JPH05320769A - Production of silicon steel sheet excellent in magnetism and film property - Google Patents

Abstract

PURPOSE:To obtain good magnetism and film properties by regulating the oxygen content in a steel sheet subjected to primary recrystallization annealing into specified one and regulating the nitrogen content after the subsequent nitriding into specified one. CONSTITUTION:Steel contg. 1 to 7% Si is subjected to fundamental stages of hot and cold rolling, primary recrystallization annealing, the coating of a separation agent for annealing and secondary recrystallization annealing to manufacture the objective grain oriented silicon steel iron sheet. At the time of adding N after the primary recrystallization annealing for the purpose of imparting the function of an inhibitor required for executing the secondary recrystallization annealing, the oxygen (O) content by a chemical analysis method of the sheet subjected to the primary recrystallization annealing is regulated to 25 to 900ppm, and the nitrogen content (N) after the subsequent nitriding is regulated to 120 to 600ppm. In this way, the nitrogen content in the grain-oriented silicon steel sheet can be optimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface coating and a method for producing a silicon steel sheet having excellent magnetic properties.

[0002]

2. Description of the Related Art 1-7 excellent in magnetic characteristics for transformers and the like
% Of Si to produce a silicon steel sheet, the primary characteristics of the steel sheet are to improve the magnetic properties necessary for improving the performance of the transformer by imparting a tensile force to the surface of the steel sheet and providing good adhesion to the steel sheet. Is important.

In the usual technique, magnesium oxide (MgO) called magnesia is applied to the steel sheet after primary annealing accompanied by decarburization.
Of fine powder of water is applied, dried as needed, and then fired in the secondary recrystallization annealing step, and reacted with Si in the steel sheet to forsterite (Mg ₂
A ceramic insulating film called SiO ₄ ) is formed. This is effective for giving tension to the steel sheet and improving the magnetic property, especially the characteristic value called iron loss, which governs the efficiency of the transformer.

Moreover, this state of forsterite formation is called the GOSS orientation of the crystal orientation of the steel sheet in the secondary recrystallization, and with respect to the steel sheet longitudinal direction (rolling direction) which is indispensable for improving the magnetic permeability and the magnetic flux density. It is also well known that it plays an important role in growing slightly coarse secondary recrystallized grains having a crystal orientation of {110} [001].

That is, even if an attempt is made to carry out secondary recrystallization without forming a sufficiently dense film during the secondary recrystallization annealing temperature rising process, fine nitrides and sulfides called inhibitors in the steel sheet remain as they are. Or, it disassembles and quickly falls out of the steel plate. Therefore, during the temperature rise, GOSS
The inhibitory effect of growing preferentially oriented grains and suppressing the growth of other oriented grains cannot be exerted, and is commonly called fine grain, and the growth of secondary recrystallized grains of GOSS oriented grains is partially or It will produce a steel sheet with extremely inferior magnetic properties, which is not done entirely. In addition, titanium oxide (such as TiO ₂ ) or another compound is added to this MgO,
It is also performed to form a denser primary coating.

However, in practice, it is not easy to stably produce a sufficient primary coating and secondary recrystallization structure even with the above technical knowledge, and in particular, various secondary recrystallization annealing conditions are industrially necessary. Although it may be changed, it is not easy in this case to form a sufficient primary film and to generate a secondary recrystallization having a sufficiently proper orientation.

[0007] One of the reasons for this is that the elucidation in the manufacturing process regarding the formation of the primary coating film and the formation of an appropriate additive in the secondary recrystallization process called an inhibitor is not yet sufficient. In particular, in the inhibitor control technique of adding N after the primary recrystallization annealing, there is a part that depends on individual experience because it is not detailed in detail how to efficiently add the optimum amount of N. As described above, the actual situation is that the stable primary coating and secondary recrystallization have not been freely controlled.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above problems in the prior art, efficiently adds N necessary for an inhibitor after primary recrystallization annealing, and stabilizes the primary coating during secondary recrystallization. Stable G formed on the surface of silicon steel
The present invention provides a method for producing a grain-oriented silicon steel sheet having secondary recrystallized grains of OSS orientation.

[0009]

The gist of the present invention is as follows. (1) Si: A steel containing 1 to 7% is melted, and a hot rolled, a cold rolled, a primary recrystallization annealing, an annealing separation material coating and a secondary recrystallization annealing of the grain-oriented electrical steel sheet are the basic steps. In manufacturing, when N is added after the primary recrystallization annealing for the purpose of giving the function of an inhibitor necessary for performing the secondary recrystallization annealing, oxygen (O) in the chemical analysis method of the primary recrystallization annealed plate is added. An amount of 25 to 900 ppm, and a nitrogen (N) amount after nitriding subsequent to the primary recrystallization annealing is 120 to 600 ppm.

