JPH02228425A - Production of grain-oriented silicon steel sheet with high magnetic flux density - Google Patents

Abstract

PURPOSE:To stably produce a grain-oriented silicon steel sheet with high magnetic flux density at a low cost by hot-rolling a slab of a silicon steel having a specific composition consisting of C, Si, Mn, S, Al, N, and Fe at low temp., carrying out nitriding annealing, and then performing final cold rolling. CONSTITUTION:A slab of a silicon steel which has a composition consisting of, by weight, 0.025-0.095% C, 2.0-4.0% Si, 0.08-0.45% Mn, <=0.012% S, 0.010-0.060% Al, 0.0030-0.0130% N, and the balance Fe with inevitable impurities and further containing, if necessary, either or both of 0.005-0.050% P and 0.05-0.25% Cr and/or <=1.5% of one or more elements among Mo, V, Nb, Sb, Sn, Ti, Te, and B is heated up to <=1200 deg.C and hot-rolled. The resulting hot rolled plate is subjected, in an as-hot-rolled state or in an annealed state, to cold rolling once or is cold-rolled twice or more, while process-annealed between the cold rolling stages, and then, the resulting cold rolled sheet is subjected to decarburizing annealing and finish annealing. At this time, in the course of the process annealing before the final cold rolling, the sheet is nitrided at 600-850 deg.C under the decomposition of nitrogen compound gas for a time as short as <2min, by which an inhibitor composed principally of (Al, Si)N is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a high magnetic flux density grain-oriented electrical steel sheet.

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

Grain-oriented electrical steel sheets use the secondary recrystallization phenomenon to form (
It is obtained by developing crystal grains having a so-called Goss orientation with a (001) axis in the rolling direction and a (110) plane.

As is well known, secondary recrystallization occurs during finish annealing, but in order to sufficiently express secondary recrystallization, fine AjNl that suppresses the growth of primary crystal grains up to the secondary recrystallization temperature range of finish annealing is required.
, MnS, MnSe and other precipitates, so-called inhibitors, must be present.

For this reason, the electromagnetic steel slab is heated to a high temperature of about 1350 to 1400'C to completely dissolve the inhibitor-forming components, such as Aj + Mn + S + Se + N, into a hot-rolled sheet or final cold-rolled sheet. The previous intermediate plate is annealed to finely precipitate the inhibitor.

By applying this type of treatment, grain-oriented electrical steel sheets with high magnetic flux density are manufactured, but as the electrical steel slabs are heated at high temperatures as mentioned above, the amount of molten scale generated is low. If the temperature is too large, it will interfere with the operation of the heating furnace. There are also problems such as high energy consumption of the heating furnace and occurrence of surface scratches.

A method for manufacturing grain-oriented electrical steel sheets that lowers the slab heating temperature is being considered. For example, in JP-A-52-24116, in addition to M, Zr, TtlBINb, Ta,
A manufacturing method is disclosed in which the slab is heated at 1100 to 1260° C. by incorporating nitride-forming elements such as V and Cr+Mo.

In JP-A-59-190324, the C content is 0.0.
A magnetic steel slab with low carbon content of 1% or less and selectively containing S, Se, and AZ and B is used as a raw material, and during primary recrystallization annealing after cold rolling, pulse annealing is performed in which the steel plate surface is repeatedly heated to a high temperature for a short period of time. By increasing the slab heating temperature to 1300
℃ or less is disclosed. Also, JP-A-59
-5622 publication, Mn is 0.08 to 0.060°S
By reducing the (Mn) (S) product to 0.007% or less, and using an electromagnetic steel slab containing Aj, P, and N as the material, we have developed a manufacturing method that reduces the slab heating temperature to 1280°C or less. is suggesting.

(Problems to be Solved by the Invention) As described above, methods using low-temperature slab heating have been studied in the production of grain-oriented electrical steel sheets, and have achieved certain effects. Consideration is required for stable expression.

The present invention heats the electromagnetic steel slab at a low temperature of 1200°C or less, thereby obtaining advantages such as prevention of molten scale, prevention of surface flaws, reduction of heating energy, and cost reduction, while industrially producing grain-oriented electrical steel sheets with high magnetic flux density. The aim is to obtain stable results.

