JPH0717953B2 - Manufacturing method of grain-oriented electrical steel sheet with excellent magnetic properties - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties.

(Prior Art) Grain-oriented electrical steel sheets are mainly used as core materials for transformers, generators, and other electric devices, and must have good magnetic properties such as excitation properties and iron loss properties. It is also important to have a good coating. The grain-oriented electrical steel sheet uses the secondary recrystallization phenomenon to make the (110) plane in the rolling plane and [00] in the rolling direction.
1) Obtained by developing a crystal grain having a so-called Goss orientation with an axis.

As is well known, this secondary recrystallization occurs during finish annealing, but in order to sufficiently develop the secondary recrystallization, it is necessary to control the growth of primary recrystallized grains up to the secondary recrystallization temperature range during finish annealing. Na
Precipitates such as AlN, MnS, MnSe and so-called inhibitors must be present.

Therefore, the electromagnetic steel slab is heated to a high temperature of about 1350 to 1400 ° C, and components that form an inhibitor, such as Al, Mn, S,
Annealing is performed in which Se, N, etc. are completely dissolved and the inhibitor is finely precipitated in the hot-rolled sheet or the intermediate sheet before the final cold rolling.

By performing such treatment, grain oriented electrical steel sheets with high magnetic flux density are manufactured, but since the heating of electromagnetic steel slabs is performed at high temperatures as described above, the amount of molten scale generated becomes large. , Interfere with the operation of the heating furnace.
There is also a problem that the energy intensity of the heating furnace is high.

On the other hand, a method of manufacturing a grain-oriented electrical steel sheet by lowering the slab heating temperature is being studied. For example, in Japanese Unexamined Patent Publication (Kokai) No. 52-24116, in addition to Al, slab heating is performed by adding a nitride-forming element such as Zr, Ti, B, Nb, Ta, V, Cr, and Mo to the steel.
Disclosed is a manufacturing method performed at ˜1260 ° C. JP 59-19
According to Japanese Patent No. 0324, an electromagnetic steel slab containing S, Se, and Al and B selectively in a low carbon content of 0.01% or less is used as a material, and the surface of the steel sheet is shortened during temporary recrystallization annealing after cold rolling. A manufacturing method is disclosed in which the slab heating temperature is set to 1300 ° C. or lower by performing pulse annealing in which high temperature heating is repeatedly performed. Further, in JP-A-59-56522, Mn is 0.08 to 0.45.
%, S is 0.007% or less, the [Mn] [S] product is reduced, and a slab heating temperature is 1280 ° C or less by using a magnetic steel slab containing Al, P, N as a raw material. Is proposed.

(Problems to be solved by the invention) As described above, in the production of grain-oriented electrical steel sheet, a method by low-temperature slab heating has been studied, and some action and effect have been exhibited, but sufficient for manifestation of secondary recrystallization. Further studies are required to industrially stably produce effective inhibitors that are difficult to stably form and have excellent magnetic properties.

The present invention, by heating the electromagnetic steel slab at a low temperature of less than 1280 ° C, ensures the development of secondary recrystallization before finish annealing while obtaining advantages such as prevention of molten scale generation, surface flaw prevention and reduction of heating energy. It is intended to industrially stably obtain a grain-oriented electrical steel sheet having excellent magnetic properties by forming such an inhibitor over the entire steel sheet.

(Means for Solving the Problems) The gist of the present invention is that C; 0.025 to 0.095%, Si; 2.0 to 4.0%, Mn; 0.08 to 0.45%, S; 0.015% or less Al; 0.010% by weight. 〜0.060%, N; 0.0030〜0.0130%, and if necessary P; 0.005〜0.045%, Cr; 0.07
~ 0.25% of 1 or 2 kinds, 1 or more kinds of Mo, V, Nb, Sb, Sn, Ti, Te, B in total less than 1.5%, and the balance is iron and unavoidable impurities Is heated to a temperature of less than 1280 ° C., hot-rolled, hot-rolled or annealed, 1
Cold rolling twice or more with intermediate or intermediate annealing in between, decarburization annealing to reduce or remove the oxide layer on the surface of the steel sheet, and then at a temperature of 500 to 900 ° C. under the condition of running the strip.
It is a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises nitriding for a short time of less than a minute, applying an annealing separator, and finish annealing.

