the steel sheet after recrystallization, but if it is excessively contained, it causes embrittlement of the steel. Therefore, the P content is set to 0.400% or less. In the case of imparting further effects such as magnetic properties as described above, 0.020% to 0.400% Sn, 0.020% to 0.400% Sb, and 0.020% to 0.400%. It preferably contains at least one selected from the group consisting of% P.

(One or more selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd: 0.0000% to 0.0100% in total)
Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd react with S in the molten steel to form sulfides, acid sulfides or both precipitates during casting of the molten steel. Hereinafter, Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd may be collectively referred to as "coarse precipitate-forming element". The particle size of the precipitate of the coarse precipitate-forming element is about 1 μm to 2 μm, which is much larger than the particle size of fine precipitates such as MnS, TiN, and AlN (about 100 nm). Therefore, these fine precipitates adhere to the precipitates of coarse precipitate-forming elements, and it becomes difficult to inhibit recrystallization and growth of crystal grains during annealing. In order to sufficiently obtain these effects, the total amount of these elements is preferably 0.0005% or more. However, if the total amount of these elements exceeds 0.0100%, the total amount of sulfide, acid sulfide, or both of them becomes excessive, and recrystallization and grain growth during annealing are inhibited. Therefore, the total content of the coarse precipitate-forming element is 0.0100% or less.

Next, the texture of the non-oriented electrical steel sheets according to the present embodiment will be described. The details of the manufacturing method will be described later, but the non-oriented electrical steel sheet according to the present embodiment has a chemical composition capable of causing α-γ transformation, and the rolling reduction in cold rolling is set to 93 to 97%, which is higher than usual. By refining the structure, {100} crystal grains become a grown structure. As a result, the non-oriented electrical steel sheet according to the present embodiment has, for example, an integrated strength of 5 or more in the {100} <011> direction, and a magnetic flux density B50 in the 45 ° direction with respect to the rolling direction is particularly high. In this way, the magnetic flux density increases in a specific direction, but an overall high magnetic flux density can be obtained on average in all directions. When the integrated strength in the {100} <011> orientation is less than 5, the integrated strength in the {111} <112> orientation, which reduces the magnetic flux density, increases, and the magnetic flux density decreases as a whole.

The accumulation intensity of the {100} <011> orientation can be measured by an X-ray diffraction method or an electron backscatter diffraction (EBSD) method. Since the reflection angles of X-rays and electron beams from the sample differ depending on the crystal orientation, the crystal orientation intensity can be obtained from the reflection intensity or the like with reference to the random orientation sample.

Next, the magnetic characteristics of the non-oriented electrical steel sheet according to the present embodiment will be described. When investigating the magnetic characteristics, the magnetic flux density is measured after the non-oriented electrical steel sheet according to the present embodiment is further annealed at 800 ° C. for 2 hours. This non-oriented electrical steel sheet has the best magnetic properties in two directions in which the smaller angle of the rolling direction is 45 °. On the other hand, the magnetic characteristics are the worst in the two directions in which the angles formed with the rolling direction are 0 ° and 90 °. Here, the 45 ° is a theoretical value, and it may not be easy to match it with 45 ° in actual manufacturing. Therefore, theoretically, if the directions in which the magnetic characteristics are the best are the two directions in which the smaller angle of the rolling direction is 45 °, the actual non-oriented electrical steel sheet is said to be 45. ° shall include those that do not (exactly) match 45 °. This is the same at 0 ° and 90 °. Further, theoretically, the magnetic characteristics in the two directions having the best magnetic characteristics are the same, but in actual manufacturing, it may not be easy to make the magnetic characteristics in the two directions the same. Therefore, theoretically, if the magnetic properties in the two directions having the best magnetic properties are the same, the same includes those that are not (strictly) the same. This is also the case in the two directions with the worst magnetic properties. It should be noted that the above angles are expressed assuming that the angles in both the clockwise and counterclockwise directions have positive values. When the clockwise direction is a negative direction and the counterclockwise direction is a positive direction, the two directions in which the smaller angle of the above-mentioned rolling directions is 45 ° are the above-mentioned rolling directions. Of the angles to be formed, the angle with the smaller absolute value is 45 ° and −45 ° in two directions. Further, the two directions in which the smaller angle formed with the rolling direction is 45 ° can be described as two directions in which the angles formed with the rolling direction are 45 ° and 135 °. When the magnetic flux density is measured in the present embodiment, the magnetic flux density B50 in the 45 ° direction with respect to the rolling direction is 1.8 T or more. Although the magnetic flux density in the 45 ° direction with respect to the rolling direction is high, a high magnetic flux density can be obtained even in the all-around average (omnidirectional average).

