KR20010028403A - A non-oriented silicon steel with low core loss and a method for producing it - Google Patents

Abstract

PURPOSE: A non-oriented electrical steel sheet having a low core loss and a method for manufacturing the same are provided to manufacture a non-oriented electrical steel sheet having a superior magnetic properties due to a low core loss by controlling added constituents of the non-oriented electrical steel sheet and manufacturing conditions. CONSTITUTION: The non-oriented electrical steel sheet having a low core loss comprises 0.01 wt.% or less of C, 3.5 wt.% or less of Si, 0.5 wt.% or less of Mn, 0.15 wt.% or less of P, 0.012 wt.% or less of S, 1.2 wt.% or less of Al, 0.006 wt.% or less of N, 0.03 to 0.3 wt.% or Sn, 0.05 to 1.0 wt.% of Cr, 0.001 to 0.010 wt.% of Ca or/and Ce, and a balance of Fe and other inevitable impurities. The method for manufacturing the non-oriented electrical steel sheet having a low core loss comprises the processes of hot rolling the steel slab after reheating the non-oriented electrical steel slab to a temperature of 1100 to 1250 deg.C, winding the reheated steel slab at a temperature of 600 to 800 deg.C, pickling and cold rolling the wound steel slab, and annealing the cold rolled steel slab at a temperature of 700 to 1050 deg.C.

Description

Non-oriented electrical steel sheet with low iron loss and manufacturing method thereof {A NON-ORIENTED SILICON STEEL WITH LOW CORE LOSS AND A METHOD FOR PRODUCING IT}

The present invention relates to a non-oriented electrical steel sheet used for iron cores of electrical equipment such as motors, transformers, and a manufacturing method thereof, and more particularly to a non-oriented electrical steel sheet having a low iron loss and a method for manufacturing such a steel sheet. .

Non-oriented electrical steel sheets used as iron cores in electric equipment such as motors and transformers are the parts with the largest energy loss when electrical energy is converted into mechanical energy. Therefore, electrical steel sheets with low iron loss should be used to reduce energy loss. In recent years, the use of low-loss materials is preferred in consideration of environmental problems as well as energy loss, which can reduce the amount of power generation, thereby restraining the construction of power plants. For example, if the power loss can be reduced by 10, it is calculated that 20 can be reduced based on 200 domestic power plants.

In order to reduce the iron loss in the non-oriented electrical steel sheet, there are a method of reducing hysteresis loss and a method of reducing vortex loss. The eddy current loss can be lowered by adjusting the thickness of the steel sheet and the additive component of the non-oriented electrical steel sheet, by increasing the Si and Al content, which increases the resistivity, and by reducing the thickness. But since all development rivers use this method, the key is to reduce hysteresis losses. The hysteresis loss is related to the material properties of the steel sheet, and can be lowered by advantageously developing the grain size, texture, and cleanliness for magnetism. The best method for reducing iron loss in electrical steel sheet is to greatly increase the grain size. will be.

To this end, Japanese Laid-Open Patent Publication No. 60-17014 provides a method of rolling 3 to 15 light-rolled after annealing the primary cold-rolled material at a low temperature. However, due to light rolling, the Si content is lower than 0.5 so that the iron loss cannot be sufficiently lowered.

In addition, in U.S. 4,293,336, Sn is added to reduce hysteresis loss, thereby making the movement of magnetic domains smooth and manufacturing it as a clean steel by controlling impurities, but there is a problem of less effect.

Therefore, the present inventors provide a non-oriented electrical steel sheet having excellent iron loss by adding Sn and Cr to a conventional non-oriented electrical steel sheet, and adding Ca and Ce alone or in combination, and to a non-oriented electrical steel sheet having such a composition. The purpose of the present invention is to provide a method for manufacturing a non-oriented electrical steel sheet that can clean the steel and lower the iron loss by controlling the temperature element during the manufacturing process of.

