JPH0689405B2 - Method for manufacturing unidirectional electrical steel sheet with high magnetic flux density - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a grain-oriented electrical steel sheet used as an iron core of an electric device as a soft magnetic material.

(Prior Art) A grain-oriented electrical steel sheet is usually composed of crystal grains having {110} <001> orientation (so-called Goth orientation) in Miller index.
A steel plate having a thickness of 0.10 to 0.35 mm and containing 4.5% or less of Si. This steel sheet is required to have excellent magnetic excitation characteristics and iron loss characteristics, and for that purpose, it is important to highly align the crystal grain orientation with the Goss orientation. The extremely high integration in the Goss orientation is achieved by utilizing a catastrophic grain growth phenomenon called secondary recrystallization.

In order to control the secondary recrystallization, it is essential to adjust the primary recrystallization structure before the secondary recrystallization and the adjustment of fine precipitates or grain boundary segregation type elements called inhibitors.
This inhibitor has a function of suppressing the growth of primary recrystallized grains other than the Goss orientation in the primary recrystallized structure and selectively growing the Goss oriented grains.

Typical examples of the precipitate include MFLittmann (Japanese Patent Publication No. Sho 30-3651) and JEMay, D. Turnbull (Trans.
Met.Soc.AIME212 (1958 No. p769 / 781) is MnS, Taguchi,
Itakura (Japanese Patent Publication No. 40-15644) uses AlN, Imanaka et al. (Japanese Patent Publication No. 51-13469) uses MnSe, Komatsu et al. (Japanese Patent Publication No. 62-452).
No. 85) presents (Al, Si) N.

On the other hand, as the grain boundary segregation type element, Saito et al. (Journal of the Japan Institute of Metals 27 (1963) p186 / 195) proposed Pb, Sb, Nb, Ag, Te, Se, S, etc. All of them are merely used as an adjunct to precipitate-type inhibitors.

Although the conditions necessary for these precipitates to function as inhibitors are not always clear, Matsuoka (Iron and Steel 53 (1967) p1007 / 1023), Kuroki et al.
43 (1979) p175 / 181,44 (1980) p419 / 424) can be summarized as follows.

(I) The presence of fine precipitates in an amount sufficient to suppress grain growth of primary recrystallized grains before secondary recrystallization.

(Ii) The size of the precipitates is large to some extent and does not change so rapidly during secondary recrystallization annealing.

Currently, there are three types of typical methods for producing unidirectional electrical steel sheets that are industrially produced.

The first technique is a double cold rolling process using MnS disclosed in Japanese Patent Publication No. Sho 30-3651 by MF Littmann, and the second technique is Japanese Patent Publication No. 40-1564 by Taguchi and Itakura.
The final cold rolling rate using AlN + MnS disclosed in Japanese Patent No.
The third technique is a double cold rolling process using MnS (or MnSe) + Sb disclosed in Japanese Patent Publication No. 51-13469 by Konaka et al. It is a thing.

In all of these technologies, in order to satisfy the requirements for securing the amount of precipitates and their refinement, the basic technology is the incorporation of inhibitors by high temperature slab heating in the hot rolling process.

That is, the slab heating temperature is 1260 ° C. or higher in the first technique, and in the second technique it depends on the amount of Si as shown in JP-A-48-51852.
In the third technique, as shown in JP-A-51-20716, the temperature is 1230 ° C. or higher, and in the embodiment in which a high magnetic flux density is obtained, it is 13
By annealing at an extremely high temperature such as 20 ° C., coarse precipitates are once solution-treated, and then various precipitates are refined during hot rolling or by subsequent heat treatment.

However, control of these precipitates is extremely difficult,
As a proposal for improvement, Japanese Patent Publication No. 14568/1979 discloses that nitrogen in a finish annealing atmosphere in which secondary recrystallization is performed by adding a nitride such as chromium nitride, titanium nitride or vanadium nitride to an annealing separator. A method for securing a partial pressure is also disclosed in Japanese Patent Publication No. 53-50008, by adding a sulfide such as Fe ₂ S to secure a sulfur partial pressure and suppressing the decomposition of the precipitates, and Methods have been proposed for stabilizing crystals.