(2) In the above (1), 0.05 to 5.0% of an antimony-based compound is contained in magnesia applied for forming a primary film mainly composed of forsterite before secondary recrystallization annealing. 8 in addition and secondary recrystallization annealing
The average rate of temperature increase from 00 ° C to the highest temperature reached is 0.1 to 8 per hour.
A method for producing steel, which is characterized in that the temperature is 0 ° C. (3) In the above (1), boron series in magnesia,
Strontium / barium-based, carbon / nitride-based, sulfide-based, and chloride-based compounds totaling one or more of 0.0
Addition of 5 to 5.0%, and 800 ℃ in secondary recrystallization annealing
~ A method for producing steel, characterized in that the average temperature rising rate of the highest reached temperature is 5 to 400 ° C per hour. (4) The method for producing a silicon steel sheet according to (1) above, wherein the partial pressure ratio of nitrogen and oxygen in the primary recrystallization annealing atmosphere is PN ₂ / P H ₂ ≦ 0.5.

The present invention will be described in detail below. Secondary recrystallization of grain-oriented silicon steel sheet is called GOSS orientation {11
It is important to grow grains of 0} <001> orientation sufficiently during secondary recrystallization annealing (also called finish annealing).
This is to coarsely recrystallize only specific grains in the primary recrystallization annealing (hereinafter referred to as primary annealing). At this time, AlN called an inhibitor (Inhibitor),
It is well known in the art that it is technically necessary to prepare fine precipitates such as Si ₃ N ₄ before finish annealing.
Then, N necessary for this purpose is added during steel melting, after primary annealing, or during other steps.

One of the constitutions of the present invention is the technical knowledge regarding the optimum addition method when N is added after the primary annealing. Here, I will supplement what is called after primary annealing, but this is because after the primary annealing or after that, the equipment that performs the nitriding reaction is installed inside or in close proximity to a part of the equipment for the primary annealing that also normally functions the decarburization reaction. This is a method of nitriding reaction in parallel.

In the case of steel having sufficiently low carbonization during steel melting, it is more important than the decarburizing function to change the oxide layer of the surface layer after the primary annealing so that the oxide film has a shape advantageous for film formation.
Here, the result of the experiment of nitriding after the primary annealing is shown. Table 1 shows the chemical composition of the sample and the manufacturing method.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

Table 2 shows the oxygen content of the primary annealed sheet of such a material and the N content of the sheet after nitriding. This relationship is shown in FIG. What is clear in this figure is that there is a clear positive correlation between the oxygen content and the nitriding content in the steel sheet after the primary annealing.

[0018]

[Table 4]

The reason why the amount of oxygen changes here is that the surface is oxidized during the primary annealing, which is a result of the following reaction which is accompanied by decarburization in the primary annealing. C + H ₂ O → CO + H ₂ (1) Fe + H ₂ O → FeO + H ₂ (2)

These reactions usually occur simultaneously, and the oxygen in the steel sheet increases as the decarburization proceeds. Now, the following study was conducted on the nitriding after the primary annealing. The nitriding reaction is expressed by the following equation. NH ₃ → N + (3/2) H ₂ (3)

However, in this reaction equation, the effect of the oxygen content of the steel sheet cannot be seen. Therefore, the amount corresponding to the oxygen content of the steel sheet was considered as the FeO content in the surface layer of the steel sheet from the above equation (2), and the following two cases were considered. 1. When it is assumed that an oxide layer (FeO or the like) does not substantially exist in the surface layer portion. F. It is expressed as follows from the Enrietto formula. N + (3/2) H ₂ ← NH ₃ (4) Equilibrium constant: K = 1.77 * 10 ⁻⁵ exp (19250 / RT) = PNH ₃ / (N · P H ₂ ^3/2 ) (5)

2. When an oxide layer (FeO, etc.) exists on the surface layer At this time, it occurs at the interface between the steel sheet and the external atmosphere (4)
It was thought that how to remove H ₂ in the reaction of the formula as a reaction system affects the nitriding. In this case, we must consider the interface region where the following two reaction systems occur simultaneously.

I. N + (3/2) H ₂ ← NH ₃ (4) K = 1.77 * 10 ⁻⁵ exp (19250 / RT) = PNH ₃ / (N · P H ₂ ^3/2 ) (5) II. FeO + H ₂ → Fe + H ₂ O (6) log K = log (P H ₂ O / P H ₂ ) = 827 / T−0.468 (7) ΔF = −3784 + 2.14T (8) where (7), ( Equation 8) is Sawamura's equation. Note that T is an absolute temperature (° K) and R is a gas constant. 1. And 2. The calculation was performed for the case.

Calculation Results I. If no oxide layer (FeO) ... (5) formula (T = 750 For _{℃) Case1 Case2 Case3 P H 2} : 0.60: 0.50: 0.35 PNH 3: 0.15: 0.35: 0.40 P N 2: 0.25: 0.15: 0.25 ↓ ↓ ↓ N = 1.4ppm N = 4.3ppm N = 8.4ppm

II. When there is an oxide layer (FeO) ... (5)
Formula + (7) Formula In this case, since the reaction occurs at the interface between Fe and FeO, the two reaction systems described above are obtained, and the existing Gas system is NH ₃ , H 2.
₂ , H ₂ O ternary system can be basically considered (N ₂ is only partial pressure adjustment).

