JPS59185725A - Production of grain-oriented electrical steel sheet having excellent magnetic characteristic - Google Patents

Abstract

PURPOSE:To produce a grain-oriented electrical steel sheet having an excellent magnetic characteristic by controlling the oxygen content in a steel sheet formed by hot rolling, annealing, cold rolling and decarburization annealing of a silicon steel slab to a specific content then subjecting the sheet to high temp. finish annealing. CONSTITUTION:A silicon steel slab contg. 0.02-0.12% C, 2.5-4.0% Si, 0.03- 0.20% Mn, 0.01-0.05% S, 0.01-0.05% solAl and 0.004-0.012% N or contg. further <=1.5% in total of 1 or >=2 kinds among Cu, Sn, Cr, Ni, Mo, V, B is hot rolled to a plate material and is subjected to annealing and a quick cooling treatment prior to final cold rolling and thereafter the plate material is subjected to final cold rolling under high rolling-down at >=80% draft. The rolled material is then subjected to decarburization annealing and high temp. annealing by a temp. elevation in an H2 atmosphere contg. N2, by which a grain-oriented electrical steel sheet is produced. The oxygen content in the steel sheet after the decarburization annealing is controlled to the range shown by the formulas (1)-(2), by which the magnetic characteristic of the electrical steel sheet is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a unidirectional electrical steel sheet with excellent magnetic properties.

Unidirectional electrical steel sheets are soft magnetic materials that are mainly used as core materials for transformers and other electrical equipment, and must have good magnetic properties in terms of excitation properties and iron loss properties. In order to obtain good magnetic properties, the axis of easy magnetization (0
01) It is important to align the axes highly in the rolling direction. In addition, plate thickness, crystal grain size, specific resistance, surface coating, etc. have a significant influence on magnetic properties.

The directionality has been greatly improved by the method of using AAN and MnS as inhibitors in the final cold rolling under heavy reduction, and now products with magnetic flux density of about 96% of the theoretical value are manufactured. I came.

Along with this, iron loss has improved significantly.

On the other hand, reflecting the rise in energy prices in recent years, transformer manufacturers are increasingly turning to low core loss materials as materials for energy-saving transformers. Amorphous and 6.5% St steel are being developed as low iron loss materials, but many problems still remain to be solved before they can be used as commercial materials for transformers.

The inventors of the present invention have repeatedly conducted various studies on reducing the iron loss of unidirectional electrical steel sheets in order to meet the needs of the times for low iron loss materials. As a result, a silicon steel slab containing At and N was hot rolled, annealed and rapidly cooled before final cold rolling, and a rolling reduction of 8
After decarburization annealing in the production of unidirectional L'' magnetic steel sheets, the final cold rolling is carried out under strong pressure on 01 L, followed by decarburization annealing, followed by high temperature finish annealing by raising the temperature in an H2 atmosphere containing N2. It has been found that iron loss can be significantly improved by controlling the oxygen content of steel sheets within a certain range.

The present invention will be explained in detail below. First, we will discuss based on experimental data.

C: 0.075%, St: 3.25%, Mn: 0
．． 070, S: 0.024%, acid soluble HT (hereinafter 5
otAt): 0.026%, N: 0.008
5%, Cu: 0.08%, Sn: 0.12% by high temperature slab heating and hot rolling.
% thickness, this hot rolled sheet is annealed, then rapidly cooled after annealing, and then 0.225Y, 0.260%.
, 0.285%. In the decarburization annealing of cold-rolled sheets, the annealing temperature was 840°C in total, the annealing atmosphere was a wet hydrogen atmosphere, the dew point of the atmosphere and the annealing time were varied, and the oxygen content was varied in the range of approximately 400 PPM to 1000 PPM. A decarburized annealed plate was obtained. Incidentally, the oxygen content of the hot coil was about 20 PPM. These decarburized annealed plates were coated with an annealing separator mainly composed of MgOi, and then heated in an atmosphere of 75% H2 and 25% N2.
The temperature was raised to 1200°C at a rate of 0°C/hr, and then H2
Finish annealing was performed in an atmosphere for 20 hours.

After annealing, the annealing separator was removed and the surface glass film was observed. The glassy surface coatings were all good. Thereafter, the magnetic properties were measured, the surface glass film was removed, and the macrostructure of the product was observed. Figure 11 shows the results of iron loss measurement and macrostructure observation.

