JP4559879B2 - Non-oriented electrical steel sheet and manufacturing method thereof - Google Patents

Description

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

  In recent years, high efficiency of electrical equipment has been strongly demanded from the viewpoint of global environmental conservation and from the viewpoint of global power and energy saving. For this reason, improvement in magnetic properties is also required for non-oriented electrical steel sheets used as iron cores for motor iron cores or small transformers.

  As a measure for improving the characteristics of such non-oriented electrical steel sheets, there is a general method of increasing the specific resistance by increasing the content of Si or Al, or reducing the eddy current loss by reducing the sheet thickness. It is. Furthermore, Mn is often added because Si and Al are made more difficult to manufacture because the steel sheet becomes brittle and rolling becomes difficult as the addition amount increases.

It is also known that the steel sheet surface layer is an important factor for reducing iron loss. Examples of methods for improving the magnetic properties by controlling the surface layer of the steel sheet include Patent Document 1, Patent Document 2, and Patent Document 3. Patent Document 1 discloses a technique in which the magnetic properties are improved by setting the internal oxide layer of the steel sheet surface layer portion to less than 1 μm, and Patent Document 2 performs cold rolling after removing the internal oxide layer, A technique for preventing the generation of an internal oxide layer by disposing the heat treatment at a predetermined water vapor partial pressure / hydrogen partial pressure is disclosed.
Patent Document 3 discloses a technique for suppressing the internal oxide layer and preventing nitridation by specifying the annealing atmosphere after cold rolling. The annealing atmosphere is not only magnetic deterioration due to the internal oxide layer, but also nitriding. It also has an effect on deterioration caused by

On the other hand, techniques that actively utilize an oxide layer generated on the surface layer are also being studied, for example, Patent Document 4 and Patent Document 5. In Patent Document 4, continuous annealing after cold rolling is performed by controlling the plate temperature of a steel sheet to 900 ° C. or lower when passing through a furnace atmosphere with a reducing atmosphere and a dew point of −15 ° C. to + 5 ° C. Techniques for suppressing wrinkles are disclosed.
In Patent Document 5, an annealing film after cold rolling is set to H ₂ : 7 to 36% and dew point of −20 ° C. to + 10 ° C., thereby forming an oxide film of 3.0 to 6.5 μm on the steel plate surface. Technology is disclosed. The above-mentioned publication discloses a technique for preventing surface squeezing without forming an internal oxide layer that deteriorates magnetic properties by controlling the furnace atmosphere, or generating a surface oxide layer without forming an internal oxide layer. ing.

Further, Patent Document 6 is characterized in that the thickness of the Al oxide layer on the steel sheet surface defined by the GDS analysis method is 1.0 μm or less by setting the hydrogen water vapor partial pressure in the finish annealing atmosphere to 0.02 or less. A non-oriented electrical steel sheet is disclosed. However, the analysis method by GDS only reveals the elements present and is not information on whether or not it is in an oxidized state, that is, the chemical state of Al. There is a need for an analytical method that can provide information on the chemical state of the product.
Therefore, the present inventors focused on and examined photoelectron spectroscopy (ESCA) as an analytical method for obtaining chemical information.
Japanese Patent Publication No. 48-19048 Japanese Patent Publication No. 48-19766 Japanese Patent Publication No.58-30368 JP-A-3-36214 Japanese Patent No. 2701314 Japanese Patent Laid-Open No. 2001-140018

  Such a technique for controlling the oxide layer on the surface is important in the case where a relatively large amount of an element that oxidizes more than Fe, such as Si and Al, is added. In order to shorten it, it tends to raise the annealing temperature, which is a very important factor. That is, conventionally, in the final finish annealing of a non-oriented electrical steel sheet, it was heated for a long time at a relatively low temperature. However, in recent years, continuous annealing at a high temperature for a short time has been required to improve productivity.

