EP0567612A4

EP0567612A4 - Nonoriented electrical steel sheets with superior magnetic properties, and methods for manufacturing thereof.

Info

Publication number: EP0567612A4
Application number: EP19920922513
Authority: EP
Inventors: Byung Keun Research Instit Bae; Sang Yun Research Institut Cha; Jong Soo Research Institut Woo; Jong Keun Research Institu Kim; Jong Koo Pohang Iron Steel Kim
Original assignee: Research Institute of Industrial Science and Technology RIST; Pohang Iron and Steel Co Ltd
Current assignee: Posco Co Ltd; Research Institute of Industrial Science and Technology RIST
Priority date: 1991-10-22
Filing date: 1992-10-22
Publication date: 1994-04-05
Also published as: CZ121893A3; RU2092605C1; CZ284195B6; JPH06503609A; CN1078270A; JP2700505B2; WO1993008313A1; EP0567612A1; CN1039352C

Abstract

The present invention relates to nonoriented electrical steel sheets being used for the core materials of electrical machinery and equipment such as various motor, generator, small size transformer and ballast core and the like, and the object of the present invention is to provide for nonoriented electrical steel sheets with superior magnetic properties by semi-process or fully-process with proper selection of composition system of the nonoriented electrical steel sheet. Further in a method for manufacturing nonoriented electrical steel sheets with superior magnetic properties by semi-process or fully-process, which is the gist of the present invention, Ni and Cu are added to a steel comprising Si of maximum 3.5 %, Al of maximum 0.7 % and Mn of less than 1 % or 0.5 %, further, sum of one kind or two kinds of Sn and Sb are simultaneously added to make basic component system, and C, P, Ca and/or rare earth element (REM) are additionally added to the basic composition system.

Description

NONORIENTED ELECTRICAL STEEL SHEETS WITH SUPERIOR MAGNETIC

PROPERTIES, AND METHODS FOR MANUFACTURING THEREOF

FIELD OF THE INVENTION δ

The present invention relates to nonoriented electrial steel sheets used for the core materials of the electrical machinery and equipment such as various motors, generators, small size transformer, ballast core and the 10 like, and methods for manufacturing^* thereof, and more specifically, to nonoriented electrial steel sheets with low iron loss and high magnetic flux density and permeability, and methods for manufacturing thereof.

lδ BACKGROUND OF THE INVENTION

The product of nonoriented electrial steel sheets, in general, can be classified according to Si content. Such product is graded a low-class product where Si content is

20 less than 1 %, a middle-class product where it has 1-2 % Si, and a high-class product where it exceeds 2 % Si. The aforesaid gradin is based on the fact that iron loss becomes low as long as Si content is more added. However, magnetic flux density or permeability decreases as long as δ Si content becomes higher. The superior magnetic properties mean that iron loss is low, and that magnetic flux density and permeability are high. Since Si, a work hardening element, adversely affects the ability of cold rolling during manufacturing process or punching during processing by connsu ers, so to speak, the electric apparatus manufacturers, it is preferable to contain a low content and to lower iron loss if possible. Thus, development of nonoriented electrial steel sheets with low Si content as well as low iron loss and high magnetic flux density and permeability is necessitated.

Iron loss of nonoriented electrial steel sheets can be largely divided into hysteresis loss and eddy current loss. Eddy current loss is decided by chemical composition of the product, thickness, frequency, etc. In the vicinity of a frequency for normal uses, 60 Hz, hystresis loss becomes more than 50 %. However, eddy current loss can be bigger than hysteresis loss where it is used for special uses with high frequency. In order to reduce eddy current loss, the element with high resistivity among chemical composition, such as Si and Al, can be more added or thickness of the final product can be thinned. In order to reduce iron loss in chemical composition, thickness and frequency under the same condition, it is important to reduce hysteresis loss. As hysteresis loss is in inverse proportion to grain growth, grain should be grown largely as far as possible. Further, by developing a (110) plane or a (200) plane parallel to the sheet surface of the product, that is, a texture in the form of {110}[u-- v-, w,] or {200} [ 2 Λ Wg] * iron loss can be lowered as well as magnetic flux density and permeability can be improved. Magnetic properties are not always improved in proportion to grain growth. But if texture of the (110) plane or the (200) plane is well formed, and if grain is grown largely, magnetic properties are improved. As (110) plane or the (200) plane of texture is well developed and texture of a (111) plane detrimental to magnetic properties can be formed little, magnetic properties can be improved.

In the method of growing grain, there is a method of adjusting component or a method of purely manufacturing steel. And by growing fine precipitates greatly, grain of the final product can be easily grown. Although purification of steel is a good method with respect to texture advantageous to magnetic properties, it is possible to use a method of inhibitin texture of the (111) plane, etc, detrimental to magnetic properties by adding special elements enabling to control texture.

The methods for manufacturing the aforesaid nonoriented electrial steel sheets are deivided into fully-process and semi-process. Steel slab is heated, hot rolled, and hot rolled sheet can be pickled after annealing. And in fully- process, hot rolled sheet is pickled, is cold rolled, and is annealed. The following process is processing by consumers, so to speak, the electric apparatus manufacturers. In semi-process, hot rolled sheet is pickled, is cold rolled, intermediate annealing is conducted, and then skin pass rolling or temper rolling is conducted. The following processes are processing by consumers, so to speak, the electric apparatus manufacturers and annealing with stress relieving. In case of fully-process, there is a double cold rolling method in which a first-order cold rolling is conducted during cold rolling and a second-order cold rolling is carried out after intermediate annealing. This method also falls into fully-process as high temperature annealing is carried out after a second-order cold rolling.

As the nonoriented electrial steel sheets manufactured by semi-process is the skin pass rolled or temper rolled product, consumers, ^' so to speak, the electric apparatus manufacturers must carry out annealing with stress relieving after processing. This annealing with stress relieving has a purpose of ^' grain growth but stress occurring during processing is relieved. As regards the nonoriented electrial steel sheets manufactured by fully- process, more or less stresses can occur during processing by consumers, so to speak, the electric apparatus manufacturers and residual stresses during high temperature annealing can be relieved. As the result, magnetic properties during annealing with stress relieving by consumers, so to speak, the electric apparatus manufacturers can be improved.

In a prior art of manufacturing the nonoriented electrial steel sheets, there is a method to improve permeability even with high iron loss by lowering Si or Al, but the method is restricted for uses due to lots of energy loss. Further, there is a method for reducing iron loss by increasing Si or Al , in which magnetic flux density and permeability were low. This method, however, has the drawbacks in efficiency of the electrical machinery. Further, the Korean Patent Application Nos. 88- 017514, 88-017924 and 89-020173 teach that the element such as Zr and B was added to Sb-bearing steel , but texture and crystal grain advantageous to magnetic property were not sufficiently developed from the final product. The Korean Patent Application No. 91-5867 teaches the method of coiling in the atmosphere after rolling with the percent reduction in thickness of more than 15 % is conducted under ferrite phase during hot rolling.- In this method without special elements, such as Sn, Ni and Cu, however, grain is small-sized and texture advantageous to magnetic properties is insufficient. And U.S.Patent No. 4,204,890 teaches the method for improving magnetic properties by developing texture to magnetic properties with continuous annealing or box annealing of hot rolled sheet of Sb-added steel. This method has the drawbacks which S should be lowered to the possible extent for grain growth. And the Japanese Published Patent Gazette No. 63- 317627 teaches the steel manufactured by semi-process, containing one kind or more than two" kinds among Sn or Sb, Ni and Cu, and adding Mn of 1.0-1.5 %, with methods for manufacturing thereof. In this method, excessive addition of Mn causes cost increase. Also, as Mn is an element easily forming austenite phase, it becomes austenite phase up to low temperature, and thus it has the drawbacks which magnetic properties are poor and especially,- magnetic flux density is low, by carrying out hot rolling under austenite phase.