In FIG. 1, the horizontal axis is the oxygen content of the decarburized plate, and the vertical axis is the iron loss value (Wl 7/sG ) of the product. In other words, it has been found that there is a close relationship between the oxygen content and the iron loss value, and that there is an optimum oxygen content that makes the iron loss value the best. @The appropriate oxygen content shows different values depending on the thickness of the material, cold rolling thickness O: 225%.

The optimal oxygen content at 0.260% and 0.285% is approximately 7'50 PPM, 650 PPM, and 6, respectively.
00 PPM was 0. In addition, the O and X marks in FIG. 1 indicate the results of macroscopic observation of the product. The mark ○ means good secondary recrystallization, and the mark X means poor secondary recrystallization. 7. A on the curve showing the oxygen content and iron loss value in Figure 1.
1. ' HA 2 r A 3 This is the critical point where secondary recrystallization defects occur. B 1 + B 2 1 B
3 points have good secondary recrystallization and iron loss is 10% of the best value.
The points of increase o al +a2 +a3 and bt
, bz +ba point is a point where the iron loss increases by a factor of 5 with respect to the best value. If each point is plotted on a coordinate system with the board thickness on the horizontal axis and the oxygen content on the vertical axis, the result will be as shown in Figure 2.

As is clear from Figure 2, the fish school (AI r A2 +
A3) I(Bl, B2 +B3
)+(al +aZ ya3)+(b
I, b, , +t)3) are approximately straight lines I, I[
.

I[[, is plotted on IV. That is, EW line 1
.

In the region between (2), the secondary recrystallization is good and the iron loss value is 10% higher than the good quantity value and becomes a good value. Further straight line 111. In the region between IV, the iron loss value becomes a very good value, which is less than the 5th factor increase of the best value.

X = Thickness of steel plate ('X), Y = Oxygen content of decarburized plate (P
PM), the straight line 1. The area sandwiched by II is expressed by the following formula % Formula % (1) The area sandwiched by straight lines ■ and ■ is expressed by the following formula.

-2500X+1213<Y≦-2500X+1363
...(2) The present invention is constructed based on this knowledge, and its gist is that C: 0.02
~0.12%, St: 2.5~4.0%, Mn:
0.03-0, 20%, S: 0.01-0.
05%, actAto, O1~0.05%, N
: Contains 0.004~0012C, and further C if necessary.
u + Sn + Cr, Ni + Mor V
.

A silicon steel slab containing a total of 15% rejection of one or more of B glazes is hot-rolled, and before the final cold rolling, annealing and one rapid cooling treatment are performed, and the final cold rolling is performed with a strong reduction of 80 factors or more. conduct,
In the production of unidirectional electrical steel sheets that undergo decarburization annealing and then high-temperature finish N'7 annealing in which the temperature is raised in an N2 atmosphere containing N2, in order to obtain good magnetic properties, the final cold rolled sheet thickness is The present invention provides an excellent patented method for manufacturing grain-oriented electrical steel sheets, which is characterized in that the oxygen content of the decarburized plate is controlled within the range of the above formula (1), more preferably within the range of the above formula (2).

The present invention is applied to a high magnetic flux density unidirectional electrical steel sheet utilized as a main inhibitor of ALNi. Uniform,
The finely precipitated A7J is N2 containing N2 from high-temperature finish annealing.
It is thought that during the temperature raising process in the atmosphere, the growth of normal primary recrystallized grains is suppressed, and it contributes to the development and growth of secondary recrystallization of the (110) (001) force potential with a high degree of integration. Quantitative secondary recrystallization mechanism in the context of AtN,
Theoretical elucidation will have to wait for future research, but it appears that during the temperature rising process of AtNFi high-temperature finish annealing, the inhibitor effect is exerted while being influenced by the atmosphere consisting of N2 and N2. After that, it is thought that through the agglomeration process, it will eventually decompose and the [N] component will be released outside the steel base.

In the case of the unidirectional electrical steel sheet of the composition according to the present invention, most of the oxygen content in the decarburized annealed sheet exists in the surface layer portion as an oxide of Si+At+Fe and the like. This surface oxidation layer becomes a wall between the internal part of the steel sheet and the atmosphere consisting of N2 and N2 during the temperature rising process of high-temperature finish annealing, and is thought to have a considerable influence on the reaction between the steel sheet and the atmosphere. .