However, even with these improved methods, it has not been possible to stably produce the highest magnetic product.

Industrially, this is an essential problem in that high-temperature slab heating uniformly disperses precipitates of a certain size and a certain amount in the entire lengthwise and widthwise direction of the coil, and changes until just before secondary recrystallization. It is practically impossible to keep it without doing so.

That is, the precipitation phenomenon is performed in a non-equilibrium state, and is strongly influenced by the thermal history and strain history before that. The actual slab has different thermal history and strain history depending on each part, and the slab itself has a non-uniform crystal structure due to macrosegregation of components in the plate thickness direction and local dispersion of α phase and γ phase. Because.

Therefore, the method for producing a grain-oriented electrical steel sheet based on inhibitor control is fundamentally lacking in industrial stability.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems in the prior art and provides a process capable of industrially and stably producing a grain-oriented electrical steel sheet having excellent magnetic properties. Was made for the purpose.

(Means for Solving the Problem) The present invention has no conventional method and idea whose main purpose is to control the thermal change behavior of the primary recrystallization structure by defining the primary recrystallization structure and the secondary recrystallization temperature. It proposes a method for stably producing different products having a high magnetic flux density.

That is, in the present invention, Si by weight%; 1.8 to 4.8%, acid-soluble A
l; 0.012 to 0.050%, N ≤ 0.01%, balance Fe and unavoidable impurities are used as the final plate thickness by one or two or more cold rolling steps with intermediate annealing, and then primary recrystallization annealing is performed. In the method for producing a unidirectional electrical steel sheet, in which the annealing separator is applied and then finish annealing is performed, the final cold rolling rate is set to 80% or more, and the average grain size D of the primary recrystallized grains during the finish annealing ( μm) at a temperature T (° C.) in the region of the following inequality, the secondary recrystallized grains are practically completely grown, and then purified. The main point is the manufacturing method.

T ≦ 20D + 700 1000 ≦ T ≦ 1100 The present invention will be described in detail below.

The present inventors have defined the texture and grain structure of the primary recrystallized grains and the secondary recrystallized temperature from the detailed study of the grain growth behavior of the secondary recrystallized grains and the primary recrystallized grains, and their thermal We obtained new knowledge that goss-oriented grains can be preferentially grown by controlling grain growth behavior.

Such knowledge is obtained by the following experiments.

% By weight, Si; 3.2-3.3%, heat-soluble Al; 0.010-0.045
%, N; 0.0030 to 0.0090%, C; 0.020 to 0.090%, Mn; 0.070 to
A slab containing 0.500%, S; 0.0030 to 0.0300% and the balance Fe and unavoidable impurities is heated to 1150 to 1400 ° C, and 2.
Hot rolled to a 3 mm thick hot rolled sheet, annealed at a temperature of 900 ~ 1200 ℃,
Cold rolling was performed at a rolling reduction of 88% to obtain a final plate thickness of 0.285 mm. This cold-rolled sheet was subjected to primary recrystallization annealing that also serves as decarburization at a temperature of 830 to 1000 ° C., and then an annealing separator containing MgO as a main component was applied to the treated steel sheet, followed by N ₂ 10% + H ₂ 90% In an atmosphere of up to 900 ℃ at a rate of 20 ℃ / hr, then 950
The temperature was rapidly raised to a predetermined temperature in the temperature range of up to 1200 ° C. and annealed at the predetermined temperature for 20 hours to sufficiently grow the secondary recrystallized grains.

At 900 ° C, a part of the sample was pulled out to investigate the primary recrystallization structure, but no grain size change was found at this time.

Fig. 1 shows the relationship between the magnetic flux density (B ₈ value) of the product thus obtained, the average diameter of the primary recrystallized grains, and the secondary recrystallization temperature.

