JPH0774386B2 - Method for manufacturing unidirectional electrical steel sheet with high magnetic flux density - Google Patents

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, and more particularly, to a slab heating temperature.
The present invention relates to a method for producing a product having an extremely high magnetic flux density by optimizing hot-rolled sheet annealing conditions in a production process at 1200 ° C. or lower, that is, a production process in which an inhibitor is produced after completion of cold rolling.

(Prior Art) A unidirectional electrical steel sheet is mainly used as an iron core material for a transformer, a generator, and other electric devices, and has good magnetic properties such as excitation property and iron loss property. It must have a good film.

The grain-oriented electrical steel sheet is obtained by utilizing the secondary recrystallization phenomenon to develop crystal grains having a so-called Goss orientation having a {110} plane in the rolling surface and a <001> axis in the rolling direction.

The secondary recrystallization phenomenon, as is well known, occurs in the finish annealing process, but in order to sufficiently develop the secondary recrystallization, the secondary recrystallization expression temperature range in the finish annealing process is used. Until then, it is necessary to allow fine precipitates such as AlN, MnS, MnSe, so-called inhibitors, which suppress the growth of primary recrystallized grains, to be present in the steel. Therefore, the electromagnetic steel slab is heated to a high temperature such as 1350 to 1400 ° C. in order to completely dissolve the inhibitor forming elements such as Al, Mn, S, Se and N. Therefore,
The inhibitor-forming element completely dissolved in the electromagnetic steel slab is finely precipitated as AlN, MnS, and MnSe by annealing at the stage of intermediate thickness before hot rolling or final cold rolling.

Japanese Examined Patent Publication No. 46-23820 uses a material of ordinary steel or silicon steel, which is essential to contain C and Al, {110} <001.
In the process step of generating secondary recrystallized grains of> orientation,
Immediately before final cold rolling, after annealing at 750-1200 ℃,
A method of precipitating a preferable size of AlN on a steel sheet by rapidly cooling 750 to 950 ° C. or less depending on the amount, and in JP-A-50-15727, a silicon steel containing C, Al, Mn, N, Cu, etc. In the production of the grain-oriented electrical steel sheet which is hot-rolled and subjected to at least one cold-rolling process, 15 seconds to 2 seconds before the final cold rolling.
Annealed at 760 to 1177 ℃ for a period of time, below 927 ℃ and 400
From the temperature above ℃ to at least 260 ℃, it is faster than natural cooling, and from the maximum temperature to below 927 ℃, 400 ℃
Up to the above temperature, a method of cooling at a slower rate than natural cooling has been proposed.

All of these methods can be applied only to a material which is hot-rolled after the slab heating temperature is raised to completely dissolve the precipitate.

When such a process is adopted, since the electromagnetic steel slab is heated to a high temperature as described above, a large amount of molten scale (slag) is generated, and the heating furnace repair frequency is increased to increase the maintenance cost. However, there is a problem that the facility operation rate is lowered and the fuel consumption rate is increased. In order to solve such a problem, research on a method for producing a grain-oriented electrical steel sheet that can lower the heating temperature of the electrical steel slab is under way. For example, in Japanese Examined Patent Publication No. 61-60896, an electromagnetic wave in which the Mn content is 0.08 to 0.45% and the S content is 0.007% or less, the [Mn] [S] product is lowered, and Al, P, and N are further contained. By using a steel slab as the raw material, a manufacturing process that allows the slab heating temperature to be less than 1280 ° C.
−291975 No. 120 is an electromagnetic steel slab containing Al, N, B, Ti, etc.
Similar processes have been proposed for heating at temperatures below 0 ° C. These methods are characterized in that the inhibitor is not prepared in the pre-process like the high temperature slab heating material, but are built in in the post-process after cold rolling. It suffices to pay attention only to the adjustment of the crystal ratio, the transformation phase, etc.).