Therefore, in addition to the above formula (2), PNH ₃ + P H ₂ + P H ₂ O = 1 (9) must be added (when considering P N ₂ , the partial pressure may be adjusted to some extent). ..

The following is obtained from the equations (5), (7) and (9).

[0028]

[0029] (T = 750 For _{℃) Case1 Case2 Case3 P H 2} : 0.20: 0.10: 0.05 P H 2 O: 0.44 ((2) equation _{constraints): 0.22: 0.11 PNH 3:} 0.36 ((3) formula ): 0.68: 0.84 ↓ ↓ ↓ N = 18ppm N = 93ppm N = 333ppm

[0030] (T = 850 For _{℃) Case4 Case5 Case6 P H 2} : 0.20: 0.10: 0.05 P H 2 O: 0.37: 0.19: 0.09 PNH 3: 0.43: 0.71: 0.86 ↓ ↓ ↓ N = 49ppm N = 224ppm N = 790 ppm When FeO is present as described above, N (nitriding amount) is extremely large.

When N ₂ partial pressure is taken into consideration, it becomes as follows. (T = 750 For _{℃) Case1 Case2 Case3 P H 2} : 0.20: 0.10: 0.05 P H 2 O: 0.44: 0.22: 0.11 P N 2: 0.2: 0.2: 0.2 PNH 3: 0.16: 0.48: 0.64 ↓ ↓ ↓ N = 8ppm N = 66ppm N = 254ppm That is, it can be seen that the nitriding amount rather decreases as the N ₂ partial pressure increases. Thus, theoretically, it has been confirmed that nitriding is easier when the primary annealed plate has an oxide layer (FeO or the like). Further, it is expected that the nitriding amount will increase as the partial pressure ratio P N ₂ / P H ₂ of nitrogen and oxygen in the atmosphere during the primary annealing and nitriding decreases.

Here, a method for measuring the amount of the oxide layer of the primary annealed plate will be described. Commonly known speed (SPEED: Sel
active Potentiostatic Etc
Hing by Electronic Diss
It is possible to analyze the precipitation morphology of the precipitation phase in the metal material by a method called the “solution method”. In this method, a metal surface is dissolved by a few μm (micrometer) using a non-aqueous solvent type electrolyte solution, and an unstable precipitation phase is left as it is on the matrix surface, and SEM-EDX, EP is used.
This is a method of locally analyzing the precipitation phase using MA, AES or the like.

The etching surface is peeled off by the replica method, and the composition of the precipitation phase and the like are analyzed. By applying this method to the primary annealed plate, it is possible to carry out the composition and quantification of the oxide of the surface layer.
It is also possible to quantify O, Al ₂ O ₃ , SiO _{2 and the} like.

On the other hand, as can be seen from the data in Table 2, the amount of oxide can be measured by directly measuring the oxygen (O) amount of the primary annealed plate by a usual chemical analysis method. As described above, the value and the nitriding amount correspond well in the experiment.

Therefore, in the present invention, the amount of oxygen (O) in a simple ordinary chemical analysis method is used as a technical index. Then, as shown in the experiment, if the oxygen content of the steel sheet after the primary annealing is 25 ppm or more, the nitriding amount of the steel sheet is stable to secure the amount of inhibitors such as AlN and Si ₃ N ₄ during the subsequent finish annealing. It is possible to obtain the required nitrogen amount of 120 ppm or more with the primary annealed plate.

A so-called MgO powder mainly composed of MgO is applied to the steel sheet surface in a slurry form on the steel sheet which has undergone primary annealing and is nitrided, and film formation and secondary recrystallization are carried out in the next finish annealing step. Here, the technical relationship under these conditions and the primary annealed plate nitrided by the method of the present invention was recognized.

Table 3 shows the results of a finish annealing pull-out experiment in which MgO powder was applied in a slurry form to a 3% Si steel sheet after primary annealing and nitriding, and the secondary annealing was performed during the secondary recrystallization annealing. Here, the powders are referred to as Sb-based and B-based, respectively. Here, a small amount of TiO ₂ (5%) and Sb ₂ (SO ₄ ) ₃ (0.2%), TiO ₂ (5%) and Na are included in the MgO powder, respectively. ₂ B ₄ O ₇ (0.3%) was added to promote the formation of forsterite.

The secondary recrystallization annealing was carried out halfway by the method shown in FIG. 2, and a so-called pull-out experiment was conducted at each temperature. Table 3 shows the results obtained by conducting GDS analysis from the surface of the steel sheet drawn out in this way and examining from which drawing temperature forsterite, that is, the Mg peak appears. Here, the temperature in () is determined to appear in the middle of the measured temperature.

[0039]

[Table 5]

What is clear from the results in Table 3 is that forsterite is formed at a lower temperature in the Sb system than in the B system. It is generally considered that the formation of forsterite is caused by the reaction of MgO and surface-concentrated Si in the steel sheet, and the reaction of 2MgO + SiO ₂ → Mg ₂ SiO ₄ .

By the way, we examined how the manufacturing process of silicon steel sheets and the properties of these steel sheets can be controlled. If the causal relationship between the formation process of the primary coating and various properties of the silicon steel sheet is clarified as described above, naturally it can be industrially reflected in the production.

