KR19990026909A - Method for manufacturing oriented electrical steel sheet with excellent decarburization and annealing productivity - Google Patents

Abstract

The present invention relates to a method for producing a grain-oriented electrical steel sheet used as iron core materials such as transformers, electric motors, generators and other electronic devices; The object is to provide a method for producing a grain-oriented electrical steel sheet excellent in decarburization and annealing productivity.

The present invention for achieving the above object by weight, Si: 2.9-3.3%, C: 0.025-0.045%, P: 0.015% or less, dissolved Al: 0.008-0.020%, N: 0.0080-0.012%, S: A steel slab of 0.007% or less, Mn: 0.12-0.32%, Cu: 0.60% or less and Fe and other unavoidable impurities is reheated at a temperature of 1250-1340 ° C, subjected to normal hot rolling, and then to 1000 ° C or less. After hot-rolled sheet annealing at temperature, followed by two cold rollings including decarbonized annealing in the middle to form a cold-rolled sheet having a final thickness. The cold-rolled sheet is then recovered and annealed in a dry atmosphere of 600 ° C. or lower, followed by MgO as a main component. Thermal cycle to cool after coating for 20 hours at 1200 ± 10 ℃ while maintaining the temperature rise rate of 700-1200 ℃ over 15 ℃ / hr by applying the anti-deposition agent. Low temperature reheating oriented electrical steel made by high temperature annealing In the method of,

The decarbonization annealing relates to a method for producing a grain-oriented electrical steel sheet having excellent de-elasticity and annealing productivity, which is performed at a temperature of 940-980 ° C. in a humid atmosphere of P _{H 2 O} / P _{H 2} : 0.60-0.98 for 2-5 minutes. Make a point.

Description

Method for manufacturing oriented electrical steel sheet with excellent decarburization and annealing productivity

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 produce a grain-oriented electrical steel sheet which can maximize annealing productivity due to its excellent decarburizing property. It is about a method.

A grain-oriented electrical steel sheet has an aggregate structure in which the orientation of grains is aligned in the direction of (110) [001], and has very good magnetic properties in the rolling direction. Therefore, it is possible to use transformers, motors, generators, and other electrical equipment by using this characteristic. It is used as an iron core.

The manufacturing process of the grain-oriented electrical steel is made of slab by dissolving the component system containing about 2-4% of silicon and grain growth inhibitor, mostly MnS or MnSe, and then reheating and hot rolling → pre-annealing → intermediate annealing. The final product is completed through a complex process such as cold rolling, decarburization annealing, coating of anti-deposition agent and 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. In this slab reheating process, it is inevitable to keep the precipitates such as MnS and AlN, which are used as grain growth inhibitors, in a solid solution for 5 hours at a high temperature of about 1400 ° C. in order to finely precipitate them. At this time, on the surface of the high temperature slab, an oxide called Pyrite (Fe ₂ SiO ₄ ), in which Si and Fe components are combined, is formed by oxidation with air. do. Molten oxide is designed to flow out partly, but most of it accumulates in the refractory of the upper part of the furnace, so that the entire internal repair for oxide removal is inevitable at the end of work. Therefore, in steel mills characterized by continuous work, economic burdens such as poor workability, reduced productivity, and higher costs are incurred.

Efforts to lower the slab reheating temperature are proceeding with full attention from leading manufacturers, and various methods are being proposed. That is, the basic component system is adjusted on the basis of heating the reheating temperature at about 1350 ° C. or less at which the pyrite oxide does not dissolve, and in addition to the component design, a precipitate management method during the manufacturing process and the like have been proposed.

To date, well-known technologies are mainly disclosed in Japan, and Korean Patent Publication No. 89-8334, Publication No. 89-882, etc., which disclose the technology in Korea.

Meanwhile, the present inventors designed a component system for hot rolling by heat treating a conventional grain-oriented electrical steel sheet in the vicinity of 1250-1340 ° C., which is the reheating temperature same as that of general steelworks, without any additional equipment supplement or new installation in the existing manufacturing process. By establishing this possible new manufacturing method, Korean Patent Application No. 93-23751 proposed additional element technologies to Korean Patent Application Nos. 94-21388, 21389, 21390, and 21391. According to the method, it was possible to produce a product having a high real rate and excellent magnetic properties in the production of the actual machine using the low temperature reheating method.

However, unlike the manufacturing procedure of conventional materials, the detonation method usually decarburizes an intermediate thickness of 0.60-0.70 mm after primary cold rolling, which requires long decarburization and lowers the productivity, and also reduces the amount of carbon remaining in the final product. It is a problem that the self-aging phenomenon occurs when the demand price is processed and used because it exceeds the control limit.