Product samples corresponding to ■, @, and θ in Figure 1 (hereinafter samples ■,
Fig. 4 shows the macrostructure of the ferrite (referred to as @, θ). This fourth
As is clear from the figure, fine grains were observed in sample ①, and samples @ and θ were recrystallized to the 100th order of magnitude. Compared to sample @, the size of crystal grains in sample θ was almost the same, but
It was observed that the grain boundaries were monotonous and the grain shape tended to be round.

Table 1 shows the G flux density B1o values of samples ■, @, and O. From this table, it is recognized that sample @ is also superior in magnetic flux density B1o.

Sample ■ in Table 1 is considered to have poor iron loss due to poor overall directionality due to the inclusion of fine grain gold. Although sample θ underwent 100-coefficient secondary recrystallization, it is thought that the degree of integration of the (110)[001] orientation was inferior to that of sample @ by 2i·li, and the iron loss was correspondingly poor.

Next, in order to examine the cause of the difference in the secondary recrystallization situation mentioned above, a decarburized annealed plate similar to the points ■, @, and θ in Fig. 1 was prepared separately, and an annealing separator was applied to it. 7 5% 10N22
Heating at a heating rate of 20°C/hr in a 5% atmosphere,
The material phase 0AtN when the temperature reached 00°C and 1000°C was analyzed. The analysis results are shown in Figure 3. As is clear from Fig. 3, AtN during high-temperature finish annealing is affected by the oxygen content of the decarburized plate.
was found to be changing. Although the relationship between the oxygen content of the decarburized plate and the increase in AtN during high-temperature finish annealing is not clear, it is likely that when the oxygen content is high, the surface oxide layer becomes slightly porous and the increase in high-temperature finish annealing increases. A large amount of nitrogen is absorbed into the steel plate from the atmosphere in a warm environment, At
This probably indicates a tendency for N to increase.

From the above, when the oxygen content of the decarburized plate is appropriate (in the case of sample @), the amount of nitrogen absorbed from the atmosphere during the temperature rise during high-temperature finish annealing is appropriate, and AtN as an inhibitor.
works most effectively, and secondary recrystallization with a high degree of accumulation of (110)[001:] orientations is obtained, but if the oxygen content is less than the appropriate amount (in the case of sample ■), the temperature increase during high-temperature finish annealing is It is thought that nitrogen absorption during the process is insufficient, the inhibitor effect of AtN is insufficient, and the normal primary recrystallized grains progress to grow and become fine grains. If the oxygen content is higher than the appropriate amount (
In the case of sample θ), there is a large amount of nitrogen absorption during the temperature rise during high-temperature finish annealing (it was mentioned above that A7N also increases, but it is still unclear whether this is the cause of secondary recrystallization with slightly poor directionality). -There is C.

Further, the influence of the oxygen content of the decarburized sheet on the secondary recrystallization is not only due to the change in AtN during the heating during high-temperature finish annealing as described above, but also due to the oxide itself near the surface layer of the steel sheet. However, we will have to wait for further research into this mechanism.

Next, we will discuss the reasons for determining the component ranges. C is 0.0
If it is less than 2%, secondary recrystallization will be poor, and if it exceeds 0.12%, it will be unfavorable in terms of decarburization and magnetic properties. Si
A good iron loss cannot be obtained when the steel is less than 2.5 inches, and when it exceeds 4 inches, the cold-rolled steel deteriorates significantly.

Mn and S are elements necessary to form MnS, and the appropriate amount of Mn to obtain a suitable inhibitor effect is 0.03 to 0.20 degrees, and preferably 0.05 to 0.00 degrees.
It is 15%. If S is less than 0.01, a sufficient inhibitor effect cannot be obtained, and if it exceeds 0.05, desulfurization during purification annealing becomes difficult, which is not preferable.

When 5oLAt is less than 0.01%, a sufficient AtN effect cannot be obtained, and when O and O' exceed 5%, secondary recrystallization becomes unstable. If N is less than 00004%, a sufficient AtN effect cannot be obtained, and if it exceeds 0.012'J, blisters will occur.

Furthermore, if necessary, in addition to the above elements, Cu g Sn +
One or more elements known to have inhibitory effects, such as Cr r Nip Mor V r B, may be included alone or in the form of a compound.

The upper limit of the total content at this time is 1.5 parts.

If this upper limit is exceeded, cold rolling properties and decarburization properties will deteriorate.