Hereinafter, the present invention will be described in detail.

The present inventors applied low-temperature slab heating in which an electromagnetic steel slab is heated at a temperature of less than 1280 ° C. and studied to stably produce a grain-oriented electrical steel sheet having excellent magnetic properties. As a result, components that form an inhibitor such as Al, N, Mn, and S are not completely dissolved in steel in the stage of slab heating, and after decarburization annealing, reduce the oxide layer on the surface of the steel sheet, or Alternatively, if it is removed and then nitrided for a short time while the strip is running, an inhibitor having a strong inhibitory action (Al, Si) N as a main composition is uniformly formed on the steel sheet,
It has been found that a grain-oriented electrical steel sheet having excellent magnetic properties can be obtained.

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

If the C content is low, the secondary recrystallization becomes unstable, so the content is made 0.025% or more. On the other hand, if the content is too large, the decarburization annealing time becomes long, so the content is made 0.095% or less.

Si is a component necessary for lowering iron loss and forming an inhibitor, so Si is contained in an amount of 2.0% or more. On the other hand, if its content increases, cracking frequently occurs during cold rolling.
% Or less.

Mn has the effect of preventing hot brittleness and improving the quality of the glass coating. To achieve this, 0.08% or more is required.
On the other hand, when the content increases, the magnetic flux density deteriorates.
0.45% or less. Further, in the present invention, the slab heating is 1280
Since it is carried out at a temperature lower than ° C, for example, the compound with S and MnS do not form a complete solid solution and MnS is not used as an inhibitor.

S is likely to cause segregation and hinders the normal growth of secondary recrystallized grains, so S is made 0.015% or less.

Al is combined with N or Si to form (Al, Si) N, which is necessary for stabilizing the secondary recrystallization. Therefore, 0.010% or more is contained. On the other hand, the slab heating temperature in the present invention is 1280.
Since Al is incompletely solid-solved at a temperature lower than 0 ° C, if the content of Al increases, unsuitable AlN is formed in the stage of hot rolling, so the content is made 0.060% or less.

N is contained in an amount of 0.0030% or more in order to combine with Al, Si and the like to have a stabilizing effect on secondary recrystallization. However, if its content increases, surface defects occur, so the content is made 0.0130% or less.

Further, if necessary, one or more of P and Cr or / and one or more of Mo, V, Nb, Sb, Sn, Ti, Te and B may be contained in addition to the above elements. At this time, P has the effect of increasing the magnetic flux density in the case of low-temperature slab heating, and 0.005% or more is necessary to achieve this effect. On the other hand, if its content increases, cold ductility deteriorates, so the content is made 0.045% or less.

Cr has the effect of enhancing the magnetic properties through expanding the range of the amount of Al for which a high magnetic flux density can be obtained.
The above is necessary. On the other hand, if its content increases, decarburization deteriorates, so the content is made 0.25% or less.

Mo, V, Nb, Sb, Sn, Ti, Te, and B are contained within 0.30% each to improve the magnetic properties, but the upper limit of the total of these is
1.5%

The electromagnetic steel slab is melted in a melting furnace such as a converter or an electric furnace, vacuum degassing treatment is applied if necessary, and is manufactured by continuous casting or ingot-slab rolling.

The electromagnetic steel slab is heated prior to hot rolling, but the heating temperature is less than 1280 ° C to save energy.
At this heating temperature, Al in the electromagnetic steel slab is not completely solid-solved and becomes incompletely solid-solved. Moreover, the solid solution temperature is higher
MnS is, of course, an incomplete solid solution.

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

Here, in the present invention, the electromagnetic steel slab is heated to a low temperature of less than 1280 ° C.

Therefore, Al, Mn, S, etc. in the steel are in an incomplete solid solution state, and as they are, there are no inhibitors such as (Al, Si) N, MnS for expressing secondary recrystallization in the steel sheet. Therefore, it is necessary to infiltrate N into the steel to form (Al, Si) N that functions as an inhibitor before secondary recrystallization occurs.

The nitriding of a steel sheet is promoted in a dry atmosphere (a gas with a low dew point).

