KR100276294B1 - The manufacturing method for oriented electric steel sheet by non decarburized - Google Patents

Abstract

PURPOSE: Provided is a method for manufacturing oriented electrical steel sheets where Mn is added in steel sheet to induce precipitation of AIN that is used as inhibitor, thereby decarburization process can be excluded. CONSTITUTION: The oriented electrical steel sheet is manufactured by reheating a steel slab comprising Si 2.5-4.0wt.%, C 0.015wt.% or less, P 0.015wt.% or less, sol-Al 0.010-0.025wt.%, N 0.007wt.% or less, S 0.007wt.% or less, Mn 0.2-0.5wt.%, Cu 0.50wt.% or less, a balance of Fe and inevitable impurities in the temperature range of 1220 to 1280deg.C; hot rolling; annealing at 800-1120deg.C under nitrogen atmospheric condition; preliminary cold rolling; process annealing at 900deg.C or less under hydrogen atmospheric condition containing nitrogen; final cold rolling at reduction ratio of 50-65%; applying MaO-agent on the surface of the steel sheet; preliminary soaking for 5hrs or more in the temperature range of 500 to 700deg.C under hydrogen atmospheric condition containing nitrogen 5-10%; temperature elevation at the rate of 100deg.C/hr or less; final soaking in the temperature range of 1150-1220deg.C under pure hydrogen gas atmosphere for 10hrs or more; and then furnace cooling.

Description

Manufacturing method of grain-oriented electrical steel sheet by non-decarburization

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used as iron core materials such as transformers, electric motors, generators and other electronic devices, and more particularly, to a method for producing a grain-oriented electrical steel sheet having excellent productivity and magnetic properties without decarburization. It is about.

A grain-oriented electrical steel sheet is a soft magnetic material having a recrystallized aggregate structure (also called a goth aggregate structure) in which the <001> direction is oriented on the (110) plane in which the magnetization is easy in the rolling direction by special processing and heat treatment. It shows excellent magnetic property in general direction and is used as iron core of transformer, motor, generator and other electric equipment.

The manufacturing process of the grain-oriented electrical steel sheet is made of about 2-4% of silicon and grain growth inhibitor and melts the component system containing mostly MnS or MnSe to make slab, and then reheating and hot rolling → pre-annealing → intermediate annealing The final product is completed through complex processes such as cold rolling, decarburization annealing, application of anti-deposition agent, and final finishing high temperature annealing. Among the complicated manufacturing processes, the most difficult in manufacturing is the slab reheating process, which is heat-treated at a high temperature. This slab reheating process is a preliminary step for finely depositing precipitates such as MnS (MnSe) used as grain growth inhibitors, and needs to be completely heated by heating at a high temperature of about 1400 ° C. However, when the slab is reheated at a high temperature as described above, the columnar texture that adversely affects the magnet grows coarsely, and the central segregation of S occurs. In order to effectively prevent this, a certain amount of carbon is added in the steelmaking step, which causes ferrite-austenite phase transformation in the hot rolling region to suppress the growth of coarse columnar tissue and form a uniform hot rolled tissue. It is known that the central segregation of S also plays a role in suppressing.

However, when carbon remains in the final product, it precipitates as carbide even in the low temperature range of 200 ° C, which greatly increases iron loss and decreases the efficiency of electronic equipment. Therefore, the added carbon undergoes the decarbonization annealing process after the second rolling. It should be removed to below 30ppm again As such, general grain-oriented electrical steel sheet manufacturing processes inevitably include high temperature slab reheating and decarburization after cold rolling due to carbon addition to form fine and uniform precipitates essential for secondary recrystallization.

In order to improve this complex manufacturing process, much efforts are being made by many steel mills around the world, and most of them are mainly focused on lowering the slab reheating temperature. These designs are based on the slab reheating temperature at about 1300 ° C. or less at which the slab does not melt, and the basic ingredient system is adjusted and added to the basic ingredient system to manage precipitates during the manufacturing process. That is, the slab reheating temperature is lowered to 1300 ° C. or lower by designing a component system within a range not forming precipitates in the steelmaking process and forming a precipitate required in a process after hot rolling.

