JPH02247331A - Production of grain-oriented silicon steel sheet with low iron loss having arbitrary magnetic flux density - Google Patents

Abstract

PURPOSE:To produce the steel sheets of various grades after the primary recrystallization of steel sheet by a simplified process by forming a steel slab heated at low temp. into the final sheet thickness by means of hot rolling and cold rolling and subjecting the resulting sheet to specific nitriding treatment under the strip traveling conditions prior to finish annealing. CONSTITUTION:A slab of a silicon steel having a composition consisting of, by weight, 0.025-0.075% C, 2.5-4.5% Si, <=0.012% S, 0.010-0.060% acid soluble Al, <=0.010% N, 0.05-0.45% Mn, and the balance iron with inevitable impurities is heated up to <=1200 deg.C and formed into the final sheet thickness by means of hot rolling and cold rolling. The resulting steel sheet is subjected, after the conclusion of decarburizing annealing (primary recrystallization), to nitriding treatment so that the amount of nitriding (N) [nitrogen increment in steel] in the steel sheet is regulated to a range between 15 and 150ppm and also a range + or -10% of the amount of nitriding determined by B8(T) (1/1000).N+1.82 corresponding to the level of magnetic flux density (B8 value) provided to the final product under the strip tranveling conditions. Subsequently, a separation agent at annealing is applied to the above steel sheet, followed by high- temp. finish annealing.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing unidirectional electrical steel sheets, and in particular to products with high magnetic flux density (B11 value) to low magnetic flux density from the same material. The present invention relates to a method for manufacturing unidirectional electrical steel sheets that can be manufactured separately.

(Prior art) Unidirectional electrical steel sheets are mainly used as iron core materials for transformers, generators, and other electrical equipment. other,
It must have a good film.

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

The secondary recrystallization phenomenon occurs during the final annealing process, but in order to ensure that secondary recrystallization occurs sufficiently, it is necessary to adjust the secondary recrystallization temperature during the final annealing process. jVN, which suppresses the growth of primary recrystallized grains up to
It is necessary to make so-called inhibitors, which are fine precipitates such as nS and MnSe, exist in the steel. Therefore, electrical steel slabs are made of inhibitor-forming elements such as jV, Mn, S,
1350~ to completely dissolve Se, N, etc.
It is heated to a high temperature of 1400°C. Therefore, the inhibitor-forming elements completely dissolved in the electromagnetic steel slab are finely divided into A7N, MnS, and MnSe by annealing at the intermediate thickness stage before the hot-rolled sheet or final cold rolling. It is allowed to precipitate.

When such a process is adopted, the electromagnetic steel slab is heated to high temperatures as mentioned above, which results in a large amount of molten scale (slag), which only increases the frequency of heating furnace repairs and increases maintenance costs. However, there are problems such as lowering the equipment operating rate and increasing the fuel consumption rate. In order to solve this problem, research is underway on a method for producing grain-oriented electrical steel sheets that can lower the heating temperature of the electrical steel slab. For example, in Japanese Patent Publication No. 61-60896, the Mn content is 0.08 to 0.45% and the S content is 0.08%. A manufacturing process has been proposed in which the slab heating temperature can be lowered to less than 1280°C by lowering the [Mnl [S] product by setting OO to 7% or less, and using an electromagnetic steel slab containing 71J, P, and N as the material. .

Currently, there are several industrialized manufacturing processes for grain-oriented electrical steel sheets based on combinations of ingredients and processing.
The resulting product properties also have their own characteristics.

For example, the manufacturing process in which MnS functions as an inhibitor is a double cold rolling method, and the magnetic flux density (B11 value) of the obtained product is about 1.84 to 1.86 T.

The manufacturing process that allows A7N to function as the main inhibitor is a one-time cold rolling method, and the magnetic flux density (B1
1 value) is high at 1.89 T or more, and the iron loss characteristics are also excellent.

Manufacturers' ideal is to use the same material with a lower level of iron1.
A simple manufacturing process that can provide products with various flux density levels as required by customers while maintaining the same number of employees is desirable.