In the self-aging phenomenon, when the demand-oriented oriented electrical steel sheet is processed and used as a transformer, the temperature of the transformer itself increases, and thus the residual carbon component inside the material becomes carbide such as Fe ₃ C and precipitates at the grain boundary. In other words, it is caused by deterioration of magnetic properties because it impedes movement of magnetic domains.

After all, this self-aging phenomenon is the most severely affected carbon among the residual components of the material, it is necessary to focus the carbon of the final product in the manufacturing process. Specifically, since the amount of residual carbon is less than 25 ppm, there is almost no self aging phenomenon with time, and the management range of the residual carbon amount of the factory itself is usually controlled to 25 ppm or less.

However, in the Korean patent application 93-23751, since decarbonization annealing at the intermediate thickness after primary rolling is applied, annealing for 4-7 minutes is inevitable for the management of residual carbon, and thus a process characterized by continuous production. As you progress, your productivity will drop tremendously. On the contrary, if decarbonization is performed in a short time to improve productivity, it is inevitable to deteriorate the product characteristics due to self-aging when the demand cannot be satisfied.

Therefore, in the production plant, a method for maximizing annealing productivity by securing decarburization in a short time is required.

The present inventors have studied various ways to solve these problems at the same time. As a result, the present inventors have found that the decarburization and annealing productivity can be significantly improved by appropriate control of the decarbonization annealing process.

That is, the present invention provides a method for producing a grain-oriented electrical steel sheet excellent in decarburization and decarbonization productivity by appropriately adjusting the decarbonization annealing performed in the middle of two cold rollings.

Method for producing a grain-oriented electrical steel sheet of the present invention for achieving the above object, by weight, Si: 2.9-3.3%, C: 0.025-0.045%, P: 0.015% or less, dissolved Al: 0.008-0.020%, N : 0.0080-0.012%, S: 0.007% or less, Mn: 0.12-0.32%, Cu: 0.60% or less, and steel slabs made of Fe and other unavoidable impurities are reheated at a temperature of 1250-1340 ° C., and hot rolled. After performing a hot rolled sheet annealing at a temperature of 1000 ° C. or lower, followed by primary cold rolling, followed by decarbonization at a temperature of 940-980 ° C. for 2-5 minutes under a humid atmosphere of P _{H 2 O} / P _{H 2} : 0.60-0.98. After the second cold rolling to make a cold rolled sheet of final thickness, the cold rolled sheet is recovered and annealed in a dry atmosphere of 600 ° C. or lower, and then wound by applying an anti-deposition agent containing MgO as a main component, and then the whole section with a hydrogen atmosphere. While maintaining the temperature increase rate of 700-1200 ℃ over 15 ℃ / hr, it is cracked for more than 20 hours at 1200 ± 10 ℃ The excitation consists of finishing high temperature annealing through a thermal cycle.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention sets the decarbonization annealing temperature to optimize the diffusion rate of carbon atoms in the thick material and controls the oxidizing ability (P _H2O / P _H2 ) conditions to change the internal oxide of the material into a porous outer oxide layer as possible as possible. It promotes external diffusion and improves decarburization.

According to the present invention, it was confirmed that the degree of decarburization is largely governed by the decarbonization temperature in the primary cold rolled material material. This is an important fact that the decarbonization of the thin material of about 0.3 mm thickness is significantly different from that in which the decarburization reaction is dominated by the surface oxide layer formation mainly depending on the oxidation capacity (P _H2O / P _H2 ) at a low temperature of 830-840 ℃.

These differences vary depending on the conditions given for decarburization, but in thick ash decarburization, the rate of diffusion of carbon atoms by temperature dominates the entire decarburization reaction.

However, according to the present invention, control of the oxidation capacity (P _{H 2 O} / P _{H 2} ) is also important in addition to the decarburization temperature. In other words, as the decarburization temperature increases, the thickness of the oxide layer on the surface of the material increases and the internal oxide layer increases, which hinders the external diffusion of carbon atoms. In particular, in materials with a relatively high Mn content of 0.32% or less, as in the present component system, the Mn component forms an internal oxide layer of MnO and MnO ₂ by moisture in a wet atmosphere, which forms an internal oxide similar to the Si component in the material. .

Therefore, in order to improve decarburization, the internal oxides such as internal MnO and SiO ₂ can be changed to a porous external oxide layer such as FeSiO ₃ or MnSiO ₃ , which is an external oxide, to promote external diffusion of carbon atoms. The decarburization at can be improved.