SUMMARY OF THE INVENTION

The present invention provides for nonoriented electrial steel sheets with superior magnetic properties, manufactured by semi-process or fully-process by properly selecting component system of nonoriented electrial steel sheets.

The present invention is that the basic component system is the component system simultaneously adding one kind or two kinds of Sn and Sb, beside addition of Cu and Ni to the steel containing maximum 3.5% of Si, maximum 0.7 % of Al and less than 1 % of Mn among component system manufactured under such steel preparation process. In addition to such elements, C, P, Ca or rare earth element(REM) can be added. As long as other impurity such as 0, S and N is little if possible, it is advantageous to magnetic properties but such impurity can be inevitably added to the certain extent. If a lot of C are added, decarburizing annealing is necessary. Among component system adding Ni and C in addition to one kind or two kinds of Sn and Sb in the aforementioned component, these elements adding only one element or two elements do not represent the property of the present invention. When it contains Ni and Cu as well as one kind or two kinds of Sn and Sb should be necessarily added at the same time, it represents the characteristic of the present invention. These elements develop textures advantageous to magnetic properties, such as (110) plane and (200) plane, and especially, enable to grow grain well.

The steel slab constructed mentioned above is manufactured with melted steel under converter, electric furnace, etc. , is manufactured with continuous casting or rough blooming, and then is charged into heating furnace under the hot state or cooled state. The steel slab heated from heating furnace is hot rolled, coiled, and then cold rolled after pickling under the state of annealed or non- annealed hot-rolled sheet. Cold rolled sheet can be manufactured by fully-process or semi-process. Fully- process is the process which pickling of hot rolled sheet is carried out, cold rolling with one cold rolling method or double cold rolling method is conducted, and then final high-temperature annealing is carried out. Semi-process is the process which a first cold rolling of hot rolled sheet is carried out, the skin pass rolling or temper rolling is done after intermediate annealing, and annealing with stress relieving must be carried out after processing by consumers, so to speak, the ^' electric apparatus manufacturers. Each manufacturing condition mentioned above can vary according to component system of steel. Also, even though the steel contains the same content of it, variation of the aforesaid condition of manufacturing process can vary the subsequent condition of manufacturing process. In the present invention, continuous annealing of hot rolled sheet can be carried out or annealing process of hot rolled sheet can be omitted, by controlling steel component and hot rolling condition so that hot finish rolling can be carried out under ferrite phase. Even though it is manufactured by such method, nonoriented electrical steel sheets which iron loss is low, and magnetic fltix density and permeability are high, among magnetic properties, is manufactured.

Of course, box "annealing of hot rolled sheet can improve magnetic properties, but the extent for improvement of magnetic properties do not reach that for added cost.

The inventor of the present invention carried out the following experiment to look over how finish rolling temperature affects magnetic properties.

A hot compression test was conducted after steel slab comprising, in the unit of weight percentage, C:0.003 %, Si:0.61 %, Mn:0.25 %, P:0.05 %, S:0.008 %, N:0.004 %, 0:0.002 %, Al:0.27 %, Ni:0.09 % , CufO.075 %^', Sn:0.09 %, residual Fe and other inevitable impurity, was hot rolled, and processing wit cylinder having 13 mm height and 8 mm diameter was conducted. Temperatures during hot compression test were 840° C under ferrite phase and 930°C under austenite phase. As a result of observing the microstructure formed by which compression deformation was done at respective temperature, just air cooled deformation structure and compression deformed structure were cooled by 10° C per hour at 800° C, and then the latter process was conducted, the element deformed at 840°C under ferrite phase appeared elongated grain in case of microstructure formed after deformation, the element deformed at 930° C under austenite phase appeared structure form made of recrystalization. And it was verified in microstructure formed after cooling that grain was not- nearly grown in case of the texture deformed at 930°C, but that grain was largely grown in case of the microstructure deformed at 840°C.

This is because that dynamic recrystallization occurs during deformation as stacking fault energy is low under austenite phase, and thus that residual deformation volume in the element is little, on the other hand that a lot of deformation volume remain after deformation under ferrite phase since dynamic recovery only takes place due to high stacking fault energy.

Accordingly, residual deformation volume in the finally finish-rolled elements under ferrite phase is more than that in the finally finish-rolled elements under austenite phase, and thus grain grows roughly even with coiling the hot rolled sheet at high temperature or with continuous annealing of the hot rolled sheet. In the present invention, size of grain appears more than- 25 μm during manufacture by fully-process, and the size of grain appears more than 50 μm during manufacture by semi- process, even if it can vary subject to Si component.

Magnetic properties are not improved in proportion to size of grain, and texture advantageous to magnetic properties also must be well formed. The steel slab comprising the aforesaid component was heated at 1230°C, was rolled with the percentage reduction in thickness of 19 % respectively at 840°C and 930°C during hot finish rolling, was cooled- by 15°C per hour at 800°C, and then was cold rolled with the thickness of 0.5 mm after pickling. High temperature annealing of cold rolled sheets was conducted in the mixed atmosphere of nitrogen and hydrogen for 2 minutes at 960°C.

As the result of researching magnetic properties with respect to the sheets which high-temperature annealing was conducted, it was observed that magnetic properties for the element which hot rolling was completed under ferrite phase was superior to that for the sheets which hot rolling was completed under austenite phase.

Also, a hot compression test for the steel comprising C.0.002 %, Si:2.1 %, Mn:0.22 %, P:0.03 %, S.-0.005 %, Ni:0.12 %, Cu:0.07 %, Sn:0.06 %, residual Fe and other inevitable impurity was conducted. The result of observation of microstructures formed after cooling reveals that phase transformation zone does not appear within the range of manufacturing condition of the present invention due to high content of Si element which is formed under ferrite phase, and typical elongated grain under ferrite phase appears. This indicates that there is a correlation between Si content and rolling temperature zone of finish rolling.

The nonoriented electrical steel sheets manufactured according to the present invention is characterized that iron loss is low even with relatively low Si content and that magnetic flux density and permeability are high even with relatively high Si content.