As one such manufacturing process, Japanese Patent Application Laid-Open No. 61-1
Japanese Patent No. 04025 discloses a technique for manufacturing products with various magnetic flux density levels by changing the reduction ratio in final cold rolling. It would be extremely advantageous in terms of product mix and other aspects if the final plate thickness could be processed under the same conditions and the final product could have various magnetic flux density levels.

(Problems to be Solved by the Invention) The present invention is based on a low-temperature slab heating process in which the heating temperature of the slab is 1200°C or less, and is a one-way process that allows a product with a target magnetic flux density level to be obtained with a simple process. The purpose of this research was to provide a method for manufacturing magnetic steel sheets.

(Means for Solving the Problems) The gist of the present invention is that C: 0.025 to 0.025 by weight.
0.075%, Si: 2.5-4.5%, S≦0.01
2%, acid-soluble At: 0.010-0.060%,
An electromagnetic steel slab containing N≦0,010%, Mn: 0.05 to 0.45%, and the balance consisting of Fe and unavoidable impurities is heated to a temperature of 1200°C or less, then hot rolled and rolled once. Alternatively, in a method for producing a grain-oriented electrical steel sheet, the final thickness is achieved by cold rolling two or more times with intervening intermediate annealing, followed by decarburization annealing, application of an annealing separator, and high-temperature finish annealing. After the completion of primary recrystallization and before high-temperature finish annealing, the amount of nitridation (N) in the steel sheet was determined while the strip was being run.
The nitriding amount (N) of the steel sheet [nitrogen increment in steel] corresponds to the magnetic flux density (Ba value) level that makes the final product have
B, (T)', (1/1000
) The steel strip is nitrided so that the amount of nitridation determined by N + 1.82 is within the range of ±10%, and the magnetic flux density is made to a target value using the same material and the same process.It has an arbitrary magnetic flux density. A method for producing a low iron loss unidirectional electrical steel sheet.

The present invention will be explained in detail below.

The inventors have developed a manufacturing process in which the heating temperature of the electromagnetic steel slab is as low as 1200°C or less, to reliably and stably produce unidirectional electromagnetic steel sheets having any magnetic flux density (B11 value). We have conducted extensive research on possible processes.

As a result, during the slab heating step, inhibitor-forming elements such as Aj, N, Mn.

By nitriding the material after decarburization annealing, that is, after completion of primary recrystallization, without completely dissolving S into the steel, while running the strip in a strongly reducing atmosphere,
(AJ, St) It has been found that by forming an inhibitor whose main composition is N and controlling the amount of nitridation, it is possible to obtain a product with a target magnetic flux density level.

In the present invention, the reason for limiting the composition of the electromagnetic steel slab used as a starting material is as follows.

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

On the other hand, if the C content is too large, exceeding 0.075%, the decarburization annealing time becomes long, which significantly impairs productivity.

When the St content is less than 2.5%, it is difficult to obtain a product with low core loss.On the other hand, when the St content is too high, exceeding 4.5%, the material may crack or crack during cold rolling. Fractures occur frequently, making stable cold rolling operations impossible.

One of the characteristics of the component system of the starting material of the present invention is that S is 0.012% or less, preferably O, OO 7% or less. Conventionally known technology, for example, Japanese Patent Publication No. 40-15
In the techniques disclosed in Japanese Patent Publication No. 644 or Japanese Patent Publication No. 47-25250, S is essential as an element forming MnS, which is one of the precipitates necessary to cause secondary recrystallization. In the above-mentioned known technology, there is a content range in which S exhibits the most effect, and this content range is defined as an amount that allows MnS to be dissolved as a solid solution in the slab heating step performed prior to hot rolling. However, in the present invention using (Aj,5i)N as an inhibitor, MnS
is not particularly required. Rather, an increase in MnS is unfavorable in terms of magnetic properties, so in the present invention,
The S content is 0. OL 2% or less, preferably 0,
OO is 7% or less.

M combines with N to form IVN, but in the present invention, it is essential to form (AI, 5i) N by nitriding the steel after the completion of the post-process, that is, the primary recrystallization. A certain amount or more of M is required. Therefore, 0.010 to 0.060% of acid-soluble M is added.