(Means for Solving the Problems) The gist of the present invention is that C; o, o2! in weight%!
5~O, 095%.

St: 2.0-4.0%.

Mn: 0.08-0.45%.

S: 0.012% or less.

AZ; 0.010-0.060%.

N, 0.0030 to 0.0130%, and optionally p; o, oos% to 0.050%,
Cr; 0.05 to 0.25% of one or two types, Mo
, Si, NbSb, Sn + Ti, Te, and B in a total of 1.5% or less, with the balance consisting of iron and unavoidable impurities. Inter-rolled, as hot-rolled or hot-rolled plate annealed,
Cold rolling is performed once or twice or more with intermediate annealing in between,
In the manufacturing method of grain-oriented electrical steel sheet, which involves decarburization annealing, applying an annealing separator, and finish annealing, the intermediate annealing before the final cold rolling is performed at 60°C.
A high magnetic flux density direction characterized by forming an inhibitor whose main composition is (Af, Si) N by nitriding for a short time of less than 2 minutes under decomposition of nitrogen compound gas at a temperature of 0°C or higher and 850°C or lower. The manufacturing method of electromagnetic steel sheet.

The present invention will be explained in detail below.

The present inventors applied low-temperature slab heating to electrical steel slabs in order to produce grain-oriented electrical steel sheets with high magnetic flux density in an industrially more stable manner. As a result, during the slab heating stage, the inhibitor-forming component NJln, 5. If N and the like are not dissolved in solid solution, the interval of M in the steel is made larger than that of high-temperature slab heating, and nitriding is performed for a short time in the intermediate annealing before the final cold rolling, highly functional inhibitors (AZ,
It has been found that S i ) N can be stably formed on a steel plate and a steel plate with high magnetic flux density can be obtained.

The composition of the electromagnetic steel slab to which the present invention is applied is as follows.

If the C content is low, secondary recrystallization becomes unstable, and even if secondary recrystallization occurs, the magnetic flux density will be low, so it is set to 0.025% or more.

On the other hand, if the content increases, the decarburization annealing time becomes longer, so the content should be 0.095% or less.

Si is a necessary component for reducing iron loss and forming an inhibitor, and is required in an amount of 2.0% or more. On the other hand, if the content increases, embrittlement becomes severe and plate breakage, edge cracking, etc. occur frequently during cold rolling, so the content should be 4.0% or less.

Kn has the effect of preventing hot brittleness and improving the quality of the glass coating, and 0.08% or more is required to achieve this effect. On the other hand, if the content increases, the magnetic flux density deteriorates, so the content should be 0.45% or less. Further, in the present invention, since the slab is heated at a temperature of 1200° C. or lower, the upper limit is set as described above, since the compound MnS with S, for example, does not form a solid solution during the heating and MnS is not used as an inhibitor.

Since S tends to cause segregation and is harmful to the development of secondary recrystallization, its content is kept at 0.012% or less, and the slab is heated at a low temperature as described above.

N combines with N or Si to form (Af, 5t)N, which is necessary for secondary recrystallization and its stability, and is 0.010
% or more. On the other hand, the slab heating temperature is 1200℃
Since M is incompletely dissolved in the solid solution below, if the M content increases, inappropriate IVN will be formed in the hot rolled sheet and the magnetic properties will deteriorate, so the M content is set to 0.060% or less.

N is contained in the steel before nitriding in an amount of 0.003Q% or more in order to combine with Af, Si, etc. to form (Aj, 5i)N necessary for stabilizing secondary recrystallization. However, if its content increases, surface defects called blisters will occur, so it should be kept at 0.0130% or less.

Furthermore, one or both of P and Cr may be contained as necessary. Also, Mo+ L Nb, Sb, sn,
Contains one or more of ri, Te, and B.

P has the effect of increasing the magnetic flux density in the case of low-temperature slab heating, and in order to exhibit this effect, 0.005% or more is required. On the other hand, if its content increases, cold rollability deteriorates, so the content should be 0.050% or less.

