JPH04224625A - Manufacture of grain-oriented high silicon steel sheet - Google Patents

Abstract

PURPOSE:To solve two problems required in the viewpoint of the manufacture of a steel sheet, to permit its hot rolling at a relatively low temp. and to obtain a product at low cost by specifying the heating conditions in a silicon steel slab having a specified compsn. before its hot rolling and executing nitriding treatment from the completion of its cold rolling to the start of secondary recrystallization at the time of its finish annealing. CONSTITUTION:A silicon steel slab constituted of, by weight, 4.8 to 7.1% Si, 0.015 to 0.055% acil soluble Al, <=0.0045% N and the balance Fe is hot-rolled, and after that, it is rolled, is subjected to primary recrystallization annealing, is coated with a separation agent for annealing and is subjected to finish annealing into a product. At this time, the heating of a slab before hot rolling is executed at a temp. T ( deg.C) for time (hour) prescribed by T<=1300-10t, and nitriding treatment is executed from the completion of its cold rolling to the start of secondary recrystallization at the time of its finish annealing. By this method, the two problems of 1) the formation of an inhibitor required at the time of secondary crystallization and 2) the security of rollability can be solved, and its rolling can be executed at a relatively low temp. at which a lubricating oil is usable at the time of cold rolling, so that a grain-oriented high silicon steel sheet can be manufactured at low cost.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing a grain-oriented high silicon steel sheet used as a soft magnetic material for iron cores of electrical equipment, etc. The present invention relates to a method for producing soft magnetic materials with unique magnetic properties.

0002

[Prior Art] The basic concept of grain-oriented electrical steel sheets is 19
It all started with the discovery of magnetic anisotropy in iron single crystals in 1926 (K. Honda, S. Kaya; Sci.R
ep. Tohoku Imp. Univ. 15 (19
26) p721). After that, N. P. Since a method for manufacturing grain-oriented electrical steel sheets was invented by Goss, grain-oriented electrical steel sheets have been greatly developed as a soft magnetic material (US Pat. No. 1,965,559).

[0003] Grain-oriented electrical steel sheets have crystal grains of {110}<
Unidirectional electrical steel sheet with 001> orientation, or {100
} A steel sheet consisting of crystal grains strongly oriented in a certain crystal orientation, such as a bidirectional electrical steel sheet with a <001> orientation. This steel sheet is required to have excellent magnetic excitation characteristics and iron loss characteristics, and for this purpose, it is important to (1) increase the degree of integration of crystal orientations and (2) add Si.

[0004] Integration of crystal orientation is achieved using a catastrophic grain growth phenomenon called secondary recrystallization. In order to perform secondary recrystallization industrially and stably, it is necessary to adjust fine precipitates or grain boundary segregation type elements called inhibitors before secondary recrystallization. The inhibitor has the function of suppressing grain growth of primary recrystallized grains and selectively growing grains with a certain specific orientation.

Research on inhibitors has been extensively conducted on silicon steel sheets containing 3% Si. Typical precipitate-type inhibitors include M. F. L
Ittmann (Special Publication No. 30-3651) and J. E. May, D. Turnbull used MnS, Taguchi and Sakakura (Special Publication No. 40-15644) used AlN, and Imanaka (Special Publication No. 51-13469) used MnSe.
, Komatsu et al. (Special Publication No. 62-45285) reported (Al
, Si)N.

On the other hand, regarding grain boundary segregation type elements, Saito et al. (Journal of the Japan Institute of Metals 27 (1963) P186/195
) suggests Pb, Sb, Nb, Ag, Te, Se, S, etc., but these are all used industrially only as supplementary substances to precipitate-type inhibitors. The conditions necessary for these precipitates to function as inhibitors are not necessarily clear, but Matsuoka (Tetsu to Hagane 5)
3 (1967) P1007/1023) and Kuroki et al. (Journal of the Japan Institute of Metals 43 (1979) P175/181, 44 (1980) P419/424), the following can be considered.

(i) The presence of a sufficient amount of fine precipitates to inhibit grain growth of primary recrystallized grains prior to secondary recrystallization. (ii) The size of the precipitates is large to some extent and does not change too rapidly during secondary recrystallization annealing. Currently, there are three typical manufacturing methods for unidirectional electrical steel sheets that are industrially produced:

The first technique is M. F. Littmann
The second cold rolling process using MnS as an inhibitor was disclosed in Japanese Patent Publication No. 30-3651 by Taguchi and Sakakura.
This technique is based on a process in which the final cold rolling reduction using AlN+MnS is strongly reduced to 80% or more, as shown in Publication No. 44.
This is due to the two-time cold rolling process using MnS (or MnSe) + Sb shown in the publication.