Even if N is less than 0.0020% or more than 0.0100%, it becomes difficult to create the desired magnetic flux density (B11 value) in the product.

If the content of Mn is too low (less than 0.050%), secondary recrystallization becomes unstable, while if the content exceeds 0.45%, it becomes difficult to obtain a product with a high magnetic flux density.

The appropriate content is 0.070-0.45%.

Note that the inclusion of trace amounts of Cu, Cr, P, B, and Ti in the steel does not impair the spirit of the present invention.

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

Electrical steel slabs are obtained by melting steel in a melting furnace such as a converter or electric furnace, subjecting the molten steel to vacuum degassing treatment as necessary, and then continuous casting or by blooming and rolling after ingot formation. It will be done.

Thereafter, the slab is heated prior to hot rolling. In the process of the present invention, the heating temperature of the slab is 1200
The heating energy consumption is reduced by setting the temperature to be as low as 0.degree.

Furthermore, MnS, which has a higher solid solution temperature, is naturally in an incomplete solid solution state at the above slab heating temperature. After heating, the electromagnetic steel slab is hot rolled and subjected to cold rolling as it is or after annealing if necessary, one time or two or more times with intervening intermediate annealing to obtain the final thickness. The hot-rolled sheet annealing or intermediate annealing is performed in a temperature range known per se for a short time.

Thereafter, decarburization annealing is performed at a temperature range of 800 to 900° C. in a wet hydrogen/nitrogen mixed atmosphere.

However, in the present invention, the slab heating temperature is 1200°C.
It is impossible to build in the inhibitor necessary for secondary recrystallization in a process prior to cold rolling. Therefore, the inhibitor required for secondary recrystallization is
It is necessary to build it up after the completion of the next crystallization and before the appearance of secondary recrystallization in final annealing. As a means for this purpose, (A7,5t)N, which functions as an inhibitor, is formed by infiltrating N into the steel.

Conventionally, nitriding of steel sheets has been performed on tight strip coils with a space factor of about 90%.

In such a tight strip coil state, the gap between the plates is as narrow as 1101I or less, resulting in very poor air permeability.

Therefore, not only does it take a long time to replace the atmosphere between the plates with a dry atmosphere, but it also takes a long time for N2 as a nitriding source to enter and diffuse between the plates. As a means to improve this, attempts have been made to nitriding the steel in the form of a loose strip-top coil, but the problem with nitriding steel in the form of a strip coil is the non-uniformity of the temperature inside the coil. The problem of non-uniformity of nitriding caused by this method is not solved, and it cannot be said to be sufficient.

In order to solve this problem, the inventors first filed a patent application in 1983.
In No. 3-100111, after decarburization annealing, fine (AI, 5t) N, which functions as an inhibitor, is formed in the steel by nitriding the steel plate while running the strip in an NHs atmosphere. I suggested that.

As a result of studying this technology in more detail, the inventors obtained new knowledge that the magnetic properties of the final product change depending on the amount of nitridation in the steel plate (strip). The present invention
It was completed based on this knowledge.

Hereinafter, the present invention will be explained in more detail based on experimental results.

As a sample material, C: 0.050% + Si: 3-3%.

Mn: 0.14% + S: 0.007%, Aj: 0.03
0%.

Cr: 0.12%, the balance is substantially Fe, and the N content is (A): 0.0080% and (B):
Two types of 0.050% vacuum melted materials were heated to 1150'C and hot rolled into hot rolled sheets with a thickness of 2.3 trm. This hot-rolled plate was heated at 1120°C x 60 seconds +900°C.
× After two-step annealing for 120 seconds, pickling and then cold rolling to a cold rolled plate of 0.29mm+thickness (final plate thickness)
And so. After that, decarburization annealing was performed at 830°C for 150 seconds, followed by nitriding at 800°C for 30 seconds with N2:15.
%, Nz: 25% in a dry atmosphere while changing the amount of NH3 added. After that, an annealing separator mainly composed of MgO and TiO2 was applied, and then 1200°C x 20 hours was applied.
Finish annealing of s was performed. Next, a tension coating treatment containing phosphoric acid M and chromic anhydride as main components was performed.

