KR100940718B1 - A method for manufacturing grain-oriented electrical steel sheet without hot band annealing - Google Patents

Abstract

The present invention relates to a grain-oriented electrical steel sheet used as iron core materials such as transformers, electric motors, generators and other electronic devices, the purpose of which is to control the cooling rate from the hot rolling to the winding section and to multiply the weight percent product of Al and N. The present invention provides a method of manufacturing a grain-oriented electrical steel sheet by controlling the hot rolled sheet without annealing.

The present invention for achieving the above object by weight, Si: 2.9 ~ 3.4%, C: 0.01 ~ 0.06%, P: 0.015 ~ 0.035%, S: 0.001 ~ 0.010%, Mn: 0.008 ~ 0.12%, Al : 0.01 ~ 0.05%, N: 0.002 ~ 0.01%, remaining Fe and other unavoidable impurities, and after reheating the steel at 1100 ~ 1200 ℃ that hot weight product of Al and N satisfy 0.0002 ~ 0.0004 , Hot-rolled sheet comprising cooling to the winding section at a cooling rate of 1 ~ 100 ℃ / sec, followed by cold rolling, followed by cold or rolling at the same time or separate treatment of decarburization and nitride annealing at 850 ~ 910 ℃, the final annealing Technical aspects are directed to a method for producing a grain-oriented electrical steel sheet by omitting annealing.

High temperature annealing, hot rolled sheet annealing, pre-annealed, oriented electrical steel sheet, secondary recrystallization

Description

Method for manufacturing oriented electrical steel sheet by omitting hot-rolled sheet annealing {A METHOD FOR MANUFACTURING GRAIN-ORIENTED ELECTRICAL STEEL SHEET WITHOUT HOT BAND ANNEALING}             

1 is a graph showing the magnetic flux density according to the product of Al% by weight and N% by weight and the cooling rate until the winding section after hot rolling.

The present invention relates to a grain-oriented electrical steel sheet used as iron core materials for transformers, electric motors, generators, and other electronic devices, and more particularly, to control the cooling rate after the hot rolling and the weight percent product of Al and N to omit the hot rolled sheet annealing. It relates to a method for producing a grain-oriented electrical steel sheet.

A grain-oriented electrical steel sheet is an electrical steel sheet having an aggregate structure in which the grain orientation is oriented in the (110) [001] direction. Since it has very excellent magnetic properties in the rolling direction, iron core materials such as transformers, motors, generators, and other electronic devices are used. Used as                         

In general, the properties required for grain-oriented electrical steel sheet include magnetic flux density and iron loss. The greater the magnetic flux density is, the better, the value of B10 measured at 1000 Amp / m is used. In addition, the smaller the iron loss is, the better it is expressed as loss per kg (Watt) at a frequency of 50 Hz and a magnetic field of 1.7 T (Tesla).

The method for manufacturing a grain-oriented electrical steel sheet can be classified into a manufacturing method by high temperature slab heating and a manufacturing method by low temperature slab heating. The hot-rolled sheet annealing in the manufacturing method by the high temperature slab heating to strengthen the {110} <001> goth aggregate structure by heating to a high temperature, and finely dispersed precipitated AlN precipitate by quenching in the cooling process to serve as decarbon annealing There are three metallurgical meanings to suppress the growth of grains in the primary recrystallization to increase the driving force of the secondary recrystallization and to form fine carbides and nitrides by quenching to strengthen the goth aggregate structure. The most important of these is the microprecipitation of AlN.

However, in the manufacturing method by low temperature slab heating, since AlN is formed through nitriding after hot-rolled sheet annealing, it is not necessary to finely deposit AlN during hot-rolled sheet annealing.

Since the invention of the method for producing the oriented electrical steel sheet by cold rolling by N.P.Goss, there have been many advances through the research. It is no exaggeration to say that the history of research on oriented electrical steel is the history of efforts to reduce iron loss. Major improvements in the studies include thinning the product, adding various elements to the components, and minimizing magnetic domains by irradiating the laser with the product. All these methods raise manufacturing costs and complicate the manufacturing process. However, as research on improving magnetic properties has recently reached its limit, many researches for reducing manufacturing costs have been conducted.