In the aforesaid nonoriented electrical steel sheets according to the present invention, improvement of magnetic properties is caused by the facts that Sn, Sb, etc. , are segregated to grain boundary, interstitial element intruding into inside of steel during manufacturing process of steel is prevented from diffusing, grain forming and texture are controlled. Cu forms large sulphurous precipitates with S and Mn. As Cu and Ni are added at the same time, corrosion resistance in high temperature is improved, and ^• surface oxidization layer is inhibited from deepening. Furthermore, during annealing, grain grows and texture of the (110) plane and (200) plane advantageous to magnetic properties is formed quite better due to combined operation of addition element. This enables to manufacture the nonoriented electrical steel sheets with superior magnetic properties. There are lots of methods indicating texture characteristic of steel sheet, but in the present invention, texture coefficient and texture parameter were indicated by Horta formula, as the formulas (1) and (2) mentioned below. The formulaf 1 ) indicates the texture coefficient of (hkl) plane selected at random from measured steel sheet, and the formula(2) indicates texture parameter as the ratio of texture coefficient between the planes (200), (100) and (310) of crystal plane advantageous to magnetic properties, and the planes (211), (222) and (321) of crystal -plane disadvantageous to magnetic properties. In the formula (1), ^_hkl ^means texture intensity of measurement test piece, IT, V. I means random intensity of standard test piece, and NL Λ means multiplicity factor. Magnetic properties are improved as texture intensity of the planes (200), (110), and (310) becomes larger, and texture intensity of the planes (211), (222) and (321) becomes smaller. Also, magnetic properties are improved as texture parameter becomes larger, and the steel according to the present invention indicates the texture parameter of more that 0.2 at least.

-^•-hkl ⁽∑ y - ------

Texture coefficient(P. ι i) = ' (\ )

(∑ _hkl • -' ¹-- )

^XR.hkl

Texture parameter(Tp) =

^P211 ⁺ ^P222 ⁺ 321

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following, the present invention is described in detail .

The present invention relates to nonoriented electrical steel sheets with superior magnetic properties comprising, in the unit of weight percentage, C:less than 0.02 %, Si: 1.0-3.5 %, niless than 1.0 %, P:less than 0.10 %, S:less than 0.01 %, N: less than 0.008 %, Al:less than 0.7 %, Ni: 0.05-1.0 %, Cu: 0.02-0.5 %, sum of one kind or two kinds of Sn and Sb: 0.02-0.2 % , residual Fe and other inevitable impurity.

Further, the present invention relates to nonoriented electrical steel sheets with superior magnetic properties, comprising the component and component range mentioned above, in which grain has the size of more than 30 μm, desirably has the size of 30-200 μm, more desirably has the size of 60-150 μm, and texture parameter calculated by Horta formula is more than 0.2, desirably is more than 0.5.

Also, the present invention relates to nonoriented electrical steel sheets with superior magnetic properties, comprising, in the unit of weigh percentage, C:less than 0.02 %, Si: less than 1.0 %, Mn: less than 0.5 %, P: less than 0.15 %, S: less than 0.01 %, N:less than 0.008 %, 0: less than 0.005 %, Al: less than 0.7 %, Ni:0.05-1.0 %, Cu:0.02-0.5 %, sum of one kind or two kinds of Sn and Sb:0.02-0.2 %, residual Fe and other inevitably containing impurity.

Further, the present invention relates to nonoriented electrical steel sheetss with superior magnetic properties comprising the component and component rage mentioned ^" above, in which grain has the size of more than 20 μm, desirably has the size of 20-250 μm, more desirably has the size of 40-200 μm, and texture parameter calculated by Horta formula is more than 0.2, desirably is more than 0.5.

Also, the present invention relates to nonoriented electrical steel sheetss with superior magnetic properties comprising, in the unit of weight percentage, C:less than 0.02 %, Si:less than 3.5 %, Mn:less than 0.5 %, P:less than 0.15 %, S:less than 0.01 %, N:less than 0.008 % , Airless than 0.7 %, Ni:0.02-1.0 %, Cu:0.02-0.5 % , sum of one kind or two kinds of Sn and Sb:0.02-0.2 %, Ca:0.001- 0.02 % and/or rare earth element(REM) :0.003-0.03 %, residual Fe, and other inevitably containing impurity.

Further, the present invention relates to nonoriented electrical steel sheetss with superior magnetic properties comprising the component and component range mentioned above, in which grain has the size of more -than 30 μm, desirably has the size of 30-250 μm, more desirably has the size of 50-200 μm, and texture parameter calculated by Horta formula is more than 0.2, desirably is more than 0.5.

Also, the present invention relates to nonoriented electrical steel sheets with superior magnetic properties comprising, in the unit of weight percentage, C: 0.02-0.06 %, Si:less than 3.5 %, Mn:less than 0.5 %, P:less than 0.15 %, S:less than 0.01 %, N.less than 0.008 %, Airless than 0.7 %, 0: less than 0.005 %, Ni:0.02-1.0 %, Cu:0.02- 0.5 % , sum of one kind or two kinds of Sn and Sb: 0.02-0.2 %, residual Fe and other inevitably containing impurity.

Further, the present invention relates to nonoriented electrical steel sheetss with superior magnetic properties comprising the component and component range mentioned above, in which grain has the size of more than 20 μm, desirably has the size of 20-250 μm, more desirably has the size of 40-180 μm, and texture parameter calculated by Horta formula is more than 0.3, desirably is more than 0.5.

In the following, reasons for restricting the compound and compound range of the steel according to the present invention are described. The aforementioned C which is the compound enabling to form texture advantageous to magnetic properties, can be added up to maximum 0.06 % considering the decarburization efficiency. However, in order to lower the residual C further, less than 0.02 % is desirable. In case that C is more than 0.008 % in the slab, decarburization annealing is possible. To inhibit magnetic aging by the residual C, restriction to less than 0.003 % is desirable.

The aforementioned Si is the basic element indicating the product properties of nonoriented electrical steel sheets well, and lowers iron loss by increasing resistivity. However, adding up to less than 3.5 % is desirable as the -aforesaid Si makes worse of the workability of cold rolling. Especially, in case that Si is less than 1.0 %, cold rollability is improved as well as magnetic flux density and permeability can be improved.

The aforesaid Mn has effects of lowering iron loss by increasing resistivity, but as it is precipitated with fine MnS by combining with S, and thus makes worse of magnetic properties, there is a problem that S should be managed low to inhibit this. Also, as more fine precipitates under Mn content more than 1.0% can be formed if reheating temperature becomes higher than 1200"C, restricting Mn content to less than- 1.0 % is desirable, and restriction of Mn up to less than 0.5 % is more desirable.

As the aforementioned P lowers eddy current loss in iron loss by increasing resistivity, and it improves magnetic properties by developing texture of the planes (200) and (110) advantageous to magnetic property, it can be added up to maximum 0.15 %. But, as the P heightens basically strength of raw material, P can be added up to 0.1 % in order to improve the workability of cold rolling.

The aforesaid S is an inevitable impurity and thus not to add it if possible is advantageous to magnetic properties. But it can be contained up to 0.01 % in the present invention. And in the present invention, even if S is contained up to 0.015 %, it does not affect magnetic properties largely in case that Mn is less than 0.5 %.

Even if volume of S affecting detrimentally magnetic properties are contained up to maximum 0.015 %, grain is easily grown, and thus magnetic properties can be improved. This is because that volume of Mn is low, added

Cu forms large sulphurous precipitates, accordingly

Mn(Cu)S which is large precipitates is formed in stead of forming fine precipitates, and thus grain is grown as well as texture advantageous to magnetic properties is formed.

As the aforesaid Al lowers iron loss by increasing resistivity and is added to grow the precipitates such as fine A1N or to deoxidize melted ^" steel during steel manufacturing process, but costs much, it is desirable to add up to maximum 0.7 % considering the improvement degree of magnetic properties.

