JPS63303009A - Manufacture of grain-oriented silicon steel sheet with superlow iron loss - Google Patents

Abstract

PURPOSE:To stably manufacture a grain-oriented silicon steel sheet with superlow iron loss, by subjecting a silicon-containing steel sheet to secondary recrystallization while applying temp. difference to the direction perpendicular to a rolling direction, by forming a high-tensile film by a CCD method, and by applying purification annealing to the above. CONSTITUTION:A continuously cast slab of silicon-containing steel is heated to about 1,390 deg.C, hot-rolled, and subjected to a single cold rolling or cold-rolled twice while process-annealed between the cold rolling stages. Subsequently, the cold-rolled sheet is subjected to primary recrystallization annealing which doubles as decarburization at about 850 deg.C. The annealed steel is wound up in a loose coil in which respective sheet surfaces are mutually separated, and then, secondary recrystallization is applied to the above in a furnace with temp. gradient while applying temp. difference to the width direction of the coil, and simultaneously, an extra thin high-tensile film is formed on the above by a CVD method. As the above film, the one consisting of one or more kinds among the nitrides and/or carbides of Ti, Zr, Hf, V, Nb, Ta, Mn, Cr, Mo, W, Co, Ni, Al, B, and Si and the oxides of Al, Ni, Cu, W, Si, Ti and Zn is suitably used. The steel sheet after film formation is heated in H2 and subjected to purification annealing so as to be formed into a product of silicon steel sheet.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing ultra-low core loss unidirectional silicon steel sheets, and in particular, to a method of manufacturing an ultra-low core loss unidirectional silicon steel sheet, in particular, secondary recrystallization annealing using a special method and surface coating formation technology using CVD. The aim is to advantageously improve iron loss characteristics by skillfully combining the following.

Remarkable development efforts in recent years to improve the electrical and magnetic properties of unidirectional silicon steel sheets, particularly to meet the extreme demands of reducing iron loss, are gradually bearing fruit. A serious problem associated with this is that when unidirectional silicon steel sheets are subjected to so-called strain relief annealing after processing and assembly, they inevitably suffer from deterioration of their properties, which limits their use. Disadvantages are pointed out.

In this specification, the following is related to the results of research and development to open up a new method that can advantageously meet the above requirements, regardless of whether or not it undergoes a high-temperature thermal history such as strain relief annealing. state

As is well known, unidirectional silicon steel sheets are products in which secondary recrystallized grains are highly concentrated in the (110) (001), or Goss, orientation, and are mainly used in transformers and other electrical equipment. When used as an iron core, the product is required to have high magnetic flux density (represented by the value B) and low iron loss (represented by the value W+?/S) as electrical and magnetic properties.

This unidirectional silicon steel plate is manufactured through a wide variety of complicated processes, but numerous inventions and improvements have been made so far, and today a product with a thickness of 0.30 ium has magnetic properties of 8.
1°1.90T or more, W, 7. ,. 1.05 W/
kg or less, and the magnetic properties of the product with a plate thickness of 0.23mm+ are BB.

1. More than 89T, Wl? /s. Unidirectional silicon steel sheets with ultra-low core loss of 0.90 W/kg or less are being manufactured.

In particular, recently there has been a marked increase in demand for reduced power loss from the perspective of energy conservation, and in Europe and the United States, when creating a transformer with low loss, the reduction in iron loss is converted into a monetary value and added to the transformer price.・The "evaluation" (iron loss evaluation) system is becoming widespread.

(Prior art) Under these circumstances, recently, the surface of a unidirectional silicon steel plate after finish annealing is irradiated with a laser in a direction approximately perpendicular to the rolling direction to introduce local microstrain to subdivide the magnetic domains. It was proposed to reduce the iron loss (see Japanese Patent Publications No. 57-2252, Japanese Patent Publication No. 57-53419, Japanese Patent Publication No. 58-26405, and Japanese Patent Publication No. 58-26406).

This magnetic domain refining technology is effective for transformer materials for laminated core transformers that are not subjected to strain relief annealing, but for material for wound core transformers that are subjected to strain relief annealing,
The disadvantage is that the local microstrain introduced by laser irradiation is released by annealing and the magnetic domain width becomes wider, so that the laser irradiation effect is lost.