(Problems to be Solved by the Invention) What is important in the manufacturing process of the present invention that the heating temperature of the electromagnetic steel slab is as low as 1200 ° C. or less is the crystal structure (average grain size, grain size distribution) of the decarburized annealed sheet. , Texture adjustment and inhibitor build-up (nitriding) after decarburization annealing. In particular, it is known that the crystal structure and texture of the decarburized annealed sheet have a great influence on the magnetic properties of the product.
No. 001778 proposes that the average diameter of primary recrystallized grains is 15 μm or more and the variation coefficient of diameter is 0.6 or less. Factors that influence this structure include the size and dispersion state of the metal structure and precipitates before cold rolling, the annealing temperature after cold rolling, and the steps that affect these are the hot rolled sheet annealing (final It includes annealing before cold rolling) and decarburization annealing.

The present invention was completed by studying in detail the relationship between the hot rolled sheet annealing conditions, the decarburizing annealing conditions, and B ₈ (magnetic flux density at a magnetizing force of 800 A / m).

The present invention will be described in detail below.

The gist of the present invention is as follows.

(1) C: 0.025-0.075% by weight, Si: 2.5-4.5%, S
≦ 0.012%, acid soluble Al: 0.010 to 0.060%, N ≦ 0.010
%, Mn: 0.070 to 0.45%, and the electrical steel slab consisting of the balance Fe and unavoidable impurities is heated to a temperature of 1200 ° C. or less, then hot rolled, once or twice with intermediate annealing. In the production of unidirectional electrical steel sheet in which the final rolling rate is 80% or more by rolling, and then decarburization annealing and finish annealing, the steel sheet before final cold rolling is heated at a primary soaking temperature of 900 to 1080 ° C for 180 ° C.
After soaking within seconds, the second soaking temperature is 750-900 ℃ for more than 30 seconds
It is characterized by performing nitriding treatment on the steel sheet between the heat treatment of cooling for at least 300 seconds and then cooling to room temperature at a rate of 10 ° C / sec or more and the decarburization annealing to the start of secondary recrystallization of the final finish annealing. To produce a grain-oriented electrical steel sheet having a high magnetic flux density.

(2) C: 0.025 to 0.075% by weight, Si: 2.5 to 4.5%, S ≤ 0.
012%, acid soluble Al: 0.010 to 0.060%, N ≤ 0.010%, Mn: 0.0
The method according to item 1 above, wherein an electromagnetic steel slab containing 70 to 0.45% and B: 0.0005 to 0.0080% and the balance Fe and inevitable impurities is used as a starting material.

(3) When the primary soaking temperature of the steel sheet before final cold rolling is t ° C, the relationship with the decarburization annealing temperature T ° C is treated within the range of ± 10 ° C of the temperature shown by T ≒ 1030-1 / 5t 3. The method according to item 1 or 2 above, wherein

In the present invention, the reasons for limiting the component composition of the electromagnetic steel slab used as the starting material are as follows.

When the content of C is less than 0.025%, the secondary recrystallization becomes unstable, and the magnetic flux density (B ₈ value) of the product becomes low, which is less than 1.80 T, even when the secondary recrystallization is performed.

On the other hand, when the content of C exceeds 0.075% and becomes too large, the decarburization annealing time becomes long and the productivity is significantly impaired.

When Si content is less than 2.5%, it is difficult to obtain a product with low iron loss, while when Si content exceeds 4.5% and too much, cracks and fractures frequently occur during cold rolling of the material. , Making stable cold rolling work impossible.

One of the characteristics of the component system of the starting material of the present invention is that S is
It is 0.012% or less, preferably 0.007% or less.
In the conventionally known technology, for example, the technology disclosed in JP-B-40-15644 or JP-B-47-25250, S is one of the precipitates necessary for causing secondary recrystallization. Was essential as a forming element of MnS. In the above-mentioned known art, there is a content range in which S exerts the most effect, and it has been defined as an amount capable of forming a solid solution of MnS in the heating step of the slab performed prior to hot rolling. However, MnS is not particularly required in the present invention using (Al, Si) N as the inhibitor. Rather, MnS
Is not preferable in terms of magnetic properties. Therefore, in the present invention, the S content is 0.012% or less, preferably 0.007% or less.

