KR20000008646A - Process for preparing directional electrical sheet having a good magnetic property and productibilities by slab low temperature reheating - Google Patents

Abstract

PURPOSE: A directional electrical sheet is prepared which has an improved magnetic property, decarbonization and productivity. CONSTITUTION: A silicon steel comprises 2.9-3.3 wt.% of silica, 0.035-0.055 wt.% of carbon, less than 0.015 wt.% of phosphor, 0.010-0.027 wt.% of acid-soluble aluminum, 0.0080-0.012 wt.% of nitrogen, less than 0.007 wt.% of sulfur, 0.10- 0.45 wt.% of manganese, 0.10-0.60 wt.% of copper, remainder of feruum and impurities. The slab is hot-rolled at 1,250-1,330°C, annealed at 1,50-1,150°C and pickled. Obtained slab is decarbonized and annealed at 750-830°C, coated by MgO antiseize compound and annealed to give the directional electrical sheet.

Description

Manufacturing method of slab low temperature reheat oriented electrical steel with excellent magnetic and productivity

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used as an iron core material such as an electronic device, and more particularly, to change the secondary cold rolling process with intermediate decarbonization annealing to primary cold rolling-decarbonation annealing process, and to provide excellent magnetic properties. It belongs to the method which can manufacture the low-temperature reheating oriented electrical steel sheet which has.

A grain-oriented electrical steel sheet has an aggregate structure in which the orientation of grains is aligned in the direction of (110) [001]. It has very excellent magnetic properties in the rolling direction and is used as a core material for transformers, generators, and other electrical equipment. . The grain-oriented electrical steel sheet was produced by reheating the high temperature material for about 4 hours at a high temperature of about 1400 ° C. in order to completely disperse the precipitates which are grain growth inhibitors and then finely deposit them. At this time, on the surface of the hot slab, an oxide called Pyrite (Fe ₂ SiO ₄ ) is formed by oxidation with air, and since the melting point is about 1340 ° C., the dioxide melts from the surface and flows into the furnace when reheated. It caused problems such as internal repairs.

In order to overcome the problems caused by the high temperature reheating, various low temperature reheating techniques have been proposed to heat the reheating temperature at a temperature of about 1350 ° C. or less where the pyrite oxide is not dissolved. These techniques basically reheat the slab at low temperature, adjust the basic component system on the basis of this, and in addition to this component design, it is a technique related to the precipitation management technique during the manufacturing process. As one of the low-temperature reheating technology, a component system was developed to heat the conventional directional electrical steel in the vicinity of 1250-1330 ° C. to perform hot rolling, and thus a new manufacturing method capable of working without additional equipment supplementation or new construction in the existing manufacturing process. In this case, additional element technologies have been proposed in Korean Patent Application No. 93-23751, 94-21388, 21389, 21390, and 21391.

In the manufacturing process of such low-temperature reoriented electrical steel sheet, generally, about 2-4% of silicon and grain growth inhibitor are dissolved in a component system containing mostly AlN or Si ₃ N ₄ to make slab, and then reheating and hot rolling. → Hot Rolled Sheet Annealing → Primary Cold Rolling → Decarbonized Annealing → Secondary Cold Rolling → Recovery Annealing → Coating Anti-Adhesive → Final High Temperature Annealing.

However, the characteristics of this low temperature reheating method should be decarbonized annealing at the intermediate thickness of 0.60 ~ 0.70mm after the first cold rolling. In addition, the increase in surface hardness due to the oxide layer formed at this time causes the reduction of rolling productivity due to the twisting phenomenon during the second rolling and the rapid fatigue of the rolling roll, and the increase of the cost due to the process burden such as the two rolling-twist annealing method. It is becoming.

As a result, if the second rolling is changed to one rolling and subsequently decarbonized annealing can solve all the problems of the existing decarburization productivity and the secondary rolling, but it overcomes the deterioration of the magnetic accompanying the first rolling. You should be able to.

