KR970007030B1 - Method of manufacturing preparation of electrical steel sheet having higt flux density - Google Patents

Abstract

In the fabrication of the oriented electric steel sheet of low temperature slab heating system, the fabricating method includes reheating to hot-roll a steel slab composed of 0.020-0.050 wt.% of C, 2.9-3.3 wt.% of Si, less than 0.016 wt.% of P, 0.018-0.030 wt.% of dissolved Al, 0.008-0.012 wt.% of N, less than 0.007 wt.% of S, 0.06-0.18 wt.% of only Ni or Cr or their combination, less than 0.32 wt.% of Mn, less than 0.6 wt.% of Cu, and the balance being Fe and inevitable impurities at a temperature of 1250-1320 degrees centigrade; controlling the thickness of the steel sheet through two cold rolling operations, coating the sheet with an annealing separator composed of principally MgO; and after raising temperature at least 25 deg.C per hour from 400-700 deg.C to 1150-1200 deg.C, annealing the sheet for at least 10 hours.

Description

Manufacturing method of high magnetic flux density oriented electrical steel sheet

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used in iron core materials such as transformers, electric motors, generators and other electronic devices, and more particularly, after the final finishing high temperature annealing process after adjusting the amount of dissolved Al in steelmaking The present invention relates to a method of manufacturing a high magnetic flux density class oriented electrical steel sheet which can secure a stabilized magnetic property by appropriately controlling the temperature increase rate at the time of temperature increase, and the present invention improves the Korean Patent Application No. 93-23751. It is.

A grain-oriented electrical steel sheet has an aggregate structure in which the orientation of grains is aligned to (110) [001], and this product has extremely excellent magnetic properties in the rolling direction. Therefore, it uses transformers, motors, oscillators, and other electronic devices. It is used as a seven core material. This (110) [001] texture is obtained by using a secondary recrystallization phenomenon, which is a nucleus having a specific orientation of nuclei, ie, the orientation of (110) [001], among the fine grains produced by ordinary recrystallization. As the entire growth of the specimens, it is necessary to suppress the growth of the primary recrystallized grains for the smooth growth of the secondary recrystallized grains in this characteristic orientation, and for this purpose, precipitates such as MnS, AlN, and BN are mainly used.

The grain-oriented electrical steel sheet products can be divided into two categories based on their magnetic characteristic values. That is, the development from the early 60's, in use the magnetic flux density B ₁₀ based on the 1.80 to 1.86 tesla (Tesla) a conventional grain-oriented electrical steel sheet and the magnetic flux density B ₁₀ value developed after the 1.89 level with the characteristics of the tesla or more efficient than in It can be divided into high magnetic flux density oriented electrical steel sheet having the characteristics of, and they have some differences in the components, manufacturing method, and error rate based on the initial grain growth inhibitor.

The manufacturing process of high magnetic flux density oriented electrical steel sheet is generally characterized by 2-4% of silicon and grain growth inhibitors, mostly containing MnS or MnSe, and after making slab (slab heating and hot rolling) → (hot rolling Plate annealing) → (1st cold rolling) → (middle annealing) → (2nd cold rolling) → (decarbon annealing) → (anneal separator) → (final high temperature annealing) → (tension coating treatment) The final product is completed through.

Among the complicated manufacturing processes of oriented electrical steel sheets, the most difficult manufacturing process is the slab heating process which performs heat treatment at high temperature. This slab heating process is performed to completely disperse the precipitates such as MnS and AlN, which are used as grain growth inhibitors, in order to precipitate out uniformly in a later step. For this, it needs to be maintained at a high temperature of about 1400 ° C for about 5 hours. Done. At this time, the surface of the hot slab becomes an oxide called Fayalite, which is composed of oxides of Si and Fe components by oxidation reaction with air.