Al combines with N to form AlN, but in the present invention, it is essential to form (Al, Si) N by nitriding the steel after the post-process, that is, after the completion of primary recrystallization. A certain amount of Al is required. Therefore, 0.010 to 0.060% is added as acid-soluble Al.

N needs to be 0.010% or less. If it exceeds this, swelling of the steel sheet surface called blister occurs. Further, it becomes difficult to adjust the primary recrystallization structure. The lower limit is 0.0020%. Below this value, it becomes difficult to develop secondary recrystallized grains.

If the content of Mn is too small, the secondary recrystallization becomes unstable, while if it is too large, it becomes difficult to obtain a product having a high magnetic flux density. The proper content is 0.070 to 0.45%.

B is in the range of 0.0005 to 0.0080%. B is an element effective as an inhibitor strengthening element especially when manufacturing a thin product having a thickness of 0.23 mm or less. If the content is less than 0.0005%, the effect is thin, but if it exceeds 0.0080%, the effect cannot be expected to increase. A preferred range is 0.0015 to 0.0050%.

In addition, the inclusion of a trace amount of Cu, Cr, P, Ti in the steel,
It does not impair the gist of the present invention.

Next, the manufacturing process of the present invention will be described.

The electromagnetic steel slab is obtained by smelting steel in a melting furnace such as a converter or an electric furnace, subjecting it to vacuum degassing treatment if necessary, and then performing continuous casting or ingot-making and slab-rolling.

After that, slab heating is performed prior to hot rolling. In the process of the present invention, the heating temperature of the slab is set to a low temperature of 1200 ° C. or less to reduce the consumption of heating energy and to make AlN in the steel incompletely in a solid solution state.

Further, MnS having a higher solid solution temperature is naturally in an incomplete solid solution state at the slab heating temperature.

This slab is hot-rolled to make a hot-rolled plate having a predetermined thickness.

Next, the hot rolled sheet annealing, which is a feature of the present invention, will be described based on experimental results.

C: 0.055%, Si: 3.3%, Mn: 0.15%, S: 0.007%, acid soluble A
After heating an electromagnetic steel slab containing l: 0.027%, N: 0.0075%, Cr: 0.12% and the balance Fe and unavoidable impurities to 1150 ℃
The hot rolled sheet was 2.3 mm. Thereafter, hot-rolled sheet annealing was performed under the following conditions.

Primary soaking temperature: 875-1200 ℃ Soaking time: 60 seconds Secondary soaking temperature: 700-950 ℃ Residence time: 120 seconds Figure 1 shows this annealing cycle.

From the secondary soaking temperature range, it was cooled with 100 ° C. hot water.

This is followed by pickling, cold rolling to 0.30 mm, then 1 hour at 830 ° C.
Decarburization annealing for 50 seconds was performed in wet hydrogen / nitrogen gas. After this
Applying an annealing separator mixed with MgO, TiO ₂ and MnN, 1200 ℃
Finish annealing was performed for 20 hours.

This result is shown in FIG.

From this, the range of B ₈ : 1.93T or more is the primary soaking temperature 900
~ 1080 ℃, the secondary soaking temperature range of 750 ~ 900 ℃. It should be noted that when the primary soaking temperature is 900 ° C, the soaking time may be increased and the temperature may be rapidly cooled. Next, using the same material, the primary soaking temperature is 1000 ℃ and the secondary soaking temperature is 900
Fig. 3 shows the relationship between the soaking time and the residence time when the temperature was set to ° C. The conditions under which B ₈ : 1.93 T or more can be obtained from this are that the primary soaking time is 15 seconds or longer, and the residence time in the secondary soaking temperature range is 30 seconds or longer. Regarding the upper limit, the primary soaking time is 180
It is not possible to find a phenomenon in which B ₈ is further improved even when it exceeds the second or when the residence time at the secondary soaking temperature exceeds 300 seconds.