To date, well-known technologies are mainly disclosed in Japan and include Korean Patent Application Publication Nos. 89-8334, 89-13200, 92-707278, 92-9999, 92-14941 and the like. These target only the manufacturing method of high magnetic flux density oriented electrical steel sheet among all oriented electrical steel sheets, and reheating is usually performed at 1150-1200 degreeC in order to prevent the said oxide melting. In addition, in order to secure the magnetic flux density value, the N component, which is one of the grain growth inhibitor components, needs to be supplemented in the process, and therefore, a denitrification facility for impregnating nitrogen into the material after the decarbonization annealing process is required. Therefore, this technique is carried out at a lower temperature than the reheating temperature of 1250-1280 ° C. of the general steelworks, which is a great cost burden due to mutual work interference and installation of additional equipment for the sedimentation reaction. In addition, the control of the addition amount of ferroalloy for the management of the precipitate is strictly limited, in particular, all of the published manufacturing processes are all the process of adding more than 0.021% of carbon, all of the published manufacturing processes decarbonized after cold rolling are all carbon It is a process to add more than 0.021%, and decarbonization annealing process after cold rolling is essential.

Therefore, the present inventors designed the component system to reheat the slab reheating temperature below 1300 ° C which is the same as the reheating temperature of the steel mill using AIN as a major grain growth inhibitor, and to perform hot rolling. Established a new manufacturing method that can work without a new application has been filed in Korea Patent Application No. 93-23751 and also applied for additional element technology in Korea Patent Application No. 94-21388,21389,21390,21391.

According to the above method, it was possible to produce a product having a high real rate and excellent magnetic properties in actual production by using a low temperature reheating method. However, this manufacturing method, unlike the manufacturing procedure of the conventional materials, decarburization is usually performed at the intermediate thickness of 0.60-0.70mm after the primary cold rolling, which requires a long time decarburization and the productivity is lowered and the amount of residual carbon in the final product. Since the control limit is over 30ppm or less, there is a problem that the efficiency is lowered due to self-aging when the demand is used.

Therefore, if the content of carbon in the steelmaking process can be controlled to the minimum possible amount, it is easy to manage the amount of residual carbon in the final product, and also to increase the productivity by eliminating the decarburization process and to supply stable quality to the demand price. It is possible.

Accordingly, the present invention actively suppresses the carbon content, and also enables low-temperature reheating of the slab using AlN as a grain growth inhibitor, adds Mn to precipitate AlN finely and uniformly, and in particular, the decarburization process is omitted, thereby improving productivity and magnetic properties. It is an object of the present invention to provide a method for producing an excellent grain-oriented electrical steel sheet.

In order to achieve the above object, the present invention is a method for producing a grain-oriented electrical steel sheet, by weight, C: 0.015% or less, Mn: 0.2-0.5%, Si: 2.5-4.0%, P: 0.15% or less, acid solubility Reheat the steel slab consisting of Al: 0.010-0.025%, N: 0.007-0.013%, S: 0.007% or less, Cu: 0.50% or less, and Fe and other unavoidable impurities at a temperature of 1220-1280 ° C., After the usual hot rolling, hot-rolled annealing at a temperature of 800-1120 ° C. under a nitrogen atmosphere, followed by an intermediate annealing at 900 ° C. or lower in a nitrogen-containing hydrogen gas atmosphere after primary cold rolling, and then a 50-65% reduction After secondary cold rolling at a rate, rolled to the final thickness, MgO-based anti-deposition agent was applied, and in a temperature range of 500-700 ° C. in a hydrogen atmosphere containing 5-10% or less of nitrogen in an elevated temperature range. 1 hour cryogenic cracking for more than one hour, the temperature is raised at a rate of less than 100 ℃ / hr and then in a 100% hydrogen gas atmosphere The present invention relates to a method for producing a grain-oriented electrical steel sheet by non-decarburizing, characterized in that the final finish annealing through a thermal cycle of cooling after cracking for at least 10 hours in the temperature range of 1150-1220 ℃.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention has the main point to design a low carbon component system capable of non-decarburizing in consideration of the amount of carbon naturally lost in the annealing process, and because of this can be reheated at low temperatures, it is possible to omit the decarburization process.