In order to solve this problem, efforts to lower the slab heating temperature have been carried out in the interest of the leading manufacturers, and various methods have been proposed. These proposals are to secure basic magnetic properties in principle that the slab performs the heat temperature below the maximum temperature (about 1320 ° C.) at which the slab does not melt. This is mainly due to the adjustment of the basic component system, i.e. the selection of a suitable grain growth inhibitor capable of forming secondary recrystallization in the (110) [001] orientation even at low temperature slab heating. Management techniques have been proposed. Known technologies up to now include Korean Patent Publication Nos. 89-8334, 89-13200, 92-702728, 92-9999, 92-14941, and Publication No. 89-882, which have been mainly studied in Japan and have disclosed the technology to Korea. They all had a magnetic flux density value of the target flux density grain-oriented electrical steel sheet of 1.89 tesla yisanggeup to B ₁₀ reference, the actual target slab heating temperature is usually 1150-1200 ℃, grain growth inhibitors in order to ensure a high magnetic flux density Nitrogen is added to the material after the decarbonization annealing process to supplement N component, one of the components in the process.

The present inventors have developed a method for manufacturing a grain-oriented electrical steel sheet that solves the above problems and has filed a patent with Korean Patent Application No. 93-23751.

However, this manufacturing method aims to produce conventional oriented electrical steel sheets with stable properties by reheating low-temperature slabs, but it is possible to secure basic magnetic properties, but high magnetic flux of 1.89 Tesla or higher level with magnetic flux density B ₁₀ value. Production of density oriented electrical steel sheet is inadequate in nature.

Accordingly, the present inventors have completed the present invention by conducting research and experiment on the production of grain-oriented electrical steel sheets having better magnetic properties, and the present invention is a fundamental and essential dissolution Al in order to maintain the strong grain growth inhibitory power. By increasing the amount, optimizing the management of precipitates in the intermediate process, and strictly controlling the heating zone of the finishing annealing process, which is the final recrystallization process, the high magnetic flux density grade oriented electrical steel sheet of 1.89 Tesla or higher based on the improved magnetic flux density B ₁₀ To manufacture, the purpose is.

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

The present invention is a method for producing a grain-oriented electrical steel sheet by low temperature slab heating method, in weight%, C: 0.020-0.050%, Si: 2.9-3.3%, P: 0.016% or less, dissolved Al: 0.018-0.030% , N: 0.0080-0.012%, S: 0.007% or less, Ni and Cr alone or in combination: 0.06-0.18%, Mn: 0.32% or less, Cu: 0.6% or less, remainder Fe and other unavoidable impurities After reheating and hot rolling at a temperature of 1250-1320 ℃, after adjusting the final thickness by two cold rolling including intermediate decarbonization annealing without performing hot-rolled sheet annealing, the intermediate recovery annealing and MgO as main components After applying an annealing separator to be wound, and then wound up, and then heated up to 400 ℃ temperature at a rate of 15 ℃ / hr or more in a hydrogen atmosphere containing 25% nitrogen, 15 ℃ / heated up to 700 ℃ at a rate of 25 ℃ / hr or more The temperature is raised to 1150-1200 ℃ at the rate of hr or more and maintained at 100% hydrogen atmosphere for 10 hours The present invention relates to a method for producing a high magnetic flux density grade oriented electrical steel sheet subjected to finish annealing.

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

The gist of the present invention is to secure a new manufacturing process for the design of a component system capable of reheating the low temperature slab and the management of the titration inhibitor. The basic grain growth inhibitor of the present invention is AlN and is in a form to assist the role of some Cu ₂ S and MnS and grain growth inhibitors. The inventors observed the behavior of the precipitates and found that the precipitation occurs when MnS precipitates first at a high temperature and then AlN precipitates around MnS during hot rolling by ordinary high-temperature reheating. Therefore, AlN precipitates are affected by MnS precipitates, which are large and unevenly formed, resulting in a lack of inhibitors having a large amount but a practical role. Therefore, the present inventors inevitably present S in Cu ₂ S state in order to make AlN more favorable for low-temperature reheating as a grain growth inhibitor, so that AlN formed during cooling during hot rolling is not affected by MnS. It was formed as fine and uniform precipitates of effective size suitable for grain growth inhibition. However, in the dissolved Al range of Korean Patent Application No. 93-23751, even if the manufacturing conditions were well adjusted, high orientation products could not be obtained due to the limitation of grain growth inhibition.

In the present invention, the amount of dissolved Al is adjusted to 0.0180-0.030% higher than that shown in Korean Patent Application No. 93-23751 in order to secure a strong suppression force for producing a high magnetic flux density oriented electrical steel sheet by AlN precipitates.

