JPS59215419A - Production of grain-oriented silicon steel sheet having high magnetic flux density - Google Patents

Abstract

PURPOSE:To produce a grain-oriented silicon steel sheet having a high magnetic flux density by specifying the content of N in the steel sheet at the start of secondary recrystallization in the stage of subjecting the silicon steel material contg. C, Si and solAl at specific ratios to secondary recrystallization annealing. CONSTITUTION:A silicon steel material consisting of 0.010-0.10% C, 2.5-4.0% Si, 0.010-0.065% solAl, and the balance Fe with inevitable impurities is subjected to secondary recrystallization annealing while a temp. gradient is given to the boundary region of the primary recrystallization region and secondary recrystallization region of final annealing in the stage of subjecting such steel material to hot rolling, cold rolling, decarburization annealing and final annealing. The content of nitrogen in the steel sheet at the start of the secondary recrystallization in the stage of such secondary recrystallization is adjusted to 130-200ppm and the steel sheet is annealed in an atmosphere contg. >=25% nitrogen and the balance hydrogen. The magnetic flux density B8 at 800AT/m magnetizing force is thus stabilized at about >=1.96T.

Description

[Detailed description of the invention] This invention has a high magnetic flux density of %VCB s of 1.96 T.
The present invention relates to a secondary recrystallization annealing method for producing the above-mentioned unidirectional silicon copper plate.

Unidirectional silicon steel sheets are used as core materials for transformers, and important features include high magnetic flux density and low iron loss at low excitations. The history of the development of unidirectional silicon steel sheets is a history of iron loss improvement, and iron loss improvement is mainly achieved by B++ (magnetizing power 800 A
This has been achieved by improving the magnetic flux density (T/m). The origins of unidirectional silicon steel sheets are N, P, and Gosa.
Many improvements have been made to this manufacturing method due to the multi-stage cold rolling process.
Unidirectional silicon steel sheets with high Bs and low iron loss have been produced. Q! jK, Special Publication No. 40-15654 and Special Publication No. 51. According to the proposal of the method described in Publication No. 13469, a high B8 unidirectional silicon steel sheet has been developed, and a low core loss unidirectional silicon steel sheet sold by Bs is currently in production. There are n.

On the other hand, in general, in industrial products, as the Bs becomes sieved, the crystal grains tend to become larger, and even if the Bs is improved beyond a certain level, the 1000 magnetic domain width increases, resulting in increased eddy current loss and metallurgical The current situation is that expectations for a reduction in iron loss of more than this n are dwindling. In order to overcome this difficulty, it is necessary to subdivide the 1000 magnetic domain width of the B8 high unidirectional silicon steel plate. Various attempts have been made in the past, and the effect of subdivision has also been confirmed.

The present inventors have developed a B8 extremely high unidirectional silicon steel plate'f.
conducted research on its production, and proposed a method of performing secondary recrystallization under a temperature gradient in Japanese Patent Application Laid-Open No. 57-2839.

FIG. 1 shows the relationship between crystal grains and crystal orientation when a primary recrystallization plate containing AtN as a precipitated phase is subjected to secondary recrystallization under a temperature gradient. That is, the figure (,) shows the state of each crystal grain, and (b) shows the (Zoo) pole figure of each crystal grain.

It can be seen from the figure that only those (crystal grains ■) closest to the ideal (110) (001) orientation (point X in the figure (b)) grow preferentially. This is the basic phenomenon of temperature gradient secondary recrystallization, and it is possible to easily produce a homogeneous silicon steel sheet with almost perfect Goss orientation.

In normal secondary recrystallization annealing, secondary nuclei first undergo nucleation and then grow into secondary recrystallized grains, but there is no clear distinction between nucleation and grain growth, and the final annealing process It is considered that they are performed at the same time. However, in temperature gradient annealing, all sharp Gosa nuclei are first generated, and only 7n grains are allowed to grow. In other words, we believe that the feature is that nucleation and grain growth are performed under separate conditions.