Conventionally, nitriding of steel sheets has been performed in the form of tight strip coils with a space factor of about 90% by applying an annealing separator containing a nitrogen compound. In such a tight strip coil state, the gap between the plates is as narrow as 10 μm or less, and the air permeability is very poor. Therefore, it not only takes a long time to replace the atmosphere between the plates with a dry atmosphere, but also a long time is required for N ₂ as a nitriding source to enter and diffuse between the plates. As a means to improve this, it has been attempted to perform nitriding treatment on a steel sheet as a loose strip coil, but it is a problem when performing nitriding treatment on a steel sheet in the form of a strip coil. Although the non-uniformity of nitridation caused by the above is reduced, it cannot be said to be sufficient.

The present inventors have conducted various studies on nitriding treatment after decarburization annealing in order to stably form (Al, Si) N having a strong inhibitory action. As a result, it was found that the nitriding of the steel sheet for forming (Al, Si) N greatly depends on the surface properties of the steel sheet. As a result of further studying this finding, when nitriding using a nitriding gas such as NH ₃ gas, NH ₃ is first dissociated and adsorbed on the surface of the steel sheet, and then active atomic N is trapped in the steel sheet. , Fe-Si oxide with a thickness of 100-200Å formed in the decarburization annealing process is present on the surface of the steel sheet as a barrier for nitrogen infiltration, which is reduced by H ₂ reduction before nitriding. It has been found that nitriding can be performed in an extremely short time by reducing with a volatile gas or removing with pickling or the like, and (Al, Si) N can be uniformly formed over the entire steel sheet.

Fig. 1 is a plot of the relationship between the nitriding time in the nitriding treatment after reduction and the amount of nitrogen in the steel, with the reduction time when the surface of the steel sheet was reduced with a gas containing H ₂ prior to the nitriding treatment as a parameter. is there. The nitriding treatment was performed by passing a steel plate in strip form at 650 to 850 ° C. It can be seen from FIG. 1 that the nitriding of the steel sheet occurs in a short time when the reduction treatment is set to 10 seconds or more. After that, an annealing separator was applied, finish annealing was performed at 1200 ° C., and magnetic characteristics were measured. The results are shown in Fig. 3. The decarburization annealing reduces the oxide layer of the steel sheet and nitrides it for a short time, which has a high magnetic flux density B ₁₀ and iron loss W _17/50.
Low and excellent magnetic properties. This is presumably because (Al, Si) N having a high inhibitor function was formed when reduction and nitridation were performed for a short time. The composition of the steel slab used in the test is% by weight, C: 0.05%, Si; 3.2%, Mn: 0.12%,
S: 0.007%, Al: 0.03%, N: 0.008%, the balance is iron and inevitable impurities, and the slab heating temperature is 1200 ° C.

In addition, Fig. 2 shows the nitriding time and the amount of nitrogen in the nitriding treatment after the treatment, with the treatment time when the oxide layer of the steel sheet after decarburization annealing was treated with a 10% hydrochloric acid solution as a parameter before the nitriding treatment. It is a plot of the relationship with. The nitriding treatment was performed by passing a steel plate in strip form at a temperature of 750 ° C. It can be seen that the pickling treatment causes subsequent nitriding in a strip passing state in a short time. Then, an annealing separator was applied and finish annealing was carried out at 1200 ° C. to measure the magnetic properties. Also in this case, the one obtained by removing the oxide layer and nitriding for a short time had excellent magnetic flux density B ₁₀ and iron loss W _17/50 . It is considered that this is because the inhibitor (Al, Si) N was stably formed.

Thus, prior to nitriding, the surface of the steel sheet is reduced with a reducing gas containing H ₂ , or hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid,
By removing the oxide on the surface of the steel sheet by pickling with a dilute pickling solution such as hydrofluoric acid, the nitriding time can be shortened and the inhibitor (Al, Si) N can be stably formed.

Nitriding is performed while the strip is running,
Since short-time nitriding is required to form (Al, Si) N having a strong inhibitory function, it is performed at a temperature of 500 ° C. or higher and 900 ° C. or lower in less than 2 minutes. At this time, it is desirable that the nitriding gas, preferably NH ₃ , is supplied in a mixed atmosphere of H ₂ and N ₂ or an atmosphere in which 100 to 100,000 ppm is supplied to the single atmosphere thereof.

