JP2011246783A - Electromagnetic steel sheet with inorganic insulating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic steel sheet with an inorganic insulating film preventing deterioration of corrosion resistance and water resistance and improved in punchability without containing a chromium compound and hence without deteriorating environment.SOLUTION: An inorganic film containing a Zr compound of 10-79.9 mass% in ZrOconversion, a B compound of 0.1-5 mass% in BOconversion, and a Si compound of 20-85 mass% in SiOconversion in rate relative to the mass of the total solid content in the inorganic film is formed on a surface of the electromagnetic steel sheet.

Description

  The present invention relates to an electrical steel sheet with an inorganic insulating coating that has no deterioration in corrosion resistance and water resistance even without containing a chromium compound, and that has advantageously improved punchability.

  Insulating coatings on electrical steel sheets used for motors, transformers, and the like are required not only for interlayer resistance but also for various characteristics such as convenience during processing and storage, and stability during use. Since electrical steel sheets are used for various applications, various insulating coatings have been developed according to the applications. When magnetic steel sheets are punched, sheared, bent, etc., the magnetic properties deteriorate due to residual strain, but when strain-removed smelting is performed at a temperature of about 750-850 ° C. to recover the deteriorated magnetic properties There are many. In this case, the insulating coating must be able to withstand strain relief annealing.

Insulation coating of electrical steel sheet is roughly divided
(1) An inorganic coating that emphasizes weldability and heat resistance and resists strain relief annealing,
(2) Resin-containing inorganic coating (also called semi-organic coating) that can withstand strain relief annealing to achieve both punchability and weldability,
(3) It is classified into three types of organic coatings that cannot be used for strain relief and annealing.

Among the three types of insulating coatings described above, as the inorganic coating of the type (1), Patent Document 1 discloses chromate, dichromate, phosphate, condensed phosphate, silicon dioxide (silica) and Among the silicates, an insulating coating composed of a single or a combination of two or more has been proposed.
Such an inorganic insulating coating has some problems in punchability but is excellent in insulation, weldability, and heat resistance, and thus is suitably used for applications requiring particularly resistance to tension pads.

As described above, since the conventional inorganic coating contains a chromium compound, there is a risk that Cr may be eluted during use to harm the environment. For this reason, with the recent increase in environmental awareness, there has been a demand for a product having an insulating coating that does not contain a chromium compound in the field of electrical steel sheets.
However, since the chromium compound in the coating effectively contributes to the corrosion resistance and water resistance of the coating, there is a concern about deterioration of these characteristics when the chromium compound is omitted.

JP 2002-294464 A

  The present invention was developed in view of the above-mentioned present situation, does not contain a chromium compound, and therefore, without deterioration of the environment, prevents deterioration of corrosion resistance and water resistance, and further improves punchability. An object of the present invention is to propose a magnetic steel sheet with an inorganic insulating coating.

Now, in order to achieve the above object, the present invention has conducted a thorough examination on the components of the inorganic coating.
As a result, it has been found that the intended purpose can be advantageously achieved by combining the three components of the Zr compound, the B compound and the Si compound at an appropriate ratio.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. An electrical steel sheet having an inorganic coating containing a Zr compound, a B compound and a Si compound on the surface,
The ratio of the Zr compound to the total solid mass of the inorganic coating is 10 to 79.9% by mass in terms of ZrO ₂ , the ratio of the B compound is 0.1 to 5% by mass in terms of B ₂ O ₃ , and the ratio of the Si compound Is an electrical steel sheet with an inorganic insulating coating, characterized by being 20 to 85% by mass in terms of SiO ₂ .

2. _{2. The} electromagnetic steel sheet with an inorganic insulating coating according to 1, wherein a phosphorus compound is further contained in a proportion of 30% by mass or less in terms of P ₂ O ₅ with respect to the total solid mass of the inorganic coating.

  According to the present invention, it is needless to say that it has excellent properties such as insulation, weldability and heat resistance, and even if it does not contain a chromium compound, there is no deterioration in water resistance and corrosion resistance, and it has excellent punchability. An improved electromagnetic steel sheet with an inorganic insulating coating can be obtained.