Accordingly, the present invention is to provide a method for manufacturing a low-temperature reheat oriented electrical steel sheet that can improve the magnetic properties while solving the problem of de-elasticity and rolling productivity by changing the existing secondary rolling to primary rolling. have.

The present invention for achieving the above object, Si: 2.9 ~ 3.3%, C: 0.035 ~ 0.055%, P: 0.015% or less, acid solubility Al: 0.010 ~ 0.027%, N: 0.0080 ~ 0.012%, S : 0.007% or less, Mn: 0.10-0.45%, Cu: 0.10-0.60%, and silicon steel slab made of Fe and other unavoidable impurities, by reheating at a temperature of 1250-1330 ° C. at low temperature, and hot rolling. After hot-rolled sheet annealing at a temperature of 1150 ℃, pickled and then made into a final thickness by one cold rolling, and then decarbonized annealing at a temperature of 750-830 ℃ in a wet atmosphere, and then applied with a fusion inhibitor containing MgO as a main component Next, the first crack at 600-700 ℃ and then the temperature increase rate of 15 ℃ / hr or more to 930-1000 ℃ 15 to 25 hours of intermediate cracking and then the temperature rising rate of 15 ℃ / hr or more to 1190 ± 20 ℃ 10 It consists of a final finishing annealing process that final cracks over time.

Hereinafter, the present invention will be described.

In the manufacturing field of low-temperature reheating oriented electrical steel sheet to which the present invention belongs, when rolling to the final thickness by primary cold rolling, the reduction ratio to the final thickness is increased, the processing energy is increased, and thus the primary recrystallized grain is large and magnetic. Because of this deterioration, secondary rolling has been used even if the productivity (decarburization productivity, rolling productivity) decreases.

By the way, the inventors of the present invention can control the hot-rolled sheet annealing process and the decarbonization annealing process related to the growth of the primary recrystallized grains even when the primary cold rolling is carried out, while suppressing the growth of the primary recrystallized grains, and finally finishing annealing. It was found that adopting three-stage annealing with intermediate cracking to greatly grow secondary recrystallized grains in the process greatly improves productivity and further improves magnetism by primary cold rolling.

The steel species to be applied to the present invention will be described as a steel grade, which is widely known as a low-temperature reheat oriented electrical steel sheet, as follows.

C acts advantageously on the fine solid dispersion of AlN precipitates, and forms an appropriate rolled structure to maintain the aggregate structure having excellent magnetic properties. To this end, more than 0.035% is added, but more than 0.55% inhibits productivity in the decarburization process, so carbon is added at 0.035-0.55%.

Si is a basic component of electrical steel sheet, which increases the resistivity of the material, thereby lowering the core loss, that is, iron loss. Therefore, more than 2.9% is added for this purpose. As it worsens, the amount of addition is limited to 2.9-3.3%.

Mn lowers the solid solution temperature of the precipitate during reheating and prevents cracks formed at both ends of the material during hot rolling. Therefore, when Mn is added above 0.10%, when Mn oxide is formed during de-carbon annealing, The adhesion of the ferrite film is deteriorated, so it is limited to 0.10-0.45%.

S is limited to less than 0.007% of the elements that cause cracks at the end of the plate during hot rolling.

Al, together with N, forms the precipitate of AlN to secure grain growth inhibition. The amount of acid-soluble Al that can be dissolved in an acid is important, not the total amount of Al management. In particular, in the one-time cold rolling method of the present invention, the crystal grain size is small and incomplete fine particles appear due to insufficient primary recrystallization inhibitory force necessary for secondary recrystallization, resulting in low magnetic flux density and poor iron loss. At 0.027% or more, the slab low heat, which is one of the basic requirements of the present invention, is not sufficiently employed as AlN, so it is not possible to obtain a precipitate required in a subsequent process, which makes the secondary recrystallization very unstable and rapidly deteriorates the magnetic properties. Limited to

N is an essential component in secondary recrystallization because it forms precipitates by reacting with acid-soluble Al and is an essential ingredient for secondary recrystallization. Below 0.0080%, the formation of precipitates is insufficient. The defect, called an aster, causes the product to deteriorate its surface properties, thus suppressing excess content.