In the present invention, C: 0.01 or less, Si: 3.5 or less, Mn: 0.5 or less, P: 0.15 or less, S: 0.012 or less, Al: 1.2 or less, N: 0.006 or less, Sn: 0.03 to 0.3, Cr: 0.05 ˜1.0, Ca or Ce alone or in a combination of 0.001 to 0.010 containing, the remainder Fe and other inevitable non-oriented electrical steel sheet, characterized in that it is composed of impurities added, and the present invention also Re-heating the slabs formed together at a temperature of 1100 to 1250 ° C., then hot rolling, winding to 600 to 800 ° C., pickling and cold rolling, and annealing the cold rolled plate at 700 to 1050 ° C. A method for producing a low non-oriented electrical steel sheet.

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

The inventors have tried to make the steel as clean as possible in order to produce non-oriented electrical steel sheet having low iron loss. To this end, in adjusting the components of the non-oriented electrical steel sheet, Sn and Cr, which segregate at grain boundaries and prevent intrusion of N, were added. In addition, in order to make steel clean, the amount of S and N contained as an impurity was added as little as possible. S should be managed as low as possible because it forms fine precipitates MnS to suppress grain growth. Inevitably added S is made of S and spheroidized and coarsened by addition of Ca and / or Ce to make steel clean.

In the production method, the slab should be reheated to a low temperature to prevent the solid solution of S, and the winding temperature should be as high as possible to allow the precipitate to grow large.

In the non-oriented electrical steel sheet thus produced, since the formation of fine precipitates that suppress grain growth is suppressed, it is possible to obtain a magnetic improvement due to the growth of grains.

Hereinafter, the reason for numerical limitation of the component system of this invention is demonstrated.

The above-mentioned C causes the magnetic aging in the final product to lower the magnetic properties during use, so the slab is less than 0.01, if necessary decarbonized annealing, it is preferable to be less than 0.003 in the final product. Decarbonization annealing can be added during cold annealing.

The Si is an element that increases the specific resistance to lower the eddy current loss during iron loss, but in the steel of the present invention is added below 3.5 in consideration of cold rolling properties.

Mn is combined with S to form MnS, which is a fine precipitate, and thus suppresses it to 0.5 or less.

P is an element that increases specific resistance and forms an aggregate structure favorable for magnetic, and may be added up to 0.15 in consideration of cold rolling property.

S is advantageously contained as low as possible because it forms a fine precipitate MnS adversely affects the magnetic properties, in the present invention is to be contained up to 0.012.

Al is an element that serves to increase the specific resistance and lower the eddy current loss, but when added to more than 1.2 is limited to less than 1.2, because the magnetic enhancement degree is small and expensive compared to the addition amount.

Since N forms fine and long AlN precipitates, it should be suppressed as much as possible, and in the present invention, it should be 0.006 or less.

Sn is an element that segregates at grain boundaries and suppresses diffusion of N. If Sn is 0.03 or less, the effect thereof is small, and if it is 0.3 or more, cold rolling is worsened. Therefore, the Sn is 0.03 to 0.3.

Cr is an element that promotes ferrite formation and combines with N to form nitride. It should be added at least 0.05 to have the effect. If it exceeds 1.0, it is added as 0.05 ~ 1.0 because the degree of improvement of magnetic is small compared to the added amount.

The Ca and Ce are removed by floating as inclusions in combination with S in the molten steel. In other words, S remaining in the molten steel is spherical in combination with Ca to facilitate grain growth in the final product. Ca and Ce may be added alone and in combination, and at least 0.001 or more may have an effect, but if it exceeds 0.010, it may act as an impurity.

Hereinafter, the manufacturing method of this invention is demonstrated.

The steel slab formed as described above is a slab manufactured from a continuous casting process after being made of molten steel in steelmaking, charged into a heating furnace before hot rolling, and heated in a temperature range of 1100 ° C to 1250 ° C, to facilitate hot rolling. In order to achieve the lowest temperature possible, the temperature should be 1100 ℃ or higher. If the maximum temperature exceeds 1250 ℃, the precipitates harmful to the magnetic, such as AlN and MnS may be re-dissolved to be finely precipitated after hot rolling, it is preferable to hot-rolled after reheating to 1100 ~ 1250 ℃ range.

