JP3380775B2 - Grain-oriented silicon steel sheet with low strain sensitivity and excellent magnetic properties - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented silicon steel sheet used for an iron core of a transformer or a power generator, and more particularly to a steel sheet having a low strain sensitivity and an effect of improving magnetic properties. The present invention relates to a grain-oriented silicon steel sheet having a large tension applying type insulating film. 2. Description of the Related Art As one of the methods for reducing iron loss of a grain oriented silicon steel sheet, there is known a means for applying tension to a steel sheet by utilizing a difference in thermal expansion coefficient between an insulating film and a steel sheet. This tension-imparting coating not only improves iron loss characteristics, but also has the effect of improving magnetostriction characteristics in an alternating magnetic field and increasing iron loss when strain is applied to a steel sheet, so-called reducing strain sensitivity. ing. The method of forming such a tension imparting type coating film is described in, for example, JP-B-59-17521 and JP-A-53-2804.
No. 3 discloses a technique using a coating liquid composed of colloidal silica, phosphate and chromic anhydride. [0003] Also, Japanese Patent Application Laid-Open Nos.
Japanese Patent No. 42332 discloses a technique for producing a low iron loss directional silicon steel sheet which does not deteriorate in iron loss value even when a linear flaw or the like is introduced into the steel sheet and subjected to strain relief annealing. This iron loss reduction effect depends on the magnetic domain segmentation effect of reducing the magnetic domain width.
However, in the case of a low iron loss directional silicon steel sheet having a linear flaw or the like introduced on the surface of the steel sheet, external strain tends to concentrate on the periphery of the flaw, which may degrade iron loss and magnetostriction characteristics.
For example, when a pinch roll for transporting a steel sheet or a measuring roll for measuring the length of the steel sheet is pressed against the steel sheet, a case where low iron loss cannot be maintained may occur. Therefore, even when a transformer is assembled using a steel sheet whose iron loss is reduced due to the effect of linear flaws or the like, the iron loss value may not be as low as expected. In particular, when used in a laminated iron core transformer, since the strain relief annealing is not performed after machining the iron core, problems such as deterioration of the iron loss value and increase in noise may occur. The above-mentioned tension imparting type coating has an effect of reducing the influence of such externally introduced strain, and the effect of the reduction increases as the coating thickness increases. Discharge of water vapor generated inside the coating during baking to the outside is hindered, and bulging defects or hole defects called blisters are easily generated in the coating. In this regard, Japanese Patent Application Laid-Open No. Hei 5-1387 discloses a technique for preventing blistering by controlling the rate of temperature rise during baking, and Japanese Patent Application No. 9-324532 discloses a technique of coating twice. Techniques for reducing the strain sensitivity by repeating the process have been disclosed, but in each case, when the coating thickness is large, blisters also occur, and the space factor decreases. SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems. By forming a suitable tension-imparting film, the strain sensitivity is small and the magnetic properties are excellent. The purpose is to obtain a grain-oriented silicon steel sheet. Means for Solving the Problems The inventors of the present invention have conducted detailed investigations and studies on the relationship between physical properties of the coating and iron loss, magnetostriction and strain sensitivity, and as a result, have increased the average density of the coating. It was found that this was extremely effective in achieving the intended purpose. The present invention has been completed based on the above new findings. That is, according to the present invention, a film having an average density of not less than 3.7 g / cm ³ and a basis weight per side of not less than 0.5 g / m ² and a surface roughness Is a grain-oriented silicon steel sheet having a small strain sensitivity and excellent magnetic properties, characterized by having a coating having a center line average roughness Ra of 0.25 μm or less. In the present invention, in order to further improve strain sensitivity, it is particularly advantageous to set the average density of the coating to 4.2 g / cm ³ or more. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, experimental results on which the present invention is based will be described. Experiment 1 A cold rolled sheet containing Si: 3 wt% and having a final thickness of 0.23 mm was subjected to decarburization and primary recrystallization annealing, and then no forsterite film was formed using an annealing separator containing lead chloride and strontium hydroxide. A material close to a mirror surface was obtained. The obtained steel sheet was plated with Cr in various thicknesses, and then an insulating coating solution containing magnesium phosphate and colloidal silica as main components was applied in various thicknesses using a roll coater.
For a minute. FIG. 1 shows the results obtained by examining the strain sensitivity of the thus obtained grain-oriented silicon steel sheet with a tensile coating in relation to the average density of the coating obtained by combining the Cr plating layer and the insulating coating.