The magnetic flux density can be measured by cutting out a 55 mm square sample from 45 °, 0 °, etc. with respect to the rolling direction and using a single plate magnetic measuring device.

Next, a method for manufacturing the non-oriented electrical steel sheet according to the present embodiment will be described. In this embodiment, hot rolling, cold rolling, and annealing are performed.

First, the above-mentioned steel material is heated and hot-rolled. The steel material is, for example, a slab manufactured by ordinary continuous casting. Rough rolling and finish rolling of hot rolling are performed at a temperature in the γ region (Ar1 or higher). That is, hot rolling is performed so that the finishing temperature of the finish rolling is Ar1 or higher. As a result, the structure is refined by transforming austenite to ferrite by subsequent cooling. When cold rolling is subsequently performed in the finely divided state, overhang recrystallization (hereinafter referred to as bulging) is likely to occur, and {100} crystal grains that are normally difficult to grow can be easily grown.

After that, the hot-rolled sheet is wound without annealing, pickled, and then cold-rolled on the hot-rolled steel sheet. Here, the higher the reduction rate, the easier it is for {100} crystal grains to grow due to subsequent bulging. Therefore, the reduction rate is set to 93% to 97% in cold rolling. Since cold rolling is performed at such a high reduction rate, bulging occurs in the subsequent annealing, and {100} crystal grains are likely to grow. In addition, since cold rolling is performed at a high rolling ratio of 93% to 97%, it is possible to easily increase the number of {100} crystal grains that are difficult to grow without performing skin pass rolling after annealing, and more like skin pass rolling. The cold rolling process can be omitted and the process can be simplified.

However, if the rolling reduction ratio exceeds 97%, it is necessary to excessively increase the thickness of the hot-rolled steel sheet, which makes it difficult to wind the hot-rolled steel sheet. Further, if the rolling reduction is less than 93%, the occurrence of bulging is insufficient in one cold rolling, and then it becomes necessary to add a step such as skin pass rolling. A high rolling reduction of 93% to 97% as in the present embodiment can be realized by using, for example, a reverse rolling mill or by using both a reverse rolling mill and a tandem rolling mill.

When the cold rolling is completed, annealing is subsequently performed. In this embodiment, annealing is performed at a temperature that does not transform into austenite. That is, it is preferable that the annealing temperature is lower than Ac1. By performing annealing in this way, bulging occurs, and {100} crystal grains are likely to grow. The annealing time is preferably 5 to 60 seconds.

As described above, the non-oriented electrical steel sheet according to the present embodiment can be manufactured.

Next, the method for manufacturing the non-oriented electrical steel sheet according to the embodiment of the present invention will be specifically described with reference to examples. The examples shown below are merely examples of the method for manufacturing grain-oriented electrical steel sheets according to the embodiment of the present invention, and the method for manufacturing grain-oriented electrical steel sheets according to the present invention is limited to the following examples. is not it.

(First Example)
By casting molten steel, ingots with the components shown in Table 1 below were produced. Here, the left side of the equation represents the value of the left side of the above equation (1). Then, the produced ingot was heated to 1150 ° C. and hot-rolled, and rolled so that the plate thickness became the value shown in Table 1. Then, after the finish rolling was completed, it was water-cooled and the hot-rolled steel sheet was wound up. The temperature (finishing temperature) at the final pass stage of the finish rolling at this time was 800 ° C., which was higher than that of Ar1. The winding temperature at the time of winding was set to 500 ° C.

Next, the scale was removed from the hot-rolled steel sheet by pickling, and cold rolling was performed at the rolling reduction rates shown in Table 1. Then, it was annealed by heating to 800 ° C., which is lower than Ac1 in a non-oxidizing atmosphere.

Further, in order to investigate the magnetic characteristics, a 55 mm square sample was sampled after the annealing, and strain relief annealing was performed at 800 ° C. for 2 hours to measure the magnetic flux density B50. As the measurement sample, a 55 mm square sample was taken in two directions of 0 ° and 45 ° in the rolling direction. Then, these two types of samples are measured, and the value in the 45 ° direction with respect to the rolling direction is set to the magnetic flux density B50 in the 45 ° direction, and the values are 0 °, 45 °, 90 °, and 135 ° with respect to the rolling direction. The average value was taken as the all-around average of the magnetic flux density B50.

