JPH0417618A - Production of grain-oriented electrical steel sheet having excellent magnetic characteristic - Google Patents

Abstract

PURPOSE:To produce the grain-oriented electrical steel sheet having excellent magnetic characteristics by controlling the nitridation quantity of a strip after the completion of primary recrystallization before high-temp. finish annealing to a specific range at the time of producing the grain-oriented electrical steel sheet having specific comps. components. CONSTITUTION:The electrical steel slab consisting, by weight%, 0.025 to 0.075 C, 2.5 to 4.5 Si, <=0.015 S, 0.010 to 0.050 Al soluble in acid, <=0.010 N, 0.05 to 0.45 Mn, and the balance Fe and unavoidable impurities is heated to <=1200 deg.C and is then hot rolled. The nitridation quantity is so controlled that the nitridation quantity [N](ppm) of the steel sheet at an average crystal grin size d(mu) attains a range of 16d-90>N>60d-1400 (lower limit value: 100ppm) while a strip travels in the stage after the completion of the primary recrystallization before the high-temp. finish annealing at the time of cold rolling the slab to a final sheet thickness, then subjecting the steel sheet to decarburization annealing, application of an annealing and separating agent, and high-temp. finish annealing. The grain-oriented electrical steel sheet having the excellent magnetic characteristics under high production is stably obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing grain-oriented electrical steel sheets with excellent magnetic properties.

[Conventional technology]

Unidirectional electrical steel sheets are mainly used as iron core materials for transformers, generators, and other electrical equipment, and in addition to having good magnetic properties such as excitation properties and iron loss properties,
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, which has a {1101 plane on the rolled surface and an <OOX> axis in the rolling direction.

As is well known, the secondary recrystallization phenomenon occurs during the finish annealing process, but in order to sufficiently express the secondary recrystallization, it is necessary to keep the temperature up to the temperature range in which the secondary recrystallization occurs during the finish annealing process. AZN, I'lnS, M suppressing the growth of primary recrystallized grains
Fine precipitates such as nSe, so-called inhibitors, must be present in the steel. Therefore, the electromagnetic steel slab contains inhibitor-forming elements such as AI, Mn, S, Se,
1350-1400 in order to completely dissolve N etc.
It is heated to a high temperature such as °C. The inhibitor-forming elements completely dissolved in the slab are annealed at the intermediate thickness stage before the hot-rolled sheet or the final cold rolling.
It is finely precipitated as N, MnS, and MnSe.

When such a process is adopted, the electromagnetic steel slab is heated to high temperatures as mentioned above, so a large amount of molten scale is generated, increasing the frequency of heating furnace repairs, increasing maintenance costs, and reducing equipment costs. There are problems such as lowering the operating rate and increasing the fuel consumption rate.

In order to solve these problems, research is underway on a method for manufacturing unidirectional electrical steel sheets that can lower the heating temperature of the electrical steel slab.

For example, in JP-A-52-24116, in addition to AI, Zr, Ti, B, Nb, Ta, V, C
By incorporating nitride-forming elements such as R and Mo into the steel, the heating temperature of the electromagnetic steel slab can be increased to 1100-1260°C.
℃ manufacturing method has been proposed.

In addition, JP-A-59-190324 discloses that the C content is as low as 0.01% or less, and S, Se, and A
The material is an electromagnetic steel slab that selectively contains I and B,
It has been proposed to reduce the heating temperature of an electromagnetic steel slab to 1300° C. or lower by performing so-called pulse annealing, in which the surface of the steel sheet is repeatedly heated at high temperature for a short period of time during primary recrystallization annealing after cold rolling.

Furthermore, Japanese Patent Publication No. 61-60896 discloses that the (Mn) (S) product is lowered by setting the Mn content to 0.08 to 0.45% and the S content to 0.007% or less. ,
P.

A manufacturing process has been proposed in which the slab heating temperature is lower than 1280° C. by using an electromagnetic steel slab containing N as the material.