Hereinafter, the present invention will be specifically described.
First, in the present invention, the reason why the blending ratio of the Zr compound, B compound and Si compound, which are essential components of the coating, is limited to the above range will be described.
In addition, the mass% of these components is a ratio with respect to the total solid content mass of an insulating film. Here, the total solid content mass is an adhesion amount after drying of the coating formed on the surface of the electromagnetic steel sheet, and can be measured from a weight decrease after removing the coating by alkali peeling.

Zr compound: 10 to 79.9% by mass in terms of ZrO ₂
In the present invention, examples of the Zr compound include zirconium acetate, zirconium propionate, zirconium oxychloride, zirconium nitrate, zirconium zirconium ammonium, zirconium carbonate potassium, zirconium zirconium chloride, zirconium sulfate, zirconium phosphate, sodium zirconium phosphate, six Examples thereof include potassium zirconium fluoride, tetranormal propoxyzirconium, tetranormalbutoxyzirconium, zirconium tetraacetylacetonate, zirconium tributoxyacetylacetonate, and zirconium tributoxy systemate.
Such a Zr compound has a strong binding force with oxygen and can be strongly bonded to an oxide, hydroxide, or the like on the Fe surface. In addition, since the Zr compound has three or more bonds, it is possible to form a tough film without using chromium by forming a network with Zr or other inorganic compounds. However, if the ratio with respect to the total solid content in the dry film is less than 10% by mass in terms of ZrO ₂ , the adhesiveness deteriorates, and the corrosion resistance, powder blowing resistance, scratch resistance, and punching resistance only deteriorate. In addition, the appearance after annealing is deteriorated due to the Si compound. On the other hand, when it exceeds 79.9% by mass, the corrosion resistance and the powder blowing resistance deteriorate, and the scratch resistance on the strain relief annealing plate also deteriorates. Therefore, the Zr compound is limited to the range of 10 to 79.9% by mass in terms of ZrO ₂ .

B compound: 0.1 to 5% by mass in terms of B ₂ O ₃
In the present invention, examples of the B compound include boric acid, orthoboric acid, metaboric acid, tetraboric acid, sodium metaborate, and sodium tetraborate, and these can be used alone or in combination. However, it is not limited to these, for example, the compound which melt | dissolves in water and produces | generates a borate ion may be sufficient, and the borate ion may superpose | polymerize linearly or cyclically.
Such a B compound advantageously contributes to solving the problem when the Zr compound is added alone. That is, when the Zr compound was added alone, the corrosion resistance and powder blowing resistance deteriorated, and the scratch resistance on the strain relief annealed plate tended to deteriorate significantly. The reason for this is considered that the Zr compound alone has a large volume shrinkage when baked, so that coating cracks are likely to occur, and a portion where the substrate is partially exposed is generated.
On the other hand, by blending an appropriate amount of the B compound in the Zr compound, the film cracking that has occurred in the case of Zr alone can be effectively alleviated, and the powder blowing resistance can be remarkably improved.
Here, if the content of the B compound with respect to the total solid content in the dry film is less than 0.1% by mass in terms of B ₂ O ₃ , the addition effect is poor. Since a defect (stick) that remains in the film and melts after the strain relief annealing occurs, the B compound was limited to a range of 0.1 to 5% by mass in terms of B ₂ O ₃ .

Si compound: 20 to 85% by mass in terms of SiO ₂
In the present invention, it is preferable to use colloidal silica, fumed silica, silane coupling agent, alkoxylane, siloxane, etc. as the Si compound from the viewpoint of improving corrosion resistance and adhesion after strain relief annealing, and particularly colloidal silica. Fumed silica is advantageously adapted.
By blending an appropriate amount of these Si compounds, a coated steel sheet having excellent corrosion resistance can be obtained. Here, if the content of the Si compound is less than 20% by mass in terms of SiO _{2 with} respect to the total solid content in the dry film, sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 85% by mass, after strain relief annealing Since the occurrence of spots is remarkable and a uniform appearance cannot be obtained, the Si compound is limited to a range of 20 to 85% by mass in terms of SiO ₂ .