Cooling rate from the secondary soaking temperature region is 10 ° C. / sec or higher B ₈ can be stably obtained. This can also be applied to annealing performed after pickling the hot rolled sheet and cold rolling. The reason why high B ₈ can be obtained by this annealing has not been clarified yet, but at present it is considered as follows.

Factors that influence the secondary recrystallization phenomenon, including the orientation of secondary recrystallization, include primary recrystallization texture (average grain size, grain size distribution), texture, and inhibitor strength.

After the completion of primary recrystallization, the texture and the grain size distribution change with the grain growth. In order to facilitate nucleation of secondary recrystallization and grain growth, the primary recrystallization structure preferably has a uniform grain size and a certain size or more.

On the other hand, the texture is oriented grains ({110} <001
It is necessary to obtain an appropriate amount of oriented grains ({111} <112> orientation, etc.) in which secondary recrystallized grains are likely to grow.

Excluding the rolling rate, the crystal grain size (recrystallization rate) of the steel sheet before cold rolling, the amount of transformation phase, the solid solution C, etc. affect.

In the process of the present invention, the presence of an inhibitor before cold rolling is not preferable because it makes it difficult to control the primary recrystallization structure. In the hot-rolled sheet annealing of the present invention, when the primary soaking temperature is increased to more than 1080 ° C, AlN is dissolved and reprecipitated, and the inhibitor is strengthened. Moreover, since the α phase and the γ phase have different solubilities, non-uniform dispersion is also increased. Therefore, the adjustment of the primary recrystallization structure becomes poor and it becomes difficult to obtain a high B ₈ material.
On the other hand, when this temperature is lower than 900 ° C., recrystallization of the hot rolled sheet does not proceed, which is disadvantageous in obtaining a preferable primary recrystallization texture. The secondary soaking temperature and the cooling rate from this temperature range are necessary to secure a certain size, a certain amount of transformation phase and solute C, which is also a factor in optimizing the primary recrystallization texture. I think it plays a role.

The optimization of the crystal structure and texture is achieved by a combination with the decarburization annealing temperature performed after cold rolling. Cold rolling is expensive
80% or more to obtain B ₈ value. In addition to decarburization, decarburization annealing has a role of adjusting the primary recrystallization structure and forming an oxide layer necessary for forming a film as described above.

This is usually carried out in a wet gas of wet hydrogen and nitrogen in the temperature range of 800 to 900 ° C., but in the present invention, the primary soaking temperature of the hot rolled sheet is t ° C. and the decarburizing annealing temperature is T ° C. Time T ≒ 1030-1 /
It has been found that a particularly high B ₈ is obtained when processed with a relationship of 5 t.

Figure 4 shows the relationship between the hot-rolled sheet annealing temperature and the decarburization annealing temperature and B _8.

C: 0.050%, Si: 3.35%, Mn: 0.12%, S: 0.008%, acid soluble A
A slab containing l: 0.028%, N: 0.0078%, B: 0.0020% and the balance Fe and unavoidable impurities was hot-rolled at 1150 ° C. to 1.8 mm and then hot-rolled sheet annealed. Set the primary soaking temperature to 950 to 1050
The secondary soaking temperature was set to 850 ° C.

After that, cold rolling to 0.20 mm and decarburization annealing were performed at a temperature of 810 to 860 ° C in a wet hydrogen / nitrogen mixed gas with a dew point of 55 ° C. After this MgO
And an annealing separator mixed with TiO ₂ and MnN are applied, and 1200 ℃ × 2
Finish annealing was performed for 0 hr. From the figure, the decarburization annealing temperature is high when the hot-rolled sheet annealing temperature is low, and the decarburization annealing temperature is low when the hot-rolled sheet annealing temperature is high.