The temperature of the nitriding treatment is set to the above, this temperature is 50
If it is less than 0 ° C, it becomes difficult to nitride in a short time,
This is because the formation of (Al, Si) N becomes poor. On the other hand, when this temperature becomes high, nitriding also decreases in this case, and the formation of (Al, Si) N acting on the development of secondary recrystallization decreases, so the upper limit is 900 ° C. Further, even if the time becomes long, an effective inhibitor (Al, Si) N is not formed, so it is necessary to set it to less than 2 minutes.

Then, an annealing separator is applied and finish annealing is performed. The annealing separator used does not need to be specified, and known ones containing MgO as a main component and those containing known additives such as TiO ₂ and B are applied. Moreover, the application to the steel plate is made into a slurry,
Alternatively, it is carried out by a known method such as electromagnetic electrostatic coating in powder form instead of slurry form. It is not necessary to specify the method for finish annealing either.

According to the present invention, excellent magnetic properties can be obtained as described above, but even if the pretreatment performed before the nitriding treatment is performed, only the very surface layer of the film formed by decarburization annealing is reduced, Alternatively, since the silica is simply removed and a sufficient amount of silica is present, a good forsterite film is formed on the surface of the steel sheet after finish annealing.

(Example) Next, this invention is demonstrated based on an Example.

Example-1 A slab having the component composition shown in Table 1 was slab-heated under the conditions shown in the same table, hot-rolled to a thickness of 2.3 mm, as-hot-rolled or annealed, and then shown in the same table. As described above, the steel sheet was cold-rolled once or twice with intermediate annealing interposed therebetween to obtain a plate thickness of 0.30 mm. After that, decarburization annealing is performed in an atmosphere consisting of H ₂ 70% with a dew point of 60 ° C. for 3 minutes at 850 ° C., and the steel sheet is run in a strip state under the conditions shown in the table to reduce the oxide layer and perform nitriding treatment. did.
Then, the annealing separator is applied to the steel sheet as a slurry,
It was dried, wound on a coil, and the coil was finish annealed. The magnetic properties and coating properties of the obtained steel sheet were measured, and the results are shown in Table 2.

Example-2 A slab having the component composition shown in Table 3 is slab-heated under the conditions shown in the same table, hot-rolled to a thickness of 2.3 mm, and as-hot-rolled or annealed in the hot-rolled sheet, and then shown in the same table. As described above, cold rolling is performed once or twice with intermediate annealing, and a plate thickness of 0.30 mm is obtained. After that, decarburization annealing was performed in an atmosphere consisting of H ₂ 70% with a dew point of 60 ° C for 3 minutes at 850 ° C, and the steel sheet was run in a strip state under the conditions shown in the same table to remove the oxide layer, and then subjected to nitriding treatment. did.
Then, the annealing separator is applied to the steel sheet as a slurry,
It was dried, wound on a coil, and the coil was finish annealed. The magnetic properties and coating properties of the obtained steel sheet were measured, and the results are shown in Table 4.

(Effects of the Invention) The present invention reduces the nitriding treatment of a steel sheet, which has been conventionally performed by finish annealing, to reduce or remove the oxide layer on the surface of the steel sheet after decarburization annealing before finish annealing, and to perform short-time nitriding in a strip state. Therefore, the grain-oriented electrical steel sheet having excellent magnetic properties can be stably obtained.

[Brief description of drawings]

FIG. 1 is a diagram plotting the relationship between the nitriding time in the nitriding treatment after reduction and the amount of nitrogen in the steel, using the reduction time when the steel sheet surface was reduced with a gas containing H ₂ prior to the nitriding treatment as a parameter, Fig. 2 shows the relationship between the nitriding time in the nitriding treatment after treatment and the nitrogen content in the steel, using the treatment time as a parameter when the oxide layer of the steel sheet after decarburization annealing was treated with a 10% hydrochloric acid solution prior to the nitriding treatment. Fig. 3 shows the magnetic properties of the grain-oriented electrical steel sheets obtained by the strip nitriding process, the strip nitriding (without oxide layer reduction treatment) process, and the strip nitriding (with oxide layer reduction treatment) process. FIG.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01F 1/16 (72) Inventor Takashi Kobayashi 1-1-1 Edamitsu, Hachimanto-ku, Kitakyushu, Fukuoka Nippon Steel & Co., Ltd. 3rd Technical Research Institute (72) Inventor Kenichi Yatsushiro 1-1-1 Edamitsu, Hachimanto-ku, Kitakyushu-shi, Fukuoka New Nippon Steel & Co., Ltd. Yahata Works

