KR20000043790A - Method for producing non-oriented electric strip with low iron loss - Google Patents

Abstract

PURPOSE: A method is provided to produce a non-oriented electric strip with low iron loss used as an iron core of electric appliances such as a motor and a transformer. CONSTITUTION: A slab contains less than 0.01wt% of C, less than 1.5wt% of Si, less than 1.5wt% of Mn, less than 0.15wt% of P, less than 0.02wt% of S, 0.005 to 0.2wt% of Al, less than 0.006wt% of M, less than 0.005wt% of O, 0.03 to 0.30wt% of Sn, 0.0004 to 0.0030wt% of B and the remain of Fe and incidental impurities. The ratio of B/N is 0.1 to 0.5. The slab is reheated, hot rolled and wound in a temperature of 550 to 850°C. Then, the slab is cleansed by acid, cold rolled and annealed in a temperature of 700 to 1050°C to be a non-oriented electric strip.

Description

Non-oriented electrical steel sheet with low iron loss and manufacturing method

The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, and more particularly to a non-oriented electrical steel sheet having a low iron loss used as an iron core of an electrical equipment such as small and medium-sized motors and transformers.

Non-oriented electrical steel sheets used as iron cores in electric appliances such as various motors, small transformers and magnetic shields are required to have low iron loss. Iron loss represents the degree of loss of electrical energy per weight of electrical steel sheet material and is expressed in W / kg. There is also a method of lowering iron loss by increasing Si, but there is a disadvantage that the manufacturing cost increases. In addition, low-cost materials have a high iron loss. Therefore, there is a need for a method that can satisfy all of these and improve the characteristics of electrical appliances.

Non-oriented electrical steel can lower the iron loss by growing grains in the tissue. Among the elements that suppress the growth of grains, a representative element is N. Among the elements for suppressing the influence of N, the representative element is N. In order to suppress the influence of N, Al may be added 0.2% or more, but the manufacturing cost becomes high.

Japanese Patent Laid-Open No. 64-39348 attempts to reduce the effect of N by adding B, but the B / N ratio is high at 0.5-1.5 so that B may be contained more than necessary. In addition, Japanese Patent Laid-Open No. 62-180014 may have a large B precipitate since the ratio of B / N is 0.5-1.5.

Korean Patent 97-65507 has a low B / N ratio of 0.1-1.5, but there is a problem that the generation of oxides may increase due to the low amount of Sol.Al, which is difficult to deoxidize sufficiently.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a non-oriented electrical steel sheet having a small crystal grain and low iron loss and a method of manufacturing the same.

The object of the present invention is by weight% C: 0.01% or less, Si: 1.5% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.02% or less, Al: 0.005-0.2%, N: 0.006% Or less, O: 0.005% or less, Sn: 0.03-0.30%, B: 0.0004-0.0030%, and a ratio of B / N of 0.1-0.5 to provide a non-oriented electrical steel sheet having low iron loss composed of balance Fe and other unavoidable impurities. Is achieved by doing so.

In the present invention, C: 0.01% or less, Si: 1.5% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.02% or less, Al: 0.005-0.2%, N: 0.006% or less And hot rolling after slab of O: 0.005% or less, Sn: 0.03-0.30%, B: 0.0004-0.0030%, and B / N ratio of 0.1-0.5, which is composed of the balance Fe and other unavoidable impurities. ; Winding to a temperature of 550-850 ° C .; Pickling and cold rolling; Annealing the cold rolled sheet at a temperature of 700-1050 ° C .; It provides a method of manufacturing a non-oriented electrical steel sheet having a low iron loss.

In the present invention, C: 0.01% or less, Si: 1.5% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.02% or less, Al: 0.005-0.2%, N: 0.006% or less And hot rolling after slab of O: 0.005% or less, Sn: 0.03-0.30%, B: 0.0004-0.0030%, and B / N ratio of 0.1-0.5, which is composed of the balance Fe and other unavoidable impurities. ; Winding to a temperature of 550-850 ° C .; Pickling and cold rolling; Annealing the cold rolled sheet at a temperature of 650-900 ° C .; Rolling at a rolling reduction rate of 1-10%; Provides a method of producing a low iron loss non-oriented electrical steel sheet consisting of.

