JP2005330527A - Non-oriented electrical steel sheet with excellent magnetic property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-oriented electrical steel sheet having excellent magnetic properties by suppressing nitridation which occurs in a steel sheet containing >0.0010% S and satisfying Sas[MnS+Cu<SB>2</SB>S]≤0.0010%. <P>SOLUTION: The non-oriented electrical steel sheet has a composition consisting of, by mass, ≤3.5% Si, ≤1.5% Mn, 0.1 to 3.0% Al, ≤0.0050% C, ≤0.0030% (more desirably ≤0.0010%) Ti, ≤0.0050% N, 0.0011 to 0.0030% S, ≥0.0005% Ca+Mg, 0.01 to 0.2% Sn and the balance Fe with inevitable impurities and satisfying Sas[MnS+Cu<SB>2</SB>S]≤0.0010% by mass. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a non-oriented electrical steel sheet used as an iron core material for electrical equipment and a method for producing the same, and particularly to a non-oriented electrical steel sheet having excellent magnetic properties.

  In recent years, due to the increase in energy saving of electric appliances worldwide, non-oriented electrical steel sheets used as iron core materials for rotating machines have been required to have higher performance characteristics. In particular, there is a strong need to reduce the iron loss that leads to the loss of the rotating machine, and the reduction of iron loss has been realized by increasing the specific resistance by increasing the Si and Al contents and increasing the crystal grain size. Furthermore, increasing the purity of steel not only promotes crystal grain growth, but also reduces the influence of precipitates formed by impurities in the steel, so that the purity of steel has been increased in recent years. For example, in Patent Document 1, S, N: 0.0020% or less, Ti, V, As: 0.0020% or less, Nb: 0.0030% or less promotes crystal grain growth and reduces low iron. A method for achieving loss is disclosed. Further, in Patent Document 2, S: 0.0010% or less promotes crystal grain growth, and Sb + 1 / 2Sn: 0.001 to 0.05% is contained, thereby providing S: 0.0010% or less. A method of reducing iron loss by suppressing nitriding of a steel plate is disclosed. For the purpose of promoting crystal grain growth and reducing iron loss in strain relief annealing, Patent Document 3 discloses a method of adding a Ca alloy, and Patent Document 4 discloses a method of adding Mg. The purpose is to make S inevitably present therein a coarse and thermally stable sulfide with Ca or Mg.

Japanese Patent Laid-Open No. 8-283835 JP-A-10-317111 JP 10-183309 A JP 2002-302746 A

  It is clear that the deterioration of iron loss due to nitriding of steel sheets occurs not only when S described in Patent Document 2 is 0.0010% or less, but also when S exceeds 0.0010%. became. The present invention has been made in view of such problems, and intends to provide a non-oriented electrical steel sheet with low iron loss.

In order to solve the above problems, the present invention has the following (1) to (4).
(1) By mass%, Si: 3.5% or less, Mn: 1.5% or less, Al: 0.1% or more and 3.0% or less, C: 0.0050% or less, Ti: 0.0030% In the following, N: 0.0050% or less, S: 0.0011% or more and 0.0030% or less, Sn: 0.01% or more and 0.2% or less, the balance consisting of Fe and unavoidable impurities, SasMnS (MnS Of S) and SasCu ₂ S (S forming Cu ₂ S) (hereinafter referred to as Sas [MnS + Cu ₂ S]) is 0.0010% or less by mass%. A non-oriented electrical steel sheet.
(2) The non-oriented electrical steel sheet according to (1), further containing 0.01% or more and 0.4% or less in total by mass% of at least one of Cu and Ni.
(3) The non-oriented electrical steel sheet according to (1) or (2), further containing 0.0005% or more in total by mass% of at least one of Ca and Mg.
(4) The non-oriented electrical steel sheet according to any one of (1) to (3), characterized in that Ti is 0.0010% or less in terms of mass%.

  ADVANTAGE OF THE INVENTION According to this invention, the nitriding problem actualized in the steel plate which made the sulfide harmless and improved the grain growth can be solved, and an electromagnetic steel plate with a lower iron loss can be provided.

The present invention is described in detail below. As a result of investigating the nitriding of the steel sheet surface, which deteriorates the magnetic properties, the present inventors have found that the S is not nitrided during the finish annealing or the strain relief annealing even if the S content is not as low as 0.0010% or less. It has been found that the characteristics may be deteriorated. As a result of investigating the cause, it was found that the amount of S producing MnS or Cu ₂ S is extremely small in the steel sheet whose magnetic properties deteriorate due to nitriding, and during annealing by adding Sn as a countermeasure. It was found that the nitriding of the steel can be suppressed and the magnetic properties can be improved. Furthermore, it was found that the texture was improved by adding Ni and Cu in combination, and that both low iron loss and high magnetic flux density were compatible, and the present invention was completed. Hereinafter, the experimental results that led to the present invention will be described.