Cu is an element that obtains the direction by adjusting the texture during high temperature annealing. If it is less than 0.10%, it does not have such an effect, and the magnetic property deteriorates. When Cu exceeds 0.60%, the oxide formed during decarbonization annealing adversely affects the formation of the insulating film. In addition to the size, the secondary recrystallized grains have a large size and good orientation, but the iron loss value is deteriorated, so the total amount of Cu is limited to 0.60%.

The above component system is a basic component condition capable of producing a grain-oriented electrical steel sheet by primary rolling while lowering the slab reheating temperature. Using this component system, the magnetic properties can be secured even when the slab heating temperature is operated at about 1250 ℃, which is the reheating temperature of ordinary carbon steel, but when the reheating temperature exceeds 1330 ℃, the surface scale of the electrical steel slab is melted and heated. As it greatly impairs workability, it is limited to 1250-1330 ℃ which is the most economical and easy in steel mill.

The slab is hot rolled after the low temperature reheating. In this case, the thickness of the hot rolled sheet is preferably 1.5-2.0 mm, for example, in order to secure an appropriate reduction ratio during cold rolling.

The hot rolled sheet is annealed, which should be made to refine the precipitates, which are inhibitors necessary for secondary recrystallization, to inhibit primary recrystallized grain growth. For this purpose, hot-rolled sheet annealing is preferably carried out at a temperature of 1050-1150 ℃. The reason is that if the hot-rolled sheet annealing temperature is less than 1050 ℃, the precipitate fineness effect is not effective, and if it exceeds 1150 ℃, it damages the texture and worsens the magnetic properties.

After hot-rolled sheet annealing as described above, the primary cold rolling after pickling to obtain the final thickness. At this time, the primary cold rolling is performed by controlling the heat generated in the plate according to the cold rolling in a usual manner (by water). At this time, the plate temperature is set to 150 ° C or higher in order to obtain an excellent directional texture. Cold rolling is preferable.

As described above, the first cold rolling is performed to obtain a cold rolled plate, followed by decarbonization annealing. At this time, decarbonization annealing is lowered than before to inhibit growth of primary recrystallized grains. That is, decarbonization annealing is carried out in a humid atmosphere of 750-830 ℃. In case of less than 750 ℃, decarburization is insufficient and self-aging occurs.If it exceeds 830 ℃, the primary recrystallized grain becomes larger than the appropriate size, weakening the secondary recrystallization driving force. Because it is difficult to secure good magnetism.

After decarbonization annealing as described above, after applying the anti-fusion agent containing MgO as a main component, it is wound to make a large coil, and then subjected to final finishing annealing, the final finishing annealing of the present invention is to add an intermediate crack to the existing two-stage annealing It is characterized by three stages of annealing. This is to prevent the growth driving force of the secondary recrystallized grains from lowering due to the growth of the primary recrystallized grains according to the primary cold rolling.

Specifically, the third stage of final annealing of the present invention will be described.

First, in the first step, in order to secure the surface quality in a hydrogen atmosphere containing 8-30% of nitrogen, after heating to 600-700 ℃ according to the conventional method and cracking for about 15-25 hours. Subsequently, in two steps, the temperature is raised to 930-1000 ° C. at a temperature rising rate of 15 ° C./hr or more, and cracked for about 15-25 hours. At this time, if the temperature rising rate is less than 15 ° C / hr or the cracking time is less than 15 hours, the secondary recrystallization becomes small and the magnetic properties are deteriorated. If the cracking temperature is more than 1000 ° C or the cracking time is more than 25 hours, the secondary recrystallization occurs. It is limited to the above because the directionality is deteriorated and excellent magnetic properties cannot be obtained. In the third step, maintaining the temperature rise rate of 15 ℃ / hr or more, and heated to a temperature of 1190 ± 20 ℃ by heating at 100% hydrogen atmosphere, which is a normal condition for purifying the steel for more than 10 hours after the high temperature annealing do.