As can be seen from the experimental results shown in Table 3, when a small amount of Sb-based compound is added to MgO, the melting of MgO is performed at a relatively low temperature, so that the temperature rising rate of the secondary recrystallization annealing is relatively high. The smaller the size, the more quickly the production of forsterite is promoted and the excellent primary coating is easily produced. The antimony (Sb) -based compound includes not only Sb ₂ (SO ₄ ) ₃ used in this experiment but other compounds containing Sb.

On the other hand, even when the B-based compound is added to MgO in a small amount even with the same low melting point compound, the melting of MgO is performed at a relatively higher temperature than that of the Sb-based compound. A relatively high velocity accelerates the production of forsterite. The boron (B) type is not only Na type, but Ca, Mg instead of Na.
Compounds containing, etc., boric acid (H ₃ BO ₃ ) and sodium borate are also included.

Further, strontium / barium system, carbon / nitride system, sulfide system, and chloride system have the same action as boron system in that they are higher melting point system than antimony system. These compounds will be collectively called non-antimony compounds. It should be noted that, although it is usual to add an oxide such as TiO _{2 to} MgO to facilitate the high temperature reaction, the effects of the above additives of the present invention are exhibited regardless of the amount of the oxide added. Therefore, even if an oxide is added to MgO, this is referred to as a plane and is regarded as a part of the base material.

As described above, according to the present invention, the primary coating, which is an important controlling factor for the properties of the silicon steel sheet, can be controlled to some extent freely by elucidating its composition distribution and combining it with a manufacturing method having a correlation therewith. became.

Now, it is necessary to touch on the method of manufacturing a silicon steel sheet. As described above, the silicon steel sheet which can be used in the present invention is limited to steel containing Al as necessary and AlN or Si ₃ N ₄ as a main inhibitor. Of course S
In addition to i and Al, Mn, S, Sn, Se, Sb, Cu,
The addition of other additive elements such as B, Nb, Ti and V to improve the magnetic characteristics does not change the basics of the present invention.

By the way, steels using AlN or Si ₃ N ₄ as an inhibitor are known, and in any case, the technique of the present invention can be applied. However, the following production methods are most suitable for further exerting the characteristics of the present invention. That is, Si is 1
Steel containing 0.1% or less of Al at the time of smelting the steel, if necessary, in a steel containing 7% to 7%, and N through denitrification annealing during or after primary annealing after cold rolling in a silicon steel sheet manufacturing process directly through a nitriding reaction to the steel sheet. The steel is characterized by including N in 120 to 600 ppm steel before secondary recrystallization annealing by a method of forcibly adding N to steel.

In the present invention, at least 1% of Si is necessary for forming forsterite as described above. On the other hand, if it exceeds 7%, the workability is extremely deteriorated and it is not suitable for industrial production.

Al is effective in forming an AlN inhibitor. However, if it exceeds 0.1%, the amount of Al ₂ O ₃ produced increases, impairing the cleanliness of sound steel, and adversely affecting the magnetic properties.

N is indispensable for forming AlN and Si ₃ N ₄ inhibitors, and in the present invention, at least 120 ppm is necessary after primary annealing, that is, before finish annealing.
On the other hand, if it exceeds 600 ppm, a compound having an inappropriate form with Al or Si is formed, which is not preferable. In order to stabilize the secondary recrystallization, 300 ppm or more is preferable. The other elements are not particularly characteristic in the present invention as compared with the conventional steel, but the following restrictions are preferable.

C must be sufficiently low during steel melting or sufficiently low during decarburization annealing of primary annealing, and is preferably 0.03% or less at the start of secondary recrystallization annealing.

If Mn is less than 0.5%, it reacts with S and becomes M.
Form an nS inhibitor. If it is 0.15% or less, it is preferable for further improving the magnetic flux density.

If the oxygen content is 0.05% or less after the steel has been melted, a large amount of Al ₂ O ₃ is not produced, which is preferable for cleanliness. In the present invention, it is particularly important to perform nitriding after or during the primary annealing, but the oxygen content of the steel sheet after the primary annealing including this nitriding must be 25 to 900 ppm. The oxygen content is controlled mainly by the dew point, but it also varies considerably depending on the gas composition. If it is less than 25 ppm, the amount of N required for secondary recrystallization for forming AlN and Si ₃ N ₄ is not sufficiently nitrided. Particularly, if it is 100 ppm or more, sufficient nitriding is performed regardless of the gas composition and gas flow rate. On the other hand, 900pp
If it exceeds m, the amount of N becomes too large, and it becomes rather difficult to perform a sufficient role as an inhibitor.

Next, the production method of the present invention other than the chemical components will be described. A thin slab that is used to cast steel in a converter or electric furnace and to adjust the composition by adding a refining process if necessary, by a continuous casting method, ingot slabbing method, or to omit the hot rolling step. A slab having a thickness of 30 to 400 mm (50 mm or less in the thin slab continuous casting method) is formed by the continuous casting method or the like. Here, 30 mm is the lower limit of productivity, and 400 mm is the upper limit for preventing abnormal distribution of Al ₂ O ₃ etc. due to center segregation. Further, 50 mm is the upper limit for suppressing the generation of coarse particles due to the low cooling rate.

