JP2603130B2 - Manufacturing method of high magnetic flux density grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density.

(Prior Art) Grain-oriented electrical steel sheets are mainly used for core materials of transformers, generators, and other electrical equipment, and must have good excitation characteristics and iron loss characteristics as magnetic characteristics.

A 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 on the rolling surface and a [001] axis in the rolling direction.

As is well known, secondary recrystallization occurs during finish annealing.However, in order to sufficiently achieve the appearance of secondary recrystallization, fine Al that suppresses the growth of primary recrystallized grains up to the secondary recrystallization temperature region of finish annealing
It is necessary to have so-called inhibitors, such as precipitates such as N, MnS, and MnSe.

For this reason, the electromagnetic steel slab is heated to a high temperature of about 1350 to 1400 ° C., and the components forming the inhibitor, for example, Al, M
2. Description of the Related Art Annealing is performed in which n, S, Se, N, and the like are completely dissolved, and an inhibitor is finely precipitated on a hot-rolled sheet or an intermediate sheet before final cold-rolling.

By performing such a process, a grain-oriented electrical steel sheet with a high magnetic flux density is manufactured, but since the heating of the electromagnetic steel slab is performed at a high temperature as described above, the amount of generated molten scale is reduced. Large and hinders operation of heating furnace.
There are also problems such as a high energy consumption unit of the heating furnace and the occurrence of surface flaws.

A method for producing a grain-oriented electrical steel sheet at a reduced slab heating temperature is being studied. For example, in Japanese Patent Application Laid-Open No. 52-24116, slab heating is performed at 1110 to 1260 ° C. by including nitride forming elements such as Zr, Ti, B, Nb, Ta, V, Cr, and Mo in addition to Al. Performed manufacturing methods are disclosed. In JP-A-59-190324, a magnetic steel slab containing a low carbon content of 0.01% or less of carbon and selectively containing S, Se, and Al and B is used as a material, and is subjected to primary recrystallization annealing after cold rolling. The slab heating temperature is increased to 1300 ° C by performing pulse annealing in which the steel sheet surface is repeatedly heated to high temperature for a short time.
The following manufacturing method is disclosed. JP-A-59-56
No. 522 discloses that Mn is set to 0.08 to 0.45%, S is set to 0.007% or less, [Mn] [S] product is reduced, and a magnetic steel slab containing Al, P, and N is used as a raw material, whereby slab heating is performed. A production method in which the temperature is set to 1280 ° C. or less is proposed.

(Problems to be Solved by the Invention) As described above, in the production of grain-oriented electrical steel sheets, a method using low-temperature slab heating has been studied, and a certain effect has been achieved. It is difficult to form an effective inhibitor, and further investigation is necessary for industrially stably manufacturing a product having a high magnetic flux density.

The present invention sets the magnetic steel slab to a low temperature of 1200 ° C or less, and industrially stabilizes grain-oriented electrical steel sheets with high magnetic flux density while obtaining advantages such as prevention of generation of molten scale, prevention of surface flaws, and reduction of heating energy. The purpose is to gain.

(Means for Solving the Problems) The gist of the present invention is that C: 0.025 to 0.0% by weight.
75%, Si: 2.5-4.5%, Mn: 0.07-0.45%, S: 0.012% or less, acid-soluble Al: 0.010-0.060%, N: 0.0030-0.010%, P:
0.007 to 0.045%, and if necessary, Cr, Mo, V, N
b, Sb, Sn, Ti, Te, B contains 1.5% or less in total
Electromagnetic steel slabs consisting of iron and unavoidable impurities,
When heated to a temperature of 1200 ° C or less, hot-rolled, hot-rolled or hot-rolled sheet annealed, cold-rolled one or more times with intermediate annealing interposed, and decarburized annealing, wet atmosphere High flux density directional electrical steel sheet characterized by mixing nitrogen with a nitrogen compound gas, decarburizing and nitriding to form an inhibitor with a main composition of (Al, Si) N, applying an annealing separator and finish annealing. Manufacturing method.

 Hereinafter, the present invention will be described in detail.

The present inventors have studied the application of low-temperature slab heating, which heats an electromagnetic steel slab to a temperature of 1200 ° C. or less, to produce a grain-oriented electrical steel sheet having a high magnetic flux density in an industrially stable manner. As a result, at the stage of slab heating, the components forming inhibitors, such as Al, Mn, S, and N, were not dissolved, and when performing decarburization annealing after cold rolling, the atmosphere was changed to a wet atmosphere mixed with nitrogen compound gas. When a steel sheet is run in strip form and denitrification is performed and nitriding is performed, it is easy to nitridate, and a substance mainly composed of (Al, Si) N having a high inhibitory function disclosed in JP-B-62-45285 is formed. It has been found that a grain-oriented electrical steel sheet having a high magnetic flux density can be stably obtained.