This is characterized by incorporating a so-called inhibitor that suppresses the growth of crystal grains after decarburization annealing. Based on this technical idea, for example,
No. 3-100111 proposed a method in which the strip is nitrided while running after completion of primary recrystallization and before high-temperature finish annealing. Furthermore, Japanese Patent Application No. 1-82393 states that there is a very strong correlation between the grain size of primary recrystallized grains and the magnetic flux density of the product, and that it is necessary to change the nitriding conditions depending on the primary crystal grain size.

[Problem to be solved by the invention]

The present invention lowers the heating temperature of the magnetic steel slab to 1,200°C or less, thereby suppressing increases in maintenance costs, decreases in equipment utilization rate, and furthermore, decreases in productivity due to high-temperature slab heating, resulting in excellent high productivity. It is an object of the present invention to provide a manufacturing method that can stably produce unidirectional electrical steel sheets having magnetic properties.

[Means to solve the problem]

The gist of the present invention is that in weight %, C: 0.02
5-0.075%, Si: 2.5-4.5%, S≦
0.015%, acid-soluble Al: 0.010-0.0
50%, N≦0.010%, Mn: 0.05-0.4
After heating a magnetic steel slab containing 5% Fe and unavoidable impurities to a temperature of 1200°C or less, it is hot rolled and cold rolled on two or more sides with intervening round or intermediate annealing. The final plate thickness is determined by decarburization annealing and nitriding treatment, but when the average grain size of the primary recrystallized grains after decarburization annealing is dgm, the (N) amount (ppm) of the steel plate is 16d90>N>
60d-1400 (lower limit: 100 ppm) after controlling the amount of nitriding under conditions that satisfy the relationship, an annealing separator is applied, and high temperature finish annealing is performed.

The present invention will be explained in detail below.

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 (Boo value) of the product will be 1. It will be as low as 80 Tesla. 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 Si content is less than 2.5%, the product thickness is 0.30 mm and the power consumption is 1.05 W/kg at W+7150.
From this point of view, the lower limit of the Si content is preferably 3.2%, since it is not possible to obtain a product with iron loss properties of the following highest grade. On the other hand, if the Si content is too high, exceeding 4.5%, the material often cracks and breaks during cold rolling, making stable cold rolling impossible.

One of the characteristics of the component system of the starting material of the present invention is that S is 0.015% or less, preferably 0.0070% or less.

As is well known, S forms MnS and acts to suppress grain growth. The present invention is characterized in that the inhibitor necessary for the development of secondary recrystallized grains is built in after decarburization annealing, and the dispersion of fine precipitates before cold rolling reduces the primary recrystallized grain size. This is not preferred in the present invention, which adjusts to obtain a high magnetic flux density. Therefore, S is set to 0.015% or less.

Furthermore, reducing the amount of S has a great effect in reducing edge cracking during hot rolling.

Al is necessary to form AIN or (AI, 5i)N and to form a precipitate necessary for secondary recrystallization, and the amount thereof is 0.010% or more and 0.050% or less. 0.
If it is less than 0.010%, a steel plate with high magnetic flux density cannot be obtained;
．． If it exceeds 0.050%, the development of secondary recrystallized grains becomes unstable.

When the N content exceeds 0.010%, swelling of the surface of the steel sheet called blister occurs.

If the Mn content is too low (less than 0.05%), secondary recrystallization becomes unstable, while if the Mn content is too large (more than 0.45%), it becomes difficult to obtain a product with a high magnetic flux density.

In addition, trace amounts of Cu, Sn, Cr+P, B,
Including Ti alone or in combination in steel is
This does not detract from the spirit of the present invention.

Next, the manufacturing process will be explained.

Electromagnetic steel slabs are produced by melting steel in a melting furnace such as a converter or electric furnace, subjecting the molten steel to vacuum degassing treatment if necessary, and then continuous casting or blooming after ingot formation. obtained by. Thereafter, the slab is heated 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 heating energy consumption, and AIN and MnS in the steel are not completely dissolved in solid solution but are in an incomplete solid solution state.

After heating, the electromagnetic steel slab is hot-rolled, either as it is or annealed if necessary, and then cold-rolled once or twice or more with intermediate annealing to achieve the final thickness. Ru. When a hot rolled sheet is annealed at a temperature of 900° C. or higher and 1200° C. or lower for at least 30 seconds or more, the magnetic properties are improved compared to the case where it is not annealed.