The technique disclosed in Patent Document 3 discloses a technique for setting the annealing atmosphere to H ₂ ≧ 45% (N ₂ ≦ 55%) in order to prevent the formation of an internal oxide layer and suppress the formation of nitride. Yes. However, when the Mn content is increased in order to improve the iron loss, an internal oxide layer is easily generated even under such conditions, and the magnetic characteristics may be deteriorated. In addition, if the H ₂ concentration is high, the cost is high. In particular, in the case of a floating furnace, the H ₂ gas is a light gas with a low specific gravity, so the force to lift the steel sheet is weakened. In addition, there is a problem that the manufacturing cost is further increased.

  In the non-oriented electrical steel sheet containing a relatively large amount of elements such as Si, Al, and Mn, the present inventors are formed on the extreme surface layer by controlling the steam hydrogen partial pressure and the dew point in the temperature raising region of finish annealing. Non-oriented electrical steel sheet with a specific composition of the surface oxide layer that can prevent the formation and nitridation of the internal oxide layer at low cost, and has no problem in plateability even in the case of a floating furnace. The electrical conductive steel sheet and its manufacturing method were discovered.

The gist of the present invention is as follows.
(1) By mass%, Si: 1% or more, Al: 0.2% or more, Mn: 0.2% or more, the balance is a steel plate made of Fe and inevitable impurity elements, and ESCA (photoelectron spectroscopy) on the surface A non-oriented electrical steel sheet characterized by holding an oxide layer mainly composed of SiO ₂ and MnO having a thickness of ₂ to 20 nm as measured by an analytical method.
(2) In mass%, Si: 1% or more, Al: 0.2% or more, Mn: 0.2% or more, and the balance is annealed after the final cold rolling of a steel plate made of Fe and inevitable impurity elements In this case, the hydrogen concentration is set to 20% or less, the steam hydrogen partial pressure ratio in the furnace atmosphere up to 650 ° C. is set to 0.35 or more and 0.5 or less, and the steam hydrogen hydrogen partial pressure ratio is set at a predetermined annealing soaking temperature of 650 ° C. or more. A method for producing a non-oriented electrical steel sheet, characterized by annealing at 0.1 to 0.3.

  According to the present invention, in the final annealing of a non-oriented electrical steel sheet containing a specific additive element, an extremely dense oxide layer is formed on the outermost surface of the steel sheet by controlling a specific temperature range to a specific partial pressure ratio. Thus, a non-oriented electrical steel sheet having good characteristics can be obtained.

Hereinafter, specific modes for carrying out the present invention will be described.
First, the non-oriented electrical steel sheet that can be used in the present invention is limited to those containing, by mass, Si: 1% or more, Al: 0.2% or more, and Mn: 0.2% or more.
In the present invention, a surface oxide layer having a specific composition is formed on the extreme surface of the steel sheet by controlling the atmosphere in the heating stage, and the formation of an internal oxide layer and nitrogen absorption are prevented by the action of this oxide layer. Therefore, it is necessary that a specific alloy element such as Si, Al, or Mn that forms a surface oxide layer is contained in the steel component in a specific amount or more.

  If the amount of Si is less than 1%, a sufficient amount of the surface oxide layer cannot be formed. If the amounts of Al and Mn are less than 0.2%, the surface oxide layer cannot form the composition of the present invention, and the effects of the present invention are obtained. It is because it is not possible. Particularly desirable are Si: 2.0% or more, Al: 0.3% or more, and Mn: 0.4% or more.

  The upper limit of each component is Si: 5.0% or less, preferably 3.5% or less, because Si is brittle, resulting in a decrease in productivity. It is 0% or less, desirably 1.5% or less, more desirably 0.8% or less, and Mn also decreases the magnetic flux density, so Mn: 2.0% or less, desirably 1.0% or less.

  Regarding the hydrogen concentration, in the case of a floating furnace, the levitation force of the steel sheet decreases and the cost also increases, so that the hydrogen concentration is 20% or less, preferably 10 to 15% or less.

Next, in the present invention, the steam hydrogen partial pressure ratio in the atmosphere up to 650 ° C. is limited to a range of 0.35 to 0.5. This is because if the amount is less than 0.35 , a sufficient amount of the outer oxide layer cannot be formed, and the effect of the present invention cannot be obtained.