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

In the non-oriented electrical steel sheet according to the present invention, N greatly affects grain growth. At this time, N is fine and precipitates mainly in linear AlN to suppress grain growth. Therefore, N and Al should be suppressed as much as possible, but inevitably added, a method that can reduce their effects can be used.

B is used as an element that can reduce the influence of N, and B is precipitated as BN due to its high bonding strength with B. However, when B is excessive, it can be precipitated as B2O3 and FeB. It should be added as much as it binds to BN and it is important not to add any other B. The method of adding an arbitrarily adjustable amount of B rather than the amount of N contained inevitably was investigated.

In addition, the amount of Al was also found to be very important. In particular, Al should be added for oxidation inhibition after tapping molten steel in the steelmaking step as an oxidation inhibitor. Therefore, the addition of B after holding O in 0.005% or less in molten steel can suppress not only the formation of AlN but also the formation of oxides generated by bonding with oxygen.

The production method of the present invention is as follows. Pulley process of steelmaking-casting-slab reheating-hot rolling-cold rolling-annealing-insulation film-shipping and semi-processing process of steelmaking-casting-slab reheating-hot rolling-annealing-hard rolling-insulation film-shipping . Semi-process is to add light rolling (1-10% skin pass) after annealing of cold rolled plate of pulley process, and this steel is characterized by the need to remove residual stress by heat treatment after punching.

In the steel of the present invention, Al is added in an amount of 0.005-0.2% to completely remove oxygen, and then B is added. And the reaction with N, steel plate B is added to the minimum to avoid making unnecessary precipitate, for this purpose B is added to 0.0004-0.0030%, B / N value of 0.1-0.5. By producing in this way, it was observed that the crystal grains grow well.

Hereinafter, the reason for numerical limitation according to the composition range of this invention is demonstrated.

Since C causes magnetic aging and degrades the magnetic properties during use, it is preferable to control the slab to 0.01% or less in the slab and to control it to 0.003% or less in the final product.

Si is an element that lowers iron loss by increasing specific resistance, but it is most effective to add 1.5% or less in the steel component of the present invention. In other words, the B-added steel is an appropriate region in which Si can lower the iron loss at 1/5% or less.

P is an element that forms a texture that is advantageous for magnetic and can be added up to 0.15% in consideration of cold rolling property.

S is advantageously contained as low as possible by forming MnS, which is a fine precipitate, to suppress grain growth. In the present invention, S is at most 0.02% or less.

Al is added at least 0.005% and up to 0.2% for sufficient deoxidation of molten steel. When added below 0.005%, deoxidation may be insufficient, resulting in a large number of oxidation inclusions, and when added in an amount of 0.2% or more, the effect of the steel is less than that of the added amount. In general, Al plays a role of reducing the effect of nitrogen, but the steel of the present invention is effective because B does not have much Al because it plays a role.

N is suppressed as much as possible by forming fine and long AlN precipitates, and in the present invention, it is 0.006 or less.

O is suppressed by forming an oxide to suppress the movement of magnetic domains in the product to lower the magnetism, and in the present invention, it is 0.005% or less.

Sn segregates at grain boundaries and suppresses diffusion of N, and serves to suppress the texture of the (222) plane which is disadvantageous to magnetism. Less than 0.03%, the effect is less. If it is 0.30% or more, cold rolling property will worsen and the shape of a hot rolled plate will be bad, and it shall be 0.03-0.30%.

B is added to the grain more advantageously by forming a coarse boron precipitate BN instead of fine AlN in combination with the N inside the material. B is added at least 0.004%, and if the amount is large, iron loss may be increased, and thus up to 0.0030% may be added. In addition, by making B / N 0.1-0.5, precipitates of nitrogen and boron can be reduced as much as possible, thereby precipitating to BN to suppress precipitates that are adverse to magnetic properties.

Hereinafter, the manufacturing method of this invention is demonstrated.

The steel slab formed as described above is manufactured from molten steel in steelmaking and then into slabs in a continuous casting process, charged into a heating furnace before hot rolling, and hot rolled after reheating in a range of 1300 ° C. or less.

The hot rolled hot rolled sheet may be wound, and by winding in a temperature range of 550-850 ° C., the hot rolled sheet may be annealed, and thus, fine precipitates may be greatly grown. This is also known as self-annealing. When winding up below 550 ℃, the effect of annealing is less. When annealing above 850 ℃, pickling may be difficult due to excessive surface oxidation. After winding, the cooled hot rolled sheet is pickled in an acid solution and cold rolled.

