KR970007033B1 - Method for manufacturing oriented electrical steel sheet - Google Patents

Abstract

In the fabrication of the oriented electric steel sheet, the fabricating method includes reheating to hot-roll a steel slab composed of 0.035-0.050 wt.% of C, 2.9-3.3 wt.% of Si, less than 0.015 wt.% of P, 0.011-0.017 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, 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 twice of cold rolling including a decarbonating annealing at 820-870 degrees centigrade without annealing the hot rolled sheet; coating the sheet with an annealing separator composed of principally MgO; and finally annealing the sheet at a high temperature of 1150-1200 degrees centigrade for at least 10 hours. The finish hot annealing is performed at raising temperature rate of 50deg.C per hour from 400-700deg.C.

Description

Manufacturing method of 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, more specifically, recovery after cold rolling by controlling the temperature rising rate of the final high temperature annealing process The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet of low-temperature slab heating method that can secure stable and excellent magnetic properties even if the annealing process itself is omitted. The present invention is an improvement of Korean Patent Application No. 93-23751.

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. Used as an iron 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. The growth of the entire specimen is abnormal. For the smooth growth of the secondary recrystallized grains in this characteristic orientation, it is necessary to suppress the growth of the primary recrystallized grains. For this purpose, precipitates such as MnS, AIN, 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 components, manufacturing method, and error rate based on initial grain growth inhibitor.

The manufacturing process of conventional grain-oriented electrical steel sheet is generally 2-4% of silicon and grain growth inhibitor, and mostly contains MnS or MnSe, and then melts to make slab (slab heating and hot rolling) → (hot rolled sheet annealing) → (1st cold rolling) → (intermediate annealing) → (2nd cold rolling) → (decarbonization annealing) → (applied annealing separator) → (final high temperature annealing) → (tension coating treatment) Finished with the product.

Among the complicated manufacturing processes of oriented electrical steel sheets, the most difficult manufacturing process is the slab reheating process which performs heat treatment at high temperature. This slab heating process is performed to completely disperse precipitates such as Mn and AIN, which are used as grain growth inhibitors, in order to precipitate finely and uniformly in a later process. It is necessary. At this time, the surface of the hot slab becomes an oxide called Fayalite in which oxides of Si and FeO are mixed by oxidation of air, and the oxide melts from the surface due to its low melting point of 1320 ° C. At this time, the molten metal is designed to flow outward, but most of it is accumulated in the refractory of the upper part and must be repaired at the end of work. Therefore, steelworks, which are characterized by continuous operation, suffer enormous economic burdens such as poor workability, reduced productivity, and cost increase. Therefore, if it is possible to work in the vicinity of 1300 ℃, which is the temperature at which the slab does not melt, that is, 1250-1280 ℃, which is the slab heating condition of ordinary steel, it can expect huge profits such as no work interference with other products.

Efforts to lower the slab heating temperature are proceeding with full attention, especially among advanced manufacturers, and various methods have been proposed. These proposals are to ensure basic magnetic properties in principle that the slab heating temperature is performed below the maximum temperature (about 1300 ° C) where the slab does not melt. This is mainly based on the composition 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 with low temperature slab heating. Management techniques have been proposed. Known technologies up to now include Korean Patent Publication Nos. 89-8334, 89-13200, 92-70728, 92-9999, 92-14941, and Publication No. 89-882, which have been mainly studied in Japan and have disclosed the technology to Korea. All of them were targeted for high magnetic flux density oriented electrical steel sheets, and the actual target slab heating temperature is 1200 ° C or lower, and is usually performed at 1150 ° C. In order to ensure high magnetic flux density, N component, one of the grain growth inhibitor components, is used in the process. To supplement, an impregnation process of impregnating nitrogen into the material after the decarbonization annealing process is essentially added. Therefore, these technologies have mutual work interference as they are managed at lower temperature than slab heating temperature of general steel, and it is inevitable to install additional facilities for sedimentation reaction. As it is difficult to secure, there is still a problem as the magnetic deviation of each processed lot in the final product is so severe that the error rate is inevitable.

The present inventors have developed a method for solving the above-mentioned problems and have filed a patent with Korean Patent Application No. 93-23751.

Korean Patent Application No. 93-23751 mentioned above proposes a method of manufacturing a grain-oriented electrical steel sheet which enables not only to manufacture a conventional grain-oriented electrical steel sheet having stable characteristics by low-temperature reheating of the slab, but also to bring about a shortening effect of some processes. have.

However, the above-mentioned application invention also involves two essential annealing treatments following two cold rollings, so that the productivity of the annealing process is lowered.