(Experiment 1)
Steels of Si: 2.1%, Mn: 0.7%, Al: 1.5% were melted by mass%. The impurity components were in the ranges of Ti: 0.0005 to 0.0008%, N: 0.0020 to 0.0024%, and S: 0.0015 to 0.0018%. These slabs were heated for 120 minutes, extracted at 1120 ° C. and hot-rolled to a thickness of 2.0 mm, subjected to hot-rolled sheet annealing at 970 ° C. for 60 seconds, and a thickness of 0. It was 35 mm. The cold-rolled sheet thus obtained was subjected to finish annealing at 900 to 1100 ° C. for 30 seconds in an atmosphere N ₂ 70% -H ₂ 30% (volume ratio), and the iron loss was measured. The results are shown in FIG. 1. As Sample 1 has a higher finish annealing temperature, a lower iron loss can be obtained, whereas for Sample 2 with a different melting chance, the iron loss at a finish annealing temperature of 1000 ° C. It became clear that the iron loss worsened at 1050 ° C. or higher. As described above, the reason why only sample 2 caused the iron loss deterioration under almost the same components and finish annealing conditions was deposited with an electron microscope. In sample 2, MnS, Cu ₂ S and complex sulfides confirmed in sample 1 were confirmed. It was found that almost no matter was observed, while S was detected from MgO, CaO and their composite oxides, and a large number of AlNs that seemed to be nitrides were observed directly under the surface layer. As a verification of this result, the sum of SasMnS and SasCu ₂ S (Sas [MnS + Cu ₂ S]) and N were analyzed. It was found that the N content was extremely high at 1050 ° C. or higher of the finish annealing and nitriding.

(Experiment 2)
Next, as a countermeasure against nitriding in finish annealing, a steel piece to which Sn was added with the same basic components as in Experiment 1 was produced in a laboratory vacuum melting furnace. At this time, a steel slab containing a small amount of Mg and Ca was also produced in order to obtain a steel with a low amount of Sas [MnS + Cu ₂ S] with the same amount of S. These steel pieces were hot-rolled to a plate thickness of 2.0 mm, subjected to hot-rolled plate annealing, and the plate thickness was set to 0.35 mm by one cold rolling. The cold-rolled sheet thus obtained was subjected to finish annealing at 1050 ° C. for 30 seconds in an atmosphere N ₂ 70% -H ₂ 30% (volume ratio), and then the components were analyzed. The results are shown in Table 2. In samples 2 to 4 where Sas [MnS + Cu ₂ S] is 0.0010% or less and Sn is less than 0.01%, nitriding is remarkable (N analysis value is high). On the other hand, it was found that even when Sas [MnS + Cu ₂ S] was 0.0010% or less, Samples 6 to 8 to which 0.03% Sn was added did not nitride (the N analysis value was low).

Thus, nitriding during annealing by the amount of S (Sas [MnS + Cu ₂ S]) forming MnS and Cu ₂ S, which are sulfides in the steel sheet, was first discovered by the present invention, and Ca and Mg It cannot be inferred from Patent Documents 3 and 4 that the sulfite is simply modified by adding N. Further, although the nitriding suppression effect of Sn is shown in Patent Document 2 at an extremely low S amount of S: 0.0010% or less, this is a book that has been found to be nitrided even when S exceeds 0.0010%. There is no analogy about the invention.

Next, the reasons for limiting the numerical values of the components in the product of the present invention will be described.
Si is an effective element for increasing the electric resistance, but if added excessively, the cold rolling property is remarkably deteriorated, so 3.5% was made the upper limit.

  Mn is an element effective for increasing the electrical resistance like Si, but if added over 1.5%, the saturation magnetic flux density is significantly reduced and the magnetic properties are deteriorated, and depending on other components. Therefore, the upper limit of the annealing temperature is restricted and the desired magnetism cannot be obtained, so the upper limit was set to 1.5%.

  Al, like Si, is an effective element for increasing the electrical resistance. While the specific resistance can be increased almost as much as Si with the same addition amount, the increase in hardness is less than that of Si, so that addition of 0.1% or more is essential for high-grade grades. However, if added in a large amount, the castability deteriorates, so 3.0% was made the upper limit.

  Since C is well known to cause magnetic aging, it is defined as 0.0050% or less. However, Ti and precipitates are formed, and the grain growth particularly at the time of strain relief annealing is deteriorated, so 0.0020% or less is desirable.

  Since Ti produces nitrides, carbides, and carbonitrides and remarkably deteriorates the grain growth, it is specified to be 0.0030% or less. In particular, when promoting crystal grain growth during strain relief annealing, 0.0010% or less is preferable.

  N is defined as 0.0050% or less in order to produce Al, Ti and nitride to remarkably deteriorate the grain growth.

  S is an important element in the present invention. Although it is desirable to reduce it as much as possible from the viewpoint of promoting crystal grain growth, 0.0011% is set as the lower limit and the upper limit is set to 0.0030% at which deterioration of crystal grain growth becomes remarkable because the manufacturing cost increases.