The reasons for limiting the component composition of the electromagnetic steel slab to which the present invention is applied are as follows.

The content of C is set to 0.025% or more because the secondary recrystallization becomes unstable when the content of C is small, and the magnetic flux density becomes low even in the case of secondary recrystallization. On the other hand, when the content increases, the decarburization annealing time increases, and it becomes difficult to control the amount of nitriding performed during decarburization.

Si is a component necessary for reducing iron loss and forming an inhibitor, and therefore, is contained in an amount of 2.5% or more. On the other hand, when the content increases, the sheet breaks, edge cracks and the like occur frequently during cold rolling.

Mn has the effect of preventing hot brittleness and improving the quality of the glass film. To achieve this, 0.07% or more is required. On the other hand, if the content increases, the magnetic flux density deteriorates. Furthermore, in the present invention, slab heating
Since the reaction is performed at a temperature of 1200 ° C. or less, for example, the compound MnS with S
Is not completely dissolved and MnS is not used as an inhibitor.

S is likely to cause segregation and is set to 0.012% or less in order to prevent normal growth of secondary recrystallized grains.

Al combines with N or Si to form (Al, Si) N,
Necessary for the appearance and stability of secondary recrystallization, for which 0.010%
It is contained above. On the other hand, the slab heating temperature is
Since incomplete solid solution of Al, if the content of Al increases, inappropriate AlN is formed at the stage of hot rolling.
0.060% or less.

N is combined with Al, Si or the like and is contained in an amount of 0.0030% or more for stabilizing secondary recrystallization. However, if the content increases, surface defects called blisters occur, so that the
010% or less.

P has the effect of increasing the magnetic flux density in the case of low-temperature slab heating, and to achieve this effect, 0.007% or more is required. On the other hand, if the content increases, the cold rolling property deteriorates, so the content is set to 0.045% or less.

Further, if necessary, one of Cr, Mo, V, Nb, Sb, Sn, Ti, Te, B
Contains more than one species.

These Cr, Mo, V, Nb, Sb, Sn, Ti, Te, B have the effect of enhancing the magnetic properties, and therefore, within 0.30% for each component,
One or more of them are contained, but if the total content of these increases, the magnetic flux density deteriorates, so the upper limit is made 1.5%.

Electromagnetic steel slabs are produced by melting in a melting furnace such as a converter or an electric furnace and continuously casting molten steel subjected to vacuum degassing as necessary, or by ingot-bulking rolling. You.

The electromagnetic steel slab is heated prior to hot rolling, and the heating temperature is set to 1200 ° C. or less to save energy, prevent generation of molten scale, and prevent surface flaws. At this heating temperature, Al in the electromagnetic steel slab is not completely dissolved but becomes incompletely dissolved. MnS having a higher solid solution temperature is, of course, incompletely solid solution.

After the slab is heated, it is hot-rolled, and if necessary, annealed, or cold-rolled without annealing. Cold rolling is performed once or twice or more with intermediate annealing therebetween to obtain a final sheet thickness.

In the present invention, since the inhibitor is not yet present in the steel sheet due to the low-temperature slab heating as described above, N is introduced into the steel before the secondary recrystallization occurs, and the inhibitor (Al, S
i) N must be formed. Therefore, in the present invention, in performing decarburization annealing after cold rolling in order to solve this problem, a steel sheet is passed through a strip in a strip shape and decarburization is performed simultaneously with decomposition of a nitrogen compound gas such as NH ₃ gas. With nitriding.
As a result, (Al, Si) N having a high inhibitory function can be easily formed in a short time and in a short time.

In order to perform both decarburization and nitriding in decarburization annealing, the above-mentioned nitrogen compound gas, for example, NH ₃ is contained in an atmosphere of 0.050% or more in a humid atmosphere, under decomposition thereof, and in an atmosphere having a dew point of −30 to + 75 ° C. It is desirable to pass the steel sheet in a strip form at a temperature of 500 to 900 ° C. within 2 minutes. If the nitriding amount at this time is 30 to 300 ppm, a grain-oriented electrical steel sheet having a high magnetic flux density can be obtained.

Thereafter, an annealing separator containing MgO as a main component is applied to the steel sheet and finish annealing is performed.

 Next, examples will be described.

Example 1. By weight, C: 0.048%, Si: 3.00%, Mn: 0.08%, Al: 0.02
5%, S: 0.006%, N: 0.0077%, P: 0.026%, the electromagnetic steel slab consisting of Fe and unavoidable impurities was heated to 1150 ° C, and then hot-rolled to a hot-rolled sheet with a thickness of 2.3 mm. did.