On the other hand, earlier in Japanese Patent Publication No. 52-24499, the surface of a unidirectional silicon steel sheet after finish annealing was mirror-finished, or the mirror-finished surface was coated with thin metal plating or an insulating coating was applied thereon. A method of manufacturing an ultra-low core loss unidirectional silicon steel sheet by coating and baking has been proposed.

However, this method of improving iron loss through mirror finishing cannot be adopted from a process perspective because it does not make a sufficient contribution to reducing iron loss at the cost of a significant increase in cost. Due to problems with adhesion, it has not been adopted in current manufacturing processes.

Japanese Patent Publication No. 56-4150 also proposes a method in which a steel plate surface is mirror-finished and then an oxide-based ceramic thin film is vapor-deposited. However, this method also has 60
High-temperature annealing at 0°C or higher causes the steel plate and the ceramic layer to separate, so it cannot be used in actual manufacturing processes.

(Problems to be Solved by the Invention) In order to take advantage of the above-mentioned mirror finish for improving iron loss, the inventors believe that the above-mentioned costs should be avoided, especially from the perspective of today's development of energy-saving materials. We believe that it is important to overcome the problems of adhesion and durability of the insulating layer without deteriorating the characteristics due to high-temperature processing, and based on this basic understanding, we have developed Particularly advantageous super iron loss can be achieved by drastic improvement of the steel plate processing method after removing oxides, including cases in which oxides on the surface of a silicon steel plate are removed and then polished to a mirror-like state. This is the object of the invention.

(Means for Solving the Problems) As a result of intensive research to achieve the above object, the inventors have discovered that after primary recrystallization annealing, which also serves as decarburization, in the manufacturing process of unidirectional silicon steel sheets, To achieve the initial objective, it is possible to perform secondary recrystallization annealing on the annealed steel sheet while applying a temperature difference in a direction approximately perpendicular to the rolling direction, and at the same time to coat the surface of the steel sheet with an ultra-thin tensile coating using the CVD method. We have obtained the knowledge that it is extremely effective for this purpose.

This invention is based on the above knowledge.

That is, this invention hot-rolls a silicon-containing steel slab,
Then, after performing cold rolling once or twice with intermediate annealing in between, primary recrystallization annealing that also serves as decarburization is performed, and then this annealed plate is wound into a loose coil with plate surfaces spaced apart from each other. , Ti, Zr, Hf,
V.

Nb, Ta, Mn, Cr, Mo, W, Co, Ni.

Ae, B, Si nitride and/or carbide and Aj2. Ultra-low core loss unidirectional silicon produced by forming an ultra-thin tensile coating mainly consisting of at least one oxide selected from the oxides of Ni, Cu, W, Si, Ti, and Zn, and then subjecting it to purification annealing. This is a method for manufacturing steel plates.

In this invention, prior to the above-mentioned secondary recrystallization annealing and ultra-thin tension coating treatment, the non-metallic layer on the surface of the decarburized and primary recrystallization annealed plate is removed, and then the polishing treatment is performed. The center line average roughness of the steel plate surface is Ra T: 0.
Finishing with a mirror finish of 4 μm or less is more advantageous in improving iron loss characteristics.

Hereinafter, the explanation will proceed according to specific experiments that led to the success of this invention.

C: 0.058% by weight (hereinafter simply expressed as %), Si:
3.35%, Mn: 0.76%, Af: 0
．． A continuously cast silicon steel slab containing 0.025%, N: 0.072%, Sn: 0.1% and Cu: 0.05% was heated at 1390°C for 4 hours and then hot rolled to obtain 1.
It was made into a hot-rolled plate with a thickness of 8 +gv+.

Then, after homogenization annealing at 1100"C for 3 minutes, rapid cooling treatment, and one round of hard cold rolling to obtain a final cold rolled sheet with a thickness of 0.23 mm. In this case, during cold rolling, 300°
C warm rolling was performed.

Thereafter, decarburization and primary recrystallization annealing were performed in wet hydrogen at 850°C, followed by treatment under the following two conditions.