To this end, in the steel slab of the present invention, carbon is not added for the purpose of improving the hot rolled structure except that it is inevitably added to adjust other components in the steelmaking process. In addition, it is desirable to adjust the minimum calcined carbon content that can be decarbonized within the range not exceeding 0.0150% in view of the amount of natural loss in slab reheating, preannealing, intermediate annealing and final high temperature annealing. .

That is, when the added content is less than 0.015%, the residual carbon content after the final high temperature annealing is 30ppm or less and is easy to manage and does not cause self-aging when used in the final electronic device.

Mn, like carbon, is an austenite forming element. When added to steel, Mn causes austenite transformation in a high temperature region so that two phase regions of austenite and ferrite phases exist to make the hot rolled structure uniform, and further facilitate the employment of AlN. In the cooling process after hot rolling, AlN is precipitated finely and uniformly. Therefore, in the present invention, by adding Mn to reduce the calcined carbon content, it is to replace the existing carbon role. In addition, Mn increases the specific resistance and decreases iron loss in the same way as Si. If the amount is added below 0.2%, the addition effect is insignificant, and when it is added more than 0.5%, the strength of steel increases and the plate shape during cold rolling is increased. It is preferable that the addition amount is in the range of 0.2 to 0.5% because the workability is poor, such as unevenness and the orientation of the 110 (001) crystal grains is lowered at the time of secondary recrystallization and the magnetic properties are lowered.

The Si increases the resistivity of the material as a basic composition of the electrical steel sheet, and serves to lower the iron loss. If the content is less than 2.5%, the specific resistance is reduced and the iron loss characteristics are deteriorated. If the content is over 4.0%, the brittleness of the steel is increased, the cold rolling property is extremely poor, and the secondary recrystallization is unstable, so the content is 2.5 to 4.0% is preferred.

S is a component that acts as a grain growth inhibitor by combining emulsions of emulsion form by combining with Cu or Mn, but when added excessively, it is segregated in the center of slab reheating and adversely affects the microstructure. It is preferable to make it contain.

Al is an important element for forming precipitates of AlN together with N to secure grain growth inhibition, and is more important in acid-soluble Al content capable of forming AlN by reacting with N rather than the total amount of Al. If the acid-soluble Al content is less than 0.010%, the secondary recrystallization becomes unstable because it does not form enough precipitates to suppress the growth of the primary recrystallization grains, and when added more than 0.025%, the amount of precipitates increases and is coarse in size. Since the effect of suppressing grain growth decreases, the addition content is preferably in the range of 0.010-0.025%.

N is an essential component in secondary recrystallization because it inhibits growth of primary recrystallized grains by reacting with acid-soluble Al to form AlN precipitates. When N is added at 0.013% or more, coarse AlN is formed to decrease grain growth inhibitory effect, and blister occurs on the surface of steel sheet, resulting in deterioration of the surface properties of the product, and addition of 0.007% or less forms sufficient AlN. Since it is not possible to suppress the effect of suppressing the secondary recrystallization, the content is unstable, so the content is preferably 0.007-0.013%.

Cu, like Mn, is an element that stabilizes secondary recrystallization by contributing to the solid solution and fine precipitation of AlN as an austenite forming element. In addition, Cu combines with S to form a precipitate called Cu ₂ S, which has the effect of suppressing grain growth. The present invention component the effect of addition of Cu to prevent S center segregation of sikimeuroseo form a Cu ₂ S, and, because of rapidly at a temperature below the temperature at which MnS is formed to form a Cu ₂ S suppressing the formation of the employed temperature is higher MnS There is. If the content is 0.5% or more, it is preferable to control Cu to 0.5% or less because secondary recrystallized grains which will adversely affect the formation of the insulating film at high temperature annealing are coarsened, and the resistivity decreases to increase iron loss.