As is apparent from FIG. 1, the average grain size D of the primary recrystallized grains
(Μm) and secondary recrystallization temperature T (℃) Within the range of T ≦ 20D + 700 (1) 1000 ≦ T ≦ 1100 (2), magnetic flux density (B ₈ value) exceeding 1.90T is obtained. Has been. The present inventors presume the reason for this as follows.

Secondary recrystallization is a competitive phenomenon between the thermal change of the primary recrystallization structure and the thermal change of the inhibitor. That is, the inhibitor weakens during the finish annealing, and the oriented grains in the vicinity of the goth are dispersed in a dot shape to nucleate and start growth. The growth rate V (cm / sec) of this secondary recrystallized grain is generally Q: Activation energy of grain growth R: Expressed as gas constant.

Therefore, if the primary recrystallized grain size (D) is large and the annealing temperature (T) is low, the growth rate of the secondary recrystallized grains is slow, and only the sharp Goss-oriented grains having a relatively high growth rate are the inhibitor. Although it becomes possible to grow while suppressing the restraining force, when the primary recrystallized grain size (D) is small and the annealing temperature (T) is high, the dispersion orientation near the Goss orientation also grows,
The degree of integration will decrease. This is the reason for defining the secondary recrystallization temperature (T) according to the primary recrystallization grain size (D) by the equation (1).

Further, with regard to the equation (2), it is assumed that the optimum temperature range in which the Goss-oriented grains are preferentially grown with respect to the primary recrystallization texture defined by the process of the final rolling reduction of 80% or more.

That is, a material having a final cold rolling rate of 50 to 90% is subjected to primary recrystallization annealing so that the average grain size of primary recrystallized grains becomes 22 to 24 μm, and secondary recrystallized grains are subjected to finish annealing at a temperature of 1050 ° C. Was grown sufficiently, as shown in FIGS. 3 and 4, sharp Goss-oriented grains were preferentially grown at a rolling reduction of 80% or more, and a product having a high magnetic flux density was obtained. When the primary recrystallized textures of these materials were investigated, as shown in FIG. 2, those having a reduction rate of 80% or more have a texture with the {111} <112> orientation as the main orientation.

As described above, the texture of the primary recrystallization structure is defined by the final cold rolling rate, and the thermal grain growth behavior is defined by the average grain size of the primary recrystallization structure and the secondary recrystallization temperature. Thereby, sharp Goss-oriented grains can be preferentially grown from the primary recrystallized grains.

Next, the inhibitor was examined. The primary recrystallization grain size is determined by the conditions (temperature and time) of the primary recrystallization annealing, but more essentially, it is greatly influenced by the inhibitor before the primary recrystallization annealing. That is, when the inhibitor required for secondary recrystallization is built in by high temperature slab heating before the primary recrystallization annealing as in the conventional case, the grain size (D ≧ 15 μm) of the present invention is obtained during the primary recrystallization annealing. Therefore, it is necessary to increase the annealing temperature or lengthen the annealing time, which increases energy cost. Further, abnormal grain growth may occur during the primary recrystallization annealing, and the secondary recrystallization may become unstable.

Therefore, for inhibitors, the reverse of the conventional method
Slab heating is performed in a low temperature range where AlN is not completely solution-treated, the inhibitor before primary recrystallization annealing is weakened, the primary recrystallization structure is adjusted, and then the inhibitor required for secondary recrystallization is nitrided. It is rational to make it.

The solution temperature of AlN is determined by the product of the amount of Al and the amount of N contained in steel, and is typically Iwayama (Journal of Magnetism and
Magnetic Materials 19 (1980) p15 / 17) shows that log [Al%] [N%] =-10062 / T + 2.72.

Therefore, the slab heating temperature may be determined by the above formula from the Al content and N content in the steel.

The nitriding method performed after the primary recrystallization structure is adjusted and before the secondary recrystallization is started is not particularly limited. Any method such as a method using an atmosphere gas having a nitriding ability such as ammonia or a method of adding a metal nitride having a nitriding ability such as manganese nitride or chromium nitride to an annealing separator may be used.