By the way, in the present invention, the magnetic steel slab is 1200
Heated to a low temperature below ℃. Therefore, AI in steel,
Mn, S, etc. are in an incomplete solid solution state, and if left as is, there will be sufficient A to cause secondary recrystallization to occur in the steel sheet.
There are no inhibitors such as lN, (AI,5i)N, etc. Therefore, before the secondary recrystallization occurs, it is necessary to infiltrate N into the steel to form (AI, 5i) N that functions as an inhibitor. In the method described in Japanese Patent Publication No. 6245285, the steel plate is nitrided in the form of a tight strip coil with a space factor of about 90%. In such a tight strip coil condition, the gap between the plates is 10
- It is narrow and has very poor ventilation. 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. In addition, non-uniform nitriding caused by non-uniform temperature within the coil and control of the amount of nitriding also became a problem. In order to solve this problem, Japanese Patent Application No. 1-91
In No. 956, fine particles (AI, 5
i) A method of forming N in steel was proposed.

When considering nitriding a steel plate (strip) in-line, it is essential that the steel plate can be nitrided in a short time (30 seconds to 1 minute).

If the steel sheet is nitrided before decarburization annealing, nitrogen can easily penetrate into the steel, but this inhibits the growth of primary recrystallized grains that are generated during decarburization annealing, and ultimately reduces the magnetic flux of the product. This results in inhibiting the orientation or growth of secondary recrystallized grains, which is directly related to density.

After adjusting the primary recrystallized grain size to a certain size, ideal nitriding can be achieved by performing nitriding treatment, for example, in the latter half of decarburization annealing.

As a result of a detailed study of this technology, the present inventors have found that a product with particularly excellent magnetic properties can be obtained under conditions where a certain relationship exists between the primary recrystallized grain size of the steel sheet and the amount of nitridation.

The present invention was completed based on this knowledge.

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

As sample material, C: 0.054%, Si: 3.3
%, Mn: 0.12%, acid-soluble Al: 0.028
%, Cr: 0.12%, N: 0.0075%, the balance consists of Fe and unavoidable impurities, and the S content is varied in the range of 0.03 to 0.15%. ℃ and hot rolled to prepare a hot rolled sheet having a thickness of 2.0 mm.

This hot-rolled plate was heated at 1120℃ for 60 seconds + 900℃ for 120 seconds.
After annealing for a second, it was rapidly cooled with hot water at 100°C, pickled, and then cold-rolled to obtain a cold-rolled plate with a thickness of 0.23 mm. Thereafter, decarburization annealing was performed at a temperature of 800 to 870° C. for 120 seconds in a warm hydrogen and nitrogen atmosphere. After this 75
Nitriding treatment at 0°C x 30 seconds with N2 near 5%, N: 25
% in a dry atmosphere with varying amounts of NH3 added. Thereafter, an annealing separator containing MgO and TiOz as main components was applied, followed by final annealing at 1200° C. for 20 hours. The results are shown in FIG. 1 in terms of the relationship between the original crystal grain size, the amount of N after nitriding, and the magnetic properties.

The crystal grain size was adjusted by a combination of the S content of the material and the decarburization annealing temperature, while the [N) amount was adjusted by the amount of NH3 added. In the figure, the ○ mark indicates the iron loss characteristic of W. It is 0.95 Sakaki/kg or more, and the * mark is 0, 94 w/k.
It shows the characteristics below g. In addition, Δ marks indicate poorly developed secondary recrystallized grains and extremely poor magnetic properties. The area in which a product with excellent magnetic properties can be obtained is 16 d-, where the amount of (N) (ppm) in the steel plate is N, and the average grain size of the crystals is d4.
9'O>N>60 d1400 is within the range, and the lower limit of N is 100 ppm. The upper limit is preferably 250 ppm or less. Exceeding this tends to have an adverse effect on film formation. This relationship holds true even if the thickness of the finished product changes.

Next, the nitriding conditions will be described.