In addition, proper control of C is important for fine precipitation during the manufacturing process of strong inhibitory force, and it is necessary to manage it somewhat to maintain proper structure during hot rolling, but in case of rolling according to decarburization to secondary thickness and secondary reduction rate Considering the processing energy securing aspects, expansion to a somewhat lower range is not a big problem.

Determination of the magnetic properties in the final product ensures that the precipitates, which are grain growth inhibitors, remain optimal during the formation of secondary recrystallization, which requires the establishment of an appropriate manufacturing process for this component system. Since this component system is AlN mid-island system with little S content, it is possible to deposit fine state which is effective for secondary recrystallization during hot rolling even in low temperature reheating method. In addition, decarbonization at a medium thickness reduces carbon content and forms a surface oxide layer, and then secondary cold rolling is required to keep secondary recrystallized grains small and uniform for preferential growth of the orientation. To this end, it is possible to secure secondary recrystallized grains having excellent characteristics in which the temperature increase rate near the first recrystallization temperature of 400-700 ° C. is aligned in the [] direction, thereby enabling the production of high magnetic flux density grade oriented electrical steel sheets.

Hereinafter, the reason for limitation of the component range and manufacturing process of this invention is demonstrated.

The C is a component that forms an appropriate hot-rolled structure to secure the magnetic properties of the high magnetic flux density directional product and imparts a high processing energy during cold rolling. At least 0.020% is required, but in the case containing 0.05% or more, If the elasticity is poor and the amount of residual carbon is high, the deterioration of the magnetism is severe when used at the demand. Therefore, the C content is preferably limited to 0.020-0.050%.

The Si is a basic component of the electrical steel sheet to increase the resistivity of the material to reduce the iron core loss, or iron loss of the magnetic properties, when the content is less than 2.9%, the iron loss characteristics are worse, when more than 3.3% Since the steel is vulnerable, the cold rolling property is extremely bad and the secondary recrystallization is unstable, which causes a bond called streak, which is a secondary recrystallization incomplete formation in the longitudinal direction, so the content of Si is 2.9-3.3%. It is desirable to limit.

The Mn lowers the solid solution temperature of the precipitate when the slab is heated, and prevents cracks formed at both ends of the material during hot rolling, but when the content is more than 0.32%, Mn is formed by the Mn oxide formed during decarbonization. Since the adhesion of the forsterite insulating film formed during high temperature annealing is deteriorated, the Mn content is preferably limited to 0.32% or less.

S forms an emulsion in the form of emulsions with Cu or Mn and acts as a grain growth inhibitor, but on the other hand, it is an element that hinders the miniaturization of AlN. In general, S is basically contained in the manufacturing process and is controlled as low as possible. Is needed. At this time, if it contains more than 0.007%, the S segregation becomes severe at the center of the slab as the slab is manufactured and solidified in the performance. Since it may appear, it is preferable to limit the content to 0.007% or less by employing a strong de-S process and the like.

The Al component forms a precipitate of AlN together with N to secure strong grain growth inhibition, and is the most important component in securing magnetic properties of high magnetic flux density class, and the amount of Al in the dissolved state rather than total Al management. Importantly, if the content is less than 0.018%, it does not have sufficient grain growth force necessary for high-orientation secondary recrystallization, which is not preferable because the grain size is uneven, so that the magnetic flux density is low and the iron loss is bad. Secondary recrystallization of (110) [001] defense with strong magnetism due to too strong growth inhibition

N is an essential component in the formation of secondary recrystallization because it forms a reaction precipitate with dissolved Al to act as a grain growth inhibitor of primary recrystallization, and when the content is less than 0.008%, the precipitate formed is insufficient and exceeds 0.012%. When added to the surface of the steel sheet defects (Blister) is caused to deteriorate the surface properties of the product, so the content of N is preferably limited to 0.008-0.012%.

The P has a property of making the steel vulnerable, so the smaller the amount of the mixture, the more advantageous, but the lower limit of the control range at the factory is 0.016%. Is preferably limited to 0.016% or less.