The above-described silicon steel component system can be used as the material of the present invention even when manufactured using a conventional dissolution method, an ingot method, a playing method, and the like, and the silicon steel component can lower the reheating temperature and produce no decarburization during the production of grain-oriented electrical steel sheet. As a basic condition, it is possible to secure the magnetic properties even if the reheating temperature is performed at 1250 ° C, which is usually the reheating temperature of ordinary carbon steel.

However, if the reheating temperature is less than 1220 ℃, because the reheating temperature is low AlN is not sufficiently dissolved in the magnetic properties, and when heated to more than 1280 ℃ coarse elongation occurs in the microstructure after hot rolling. The cause of the stretched grains is that when the slab is reheated to a high temperature of 1280 ° C. or higher, crystal grains grow coarse, and when hot-rolled, the coarse grains are deformed and elongated in the rolling direction. Such stretched grains do not recrystallize later in the cold rolling and annealing process, but continue to be finely recrystallized in the final high temperature annealing to generate streaks, thereby lowering magnetic properties. Therefore, it is desirable to ensure excellent magnetic properties and to heat it to 1220-1280 degreeC which is the most economical temperature in a steel mill.

In this way, the preheating of the reheated slab by hot rolling to make a hot rolled sheet is preferably heat-treated in a nitrogen atmosphere to re-precipitate AlN that could not be precipitated during hot rolling. At this time, when the annealing temperature is above 1120 ℃, AlN which has already been precipitated becomes coarse, so that the effect of inhibiting grain growth is reduced. At temperatures below 800 ℃, the reprecipitation effect is small and sufficient oxidation layer formation is difficult, so that pickling becomes difficult. It is preferable to anneal.

In addition, in the cold rolling that is pre-annealed and pickled after pickling, the second recrystallization becomes unstable in the case of one-time cold rolling because the grain growth inhibition force is smaller than that of the recrystallization growth driving force. Cold roll. Intermediate annealing performed between the first and second rolling processes is performed to recover or recrystallize the structure deformed by cold rolling, and is different from ordinary annealing combined with ordinary decarbonization annealing. Essentially, the dew point temperature is maintained at 50 ° C. or higher, but in the present invention, decarburization is unnecessary, thereby simplifying the intermediate annealing process. At this time, when the annealing temperature is 900 ° C. or higher, the precipitate grows coarsely, and the recrystallized grain grows coarsely and the magnetic properties deteriorate.

In the two stage cold rolling including intermediate annealing, the final cold rolling rate is important regardless of the rolling method.If the rolling reduction is less than 50%, the direction improvement effect of the secondary recrystallization by the improvement of the primary recrystallization texture is weak.65 When the rolling ratio is more than%, secondary recrystallization becomes unstable and complete secondary recrystallization cannot be obtained. Therefore, it is preferable to perform secondary cold rolling at a rolling reduction of 50-65%.

The cold rolled sheet is cold rolled to the final thickness and the final high temperature annealing is performed after coating the annealing separator Mg0. Since the feature of the present invention is the final high temperature annealing without undergoing a separate annealing process after the second rolling, In this case, primary recrystallization during hot annealing is very important. Therefore, the primary recrystallization should be stably formed by cracking for 5 hours or more at a low temperature section of 500 to 700 ° C., so that the secondary recrystallized grains formed thereafter are more oriented in the (100) [001] direction where magnetization is easy. Because of the ordered texture, it is possible to secure much better magnetic properties than conventional oriented electrical steel sheets.

If it does not crack for a long time in this temperature range, the primary recrystallization will be unstable, and the secondary recrystallization structure will also be unstable and the magnetic properties will deteriorate.

At this time, it is preferable to use hydrogen gas containing 5-25% or less of nitrogen to remove residual impurities such as C, N, and S after forming the oxide layer and completing the second recrystallization.

After the low temperature cracking in the above atmosphere, the temperature increase rate to the final annealing temperature should be controlled at less than 100 ° C / hr in which the driving force of the grain growth according to the elevated temperature does not exceed the inhibitory power of the grain growth inhibitor such as AlN. Therefore, the temperature is raised to a temperature range of 1150-1220 ° C. at a heating rate of less than 100 ° C./hr, and cracks in a 100% hydrogen gas atmosphere for 20 hours or more, and the final high temperature annealing temperature is less than 1150 ° C. or the cracking time is less than 1 hour. The complete secondary recrystallization does not occur, and smooth removal of impurities is difficult. In addition, annealing at more than 1220 ℃ shortens the life of the annealing equipment is uneconomical.