Such a technical idea of properly using the inhibitor before and after the primary recrystallization has never existed in the past, and was first revealed by the discovery of the importance of the primary recrystallization structure.

Thus, the invention of claim 2 relates to the incorporation of an inhibitor for rationally adjusting the primary recrystallization structure.

Next, an embodiment of the present invention will be described.

In the present invention, the components contained in the slab include, by weight%, Si; 1.8 to 4.8%, acid-soluble Al; 0.012 to 0.050%, N; ≤
0.010%, balance Fe and unavoidable impurities. These are essential components, and other components are not particularly limited.

If the Si content exceeds 4.8%, the material is likely to crack during cold rolling, making rolling impossible. On the other hand, if the Si content is lowered, α → γ transformation occurs during finish annealing and the crystal orientation is destroyed, so 1.8% or more, which does not substantially affect the crystal orientation due to the α → γ transformation, is defined as a limited range. To do.

Acid-soluble Al combines with N to become AlN and functions as an inhibitor. In particular, in the case of nitriding in a later step, it is effective to make it exist as free Al. The limit range is 0.012 to 0.050% where the magnetic flux density increases.

If N exceeds 0.01%, holes in the steel sheet called blister are generated, so 0.01% or less is made the limiting range.

As described above, the heating temperature of this slab is set to a temperature below the complete solid solution temperature of AlN based on the amounts of Al and N. Generally, if the hot rolling temperature is too low, the deformation resistance becomes large and it becomes difficult to secure the shape of the steel sheet.
Further, when the temperature is 1270 ° C. or higher, the slab surface is oxidized and a melt called “Noro” is generated. Therefore, the temperature is preferably in the range of 1000 to 1270 ° C. The heated slab is subsequently subjected to hot rolling.

The hot-rolled sheet may be used in a temperature range of 750 to 1200 ° C, if necessary.
Annealed for seconds to 30 minutes. Then, the final plate thickness is obtained by performing one cold rolling or two or more cold rolling with intermediate annealing. At that time, in order to obtain a predetermined primary recrystallization texture, it is an essential requirement that the final cold rolling rate is 80% or more.

The material after cold rolling is usually subjected to primary recrystallization annealing which also serves as decarburization in order to remove carbon contained in steel. Here, it is necessary to determine the annealing conditions (temperature and time) so that the average grain size is at least 15 μm or more.

An annealing separator is applied to the material thus obtained, and then secondary annealing and finishing annealing for the purpose of purification are applied.

After the primary recrystallization annealing, the secondary recrystallization is stably performed by strengthening the inhibitor by nitriding before starting the secondary recrystallization.

In the finish annealing, a heat cycle is required to completely grow the secondary recrystallized grains in a predetermined temperature range according to the average grain size of the primary recrystallized grains. The method may be either holding at the corresponding temperature or gradually heating.

(Example) Example 1 Si: 3.28%, acid soluble Al; 0.027%, N; 0.0060% by weight
%, Mn; 0.14%, S; 0.007%, and a slab consisting of the balance Fe and unavoidable impurities was heated to a temperature of 1150 ° C. and 1300 ° C., and then hot rolled to obtain a 1.8 mm-thick hot rolled sheet. This hot-rolled sheet was annealed at 1150 ° C for 30 seconds and subsequently at 900 ° C for 30 seconds. Next, cold rolling was performed at a reduction rate of 89% to a final sheet thickness of 0.20 mm, and primary recrystallization annealing that also serves as decarburization at 850 ° C. for 90 seconds was performed. After that, an annealing separator containing MgO with ferromanganese nitride added for the purpose of nitriding is applied, and then finish annealing is performed with N ₂ : 25% + H ₂ 75%.
The following two cycles were carried out in the atmosphere.

(A) Heat up to 1200 ° C at 30 ° C / hr.

(B) After heating up to 1070 ℃ at 30 ℃ / hr and holding for 10 hours, 30
The temperature was raised to 1200 ° C at ℃ / hr and then maintained at 1200 ° C for 20 hours in an atmosphere of H ₂ : 100% for purification. The properties of the obtained product are shown in Table 1.