The upper limit of the content of each element is Cu + Sn, Cr
, for NirMo + V, it is section 0.3, and for B, it is section 0.01. When the upper limit values for each element are exceeded, hot-rollability, pickling properties, cold-rollability, and decarburization properties deteriorate, resulting in poor workability.

A silicon steel slab made of the above components is heated to a predetermined temperature,
It is hot rolled and subjected to annealing and quenching treatments before final cold rolling. These are A! Known conditions for grain-oriented electrical steel sheets with Ni as the main inhibitor are employed.

In the final cold rolling, strong reduction cold rolling is carried out at a rolling reduction of 80. This is because it is difficult to obtain excellent magnetic properties if the rolling reduction is low.

The steel sheet is then subjected to decarburization annealing, where the oxygen content of the steel sheet is inversely controlled in relation to the thickness of the steel sheet, as described above. This control is performed by changing the dew point of the annealing atmosphere, the annealing time, and the composition of the atmospheric gas. For example, dew point I'i5
'O~75°C, annealing time is 1~6 minutes. After that, an annealing separator is applied, dried, and finish annealed.

By the way, several techniques have been disclosed to completely regulate the oxygen basis weight of a decarburized plate of a unidirectional foundation steel plate.

These are all related to the formation of an insulating film,
This is different from the present invention.

For example, the invention described in JP-A-55-65367 relates to a method for forming a forsterite insulating film.
* Cor Nir Cr + Zn + Mg r
A nitrate aqueous solution containing one or more types of Mn yAt is applied and decarburized annealed to give an oxygen basis weight of 1.0 to 2,097 m.
2, an oxide film mainly consisting of SrO2 and fayalite is formed, then an annealing separator is applied, and a final annealing is performed to improve the forsterite insulating film.
This is a technology for improving the forsterite insulation coating 4, which is based on applying a sulfate aqueous solution prior to decarburization annealing.
``The basic idea is different from the present invention, which concerns a method for improving iron loss of unidirectional electrical steel sheets used as f-inhibitors.In addition, the invention described in JP-A-55-110726 uses high This relates to a method for forming an insulating film on a magnetic flux density unidirectional silicon steel sheet, in which the oxygen basis weight is set to O17 to 2.8 g/m2 by decarburization annealing to an FC steel sheet,
This is a technology for improving glassy coatings, which consists of applying an MgO-based annealing separator and annealing for a long time at a specific temperature of 800 to 920°C by introducing an inert neutral gas.
Concerning a method for improving iron loss of a unidirectional electrical steel sheet that does not contain b2, does not require long-term secondary recrystallization annealing at a temperature range of 800 to 920°C, and has an inherently good glassy coating, and utilizes AtN as an inhibitor. The basic idea is different from the present invention.

Furthermore, the invention described in JP-A No. 56-72178 is a method for forming a forsterite insulating film, and when an annealing separator is applied and final annealing is performed, the amount of oxygen permeable in the subscale and the applied amount of the annealing separator are specified. With the quantitative relationship of
This technology aims to improve the forsterite insulating film, and it is a technology that aims to improve the forsterite insulating film.
The basic idea is different from that of the present invention, which is concerned with improving the iron loss of unidirectional electrical steel sheets using the present invention as an inhibitor.

Next, examples of the present invention will be described.

Example I C: 0.060%, Si: 3.00%, Mn: 0
．． 085 section, S: 0.025 section, 5otAt: 0.0
Section 28, a silicon steel slab containing N: 0.0080% and other trace amounts of unavoidable elements is finished into a 23% thick hot-rolled plate, and this hot-rolled plate is annealed at 1130°C for 4 minutes, rapidly cooled after annealing, and then cooled. It was cold rolled to a rolling thickness of 0.260'X and 0.285%. The obtained cold-rolled sheets were decarburized and annealed at 850° C. while changing the dew point of the wet hydrogen atmosphere and the annealing time. After decarburization and dulling M
Apply an annealing separator mainly containing gO, H75%, 'N2
1200℃ at a rate of 25℃/hr in a 25% atmosphere
After that, purification annealing was performed for 2.0 hours in an H2 atmosphere. The magnetic properties of the product were as follows.