The slab is reheated to 1000 to 1400 ° C. by gas heating, electric heating, etc., and then hot rolled to obtain a hot coil having a thickness of 10 mm or less. Here, 1000 ° C. is the lower limit of AlN melting, and 1400 ° C.
Is the upper limit of surface roughness and material deterioration. Further, 10 mm is the upper limit for obtaining a cold speed at which an appropriate precipitate is formed. In the thin slab continuous casting method, it is possible to directly form a coil, and for that purpose, it is preferably 10 mm or less.

The hot coil made in this way is again heated to 80
Annealing at 0 to 1250 ° C. is often performed to improve magnetism. Here, 800 ° C. is the lower limit for remelting AlN, and 1250 ° C. is the upper limit for preventing AlN coarsening.

After this treatment step, the hot coil is pickled directly or batchwise and then cold rolled. Cold rolling is performed at a rolling reduction of 60 to 95%, 60% being the limit of recrystallization in the present invention, preferably 70% or more by primary annealing and increasing {111} [112] oriented grains, It is the lower limit for promoting the generation of GOSS oriented grains during secondary recrystallization annealing,
On the other hand, if it exceeds 95%, secondary recrystallization annealing causes GOSS-oriented grains, which are called swinging GOSS grains, to rotate in the plane of the plate to produce grains unfavorable to the magnetic properties.

The above is the case of manufacturing by the so-called single cold rolling method. However, in the case of performing cold rolling-annealing-cold rolling called the double cold rolling method, the first rolling reduction is 10 to 80%, The second rolling reduction is 50 to 95%. Here, 10% is the minimum reduction ratio necessary for recrystallization, 80% and 95% are the upper limit reduction ratios for producing proper GOSS-oriented grains during secondary recrystallization, respectively, and 50% in the double cold rolling method. Is the lower limit of the reduction ratio that appropriately leaves the {111} [112] oriented grains during the primary annealing.

It is also commonly called "interpass aging", and it is effective to improve the magnetic properties by heating the steel sheet in the range of 100 to 400 ° C by an appropriate method during the cold rolling. 10
Below 0 ℃, there is no effect of aging, while at 400 ℃
If it exceeds the limit, dislocations will be recovered.

Thereafter, the primary annealing is carried out by either the single cold rolling method or the double cold rolling method, and it is effective to carry out decarburization by this annealing. As described above, C is not preferable for the growth of secondary recrystallized grains, and if it remains as an impurity, it causes deterioration of iron loss. It is preferable that C be lowered during the melting of the steel because not only the decarburization step is shortened but also {111} [112] oriented grains are increased. By setting an appropriate dew point in this decarburization annealing step, the oxide layer necessary for subsequent primary film formation is secured. Primary annealing temperature is 700-950
C is preferred. Here, 700 ° C. is the lower limit temperature at which recrystallization is possible, and 950 ° C. is the upper limit temperature at which the generation of coarse particles is suppressed.

Further, in the present invention in which AlN or N of Si ₃ N ₄ inhibitor is forcibly added by the nitriding method or the like during the primary annealing, the nitriding method with ammonia (NH ₃ ) or the like is continuously performed during or immediately after the primary annealing. Nitriding is performed. In this case, the temperature of the nitriding method is preferably 600 to 950 ° C. Here, 600 ° C. is the lower limit for causing the nitriding reaction, while 950 ° C. is the upper limit for suppressing the generation of coarse particles.

In the present invention, the nitriding is preferably performed after the primary recrystallization annealing, but industrially, a partition is provided on the rear surface of the same furnace, the atmosphere is slightly changed as necessary, and NH ₃ gas is flowed, or Since they are performed in close proximity to each other, they are often nitrided in parallel with primary recrystallization. At this time, as described above, the lower the N ₂ partial pressure is, the larger the nitriding amount is, and the partial pressure ratio P N ₂ / P H ₂ of nitrogen and oxygen is preferably 0.5 or less.

Primary annealing or the above nitriding method is performed, and then magnesium oxide (MgO is the main component.
A powder (referred to as gO) is dissolved in water or an aqueous solution containing water as a main component to form a slurry, which is applied to a steel sheet. At this time, a trace amount of an appropriate compound may be added for the purpose of facilitating the melting of the MgO powder during the subsequent secondary recrystallization annealing and promoting the forsterite formation reaction. Ti
When O ₂ is added, it is preferably 1 to 15%, but 1% is the lower limit at which the effect of promoting the forsterite reaction is exhibited, and if it exceeds 15%, the amount of MgO decreases and the forsterite reaction does not proceed.

Antimony compounds such as Sb ₂ (SO ₄ ) ₃ are effective in melting MgO at a relatively low temperature, and when added, 0.05 to 5% is preferable. Here, 0.05% is the lower limit for causing the above-mentioned low-temperature melting, while if it exceeds 5%, it is too much to inactivate the original reaction of MgO forsterite.