The Cu combines with S to form a precipitate of Cu ₂ S, solid solution at the lowest temperature among the precipitates, and precipitates at low temperature during hot rolling to supplement the grain growth inhibiting ability of AlN, and to stabilize the primary recrystallization, thereby recrystallizing the secondary recrystallization. When the addition amount exceeds 0.6%, the oxide formed during decarbonization annealing adversely affects the formation of the insulating film, and the size of the secondary recrystallized grain is so large that the magnetic flux density is good, but the iron loss is deteriorated. Since the total Cu amount is preferably limited to 0.6% or less.

Since the Ni and Cr not only refine the primary recrystallized grain but also have a large effect of dispersing precipitates, the slab heating temperature can be widened more broadly, so that the slab heating temperature is basically used at 1250-1320 ° C. alone or in combination of two. At least 0.06% or more is required to be added, and when 0.18% or more is added, the decarburizing property is deteriorated later by combining with the C component in the material. Ni and Cr are preferably limited to 0.06-0.18% alone or in combination.

The above component system is an essential condition to lower slab heating temperature, which is the biggest problem in producing oriented electrical steel sheet. When using this component system, it is possible to secure excellent magnetic properties even when the slab heating temperature is operated at 1250 ℃, the slab heating temperature of ordinary steel. It is possible that the economic effect is great.

At temperatures below 1250 ° C, precipitates such as AlN have a coarse and nonuniform distribution with less grain growth inhibition, which is not good because secondary recrystallization becomes unstable, and above 1320 ° C, electrical steel slabs start to melt and have a real rate. Since it is low, the slab heating temperature in the present invention is preferably limited to 1250-1320 ° C., which is the most economical and easy slab heating temperature in steel mills.

Next, the steel slab formed as described above is heated to the above-described heating temperature, and then hot rolled and then hot-rolled sheet annealing is made by primary cold rolling, preferably to a thickness of 0.60-0.75 mm, Decarbonization annealing is preferably performed at a wet temperature range of 820-870 ° C., followed by secondary cold rolling to a final thickness, and then preferably an intermediate recovery annealing at 500-600 ° C., followed by annealing separation based on MgO. After application of the agent, it is wound up and preferably subjected to final high temperature annealing in a 100% hydrogen atmosphere at 1150-1200 ° C. for at least 10 hours. By keeping it at or above C / hr, a grain-oriented electrical steel sheet having a high magnetic flux density is produced.

One of the features of the present invention is the final temperature rise rate during the final high temperature annealing is applied to the normal conditions of 15 ℃ / hr or more, the temperature increase rate in the 400-700 ℃ temperature range is special to ensure the high magnetic flux density class of the present invention The condition needs to be controlled. That is, the temperature increase rate at the initial 400-700 ° C., which is the temperature range at which the first recrystallization is completed, must be maintained at a temperature increase rate of 25 ° C. or more per hour. The reason for this is that when heated at a lower speed, an adverse aggregate structure with a goth orientation favoring final magnetism is formed.

At this time, the atmospheric gas in the temperature increase section is preferably hydrogen gas containing 25% nitrogen.

Other final finishing The cracking conditions at the time of high temperature annealing are basically subjected to a physiological cracking treatment for 10 hours or more at a temperature range of 1150 to 1200 ° C, but are not particularly limited in the conditions of the present invention.

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

(Example 1)

By weight, Si: 3.05-3.21%, C: 0.29-0.43%, Mn: 0.196-0.225%, S: 0.003-0.006%, N: 0.009-0.012%, P: 0.013-0.014%, Cu: 0.477- Based on 0.513%, Cr: 0.04%, Ni was added thereto, and the sum was 0.093-0.0117% as the basic component system, and the amount of dissolved Al was changed therein to be dissolved in five component systems as shown in Table 1 below.

200 mm thick slabs of these compositions were prepared and reheated at 1275 ° C. for 3 hours, followed by hot rolling to make hot rolled plates having a thickness of 2.3 mm. Thereafter, without performing hot-rolled sheet annealing, primary cold rolling was performed to adjust the thickness to 0.60 mm, followed by decarbonization annealing in a wet atmosphere at 850 ° C., and final cold rolling to a thickness of 0.30 mm. Subsequently, the intermediate recovery annealing at 550 ℃, MgO was applied to the winding coil. After the final finishing annealing, the temperature was raised by initial quenching, and then the temperature increase rate up to 400-700 ° C. was raised to 30 ° C. per hour, and the temperature thereafter was raised to the normal condition of 25 ° C. per hour to be heated to the final 1200 ° C. After cooling at high temperature for 20 hours at high temperature, a high magnetic flux density grade oriented electrical steel sheet was prepared. Atmospheric gas at this time was 25% nitrogen-containing hydrogen gas during heating, and the others were carried out in a 100% hydrogen atmosphere.