  Sn is an essential element of the present invention for suppressing nitriding during annealing. If the content is less than 0.01%, the effect cannot be obtained, so 0.01% was made the lower limit. Moreover, even if it exceeds 0.2%, the effect is saturated and the cost becomes high, so 0.2% was made the upper limit. The Sn containing method is not particularly defined, but an alloy containing Sn may be added, or a scrap containing Sn such as a tin can may be added if low cost is desired.

  When Cu and Ni are combined with Sn, the effect of suppressing nitriding becomes stronger, but for that purpose, it is necessary to add at least 0.01% or more. Furthermore, it is possible to obtain a texture that is favorable for magnetic properties by combining with Sn. However, the effect is saturated when it exceeds 0.4%, so the upper limit was made 0.4%.

If the sum of SasMnS and SasCu ₂ S exceeds 0.0010%, the crystal grain growth and iron loss during finish annealing or strain relief annealing deteriorate, so the upper limit of the sum is set to 0.0010%.

Ca and Mg, since it is possible to generate a stable sulfide at high temperatures than MnS and Cu ₂ S, in the steel containing from 0.0011 to 0.0030% of S, the sum of SasMnS and SasCu ₂ S 0 It is contained for the purpose of making it 0010% or less. However, if Ca + Mg is less than 0.0005%, sulfide is hardly generated, so the lower limit was made 0.0005%. In addition, although it does not prescribe | regulate especially about the containing method of Ca and Mg, you may add as an alloy to the deoxidized molten steel, and you may make it contain by reduction | restoration of slag or a refractory.

In a laboratory vacuum melting furnace, by mass%, C: 0.0024%, Si: 3.1%, Mn: 0.2%, Al: 1.1%, Ti: 0.0008%, S: 0.0020%, N: 0.0017%, Ca: 0.0003%, Mg: 0.0007%, Sn: 0.003-0.187%, Cu: 0.015%, Ni: 0.021% The steel piece containing was produced. These steel pieces were heated at 1075 ° C. for 90 minutes, and then immediately hot-rolled to a sheet thickness of 2.3 mm, subjected to hot-rolled sheet annealing at 1050 ° C. for 60 seconds, The plate was 0.50 mm thick, and was annealed at 1050 ° C. for 20 seconds in an atmosphere N ₂ 70% -H ₂ 30%. Table 3 shows the results of measurement and observation of Sas [MnS + Cu ₂ S], N, iron loss W15 / 50, and magnetic flux density B50 of each sample thus obtained. In any sample, Sas [MnS + Cu ₂ S] is 0.0010% or less, but in samples 1 and 2 with Sn: less than 0.01%, ΔN (N amount after annealing−steel N amount) is high, and nitriding The iron loss was also bad. On the other hand, samples 3 to 6 with Sn: 0.01% or more were not nitrided, and good iron loss was obtained.

In a laboratory vacuum melting furnace, in mass%, C: 0.0011%, Si: 1.5%, Mn: 0.5%, Al: 0.6%, Ti: 0.0013%, S: Steel slabs containing 0.0017%, Sn: 0.055%, Ca: 0.0007% and varying the amounts of Cu and Ni were produced. These steel pieces were heated at 1100 ° C. for 60 minutes, and then immediately hot-rolled to a sheet thickness of 2.7 mm, subjected to hot-rolled sheet annealing at 1000 ° C. for 60 seconds, and cold-rolled once. The plate thickness was 0.50 mm, finish annealing was performed at 850 ° C. for 15 seconds in an atmosphere N ₂ 85% -H ₂ 15%, and further, strain relief annealing was performed at 750 ° C. for 2 hours in an atmosphere N ₂ 100%. Table 4 shows the results of measurement and observation of Sas [MnS + Cu ₂ S], N, iron loss W15 / 50, and magnetic flux density B50 of each sample thus obtained. In all the samples, despite the Sas [MnS + Cu ₂ S] being 0.0010% or less, nitriding after strain relief annealing was suppressed to a low level and good iron loss was obtained, but Cu + Ni was 0.2 %, Samples 3, 5 and 6 had better iron loss and higher magnetic flux density.

The figure which shows the relationship between finish annealing temperature and iron loss.

Claims (4)

In mass%, Si: 3.5% or less, Mn: 1.5% or less, Al: 0.1% or more and 3.0% or less, C: 0.0050% or less, Ti: 0.0030% or less, N : 0.0050% or less, S: 0.0011% or more and 0.0030% or less, Sn: 0.01% or more and 0.2% or less, and the balance consisting of Fe and inevitable impurities, forming SasMnS (MnS S) and SasCu ₂ S (S forming Cu ₂ S) (hereinafter referred to as Sas [MnS + Cu ₂ S]) is 0.0010% or less by mass%. Non-oriented electrical steel sheet.   The non-oriented electrical steel sheet according to claim 1, further comprising 0.01% or more and 0.4% or less in total by mass% of at least one of Cu and Ni.   The non-oriented electrical steel sheet according to claim 1 or 2, further comprising 0.0005% or more in total by mass% of at least one of Ca and Mg.   The non-oriented electrical steel sheet according to any one of claims 1 to 3, wherein Ti is 0.0010% or less in terms of mass%.

Images