In order to improve the productivity in such a manufacturing process, it is required to shorten the process as much as possible, and the present inventors conducted research and experiment to omit the secondary recovery annealing process itself in order to meet such demands, and then strictly abide the final annealing process conditions. Management has led to the development of a method for producing a grain-oriented electrical steel sheet that can secure the magnetic properties that can be secured in a normal process.

The present invention is a method of manufacturing a grain-oriented electrical steel sheet after the cold rolling to the final thickness by precisely controlling the primary recrystallized grain by controlling the temperature rising rate of the constant temperature section at the final high temperature annealing to secure the driving force of the secondary recrystallization It is an object of the present invention to provide a method for producing a grain-oriented electrical steel sheet which can secure magnetic properties equivalent to or higher than that of a conventional grain-oriented electrical steel sheet even if the intermediate recovery annealing process itself is omitted.

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

The present invention is in weight%, C: 0.035-0.050%, Si: 2.9-3.3%, P: 0.015% or less, dissolved Al: 0.011-0.017%, N: 0.0080-0.012%, S: 0.007% or less, Ni and Cr alone or composite: 0.06-0.18%, Mn: 0.32% or less, Cu: 0.6% or less, remainder Fe and other unavoidable impurities The steel slab of the composition is reheated at a temperature range of 1250-1320 ° C., hot rolled, and then hot rolled. After performing annealing and adjusting the final thickness by two cold rollings including decarbonization annealing at 820-870 ℃, applying intermediate recovery annealing and annealing separator (Anti-fusion). In the method of producing a grain-oriented electrical steel sheet by heating in a hydrogen gas atmosphere containing 25% nitrogen and performing a final finishing high temperature annealing treatment at 100% hydrogen atmosphere for 10 hours at 1150-1200 ° C., the intermediate recovery annealing is performed. Omitted and, instead, the temperature increase rate at 400-700 ° C. during the final high temperature annealing is 50 ° C. / The present invention relates to a method for producing a grain-oriented electrical steel sheet, which is maintained at hr or less.

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

The gist of the present invention is to omit the intermediate recovery annealing process performed after the rolling to the final thickness in the low temperature reheating operation technology and to supplement the metallurgical inaccuracy of this part in the state of the subsequent process. In conventional oriented electrical steel sheet production by the conventional two-rolling method, the annealing process after the secondary rolling is the recovery of the processing energy imparted during rolling and the completion of the primary recrystallization, and this primary recrystallization state is the final The secondary recrystallization state using the abnormal growth shape of the primary recrystallized grains generated in the finishing hot annealing process is determined.

However, the annealing process after the second final rolling in the low temperature reheating method of Korean Patent Application No. 93-23751, which has been proposed and patented by the present inventors, restores the processing structure at the time of rolling at a low temperature of 500-600 ° C. In the final finishing high temperature annealing process performed by a conventional method, only normal grain growth occurs when primary recrystallization is formed due to excess temperature, so that the orientation of crystal grains is easy to magnetize (110) [001. It is not possible to obtain a directional product that requires only the aggregates arranged in the direction. The secondary recovery annealing method proposed by the present inventors in the above patent application is advantageous for rapid heating up to 750-800 ° C. and a proper recrystallization up to 1200 ° C., which is a processing method in a general final finishing high temperature annealing process. Controlled elevated temperatures were essential and this treatment was essential to ensure the best magnetic properties. However, at the production site, the two annealing processes performed by two rollings have considerable loads in terms of equipment management, productivity, and workability, so that a single process shortening can produce huge profits if it can secure the equivalent magnetic characteristics. This becomes possible. Therefore, the present inventors have studied the second recrystallization principle and growth mechanism in order to omit the secondary recovery annealing process itself, and as a result, the temperature increase rate at the low temperature part of the final finishing annealing process is 50-100 ° C / hr considering the conventional productivity. Instead of the high temperature rise, the secondary rolling structure is restored in the 400-500 ° C. temperature range by heating up to 400 ° C. in a conventional manner and gradually raising the temperature below 50 ° C. per hour in the temperature range of 100 ° C. to 700 ° C., and 500 At -650 ° C, fine and uniform primary recrystallized grains can be obtained.

The fine and uniform primary recrystallized grain thus secured ensures the driving force of the secondary recrystallization occurring at a temperature range of 870-970 ° C., thereby ensuring that the orientation of the grain is aligned in the (110) [001] direction. Recrystallized grains can be obtained.

Hereinafter, the reason for limitation of the component range of this invention, a manufacturing process, etc. are demonstrated.

C is required to form at least 0.035% or more as an element to stabilize the development of secondary recrystallization by forming an appropriate hot-rolled structure, but when it contains 0.050% or more, decarburization annealing becomes difficult, resulting in poor workability and residual carbon. If the amount is high, the deterioration of the magnetic is severe, it is preferable to limit the content of C to 0.035-0.050%.