[0009] In all of these techniques, in order to ensure the amount of precipitates and satisfy the requirements for refinement, the basic technique is to create an inhibitor by heating the slab at a high temperature under hot rolling conditions. That is, the slab heating temperature is 1260°C or higher in the first technology, and 1260°C or higher in the second technology.
As shown in Publication No. 52, it varies depending on the amount of Si, but
In the case of 3% Si, the temperature is 1350°C or higher, and in the third technology, the temperature is 1230°C as shown in Japanese Patent Application Laid-Open No. 51-20716.
℃ or more, especially 132 in examples where high magnetic flux density can be obtained.
By annealing at an extremely high temperature such as 0° C., coarse precipitates are once dissolved, and then various precipitates are refined during hot rolling or by subsequent heat treatment.

On the other hand, when the amount of Si is increased, the magnetocrystalline anisotropy decreases, the specific resistance increases, and magnetic properties such as excitation characteristics and iron loss characteristics are improved. In particular, the amount of Si is approximately 6.5
It is widely known that when % is added, the magnetostriction becomes zero and the excitation characteristics are extremely improved. However, when the amount of Si is increased, the hardness increases and the elongation decreases (Bozor
th; Ferromagnetism (1951) P
77) In particular, steel sheets containing 4.8% or more of Si cannot be subjected to normal cold rolling and must be warm rolled.

It is a well-known fact from Japanese Patent Publication No. 35-18709 that the rollability of high-silicon steel sheets is improved by increasing the rolling temperature. However, the special public official
As stated in Publication No. 09, the temperature during rolling was set at 350~350°C.
In order to maintain the temperature at 425°C, the heat generated during rolling is insufficient, and a rolling machine with a built-in heating device is required. Furthermore, in the temperature range of 400°C or higher, the lubricating oil used during cold rolling cannot be used. Since this is not possible, the cost will be extremely high.

[0012] Therefore, from the viewpoint of economic efficiency, it is an important issue to be able to roll at least at 380°C or lower, at which lubricating oil can be used during cold rolling. Therefore, when designing the process for manufacturing grain-oriented high silicon steel sheets, (1)
forming the necessary inhibitor for secondary recrystallization, (2
) Ensuring rollability is an important issue.

[0013] When an inhibitor is formed by heating a high-temperature slab according to the prior art, the high-silicon steel plate has a large amount of Si, so it becomes an α single phase in this temperature range, and the grains grow large as it is solutionized. As a result, the grain size after hot rolling also increases, resulting in a significant deterioration in rolling properties. Takada et al.
In JP-A No. 63-26330, a conventional grain-oriented silicon steel sheet containing 3% Si is heated in an atmosphere containing SiCl4 to siliconize it, and then the non-uniformity of silicon concentration in the sheet thickness direction is investigated. In order to solve this problem, we have proposed a method of applying diffusion annealing. However, in this process,
There is a major cost problem due to the additional high-temperature, long-time annealing.

[0014]

[Problems to be Solved by the Invention] It is an object of the present invention to provide a process that solves the above-mentioned two problems necessary for manufacturing grain-oriented high-silicon steel sheets and can be manufactured at low cost. It is something to do.

[0015]

[Means for Solving the Problems] The gist of the present invention is as follows. (1) Si; 4.8-7.1% by weight, acid-soluble Al;
A silicon steel slab consisting of 0.015 to 0.055%, N≧0.0045%, balance Fe and unavoidable impurities is hot rolled, followed by rolling, primary recrystallization annealing, application of an annealing separator, and final annealing. In a method for producing grain-oriented high-silicon steel sheets, which are made into products by processing in each process, the slab is heated before hot rolling at a temperature T (°C) and a time t (hr) defined by the following inequality, and A method for producing a grain-oriented high silicon steel sheet, characterized in that a nitriding treatment is performed after cold rolling until the start of secondary recrystallization during final annealing.

T≦1300-10t (2) After hot rolling, 3
2. The method for producing a grain-oriented high-silicon steel sheet according to item 1 above, characterized in that annealing is performed for 0 seconds to 1 hour. The present inventors first learned from research on the rollability of high-silicon steel sheets that it is important to make the steel sheet before rolling have a small grain size and a uniform structure in the thickness direction.