Conventional techniques for reducing the manufacturing cost of oriented electrical steel sheet include Korean Patent Application No. 1996-63078, 1996-71517, 1997-53791, 1997-37247. The prior art relates to a method for producing a grain-oriented electrical steel sheet characterized in low temperature heating slab. Conventional hot slab heating method has low material recovery rate and high manufacturing cost, while the above-mentioned conventional technologies, which are characterized by low temperature slab heating, have good recovery rate of the material and very low loss of material even in the post process, and also require high temperature hot rolling. The cost of manufacturing can be drastically reduced. However, both the hot slab heating and the low temperature slab heating generally must perform hot-rolled sheet annealing (also referred to as pre-annealing) for the purpose of eliminating unevenness of the tissue after hot rolling and finely depositing and dispersing precipitates. However, the hot rolled sheet annealing not only consumes a large amount of thermal energy during the process but also requires a huge investment cost because a hot rolled sheet annealing furnace must be constructed when a new plant for oriented electrical steel sheet is newly added.

Korean Patent Publication No. 1994-0008934 is a conventional technique for manufacturing a grain-oriented electrical steel sheet to omit the hot-rolled sheet annealing to solve the cost increase problem caused by the hot-rolled sheet annealing. The prior art claims that the hot rolled sheet annealing can be omitted by winding at 600 ° C. or lower after hot rolling. However, when the low temperature winding, there is a problem that the mechanical strength of the plate is increased and the cold rolling productivity is not good.

In addition, another prior art that can omit the hot rolled sheet annealing is the Republic of Korea Patent Registration No. 0139247. The prior art proposes a manufacturing method of eliminating the hot rolled sheet annealing by adjusting the hot rolling temperature according to the reduction ratio of the tempered hot rolling and the amount of Al and N. However, the prior art has a problem that the manufacturing method is not only very demanding, but also because the production method must be continuously changed according to the components of the slab, the productivity is reduced when applied to the actual process.

In addition, Japanese Patent No. 2878501 is another prior art which can omit the hot rolled sheet annealing. The prior art omits the hot rolled sheet annealing by managing the amount of Al and N to Al (%)-27 / 14N (%)> 0.0100, but the prior art has a problem that it is difficult to properly control AlN precipitates.

The present invention is to solve the above problems of the prior art, by controlling the cooling rate from the hot rolling to the winding section after hot rolling, and by controlling the weight percent product of Al and N by producing a grain-oriented electrical steel sheet without annealing To provide, the purpose is.

The present invention for achieving the above object by weight, Si: 2.9 ~ 3.4%, C: 0.01 ~ 0.06%, P: 0.015 ~ 0.035%, S: 0.001 ~ 0.010%, Mn: 0.008 ~ 0.12%, Al : 0.01 ~ 0.05%, N: 0.002 ~ 0.01%, remaining Fe and other unavoidable impurities, and after reheating the steel at 1100 ~ 1200 ℃ that hot weight product of Al and N satisfy 0.0002 ~ 0.0004 After cooling to the winding section at a cooling rate of 1 ~ 100 ℃ / sec, then wound, cold rolling, and then at the same time or separated treatment of decarburization and nitride annealing at 850 ~ 910 ℃, and finally annealing.

Hereinafter, the present invention will be described in more detail.

If the hot-rolled sheet annealing is omitted, the secondary recrystallization becomes unstable and the magnetism deteriorates. Therefore, when omitting the hot rolled sheet annealing, it is necessary to stabilize the secondary recrystallization. The reason why the magnetization becomes worse due to the omission of the hot-rolled sheet annealing is that the size of the primary recrystallized grain becomes fine and the development of the aggregate structure is disadvantageous to the secondary recrystallization. In the method of manufacturing a grain-oriented electrical steel sheet by high temperature slab heating, since the primary recrystallization grain growth inhibitory strength by the precipitate is strong, the smaller the size of the primary recrystallized grain is advantageous for the secondary recrystallization. However, the low-temperature slab heating method of the present invention has a weak grain growth suppression force of the primary recrystallized grain because the method of injecting nitrogen into the steel sheet after hot rolling. Generally, when the primary recrystallization diameter is about 20 ~ 30㎛ is known to be the best for the magnetic. By the way, if the hot-rolled sheet annealing is omitted, the primary recrystallized grain becomes small by about 5 to 10 µm. As the size of the primary recrystallized grains decreases, the secondary recrystallization temperature is lowered, which hinders the secondary recrystallization of the goth texture. In addition, if the hot-rolled sheet annealing is omitted, the strength of {110} <001> decreases, the nucleus of the secondary recrystallization decreases, and the grains deviated from the rolling direction of the <001> axis are secondary recrystallized, resulting in poor magnetic properties.

The present inventors have found that the above-mentioned phenomena caused by hot-rolled sheet annealing can be prevented from miniaturization and non-uniformization of AlN precipitates by controlling the cooling rate after the end of hot rolling.

Hereinafter, look at from the reasons for limiting the components of the present invention.

Si: 2.9-3.4 wt%

The Si is an element that serves to lower the iron loss by increasing the specific resistance value, when less than 2.9% by weight of the iron loss properties are worse, when added in excess of 3.9% by weight of the steel is weak and cold rolling property is very bad, its content Is preferably limited to 2.9 to 3.4% by weight.