When the temperature gradient is increased (for example, when temperature gradient annealing is performed on a veneer), sharp GO8!1 grains can be grown without producing island grains at the grain growth front. This is the so-called thermal inhibition caused by temperature gradient, y
It can be explained that this is because the growth of primary recrystallized grains is suppressed by thermal inhjbition and the grain growth of 001111 grains is made dominant. However, industrially, final annealing is carried out using 5 to 20 ton coils, so it is quite difficult to secondary recrystallize the entire steel plate under a high temperature gradient. Therefore, in addition to the carbon thermal inhibition effect, it is believed that the suppression effect by the precipitates is important in industrial terms.

The present invention utilizes the high B8 effect of temperature gradient annealing, which was confirmed in the laboratory as described above, in industrial-scale coil annealing.
The purpose is to provide a method for stable performance.

That is, in the present invention, c: o, oio ~ 0.10%, Si: 2.
5-4.0%, acid-soluble At: 0.010-0.06
5%, balance Fe and unavoidable impurities, during full hot rolling, cold rolling, decarburization annealing and final annealing, the final recrystallization region and the secondary recrystallization region are When carrying out secondary recrystallization annealing while applying a temperature gradient to the boundary region of the regions, a magnetic flux density quotient characterized in that the nitrogen content in the steel sheet is set to 130 to 200 PPM at the start of crystallization. The gist of this paper is a method for manufacturing grain-oriented silicon steel sheets.

The present invention will be explained in detail below.

First, the present inventors performed secondary recrystallization annealing 37 under a temperature gradient by heating the coil 1 from the upper surface as schematically shown in FIG. -I went. Figure 3 shows a cross-sectional view of the furnace and coil used. The furnace 7 has a ceiling heater 4 and a side heater 5 as heaters, and these can independently control the long sword. The outer and inner circumferential parts of the coil 1 are insulated by a heat insulating material 6, and the coil is devised so that it receives heat only from the upper end surface as much as possible. A temperature gradient was created in the width direction of all the coils while maintaining the upper end temperature of the coil and the lower end temperature higher than fLK.BsN of the unidirectional silicon steel sheet manufactured by the above method
Even under almost the same heat treatment conditions, η・[B
It is not always possible to obtain 1.96 T or less, which is the goal of the present inventors, at 1.8 and depending on the annealing condition.
In some cases, it was less than 96 T.

FIG. 4 shows a part of the grain structure of case U), which was annealed under the temperature gradient under the heat treatment conditions shown in FIG. 3 for a 5 ton coil, and the corresponding value of B8. In the case of Figure (a), the crystal grains grow linearly from the top of the coil, and the B8 value (with a surface coating) is extremely V.
tl is the same throughout the sample.

On the other hand, in the case of (b) in the same figure, unlike (,), a single grain does not cover the entire sample, and other grains are generated here and there, and there are also island grains trapped among large grains. is characteristic. It was found that B8 in the region where single grains grow linearly is extremely high, but B8 in the region where other grains are mixed is slightly inferior.

Figure 5(a) is an enlarged view of the previous figure and Figure 4(b), showing large grains (A, B) growing from the upper end of the coil.
,C.

G, F, etc.) and the grain that appeared before the growth front of this grain (
D, E, etc.) and 9 particles remaining in the vagina (■, ■,
0, etc.) are observed. The small crystal grains of Koori et al. are shown in Figure 5 (
As shown in the pole figure and the first orientation table shown in b), the orientation is much worse than that of large grains 3 and 9, which causes deterioration of B8.

That is, obtaining the highest B8 by temperature gradient annealing is achieved by not allowing grains with other orientations to form before the growth front of grains with good orientation that have started to grow.

Table 1: Crystal orientation of crystal grains A, B, C, D, E, F, and G. The present inventors further conducted research and found that
As a result of considering the stabilization method of 8, the secondary ¥+
It was confirmed that a high B8 effect could be stably obtained by increasing the amount of N contained in the steel at the start of crystallization.
Ta. That is, by reducing the properties of the annealing separator, especially the B content in MgO, and by increasing the N2 content in the annealing atmosphere, secondary recrystallization - N uniformity in the steel at the start]
It has been concluded that a large amount of B8 is stably absorbed in large amounts, which causes high B8 or stable absorption.
Next, I will explain the process that led to the above conclusion. First, the present inventors investigated the influence of the atmosphere and annealing separator on B8 in secondary recrystallization annealing under a temperature gradient. The sample size is 2
Approximately 20 such steel plates were laminated, placed in a temperature gradient furnace with 6 heating zones, and rolled under a temperature gradient of approximately 5 mm. The grains were grown in the direction perpendicular to the direction.
9 Figure 6 shows the relationship between the annealing atmosphere and B8, and it can be seen that B8 strongly depends on the annealing atmosphere.The larger the N2%, the more B8 becomes oriented. Figure 7 shows boron (B) in the annealing separator MgO.
This shows the relationship between the inclusion and B8. It is shown that B8 becomes madder when MgO with a lower B content is used.