Based on this knowledge, (1) the slab is heated at a low temperature to suppress grain growth, and (2) Al as a precipitate is
It has been found that by suppressing grain growth during hot rolling by utilizing N, the structure of the hot rolled sheet can be controlled and the rolling properties can be significantly improved. Therefore, under the above conditions that satisfy the requirements for rollability, it is essentially impossible to form an inhibitor by the above-mentioned high-temperature slab heating. Therefore, as a result of investigating various methods for strengthening the inhibitor required for secondary recrystallization, it was found that it is effective to strengthen the inhibitor by nitriding after cold rolling. Through these steps, we found conditions that achieve both (1) securing rollability and (2) securing the inhibitor necessary for secondary recrystallization.
invented the present invention.

The present invention will be explained in detail below. Si;6
．． 6%, acid soluble Al; 0.027%, N; 0.007
%, Mn; 0.16%, S; 0.007%, C; 0.0
1%, the remainder substantially Fe
After annealing at 400°C for 1 to 10 hours, hot rolling is performed.2.
It was made into a hot-rolled plate with a thickness of 3 mm. This steel plate was warm rolled at 250°C to have a thickness of 0.3 mm. Figure 1 shows the relationship between slab heating conditions and rollability. It can be seen from FIG. 1 that rollability is good within the range of T≦1300-10t for heating temperature T (° C.) and heating time t (hr).

When the structure of the steel plate cracked during rolling was investigated immediately after slab heating, it was found that the grains had become significantly larger. This is considered to be because the precipitated AlN present in the slab becomes a solution and loses its ability to inhibit grain growth. Next, in order to examine the influence of precipitates, Si;
6.6%, C; 0.005%, Mn; 0.16%, S;
0.007%, acid-soluble Al; 0.005-0.300
, N; 0.001 to 0.011, the remainder being substantially Fe. After heating the slab at 1200°C for 1 hour, 2.3 m
It was made into a hot-rolled plate with a thickness of m. This hot-rolled plate was warm rolled at 250°C to have a thickness of 0.30 mm. Figure 2 shows the components (Al, N
) shows the relationship between rollability and rollability. From FIG. 2, acid-soluble Al; 0.
0.015% or more, N: 0.0045% or more shows that the rollability is good.

As mentioned above, by effectively utilizing the precipitated AlN and keeping the slab heating conditions within an appropriate range, 1.
It became possible to easily roll at a rolling temperature of 20 to 380°C. Furthermore, rolling properties are improved by heat-treating this hot-rolled sheet in a temperature range of 800 to 1100°C for 30 seconds to 1 hour.

FIGS. 3 to 5 show changes in the structure in the thickness direction due to heat treatment. As can be seen from this figure, the hot-rolled sheet has a two-layer structure, with the surface part having a recrystallized structure and the center part having a processed structure. In such a two-layer structure, each layer has different deformability, so cracks may occur starting at the boundary. By heat-treating a hot-rolled sheet at a temperature of 800° C. or higher, the processed structure in the center recrystallizes, becoming a uniform structure in the thickness direction, and improving rolling properties. In addition, the annealing temperature is 110
If the temperature exceeds 0°C, the texture becomes random as shown in FIG. 6, making it difficult for secondary recrystallization to occur.

FIG. 7 shows acid-soluble Al; 0.0265%;
N; 0.0080%, acid-soluble Al; 0.002 in Figure 8
3%, N; 0.0025% hot-rolled sheet annealed at 980° C. for 30 seconds. From FIGS. 7 and 8, it can be seen that the plate containing the ingredients within the range of the present invention (FIG. 7) has a small and uniform crystal grain size. Based on the above results, Si; 6.6%;
Acid soluble Al; 0.035%, N; 0.008%, Mn
;0.16%, S;0.008%, C;0.004%,
The slab, the remainder of which essentially consisted of Fe, was heated at 1200° C. for 1 hour and then hot rolled to form a hot rolled sheet with a thickness of 2.0 mm. This hot-rolled plate was annealed at 1000°C for 2 minutes, and then
Warm rolling was carried out at 0° C. to give a final thickness of 0.30 mm. 7
Primary recrystallization annealing was performed at 80°C for 2 minutes in wet hydrogen gas,
Next, after applying an annealing separator containing magnesia as a main component, finish annealing was performed at 1200° C. for 10 hours, but no secondary recrystallization occurred. This is considered to be because a sufficient amount of the inhibitor was not secured because high-temperature slab heating to make AlN into a solution was not performed.