As the aforesaid N which is an impurity, forms fine precipitates and makes worse of magnetic properties, it is advantageous to contain^' little if possible and is allowable to contain up to maximum 0.008 %.

The aforesaid 0 which is an impurity, is deoxidized by Al, etc., but increase of 0 among final compound during steel manufacturing means increase of fine precipitates or nonmetallic inclusions. As the result, it is desirable to contain little if possible, for improvement of steel purification and for advantageous growth of grain. As the (111) plane, etc, detrimental to magnetic properties among textures can be reduced by containing 0 little, it is desirable to restrict the contents up to 0.005 %.

The aforesaid Ni has a little effects on the independent addition, grows grain by adding in combination with the element including Cu, P, etc, forms texture advantageous to magnetic properties, and thus lowers iron loss by increasing resistivity. But Ni costs high, and it is desirable to add up to maximum 1.0 % considering improvement degree of magnetic properties subject to addition volume. Also, it improves corrosion resistance during high-temperature annealing and corrosion resistance of P addition steel, and it is desirable to add up to minimum 0.02 % considering improvement degree of magnetic properties. More desirable content of the aforesaid Ni is O.Oδ-l.O %.

As for the aforesaid Sn or Sb, combined addition of one kind or two kinds is possible. These elements^" are added to control grain form as segregation elements, to inhibit the (111) plane detrimental to magnetic properties from growing, and to develop textures advantageous to magnetic properties. If addition volume of these elements is less than 0.02 %, the addition effects are little, and if it is more than 0.2 %, cold rolling of hot rolled sheets is difficult. Accordingly, it is desirable to restrict sum of one kind or two kinds of Sn or Sb to be 0.02-0.2 % . However, if Cu is added up to less than 0.4 %, Sn or Sb can be -added up to maximum 0.3 % independently or in combination.

The aforesaid Cu has an effect on increasing corrosion resistance, lowering iron loss by increasing resistivity, forming large posphurous precipitates, growing grain largely, developing well texture advantageous to magnetic properties, and increasing rapidly oxidizing resistance of P addition steel. And, as Cu is added at the same time in comparison with Ni independent addition steel , oxidization especially on high temperature can be inhibited. To keep better surface without cracks of hot-rolled sheets for the steels adding simultaneously with segregation element of grain boundary including Sn, etc.,' Cu is added up to maximum 0.5 % and magnetic properties can be improved by adding more than 0.02 % at least. Accordingly, it is desirable to restrict the Cu content to 0.02-0.5 %. However, in the steel to which Sn or Sb was added up to more than 0.2 % independently or in combination, surface form of hot rolled sheet can be satisfied with adding Cu up to 0 . 4 % .

The aforesaid Ca or REM can be added independently or in combination, and it functions to grow grain by roughing 5 the precipitates including fine MnS, etc, whereby magnetic properties of product can be improved. As for REM, addition of one kind or more than two kinds with 0.003- 0.03 % enables to inhibit texture of the surface (111) disadvantageous to magnetic properties which nucleation 0 occLirs around fine precipitates.

In the following, a method for manufacturing nonoriented electrical steel sheets according to the present invention is described. -5

The present invention relates to a method for manufacturing nonoriented electrical steel sheets with superior magnetic properties, by fully-process in which a steel slab comprising, in the unit of weight percentage, 0 C:less than 0.02 %, Si:1.0-3.5 %, Mn less than 1.0 %, Prless than 0.10 %, S:less than 0.01 %, N: less than 0.008 %, Airless than 0.7 %, Ni:0.05-1.0 %, Cu:0.02-0.5 %, sum of one kind or two kinds of Sn and Sb:0.02-0.2 %, residual Fe and other inevitable impurity, is hot rolled, annealing of hot rolled sheet is conducted, is pickled, a first-order cold rolled or a second-order cold rolled with a cold rolling method, high-temperature annealing of cold rolled plane is conducted, and annealing with stress relieving is conducted. After the steel slab comprising the aforesaid compound range is charged into hot rolling heating furnace, is heated and is hot rolled, it is desirable to coil at more than 600° C and slab can be heated up to 1250° C.

Hot rolled sheet which was hot rolled as mentioned above is annealed, and with respect of annealing method of the aforesaid hot rolled sheet, continuous annealing method which annealing is conducted at 700-1100° C during 10 seconds-20 minutes, or box annealing method which annealing is conducted at 600-1000^βC during 30 minutes-10 hours. As grain does not grow sufficiently if annealing time by continuous annealing method is less than 10 seconds, magnetic properties deteriorate. If the annealing time is more than 20 minutes, restriction of facility is accompanied. As the result, it is desirable to restrict continuous annealing time of hot rolled sheet to 10 seconds-20 minutes.

Further, in case of the aforesaid box annealing method, an effect of box annealing is little if the box annealing time is less than 30 minutes, and productivity deteriorates if more than 10 hours. As the result, it is desirable to restrict box annealing time to 30 minutes-10 hours.

Hot rolled sheet which was annealed by continuous annealing method or box annealing method is pickled by a normal method, one stage cold rolled or a first-order cold rolled, intermediate annealing is conducted, a second- order cold rolled by double cold rolling method, and high temperature annealing is conducted.

The aforesaid high temperature- annealing is conducted by continuous annealing within the temperature range of 700-1100°C during less than 10 minutes, and it is desirable to carry out the annealing in the atmosphere of 100 % nitrogen gas or mixed gas of nitrogen and hydrogen, and others.

If C content of the aforesaid cold rolled sheet is more than 0.008 %, decarburization can be conducted in the mixed atmosphere of nitrogen and hydrogen during less than 10 minutes with the dew point of 20-70°C before high temperature annealing. If C content is more than 0.003 % subject to consumers' necessity, heat treatment can be conducted by cosumers, so to speak, the electric apparatus manufacturers with decarburization atmosphere during annealing with stress relieving. Insulation coating can be done after high temperature annealing of the aforesaid coled rolled sheet, and cosumers, so to speak, the electric apparatus manufacturers can^"carry out bluing heat treatment for non-coated product.

It is desirable to control the aforesaid manufacturing process condition, whereby grain of the nonoriented electrial steel sheets according to the present invention manufactured as mentioned above has the size of 30 μm, desirably the size of 30-200 μm and more desirably the size of 60-150 μm, and texture parameter calculated by Horta formula is more than 0.2 and desirably more than 0.5.

Further, the present invention relates to a method for manufacturing nonoriented electrial steel sheets with superior magnetic properties, by semi-process in which a steel slab comprising, in the unit of weigh percentage, C:less than 0.02 %, Sijless than 1.0 %, Mnrless than 0.5 %, Prless than 0.15 %, S:less than 0.01 %, Nrless than 0.008 %, Orless than 0.005 %, Airless than 0.7 %, Ni:0.05- 1.0%, Cu: 0.02-0.5%, sum of one kind or two kinds of Sn and Sb:0.02-0.2 %, residual Fe and other inevitable impurity is hot rolled, annealing of hot rolled sheet is conducted, is pickled, is cold rolled, intermediate annealing is conducted, is skin pass rolled and annealed, and by fully- process in which the steel slab comprising the aforesaid compound is hot rolled, annealing of hot rolled sheet is conducted, is pickled, cold rolled, and is annealed.