The finish rolling temperature of the finishing rolling during hot rolling is finished on the ferrite phase. In order to obtain a hot rolled sheet having a good shape, it is preferable to carry out on a ferrite phase of 800 ° C. or higher as much as possible.

The coiling of the hot rolled sheet is carried out at a temperature range of 600 ° C to 800 ° C, and can be cooled in a coil state in the air.

The wound-cooled hot rolled sheet is cold rolled after pickling without hot rolled sheet annealing or hot rolled sheet annealing. In the case of performing hot-rolled sheet annealing, the annealing temperature is preferably set to 800 ° C. to 1150 ° C., because the annealing temperature is less than 800 ° C. because the annealing temperature is less than that. Cold rolling can be performed by a conventional method, for example, rolling once with a rolling reduction of 70 or more. Next, the annealing of the cold rolled sheet is carried out at a temperature in the range of 700 to 1050 ° C., but is preferably performed continuously for 30 seconds to 5 minutes. If the annealing temperature is less than 700 ℃ grain growth is insufficient, if higher than 1050 ℃ the surface temperature is excessively high may cause surface defects on the surface of the plate and the magnetic properties may worsen. At this time, the annealing atmosphere may be hydrogen, nitrogen or a mixed atmosphere thereof. If C is high in the slab components, decarbonization can be carried out at cold rolling annealing at a dew point of 10 to 50 ° C. Decarbonization annealing can be carried out in the temperature range of 750 ~ 850 ℃. The annealing plate is shipped at the demand price after the insulation coating treatment. The insulation coating may be treated with organic or inorganic and organic / inorganic composite coating, and may be coated with other insulating coating.

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

Example 1

Steel slabs having the components shown in Table 1 below were prepared, and the prepared slabs were heated at 1150 ° C. for 2 hours, hot rolled to 2.0 mm, and then wound and cooled in air. The cooled hot rolled sheet was annealed for 5 minutes at the temperature shown in Table 2 or without hot rolled sheet annealing, but cold-rolled after pickling and cold rolled at the temperature shown in Table 2, where the annealing atmosphere was hydrogen 20 and nitrogen. It was 80 and done for 2 minutes. Next, the annealing plate was cut and the magnetic properties and grain size were investigated and the results are shown in Table 2 below.

Steel grade C Si Mn P S Al N Sn Cr Ca Inventive Steel a 0.002 1.05 0.27 0.013 0.0024 0.34 0.0020 0.10 0.25 0.0051 Inventive Steel b 0.003 1.02 0.26 0.012 0.0021 0.35 0.0025 0.09 0.45 0.0021 Comparative Steel a 0.003 1.01 1.02 0.015 0.0025 0.35 0.0017 0.10 0.06 0.0020 Comparative Steel b 0.002 1.04 0.27 0.014 0.0022 0.36 0.0016 0.01 0.30 0.0025 Comparative Steel c 0.003 1.05 0.16 0.013 0.0020 0.35 0.0023 0.10 0.25 0.0003

In Table 1, the comparative steel (a) has a higher Mn than the component range of the present invention, the comparative steel (b) has a low Sn content, and the comparative steel (c) has a low Ca content.

Sample Number Steel grade Hot Rolled Sheet Winding Temperature (℃) Hot Rolled Annealing Temperature (℃) Cold Rolled Annealing Temperature (℃) _Iron loss (W _15/50 ) W / kg Crystal grain size (㎛) Invention 1 Inventive Steel a 650 none 1000 3.82 89 Invention 2 Inventive Steel a 700 900 1000 3.52 95 Invention 3 Inventive Steel a 700 1000 1030 3.45 102 Comparative Material 1 Inventive Steel a 550 1000 1000 4.12 65 Comparative Material 2 Inventive Steel a 700 950 650 5.12 45 Invention 4 Inventive Steel b 700 950 1000 3.33 104 Comparative Material 3 Inventive Steel b 700 950 1200 3.99 95 Comparative Material 4 Comparative Steel a 700 950 1000 3.98 92 Comparative Material 5 Comparative Steel b 700 950 1000 4.12 83 Comparative Material 6 Comparative Steel c 700 950 1000 4.25 75 W _15/50 : Loss caused by magnetizing to 1.5 Tesla at 50 Hz