When manufactured by the pulley process, the cold rolled sheet is subjected to cold roll annealing in a continuous process for more than 30 seconds at a temperature of 700-1050 ° C for 5 minutes or less, and the annealing plate is shipped at the demand price after insulation coating treatment. When annealing below 700 ℃ in cold rolled annealing, recrystallization is insufficient, and when annealing above 1050 ℃, an oxide layer may be generated on the surface. If thens above 700-1050 ℃, an oxide layer may be generated on the surface. Anneal to range. The annealing time is annealed at 30 seconds or more and 5 minutes or less.

In the case of manufacturing with semi-process, cold rolled sheet is subjected to cold roll annealing in continuous process for more than 30 seconds at less than 30 seconds at the temperature of 650-900 ℃. If the demand is needed, insulating film can be applied. When annealing below 650 ℃ during cold rolling annealing, recrystallization is insufficient, and when annealing above 900 ℃, grain growth may be excessive, resulting in uneven grain growth during stress relief annealing after processing. When the skin pass is less than 1%, the grain growth is insufficient when the stress relief annealing is performed, and when it is 10% or more, recrystallization occurs and the grain size becomes 1-10%.

The non-oriented electrical steel sheet shipped at the demand price is punched into the shape desired by the demand, and the stressed material can be stress-annealed if necessary. Stress relief annealing is carried out in a non-oxidizing atmosphere, it can be carried out for 10 minutes or more in the range of 700-850 ℃.

It will be described in more detail through the following examples.

(Example 1)

As an example of the inventive steel produced by the semi-process, steel slabs having the components shown in Table 1 were prepared, steel type B / N is the invention steel 0.26, invention steel b is 0.31, comparative steel asms 0.83, comparative steel b Was 1.90. The steel slabs were heated to 1180 ° C., hot rolled to a thickness of 2.0 mm in a conventional manner, wound and cooled as shown in Table 2. The cooled hot rolled plate was pickled, cold rolled, and subjected to skin pass as shown in Table 2 after annealing, and the thickness after light rolling was 0.5 mm. The annealing of the cold rolled sheet was carried out in a mixed atmosphere of 20% hydrogen and 80% nitrogen, and the stress relief annealing was performed at 100% nitrogen atmosphere. The stress relief annealing was heated at 790 ° C. for 60 minutes and then furnace cooled. The destressed sample was measured for magnetism and grain size.

In Table 2, the comparative material 1 had a low annealing temperature, and the comparative material 2 was caused by the low rolling ratio of 0.5%. Comparative material 3 was found to be grainy due to the high annealing temperature. Comparative materials 4 and 5 were found to have a small grain size and a high iron loss due to the value of B / N exceeding the range of the invention.

Steel grade C Si Mn P S Al N O Sn B Inventive Steel a 0.004 0.45 1.25 0.072 0.002 0.015 0.0030 0.001 0.09 0.0008 Inventive Steel b 0.003 0.46 1.26 0.070 0.003 0.008 0.0038 0.001 0.15 0.0012 Comparative Steel a 0.003 0.47 1.25 0.071 0.002 0.003 0.0030 0.002 0.10 0.0025 Comparative Steel b 0.003 0.46 1.24 0.073 0.002 0.0005 0.0022 0.006 0.09 0.0042

Sample Number Winding temperature (℃) Annealing Temperature (℃) Light rolling rate (%) _Iron loss (W _15/50 ) W / kg Crystal grain size (μm) Steel grade Invention 1 720 800 6 3.1 120 Inventive Steel a Invention Material 2 720 750 6 3.0 125 Inventive Steel a Comparative material 1 720 600 6 3.9 92 Inventive Steel a Comparative material 2 720 750 0.5 4.2 86 Inventive Steel a Invention 3 800 800 8 2.95 132 Inventive Steel a Invention 4 800 850 6 2.96 135 Inventive Steel b Comparative material 3 800 950 6 3.8 102 Inventive Steel b Comparative material 4 800 800 6 4.1 105 Comparative Steel a Comparative material 5 800 800 6 4.3 95 Comparative Steel b

(Example 2)

As an example of the steel of the invention in which the pulley process was manufactured, steel slabs having the components shown in Table 3 were prepared, and steel grades B / N were invention steel c of 0.40 and comparative steel c of 1.66. The steel slabs were heated to 1200 ° C., hot rolled to a thickness of 2.3 mm in a conventional manner, and wound and cooled as shown in Table 4. The cooled hot rolled plate was pickled and cold rolled to a thickness of 0.5 mm. Annealing of the cold rolled plate was carried out in a mixed atmosphere of 20% hydrogen and 80% nitrogen. The annealed material was cut after insulation coating treatment to measure magnetism and grain size.