Boron-based compounds such as Na ₂ B ₄ O ₇ and strontium / barium-based, carbon / nitride-based, sulfide- and chloride-based compounds having the same action as those at a relatively higher temperature than antimony-based compounds. It is effective in melting MgO, and when added, 0.05 to 5% is preferable. Here, 0.05% is the lower limit for exerting the above effect,
On the other hand, if it exceeds 5%, the original reaction of MgO forsterite is inactivated, which is not preferable.

It should be noted that these compounds can be added in combination with each other. However, when an antimony low-temperature melting type compound and a boron-based or other relatively high-temperature melting type compound are mixed and used, the effect is close to that of the high-temperature melting type compound, but it does not contradict the gist of the present invention. In that case, it is preferable to adopt the high temperature melting type temperature rising rate of the present invention.

The percentage of the compound added here is MgO.
The weight ratio is shown in% when the weight of 100% is taken as 100%. Secondary recrystallization annealing has a maximum temperature of 1100 to 130
It is preferably carried out at 0 ° C. 1100 ° C. is the lower limit temperature at which the secondary recrystallization is performed, while if it exceeds 1300 ° C., the crystal grains become too coarse and iron loss is deteriorated. Note that, as described above, the nitriding method in which N is additionally added from the atmosphere or the like may be performed at a relatively previous stage during the secondary recrystallization annealing.

Now, the temperature rising rate of the secondary recrystallization annealing is particularly important in the present invention. That is, it is necessary to change the heating rate depending on the type of compound added to MgO. When an antimony-based compound is added to MgO, it is necessary that the average heating rate from 800 ° C. to the highest reached temperature is 0.1 to 80 ° C. per hour, which is relatively small. Here, 0.1 ° C./hour is the lower limit of the industrial heating rate, while MgO melts at a low temperature when an antimony-based compound is added as described above, so that forsterite is formed more quickly and reliably. The rate of temperature rise is 8
It is necessary to keep it at 0 ° C./hour or less.

On the other hand, in the case of boron type, strontium / barium type, carbon / nitride type, sulfide type and chloride type, the average heating rate is preferably 5 to 400 ° C. per hour. That is, in the case of adding a high temperature melting type compound, melting of MgO occurs at a relatively high temperature, and therefore a temperature rising rate of 5 ° C./hour or more is required in order to reach a high temperature quickly. Secondary recrystallization itself is not sufficiently performed due to the relationship with the inhibitor.

The above is an important part of the method for producing a silicon steel sheet according to the present invention, but industrially, for the purpose of further improving the insulation characteristics and magnetic characteristics, the production of a secondary coating film of an organic or inorganic substance on the steel sheet, Further, it is often accompanied by several steps such as a magnetic domain control method by a non-contact type method such as mechanical or laser addition, and subsequent generation of a tertiary film for preventing dusting.

[0071]

Example 1 Steels having chemical compositions shown in Table 4 were melted in a converter and manufactured under the conditions shown in Table 5.

[0072]

[Table 6]

[0073]

[Table 7]

[0074]

[Table 8]

The hot-rolled sheet was partially annealed under the following conditions:
120 ° C. × 30 seconds. A part of aging between passes during cold rolling was carried out under the condition of 250 ° C. Here, the nitridation subsequent to the primary recrystallization annealing, which is particularly important in the present invention, is carried out by making the atmosphere try with the same gas composition in the inner part of the furnace in which the partition is provided in the same furnace and flowing a certain amount of NH ₃ gas. It is a thing.

The amount of oxygen and the amount of nitriding (the amount of nitrogen) of the steel sheet after such primary annealing are shown in the same table.

The amount of oxygen mainly changes considerably depending on the dew point. The reason why the nitriding amount fluctuates to some extent with respect to the oxygen amount is considered to be due to a change in the circulating state of the atmosphere in the furnace.

Further, powder was applied to this steel plate,
Dissolve the powder in water, make a slurry, and apply 35
It was dried at 0 ° C. The type of powder, plain is M
The composition is gO + TiO ₂ (5%), and Sb-based is Mg
O + TiO ₂ (5%) + Sb ₂ (SO ₄ ) ₃ (0.2
%), And the B type is MgO + TiO.
₂ (5%) + Na ₂ B ₄ O ₇ (0.3%). Here,% is an important ratio when the weight of MgO is 100%.

After that, secondary recrystallization annealing was performed while changing the average heating rate from 800 ° C. to the highest temperature reached. The maximum reaching speed is 1200 ° C. here. After further washing with water,
After applying a phosphoric acid-based insulating coating (secondary coating) by heating, the plate is removed and strain relief annealing is performed at 850 ° C. for 4 hours (N ₂ 90-H ₂
10, Dry), and a film and macro appearance inspection, magnetic measurement, adhesion test, etc. were performed. Table 5 shows the results.

Here, the film appearance inspection is conducted by ○: scale,
No shimou defect, △: Slight mottle defect, ×:
It shows that there are many scales and shimofuri and the film is not sufficiently formed. Here, the scale means that the coating is widely peeled off to some extent, and the shimofuri is a point-like peeling defect. In addition, the macroscopic visual inspection shows that ◯: sufficient secondary recrystallization is completed, Δ: fine grains are partially observed, and x: fine grains are observed on the entire surface.