C: 0.01 ~ 0.06% by weight

The C is an element that plays a role of fine solid dispersion of AlN precipitates, forming a rolled structure, and providing processing energy during cold rolling, and when less than 0.01% by weight is added, fine grains are formed in the central part of the final product to exhibit magnetic properties. It is preferable to limit the content to 0.01 to 0.06% by weight, since the primary recrystallized grains become fine when the amount thereof is added in excess of 0.06% by weight, and the texture is adversely formed on the magnetic body.

In the present invention, the content of C is controlled to 0.01 to 0.06% by weight, which is lower than that of the conventional manufacturing method, which helps to prevent the refining of primary recrystallized grains and to improve the texture of the aggregates. That is, if the carbon content is low, the site where austenite-ferrite phase transformation occurs during hot rolling is reduced, and the grain size increases after primary recrystallization annealing, which is more advantageous for magnetic properties.

P: 0.015 to 0.035 wt%

P is an element contributing to suppressing grain growth of the primary recrystallization. If the content of P is less than 0.015% by weight, the grain growth inhibiting effect is not provided. It is preferable to limit the content to 0.015 to 0.035% by weight.

S: 0.001-0.010 wt%

If the S is managed to less than 0.001% by weight, the steelmaking cost is increased, and when it exceeds 0.010% by weight, MnS precipitates are formed and the primary recrystallized grain becomes fine, which is detrimental to the development of the secondary recrystallized, and the content is 0.001 to 0.010% by weight. It is desirable to limit to%.

Mn: 0.008 to 0.12 wt%

The Mn is an element that lowers the solid solution temperature of the precipitate during reheating and prevents cracks formed at both ends of the material during hot rolling. When Mn is added less than 0.008% by weight, the crack preventing effect is not obtained, and 0.12% by weight If it is added in excess, it forms Mn oxide, which not only deteriorates iron loss but also increases the amount of austenite, thereby reducing the size of the primary recrystallized grains. Therefore, the content is preferably limited to 0.008 to 0.12% by weight.

Al: 0.01 ~ 0.05% by weight

Al is an element which forms AlN precipitates with N to secure grain growth inhibitory power. When Al is less than 0.01% by weight, Al decreases grain growth inhibitory power due to insufficient precipitation of AlN and does not cause secondary recrystallization. Since AlN particles are coarsened and secondary recrystallization does not occur, it is preferable to limit the content to 0.01 to 0.05% by weight.

N: 0.002-0.01 wt%

N is an element which forms AlN precipitate with Al, and if less than 0.002% by weight of secondary recrystallization does not occur, and if it exceeds 0.01% by weight, the rolling property is inferior and AlN is coarse to deteriorate the magnetism. It is preferable to limit to 0.01% by weight.

In the present invention, the effect of improving the magnetic properties by the cooling rate up to the winding section is different depending on the amount of Al and N, and if the amount of Al and N is properly controlled, there is an effect of slowing down the cooling rate.

Therefore, in the present invention, the Al and N are formed of AlN precipitates to secure grain growth suppression force, and for this purpose, the magnetic properties are improved by managing the product of the weight percents of the two elements. If the value of (Al wt%) X (N wt%) is less than 0.0002, fine AlN is precipitated, and if it exceeds 0.0004, AlN precipitate formed from decarburization and nitridation after cold rolling becomes too coarse, making it difficult to develop secondary recrystallization. Therefore, the weight percent product of Al and N is preferably limited to 0.0002 ~ 0.0004.

The remainder other than the above composition is composed of Fe and other unavoidable impurities.

The steel formed as described above is reheated to 1100 ~ 1200 ° C. and then hot rolled. If the reheating temperature is less than 1100 ℃ hot rolling end temperature is less than 900 ℃ is difficult to hot rolling, if it exceeds 1200 ℃ AlN fine precipitate during hot rolling is not good for magnetic, the reheating temperature is 1100 ~ 1200 It is preferable to limit to ℃.