[0023] As a result of examining various methods of strengthening the inhibitor, it was found that strengthening the inhibitor by nitriding is effective. That is, the same primary recrystallization plate as above was subjected to nitriding treatment in an atmospheric gas containing ammonia. At that time, the amount of nitridation was varied depending on the ammonia content. Next, after applying an annealing separator containing MgO as a main component, finish annealing was performed.

FIG. 9 shows the relationship between the amount of nitridation and the magnetic flux density (B8 value) of the product. As is clear from Fig. 9, by nitriding the steel plate so that the nitrogen content of the steel plate is 0.005% or more, preferably 0.01% or more, the growth of primary recrystallized grains is suppressed and secondary recrystallization is performed. do. Next, embodiments of the present invention will be described. The molten steel used in the present invention may be produced by any method such as a converter or an electric furnace, but the following content ranges as components are essential.

[0025] The Si content is mainly 6.5% because the goal of the present invention is to establish a process for industrially manufacturing high-silicon steel sheets containing approximately 6.5%, which has the maximum magnetic permeability. It suffices if it is within a range with some width. The lower limit of the amount of Si is 4.8%, which is not conventionally available on the market, and the upper limit is 7.1%, beyond which the magnetic properties deteriorate. acid soluble A
L combines with N to form precipitates, which suppresses the growth of crystal grains during slab heating, hot rolling, and hot rolled sheet annealing, thereby improving rollability. In addition, by applying nitriding treatment after rolling,
Before the secondary recrystallization, AlN and (Al, Si)N are formed to ensure the amount of inhibitor required for the secondary recrystallization. From the point of view of rolling properties, acid-soluble Al is required to be 0.15% or more,
Since 0.12 to 0.55% is necessary from the point of view of secondary recrystallization, the limited range is set to 0.015 to 0.055% in consideration of both.

As mentioned above, N combines with Al to improve rolling properties. In order to obtain this effect, the molten steel must be 0.
It is necessary to contain 0.045% or more. Regarding C, H. C. Fiedler (Journal
of Iron and Steel In
Institute (1967) P158/160) reported that rolling properties are improved by adding them, but in the present invention, when microstructure is controlled by utilizing precipitates and slab heating conditions, , turned out to be rather harmful. Rollability is improved by preferably controlling C to 0.025% or less.

[0027] Here, the slab heating is performed at T≦1300-10t.
One of the requirements of the present invention is to carry out the test under these conditions. If the slab is heated at too low a temperature, the shape of the steel plate will deteriorate, so it is desirable to heat the slab at a temperature of 1000° C. or higher. The hot-rolled sheet is rolled immediately or after a short annealing step to obtain the final thickness. This short time annealing is carried out at 800-1100℃.
Rollability is further improved by applying the rolling in a temperature range of 30 seconds to 1 hour.

[0028] In the present invention, rolling is carried out at 1
It is necessary to carry out the process in a temperature range of 20 to 380°C. When this warm rolling is performed to a reduction rate of about 70%, subsequent rolling can be performed at room temperature. In order to obtain the texture necessary for secondary recrystallization, the final rolling reduction of 80% or more is basically required for unidirectional electrical steel sheets as disclosed in Japanese Patent Publication No. 15644/1973. In addition, for bidirectional electrical steel sheets, basically the
It is necessary to apply the cross rolling method disclosed in Japanese Patent Publication No. 57 or Japanese Patent Publication No. 38-8218.

[0029] This steel plate is subjected to primary recrystallization annealing in a temperature range of 700 to 900°C, coated with an annealing separator, and final annealed for the purpose of secondary recrystallization and purification. At that time, one of the requirements of the present invention is to perform the nitriding treatment after the rolling process and before the appearance of secondary recrystallization during final annealing. There are no particular limitations on the nitriding method. Conventional techniques include mixing nitrogen gas into the atmosphere gas during final annealing, nitriding using a gas with nitriding ability such as ammonia, and separating metal nitrides with nitriding ability such as manganese nitride and chromium nitride by annealing. A method such as adding it to a drug can be used.