In Table 4, Comparative Material 6 had a low annealing temperature, and Comparative Steel c was determined to have high iron loss even if the conditions were changed as in Comparative Materials 6 to 8 because the value of B / N exceeded the range of the invention.

Steel grade C Si Mn P S Al N O Sn B Invention steel c 0.003 1.21 0.24 0.012 0.003 0.010 0.0022 0.002 0.11 0.0009 Comparative Steel c 0.002 1.22 0.26 0.011 0.003 0.002 0.0021 0.003 0.12 0.0035

Sample Number Winding temperature (℃) Annealing Temperature (℃) _Iron loss (W _15/50 ) W / kg Crystal grain size (μm) Steel grade Invention 5 750 950 3.5 80 Invention steel c Invention Material 6 800 950 3.4 85 Invention steel c Comparative Material 6 800 650 4.9 52 Invention steel c Comparative material 7 500 950 4.2 62 Comparative Steel c Comparative Material 8 800 950 3.9 68 Comparative Steel c

(W _15/50 ; iron loss when magnetized to 1.5 Tesla at 50 Hz)

(Example 3)

By weight% C: 0.003%, Si: 0.41%, Mn: 0.25%, P: 0.071%, S: 0.001%, Al: 0.011%, N: 0.0025%, Sn: 0.09%, B: 0.0010% and B / N is 0.4, the slab composed of the balance Fe and other impurities is vacuum-dissolved, heated to 1150 ° C., then hot rolled to 850 ° C., wound and cooled at a temperature of 800 ° C., and then to a thickness of 0.50 mm after pickling. Cold rolled. The cold rolled sheet was annealed in an atmosphere of 20% hydrogen and 80% nitrogen at 850 ° C., and then de-strained and annealed at 790 ° C. for 60 minutes after cutting. _Iron loss (W _15/50 ) among the magnetic properties was 4.31 W / kg. As a result of testing the material, the grain size was 92 m.

As described above, according to the present invention, the content of iron loss is reduced in the non-oriented electrical steel sheet used as the iron core of electrical equipment such as small and medium-sized motors and transformers.

Claims (3)

By weight% C: 0.01% or less, Si: 1.5% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.02% or less, Al: 0.005-0.2%, N: 0.006% or less, O: 0.005% Or less, Sn: 0.03-0.30%, B: 0.0004-0.0030% and B / N ratio of 0.1-0.5, low iron loss non-oriented electrical steel sheet, characterized in that it is composed of the balance Fe and other unavoidable impurities. By weight% C: 0.01% or less, Si: 1.5% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.02% or less, Al: 0.005-0.2%, N: 0.006% or less, O: 0.005% Or a hot rolling step of reheating the slab composed of Sn: 0.03-0.30%, B: 0.0004-0.0030%, and B / N ratio of 0.1-0.5, balance Fe and other unavoidable impurities; Winding to a temperature of 550-850 ° C .; Pickling and cold rolling; Annealing the cold rolled sheet at a temperature of 700-1050 ° C .; Method for producing a low iron loss non-oriented electrical steel sheet, characterized in that consisting of. By weight% C: 0.01% or less, Si: 1.5% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.02% or less, Al: 0.005-0.2%, N: 0.006% or less, O: 0.005% Or a hot rolling step of reheating the slab composed of Sn: 0.03-0.30%, B: 0.0004-0.0030%, and B / N ratio of 0.1-0.5, balance Fe and other unavoidable impurities; Winding to a temperature of 550-850 ° C .; Pickling and cold rolling; Annealing the cold rolled sheet at a temperature of 650-900 ° C .; Rolling with a rolling reduction of 1-10%; a method of producing a low iron loss non-oriented electrical steel sheet, characterized in that consisting of.