The underline in Table 1 shows the conditions outside the scope of the present invention. No. which is an example of the invention. 101-No. In 112, the magnetic flux density B50 was a good value in both the 45 ° direction and the average all around. On the other hand, No. 113, No. Since 114 had a low rolling reduction in cold rolling, it was less likely to cause bulging and had poor magnetic properties. In addition, No. Although the 115 has good magnetic characteristics, the hot-rolled steel sheet has a thickness of 8 mm, and it is very difficult to wind it up by hot-rolling or to process it in a post-process. In addition, Comparative Example No. Although the thickness of 116 after hot rolling was thin, the steel plate became too thin, so that the steel plate cracked in the middle and the test was interrupted.

(Second Example)
By casting molten steel, ingots with the components shown in Table 2 below were produced. Here, the left side of the equation represents the value of the left side of the above equation (1). Then, the produced ingot was heated to 1150 ° C. and hot-rolled, and rolled so that the plate thickness became 3.0 mm. Then, after the finish rolling was completed, it was water-cooled and the hot-rolled steel sheet was wound up. The temperature (finishing temperature) at the final pass stage of the finish rolling at this time was 800 ° C., which was higher than that of Ar1. The winding temperature at the time of winding was set to 500 ° C.

Next, the scale was removed from the hot-rolled steel sheet by pickling, and cold rolling was performed at a rolling reduction of 95% until the sheet thickness became 0.15 mm. Then, it was annealed by heating to 800 ° C., which is lower than Ac1 in a non-oxidizing atmosphere.

Further, in order to investigate the magnetic characteristics, a 55 mm square sample was sampled after the annealing, and strain annealed at 800 ° C. for 2 hours to measure the magnetic flux density B50 and the iron loss W10 / 400. The magnetic flux density B50 was measured in the same procedure as in the first embodiment. On the other hand, the iron loss W10 / 400 was measured as the energy loss (W / kg) of the whole circumference average generated in the sample when an alternating magnetic field of 400 Hz was applied so that the maximum magnetic flux density was 1.0 T. The measurement results are shown in Table 3.

No. 2001-No. All of 214 were invention examples, and all had good punching accuracy, floating amount, and magnetic characteristics. In particular, No. 202-No. 204 is No. 201, No. No. 205-No. The magnetic flux density B50 is higher than that of 214, and No. No. 205-No. 214 is No. 2001-No. The iron loss W10 / 400 was lower than that of 204.

Claims (4)

By mass%
C: 0.010% or less,
Si: 1.50% to 4.00%,
sol. Al: 0.0001% to 1.0%,
S: 0.010% or less,
N: 0.010% or less,
One or more selected from the group consisting of Mn, Ni, Co, Pt, Pb, Cu, Au: 2.50% to 5.00% in total,
Sn: 0.000% to 0.400%,
Sb: 0.000% to 0.400%,
P: 0.000% to 0.400%, and one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd: 0.0000% in total Contains 0.0100%,
Mn content (mass%) is [Mn], Ni content (mass%) is [Ni], Co content (mass%) is [Co], Pt content (mass%) is [Pt], Pb content The amount (% by mass) is [Pb], the Cu content (% by mass) is [Cu], the Au content (% by mass) is [Au], the Si content (% by mass) is [Si], sol. The Al content (% by mass) was changed to [sol. When [Al] is set, the following equation (1) is satisfied.
A process of hot-rolling a steel material having a chemical composition in which the balance is composed of Fe and impurities to obtain a hot-rolled steel sheet.
The process of cold rolling the hot-rolled steel sheet and
It has a step of annealing after the cold rolling.
A method for producing a non-oriented electrical steel sheet, characterized in that the final pass of finish rolling during hot rolling is performed at a temperature of Ar1 or higher, and the cold rolling is performed at a rolling reduction of 93% to 97%.
([Mn] + [Ni] + [Co] + [Pt] + [Pb] + [Cu] + [Au])-([Si] + [sol.Al])> 0% ... (1) The steel material is by mass%
Sn: 0.020% to 0.400%,
Sb: 0.020% to 0.400%, and
P: The method for producing a non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet is contained at least one selected from the group consisting of 0.020% to 0.400%. The steel material is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd in mass%: 0.0005% to 0.0100% in total. The method for producing a non-directional electromagnetic steel sheet according to claim 1 or 2, wherein the non-directional electromagnetic steel sheet is contained. The method for producing a non-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the annealing is performed at a temperature lower than Ac1.