This hot-rolled sheet was annealed at 1120 ° C. for 3 minutes and then cold-rolled to a final sheet thickness of 0.30 mm. The obtained strip was then subjected to a dew point of 65 ° C. and 5000 ppm ｛[(NH ₃ ) / (H ₂ : 75% + N ₂ : 25
%)] = Decarburization annealing at 850 ° C. for 1.5 minutes in a mixed gas atmosphere of H ₂ containing NH ₃ at a volume ratio of ₃ : 75% + N ₂ : 25%, followed by nitriding together with decarburization. The nitriding amount at this time was 240 ppm.

After that, the strip was cooled, then water was added to the annealing separator to form a slurry, and the slurry was applied using a roll coater.Then, the temperature was increased in a drying oven until the strip temperature reached 180 ° C to remove moisture, It was wound up to form a strip coil.

The strip coil was charged into a finish annealing furnace, and normal finish annealing was performed. Table 1 shows the magnetic properties and glass film properties of the obtained products.

The comparative material was prepared by nitriding a steel sheet by supplying nitrogen from a nitriding source added to the atmosphere gas and the annealing separator in a finish annealing furnace.

Example 2. By weight, C: 0.060%, Si: 3.30%, Mn: 0.14%, Al: 0.03
0%, S: 0.010%, N: 0.0085%, P: 0.030%, Mo: 0.008
%, V: 0.005%, magnetic steel slab consisting of balance Fe and unavoidable impurities is heated to 1150 ° C, hot-rolled, and
A 2.0 mm hot rolled sheet was used.

This hot-rolled sheet was annealed at 1120 ° C. for 3 minutes and then cold-rolled to a final sheet thickness of 0.23 mm. The obtained strip was then subjected to a dew point of 55 ° C. and 8000 ppm ｛[(NH ₃ ) / (H ₂ : 75% + N ₂ : 25
%)] = Decarburization annealing at 850 ° C. for 2 minutes in a mixed gas atmosphere of H ₂ : 75% + N ₂ : 25% containing NH ₃ at a volume ratio of _3, and nitriding together with decarburization. The nitriding amount was 180 ppm.

After that, the strip was cooled, then water was added to the annealing separator to form a slurry, and the slurry was applied using a roll coater.Then, the temperature was increased in a drying oven until the strip temperature reached 180 ° C to remove moisture, It was wound up to form a strip coil.

The strip coil was charged into a finish annealing furnace, and normal finish annealing was performed. Table 2 shows the magnetic properties and glass film properties of the obtained product.

The comparative material was prepared by nitriding a steel sheet by supplying nitrogen from a nitriding source added to the atmosphere gas and the annealing separator in a finish annealing furnace.

(Effects of the Invention) According to the present invention, the magnetic steel slab is heated at a low temperature of 1200 ° C or less, and the direction of high magnetic flux density is obtained while obtaining benefits such as prevention of generation of molten scale, prevention of surface flaws, and reduction of heating energy. A magnetic steel sheet can be obtained industrially stably.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Masahiro Yamamoto 1-1-1 Edamitsu, Yawatahigashi-ku, Kitakyushu-city, Fukuoka Prefecture Inside Nippon Steel Corporation Yawata Works (56) References JP-A-1-301820 (JP) JP-A-2-200733 (JP, A) JP-A-2-259017 (JP, A) JP-B-62-45285 (JP, B2)

Claims (2)

(57) [Claims] (1) C: 0.025-0.075% by weight, Si: 2.5-4.
5%, Mn: 0.07 to 0.45%, S: 0.012% or less, acid-soluble Al: 0.01
An electromagnetic steel slab containing 0 to 0.060%, N: 0.0030 to 0.010%, and P: 0.007 to 0.045%, with the balance being iron and unavoidable impurities, is heated to a temperature of 1200 ° C or less, hot-rolled, As-rolled or hot-rolled sheet annealed, cold rolled one or more times with intermediate annealing interposed, and decarburized annealing mixed with a nitrogen compound gas in a humid atmosphere and nitrified with decarburization ( Al, S
i) A method for producing a high magnetic flux density grain-oriented electrical steel sheet, comprising forming an inhibitor containing N as a main composition, applying an annealing separator, and performing finish annealing. 2. C: 0.025-0.075% by weight, Si: 2.5-4.
5%, Mn: 0.07 to 0.45%, S: 0.012% or less, acid-soluble Al: 0.01
0-0.060%, N: 0.0030-0.010%, P: 0.007-0.045%, and in addition, one or more of Cr, Mo, V, Nb, Sb, Sn, Ti, Te, B, 1.5% or less in total Containing, the remainder is heated to a temperature of 1200 ° C. or less, electromagnetic steel slab consisting of iron and unavoidable impurities,
Hot-rolled, hot-rolled or hot-rolled sheet annealed, cold-rolled one or more times with intermediary annealing interposed, and decarburized annealing mixed with nitrogen compound gas in a humid atmosphere A method for producing a high magnetic flux density grain-oriented electrical steel sheet, comprising nitriding with carbon, forming an inhibitor mainly composed of (Al, Si) N, applying an annealing separator, and finish annealing.