The temperature for nitriding the steel plate is 700-900°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 one in which NH3 gas is added to N2 or a mixed gas of N2 and N2.

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 Tie 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: o, oso%, Si: 3.3%, Mn
: 0.12%, Al: 0.028%, S:
0.009%, Cr: 0.12%, N: 0.0
075%, balance Fe and unavoidable impurities
i. A steel slab is heated to 1200°C and hot rolled; 2.
It was made into a hot-rolled plate with a thickness of 3 mm.

This hot-rolled sheet was annealed at 1120°C for 2.5 minutes + 900°C for 2 minutes, and then cooled in a vortex at 100°C. It was then pickled and cold rolled to a final thickness of 0.30 mm+.

Next, decarburization annealing was carried out at a temperature of 800" C, 1830 C, 1850 C for 120 seconds. The atmosphere gas was 25% N2,
A mixed gas of 75% N2 was used, and the dew point was 50°C.

The average grain size after decarburization annealing is 15p, 21p, and 21p, respectively.
It was 26trm. Next, NH was added to a dry atmosphere gas containing 25% N and 75% N, and the mixture was heated at 750°C
Second nitriding treatment was performed. The amount of (N) after nitriding is approximately 15
They were 0 ppm, 220 ppm, and 310 ppm.

Thereafter, an annealing separator containing a mixture of MgO and TiO2 was applied, and annealing was performed at 1200° C. for 20 hours. The magnetic properties are shown in Table 1.

Excellent magnetic properties were obtained within the N amount range that satisfied the conditions of the present invention for each crystal grain size.

<Example 2> By weight, C: 0.045%, Si: 3.2%, Mn
: 0.10%, AI: 0.030%, s: o
, oos%, N: 0.0070%, balance Fe and unavoidable impurities, a magnetic steel slab was heated to 1150° C. and then hot rolled to obtain a hot rolled sheet with a thickness of 2.3n+m. This hot rolled sheet was pickled and cold rolled to a final thickness of 0.35 mm. Next, decarburization annealing was performed at 820°C and 850°C.
The test was carried out for 160 seconds at a temperature of .

A mixed gas of 225% N and 75% N was used as the atmospheric gas, and the dew point was 60°C. The average grain size of the decarburized annealed plate is 1
It was 9uTn and 25-. After this, N225%, N27
Add NH to 5% dry atmosphere gas and heat at 750°C.
After nitriding for 30 seconds, the amount of (N) after nitriding was approximately 1
50 ppm and 250 ppm. After this, MgO and T
Apply an annealing separator mixed with iO□ and heat at 1200℃ x 2
Annealing was performed for 0 hours.

The magnetic properties are shown in Table 2.

Those within the condition range of the present invention have excellent magnetic properties.

(Effects of the Invention) According to the present invention, a unidirectional electrical steel sheet with excellent magnetic properties can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the primary recrystallized grain size, the amount of N after nitriding, and the magnetic properties.

Claims (2)

[Claims] (1) C: 0.025-0.075%, Si: 2 by weight
．． 5-4.5%, S≦0.015%, acid-soluble Al: 0
．． 010-0.050%, N≦0.010%, Mn:0
．． A magnetic steel slab containing 05 to 0.45% with the remainder Fe and unavoidable impurities is heated to a temperature of 1200°C or less, hot rolled, and then cooled once or twice or more with intermediate annealing. In a method for producing grain-oriented electrical steel sheets in which the plate is rolled to the final thickness, then decarburized annealed, coated with an annealing separator, and then subjected to high-temperature finish annealing, the stage after completion of primary recrystallization and before high-temperature finish annealing The amount of nitrogen [N] (ppm) in the steel sheet at the average grain size d (μm) under the conditions in which the strip is run at 16d-90>N>60d-14
A method for producing a grain-oriented electrical steel sheet with excellent magnetic properties, the method comprising controlling the amount of nitriding to be within the range of 0.00 (lower limit: 100 ppm). (2) The method for producing a unidirectional electrical steel sheet with excellent magnetic properties according to claim 1, characterized in that the hot rolled sheet is annealed at a temperature of 900°C or more and 1200°C or less.