The grain size, magnetic flux density (Be value), and iron loss value (W+, 15°) of the steel plate after final annealing were measured.

The results are shown in FIGS. 1 and 2 in correspondence with the amount of nitridation of the steel plate. As is clear from Fig. 1, the grain size of the product is ASTM k(X
I) is as small as No. 5 or 6, gradually increases when the amount of nitridation exceeds 60 ppm, and becomes No. 2 or 3 when the amount of nitridation exceeds 1100 ppm.

Also, as is clear from Figure 2, the magnetic flux density (B, value)
increases almost linearly as the amount of nitridation increases, and becomes saturated when the amount of nitridation exceeds 140 ppm. This can be determined by the amount of nitridation, regardless of the amount of nitrogen in the steel.

From this, it can be seen that within the range of nitriding amount from 15 to 150 ppm, there is a relationship as follows: BS(T)#(1/1000)-N+1.82 (N: nitriding amount).

Based on this knowledge, the steel plate after decarburization annealing is nitrided within a range of ±10% of the nitriding amount determined by the above formula, depending on the target magnetic flux density (Be value).

The iron loss of the product shows a low value in the high magnetic flux density (B value) region, while even in the low magnetic flux density (B a value) region,
Because the secondary recrystallized grains have become smaller, it shows values comparable to those of conventional products.

Next, the conditions for nitriding will be described.

The temperature for nitriding the steel plate is 700 to 900°C, preferably around 800°C. If the temperature exceeds 900°C, the texture of the steel plate (strip) changes, resulting in poor secondary recrystallization.

The nitriding treatment time is not particularly limited, but when considering in-line nitriding of the steel plate, it is preferably about 30 to 60 seconds.

The atmosphere is N2 or a mixed gas of Hz and N2 to which NH gas is added.

It is preferable that the dew point of the atmosphere is low (dry).

An annealing separator containing MgO as a main component is applied to the steel plate after the nitriding treatment. Known additives such as TiO□ may be added to this annealing separator.

Finish annealing is performed at a high temperature of 1100° C. or higher to develop secondary recrystallized grains and form a good insulation film on the steel sheet.

(Example) Example 1 By weight, C: 0.052%, Si: 3.2%, Mn:
0.14%, acid soluble A7: 0.028%, S
Fo, 006%, N: 0.0075%, remaining 2F
A magnetic steel slab consisting of e and unavoidable impurities is heated to 11
After heating to 50° C., hot rolling was performed to obtain a hot rolled sheet having a thickness of 2.3 mm. This hot-rolled plate was annealed at 1120° C. for 3 minutes, and then cold-rolled to a final thickness of 0.30 m++. This cold-rolled sheet was decarburized and annealed at 850°C for 120 seconds in a mixed gas atmosphere of 15% dew point: 60°C, Hz:
pp…([(NH1)/(N2: 75% 10N)
The nitriding process was carried out at 750°C for 30 seconds in a dry atmosphere of N2nimo gas containing N2H3 (volume ratio). Next, after applying an annealing separator containing MgO and Ti0z, final annealing was performed for 1200″CX20hrs. The relationship was as follows.

As is clear from the above table, the magnetic properties of the final product can be controlled by controlling the amount of nitridation of the material after decarburization annealing.

Example 2 By weight, C: 0.048%, St: 3.5%, Mn:
0.12%, Aj: 0.030%, s:o, oos%,
N: 0.0 (180%, remainder 1e and unavoidable impurities) A magnetic steel slab was heated to 1200'C and then hot rolled to obtain a hot rolled sheet with a thickness of 1.6 mm.This hot rolled sheet was annealed at 1120"C for 2 minutes + 900℃ for 2 minutes (two-stage annealing), then cold rolled to a thickness of 0.1
The final plate thickness was 70 mm. Then, dew point: 55' (
After performing decarburization annealing at 830° C. for 90 seconds in a mixed gas atmosphere of 5% near Hz and 25% Nz, nitriding treatment was performed under the same conditions as in Example 1. After that, MgO and T
Apply an annealing separator containing i0z and heat at 1200°C for 20h.
Final annealing of rs was performed.