Next, the present inventors subjected about 5 tons of coil to temperature gradient annealing in the equipment shown in FIG. 4, with the atmosphere replaced by MgO seed η. The results are shown in Figure 8.
The average value of B8 in the region where the temperature gradient is about 5 degrees or more at a board temperature of about 950°C is shown.

The content of OB in fldgo is small, and B8 is high in the field sound of 100% N2, and N225% + H□7
Even if the air is 5% open, if B is 100 PPM, this indicates that B8 is not cylindrical.

Figure 9 shows N (f, (and B) in the copper plate at the start of secondary recrystallization.
This shows the relationship between 8. There is a tendency for B8 to increase as N-M increases. It is shown that the necessary N amount can be controlled by adjusting the N2% of the working atmosphere and the B amount of MgO, and the B8 improvement effect by temperature gradient annealing can be sufficiently VC. Regarding the amount of N required for fc for dv volatilization, 200
It is difficult to stably absorb more than PPM, and B8 almost reaches saturation at 180 to 200 PPM, so even if it can contain more than 200 PPM, 2
Since it was expected that it would be disadvantageous for purification after the next recrystallization,
The upper limit was set to 200 PPM. In addition, in order to stably achieve B8≧1.96T, which is the objective of the present invention, approximately 130
The lower limit was set as PPM or so.

The reason why the effect of improving B8 by temperature gradient secondary zeolite annealing becomes more pronounced with an increase in Nm in the steel sheet is not necessarily clear at present, but the following can be inferred from the above-mentioned experimental examples. That is, since N absorption during the secondary recrystallization annealing becomes easy, a large amount of A7N is formed, and the secondary recrystallization start temperature at which the inhibitor effect is strong increases. Kon
is a new 2nd-F co”K at the 2nd-order recrystallization growth front.
This means that the occurrence of crystallization is suppressed. In this way, the sharp gun that has already occurred is the Goas direction Kinnan 2
The next recrystallized grains grow toward the low temperature region, and the quotient is extremely low.
This results in crystal grains having a diameter of 8.

Example 1°C: 0.058%, St: 2.95%, Mn: 0.08
3%ls゛0.025%, AtO, 025%, N:0.
About 100 PPM of MgO was coated on a boron-containing button to about 5 tons of primary recrystallized plate coil obtained by continuous casting sump full hot rolling, cold rolling and charcoal annealing treatment containing 0.008%. This coil was subjected to temperature gradient annealing in an atmosphere of 25% N and 75% H2.

The temperature increase rate is 50 Vhr from room temperature to 650°C, 6
The temperature ranged from 50 to 1200°C by 20°C/hr't''. In order to create a temperature gradient, a heating aid was placed around the outer circumference of the coil and the coil was heated from the top. The average of B8 was 1.975 Te5la.

Example 2°C: 0.062%, Si2.98%, Mn
20,075%, s:0.028%, A
Example 1 containing t: 0027%, N: 0.0082%
One of the two 5-ton coils obtained in the same manner as above was coated with MgO gold having a boron content of about 390 PPM, and the other 5-ton coil was coated with MgO gold with a boron content of about 1300 PPM.

These coils were subjected to temperature gradient annealing in a 100% N2 atmosphere in the same manner as in Example 1. Temperature gradient is approximately 5VcTr
The average of B8 in the area above L is 1.983Tes in the former
las latter is 1.967 Te5la is l = v fc
.