The present invention is based on the results of the metallurgical confirmation, the decarburization temperature in the range of 940-980 ℃ as the optimal management criteria of the decarbonization annealing process, and the oxidation capacity (P _H2O / P _H2 ) in the wet atmosphere of 0.60-0.98 At this time, the proper decarburization time is 2-5 minutes.

This can be compared to the annealing treatment as time reduction of about 30% that of the conventional temperature 890-910 ℃, oxidizing ability (P _H2O / P _H2) conditions can be improved by about 30% from 0.50 to 0.60 the annealing productivity.

Hereinafter, the reason for numerical limitation of the present invention steel will be described.

C is advantageous to finely disperse AlN precipitates, form an appropriate rolled structure, and give processing energy during cold rolling, so it is advantageous to manage it upwards as much as possible. It is preferable to add in 0.045% of range.

Si plays a role of lowering iron loss by increasing the specific resistance of the material, but the iron loss property is bad at the addition content below 2.9%, and the steel is vulnerable when the addition content is above 3.3%, so the cold rolling property is extremely bad. It is preferable to limit 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.If less than 0.12%, Mn is disadvantageous for the formation of precipitates. Since the adhesion of the forsterite film formed during annealing is deteriorated, it is preferable to add 0.12-0.32%.

S needs to be managed as low as possible, and if it contains more than 0.007%, it is difficult to employ and diffuse the central segregation part during low temperature reheating in hot rolled steel.

Al is the central element that forms the precipitate of AlN together with N to secure grain growth inhibition. If it is less than 0.008%, Al does not have sufficient reverse force necessary for secondary recrystallization, so the grain size is small and incomplete fine particles appear. In the case of, the inhibitory force is so strong that it is difficult to form secondary recrystallization, and the magnetic property is rapidly deteriorated. Therefore, Al is preferably limited to 0.008-0.020%.

N forms an reacted precipitate with dissolved Al, which is an essential component for secondary recrystallization. If it is less than 0.008%, N is insufficient to form precipitates, and when it is added at 0.012% or higher, a blister defect occurs on the surface of the steel sheet. Since it deteriorates, excess content is suppressed.

Cu combines with S, which is an impure component, to form a precipitate of Cu ₂ S, and it is advantageous to add as much as possible because it is solid-solution at the lowest temperature among the precipitates. However, if more than 0.6%, the oxide formed during decarbonization annealing adversely affects the formation of the insulating film, so it is limited to 0.6%.

The above component system is a basic condition for lowering the reheating temperature in manufacturing the grain-oriented electrical steel sheet. Silicon steel slab of the composition as described above can secure the magnetic properties even if the reheating temperature is usually worked at 1250 ℃ reheating temperature of ordinary carbon steel, when the reheating temperature exceeds 1340 ℃ electrical steel slab begins to melt Because of the temperature, it is limited to 1250-1340 ℃ which is the most economical temperature in steel mills.

The reheated slab in this manner is hot rolled in a conventional manner, followed by hot roll annealing at a temperature of 1000 ° C. or lower, and two cold rollings including intermediate annealing.

At this time, when the primary cold rolling, the intermediate thickness should be adjusted so that the final secondary cold rolling rate is 46-69%. That is, when the secondary cold rolling ratio is 46% or less and 69% or more, the driving energy required for secondary recrystallization is too small, so that the recrystallization is unstable and the magnetic properties are deteriorated.

The present invention is characterized in that the decarbonization annealing process performed between the first and second cold rolling processes is appropriately controlled. That is, at a temperature of 940-980 ℃ P _H2O / P _H2: 2-5 minutes in a humid atmosphere is performed for 0.60 to 0.98.

If the decarbonization annealing temperature is lower than 940 ° C., the decarburization is poor, and if the decarbonization annealing temperature is higher than 980 ° C., there is a possibility of decomposition of dissolved AlN, which is not preferable in terms of magnetic compatibility.

In addition, when P _H2O / P _H2 which exhibits oxidizing ability is not more than 0.60, decarburization is poor, and when it is 0.98 or more, the surface coating formed is black and discolored, thereby deteriorating characteristics. At this time, the proper decarburization time is within 2-5 minutes, it is preferable to determine the appropriate time in consideration of sufficient decarburization.

After the intermediate annealing is finished, the second cold rolling is adjusted to the final thickness, and then recovered and annealed at a temperature of 600 ° C. or lower, and coated with a fusion inhibitor containing MgO as a main component to make a large coil, followed by finishing annealing.

Finishing annealing is performed at 100% hydrogen atmosphere to maintain the temperature increase rate of 700-1200 ° C over 15 ° C / hr, and to undergo annealing through a heat cycle that is cooled after cracking for 20 hours at a temperature of 1200 ± 10 ° C. By doing so, a grain-oriented electrical steel sheet excellent in decarburization and magnetic properties of the product can be produced.