In the configuration of the present invention, the primary cold rolling is carried out, and other process conditions except for the conditions of hot-rolled sheet annealing temperature, decarbonization annealing, and final finishing annealing are performed to improve the magnetic properties by inhibiting primary recrystallized grain growth. The changes can be made by those skilled in the art under ordinary conditions, and it is natural that such changes are interpreted without departing from the spirit and scope of the present invention.

Hereinafter, the present invention will be described in detail through examples.

Example 1

Si: 3.05%, C: 0.041%, P: 0.015%, Acid Soluble Al: 0.020%, N: 0.0098%, S: 0.005% by weight, Mn: 0.37%, Cu: 0.44% A thick slab was made. This was reheated at a temperature of 1290 ° C. without surface melting for 3.5 hours, followed by hot rolling to obtain a hot rolled sheet having a thickness of 2.0 mm. Then hot-rolled sheet annealing at 900-1200 ℃ and cold rolling at a temperature of 50-250 ℃ to 0.30mm, the final thickness after pickling, using this rolled plate wet 25% H ₂ + 75% N ₂ atmosphere gas Decarbonization annealing was carried out at a temperature of 850 ° C. for 3 minutes. The decarbonized annealing plate was coated with a fusion inhibitor containing MgO as a main component, dried, and then wound up to make a large coil, followed by final high temperature annealing. At this time, the final finishing annealing is heated to 600 ℃ at a heating rate of 120 ℃ per hour in a hydrogen atmosphere containing 8-30% of nitrogen and then cracked for 20 hours, and then heated up to 950 ℃ at a heating rate of 18 ℃ / hr After 20 hours of cracking, the resulting product was heated to 1200 ° C. at a heating rate of 18 ° C./hr, and then cracked for 15 hours in a 100% hydrogen atmosphere, followed by a thermal cycle of cooling. At this time, the magnetic properties after the finish annealing according to the hot rolled sheet annealing temperature and cold rolling temperature are shown in Table 1 below.

division Hot Rolled Annealing Temperature (℃) Cold rolling temperature (℃) _Iron loss, W _17/50 (w / kg) Conventional material a 900 50 1.76 Comparative material b 950 150 1.74 Comparative material c 1050 100 1.39 Invention 1050 150 1.25 Invention 1150 250 1.22 Comparative material f 1200 200 1.47

As shown in Table 1, the hot rolled sheet annealing temperature shows good iron loss characteristics at a temperature of 1050-1150 ℃, cold rolling temperature is more excellent than the iron loss characteristics at 150 ℃ or more. However, in the case of the comparative material and the conventional material outside this range, the magnetic properties were rapidly deteriorated, and thus were excluded from the scope of the present invention.

Example 2

Decarbonization annealing was carried out in an annealing temperature range of 700-850 ° C. in a wet hydrogen atmosphere at a dew point temperature of 50-58 ° C. using a rolled plate having a thickness of 0.30 mm of Example 1, followed by coating a fusion inhibitor containing MgO as a main component. After drying, each was wound up to form a large coil, followed by a final finishing annealing process as in Example 1. At this time, the magnetic properties after finishing carbon annealing after decarbonization annealing were investigated and are shown in Table 2 below.

division Decarburization Temperature (℃) Decarburization time (min) Residual carbon (%) _Iron loss, W _17/50 (w / kg) Comparative Material 1 700 3 0.0085 1.35 Comparative Material 2 720 5 0.0064 1.32 Invention 3 750 One 0.0055 1.30 Invention 4 750 3 0.0042 1.27 Invention 5 800 3 0.0029 1.22 Comparative Material 6 830 7 0.0022 1.47 Comparative Material7 850 3 0.0018 1.65

As shown in Table 2, the decarbonization annealing conditions proposed by the present invention showed excellent magnetic properties, but when the decarbonization annealing temperature is too low, a large amount of residual carbon may be present, resulting in a self aging phenomenon. In the upward direction, iron loss, which is one of magnetic properties, is worsened and excluded from the scope of the present invention.