(a) After decarburization and primary recrystallization annealing, it is made into a loose coil as it is.

(b) After decarburizing and annealing the 1 Valor crystal, pickling is performed to remove surface oxides, and then electrolytic polishing is performed to obtain center line average roughness Ra = 0
．． After mirror polishing to 1 μm, it is wound into a loose coil.

Thereafter, treatment was carried out using a temperature gradient furnace CVD apparatus as schematically shown in FIG. In FIG. 1, reference numeral 1 denotes a chamber for performing purification treatment, into which H2 gas is introduced through piping 2, while the exhaust gas is discharged through piping 3. Further, 4 is a CVD reaction chamber equipped with a temperature gradient furnace, 5 is an inlet for various reaction gases, and 6 is an outlet for guiding exhaust gas out of the furnace. 7 is a cylinder that moves the loose coil up and down, 8 is a loose coil, 9 is a stand on which the loose coil is placed, and 10 is a heater.

A loose coil 8 is charged into the CVD reaction chamber 4 equipped with the temperature gradient furnace shown in Fig. 1, and the furnace has a maximum temperature of 1050°C and a temperature gradient (approximately 1″C/cm) toward the bottom of the furnace. The loose coil is moved upward in the chamber at a speed of 20 mm/h using the cylinder 7 to perform secondary recrystallization in a direction approximately perpendicular to the rolling direction (direction C), and at the same time, TiCl4, N2, and Hl are introduced into this chamber. Introduce a mixed gas, and in that atmosphere
A thin film of TiN with a thickness of 0.9 μm was formed on the surface of the steel plate under reduced pressure of mb.

After that, in the purification chamber, the temperature was 1200°C1 in dry H2.
After 8 hours of treatment, purification treatment of the steel plate and C in the T i N coating were performed.
A product was prepared by removing I at the same time.

For comparison, following the usual process, decarburization and primary recrystallization annealing were performed in wet hydrogen at 850'C, and then an annealing separator containing MgO as a main component was applied to the surface of the steel sheet. After secondary recrystallization in the C direction in a normal N2 atmosphere using the temperature gradient furnace shown in Figure 1, the product was purified in dry H2 at 1200°C for 28 hours.

Furthermore, for comparison, decarburization and
After primary recrystallization annealing, an annealing separator mainly composed of MgO is applied to the surface of the steel sheet, and then the temperature is raised from 850°C to 1050°C using a normal soaking box annealing furnace. After secondary recrystallization (in a nitrogen atmosphere), the product was purified in dry H at 1200°C for 8 hours.

Table 1 summarizes the magnetic properties of the products when processed under these conditions.

As is clear from the table, the magnetic properties of the products vary greatly depending on the processing conditions. That is, in the normal process (4), BIG is 1.94T and W+t/so is 0.88w/
It is about kg. Furthermore, C direction 2 due to recent temperature gradient
Next recrystallization annealing (e.g. N, Takahashi et al.
al, :IEFiE Trans, Magneti
cs, Vol, Mag-22 (1986) +P, 4
90. Nobuyuki Takahashi: Introduction to magnetic materials, (1986), P
, 27 and Yoshiyuki Ushigami, Tadashi Nakayama, Tadamasa Nozawa: Summary of the Lecture at the Japan Institute of Metals, April 1985, p. 373)
In processing, B1° is 1.95T, WIt/sa is 0.7
The characteristics are quite good at 8w/kg.

On the other hand, at the same time as the secondary recrystallization treatment in the C direction of this invention,
When a TiN film is formed by VD treatment, the magnetic properties are: E3to is 1.967, W, ..., o is 0.72 to 0.
．． It has been significantly improved to 60w/kg.

The magnetic properties, especially the iron loss characteristics, obtained by such treatment show that the iron loss is significantly reduced when an ultra-thin tension film of TiN is formed by CVD at the same time as secondary recrystallization in the C direction.

(Function) The reason for the above-mentioned improvement in magnetic properties is thought to be as follows.