Claims (4)

[Claims] 1. By weight%, C: 0.025 to 0.095%, Si; 2.0 to 4.0%, Mn; 0.08 to 0.45%, S; 0.015% or less Al; 0.010 to 0.060%, N; 0.0030 to 0.0130% are included. , Electromagnetic steel slab with the balance consisting of iron and unavoidable impurities is heated to a temperature of less than 1280 ° C, hot-rolled, as-hot-rolled or hot-rolled sheet annealed once or twice with intermediate annealing sandwiched. Cold-rolled, decarburized and annealed to reduce or remove the oxide layer on the surface of the steel sheet, and then nitrid at a temperature of 500 to 900 ° C for a short time of less than 2 minutes under the condition of running the strip, and then annealed and separated. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises applying an agent and finishing annealing. 2. By weight%, C: 0.025 to 0.095%, Si; 2.0 to 4.0%, Mn; 0.08 to 0.45%, S; 0.015% or less Al; 0.010 to 0.060%, N; 0.0030 to 0.0130% are included. , Further, P; 0.005 ~ 0.045%, Cr; 0.07 ~ 0.25% containing one or two kinds, the balance is an iron and unavoidable impurities electromagnetic steel slab heated to a temperature of less than 1200 ℃,
After hot rolling, hot rolling as-rolled or hot-rolled sheet annealing, cold rolling once or twice with intermediate annealing sandwiched, decarburization annealing, and reducing or removing the oxide layer on the steel sheet surface Manufacture of grain-oriented electrical steel sheet with excellent magnetic properties, which is characterized by nitriding for a short time of less than 2 minutes at a temperature of 500 to 900 ° C while running a strip, and applying an annealing separator to finish annealing. Law. 3. By weight%, C: 0.025 to 0.095%, Si; 2.0 to 4.0%, Mn; 0.08 to 0.45%, S; 0.015% or less Al; 0.010 to 0.060%, N; 0.0030 to 0.0130% are included. In addition, a magnetic steel slab containing one or more of Mo, V, Nb, Sb, Sn, Ti, Te and B in a total amount of 1.5% or less, and the balance being iron and unavoidable impurities, at a temperature of less than 1280 ° C. Heated to
After hot rolling, hot rolling as-rolled or hot-rolled sheet annealing, cold rolling once or twice with intermediate annealing sandwiched, decarburization annealing, and reducing or removing the oxide layer on the steel sheet surface Manufacture of grain-oriented electrical steel sheet with excellent magnetic properties, which is characterized by nitriding for a short time of less than 2 minutes at a temperature of 500 to 900 ° C while running a strip, and applying an annealing separator to finish annealing. Law. 4. By weight%, C: 0.025 to 0.095%, Si; 2.0 to 4.0%, Mn; 0.08 to 0.45%, S; 0.015% or less Al; 0.010 to 0.060%, N; 0.0030 to 0.0130% are included. , And further contains P; 0.005-0.045%, Cr; 0.07-0.25%, one or two kinds, and Mo, V, Nb, Sb, Sn, Ti, Te, B, one or more kinds in total of 1.5% or less. , Heating the electromagnetic steel slab, the balance of which consists of iron and unavoidable impurities, to a temperature below 1280 ° C,
After hot rolling, hot rolling as-rolled or hot-rolled sheet annealing, cold rolling once or twice with intermediate annealing sandwiched, decarburization annealing, and reducing or removing the oxide layer on the steel sheet surface Manufacture of grain-oriented electrical steel sheet with excellent magnetic properties, which is characterized by nitriding for a short time of less than 2 minutes at a temperature of 500 to 900 ° C while running a strip, and applying an annealing separator to finish annealing. Law.