In the present invention, in addition to the three components described above, a phosphorus compound can also be contained.
When this phosphorus compound is contained in a large amount, P elutes during use of the electrical steel sheet, thereby causing problems such as deterioration of corrosion resistance due to deterioration of moisture absorption resistance.
Phosphorus compound: 30% by mass or less in terms of P ₂ O ₅ The phosphorus compound in the present invention contains various phosphoric acids and phosphates. Here, for example, orthophosphoric acid, anhydrous phosphoric acid, linear polyphosphoric acid, and cyclic metaphosphoric acid are preferable as phosphoric acid, and magnesium phosphate, aluminum phosphate, calcium phosphate, zinc phosphate and the like are preferable as the phosphate. It is.
Such phosphorus compounds effectively contribute to the improvement of corrosion resistance and scratch resistance, but if the ratio to the total solid content in the dry film is 30% by mass or less, unreacted substances remain in the film. Therefore, the phosphorus compound is preferably contained in an amount of 30% by mass or less in terms of P ₂ O ₅ . In addition, in order to fully demonstrate the effect of these components, it is preferable to contain 1 mass% or more by the ratio with respect to the total-solid mass in a dry film.

Moreover, Al compound is mentioned as another inorganic compound.
As such an Al compound, an Al compound comprising a hydroxyl group and an organic acid and / or a dehydration reaction product thereof is preferably applied, and examples thereof include alumina sol. In order to apply and bake the steel sheet with a water-based paint, the Al compound is preferably one that can be dissolved in water or dispersed in a colloidal or suspended state. The shape may be any shape such as a feather shape or a spherical shape as long as there is no problem in characteristics.
In addition, it is preferable that the addition amount of this Al compound shall be 10 mass% or less with respect to the total solid content mass of an insulating film from a viewpoint of maintaining sufficient film characteristics.

Further, in the present invention, in addition to the above-described components, inclusion of commonly used additives and other inorganic compounds is not disturbed.
Here, the additive is added in order to further improve the performance and uniformity of the insulating coating, and examples thereof include a surfactant, a rust inhibitor, a lubricant, and an antioxidant. In addition, it is preferable that the compounding quantity of this additive shall be 10 mass% or less with respect to the total solid content mass of an insulating film from a viewpoint of maintaining sufficient film characteristics.

In the present invention, the electromagnetic steel sheet as a material is not particularly limited, and any conventionally known steel sheet is suitable.
That is, so-called soft iron plates (electric iron plates) with high magnetic flux density, general cold steel plates such as SPCC, non-oriented electrical steel plates containing Si or Al to increase specific resistance, and directional electrical steel plates Are advantageously adapted.

Next, a method for forming an insulating film will be described.
In this invention, it does not prescribe | regulate especially about the pre-processing of the electromagnetic steel plate which is a raw material. That is, although it may be untreated, it is advantageous to carry out a degreasing treatment such as alkali or pickling treatment such as hydrochloric acid, sulfuric acid or phosphoric acid.
Then, an insulating film is formed on the surface of the electrical steel sheet by applying and baking a treatment liquid containing a Zr compound, a B compound and an Si compound, further a phosphorus compound, and additives as necessary at a predetermined ratio. Let it form. Various methods such as a roll coater, a flow coater, a spray, and a knife coater that are generally used in industry can be applied as a method for applying the insulating coating treatment liquid. In addition, as for the baking method, a hot air method, an infrared method, an induction heating method, or the like, which is usually performed, can be used. The baking temperature should just be a normal level, and should just be about 150-350 degreeC by ultimate steel plate temperature.

The electrical steel sheet with an insulating coating of the present invention can be subjected to strain relief annealing to remove, for example, strain due to punching. As a preferable strain relief annealing atmosphere, an atmosphere in which iron is not easily oxidized, such as an N ₂ atmosphere and a DX gas atmosphere, is recommended. Here, the dew point is set high, for example, Dp: about 5 to 60 ° C., and the corrosion resistance can be further improved by slightly oxidizing the surface and the cut end face. Moreover, as preferable strain relief annealing temperature, it is 700-900 degreeC, More preferably, it is 700-800 degreeC. The holding time of the strain relief annealing temperature is preferably longer, but more preferably 2 hours or longer.