Cr has the effect of increasing the magnetic properties by expanding the range of 71+7 amount at which high magnetic flux density can be obtained, and 0.05% or more is required to achieve this effect. On the other hand, if the content increases, decarburization performance deteriorates, so the content is set to 0.25% or less.

MO, V, Nb, Sb, 5nlTi, Te, B are added at 0.30% for each component as necessary to improve magnetic properties.
However, if the total content of these components exceeds 1.5%, the magnetic flux density will deteriorate, so the upper limit of the total amount is 1.5%.

Electrical steel slabs containing the above components, with the remainder consisting of iron and unavoidable impurities, are melted in a melting furnace such as a converter or electric furnace, subjected to vacuum degassing treatment as necessary, and then continuously cast or ingot-formed. - Manufactured by blooming rolling.

Electrical steel slabs are heated prior to hot rolling, but the heating temperature is such that it does not harm the secondary recrystallization of S, does not completely dissolve AJN and MnS generated during slab manufacturing, and prevents subsequent nitriding. In order to form the inhibitor (A/, 5i)N, the temperature is set to 1200° C. or lower. Such heating is very effective not only in terms of energy saving, but also in terms of preventing the occurrence of melted scale, preventing surface flaws, and reducing costs.

After heating the slab, it is hot rolled and optionally annealed, or cold rolled without annealing. Cold rolling is performed once or twice or more with intermediate annealing in between to obtain the final plate thickness.

In the present invention, as mentioned above, since the slab is heated at a low temperature, no inhibitor is present in the steel sheet. For this reason, N is introduced into the steel to form an inhibitor (AI, St) N before final annealing to cause secondary recrystallization.

(jV, 5i)N, which has a strong inhibitory effect, cannot be obtained simply by adding N to a steel plate. Therefore, the present inventors conducted research to solve this problem and found that it is best to nitridize the steel plate for a short time during intermediate annealing before final cold rolling. Nitriding is carried out for a short time of less than 2 minutes under the decomposition of nitrogen compound gas.
The reason why it is carried out at 00°C or higher is that if this temperature is low, (k!, S i )N, which has a strong inhibitory effect, will not be formed.
Further, if the temperature becomes too high, the amount of nitridation decreases, and in this case as well, (N, 5i)N is not formed. The reason why nitriding is carried out for less than 2 minutes under the decomposition of nitrogen compound gas is that nitriding for 2 minutes or more does not increase the magnetic flux density of the product. The atmosphere under decomposition of nitrogen compound gas does not necessarily mean that the entire atmosphere is like that; for example, the atmosphere of I+, N, etc. must contain 0.1% or more of nitrogen compound gas such as NHi or NO. The amount of nitriding may be 90 to 3'OO ppm.

Further, in the case of a single cold rolling method, the intermediate annealing before the final cold rolling corresponds to the annealing of the hot rolled sheet.

After nitriding, it is cold rolled, decarburized and annealed, coated with an annealing separator, and finished annealed.

Next, examples will be described.

Example-1 A slab having the composition shown in Table 1 was heated under the conditions shown in the same table, hot rolled to a thickness of 2.3fflI11, and then either as hot rolled or annealed as a hot rolled sheet, and intermediate annealed. It was sandwiched and cold rolled to have a thickness of 0.30, 0.25, and 0.20 an.

In the intermediate annealing, nitriding was carried out under the conditions shown in the same table in an atmosphere of H and N mixed with 10% NH3. After that, decarburization annealing is performed at 85
0°C for 3 minutes, dew point 60°C (z; 75%, Hz;
The annealing was carried out in an atmosphere consisting of 25%, and then an annealing separator was applied to the steel plate, and final annealing was carried out at 1200°C.

The magnetic properties and coating properties of the obtained steel plate were measured, and the results are shown in Table 2.

(Effect of the invention) As is clear from the examples, a highly functional inhibitor (Aj, 5t
) By forming N, a grain-oriented electrical steel sheet having a high magnetic flux density can be obtained by fully utilizing the advantages of low-temperature slab heating.

(Note) 1. Film adhesion; Diameter λ that does not peel off when bent 180 degrees. Film defect: Spot-like, sparkling metallic luster in areas where there is no glass film.

