JP2005350687A - Manufacturing method of non-oriented electromagnetic steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-oriented electromagnetic steel sheet having a high magnetic flux density and low core loss required as an iron core material of electric equipment and excellent magnetic characteristics not possible heretofore. <P>SOLUTION: The manufacturing method of the non-oriented electromagnetic steel sheet includes hot rolling a slab containing, by mass %, ≤0.4% Si, 2.5 to 4.5% Ni, ≤0.5% Mn, P 0.01 to 0.2%, and the balance Fe and inevitable impurities, then subjecting the slab to pickling and light draft rolling of 3 to 15%, subjecting the worked and hot rolled sheet to hot rolling and annealing for ≥10 seconds and ≤5 minutes at a temperature from 740°C up to Ac 1 point, then subjecting the sheet to intermediate annealing for ≥10 seconds and ≤5 minutes in an α+ γ2 phase region from an α region of ≥700°C after cold rolling and thereafter subjecting the sheet further to skin pass rolling of the draft 3 to 15%. The atmosphere of the hot rolling annealing and intermediate annealing is specified to hydrogen ≥20% and dew point ≤10°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a non-oriented electrical steel sheet, which is used as an iron core material for electrical equipment, has not only low iron loss but also high magnetic flux density and has unprecedented excellent magnetic properties.

  In recent years, in the fields of electrical machinery, especially rotating machines where non-oriented electrical steel sheets are used as iron core materials, and in the fields of medium and small transformers, global power conservation, energy conservation, and global environmental conservation such as CFC regulations Among these trends, the trend toward higher efficiency is spreading rapidly. For this reason, there is an increasing demand for non-oriented electrical steel sheets to improve their characteristics, that is, to achieve high magnetic flux density and low iron loss.

The reduction of iron loss in non-oriented electrical steel sheets is mainly achieved by reducing Joule heat loss due to eddy current loss flowing in each steel sheet forming the iron core during use by increasing the electrical resistivity by adding Si and Al. I came.
On the other hand, as energy loss of the entire device including the rotating machine and the iron core, the contribution of copper loss, which is Joule heat loss caused by current flowing through the coil wound around the iron core, cannot be ignored. In order to reduce this copper loss, it is effective to reduce the current density required to excite the same magnetic field strength, and development of a material that exhibits a higher magnetic flux density with the same excitation current is indispensable. . That is, development of an ultra high magnetic flux density non-oriented electrical steel sheet is essential.

As described above, the realization of low iron loss ultra high magnetic flux density non-oriented electrical steel sheets enables both rotating machines and iron cores to be miniaturized. By reducing the weight, energy loss during operation can be reduced.
Further, in the rotating machine, the torque increases, and a more compact and high-output rotating machine is realized.
Thus, the realization of a low iron loss ultra high magnetic flux density non-oriented electrical steel sheet can not only reduce energy loss during operation of the iron core and rotating machine, but also spread to the entire system including that. Some effects are immeasurable.

  When overviewing the conventional high magnetic flux density non-oriented electrical steel sheet manufacturing method, Patent Document 1 attempts to coarsen the hot rolled crystal structure by setting the hot rolling end temperature to 1000 ° C. or higher, and omit hot rolling sheet annealing. A method for coarsening the crystal structure before cold rolling is disclosed. However, in the actual finishing hot rolling machine, it is difficult to eliminate the temperature distribution in the coil hand direction because the rolling speed at the time of biting and the rolling speed in the steady rolling state are different, and the magnetic characteristics are in the longitudinal direction of the coil. There was a disadvantage of fluctuating.

  In Patent Document 2, C <0.01%, Si: 0.5 to 3.0%, Mn: 0.1 to 1.5%, Al: 0.1 to 1.0%, P: 0.0. Hot-rolled sheet made of steel containing 005 to 0.016% and S <0.005% is pickled, and then cold-rolled at a reduction rate of 5 to 20% under light pressure, and this is 850 to 1000 ° C. A technique is disclosed in which a hot-rolled sheet subjected to light reduction at 0.5 to 10 minutes or 750 to 850 ° C. for 1 to 10 hours is annealed and then annealed after the final cold rolling. In this method, the magnetic flux density is not sufficiently improved as compared with the conventional hot-rolled sheet annealing method, and it has not been able to meet the recent demands of consumers for improving the magnetic properties of non-oriented electrical steel sheets.

Furthermore, as a method for improving the magnetic properties of the non-oriented electrical steel sheet by improving the primary recrystallization texture, Sn addition as in Patent Document 3, Sn and Cu addition as in Patent Document 4, or Patent Document 5 For example, a method for producing a non-oriented electrical steel sheet having excellent magnetic properties by improving the texture by adding Sb has been disclosed. However, even with the addition of these texture control elements, such as Sn, Cu, or Sb, it has not been possible to meet the demand for ultrahigh magnetic flux density low iron loss non-oriented electrical steel sheets of recent customers. .
In addition, the manufacturing process such as the finishing annealing cycle as described in Patent Document 6 has been taken, but all of them have achieved low iron loss, but the magnetic flux density is not so much. There was no effect.