Example 3 C: 0.062%, St: 2.90%, Mn: 0
．． 071%, s: 0.026%, At: 0.026%,
A 10-ton coil was prepared by coating MgO gold with a boron content of about 390 PPM on a primary recrystallized plate obtained by completely hot rolling, annealing, and cold rolling a continuous E slab containing 0.008% N. This coil was subjected to secondary recrystallization annealing under a temperature gradient in a 100% N2 atmosphere. The temperature increase rate is 50Vhr from room temperature to 650'C.

The temperature was increased from 650°C to 1200°C at 15'C/hr.

In order to anneal the entire coil under a predetermined temperature gradient, the coil was raised during annealing. That is, until the upper end surface of the coil reaches the secondary recrystallization temperature, the upper end surface is submerged to the same height as the hearth, and then, when the upper end surface begins to undergo secondary recrystallization, the secondary recrystallization temperature is lowered. The coil was raised at a rate corresponding to the growth rate of the recrystallized grains. During this time, cooling gas was passed through the pace plate to remove heat from the bottom of the coil in order to create a temperature gradient.The temperature of the coil annealed in this way was 1050℃.
B8 in the area where the temperature gradient is about 35° CAJ or more
The average of is 1.985Teala T l(>7'c
.

FIG. 1O (a), (b) p (c) Ic The macrostructure of the secondary recrystallized grains according to the above embodiment is shown. (a) shows the outer periphery of the coil winding thickness, (b) shows the same at the center, and (c) shows the macro k]↓ weave at the inner periphery. Coil winding thickness outer periphery, center,
Inner chair! As can be seen, the grains generated at the upper end of the coil (upper side in the figure) grow linearly in the direction perpendicular to the rolling direction, and there are hardly any island grains. In such crystal grains, minute orientation fluctuations (the inclination of the [001] axis with respect to the rolled surface) caused by the coil set during secondary recrystallization annealing and the flattening annealing result in almost all A1: Imaginary changes in orientation. G0
An image close to 38 directions can be obtained.

[Brief explanation of drawings]

Figure 1 shows the relationship between crystal grains and crystal orientation when a primary recrystallization plate containing AtN 2f extruded phase is subjected to secondary recrystallization under a temperature gradient, and (a) shows the relationship between each crystal grain. (b) is the (100) pole figure of each crystal grain, the second
The figure shows the mode of heating from the top surface of the coil when performing secondary recrystallization annealing under a temperature gradient.
Figures 4(a) and 4(b) show an example of an apparatus for carrying out secondary recrystallization annealing and a cross section of the coil. Part of the macrostructure of the crystal grains of the coil and its corresponding BBO
Figure 5 (, ) is an enlarged view of the macrostructure in Figure 4 (b), Figure 5 (b) is its pole figure, and Figure 6 () is a diagram showing the values.
The figure shows the relationship between the annealing atmosphere and B8. Figure 7 shows the relationship between the boron content in the annealing separator MgO and B8. Figure 8 shows the annealing atmosphere and the boron content in the annealing separator MgO. Figure 9 shows the relationship between Ni- and B8 during secondary recrystallization, Figure 10 (a) (b) shows the relationship between the amount and BR.
) and (c) are diagrams showing the macrostructure of secondary recrystallized grains of the coil obtained in Example 3. Figure 1] 197= Broom 2 Figure 1 Be', LJ. Fig. 5 (αn$5 times (b) R・ρ.〃225% 76% Nz100 table 7th H pull Har β content 8th mouth

Claims (3)

[Claims] (1) C: 0.010-0.10%, Si: 2
．． 5-4.0%, acid-soluble At: 0.010-0.0
When hot rolling, cold rolling, decarburization annealing, and final annealing a silicon steel material containing 65% Fe and unavoidable impurities, the primary recrystallization region and the secondary recrystallization region of the final annealing are Unidirectionality with high magnetic flux density, characterized in that when secondary recrystallization annealing is performed while giving a temperature gradient to the boundary region, the nitrogen content in the steel plate is set to 130 to 200 PPM at the start of secondary recrystallization. Method of manufacturing silicon steel plate. (2) The method according to claim 1, wherein the secondary recrystallization annealing atmosphere contains 25% or more hydrogen and the remainder p hydrogen. (3) Add 800 PPM of B to the electromagnetic steel material before final annealing.
The method according to claim 1, wherein an annealing separator made of MgO, which will be referred to below, is applied.