The Si is a basic component of the electrical steel sheet to increase the resistivity of the material to reduce the core loss, or iron loss of the magnetic properties, when the content is less than 2.9%, the iron loss characteristics worsen, if the content is 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 is a component that lowers the solid solution temperature of the precipitate during slab heating and prevents cracks formed at both ends of the material during hot rolling. When Mn is added at a content of more than 0.32%, the Mn oxide is formed at high temperature by annealing. Since the adhesion of the formed fosderite insulating film is deteriorated, the content of Mn is preferably limited to 0.32% or less.

The S forms a precipitate in the form of an emulsion with Cu or Mn and acts as a grain growth inhibitor, and thus serves as an auxiliary function of AIN. Typically, S is basically contained in a manufacturing process and needs to be managed as low as possible. At this time, if it contains more than 0.007%, S segregation becomes severe at the center of the slab as the slab is manufactured and solidified in the performance. Because it may appear, it is preferable to limit the content to 0.007% or less by strongly suppressing by employing a de-S process.

The A1 component is a central element which forms precipitates of AIN together with N to secure grain growth inhibition, and is important for the amount of Al in the dissolved state, not the total amount of Al management. When the content is less than 0.011%, sufficient amount for secondary recrystallization is required. Since it does not have the grain growth inhibitory effect, it is not preferable because the final grain size is small and incomplete fine grains are generated, and when it exceeds 0.017%, the secondary recrystallization of the (110) [001] orientation with excellent magnetic strength is too strong. Since the magnetic properties deteriorate rapidly due to difficulty in the development of, the content of Al is preferably limited to 0.011-0.017% by the amount of dissolved Al.

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 better. However, the lower limit of the control range at the factory is 0.015%. The content is preferably limited to 0.015% or less.

The Cu is combined with S to form a precipitate of Cu ₂ S, the solid solution at the lowest temperature of the precipitate and precipitated at low temperatures during hot rolling to supplement the grain growth inhibition of AIN to facilitate secondary recrystallization, If the addition time exceeds 0.6%, the oxide formed during decarbonization annealing will not only have a bad effect on the formation of the insulating film, but the secondary recrystallized grains will be too large, so that the magnetic flux density is good, but the iron loss may deteriorate. It is desirable to limit it 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. Since at least 0.06% or more is required to be added, and when 0.18% or more is added, the Ni and Cr are limited to 0.06-0.18%, alone or in combination, because the decarburizing property becomes worse later.

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 working 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 AIN have a coarse and uneven distribution, which is a form of low grain growth inhibition, and thus secondary recrystallization becomes unstable, and above 1320 ° C, electrical steel slab starts to melt and the real rate Since the slab heating temperature in the present invention is lowered, it is preferable to limit the slab heating temperature to 1250-1320 ° C., which is the most economical and easy slab heating temperature in steel mills.

The steel slab formed as described above is heated to the above-described heating temperature, and then subjected to two cold rolling and final finishing high temperature annealing treatments including hot rolling and decarbonization annealing in a conventional manner, thereby obtaining a grain-oriented electrical steel sheet having excellent magnetic properties. Is manufactured.

That is, the steel slab formed as described above is heated to the above-mentioned heating temperature, and then hot-rolled and then hot-rolled sheet annealing is performed by primary cold-rolling, preferably made of 0.55-0.75 mm thick, and preferably For example, decarbonization annealing in a wet hydrogen atmosphere of 820-870 ℃, followed by secondary cold rolling to the final thickness, and then skipped the intermediate recovery annealing itself at low temperature, and an annealing separator (MgO) as the main component Apply.

Subsequently, the final finishing high temperature annealing that cracks for 10 hours or more at 1150-1200 ° C. must be performed. In this final finishing high temperature annealing treatment, the secondary rolling structure is recovered in the component system of the present invention and the temperature range where primary recrystallization occurs is 400-. The temperature increase rate at 700 ° C. should be raised to 50 ° C./hr or less, because when the temperature rise rate is 50 ° C./hr or more, it is difficult to secure a fine and uniform primary recrystallized grain which is a driving force for secondary recrystallization. This is because secondary recrystallization hardly occurs, so that partial microcrystal grains are formed or magnetic properties are extremely deteriorated due to the formation of almost full grains.

At this time, the atmosphere gas during the final finishing high temperature annealing is a conventional method, the atmosphere gas in the heating section first is hydrogen gas containing 25% nitrogen, the crack section at 1150-1200 ℃ hydrogen is 100 ℃ hydrogen gas.