The relationship between the amount of NH added, the amount of nitriding, and the magnetic properties of the product was as follows.

Finish annealing was performed at 1200°C for 20 hours.

The relationship between the amount of nitridation in the steel sheet and the magnetic properties of the product was as follows.

Example 3 By weight, C: 0.050%, Si: 3.0%, 'An
: 0.15%, acid soluble A7 F 0.032%, S
? 0.007%, N: 0.0082%, balance: Fe
and an electromagnetic steel slab consisting of unavoidable impurities.
After heating to 0° C., hot rolling was performed to obtain a hot rolled sheet having a body thickness of 2.3 mm.

This hot rolled sheet was pickled and then cold rolled to a thickness of 0.34 mm. Next, dew point: 60°C, Hz: 15% NZ
: After decarburizing annealing at 830°C for 150 seconds in a 25% mixed gas atmosphere, nitriding was performed at 800'CX for 30 seconds in a dry atmosphere of H2 and N2 mixed gas containing NH3. . After that? After applying an annealing separator containing IgO and TiO□, Example 4 by weight, C: 0.060%, Si: 3.3%, Mn:
0.12%, acid soluble Al 70.032%, s:
An electromagnetic steel slab consisting of 0.010% N, 0.0080% N, the balance diFe and inevitable impurities was heated to 1150°C and then hot rolled to form a hot rolled plate with a thickness of 2.0 m.

This hot rolled sheet was pickled and then cold rolled to a thickness of 1.30 mm. Then 1100℃ x 120 seconds +900℃
After annealing for 120 seconds (two-stage annealing), it was pickled again and cold rolled to a thickness of 0.14 mo+.

After that, decarburization annealing was performed at 830°C for 70 seconds at a dew point of 50
The steel plate (strip) was subjected to nitriding treatment at 750"C for 30 seconds in a dry atmosphere of H23N2 mixed gas containing NH. Next, after applying an annealing separator containing MgO and TtO□, finish annealing was performed at 1200°C for 20 hours.

The relationship between the amount of nitridation in the steel plate (strip) and the magnetic flux density of the product is shown below.

For example, since it is possible to manufacture products of various grades after the primary recrystallization of a steel plate, the production structure can be simplified and manufacturing costs can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of nitridation in a steel plate (strip) and the grain size of the product, and FIG. 2 is a diagram showing the relationship between the amount of nitridation in a steel plate (slid-IJ tube) and the magnetic properties of the product. 100 1.93 (Effect of invention)

Claims (1)

[Claims] (1) By weight, C: 0.025-0.075%, Si:
2.5-4.5%, S≦0.012%, acid-soluble Al:
0.010-0.060%, N≦0.010%, Mn:
An electromagnetic steel slab containing 0.05 to 0.45% and the balance consisting of Fe and unavoidable impurities is heated to a temperature of 1200°C or less and then hot rolled, with one or intermediate annealing 2 In a method for producing grain-oriented electrical steel sheets, the plate is cold-rolled several times or more to achieve the final thickness, then decarburized and annealed, coated with an annealing separator, and then high-temperature finish annealed. Under the conditions in which the strip is run in the previous stage, the nitriding amount (N) of the steel sheet corresponds to the magnetic flux density (B_■ value) level that makes the final product have the nitriding amount (N) of the steel sheet.
) The steel strip is nitrided so that the [nitrogen increment in the steel] is within the range of 15 to 150 ppm and within ±10% of the nitriding amount determined by B_■(T)≒(1/1000)・N+1.82. A method for manufacturing a low core loss unidirectional electrical steel sheet having an arbitrary magnetic flux density, characterized in that the magnetic flux density is manufactured to a target value using the same material and the same process. (2) The method for producing a low core loss unidirectional electrical steel sheet having an arbitrary magnetic flux density according to claim 1, wherein the electrical steel slab is hot-rolled and then the hot-rolled sheet is annealed.