After the steel slab constructed as mentioned above is charged into hot rolling heating furnace, is heated, and is hot rolled, it is desirable to coil at more than 600° C and the slab can be reheated up to 1300° C.

The aforesaid hot rolling is conducted whereby final temperature of finish rolling is more than 750° C under ferrite phase of less than Ar, point. At this time, magnetic flux density and permeability of product are poor when final temperature of finish rolling is more than Arl point, and rolling load during compression rolling becomes excessive when the temperature is less than 750°C.

The sheet which was hot rolled as mentioned above can be annealed by continuous annealing method or box annealing method. If hot rolled sheet is annealed by continuous annealing, it is desirable to carry out the annealing at 700-1000° C during 10 seconds-20 minutes. If it is annealed by box annealing, it is desirable to carry out the annealing at 600-950° C during 30 minutes-10 hours.

Grain does not grow sufficiently if annealing time by the aforesaid continuous annealing is less than 10 seconds or the annealing temperature is less than 750°C, magnetic properties deteriorate if the annealing temperature is more than 1000°C, and productivity deteriorates if the annealing time is more than 20 minutes. As the result, it is desirable to restrict annealing temperature by continuous annealing up to 700-1000°C and the annealing time up to 10 seconds-20 minutes.

If annealing temperature by the aforesaid box annealing is less than 600°C and the annealing temperature is less than 30 minutes, grain does not grow sufficiently and thus effects of box annealing are little. If the annealing temperature is more than 950° C, magnetic properties deteriorate. Also, if the annealing time more than 10 hours, it is not economical. As the result, it is desirable to restrict the annealing temperature up to 600- 9δO°C and the annealing time up to 30 minutes-10 hours. Annealing atmosphere can be non-oxidizing atmosphere during continuous annealing or box annealing. Hot rolled sheet which was annealed as mentioned above is put in acid solution such as HC1 , is pickled and is cold rolled.

In case of manufacturing nonoriented electrical steel sheets by fully-process, cold rolled plane is high- temperature annealed at 700-1050°C during less than 10 minutes. Cosumers, so to speak, the electric apparatus manufacturers can carry out annealing with stress relieving after processing where necessary, and decarburization annealing can be conducted before high- temperature annealing if C is high. This decarburization annealing can be conducted in the mixed atmosphere of hydrogen and nitrogen by normal method.

Meanwhile, in case of manufacturing nonoriented electrical steel sheets by semi-process, with respect to the cold rolled cold sheet, intermediate annealing is conducted at 650-950° C for less than- 5 minutes, skin pass rolling is conducted with the percentage reduction in thickness of 2.0-15.0 %, and annealing with stress relieving for relieving stress and for grain growth is conducted after processing by cosumers, so to speak, the electric apparatus manufacturers. If intermediate annealing sheet is rolled with less than 2.0 %, grain is not sufficiently grown, and if the sheet is rolled with the percentage reduction in thickness of more than 15.0 %, grain becomes smaller and thus magnetic properties deteriorate. As the result, it is desirable to restrict 5 the percentage reduction in thickness during rolling up to 2.0-lδ.O %. Insulation coating can be done as for each product(steel sheet) manufactured by the aforesaid fully- process and semi-process before forwarding to cosumers, so to speak, the electric apparatus manufacturers. Bluing 10 treatment can be conducted as for non-coated product 'during heat treatment by cosumers, so to speak, the electric apparatus manufacturers.

In case of manufacturing nonoriented electrical steel Iδ sheets by fully-process, it is desirable to control the manufacturing process condition whereby grain of the steel has the size of more than 20 μ , desirably has the size of 20-150 μm, more desirably has the size of 40-120 μm, and texture parameter calculated by Horta formula is more than 0 0.2, desirably is more than 0.5.

Meanwhile, in case of manufacturing nonoriented electrical steel sheets by semi-process, it is desirable to control the manufacturing process condition whereby δ grain of the steel has the size of more than 60 μm, desirably δ0-2δ0 μm, more desirably 80-200 μ , and texture parameter calculated by Horta formula is more than 0.2 and desirably is more than 0.5. Further, the present invention relates to a method for manufacturing nonoriented electrical steel sheets with superior magnetic properties, in which a steel slab comprising, in the unit of weight percentage, Crless than 0.02 %, Sirless than 3.5 %, Mn: less than 0.5 %, P:less than 0.15 %, Srless than 0.015 %, Al : less than 0.7 %, Orless than 0.005 %, Nrless than 0.008 %, sum of one kind or two kinds of Sn and SbrO.02-0.3 %, Ni:0.02-1.0 %, Cu:0.02-0.4 %, residual Fe and other inevitably containing impurity is heated, is hot rolled whereby finish rolling is conducted under .ferrite phase of more than 800°C with the percentage reduction in thickness of more than 7 %, hot rolled sheet is coiled at more than 600° C, is cooled in the air, is pickled, is cold rolled with one stage cold rolling method or double cold rolling method, and is high- temperature annealed within the range of 700-1100°C during 10 seconds-10 minutes.

After the steel slab constructed as mentioned above is charged into hot rolling .heating furnace, hot rolling is conducted. Reheating of slab is possible up to 1300° C but the temperature of less than 1250° C is more desirable. This is because that A1N, MsS and sulphurous precipitates containing Cu are likely to grow roughly at up to 12δO°C, but if more than 1300°C, precipitates are resolved and thus fine precipitates detrimental to magnetic properties can be formed.

Finish rolling temperature during hot rolling is important, and especiallj- in order to manufacture nonoriented electrical steel sheets which iron loss is low, magnetic flux density and permeability are high, and thus magnetic properties are superior, finish rolling should be conducted under ferrite phase having the finish rolling temperature of more than 800°C. Also, it is desirable for the percentage reduction in thickness to be more than 7 %. This is because that grain under ferrite phase is easily grown with finish rolling reduction ratio more than 7 %.

In the present invention, finish hot rolling is conducted with the percentage reduction in thickness of at least more than 7 % at more than 800°C under ferrite phase of less than Ar-_j point temperature, that is, at higher temperature under ferrite phase, and high-tenvperature annealing is conducted. Thus, magnetic properties are improved as final grain is easily grown.

Meanwhile, as phase transformation temperature does not appear in a steel having Si of more than 1.5 %, maximum limit of finish rolling temperature can be decided by reheating temperature.

If hot rolling is conducted with the percentage reduction in thickness of less than 7 % or at the finish rolling temperature of less than 800° C, magnetic properties deteriorate as grain does not grow sufficiently. In this finish rolling, magnetic properties are improved even with the percentage reduction in thickness of 50 %, maximum limit of final percentage reduction in thickness is not restricted, and the percentage reduction in thickness of not more than 50 % is desirable considering deformation resistance.

The sheet which was hot rolled as mentioned above is coiled at more than 600°C, and final grain product is grown largely by cooling in the air with a normal method during coiling. If coiling temperature is not more than 600° C, final grain is not grown sufficiently and thus magnetic properties deteriorate.

The maximum limit of the aforesaid coiling temperature is not specially restricted, and coiling is possibly conducted at not more than finish rolling temperature after finish rolling under ferrite phase.