Example 2 The primary recrystallized plate of the slab heating temperature of 1300 ° C. of Example 1 was subjected to an additional heat treatment of 950 ° C. Primary recrystallized grain size is 2
It was 0 μm. Finish annealing was performed under the same conditions as in Example 1. The properties of the obtained product are shown in Table 2.

Table 2 Finishing Annealing Cycle Magnetic Flux Density A 1.87T B 1.92T Example 3 Weight%, Si; 3.3%, Acid Soluble Al; 0.030%, N; 0.003%,
A slab containing C; 0.048%, Mn; 0.13%, S; 0.010%, and the balance Fe and unavoidable impurities was heated to a temperature of 1100 ° C and then hot rolled to obtain a hot rolled sheet having a thickness of 2.0 mm. 1000 this hot rolled sheet
After annealing at ℃, it was cold-rolled with a rolling reduction of 89% to give a final plate thickness of 0.23 mm. After that, primary recrystallization annealing was performed at 800 ° C, 850 ° C, and 900 ° C for 120 seconds, which also serves as decarburization. Then, after performing a nitriding treatment with an ammonia atmosphere gas so that the amount of nitrogen increase was 0.02 to 0.03%, an annealing separator was applied and finish annealing was performed. Finish annealing is 1000 ℃ in N ₂ : 10% ＋ H ₂ 90% atmosphere gas.
Up to 25 ℃ / hr and then at 5 ℃ / hr 11
After raising the temperature to 00 ° C, the temperature was raised again to 1200 ° C at 25 ° C / hr, and the atmosphere gas was switched to H ₂ 100% for purification.

A part of the sample was pulled out at 1000 ℃ and 1100 ℃, and it was confirmed that the secondary recrystallization was substantially performed in this temperature range. The properties of the obtained product are shown in Table 3.

Table 2 Primary recrystallization temperature Primary recrystallization grain size Magnetic flux density B ₈ 800 ℃ 14μm 1.89T 850 ℃ 24μm 1.94T 900 ℃ 27μm 1.95T (Effect of the invention) By controlling the secondary recrystallization temperature and controlling the thermal behavior of the primary recrystallization structure, it is possible to stably produce a grain-oriented electrical steel sheet with a high magnetic flux density, so its industrial effect is extremely remarkable. is there.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the magnetic flux density (B ₈ value), the average grain size of primary recrystallized grains, and the secondary recrystallized temperature. Figure 2 shows the final cold rolling rate (a) 70%, (b) 80%,
(C) A (200) pole figure showing 90% primary recrystallization texture. FIG. 3 is a diagram showing the relationship between the magnetic flux density (B ₈ value) and the final cold rolling rate. Figure 4 shows the final cold rolling rate (a) 70%, (b) 80%,
(C) It is a figure which shows the secondary recrystallization orientation distribution of 90% of products.

Claims (2)

[Claims] 1. Si: 1.8 to 4.8% by weight, acid-soluble Al; 0.01
A steel sheet consisting of 2 to 0.050%, N ≤ 0.01%, the balance Fe and unavoidable impurities was subjected to the primary recrystallization annealing after one or two or more cold rolling steps with intermediate annealing to obtain the final sheet thickness. In the method for producing a grain-oriented electrical steel sheet, in which a post-annealing separator is applied and finish annealing is applied, the final cold rolling rate is set to 80% or more, and the average grain size D (μm) of the temporary recrystallized grains during finish annealing According to the above, at a temperature T (° C.) within the region of the following inequality, the secondary recrystallized grains are grown substantially completely, and then purified, and a method for producing a grain-oriented electrical steel sheet having a high magnetic flux density is provided. . T≤20D + 700 1000≤T≤1100 2. The heating temperature of the slab before hot rolling is performed at a temperature at which Al and N are not completely solutionized, and during the period from after the primary recrystallization annealing to the start of secondary recrystallization in finish annealing. The method for manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density according to claim 1, wherein a nitriding treatment is performed.