Example 3

Using a rolled plate of 0.30 mm thickness in Example 1, decarbonization annealing was carried out at 800 ° C. for 3 minutes in a humid hydrogen atmosphere with a dew point temperature of 50-58 ° C., followed by applying and drying MgO-based fusion inhibitor. After making it into a large coil, the final finishing annealing was heated to 600 ° C. at an elevated temperature of 120 ° C. per hour in a hydrogen atmosphere containing 8-30% nitrogen, followed by primary cracking for 25 hours, and then 15 ° C./hr or more. After heating up to 850-1150 ℃ for 15-30 hours by intermediate temperature cracking, the temperature was maintained at 15 ℃ / hr or more and heated to 1180 ℃, and then cracked for 20 hours at 1180 ℃ with 100% hydrogen atmosphere. After performing the annealing through the heat cycle to cool after cooling to investigate the magnetic properties according to the intermediate cracking conditions are shown in Table 3 and Table 4 below.

division Medium cracking temperature (℃) Intermediate Crack Time (min) _Iron loss, W _17/50 (w / kg) Surface quality Comparative Material 1 none none 2.01 Good Comparative Material 2 850 25 1.75 Good Comparative Material 3 930 15 1.45 Good Invention 4 930 20 1.25 Good Invention 5 980 25 1.22 Good Invention 6 1000 15 1.23 Good Comparative Material7 980 30 1.22 Bad Comparative Material 8 1050 20 1.53 Good Comparative Material 9 1150 20 1.79 Bad

division Temperature rise rate (℃ / hr) _Iron loss, W _17/50 (w / kg) Surface quality 600-930 ℃ 930-1200 ℃ Comparative Material 1 10 10 1.69 Good Invention 2 15 15 1.24 Good Invention 3 25 25 1.22 Good

As shown in Table 3 above, when the cracking process was performed for 15-25 hours at the intermediate crack temperature of 930-1000 ° C., the magnetic properties were stably secured. If the time was too short, the magnetic properties could not be secured. If too long, the appearance quality was found to be poor.

In particular, even when the intermediate crack annealing is not treated or the middle crack temperature is low or high, the magnetism was very poor.

In addition, the magnetic change according to the temperature increase rate is shown in Table 4, but all of the magnetic properties could be secured at 15 ° C. or higher, but the magnetic properties were poor at low temperature rising conditions of less than 15 ° C./hr.

As described above, the present invention uses the primary cold method in the conventional method for producing a grain-oriented electrical steel sheet by heating the low temperature material, so that rolling productivity can be increased by rolling in the absence of oxide, and decarbonized annealing at the final thickness. It is effective in producing a grain-oriented electrical steel sheet having excellent magnetic properties economically, such as improved decarburization and additionally shortening the process.

Claims (1)

Si: 2.9 ~ 3.3%, C: 0.035 ~ 0.055%, P: 0.015% or less, acid soluble Al: 0.010 ~ 0.027%, N: 0.0080 ~ 0.012%, S: 0.007% or less, Mn: 0.10-0.45 In the method for producing a low-temperature reheat oriented electrical steel sheet comprising a step of reheating a silicon steel slab composed of%, Cu: 0.10-0.60% and Fe and other inevitable impurities at a temperature of 1250-1330 ° C, Like the low-temperature reheating and hot rolling, hot-rolled sheet annealing at a temperature of 1050-1150 ℃, then pickled and then made the final thickness by primary cold rolling, and then decarbonized to a temperature of 750-830 ℃ in a wet atmosphere After applying MgO-based fusion preventive agent, first crack at 600-700 ℃, and then increase the temperature to 930-1000 ℃ with a temperature increase rate of 15 ℃ / hr or more, and after 15-25 hours intermediate crack, It includes the final finishing annealing process of raising the temperature to 1190 ± 20 ℃ at the temperature raising rate and performing final cracking treatment for 10 hours or more. The method as claimed in the W yirueojim magnetic and has excellent low-temperature slab reheating oriented electrical steel sheet production group.