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

(Example 1)

A slab having a thickness of 200 mm having the composition of the following Table 1 was prepared and hot rolled after reheating at 1275 ° C. for 3 hours to make a hot rolled sheet having a thickness of 2.3 mm. Thereafter, without hot-rolled sheet annealing, it was cold rolled after pickling to adjust the thickness to 0.60 mm. Final cold rolling was performed at a thickness of 0.30 mm through decarburization annealing in a wet atmosphere at 860 ° C.

Next, the main components of the cold-rolled cold rolled sheet as described above, as in the conventional method, were annealed at 100 ° C. in a dry 100% nitrogen atmosphere for 2 minutes at 550 ° C., and MgO was used as a main component. After applying an annealing separator roll and winding the invention, the invention was made into a coil mass at a hydrogen gas atmosphere containing 25% nitrogen at 80 ° C / hr in the case of conventional materials and at a temperature increase rate of 25 ° C / hr in the case of invention materials. After the temperature was raised to 700 ° C., a final high temperature annealing process was performed at a temperature rising rate of 20 ° C./hr to 1200 ° C. and maintained at 100% hydrogen atmosphere at this temperature for 20 hours to prepare a conventional grain-oriented electrical steel sheet.

Magnetic flux density (B ₁₀ value) and iron loss (W _17/50 value) of the _grain- oriented electrical steel sheet manufactured as described above were measured, and the results are shown in Table 2 below.

Table 1 (Unit: wt%)

TABLE 2

As shown in Table 2, the annealing treatment as in the present invention as compared to the prior art to perform the secondary intermediate recovery annealing at a temperature of 550 ℃ in the C-1 and C-2 composition, 400-700 at the final annealing It can be seen that the invention material having a temperature increase rate of 25 ° C./hr exhibits characteristics similar to or slightly superior to those of the conventional material in magnetic flux density and iron loss characteristics.

Therefore, it can be seen that the present invention is more economical because it can bring a shortening of the manufacturing process.

(Example 2)

A slab having a thickness of 200 mm was manufactured using the melted material of Table 1, followed by hot rolling after reheating at 1275 ° C. for 3 hours to make a hot rolled plate having a thickness of 2.3 mm. Thereafter, without cold-rolled annealing, primary cold rolling was performed to adjust the thickness to 0.65 mm, followed by decarbonization annealing in a wet atmosphere at 850 ° C., and final cold rolling to a thickness of 0.30 mm. After the second recovery annealing was omitted, immediately after application of an annealing separator containing MgO as a main component, and then wound up to make a coil mass, and then rapidly heated up to 400 ℃ and then the temperature increase rate from 700 ℃ to 10-100 ℃ / hr After heating to 1200 ℃ at a temperature increase rate of 20 ℃ / hr and then subjected to the process of final high temperature annealing to cool after 20 hours cracking. At this time, the atmospheric gas is 25% nitrogen + 75% hydrogen while raising the temperature in the other 100% hydrogen atmosphere to prepare a conventional grain-oriented electrical steel sheet. Among these magnetic properties, magnetic flux density B ₁₀ and iron loss W _17/50 were measured, and the results are shown in Table 3 below.

TABLE 3

As shown in Table 3, the slower the initial temperature increase rate, the better the magnetic characteristics, but exhibits a favorable magnetic characteristic up to 50 ° C./hr, which is the condition of the present invention. The recrystallization is unstable, the fine grains appear, it can be seen that the magnetic deterioration is rapidly deteriorated, in which case it becomes difficult to commercialize.

Claims (1)

By weight% C: 0.035-0.050%, Si: 2.9-3.3%, P: 0.015% or less, dissolved Al: 0.011-0.017%, N: 0.0080-0.012%, S: 0.007% or less, Ni and Cr alone or Composite: 0.06-0.18%, Mn 0.32% or less, Cu: 0.6% or less, remainder Fe and other unavoidable impurities The steel slab of the composition is reheated at a temperature range of 1250-1320 ° C. and hot rolled, and then hot-rolled sheet annealing is not performed. After adjusting to final thickness by two cold rolling including decarbonization annealing at 820-870 ℃, after applying intermediate recovery annealing and annealing separator (Melting prevention agent) mainly composed of MgO, it contains 25% nitrogen. In the method of producing a grain-oriented electrical steel sheet by heating in a hydrogen gas atmosphere and performing a final finishing high temperature annealing treatment at 100% hydrogen atmosphere for 10 hours at 1150-1200 ° C., the above-mentioned intermediate recovery annealing is omitted, and instead When the final finishing high temperature annealing the temperature increase rate at 400-700 ℃ 50 Method for producing a grain-oriented electrical steel sheet, characterized in that maintained at less than ℃ / hr.