The adhesion amount of the insulating coating is not particularly limited, but is preferably about 0.05 to 5 g / m ² per side. The adhesion amount, that is, the total solid mass of the insulating coating of the present invention can be measured from the weight reduction after removing the coating by alkali peeling. Moreover, when there is little adhesion amount, it can measure from the calibration curve of a fluorescent X ray and an alkali peeling method. If the adhesion amount is 0.05 g / m ² or more, it is possible to satisfy the insulation with corrosion, whereas if 5 g / m ² or less, not only the adhesion is improved, blistering during baking occurs Without causing a decrease in paintability. More preferably, it is 0.1-3.0 g / m < ² >. The insulating coating is preferably on both sides of the steel plate, but depending on the purpose, only one side may be used. Further, depending on the purpose, only one side may be applied, and the other side may be another insulating film.

Hereinafter, although the effect of the present invention is concretely explained based on an example, the present invention is not limited to these examples.
A Zr compound, a B compound and an Si compound, and further a phosphorus compound and other additives are added to deionized water so that the ratio of the insulating coating after drying to the total solid content is the ratio shown in Table 1. It was. The total solid concentration of each component relative to the amount of deionized water was 50 g / l.
Each of these treatment liquids was rolled onto the surface of a test piece cut into a size of width: 150 mm and length: 300 mm from a magnetic steel sheet “A230 (JIS C 2552 (2000))” having a thickness of 0.5 mm. After applying and baking at a reached steel plate temperature shown in Table 1 with a hot air baking oven, the plate was allowed to cool to room temperature to form insulating coatings on both sides.

Table 2 shows the results of examining the corrosion resistance and powder blowing resistance of the electromagnetic steel sheet with an inorganic insulating coating thus obtained.
Furthermore, after performing strain relief annealing at 750 ° C. for 2 hours in a nitrogen atmosphere, the scratch resistance, sticking property, TIG weldability, punchability, water resistance, and appearance after strain relief annealing were investigated, The obtained results are also shown in Table 2.
The types of Zr compounds are shown in Table 3, the B compounds are shown in Table 4, the types of Si compounds are shown in Table 5, and the types of phosphorus compounds and nitrate compounds are shown in Table 6, respectively.

In addition, the evaluation method of each characteristic is as follows.
<Corrosion resistance>
Each test material on which an insulating coating is formed is held in a constant temperature and humidity chamber at a relative humidity of 98% or more and a temperature of 50 ° C. for 2 days, the rust generation area ratio on the surface of the test piece is obtained, and the corrosion resistance is determined as follows. Evaluation was made according to criteria. In addition, a rust generation | occurrence | production area ratio is a percentage of the sum total of the rust generation | occurrence | production area with respect to the total area observed visually.
(Criteria)
◎: Rust generation area ratio less than 5% ○: Rust generation area ratio 5% or more and less than 20% △: Rust generation area ratio 20% or more and less than 50% ×: Rust generation area ratio 50% or more

<Powder resistance>
Test conditions: Felt contact surface width 20 mm × 10 mm, load: 0.4 MPa (3.8 kg / cm ² ), and simple reciprocation of the coating surface 100 times. The rubbing trace after the test was visually observed to evaluate the peeling state and the powder blowing state of the coating film.
(Criteria)
A: Almost no rubbing traces are observed. ○: Some rubbing traces and slight powder blowing are observed. Δ: The peeling of the coating proceeds and the rubbing traces and powder blowing are clearly seen. Dust is enormous

<Scratch resistance after annealing>
Test conditions: The surface of the test material annealed by holding at 750 ° C. for 2 hours in an N ₂ atmosphere was scratched with a steel plate shear edge, and the degree of scratches and powder blowing was visually determined.
(Criteria)
◎: Scratches and powder blowing are hardly observed. ○: Slight rubbing and slight powder blowing are observed. △: Rub and powder blowing are clearly recognized. Is enormous