There are the following four techniques for achieving high magnetic flux density by adding Ni.
Patent Document 7 discloses a method for achieving high magnetic flux density and low iron loss by adding elements such as Sn, Sb, and Cu in addition to Ni. However, in actual production, the cooling rate during rapid solidification during casting is controlled, or once it is cooled, it is heated again above the Ac3 transformation point, etc., so that the cooling rate in the two-phase region from the Ar3 point to the Ar1 point is increased. There is a problem in that it needs to be controlled and causes an increase in manufacturing cost.

Patent Document 8 discloses a high magnetic flux density and low anisotropy material by adding Ni. However, in actual production, it is necessary to perform annealing by heating to the Ac3 point or higher. There was a problem that iron loss was likely to deteriorate due to internal oxidation.
Patent Document 9 discloses a high magnetic flux density low anisotropy material and its manufacturing method by adding Ni, but in the actual manufacturing method, hot-rolled sheet annealing or self-annealing is essential, and during these annealing The problem that the internal oxidation of Ni occurs and the iron loss tends to deteriorate was not improved.

Inventors disclosed an ultra-high magnetic flux density non-oriented electrical steel sheet and a method for manufacturing the same in Patent Document 10, but customers were also required to reduce iron loss at the same time, and there were still development issues. .
Japanese Examined Patent Publication No. 62-61644 Japanese Patent Publication No. 8-32927 JP-A-55-158252 JP 62-180014 A Japanese Patent Laid-Open No. 59-100197 JP-A-57-35626 JP-A-6-271996 JP-A-8-246108 JP-A-8-109449 JP 2002-294415 A

  An object of the present invention is to solve such problems in the prior art and to provide a non-oriented electrical steel sheet having an ultrahigh magnetic flux density and a low iron loss.

The gist of the present invention is as follows.
(1) In mass%,
Si: 0.4% or less,
Ni: 2.5-4.5%,
Mn: 0.5% or less,
P: 0.01-0.2%
The slab containing the remaining Fe and unavoidable impurities is hot rolled, then pickled, subjected to light rolling at 3% to 15%, and this processed hot rolled sheet is heated for 10 seconds at a temperature from 740 ° C. to Ac1 point. Hot-rolled sheet annealing is performed for 5 minutes or less, and after cold rolling, intermediate annealing is performed for 10 seconds or more and 5 minutes or less in the α + γ2 phase region from the α region at 700 ° C. or higher, and then the rolling reduction is 3% to 15%. A method for producing a non-oriented electrical steel sheet, characterized by subjecting to skin pass rolling.
(2) The method for producing a non-oriented electrical steel sheet according to (1), wherein an atmosphere of the hot-rolled sheet annealing and intermediate annealing is 20% or more of hydrogen and a dew point is 10 ° C. or less.

  According to the present invention, not only the magnetic flux density is higher than the conventional non-oriented electrical steel sheet, but also an excellent magnetic non-oriented electrical steel sheet with low iron loss can be manufactured, and in the industrial field used as an electric iron core, It brings about extremely good effects such as energy saving and downsizing.

  Inventors performed technology development in view of patent document 10, and examined the technique of giving a skin pass before hot-rolled sheet annealing and after intermediate annealing. As a result, it was found that by performing hot-rolled sheet annealing under appropriate temperature control, the crystal of the product was significantly coarsened, and at the same time a high magnetic flux density was obtained, and the present invention was completed.

First, components will be described below.
Since Si is harmful by reducing the magnetic flux density of the product in the present invention, its content is limited to 0.4% or less.

  If the Ni content is less than 2.5%, the ultra-high magnetic flux density intended by the present invention, that is, the value of B50 cannot achieve 1.80 T or more, and if it exceeds 4.5%, the value of B50 is not achieved. Since there is a tendency to decrease, the Ni content is specified to be 2.5 to 4.5%.

  Since Mn is harmful because it reduces the magnetic flux density of the product in the present invention, its content is limited to 0.5% or less.

  Since Al is harmful because it reduces the magnetic flux density of the product in the present invention, it is at an inevitable impurity level.

  P is an extremely high magnetic flux density with a B50 value of 1.80 T or more in the present invention, a measured value of the magnetic flux density B50L measured only with the L direction sample, and a measured value of the magnetic flux density B50C measured only with the C direction sample. In order to simultaneously achieve the difference, that is, the LC difference of the magnetic flux density B50 is 0.035 T or less, it is added in the range of 0.01 to 0.2%. When the P content is less than 0.01%, the LC difference of the magnetic flux density B50 does not become 0.035T or less, so it is specified to be 0.01% or more. If the P content exceeds 0.2%, the magnetic flux density decreases, so it is specified to be 0.2% or less.

  If the C content exceeds 0.0030%, magnetic aging occurs and the iron loss during use deteriorates.

In the present invention, the reduction of S and N makes it possible to achieve both ultrahigh magnetic flux density and low iron loss.
S and N are partly re-dissolved during slab heating in the hot rolling process, and fine precipitates of MnS and AlN are re-precipitated during hot rolling to suppress grain growth during finish annealing. It causes the loss to worsen. For this reason, it is desirable for both the contents to be 0.0030% or less.