The magnetic measurement is SST of a single plate of 60 × 300 mm.
The test method was used to measure B ₈ (magnetic flux density of 800 A / m, unit: Gauss) and W _17/50 (iron loss at 50 Tesla at 1.7 Tesla, unit: watt / kg). The adhesion test is a bending test in which a steel plate is wound around a cylinder having a diameter of 20 mm, and the judgment is ◯: no crack in the coating, Δ:
The film was evaluated for fine cracks, and x: almost full width.

As shown in Table 5, the nitriding amount (nitrogen amount) is sufficiently within the range of the present invention in the primary annealing conditions, in particular, the amount of oxygen is within the range of the present invention. Was 100 ppm or more, a stable and sufficient amount of nitriding was obtained. On the other hand, the gas composition having a high H ₂ partial pressure has a large amount of nitriding even with the same oxygen content. Further, in particular, those in which the kind of MgO powder and the average temperature rising rate of finish annealing are included in the present invention have good magnetic characteristic values.

Example 2 Steel having the chemical composition shown in Table 6 was melted by vacuum melting at 150 kg.

[0084]

[Table 9]

[0085]

[Table 10]

This was heated at 1150 ° C. and hot-rolled to obtain a hot-rolled plate having a plate thickness of 2.3 mm. This hot-rolled sheet was partially hot-rolled and annealed (1120 ° C. × 30 seconds), then pickled and then rolled down 9
Cold rolled at 0% to a thickness of 0.23 mm,
So-called aging between passes is performed by heating at 0 ° C.

Thereafter, this was washed with oil and N ₂ 25% -H
Were primary annealing which serves as a decarburization 830 ° C. × 120 seconds dew point Table 6 ₂ 75% gas composition. Further, this primary annealed sheet was annealed in a furnace having a gas composition of dry N ₂ 25% + H ₂ 75% while flowing NH ₃ into the furnace to anneal at 750 ° C. for 30 seconds. In this case, the table shows the oxygen content of the steel sheet after primary annealing and the N content of the steel sheet after nitriding. The following powder coating was applied to this steel sheet.

The types of powder in Table 6 adopted any one of the following conditions. (1) MgO + TiO ₂ [5%] (plane) (2) MgO + TiO ₂ [5%] + Sb ₂ (SO ₄ ) ₃
[0.2% (= Sb system), 0.02% (= low Sb system),
6.0% (= high Sb system)] (3) MgO + TiO ₂ [5%] + Na ₂ B ₄ O
₇ [0.3% (= B type), 0.03% (= low B type),
7.0% (= high B type)] (4) MgO + MgSO ₄ [4.0%] + FeSO
₄ [0.1%] + Na ₂ B ₄ O ₇ [0.5%] (Sulfide type) (5) MgO + SrCO ₃ [0.08%] + BaCl ₂
[0.5%] + Ba (OH) ₂ [0.1%] (strontium / barium system) (6) MgO + V ₂ O ₅ [5%] + CrN [3%]
(Carbon / nitride type) (7) MgO + MnO ₂ [0.2%] + TiO ₂ [8
%] + TiCl ₄ [0.5%] (Chloride type) The powder is dissolved in water to form a slurry,
It was dried at 0 ° C. After that, secondary recrystallization annealing was carried out while changing the average heating rate from 800 ° C. to the highest reached temperature variously. Further, after washing with water, a phosphoric acid-based insulating coating (secondary coating) is applied by heating, and then the plate is removed and strain relief annealing is performed at 850 ° C. for 4 hours (N ₂ 90-H ₂ 10, Dry). Appearance inspection, magnetic measurement, film tension measurement, adhesion test, etc. were performed. Table 6 shows the results.

Here, the appearance of the coating film is inspected by ◯: scale,
No shimou defect, △: Slight mottle defect, ×:
It shows that there are many scales and shimofuri and the film is not sufficiently formed. Here, the scale means that the coating is widely peeled off to some extent, and the shimofuri is a point-like peeling defect. In addition, the macroscopic visual inspection shows that ◯: sufficient secondary recrystallization is formed, Δ: fine particles are partially observed, and x: fine particles are observed on the entire surface.

Magnetic measurement is SST of 60 × 300 mm single plate.
The test method was used to measure B ₈ (magnetic flux density of 800 A / m, unit: Gauss) and W _17/50 (iron loss at 50 Tesla at 1.7 Tesla, unit: watt / kg). The adhesion test is a bending test in which a steel plate is wound around a cylinder having a diameter of 20 mm, and the judgment is ◯: no crack in the coating, Δ:
The film was evaluated for fine cracks, and x: almost full width.

As shown in Table 6, in the MgO powder containing the antimony-based compound, the temperature rising rate of the finish (secondary recrystallization) annealing is small as in the present invention, and the oxygen content in the primary annealing is small. And the nitrogen content in the range of the present invention is good in all of the above-mentioned characteristics, on the other hand, at a relatively high temperature such as boron-based, sulfide-based, strontium-barium-based, carbon-nitride-based, chloride-based. The one to which the compound that melts MgO is added has a high rate of temperature rise in the secondary recrystallization annealing as in the present invention, and all the above-mentioned characteristics are good when the other conditions are within the scope of the present invention. On the other hand, in the plain material, when the temperature rising rate is smaller, various properties tend to be better, but the characteristic values tend to be slightly inferior to those when the antimony-based compound is added.