The surface of the steel sheet on which the inorganic oxide layer film is formed by the high temperature annealing may be coated with a tension after high temperature annealing for the purpose of improving insulation and improving iron loss characteristics due to micronization.

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

Example 1

Si: 3.12%, acid soluble Al: 0.013%, N: 0.13%, S: 0.005%, Cu: 0.47% by weight, the amount of carbon is changed as shown in Table 1, the balance Fe and inevitable A steel made of impurity was made of a slab having a thickness of 230 mm. After reheating the slab for 4.5 hours at 1250 ° C., it was hot rolled to form a hot rolled sheet having a thickness of 2.3 mm, followed by pre-annealing in a nitrogen atmosphere at 950 ° C., followed by pickling, followed by primary cold rolling to a thickness of 0.6 mm.

The cold rolled sheet was subjected to an intermediate annealing at 850 ° C., followed by final cold rolling to 0.3 mm, followed by application of the cold rolled sheet to an annealing separator, followed by final high temperature annealing.

The high temperature annealing was first performed at 600 ° C. for about 10 hours, and then elevated to 1200 ° C. at a temperature rising rate of 20 ° C./hr, and secondary cracking was performed for 10 hours or more so that secondary recrystallization occurred completely. At elevated temperature, the gas was used at 25% N ₂ + 75%, and pure water was used in the 1200 ° C cracking section.

At this time, the residual carbon after the pre-annealed and the final high-temperature annealing was measured, and also the magnetic properties of the hot annealing plate was measured and the results are shown in Table 1 below.

TABLE 1

As shown in Table 1, in the case of the invention material (1-3) having a low carbon content of 150 ppm or less, the residual carbon content after the final high temperature annealing satisfies the management criteria of 30 ppm or less even if it is not decarburized separately. Was higher than 1.872 Tesla and the iron loss property was lower than 1.22W / kg. However, in the case of the comparative material (2), if the low carbon content of 230ppm is not decarbonized annealing, the residual carbon content after the final high temperature annealing is large, so that the secondary recrystallization is unstable and the magnetism is greatly deteriorated. In the case of the comparative material (1) with low carbon content of 183 ppm, the carbon was removed to the final high temperature annealing and the magnetism was good, but the iron loss characteristics were likely to deteriorate rapidly in terms of demand. I could see that.

Example 2

Fixed carbon at 0.010%, Si: 3.3%, acid soluble Al: 0.015%, N: 0.010%, S: 0.004%, Cu: 0.42%, and the amount of Mn is 0.12, 0.24, 0.41, 0.49, A slab of 230 mm was made by varying 0.65%. The slab was reheated at 1280 ° C. for 4.5 hours and hot rolled to form a 2.3 mm thick hot rolled sheet and preannealed in a nitrogen atmosphere at 950 ° C. Cold rolling was firstly rolled to a thickness of 0.6 mm, intermediately annealed at 830 ° C., and finally cold rolled to a thickness of 0.3 mm. The final rolled sheet was degreased and coated with an annealing separator, followed by final high temperature annealing, wherein the high temperature annealing was first performed at 550 ° C. for 10 hours at low temperature, followed by heating up to 1200 ° C. at a temperature rising rate of 20 ° C./hr. Second cracking was performed for more than 10 hours to completely re-crystallize. At elevated temperature, the gas was used for nitrogen-containing water-induced atmosphere, and impurities were removed by using pure water in the 1200 ° C cracking section. The magnetic properties of the final high temperature annealing plate according to the Mn content are shown in Table 2 below.