  Ti forms nitrides and sulfides and deteriorates the iron loss of the product. Therefore, the content of Ti and S and N is preferably 0.004% or less.

Next, process conditions will be described.
The steel slab composed of the above components is melted in a converter and manufactured by continuous casting or ingot-bundling rolling. The steel slab is heated by a known method. The slab is hot rolled to a predetermined thickness.

  In the present invention, it is important to perform a light reduction of 3 to 15% on the hot-rolled sheet before the hot-rolled sheet annealing. The pickling is preferably performed before light pressure. If the rolling reduction is less than 3%, the effect is not sufficient, and if it exceeds 15%, recrystallized grains are generated and the iron loss is remarkably reduced.

  Thereafter, the processed hot-rolled sheet is subjected to hot-rolled sheet annealing at a temperature from 740 ° C. to Ac1 point for 10 seconds to 5 minutes. If it is less than 740 ° C., the effect of annealing cannot be obtained, and if it exceeds the Ac 1 point, the magnetic flux density is remarkably lowered. If the annealing time is less than 10 seconds, the effect cannot be obtained, and if it exceeds 5 minutes, the effect is saturated and uneconomical.

The hot-rolled sheet subjected to the hot-rolled sheet annealing is finished to an intermediate sheet thickness by intermediate rolling. Thereafter, intermediate annealing is performed. The intermediate annealing is preferably performed for 10 seconds to 5 minutes in the α region to the α + γ2 phase region. If it is less than 10 seconds, the effect is not sufficient, and if it exceeds 5 minutes, the effect is saturated and uneconomical.
The reason why the annealing temperature range is set from the α range to the α + γ2 phase range is that when the intermediate annealing is performed at a temperature higher than this, the value of the magnetic flux density is remarkably lowered. It is preferable that the temperature in the α range is 700 ° C. or higher. Further, the hydrogen content in the annealing atmosphere is preferably 20% or more. This is to prevent internal oxidation of Ni during high temperature annealing. For the same reason, the dew point must be 10 ° C. or lower.

  Thereafter, further 3% to 15% skin pass rolling is performed. If the skin pass rolling rate is less than 3%, the effect is insufficient. If the skin pass rolling rate is more than 15%, the reverse effect is obtained, and the iron loss is deteriorated.

  The steel sheet according to the present invention is then punched into a core shape and then subjected to magnetic annealing. The temperature of magnetic annealing is preferably 650 ° C. or more and less than Ac 1 ° C., and the time is preferably 3 minutes or more and 5 hours or less. When the temperature is lower than 650 ° C., the effect of magnetic annealing is not sufficient, and when the temperature is higher than Ac 1, the iron loss is greatly deteriorated. The reason for setting the magnetic annealing time to 3 minutes or more is that the effect is insufficient if it is less than 3 minutes, and if it exceeds 5 hours, the effect is saturated and uneconomical.

  The atmosphere of magnetic annealing is preferably performed at a hydrogen atmosphere of 20% or more and a dew point of 10 ° C. or less. This is because if the atmosphere is less than 20% hydrogen or the dew point exceeds 10 ° C., the surface of the product becomes oxidative and the magnetic properties deteriorate.

Next, examples of the present invention will be described.
The slab for non-oriented electrical steel having the components shown in Table 1 was heated by a normal method and finished to 2.7 mm by hot rolling. Subsequently, pickling was performed, 5% skin pass was performed, and annealing was performed in a 100% hydrogen DRY (dew point = −10 ° C.) atmosphere at 750 ° C. for 1 minute. Thereafter, it was finished to a thickness of 0.54 mm by cold rolling and subjected to an intermediate annealing at 750 ° C. for 30 seconds. This was finished to a thickness of 0.50 mm by the final skin pass, cut into Epstein samples, and magnetic (SRA) annealing was performed in an atmosphere of 100% hydrogen (dew point = −10 ° C.) for 2 hours. Table 1 shows the components of the present invention and comparative examples, and Table 2 shows the magnetic measurement results.
Thus, by adding an appropriate amount of Ni and processing appropriate process conditions, it is possible to manufacture a non-oriented electrical steel sheet having a high magnetic flux density B50 and a low iron loss value.

Claims (2)

% By mass
Si: 0.4% or less,
Ni: 2.5-4.5%,
Mn: 0.5% or less,
P: 0.01-0.2%
The slab containing the remaining Fe and unavoidable impurities is hot rolled, then pickled, subjected to light rolling at 3% to 15%, and this processed hot rolled sheet is heated for 10 seconds at a temperature from 740 ° C. to Ac1 point. Hot-rolled sheet annealing is performed for 5 minutes or less, and after cold rolling, intermediate annealing is performed for 10 seconds or more and 5 minutes or less in the α + γ2 phase region from the α region of 700 ° C. or higher, and then the rolling reduction is 3% to 15%. A method for producing a non-oriented electrical steel sheet, characterized by subjecting to skin pass rolling. The method for producing a non-oriented electrical steel sheet according to claim 1, wherein an atmosphere of the hot-rolled sheet annealing and intermediate annealing is 20% or more of hydrogen and a dew point is 10 ° C or less.