In the configuration of the present invention, other process operating conditions except for the decarbonization annealing conditions are set forth in the present invention which has been filed by the present inventor, and the present invention is not particularly limited.

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

Example 1

By weight ratio Si: 3.16%, C: 0.039%, P: 0.014%, dissolved Al: 0.015%, N: 0.009%, S: 0.005%, Mn: 0.23%, Cu: 0.41% and the rest of Fe and other unavoidable impurities The slab with a thickness of 200 mm was hot rolled after low temperature reheating for 3.5 hours at a temperature of 1320 ° C. without surface melting, thereby making a 2.3 mm thickness hot rolled plate. Subsequently, hot-rolled sheet annealing was performed at 950 ° C, followed by primary cold rolling to 0.70 mm thickness after pickling, followed by decarbonization annealing. Decarbonization annealing was carried out variously under the conditions shown in Table 1, in the case of the prior art, 32.5H ₂ + 67.5N ₂ atmosphere, P _{H 2 O} / P _{H 2} at a temperature of 910 ℃ for 3 minutes at a dew point of 0.56. After decarbonization annealing as described above to measure the residual carbon amount of the material is shown in Table 1.

After the second cold rolling, the final thickness was adjusted to 0.30mm. After application of recovery annealing and fusion inhibitor containing MgO as a main ingredient in a dry atmosphere at 550 ℃, it was dried and wound up to make a large coil. It was. At this time, the final finishing annealing is performed with 100% hydrogen atmosphere, while maintaining the temperature raising rate of 700-1200 ° C at 18 ° C / hr while cracking for 25 hours at 1200 ° C. made. And after measuring the surface shape and magnetic properties of these specimens, the results are summarized in Table 1 below.

As shown in Table 1, in the case of the conventional materials, the product characteristics such as surface shape and magnetic properties are good, but the residual carbon content of the material is high at 46 ppm, which may cause magnetic deterioration due to aging.

In addition, in the case of the comparative material (1-2) out of the temperature condition of the decarbonization annealing condition of the present invention, it was found that the product characteristics were somewhat poor due to the high residual carbon content or the black surface shape.

In addition, in the case of the comparative carbon annealing decarbonized under the conditions lower than the oxidizing ability proposed in the present invention, the surface coating is thin, and the comparative material decarbonized annealing under the conditions higher than the oxidizing ability proposed in the present invention (4). ), The surface shape was black and the overall film properties were poor.

In addition, in the case of the comparative material 5, which lacked the decarbonization time, the decarburization property was insufficient, and the film formation was insufficient. In the case of the excessively annealed comparative material, the film formation was uneven and the surface became black, resulting in deterioration of characteristics. .

On the contrary, in the case of the inventive material (1-7) which satisfies the decarbonization annealing condition of the present invention, the residual carbon content was 25 ppm or less, and the film and the magnetic properties were good, and thus an excellent product could be produced. In addition, the annealing time is excellent because the decarburizing property is excellent to reduce the annealing time.

As described above, according to the present invention, it is possible to provide a method for manufacturing a low-temperature reheating oriented electrical steel sheet having excellent decarburization and annealing productivity, and the steel sheet provided has no magnetic aging phenomenon and an electric device manufacturing field such as a transformer requiring excellent magnetic properties. There is an effect that can be applied to.

Claims (1)

By weight%, Si: 2.9-3.3%, C: 0.025-0.045%, P: 0.015% or less, dissolved Al: 0.008-0.020%, N: 0.0080-0.012%, S: 0.007% or less, Mn: 0.12-0.32 %, Cu: 0.60% or less and steel slab made of Fe and other unavoidable impurities are reheated at a temperature of 1250-1340 ° C, subjected to ordinary hot rolling, and then hot rolled annealing at a temperature of 1000 ° C or less, and then Cold rolling is carried out two times including decarbonization annealing to make a cold rolled plate of final thickness. Then, the cold rolled sheet is recovered and annealed in a dry atmosphere of 600 ° C or lower, followed by winding up by applying an anti-deposition agent containing MgO as a main component. Is a hydrogen atmosphere, while maintaining the temperature increase rate of 700-1200 ° C over 15 ° C / hr, after finishing for 20 hours at a temperature of 1200 ± 10 ° C, undergoing a heat cycle for cooling In the manufacturing method of the steel sheet, The decarbonization annealing is a method of manufacturing a grain-oriented electrical steel sheet having excellent de-elasticity and annealing productivity, characterized in that it is performed for 2-5 minutes in a humid atmosphere of P _{H 2 O} / P _{H 2} : 0.60-0.98 at a temperature of 940-980 ℃. .