Shown in Here, the densities of the Cr plating and the insulating film are respectively
6.8 g / cm ³ and 2.4 g / cm ³ . Regarding the strain sensitivity, the amount of change in the iron loss W _17/50 value when a measuring roll composed of a steel roll having a diameter of 100 mm and a width of 50 mm was passed through while being pressed at a roll reduction force of 15 kgf / cm. Was evaluated. The figure also shows the results of a survey conducted when a forsterite film and an insulating film made of magnesium phosphate and colloidal silica were formed according to the conventional method. As shown in the figure, the average density of the coating is
3.7 g / in the case of cm ³ or more, deterioration of core loss can be suppressed to below 0.02 W / kg, in particular 4.2 g / c the average density of the coating
When m ³ or more, the iron loss degradation was almost constant at 0.01 W / kg. In contrast, in the conventional folder average density of the coating obtained by combining the insulating coating of stellite coating with phosphoric acid and colloidal silica was about 2.7 g / cm ^3, deterioration degree of the iron loss met about 0.04 W / kg Was. Generally, the cost of iron loss reduction by the tension application type coating is about 0.02 W / kg,
Therefore, if the average density of the coating is less than 3.7 g / cm ³ , the improvement is offset. Experiment 2 A cold-rolled sheet containing Si: 3 wt% and having a final thickness of 0.23 mm was subjected to decarburization / primary recrystallization annealing, and then an annealing separator mainly composed of MgO was applied thereto, followed by final finishing annealing. After the directional silicon steel sheet with the forsterite coating obtained by performing the above, after light pickling with phosphoric acid, it consists of magnesium phosphate and colloidal silica with TaN, NbN, Si ₃ N ₄ dispersed on the surface. A coating liquid and a coating liquid which does not disperse nitrides were applied, and baked at 800 ° C. for 1 minute. In addition,
The thickness of the obtained films including the forsterite film was 3.9 g / cm ² per one side. FIG. 2 shows the result of examining the magnetostriction characteristics of the obtained sample at a magnetic flux density B of 1.7 T and a frequency of 50 Hz. FIG. 1 shows a magnetostriction-compression stress characteristic curve.
As shown in the figure, it can be seen that the compressive stress characteristics with respect to the magnetostrictive vibration are improved as the coating film sample has a higher average density. As described above, although the reason why the strain sensitivity of a steel sheet is improved by forming a coating having a large average density has not been clearly elucidated, it is not clear yet. It is considered that the high inertia of the high-density coating and the rigid coating against the increase in micromagnetic vibration act in a direction to suppress the increase in the vibration. The preferred composition range of the grain-oriented silicon steel sheet of the present invention will be described below. As components of the steel sheet used in the present invention, Si is 1.5 to 7.0 wt%, and Mn is 0.03 to 2.5 wt%.
Desirably, it is contained. In other words, Si and Mn are effective components for increasing the electrical resistance of the product and reducing iron loss, but if none of them is below the lower limit of the above range, the effect of the addition is poor, while the content of Si is 7.0 wt%. If Mn exceeds 2.5 wt%, Mn will induce γ transformation during heat treatment to deteriorate magnetic properties. In addition to the above elements, known inhibitor components such as Al, B, Bi, Sb, Mo, Te, Sn, P, Ge,
As, Nb, Cr, Ti, Cu, Pb, Zn, In and the like can be contained alone or in combination. In addition, impurities such as C, S, and N all have harmful effects on magnetic properties.
Particularly, since iron loss is deteriorated, it is preferable to suppress the content of C to 0.003 wt% or less, S: 0.002 wt% or less, and N: 0.002 wt% or less. The slab of the molten steel adjusted to the above preferable composition is formed by a continuous casting method or an ingot-bulking method, followed by hot rolling, cold rolling, decarburization / primary recrystallization annealing and A final finish annealing is performed to obtain a grain-oriented silicon steel sheet. As a surface after final finish annealing, when forming an anisotropic film by an electroplating method, it is only necessary that the resistance value is low enough to allow conduction even if forsterite is present, and of course, even if it does not exist good. When a metal film is formed by a hot-dip plating method or an electroless plating method, a final finish-annealed sheet having a usual forsterite film can be used as it is. Further, although it is effective even on a ground iron surface in which an inorganic coating such as forsterite is simply removed, it is more effective to reduce the iron loss value by performing a smoothing treatment on the surface.