  Next, at 650 ° C. or higher, the steam hydrogen partial pressure ratio is limited to 0.1 to 0.3. The reason is that at 650 ° C. or higher, an internal oxide layer may be formed even if the partial pressure ratio exceeds 0.3, and the magnetism may be deteriorated. Below 0.1, the external oxide layer of the present invention is reduced and the present invention is reduced. This is because the above effect cannot be obtained. More desirably, it is in the range of 0.2 to 0.3. If it is less than 0.2, the effect of suppressing nitridation of the oxide layer formed on the surface layer is somewhat inferior.

  The reason for setting different annealing atmospheres with 650 ° C. as a boundary condition is that, in the case of heating for continuously annealing a non-oriented electrical steel sheet, the temperature is usually set to a predetermined temperature in a short time such as several seconds to several tens of seconds. To reach. In such a case, since the oxidation reaction is difficult to proceed due to the low temperature at the beginning of the temperature rise, only the outermost surface of the steel sheet is likely to be oxidized, whereas when the temperature becomes higher, the inner surface is relatively closer to the inner side. There is a possibility of oxidation. As a result of studies by the present inventors, it has been empirically found that the influence of these two mechanisms is switched around 650 ° C.

  In order to prevent the formation of an internal oxide layer or to prevent nitrogen absorption, it is necessary to form a dense oxide layer with an external oxidation type oxide layer on the steel plate surface. The external oxidation type is an oxide layer formed on the surface of the steel sheet, and is generally an oxide layer generated in a so-called dry atmosphere with a low dew point. In continuous annealing performed in a hydrogen-nitrogen mixed atmosphere, , A very thin layer of several nm to several tens of nm. Since such an external oxidation type oxide layer is formed on the outermost layer of the surface layer, it can be detected by an infrared spectrometer or photoelectron spectroscopy (ESCA).

  FIG. 1 is an ESCA depth chart of a non-oriented electrical steel sheet according to an embodiment of the present invention, and FIG. 2 is an ESCA depth chart of a comparative example. The ESCA depth chart records information in the depth direction from the outermost layer by repeatedly measuring the surface of the steel plate by ESCA and then repeating the ESCA measurement after sputtering the extreme surface layer of the steel plate.

The details of FIG. 1 are as follows: Si: 3.0%, Al: 0.4%, Mn: 0.5%, others using hot-rolled sheet containing iron and inevitable impurities as a test material. This is an example in which a sample obtained by cold rolling, heating at 1000 ° C. for 30 seconds, and performing a steam hydrogen partial pressure ratio up to 650 ° C. at 0.35 and 650 ° C. or more at 0.2 is measured by photoelectron spectroscopy (ESCA).
The horizontal axis of the chart is the binding energy (eV), which changes depending on the chemical state of the element, so that the state of the element (for example, the oxidation state or the metal state) can be detected, and the vertical axis indicates the relative intensity.
A plurality of chart lines can be seen, indicating the sputtering time from above and analyzing from the sample surface toward the inside. The uppermost layer is the outermost layer, the second is 18Å in terms of Si, the third is 53Å, the fourth is 123Å, the fifth is 193Å, the sixth is 368３６, and the thickness of the oxide layer is about 19 nm.

  FIG. 2 is a comparative example in which the same sample was subjected to a steam hydrogen partial pressure ratio of 0.40 up to 650 ° C. and 650 ° C. or higher at the same partial pressure ratio of 0.08, and displayed on the same scale as the chart of FIG. It is.

Comparing FIG. 1 and FIG. 2, it can be seen that the peak of Mn is larger in FIG. 1 than in FIG. 2, and the ratio of Mn and Si is different. Further, in FIG. 1, a plurality of oxidation states are detected from the O peak, and it is estimated that a plurality of oxides are present, whereas in FIG. 2, only one main peak is detected, and the Si peak is detected. In addition, in FIG. 2, it is presumed that SiO ₂ is the main oxide in FIG. The thickness of the oxide layer is about 12 nm.

In the case of the present invention shown in FIG. 1, the elements Si and Mn are detected, and it is presumed that a composite oxide of SiO ₂ and MnO ₂ is formed. In the comparative example, Si, Al, and Mn are detected. However, it is estimated that the oxide layer is mainly composed of SiO ₂ , and it can be seen that the generated oxide layers are completely different.