Also, when the sheet which was hot rolled as mentioned above is coiled, it is desirable to coil at more than 600° C and then to conduct a slow cooling with the cooling speed of not more than 30°C per hour on the basis of middle part of hot coil after coiling. By having such slow cooling, annealing of hot rolled sheet can be omitted.

Even in case that hot rolled sheet is cooled in the air, cooling speed of maximum 30°C per hour is obtainable on the basis of atmospheric temperature of 25° C. Slow cooling can be conducted with the method of putting on concurrent heating cover or using other shut place. Such method has an advantage to reduce the temperature difference between middle part of hot rolled sheet and edge part of it during cooling in the air. In case of using concurrent heating cover, the concurrent heating cover should be the material endurable to heat, and hot insulation can be done by putting the cover on hot coil one by one or by stacked state, during cooling. By putting a concurrent heating cover, cooling in the air is conducted, and by blowing non-oxidizing gas such as nitrogen into the concurrent heating cover, oxidization of hot rolled sheet can be inhibited. By coiling hot rolled sheet with the aforesaid method, final grain is largely grown after high-temperature annealing.

By pickling the hot rolled sheet which was coiled and cooled as mentioned above, in acid solution using HCl solution, scale of hot rolled sheet surface is removed. Pickled hot rolled sheet is cold rolled and cold rolling can be conducted with one stage cold rolling method or double cold rolling method.

Final sheet which was cold rolled as mentioned above is high-temperature annealed after degreasing a normal rolling lubrication with alkaline solution. High- temperature annealing is subjected to Si content but it is desirable to conduct high-temperature annealing with the range of 700-1100°C during 10 seconds-10 minutes. This is because that grain does not grow sufficiently during annealing if annealing temperature is not more than 700° C or annealing time is less than 10 seconds, and that magnetic properties deteriorate due to excessive oxidization during annealing if annealing temperature is more than 1100°C or annealing time exceeds 10 minutes.

In case of manufacturing nonoriented electrical steel sheets as mentioned above, it is desirable to control the manufacturing process condition whereby grain of the steel sheet has the size of more than 25 μ , desirably has the size of 25-200 μm and more desirably has the size of 30- 150 μm, and texture parameter is more than 0.2 and more desirably is more than 0.5.

The present invention relates to a method for manufacturing nonoriented electrical steel sheets with superior magnetic properties, by fully-process in which a steel slab comprising, in the unit of weight percentage, Crless than 0.02 %, Sirless than 3.5 %, Mnrless than 0.5 %, Prless than 0.15 %, S: less than 0.01 %, Nrless than 0.008 %, Al: less than 0.7 %, Ni : 0.02-1.0 %, Cu:0.02-0.5 %, sum of one kind or two kinds of Sn and Sb:0.02-0.2 %, Ca:0.001-0.02 % and/or REM:0.003-0-.3 %, residual Fe and other inevitably containing impurity is hot rolled, is coiled, is pickled as hot rolled sheet is or after hot rolled sheet is annealed, is cold rolled with one stage cold rolling method or double cold rolling method, and is high-temperature annealed, or by semi-process in which the steel slab comprising the aforesaid composition is hot rolled, is pickled as hot rolled sheet is or after hot rolled sheet is annealed, a first-order cold rolled, intermediate annealing is conducted, and skin pass rolling is conducted.

In the aforesaid manufacturing method according to the present invention, by adding more than one kind of Car0.001-0.02 % or REM:0.003-0.03 % to the element adding Sn or Sb independently or in combination, and component system adding Ni and Cu in combination, impurities such, as MnS detrimental to- magnetic properties is grown greatly, grain is grown, and texture advantageous, to .magnetic properties is formed whereby magnetic properties are improved. As Ca or REM element precipitates impurity greatly to enable to manufacture pure steel, and grain is easily grown during high-temperature annealing after cold rolling, texture of the (111) plane detrimental to magnetic properties occurring around impurity becomes little, texture advantageous to magnetic properties develops well, and accordingly magnetic properties become superior.

In the melted steel manufactured ^' during steel manufacturing process, each element is inputted before continuous casting, slab solidified with crude metal or steel ingot is made. Ca can be inputted before or during degasification. When REM element is inputted during degasification or continuous casting operation, actual yield ratio becomes high. Other addition element can be inputted at any process from starting point to degasification process.

The steel slab manufactured as mentioned above is 5 charged into heating furnace in order to conduct hot rolling and the hot rolling is conducted after heating and heat-keeping operation. In the hot rolling, there are no problems if final temperature is higher than 7δ0°C. It is desirable to coil hot rolled sheet at higher than δ00°C

10 in order to make final hot rolled sheet. The sheet which was hot rolled as- mentioned above is cold rolled with final thickness after pickling. Before pickling, hot rolled sheet can be annealed with continuous annealing or box annealing. By such annealing, magnetic properties are lδ improved further. It is desirable to conduct such annealing at higher than 700° C.

The aforesaid hot rolled sheet can be a first-order cold rolled, intermediate annealing can be conducted

20 within the range of 700-1000° C, and then a second-order cold rolling can be conducted. In case of manufacturing nonoriented electrical steel sheets by fully-process, it is desirable to conduct high-temperature annealing within the temperature range of 700-1100° C with respect to coled δ rolled sheet. Also, in case of manufacturing nonoriented electrical steel sheets by semi-process, a second-order cold rolling can be conducted with less than 15 %, it can be forwarded to cosumers, so to speak, the electric apparatus manufacturers without high-temperature annealing, and annealing with stress relieving can be conducted after processing by cosumers, so to speak, the electric apparatus manufacturers.

Final product can be forwarded to cosumers, so to speak, the electric apparatus manufacturers after insulation coating.

In case of manufacturing nonoriented electrical steel sheets by fully-process, it is desirable to control the manufacturing process condition whereby grain of the steel sheet has the size of more than 30 μm, desirably has the size of 30-200 μm, more desirably has the size of 50-150 μ , and texture coefficient calculated by Horta formula becomes more than 0.2 and desirably becomes more than 0.5.

Meanwhile, in case of manufacturing nonoriented electrical steel sheets by semi-process, it is desirable to control the manufacturing process condition whereby grain of the steel -sheet has the size of more than 50 μm, desirably has the size of 50-250 μm, more desirably has the size of 80-200 μm, and texture coefficient calculated by Horta formula becomes more than 0.3 and desirably becomes 0.5.

Further, the present invention relates to a method for manufacturing nonoriented electrical steel sheets with superior magnetic properties, by fully-process in which a steel slab comprising, in the unit of weight percentage, CrO.02-0.06 %, Sir less than 3.5 %, Mn: less than 0.5 %, P: less than 0.15 %, Srless than 0.01 %, Nrless than 0.008 %, Airless than 0.7 %, Orless than 0.005 %, sum of one kind or two kinds of Sn and Sb: 0.02-0.2 %m Nir 0.02-1.0 %, Cu:0.02-0.05 %, residual Fe and other inevitably adding impurity is hot rolled, is pickled, is cold rolled with one stage cold rolling method or double cold rolling method, decarburization annealing of coled rolled sheet is conducted at the temperature range of 750-900° C in the mixed atmosphere of 60-90 % nitrogen and 40-10 % hydrogen with the dew point of 30-60°C, and final high-temperature annealing is conducted, or by semi-process in which the steel slab comprising the aforesaid composition is hot rolled, is pickled, is a first-order cold rolling is conducted, intermediate annealing and skin pass rolling are conducted, is processed by cosumers, so to speak, the electric apparatus manufacturers, and annealing with stress relieving is conducted.