[0092]

According to the present invention, the nitriding amount of the grain-oriented electrical steel sheet can be optimized and good magnetic properties and coating characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of oxygen in a primary annealed plate and the amount of nitrogen in a nitrided plate.

2A, 2B and 2C are annealing cycles of a pull-out test of secondary recrystallization annealing.

[Procedure amendment]

[Submission date] June 12, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 4

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

(2) In the above (1), 0.05 to 5.0% of an antimony-based compound is contained in magnesia applied for forming a primary film mainly composed of forsterite before secondary recrystallization annealing. 8 in addition and secondary recrystallization annealing
The average rate of temperature increase from 00 ° C to the highest temperature reached is 0.1 to 8 per hour.
A method for producing steel, which is characterized in that the temperature is 0 ° C. (3) In the above (1), boron series in magnesia,
Strontium / barium-based, carbon / nitride-based, sulfide-based, and chloride-based compounds totaling one or more of 0.0
Addition of 5 to 5.0%, and 800 ℃ in secondary recrystallization annealing
~ A method for producing steel, characterized in that the average temperature rising rate of the highest reached temperature is 5 to 400 ° C per hour. (4) A method of manufacturing a silicon steel sheet the ratio of the partial pressures of nitrogen and hydrogen in the primary recrystallization annealing atmosphere in the above (1) is a _{PN 2 / P H 2 ≦ 0.5} .

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

When N ₂ partial pressure is taken into consideration, it becomes as follows. (T = 750 For _{℃) Case1 Case2 Case3 P H 2} : 0.20: 0.10: 0.05 P H 2 O: 0.44: 0.22: 0.11 P N 2: 0.2: 0.2: 0.2 PNH 3: 0.16: 0.48: 0.64 ↓ ↓ ↓ N = 8ppm N = 66ppm N = 254ppm That is, it can be seen that the nitriding amount rather decreases as the N ₂ partial pressure increases. Thus, theoretically, it has been confirmed that nitriding is easier when the primary annealed plate has an oxide layer (FeO or the like). The atmosphere at the time of primary annealing nitride is expected to be much nitrogen and small enough amount nitride of partial pressure ratio P N ₂ / P H ₂ for hydrogen.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0062

[Correction method] Change

[Correction content]

In the present invention, the nitriding is preferably performed after the primary recrystallization annealing, but industrially, a partition is provided on the rear surface of the same furnace, the atmosphere is slightly changed as necessary, and NH ₃ gas is flowed, or Since they are performed in close proximity to each other, they are often nitrided in parallel with primary recrystallization. In this case it is the amount of nitride is low N ₂ partial pressure as described above is large, the partial pressure ratio P N ₂ / P H ₂ in nitrogen and hydrogen is preferably 0.5 or less.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location H01F 1/16 A (72) Inventor Hodaka Hodaka No. 1-1 Tobata-cho, Tobata-ku, Kitakyushu City Made in New Japan Inside the Yawata Works,

Claims (4)

[Claims] 1. A directional electromagnetic system in which a steel containing Si: 1 to 7% is smelted and hot rolling, cold rolling, primary recrystallization annealing, application of an annealing separator and secondary recrystallization annealing are the basic steps. In the production of a steel sheet, when N is added after the primary recrystallization annealing for the purpose of imparting the function of an inhibitor necessary for performing the secondary recrystallization annealing, oxygen ( The amount of O) is 25 to 900 ppm, and the amount of nitrogen (N) after nitriding following the primary recrystallization annealing is 120 to 60
A method for producing a silicon steel sheet having excellent magnetic properties and coating characteristics, which is characterized by setting the content to 0 ppm. 2. An antimony-based compound is added in an amount of 0.05 to 5.0% to magnesia which is applied to form a primary film mainly composed of forsterite before secondary recrystallization annealing, and the secondary The method for producing a silicon steel sheet having excellent magnetic properties and coating properties according to claim 1, wherein an average heating rate from 800 ° C. to the maximum reached temperature in recrystallization annealing is 0.1 to 80 ° C. per hour. 3. A magnesia applied for forming a primary coating contains boron, strontium / barium, charcoal.
Addition of one or more of nitride-based, sulfide-based, and chloride-based compounds in a total amount of 0.05 to 5.0%, and an average temperature rise from 800 ° C to the maximum reached temperature in the secondary recrystallization annealing. The method for producing a silicon steel sheet having excellent magnetic properties and coating properties according to claim 1, wherein the speed is set to 5 to 400 ° C. per hour. 4. Silicon having excellent magnetic properties and coating properties according to claim 1, wherein the ratio of the partial pressures of nitrogen and oxygen in the primary recrystallization annealing atmosphere is P N ₂ / PH ₂ ≦ 0.5. Steel plate manufacturing method.