Cold rolled plate thickness Oxygen of decarburized plate W1715oB1o
Notes (Mn) Content (PFM) (W#)
(T) ○ mark: Invention 0.260 460
1.18 1.86〃670 0.98 1.
95 0tt 740 1.
01 1.93 0tt 83
0 1.10 1.880.285 4
00 1.20 1.84p 47
0 1.05 1.94 0tt
600 0.99 1.96 0
// 780 1.12 1
．． 87 Example 2 C: 0.074%, Si: 3.25%, Mn: 0,
075 section, S: 0.025 section, 5otA1.
: 0.0 2 6 壬, N : 0.0083%
, Cu:0.08%, Sn20.
A silicon image slab containing 12% and other trace elements is finished into a 2.3% thick hot rolled plate and hot rolled i'11120
Annealed at ℃ for 4 minutes, rapidly cooled after annealing, and then cold-rolled to a thickness of 0.
It was cold rolled to 225% and 0.260%. The obtained cold-rolled sheet was decarburized and annealed at 840° C. for 4 minutes in a wet hydrogen atmosphere with different fog points. MgO after decarburization and sintering? The main annealing separator was applied and heated at 20℃/in an atmosphere of 80% N2 and 220% N2.
The temperature was raised to 1200° C. at a rate of 200° C., and then purification annealing was performed in an H2W atmosphere for 20 hours. The magnetic properties of the product were as follows.

0.225 500 1.15 1.851/
660 0.88 1.94 0, l'
750 0,84 1.95 0p,,
890 0.96 1.900.260
470 1.13 1.871/ 640
0.94 1.95 0/l 750
1.02 1.92 0// 870
1.08 1.89

[Brief explanation of drawings]

The first section is the iron loss W, 7/, due to the oxygen content of the decarburized plate. Figure 2 is a diagram showing the measurement results of the macrostructure.
Figure 3 shows the relationship between the plate thickness and the acid purple content of the decarburized plate in the present invention based on the figure.
Figure III, p. 4 showing the change in tN is a diagram showing the macrostructure of the sample. Figure 2 □ Solitary confinement (m/m) Figure 3 ￥4 meters 9θθ
lθθθ Tightness (0C) Figure 4 (a) Continued from page 1 0 Inventor: Osamu Tanaka To Kitakyushu City, Nippon Steel Corporation Production Technology Laboratory, 1-1-1 Edamitsu, Hatto-ku

Claims (3)

[Claims] (1) C: 0.02-0.12%, Si: 2.5
~480%, Mn: 0.03~0.20%, S
: 0.01~0.05%, acid soluble At: 0.01~
0.05%, N: 0.004 to 0.012% ffi, the balance Fe and trace amounts of unavoidable elements are hot-rolled, and before the final cold rolling, annealing and quenching treatment are performed, followed by rolling. In the production of unidirectional electrical steel sheets, which are subjected to final cold rolling under strong reduction of 80% or more, decarburized annealing, and then high-temperature finishing annealing in which the temperature is raised in an H2 atmosphere containing N2, A method for manufacturing a patented magnetic steel sheet characterized by controlling the oxygen content of the i-sheet within the range given by the following formula. -2 5 0 0X+1 1 6 3<Y≦-2500
X+1413 However, X-thickness of the steel plate (X), Y-oxygen content of the steel plate (PPM). (2) C: 0.02-0.1 2%, St: 2.5-4
．． 0 Chi, Mn: 0.0 3~0.2 0
%, S: 0.01-005%, acid-soluble At: 0.
01-0,05 ratio, N: 0.04-0, 012%'e included, and further Cu + Sn + Cr r NirMo
, V , B type 1 trench 2i71j top is 1 in total
．． A silicon-copper slab containing 5 strips or less is hot rolled, annealed and quenched before the final cold rolling, final cold rolled with a strong reduction of tx80% J; 1, followed by decarburization annealing. N2
In the FA construction of grain-oriented electrical steel sheets, which undergoes high-temperature finish annealing externally in a H2 atmosphere containing decarburization g. A method for producing a grain-oriented electrical steel sheet with excellent ω-feelability, characterized by controlling the oxygen content of a copper sheet after E-blurring to a range given by a total order equation. -2500X+1 163<:Y<-2500X+14
1'3 However, X - the thickness of the silver plate (in ), Y - the oxygen content of the copper plate: (PPM). (3) The method according to claim 1, wherein the oxygen content of the steel sheet after decarburization annealing is within the range expressed by the following formula. -2500X+1213<Y<-2500X+1363
(4) The method according to claim 2, wherein the oxygen content of the intercalary plate after decarburization annealing is ≦6. -z5oox+1zx3<y<-2soox+1363