For example, there may be mentioned a mirror-finished surface with a surface roughness as small as possible by thermal etching or chemical polishing, or a graining-like surface obtained by crystal orientation enhancement treatment by electrolysis in an aqueous halide solution. According to the present invention, in the above-described grain-oriented silicon steel sheet with a coating, the average density of the coating excluding the ground iron portion of the steel sheet is 3.7 g / cm ³ or more, preferably 4.2 g / cm ³ or more. It is important. That is, by increasing the average density, the inertia and hardness of the coating can be increased, and the strain sensitivity of the steel sheet can be reduced. For this purpose,
The average density of the coating portion excluding the base iron portion needs to be 3.7 g / cm ³ or more, preferably 4.2 g / cm ³ or more. , As shown supra Figure 1, by the average density of the coating and 3.7 g / cm ³ or more, it is possible to suppress deterioration of the iron loss below 0.02 W / kg, in particular the average of the film density because Is set to 4.2 g / cm ³ or more, the deterioration of iron loss can be suppressed to 0.01 W / kg. In the case of a metal film formed by plating, there is no insulating film, so it is necessary to form an insulating coating on the electrodeposited layer. It is necessary to control the average density as a coating. Here, the average density of the coating can be calculated by the following equation. Average density = (weight difference before and after film formation) / (sample steel sheet area × average film thickness) In the above formula, (sample steel sheet area) is twice the sample size in the case of double-side coating. Become. The average film thickness can be determined by a normal film thickness meter such as an electromagnetic film thickness meter or an eddy current film thickness meter, or by observing a cross section of a steel sheet using an optical microscope or an SEM. In this experiment, the film thickness was measured using an electromagnetic film thickness meter. Furthermore, when measuring using a sample after the film is formed, only the film is mechanically or chemically ground, and the weight difference before and after that is divided by (the steel sheet area of the sample × the thickness of the film reduced by the grinding). Can be obtained by doing Average density = weight difference before and after grinding / (area of steel sheet of sample × thickness of coating) As an insulating coating, it is more effective to reduce iron loss if it has a tension imparting effect. A general coating may be used as long as it has an insulating property. Further, as the kind of the tension film, a phosphate-colloidal silica-chromic acid type coating which has been conventionally used for a grain oriented silicon steel sheet having a forsterite film has advantages in terms of its effect, cost, uniform processing property, and the like. Is preferred. The thickness of the coating is preferably in the range of about 0.3 to 10 μm from the viewpoint of the effect of imparting tension, the space factor, and the adhesion of the coating.
In addition, as the tension coating, besides the above, see JP-A-6-65.
754, JP-A-6-65755 and JP-A-6-65755
It is also possible to apply an oxide-based coating such as boric acid-alumina proposed in JP-A-299366. As a means for increasing the average density of the coating, for example, a method of dispersing fine particles in a tension coating to increase the average density of the coating is effective.
It is preferable to disperse and add carbides such as C, WC and TaC, nitrides such as HfN, TaN and CrN, and ceramics and metal powders such as borides and oxides. In the case of insoluble fine particles, it is necessary to take measures such as strong stirring so that the particles are uniformly dispersed in the coating. Next, the appropriate thickness of the high-density coating will be described. The thickness of the coating is 0.5
If it is less than g / cm ² , the insulating coating does not have the effect of suppressing magnetostrictive vibration, and good magnetostriction characteristics cannot be obtained regardless of the average density. To 0.5 g / cm ² or more. The upper limit is 15 g / cm ² from the viewpoint of blisters, space factor, and film adhesion.
It is desirable to set it to the following level. In the case where the above-described metal coating is included, the total thickness with the insulating coating is defined as the thickness of the coating. The properties of the coating surface also affect the strain sensitivity, and the smoother the coating surface, the smaller the iron loss value degradation when applying external strain. On the other hand, if the unevenness of the coating surface is large, it may be due to the high density and solid coating, or the added external strain may concentrate around the unevenness and cause local iron loss deterioration. It is estimated that the loss value increases.
Here, the appropriate surface roughness of the coating is the center line average roughness Ra of 0.