As shown in Table 2, the comparative material (1) has a low grain growth because the hot rolled sheet winding temperature is too low. The comparative material 2 had a cold rolled sheet annealing temperature too low, whereas the comparative material 3 had a cold rolled sheet annealing temperature too high, and the surface was poor, which also affected the magnetic properties. Comparative materials (4) to (6) out of the component range of the invention was poor in magnetic. On the other hand, the invention material worked in the scope of the invention, the iron loss and crystal grain size was excellent, the magnetic properties were good.

Therefore, it was investigated that excellent magnetic properties can be obtained if manufactured in the component range and manufacturing conditions of the invention.

Example 2

By weight, C: 0.004, Si: 2.85, Mn: 0.16, P: 0.01, S: 0.002, Al: 0.82, N: 0.0014, Sn: 0.11, Cr: 0.25, and Ce: 0.0025 and the balance Fe and other impurities The resulting slab was heated to 1150 ° C., hot rolled, hot rolled to a thickness of 1.8 mm, wound at 700 ° C., and then annealed at 1100 ° C. for 10 minutes. The cooled hot rolled sheet was cold rolled to a thickness of 0.5 mm after pickling. The cold rolled sheet was annealed at 1000 ° C. for 3 minutes in an atmosphere of hydrogen 20 and nitrogen 80. After annealing, the organic and inorganic mixture was coated continuously and then cut. Then, as a result of examining magnetic properties and grain size, the iron loss (W _15/50 ) of the magnetic properties was _2.45 W / kg, the grain size was 150㎛.

(Example 3)

By weight, C: 0.003, Si: 2.15, Mn: 0.25, P: 0.011, S: 0.0015, Al: 0.45, N: 0.002, Sn: 0.09, Cr: 0.35, and Ce: 0.0013 and the balance Fe and other impurities The resulting slab was heated to 1150 ° C. and then hot rolled to a thickness of 2.0 mm, wound at 700 ° C., and placed in an annealing furnace of a nitrogen atmosphere heated to 1050 ° C. for 1 hour, followed by quenching. The furnace cooled hot rolled plate was cold rolled to a thickness of 0.5 mm after pickling. The cold rolled sheet was annealed at 1000 ° C. for 2 minutes in a dry atmosphere of nitrogen 80 and hydrogen 20. After annealing, the organic and inorganic mixtures were coated successively, cut and measured for magnetic properties. In addition, the grain size was examined after stress relief annealing in a nitrogen atmosphere at 790 ℃ for 1.1 hours. As a result, the iron loss (W _15/50 ) of the magnetic properties before the heat treatment was 2.7W / kg, the grain size after the heat treatment was 135㎛.

As described above, the present invention has the effect of controlling the additive component of the non-oriented electrical steel sheet and the manufacturing conditions, thereby producing a non-oriented electrical steel sheet having low iron loss and excellent magnetic properties.

Claims (3)

By weight, C: 0.01 or less, Si: 3.5 or less, Mn: 0.5 or less, P: 0.15 or less, S: 0.012 or less, Al: 1.2 or less, N: 0.006 or less, Sn: 0.03 to 0.3, Cr: 0.05 to 1.0, A non-oriented electrical steel sheet having low iron loss composed of 0.001 to 0.010 of Ca or Ce alone or in combination, and composed of residual Fe and other inevitable impurities. After reheating the slab formed as described in claim 1 to a temperature of 1100 ~ 1250 ℃ hot rolling, winding at 600 ~ 800 ℃ temperature, pickling and cold rolling, annealing the cold rolled sheet at 700 ~ 1050 ℃ temperature Method for producing a non-oriented electrical steel sheet having a low iron loss. The method of manufacturing a non-oriented electrical steel sheet having low iron loss according to claim 2, wherein a process of performing hot-rolled sheet annealing at a temperature range of 800 to 1150 ° C is added before pickling the cooled hot-rolled sheet after the winding.