In the present invention, as a measure of the decarburization annealing temperature (T), T≈1030-1 / 5t in relation to the primary soaking temperature (t) before final cold rolling.
It can be calculated as ± 10 ° C.

The atmosphere gas is a mixed gas of hydrogen and nitrogen and the dew point is
30 ℃ or higher is recommended.

After decarburization annealing, a nitriding agent, for example, an annealing separator containing Mgo and TiO ₂ added with MnN, CrN and the like is applied, and then finish annealing is performed at a temperature of 1100 ° C. or higher. A gas having a nitriding ability may be used as the atmosphere gas for finish annealing.

As another embodiment, after decarburization annealing, a short time annealing is performed at a temperature of 700 to 800 ° C. in an atmosphere containing a gas having a nitriding ability such as NH ₃ to perform nitriding, and then a known annealing separator is applied to finish. Annealing can also be performed. An example will be described below.

Example 1 C: 0.054%, Si: 3.25%, Mn: 0.14%, S: 0.007%, acid-soluble A
A magnetic steel slab consisting of l: 0.028%, N: 0.0075%, Cr: 0.10%, the balance Fe and unavoidable impurities was heated to 1150 ° C and hot-rolled to obtain a 2.3 mm hot-rolled sheet.

This was annealed under the following conditions.

a) 1120 ° C x 2 minutes → 100 ° C cooling in hot water b) 1120 ° C x 2 minutes + 900 ° C x 2 minutes → 〃 c) 1000 ° C x 2 minutes + 900 ° C x 2 minutes → 〃 d) 900 ° C x 4 minutes → 100 Then, this was pickled and then cold-rolled once to give a final plate thickness of 0.29 mm. Then, perform decarburization annealing at 830 ° C for 150 seconds in a wet hydrogen / nitrogen mixed gas with a dew point of + 60 ° C, and then add T to MgO.
An annealing separator containing 5% by weight of iO ₂ and 5% by weight of manganese ferronitride was applied. Then 120 at a heating rate of 15 ° C / hr
The temperature was raised to 0 ° C and annealing was performed for 20 hours. A mixed gas of N ₂ 50% and H ₂ 50% was used as the atmosphere of this temperature rising process, and H ₂ 100% was set at the time of soaking at 1200 ° C. The magnetic flux density of the product was as follows.

In method c) d) of the present invention, a high magnetic flux density of B ₈ : 1.94T or more was obtained.

Example 2 C: 0.056%, Si: 3.45%, Mn: 0.15%, S: 0.006%, acid-soluble A
A slab containing l: 0.030%, N: 0.0080%, B: 0.0008% and the balance Fe and unavoidable impurities was hot-rolled to 1.6 mm at 1200 ° C, and then hot-rolled sheet annealing was performed under the following conditions.

a) 1120 ° C x 2 minutes + 850 ° C x 2 minutes → 100 ° C in hot water d) 1000 ° C x 2 minutes + 850 ° C x 2 minutes → 〃 c) 950 ° C x 2 minutes + 850 ° C x 2 minutes → 〃 Pickling after this Then, it was cold rolled to 0.17 mm, and then decarburized and annealed at 840 ° C for 70 seconds in a wet hydrogen nitrogen atmosphere with a dew point of 50 ° C. After this, in MgO, TiO ₂ : 5 wt% and ferromanganese ferronitride: 3 wt%
And the annealing separator was added. Then, the temperature was raised to 1200 ° C. at a heating rate of 8 ° C./hr and annealed for 20 hours. The atmosphere during this heating process uses a mixed gas of N ₂ : 25% and H ₂ : 75% up to 800 ° C, and N ₂ : 75% above 800 ° C up to 1200 ° C.
A mixed gas of H ₂ : 25% was used, and H ₂ : 100% was set when soaking at 1200 ° C. The magnetic flux density of the product was as follows.

Very high magnetic flux densities were obtained in methods b and c according to the invention.