Recently, by annealing the coil while applying a temperature gradient in the vertical direction (direction perpendicular to the rolling direction) during final annealing, secondary recrystallized grains grow in the direction perpendicular to the rolling direction and are slightly inclined with respect to the longitudinal direction of the steel sheet. Attempts have been made to develop secondary recrystallization with an angle (2° to 3°) (see processing conditions (3) in Table 1), but at the same time this method was carried out, a loose coil was used to develop a CVD reaction. This method aims to reduce iron loss by forming a TiN ceramic tensile coating on the surface of the steel sheet, and at the same time, in contrast to these conventional methods, which use a forsterite underlayer coating, there is a limit to the reduction in iron loss. In this invention, apart from this, by applying an ultra-thin tensile coating such as TiN, it is possible to effectively impart elastic tensile tension to the steel sheet, and it is possible to overcome the above-mentioned limit and create a unidirectional silicon steel sheet with even lower core loss. This made it possible to manufacture

Next, the manufacturing process of the unidirectional silicon steel sheet will be described in more detail, including a general explanation.

First, the starting material has conventionally known unidirectional silicon steel material components, such as ■C: 0.01~o, oso%, Si: 0
．． 25-4.5%, Mn: 0.01-0.2%,
Mo: 0.003-0.1%, Sb: 0.0
Composition containing 0.05 to 0.2%, one or both of S or Se in total 0.005 to 0.05% C: 0.01 to 0.08%, Si: 2. O~
4.0%, s: o, oos~0.05%, N:
0.001~0.01%, Affi: 0.01~
0.06%, Sn: 0.01-0.5%, Cu
: 0.01~0.3%, Mn: 0.01~
Composition containing 0.2% ■C70, 01-0.06%, Si: 2.0-4
．． 0%, S: 0.005-0.05%, B: 0
．． 0003-0.0040%, N: 0.001-0
．． 01%, Mn: 0.01-0.2%.Next, the hot-rolled sheet may be subjected to homogenization annealing at 800-1100°C and then cooled once, if necessary. One-time cold rolling method in which the final plate thickness is obtained by inter-rolling, or two-step cold rolling method in which intermediate annealing is usually performed at 850°C to 1050'C and further cold rolling is performed, in the latter case, the initial rolling reduction is about 50% to 80%, and the final rolling reduction is about 50% to 85% Te 0.15IIIm to 0.3
The final cold-rolled sheet thickness is 5 mm.

After finishing the final cold rolling, the steel plate finished to the product thickness is subjected to decarburization and primary recrystallization annealing treatment in wet hydrogen at 750°C to 850°C after surface degreasing.

After that, the copper plate is left as it is, or the oxide film on the surface is removed by known chemical methods such as pickling, or mechanical methods such as cutting and grinding, and then chemical polishing methods such as chemical polishing, electrolytic polishing, etc. After finishing the steel plate surface to a mirror-like state with a center line average roughness Ra of 0.4 μm or less using conventional methods such as mechanical polishing methods, loose coils are produced in which a gap is created between the plate surfaces. Wind it up.

Next, secondary recrystallization annealing is performed, but in this invention, especially 2
At the same time, the secondary recrystallized grains are grown in a direction perpendicular to the rolling direction (preferential growth in the C direction), and at the same time, a tension film of carbides, nitrides, oxides, etc. is formed on the surface of the steel sheet by a CVD reaction.

The above process uses a CVD furnace with a temperature gradient as shown in Figure 1 above, and inserts a loose coil into the furnace to create a temperature gradient in the width direction of the coil while producing secondary recrystallized grains. This can be achieved by simultaneously developing a CVD process.

Here W4vi, the ultra-thin tension coating to be formed on the surface is T
i, Zr, Hf, V, Nb, Ta, Mn, Cr.

Mo, W, Co, Ni, Aj! , B, nitrides and/or carbides of Si and AN, Ni, Cu.

At least one selected from oxides of W, Si 2 , Ti 2 and Zn is advantageously suitable.

Further, the thickness of the tension coating is preferably about 0.05 to 5.0 μm.

After such treatment, it is necessary to perform annealing in dry hydrogen at 1000° C. or higher for 1 to 20 hours to purify the steel sheet.

Furthermore, it is necessary to apply and bake an insulating film containing phosphate and colloidal silica as the main components on the ultra-thin tension film produced in this way when using a large-capacity transformer of up to 1 million KVA. For the formation of this insulating coated and baked layer, conventionally known methods may be used as they are.