Magnetic flux density and iron loss were measured for the grain-oriented electrical steel sheet prepared as described above, and the results are shown in Table 2 below.

TABLE 1

TABLE 2

As shown in Table 2, in the case of the invention material (1-3) starting from the invention steel (1-3) having a dissolved Al content of 0.018-0.030% corresponding to the present invention range, the magnetic flux density value was based on B ₁₀ . to this value or more 1.89Tesla is secured, and also, it can be seen that this represents a low value not more than 1.09W / kg in W _17/50 standards, even if the iron loss.

However, in the case of the comparative material (a) starting from the comparative steel (a) having a smaller amount of dissolved Al than the scope of the present invention, secondary recrystallization occurred, but the magnetic properties were poor due to poor directionality, and the amount of dissolved Al also appeared. In the case of the comparative material (b) having a high comparative steel (b) as a starting material, it can be seen that the magnetic properties are rapidly deteriorated due to the presence of fine grains partially composed of normal grains.

(Example 2)

A slab having a thickness of 200 mm prepared as invented steel (2) of Table 1 was prepared, and re-heated at 1275 ° C. for 3 hours, followed by hot rolling to make a hot rolled sheet having a thickness of 2.3 mm. Then, the first cold rolling without performing the hot-rolled sheet annealing was adjusted to 0.65mm thickness, and the final cold rolling to 0.30mm thickness through decarbonization annealing in a wet atmosphere of 860 ℃. Subsequently, the final finishing high temperature annealing treatment was performed after the intermediate annealing and MgO application at 550 ° C. The finishing annealing condition was changed in the temperature increase rate of the 400-700 ℃ section of the primary financial crystal forming section as shown in Table 3 below, and the 700-1200 ℃ temperature rising rate was fixed at 25 ℃ / hr, the normal temperature rising condition, 1200 ℃ A thermal cycle was used to cool after 20 hours cracking at. At this time, the atmospheric gas was 25% nitrogen + 75% hydrogen while raising the temperature, and the others were performed in 100% hydrogen atmosphere.

After annealing, magnetic properties were investigated according to the rate of temperature increase at 400-700 ° C. and are shown in Table 3 below.

TABLE 3

As shown in Table 3 above, when the final finishing annealing was raised to a temperature increase rate in accordance with the present invention in the temperature range of 400-700 ℃ [Inventive material (4-6)], the magnetic flux density is 1.90 Tesla on the basis of B ₁₀ indicates an excellent value or more, the iron loss value can be seen that indicates a low value of less than 1.09W / kg in W _17/50 standards.

However, it can be seen that in the case of the comparative materials (c and d) having a temperature increase rate lower than the range of the present invention, the secondary recrystallization itself is unstable, so that a large amount of microcrystal grains exist in part and the magnetic properties are relatively inferior.

Claims (1)

In the method for producing a grain-oriented electrical steel sheet by low temperature slab heating method, in weight%, C: 0.020-0.050%, Si: 2.9-3.3%, P: 0.016% or less, dissolved Al: 0.018-0.030%, N: Steel slab composed of 0.008-0.012%, S: 0.007% or less, Ni and Cr alone or combined 0.06-0.18%, Mn 0.32% or less, Cu: 0.6% or less, Fe and other unavoidable impurities After reheating and hot rolling in the temperature range of, after adjusting the final thickness by two cold rolling including intermediate decarbonization annealing without performing hot-rolled sheet annealing, an annealing separator mainly composed of intermediate recovery annealing and MgO The method of manufacturing a high magnetic flux density-grade oriented electrical steel sheet, characterized in that after the application of the final finishing annealing at 400-700 ℃ at a rate of 25 ℃ / hr or more, and then at the final finishing annealing at 1150-1200 ℃ for more than 10 hours.