  The present inventors have various forms depending on the constituent elements and the ratio of the oxide to be generated even if it is such a thin oxide layer. It has been found that it is possible to suppress this.

The oxide layer mainly composed of SiO ₂ and MnO ₂ in the present invention, is formed from a other oxides SiO ₂ and MnO _2, when subjected to ESCA measurement, mainly SiO ₂ and MnO ₂ in which both are detected, but not limited to, the presence ratio of SiO ₂ and MnO ₂ which is converted from the peak intensity ratio of 3: 7 to 8: 2 by weight is preferred. If it is less than 3: 7, the effect of suppressing nitrogen absorption is small, and if it exceeds 8: 2, the oxide layer tends to be thick.

  The reason why the thickness of the oxide layer itself is limited to 2 nm to 20 nm is that if it is less than 2 nm, the effect of suppressing nitrogen absorption is still small, and if it exceeds 20 nm, magnetic deterioration due to the internal oxide layer may occur. Preferably it is the range of 8 nm to 20 nm.

The expression mechanism of the present invention has not been clarified in detail. However, since the remarkable effect is exhibited by the oxide layer having a thickness of only a few dozen nm, it is presumed that the structure of the oxide layer has a great influence.
For particular produced in oxidation of the steel sheet easily SiO _2, MnO _2, Al ₂ O _3, but ternary phase diagram is known, many SiO ₂ -Al ₂ O ₃ less MnO ₂ according to which region In, mullite is likely to be generated, and corundum is likely to be generated in a region with a small amount of SiO _{2 and a} large amount of MnO ₂ —Al ₂ O ₃ . On the other hand, it is known that various crystal forms including tridymite and spesatite exist in a region where Al ₂ O ₃ is small and SiO ₂ —MnO ₂ is large.

  In such regions, oxides of various crystal forms fill the gaps between them, so that an outer oxide layer that densely covers the steel sheet surface layer is formed to reduce the permeability of oxygen and nitrogen, increase the inner oxide layer, It is presumed that nitrogen absorption will be prevented, and there are still many unclear points, but within the scope of the present invention, oxides such as cristobalite, tridymite, spessite, mullite, or a mixed form thereof are formed. It is estimated that

1. About steel consisting of Si: 3.0%, Al: 0.1-1.0%, Mn: 0.05-0.8%, C: 0.0011%, and others including Fe and inevitable impurities. A 0 mm hot-rolled sheet was produced. The hot-rolled sheet was annealed at 1000 ° C. for 30 seconds and then cold-rolled to 0.35 mm. Furthermore, as final annealing, it heated at 1050 degreeC for 30 second, the final finishing annealing was performed on the conditions of Table 1, respectively, and the magnetic characteristic was evaluated by LC average value by SST method. The oxide layer thickness in the table was measured from the peak of oxygen and silicon by photoelectron spectroscopy.
As shown in Table 1, the effect of the present invention was clarified.

It is an ESCA depth chart of the non-oriented electrical steel sheet in the Example of this invention. It is an ESCA depth chart of the non-oriented electrical steel sheet in a comparative example.

Claims (2)

In mass%, Si: 1% or more, Al: 0.2% or more, Mn: 0.2% or more, the balance is a steel plate made of Fe and unavoidable impurity elements, ESCA (photoelectron spectroscopy) on the surface A non-oriented electrical steel sheet, characterized by holding an oxide layer mainly composed of SiO2 and MnO having a thickness of ₂ to 20 nm as measured by. In mass%, Si: 1% or more, Al: 0.2% or more, Mn: 0.2% or more, the balance is the final cold-rolled steel sheet made of Fe and inevitable impurity elements, when annealing, The hydrogen concentration is 20% or less, the steam hydrogen partial pressure ratio in the furnace atmosphere up to 650 ° C. is 0.35 or more and 0.5 or less, and the steam hydrogen hydrogen partial pressure ratio is 0.1 at a predetermined annealing soaking temperature of 650 ° C. or more. The manufacturing method of the non-oriented electrical steel sheet characterized by annealing at 0.3.

Images