(Example) Point finger open earth C: 0.044%, S i: 3.40%, Mn
: 0.068%, Mo: 0.021%, Se
After uniform annealing at 900°C for 3 minutes, a hot rolled sheet containing Sb: 0.020% and Sb: 0.024% was homogenized at 950°C.
0.2 by performing two cold rollings with intermediate annealing of C.
A final cold-rolled sheet with a thickness of 3 mm was obtained.

After that, decarburization and primary recrystallization annealing were performed at 820'C for 3 minutes, and stainless steel spacers (0,31
After inserting the φ) and winding it into a loose coil, it is placed into a furnace with a maximum temperature of 950″C and a steep temperature gradient (approximately 30′C/cm) toward the top of the furnace. h
The coil is charged in a direction approximately perpendicular to the rolling direction at a speed of 2.
Simultaneously with subsequent recrystallization, Si and N were formed on the surface of the steel sheet to a thickness of 0.7 to 0.8 μm by CVD reaction, and then purification annealing was performed in dry hydrogen at 1180″C1 for 5 hours.

The magnetic properties of the thus obtained product were as follows.

B+o: 1.93T, W+? zso!
0.65w/kg Sushin 1 Tsuji λ C: 0.064%, Si: 3.46%, Mn
: 0.076%, A1: 0.025%, S
? A hot-rolled sheet containing 0.026% and N: 0.0066% was uniformly annealed at 900°C for 3 minutes and then rapidly cooled, and then warm rolled at 300°C to obtain a 0.20+
A final cold-rolled sheet with a thickness of u+ was obtained.

After that, after primary recrystallization annealing that also serves as decarburization in wet hydrogen at 850°C, the oxide film is removed by pickling, and mirror polishing is performed by electrolytic polishing, after which the maximum temperature is 1000°C.
There is a steep temperature gradient (approximately 20°C/cm) towards the top of the furnace.
), the temperature was raised at a rate of about 10 to 15 II.../h, and secondary recrystallization and CVD reaction were performed simultaneously. The CVD reaction at this time was ■TiN.

■BN, ■S 13 N a +■/IN, ■HfN,
■CrN.

■VN, ■T i C, ■SiC, [phase] WC, ■Nb
C.

@Cr1C3, ■TaC, @)Aj! gos,■5i
O-.

■Ti0z, @Zr0t, @Tact, ■Ti
(C, N) tension coatings each 0.7 to 1.5 mm
It was covered thickly.

Here, as a reactive gas, N2 is used when forming a nitride film.
A small amount of NH or gas was used, C, H, or CH gas was used when forming a carbide film, and O2 gas was used when forming an oxide film.

Thereafter, purification annealing was performed in dry H2 at 1200°C for 8 hours.

Table 2 summarizes the results of investigating the magnetic properties of each product obtained.

Table 2 (Effects of the Invention) Thus, according to the present invention, it is possible to stably obtain a unidirectional silicon steel sheet with extremely excellent iron loss characteristics.

[Brief explanation of drawings]

FIG. 1 shows secondary recrystallization annealing and CV according to the present invention.
FIG. 2 is a schematic diagram showing a reaction furnace suitable for use in simultaneous implementation of D processing. Figure 1

Claims (1)

[Claims] 1. A silicon-containing steel slab is hot-rolled, then cold-rolled once or twice with intermediate annealing in between, and then subjected to primary recrystallization annealing that also serves as decarburization; Next, this annealed plate is wound into a loose coil with plate surfaces spaced apart from each other, and then secondary recrystallization is performed while applying a temperature difference in the width direction of the coil, and at the same time Ti, Zr, Hf, V, Nb, Ta,
Nitride and/or carbide of Mn, Cr, Mo, W, Co, Ni, Al, B, Si and Al, Ni, Cu, W, Si, Ti, Zn
1. A method for producing an ultra-low core loss unidirectional silicon steel sheet, which comprises forming an ultra-thin tensile coating consisting mainly of at least one kind of oxides selected from the group consisting of oxides, and then subjecting it to purification annealing.