<Sticking>
Ten samples of 50 mm square were stacked and annealed under a condition of 750 ° C. for 2 hours under a nitrogen atmosphere while applying a load of 20 kPa (200 g / cm ² ). Next, a weight of 500 g was dropped on the test material (steel plate), and the drop height when dividing into 5 parts was investigated.
(Criteria)
◎: 10 cm or less ○: More than 10 cm, 15 cm or less Δ: More than 15 cm, 30 cm or less ×: More than 30 cm

<TIG weldability>
The specimen was laminated at a pressure of 9.8 MPa (100 kgf / cm ² ) so as to have a thickness of 30 mm, and TIG weldability was performed on the end portion under the following conditions.
・ Welding current: 120A
Ar gas flow rate: 6 liters / min
-Welding speed: 10, 20, 30, 40, 50, 60, 70, 70, 90, 100 cm / min
(Criteria)
The superiority or inferiority was determined by the magnitude of the welding speed at which the number of blow holes satisfied 5 or less per bead.
◎: 60 cm / min or more ○: 40 cm / min or more, less than 60 cm / min Δ: 20 cm / min or more, less than 40 cm / min ×: less than 20 cm / min

<Punchability>
The test material was punched using a 15 mmφ steel die until the burr height reached 50 μm, and the number of punches was evaluated.
(Criteria)
◎: 1 million times or more ○: 500,000 times or more, less than 1 million times △: 100,000 times or more, less than 500,000 times ×: less than 100,000 times

<Water resistance>
The specimen was exposed to boiling water vapor for 30 minutes, and the appearance change was visually observed.
(Criteria)
◎: No change ○: Slightly discolored visually △: Discolored clearly visible ×: Film dissolution

<Appearance after strain relief annealing>
The specimen was visually observed for appearance after being held at 750 ° C. for 2 hours in an N ₂ atmosphere and then cooled to room temperature.
(Criteria)
◎: When the appearance after annealing is completely uniform ○: When the appearance after annealing is uneven △: When there is a spotted pattern on the appearance after annealing ×: A noticeable spotted pattern is found on the appearance after annealing If you can

As shown in Table 2, the electromagnetic steel sheet with an inorganic insulating coating obtained according to the present invention is excellent in corrosion resistance and powder blowing resistance, as well as scratch resistance after strain relief annealing, sticking property, It was excellent in TIG weldability, punchability and water resistance, and also in appearance after strain relief annealing.
On the other hand, Comparative Examples 1 and 2 in which the Zr compound deviated from the appropriate range were inferior in corrosion resistance, powder blowing resistance and scratch resistance after annealing. In particular, Comparative Example 1 was inferior in appearance after annealing.
Further, Comparative Example 3 in which the B compound was less than the lower limit was inferior in corrosion resistance, powder blowing resistance and post-anneal scratch resistance, while Comparative Example 4 in which the B compound exceeded the upper limit was inferior in sticking property.
Comparative Example 5 in which the Si compound was less than the lower limit was inferior in corrosion resistance, while Comparative Example 6 in which the Si compound exceeded the upper limit was inferior in powder blowing resistance and scratch resistance after annealing.
Further, Comparative Examples 7 and 8 containing a phosphorus compound in a large amount exceeding the appropriate range were inferior in water resistance.

Claims (2)

An electrical steel sheet having an inorganic coating containing a Zr compound, a B compound and a Si compound on the surface,
The ratio of the Zr compound to the total solid mass of the inorganic coating is 10 to 79.9% by mass in terms of ZrO ₂ , the ratio of the B compound is 0.1 to 5% by mass in terms of B ₂ O ₃ , and the ratio of the Si compound Is an electrical steel sheet with an inorganic insulating coating, characterized by being 20 to 85% by mass in terms of SiO ₂ . The electromagnetic steel sheet with an inorganic insulating coating according to claim 1, further comprising a phosphorus compound in a proportion of 30% by mass or less in terms of P ₂ O ₅ with respect to the total solid mass of the inorganic coating.