Claims (4)

[Claims] (1) C in weight%; 0.025-0.095%, Si;
2.0 to 4.0%, Mn; 0.08 to 0.45%, S; 0.012% or less, Al; 0.010 to 0.060%, N; 0.0030 to 0.0130%. A magnetic steel slab containing iron and unavoidable impurities is heated to a temperature of 1200°C or less and hot rolled,
A method for producing a grain-oriented electrical steel sheet, which comprises annealing the as-hot-rolled or hot-rolled sheet, cold rolling once or twice or more with intermediate annealing, decarburizing annealing, applying an annealing separator, and finish annealing. In the intermediate annealing before the final cold rolling, at a temperature of 600°C or more and 850°C or less, the product is nitrided for a short time of less than 2 minutes under the decomposition of nitrogen compound gas to form an inhibitor whose main composition is (Al, Si)N. A method for producing a high magnetic flux density grain-oriented electrical steel sheet. (2) C in weight%; 0.025-0.095%, Si;
2.0 to 4.0%, Mn; 0.08 to 0.45%, S; 0.012% or less, Al; 0.010 to 0.060%, N; 0.0030 to 0.0130%. Contains, furthermore, P; 0.005 to 0.050%, Cr
; An electrical steel slab containing 0.05 to 0.25% of one kind or two kinds, with the balance consisting of iron and unavoidable impurities,
Heating to a temperature of 00°C or less, hot rolling, annealing as hot rolled or hot rolled sheet, cold rolling once or twice or more with intermediate annealing, decarburizing annealing, annealing separator In the method for producing grain-oriented electrical steel sheets, which involves coating and final annealing, nitriding is performed for a short time of less than 2 minutes at a temperature of 600°C or more and 850°C or less under decomposition of nitrogen compound gas during intermediate annealing before final cold rolling. (A
1. A method for producing a high magnetic flux density grain-oriented electrical steel sheet, the method comprising forming an inhibitor whose main composition is l, Si)N. (3) C in weight%; 0.025-0.095%, Si;
2.0 to 4.0%, Mn; 0.08 to 0.45%, S; 0.012% or less, Al; 0.010 to 0.060%, N; 0.0030 to 0.0130%. Contains, furthermore, Mo, V, Nb, Sb, Sn, Ti,
An electrical steel slab containing one or more of Te and B in a total of 1.5% or less, with the balance consisting of iron and unavoidable impurities,
Heating to a temperature of 00°C or less, hot rolling, annealing as hot rolled or hot rolled sheet, cold rolling once or twice or more with intermediate annealing, decarburizing annealing, annealing separator In the method for producing grain-oriented electrical steel sheets, which involves coating and final annealing, nitriding is performed for a short time of less than 2 minutes at a temperature of 600°C or more and 850°C or less under decomposition of nitrogen compound gas during intermediate annealing before final cold rolling. (A
1. A method for producing a high magnetic flux density grain-oriented electrical steel sheet, the method comprising forming an inhibitor whose main composition is l, Si)N. (4) C in weight%; 0.025-0.095%, Si;
2.0 to 4.0%, Mn; 0.08 to 0.45%, S; 0.012% or less, Al; 0.010 to 0.060%, N; 0.0030 to 0.0130%. Contains, furthermore, P; 0.005% to 0.050%, C
r; 0.05 to 0.25% of one or two types, Mo, V,
An electrical steel slab containing a total of 1.5% or less of one or more of Nb, Sb, Sn, Ti, Te, and B, with the balance consisting of iron and unavoidable impurities, is heated to a temperature of 1200 ° C. or less,
Hot rolled, as hot rolled or hot rolled plate annealed, cold rolled once or twice or more with intermediate annealing in between, decarburized annealed,
In a method for producing grain-oriented electrical steel sheets in which an annealing separator is applied and finish annealed, intermediate annealing before final cold rolling is performed at a temperature of 600°C or higher and 850°C or lower for a short period of less than 2 minutes under decomposition of nitrogen compound gas. A method for producing a high magnetic flux density grain-oriented electrical steel sheet, which comprises nitriding to form an inhibitor whose main composition is (Al, Si)N.