In the aforesaid manufacturing method according to the present invention, texture is improved and thus, especially, permeability is improved by conducting decarburization annealing with respect to C which is known as the element deteriorating magnetic properties by making small grain size of the final sheet.

After the steel slab constructed as mentioned above is charged into reheating furnace, is heated, and is hot rolled, it is desirable to coil at the temperature of higher than 500°C. Reheating temperature of the slab is possible up to 12δO°C.

The sheet which was hot rolled as mentioned above can be cold rolled after pickling without annealing process. Also, it can be cold rolled after annealing and pickling. The hot rolled sheet can be annealed with continuous annealing method or box annealing method, and it is desirable to conduct annealing at the temperature range of 700-1100°C during 10 seconds-20 minutes in case of the continuous annealing, and at the temperature range of 600- 1000°C during 30 minutes-10 hours in case of the box annealing. Meanwhile, the box annealing prevent oxidation of the sheet surface caused by long hours' annealing as this annealing can be conducted in the non-oxidizing atmosphere including nitrogen or others.

In case of manufacturing nonoriented electrical steel sheets by fully-process, one stage cold rolling or a first-order cold rolling is conducted, intermediate annealing is conducted normally at the temperature range of 700-1000°C, double cold rolling for a second-order cold rolling Is conducted, and the coled rolled sheet is high- temperature annealed after decarburization annealing. It is desirable to conduct the decarburization annealing by continuous annealing method at the temperature range of 750-900°C in the atmosphere of 60-90 % nitrogen and 40-10 % hydrogen with the dew point of 30-60°C during 1-10 minutes. When such decarburization annealing is conducted, decarburization is to be insufficient if content of nitrogen and hydrogen in the atmosphere is too much or less, and residual C after decarburization becomes much if the dew point is too high or low.

It is desirable to conduct such high-temperature annealing at 700-1100°C during less than 10 minutes because that annealing time becomes long if annealing temperature is not higher than 700° C, and that deep internal oxidation layer occurs on the sheet surface whereby magnetic properties deteriorate if annealing temperature is higher than 1100° C.

In case of manufacturing nonoriented electrical steel sheets by semi-process, a first-order cold rolling is conducted, intermediate annealing is conducted at^' 650- 950° C during less than 10 minutes, and it is processed by cosumers, so to speak, the electric apparatus manufacturers after skin pass rolling with 2-15 % is conducted. During such intermediate annealing, decarburization annealing can be conducted. In this case, it is desirable to conduct continuous annealing at 750- 900° C during 1-10 minutes in the - mixed atmosphere of nitrogen and hydrogen, and thus to obtain decarburization.

In case of decarburization annealing during such intermediate annealing, it is desirable to conduct the annealing at the dew point of 30-60° C in the mixed atmosphere of 60-90 % nitrogen and 40-10 % hydrogen because that decarburization becomes ins ifficient if content of nitrogen and hydrogen is too much or little, and that residual C after decarburization becomes too much if the dew point is too high or low. 5

Further, decarburization annealing can be conducted during annealing with stress relieving by cosumers, so to speak, the electric apparatus manufacturers. In this case, it is desirable to conduct the decarburization annealing 10 during annealing with stress relieving at 7δ0-8δ0°C in the atmosphere of 60-90 % nitrogen and 40-10 % hydrogen with the dew point of 30-60°C.

When such annealing is conducted, decarburization

Iδ becomes insufficient if contents of nitrogen and hydrogen are too much or little, and residual C after decarburization becomes too much if the dew point is too high or low.

0 In case of manufacturing nonoriented electrical steel sheets by fully-process, it is desirable to control the manufacturing process condition whereby grain of the steel sheet has the size of more than 20 ^'μm, desirably has the size of 20-180 μm, more desirably has the size of 30-lδO δ μm, and texture parameter calculated by Horta formula becomes more than 0.3 and desirably becomes more than O.δ.

Meanwhile, in case of manufacturing nonoriented electrical steel sheets by semi-process, it is desirable to control the manufacturing process condition whereby grain of the steel sheet has the size of more than δO μm, desirably has the size of δ0-250 μm, more desirably has the size of 80-200 μm, and texture parameter calculated by Horta formula becomes more than 0.3 and desirably becomes more than 0.5.

The present invention is described in more detail through the following embodiments.

Example 1

The slab constructed under steel manufacturing process, comprising the composition listed in the following Table 1 is heated at 1220°C, is hot rolled as listed in the following Table 2 to make the thickness of 2.3 mm, is coiled, annealing of hot rolled sheet is conducted, and is cold rolled with the thickness of 0.5 mm. The coled rolled sheet was annealed in the atmosphere of 20 % hydrogen and 80 % nitrogen for 3 minutes. After annealing with stress relieving was conducted at 790° C in the atmosphere of 100 % nitrogen for 2 hours with respect to coled rolled and annealed sheets, magnetic properties were measured respectively and the measured results are indicated in the following Table 2. As indicated in the Table 2, it can be seen that the invention product(l-4) which invention steel(a-d) covering the composition range of the present invention was manufactured in accordance with the manufacturing condition of the present invention, has superior magnetic properties in comparison with comparative product(1-7) which was made of comparative steel(a-e) deviating from composition range of the present invention.

As the result of measuring the size of grain with respect to each test piece listed in the following Table 2, comparative materials 1, 2 and 3 had the size of 52 μm, 56 μm and 47 _μm respectively, and comparative product(4-7) had the range of 56-63 μm. But invention product(l-4) had the range of 65-98 μm. Namely, grain size of the present invention product(l-4) has the larger value than comparative product(1- ) .

Table 1

Table 2

(^*'^*) Wi5/5θ(W/kg) r Core less or iron _.loss when magnetized from 60 Hz to 1.5 Tesla

B5θ(Tesla) Magnetic flux density inducing when magnetized to 5000 A/m

/ .5 Permeability when magnetized at 50 Hz to obtain 1.5 Tesla

Example 2

As described in the following Table 3, a slab comprising different content of Cu and Sn was reheated at 1200°C, finish rolling of hot rolling was completed at

850°C to make the thickness of 2.3 mm, was coiled at 700°C, annealing of hot rolled sheet was conducted at 800° C during 3 hours, and was pickled. After pickling, hot rolled sheet was cold rolled with the thickness of 0.5 mm, and high-temperature annealing was conducted at 950° C during 2 minutes. After that, magnetic properties were measured and the measured results were indicated in the following Table 4 together with_* the surface condition of cold rolled sheets.

Table 3

0

Table 4

5

0

δ

(*) P15/50(ϊ/kg)r Core Loss nhen magnetized from 50 Hz to 1.5 Tesla B50 (Tesla) : Magnetic flux density inducing uihen magnetized to

5000 A/m μ .5 - ' Permeability ichen magnetized at 50 Hz to obtain

1.5 Tesla

As indicated in the above Table 4, it can be seen that the invention product (1,2) which invention steel ( a, b) covering the composition range of the present invention was manufactured in accordance with the manufacturing condition of the present invention, has superior magnetic properties as well as satisfactory rolling status of coled rolled sheet in comparison with comparative product(l) δ which was made of comparative steel(a) deviating from composition range of the present invention.