Example 3 C: 0.045%, Si: 3.45%, Mn: 0.14%, S: 0.007%, acid-soluble A
A magnetic steel slab consisting of l: 0.030%, N: 0.0073%, balance Fe and unavoidable impurities was heated to 1150 ℃ and then hot rolled.
A hot rolled sheet was obtained with a thickness of 2.0 mm.

This was pickled and cold rolled to a thickness of 1.3 mm.

This was annealed under the following two conditions.

a) 1000 ° C × 4 minutes → 80 ° C cooling in hot water b) 1000 ° C × 2 minutes + 850 ° C × 2 minutes → 〃 After this, pickling and cold rolling to 0.145 mm. Then, decarburization annealing at 830 ° C. for 70 seconds was performed in a wet hydrogen / nitrogen mixed gas.

NH ₃ to Dry mixed gas of 75% and 25% nitrogen hydrogen Thereafter: 100
Nitriding was performed at 750 ° C for 30 seconds by adding 0 ppm.

Next, an annealing separator containing MgO and TiO ₂ was applied and the temperature was set to 1200 ° C.
Finish annealing was performed for 20 hours.

The magnetic properties were as follows.

(Effects of the Invention) According to the present invention, it is possible to manufacture a high magnetic flux density unidirectional magnetic steel sheet having extremely excellent magnetic properties.

[Brief description of drawings]

FIG. 1 is a diagram showing an annealing cycle of a hot-rolled sheet, FIG. 2 is a diagram showing effects of primary soaking temperature and secondary soaking temperature on B ₈ (T) characteristics, and FIG. 3 is primary soaking temperature. FIG. 4 is a diagram showing the influence of time and secondary soaking residence time on the B ₈ (T) characteristic, and FIG. 4 is a diagram showing the relationship between the hot rolled sheet annealing temperature, the decarburizing annealing temperature and the B ₈ characteristic.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yozo Suga 1-1-1 Edamitsu, Hachimanto-ku, Kitakyushu City, Fukuoka Prefecture, Nippon Steel & Co., Ltd. 3rd Technical Research Laboratory (56) Reference JP 62-70521 ( JP, A) JP 63-11408 (JP, B2)

Claims (3)

[Claims] 1. C: 0.025-0.075% by weight, Si: 2.5-4.5 by weight
%, S ≦ 0.012%, acid-soluble Al: 0.010 to 0.060%, N ≦ 0.
An electromagnetic steel slab containing 010% and Mn: 0.070 to 0.45% and the balance Fe and unavoidable impurities is heated to a temperature of 1200 ° C. or lower, then hot rolled and inserted once or by intermediate annealing.
In the production of unidirectional electrical steel sheet in which the final rolling rate is 80% or more by rolling more than once, and then decarburization annealing and finish annealing, the steel sheet before final cold rolling is subjected to 1
After soaking within 80 seconds, the second soaking temperature is kept at 750 to 900 ° C for 30 seconds to 300 seconds, and then cooled to room temperature at a rate of 10 ° C / sec or more Heat treatment and decarburization annealing to final finishing annealing The method for producing a unidirectional electrical steel sheet having a high magnetic flux density, which comprises subjecting a steel sheet to a nitriding treatment before the start of secondary recrystallization. 2. C: 0.025 to 0.075%, Si: 2.5 to 4.5%, S by weight
≦ 0.012%, acid soluble Al: 0.010 to 0.060%, N ≦ 0.010%, M
n: 0.070 to 0.45%, B: 0.0005 to 0.0080%, balance Fe
The method according to claim 1, wherein an electromagnetic steel slab consisting of and unavoidable impurities is used as a starting material. 3. When the primary soaking temperature of the steel sheet before final cold rolling is t ° C., the relationship with the decarburization annealing temperature T ° C. is within a range of ± 10 ° C. of the temperature indicated by T≈1030-1 / 5t. Method according to claim 1 or 2, characterized in that it is processed.