25 μm or less. Even if the magnetic domain is subdivided by irradiating the steel sheet thus obtained with a laser or a plasma flame for the purpose of further reducing iron loss, there is no problem in the adhesion of the insulating film. In addition, in order to refine magnetic domains at any stage of the process of manufacturing a grain-oriented silicon steel sheet, forming grooves at regular intervals by etching or tooth-shaped rolls on the surface is also effective as a means for further reducing iron loss. . EXAMPLE 1 A cold-rolled sheet rolled to a final sheet thickness of 0.23 mm containing Si: 3% by weight was subjected to decarburization and primary recrystallization annealing, and then to a metal chloride mainly composed of MgO. After the application of the annealing separating agent, a final finish annealing including a secondary recrystallization process and a purification process was performed to obtain a material having no forsterite film and a surface state close to a mirror surface. Then, for some materials, subjected to chemical polishing in an electrolytic polishing or H ₂ O ₂ -HF solution in an aqueous NaCl solution, after further magnetically smooth surface, Cr as a plating bath
Electroplating of Cr was performed using a surge bath consisting of O ₃ : 250 g / l and sulfuric acid: 2.5 g / l. Thereafter, an aqueous treatment liquid containing magnesium phosphate, colloidal silica and magnesium chromate as main components was applied as a tension coating, and baked at 800 ° C. to form films having various thicknesses. The grain-oriented silicon steel sheet thus obtained was passed through a measuring roll at a roll reduction force of 15 kgf / cm, and the change in iron loss _{W17 / 50} value before and after the introduction of strain was examined. The surface roughness of the grain-oriented silicon steel sheets obtained was all in the range of 0.18 to 0.23 μm. Table 1 shows the obtained results. [Table 1] As is clear from the table, when the average density of the combined Cr + tension coat is low or the thickness of the coating is not sufficient (samples Nos. 5 to 7), the iron loss value is significantly increased by introducing strain. Deteriorated. On the other hand, all of the conforming examples (samples Nos. 1 to 4) satisfying the requirements of the present invention were low in sensitivity to strain and could effectively suppress the deterioration of the iron loss value. Example 2 A cold-rolled sheet rolled to a final sheet thickness of 0.23 mm containing Si: 3% by weight was subjected to decarburization / primary recrystallization annealing, and then an annealing separator containing MgO as a main component was applied. Then, a final finish annealing including a secondary recrystallization process and a purification process was performed to obtain a grain-oriented silicon steel sheet with a forsterite film. Next, a part of the steel plate was subjected to an acid pickling treatment to remove a part or all of the forsterite, thereby changing the glass coating amount and the surface roughness. After that, the obtained material was subjected to Ni-P electroless plating. The plating bath used was an acidic bath composed of nickel sulfate: 40 g / l, sodium hypophosphite: 10 g / l, and sodium acetate. Here, the average density of only the Ni—P layer was 7.7 g / cm ³ . The electroless plating layer had good plating uniformity and almost inherited the surface roughness before plating. Thereafter, an aqueous treatment liquid containing aluminum phosphate, colloidal silica and chromic anhydride as main components was applied as a tension film, and baked at 800 ° C. to form films of various thicknesses. Table 2 shows the results obtained by examining the surface roughness, coating average density, coating thickness, and the amount of iron loss deterioration due to the introduction of strain evaluated in the same manner as in Example 1 of the obtained steel sheet. In addition, in the same table, the magnetostriction-compression stress characteristics were measured, and the results of a survey on the magnetostriction value λpp when the compressive applied stress σ = 5.0 MPa are also shown. [Table 2] As shown in the table, in Samples Nos. 12 and 14, which were not subjected to Ni-P plating, since the average film density was low, the strain sensitivity was large and the iron loss value was significantly deteriorated.
Moreover, the magnetostrictive vibration also increased. Sample No. 13 in which the film thickness was less than the lower limit also showed large iron loss value deterioration and magnetostriction value λpp. In this regard, sample No. 4 exhibited a low magnetostriction value because both the average film density and the film thickness were within the applicable range, but the surface roughness exceeded the upper limit, and the amount of deterioration of the iron loss value was large. On the other hand, all of the conforming examples (samples Nos. 1 to 3) satisfying all the requirements of the present invention exhibited extremely small iron loss deterioration and exhibited excellent magnetostriction characteristics. In addition, the influence by the removal of the forsterite film was not particularly found. As described above, according to the present invention, it is possible to increase the average density of the insulating film without particularly increasing the thickness of the insulating film.
In addition, by reducing the surface roughness, it is possible to stably obtain a grain-oriented silicon steel sheet having low strain sensitivity and excellent magnetic properties, which has a great advantage to the industry.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing a relationship between an average density of a coating film excluding a base iron part and a variation in iron loss. FIG. 2 is a magnetostriction-compression stress characteristic curve diagram with the average density of a coating as a parameter.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Michio Komatsubara, Inventor 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. JP-A-3-215679 (JP, A) JP-A-63-227719 (JP, A) JP-A-5-226134 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 22/00-22/86 H01F 1/16

Claims (1)

(57) [Claims] [Claim 1] The average density of the coating excluding the base iron part is 3.7 g / c
m ³ or more, and the weight per side is 0.5 g / m
² or more film thickness and surface roughness 0.25 in center line average roughness Ra
A grain-oriented silicon steel sheet having a small strain sensitivity and excellent magnetic properties, characterized by having a coating of not more than μm.