[0030]

[Example] Example 1 By weight, Si: 5.5%, acid-soluble Al: 0.027%,
N; 0.007%, Mn; 0.16%: S; 0.007
%: Contains C; 0.004%, the remainder is substantially Fe.
After annealing the slab at 1300°C and 1150°C for 3 hours, it was hot rolled to a thickness of 1.6 mm. Then at 900℃ 2
It was annealed for minutes and warm rolled to 0.5 mm at a temperature of 220°C. It was then cold rolled at room temperature to a final thickness of 0.20 mm. This cold-rolled sheet was annealed at 800°C for 2 minutes in a wet hydrogen atmosphere, and then annealed at 800°C for 2 minutes in an ammonia atmosphere.
Nitriding treatment was applied. When I checked the nitrogen increase amount, it was 0.02%.
Met. MgO was applied as an annealing separator and 1200
Finish annealing was performed at ℃ for 10 hours.

[0031] The material subjected to slab heating at 1300°C cracked during warm rolling, and samples could not be taken. Slab heating 1
The material at 150° C. underwent secondary recrystallization, and the magnetic flux density was 1.65 Tesla (B8 /Bs ~ 0.9; Bs is the saturation magnetic flux density) as a B8 value. Example 2 By weight Si: 6.5%, acid soluble Al: 0.035%,
N; 0.006%, Mn; 0.15%, S; 0.007
%, C: 0.02%, and the remainder substantially consisted of Fe. The slab was annealed at 1200° C. for 1 hour, and then made into a hot rolled sheet with a thickness of 1.6 mm. This hot-rolled sheet is heated to 1000℃ as it is.
After annealing for 2 minutes at 270° C., the material was rolled to a thickness of 0.7 mm, and then cross-rolled in the right angle direction to a thickness of 0.35 mm. This cold-rolled sheet was subjected to primary recrystallization annealing at 780° C. for 2 minutes in a wet hydrogen atmosphere. After that, apply an annealing separator and
Finish annealing was performed at 0°C for 10 hours. At that time, 5% ferromanganese nitride was added to the annealing separator for the purpose of nitriding. The results are shown in Table 1.

[0032]

[Table 1]

[0033]

[Effects of the Invention] According to the present invention, when designing a process for producing grain-oriented high silicon steel sheets, it is possible to (1) form an inhibitor necessary for secondary recrystallization, and (2) ensure rollability. It is possible to provide a process that can solve these two problems and produce grain-oriented high-silicon steel sheets at low cost.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between slab heating temperature, time, and rollability.

FIG. 2 is a diagram showing the relationship between the amount of acid-soluble Al and N in steel and the rollability.

FIG. 3: Acid-soluble Al: 0.0265%, N: 0.00
This is a photograph of the metallographic structure of a cross section of an 80% hot-rolled sheet.

．．

[Figure 4
] Acid-soluble Al: 0.0265%, N: 0.0080%
It is a photograph of the metallographic structure of a cross section of a hot-rolled annealed plate (annealed at 830°C).

FIG. 5: Acid-soluble Al: 0.0265%, N: 0.00
This is a photograph of the metallographic structure of a cross section of an 80% hot-rolled annealed plate (annealed at 900°C).

FIG. 6 is a diagram showing changes in texture due to annealing of a hot rolled sheet.

FIG. 7: Acid-soluble Al 0.0265%, N; 0.008
It is a photograph of the metallographic structure of a cross section after 0% hot-rolled sheet annealing.

FIG. 8 Acid-soluble Al: 0.0023%, N: 0.00
It is a photograph of the metallographic structure of a cross section after 25% annealing of a hot rolled sheet.

[Figure 9] Nitrogen increase amount due to nitriding treatment and magnetic flux density of product (B
FIG. 8 is a diagram showing the relationship between

Claims (2)

[Claims] Claim 1: Si: 4.8-7.1% by weight, acid-soluble Al: 0.015-0.055%, N≧0.004
A silicon steel slab consisting of 5% iron, the balance being Fe and unavoidable impurities is hot-rolled, and then processed through the following steps: rolling, primary recrystallization annealing, application of an annealing separator, and final annealing. In the manufacturing method of silicon steel sheets, the slab is heated before hot rolling at a temperature T (
C) and time t (hr), and the nitriding treatment is performed after cold rolling until the start of secondary recrystallization during final annealing. T≦1300-10t 2. The method for producing a grain-oriented high silicon steel sheet according to claim 1, wherein after hot rolling, annealing is performed at a temperature range of 800 to 1100° C. for 30 seconds to 1 hour.