TABLE 2

As shown in Table 2, in the case of the comparative material (3) having a Mn content of 0.12%, due to the low austenite transformation, AlN was not sufficiently dissolved, so that the magnetic properties were somewhat low, and the Mn content was 0.24 to 0.49. In the case of the increased invention material (4-6), the solid solution of AlN increased due to the austenite transformation, showing excellent magnetic properties. However, in the case of the comparative material 4 to which 0.65% Mn was added, the rolling property was inferior, and the orientation of the secondary recrystallization was poor, and the magnetic properties were deteriorated.

Example 3

Slab composed of C: 0.012%, Si: 3.5%, Mn: 0.41%, acid soluble Al: 0.019%, N: 0.010%, S: 0.007%, Cu: 0.48%, balance Fe and other unavoidable impurities Was prepared. The slab reheating temperature was changed from 1220 to 1320 ℃ for 4.5 hours, reheated and hot-rolled to make a 2.3mm thick hot rolled sheet, followed by pre-annealing the hot rolled sheet in a nitrogen atmosphere at 1105 ℃, and then pickling thickness 0.6. First cold rolling in mm, and after the intermediate annealing at 880 ℃ in a mixed gas atmosphere of nitrogen and hydrogen, the final cold rolling to a thickness of 0.3mm. The plate, which was cold rolled to the final thickness, was coated with MgO, and then wound and subjected to final high temperature annealing. The final high temperature annealing was performed at 600 ° C. for 10 hours and the first low temperature crack, followed by heating up to 1200 ° C. at a heating rate of 20 ° C./hr, and then cracking for 10 hours or more so that secondary recrystallization occurred completely. At high temperature annealing, the gaseous gas containing 25% N ₂ was used at elevated temperatures, and 100% H ₂ gas was used in the 1200 ° C cracking section to remove impurities along with the completion of secondary recrystallization.

At this time, the magnetic properties of the final high temperature annealing plate according to the slab reheating temperature were measured and the results are shown in Table 3 below.

TABLE 3

As shown in Table 3, in the case of the comparative material (6-7) having a reheating temperature of 1300 ℃ or more, streaks occurred in the macrostructure of the final high temperature annealing plate, and the magnetic properties (Blo) were very inferior to 1.742 Tesla. . However, the invention material (7-9) reheated to a temperature of 1280 DEG C or lower did not have streaks and exhibited excellent magnetic properties. On the other hand, in the case of the comparative material (5) having a reheating temperature of 1200 ° C., since the reheating temperature was low, AlN was not sufficiently dissolved so that the magnetic property was low as 1.766 Tesla.

As described above, the present invention can provide a method for producing a grain-oriented electrical steel sheet having excellent productivity and magnetic properties by allowing low-temperature reheating, and in particular, eliminating the decarburization process, through the control of steel composition and manufacturing conditions. There is an effect that can be applied to the field of manufacturing electric devices such as transformers, which have no magnetic aging and require excellent magnetic properties.

Claims (1)

(Correction) In the method for producing a grain-oriented electrical steel sheet, in weight%, C: 0.015% or less, Mn: 0.2-0.5%, Si: 2.5-4.0%, P: 0.015% or less, acid-soluble Al: 0.010-0.025% Steel slab consisting of N: 0.007-0.013%, S: 0.007% or less, Cu: 0.50% or less, and Fe and other unavoidable impurities, was reheated at a temperature of 1220-1280 ° C., followed by ordinary hot rolling. Next, hot-rolled sheet annealing is carried out at a temperature of 800-1120 ° C. under a nitrogen atmosphere, and after the first cold rolling, an intermediate annealing is performed at 900 ° C. or lower in a nitrogen-containing hydrogen gas atmosphere, and then second cold rolling at a rolling reduction ratio of 50-65%. After rolling to the final thickness, Mg0 as a main component was applied, and an anti-deposition agent was applied.In the elevated temperature range, the primary cryogenic cracking was performed for 5 hours or more in a temperature range of 500-700 ° C. in a hydrogen atmosphere containing 5-10% nitrogen. 10 hours or more at a temperature range of 1150-1220 ° C. in a 100% hydrogen gas atmosphere. The method of after the heat cycle of cooling after eleven-oriented electrical steel sheet according to the mutal burnt characterized in that the final annealing.