After the hot rolling, it is cooled at a cooling rate of 1 ~ 100 ℃ / second to the winding section, and then wound. Typically, hot rolling is terminated at 850 ~ 1000 ℃ and quenched by spraying water to the winding section. However, in order to omit the hot-rolled sheet annealing process, it is important to appropriately control the cooling rate of the temperature section to 500-700 ° C, which is the usual winding temperature after hot rolling. This is because the cooling rate up to the winding section affects the microstructure of the hot rolled plate and the size and dispersion of AlN precipitates. Appropriate control of the cooling rate to the winding section enhances the strength of the {110} <001> goth aggregate structure of the surface layer and prevents microdispersion of precipitates, thereby making the hot rolled sheet and the primary recrystallized microstructure uniform. Even if the annealing is omitted, the primary recrystallized grain size can be controlled to an appropriate size of 20 to 30 μm in diameter. If the cooling rate is less than 1 ℃ / second productivity is lowered, if it exceeds 100 ℃ / second AlN is precipitated fine uniformly, the size of the primary recrystallized grains is small, the secondary recrystallization temperature is lowered, the magnetic deterioration, Cooling rate is preferably limited to 1 ~ 100 ℃ / second.

After the winding, it is cold rolled, and then treated at the same time or separately by decarburization and annealing at 850 to 910 ° C. The decarburization and annealing are preferably carried out in the range of 850 to 910 ° C. according to the amount of annealing separator in a humid atmosphere of hydrogen and nitrogen containing ammonia gas. If the decarburization and annealing temperature is lower than 850 ° C or higher than 910 ° C, no appropriate primary recrystallized texture is formed, which is not good for magnetic properties. In the present invention, it is limited to 850 ~ 910 ℃ 30 ~ 50 ℃ higher than the normal decarburization and nitride annealing temperature as described above, because it is effective to improve the magnetic properties by preventing the miniaturization of primary recrystallized grains.

After the decarburization and annealing, annealing separator is applied. Usually, the annealing separator uses what has MgO as a main component. When applying the annealing separator, it is preferable that the slurry is applied in the form of a cobalol.

After application of the annealing separator, high temperature annealing is carried out in a conventional manner. The conventional high temperature annealing is carried out with a nitrogen-containing hydrogen atmosphere of 25% or less in all sections, the temperature rising rate of the 700 ~ 1200 ℃ section maintained at 15 ℃ / hour or more, and then cracked for more than 20 hours at 1190 ~ 1210 ℃ Do it in a way.

After the finishing high temperature annealing, a coating agent is applied. As the coating agent, a coating agent usually composed of phosphate, colloidal silica, and chromic anhydride is used.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

By weight, the slab comprising Si: 3.12%, C: 0.042%, P: 0.015%, S: 0.005%, and Mn: 0.01% was reheated to 1180 DEG C and hot rolled to 2.3 mm thickness. . The hot rolling was finished at 930 ° C and the winding temperature was set at 600 ° C. At this time, the experiment was performed by variously setting the cooling rate from the weight percent product of Al and N and to the winding temperature after the end of hot rolling. The hot rolled sheet annealing was omitted, and the hot rolled sheet was pickled and cold rolled to a final thickness of 0.30 mm. Decarburization and nitride annealing were subjected to annealing which simultaneously carried out decarburization and nitriding in a humid atmosphere of hydrogen nitrogen containing ammonia at 880 ° C. for 3 minutes. After coating with MgO, a high temperature annealing was performed at a rate of 15 ° C. per hour to 1200 ° C. At this time, the magnetic flux density according to the cooling rate from the weight percent product of Al and N and the end of the hot rolling to the coiling temperature is shown in FIG. 1.

As can be seen in Figure 1, the weight percent product of Al and N in the range of 0.0002 ~ 0.0004, and the cooling rate until the coil is wound up after the end of hot rolling to maintain the temperature below 100 ℃ / seconds to prevent the microprecipitation of AlN It can be advantageous to magnetism.

As described above, the present invention can significantly reduce the production cost by omitting the hot rolled sheet annealing process of the grain-oriented electrical steel sheet, and even if the hot rolled sheet annealing is omitted, it is possible to secure stable magnetic properties without complicated control of the process. .

Claims (1)

By weight%, Si: 2.9 to 3.4%, C: 0.01 to 0.06%, P: 0.015 to 0.035%, S: 0.001 to 0.010%, Mn: 0.008 to 0.12%, Al: 0.01 to 0.05%, N: 0.002 to 0.01%, the remaining Fe and other unavoidable impurities, and re-heated at 1100 ~ 1200 ℃ hot-rolled steel, the weight percent product of Al and N satisfying 0.0002 ~ 0.0004, at a cooling rate of 1 ~ 100 ℃ / second After cooling up to the winding section, winding up, cold rolling, and simultaneously or separating the decarburization and nitridation annealing at 850 ~ 910 ℃, and finally raising the temperature of 700 ~ 1200 ℃ in a nitrogen atmosphere of 25% or less. The method of manufacturing a grain-oriented electrical steel sheet by omitting the hot-rolled sheet annealing comprising maintaining the temperature at 15 ℃ / hour or more, and then annealing by cracking at 1190 to 1210 ℃ 20 hours or more.

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