Example 3

A steel slab comprising, in the unit of weight percentage, C:0.006 %, Si:2.95 %, Mn:0.35 % , P:0.03 %, S:0.005 %, Al.0.28 %, N:0.003 % , Sn:0.11 %, Ni:0.2δ % and Cu:0.16 % was heated at 1200°C, was hot rolled with the thickness of 2 mm and the final temperature of finish rolling of 900° C under ferrite phase, was coiled at 700° C, annealing of hot rolled sheet was conducted under the condition listed in Table 5, was pickled, a first-order cold rolling was conducted with the thickness of 1.0 mm, intermediate annealing was conducted at 900° C for 2 minutes, a second-order cold rolling was conducted to be the thickness of 0.5 mm with the percentage reduction in thickness of 50 %, and cold rolling with double cold rolling method was conducted. Then the final cold rolled sheet was high-temperature annealed at 1050° C during 3 minutes, was cut, and annealing with stress relieving was conducted at 790°C during 2 hours. After that, magnetic properties were measured and the measured results were indicated in the following Table 5. Table 5

(*) W15/50(W/kg) : Core Loss rohen magnetized from 50 Hz to 1.5 Tesla B50 (Tesla) : Magnetic flux density inducing when magnetized to 5000 A/m μι ς ' Permeability mhen magnetized at 50 Hz to obtain

¹ 1.5 Tesla

As indicated in Table 5, it can be seen that the invention product(a-c) which was annealed under the condition which accords to the present invention has superior magnetic properties in comparison with the comparative product(a) which annealing of hot rolled sheet was conducted under the condition deviating from the range of the present invention.

As stated above, the present invention has effects on maximizing efficiency of electrical product and energy conservation by providing nonoriented electrical steel sheets having low iron loss and high magnetic flux density and permeability.

Example 4

Each test piece was manufactured by semi-process in which a steel slab comprising the composition listed in the following Table 6 was heated at 1210°C, was hot rolled under the condition listed in the following Table 7, was coiled, annealing of hot rolled sheet was conducted, was cold rolled, intermediate annealing and skin pass rolling were conducted, and heat treatment by cosumers, so to speak, the electric apparatus manufacturers was conducted. Final thickness of the test piece was 0.47 mm and annealing was conducted in the nitrogen atmosphere.

With respect to the test piece manufactured as mentioned above, magnetic properties were measured and the measured results were indicated as the average value of rolling direction and opposite direction of rolling. Table 6

Steel kinds Si Mn Al Ni Cu ! Sn

Invention 0. 0. 0. .0. 0. 0. 0. 0. 0. 0. 0. steel a 005 51 ! 30 08 005 30 003 003 31 25 11

Comparative 0. 0. 0. 0. 0. 0. 0. 0. steel a 005 32 04 006 26 003 003 30 12

0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 005 30 04 005 26 003 002 25 30 15

0. 1. 0. 0. 0. 0. 0. 0. 0. 0. 005 25 04 005 26 003 006 27 25 12

0. 1. 0. 0. 0. 0. 0. 0. 0. 0. 005 -25 04 005 26 003 002 31 12

Table 7

B₅₀(Tesla) Magnetic flux density inducing when magnetized to 5000 A/m i.5 Permeability when magnetized at.50 Hz to obtain 1.5 Tesla

Ar Phase transformation boundary temperature into ferrite phase As indicated in the above Table 7, it can be seen that the invention product(l) according to the present invention has superior magnetic properties in comparison with the comparative product(l-4) which was made, of comparative steel(a) without content of Cu, comparative steel(b) with 0.8 % Mn, comparative steel(c) with 1.1 % Si, 0.55 % Mn, and 0.002 % 0, and comparative steel(d) with 1.25 % Mn.

Example 5

A slab comprising the composition listed in the following Table 8 was heated at 1200°C and was hot rolled as listed in the following Table 9, was coiled, and was pickled, was cold rolled and annealing of coled rolled sheet was conducted. The atmosphere during annealing of coled rolled sheet was 20 % H and 80 % N^. After the coled rolled sheet was annealed with stress relieving at 790°C in the atmosphere of 100 % Ng during 2 hours, magnetic properties were measured and the measured results were indicated in the following Table 9. The magnetic properties indicated in the following Table 9 were measured under the condition listed in Table 7 of Example 4. Table 8

Table 9

As indicated in Table 9, it can be seen that the invention product( 1-5 ) which accords to composition system and manufacturing condition of the present invention has superior characteristic in comparison with other 5 comparative product(l) and comparative product(2) having the same compound system of the present invention but deviating from the range of manufacturing condition of the present invention.

10

Example 6

The slab of invention steel(c) presented in Table 8 of the above Example 5 was heated at 1200°C, was hot rolled lδ as listed in the following Table 10, was coiled, was pickled, was cold rolled, and annealing of coled rolled sheet was conducted in the atmosphere of hydrogen and nitrogen. The coled rolled sheet was annealed and cut, and then was annealed at 790° C in the atmosphere of 20 % H₂ and 0 80 % N^T2 during 2 hours. After that, magnetic properties were measured and the measured results were indicated in the following Table 10. The magnetic properties presented in the following Table 10 was measured under the same condition as that listed in Table 7 of the Example 4. δ Table 10

As indicated in the above Table 10, it can be seen that the invention product(7-10) made of the invention steel(c) having the composition range of the present invention with the fixed hot rolling finish rolling temperatureCC), coiling temperature(°C) and annealing condition of coled rolled sheet, as well as with variation of hot rolled sheet annealing condition within the range of the present invention has superior magnetic properties.-

Example 7

A steel slab comprising, in the unit of weight percentage, C:0.003 %, Si:0.52 %, Mn.0.45. %, P:0.06 % , S:0.004 %, Al:0.30 %, N:0.002 %, 0:0.003 %, Ni:0.35 % , Cu:0.21 %, Sn:0.11 % and residual Fe was reheated and manufactured by semi-process as shown on the following Table 11. Intermediate annealing of coled rolled sheet was conducted in the mixed atmosphere of hydrogen and nitrogen, skin pass rolling was conducted and heat treatment was conducted at 790°C in the nitrogen atmosphere during 2 hours by cosumers, so to speak, the electric apparatus manufacturers. With respect to each

10 test piece manufactured as mentioned above, magnetic properties were measured and the measured results were indicated in the following _. Table 11. The magnetic properties presented in the following Table 11 was measured under the same condition as that presented in

Iδ Table 7 of the above Example 4.

Table 11

o

0

As indicated in the above Table 11, the invention product(l-δ) manufactured by semi-process which accords to the present invention, has superior magnetic properties in comparison with the comparative product(l) which final hot rolling was conducted under austenite phase.

Example 8

A steel slab comprising, in the unit of weight percentage, CO.005 %, Si:0.8δ %, Mn:0.2δ %, P:0.06 %, SrO.OOδ % , Al:0.3δ %, N:0.002 %, Ni:0.25 %, Cu:0.17 %, Sn:0.21 % and residual Fe was reheated at 1230°C, and hot rolled sheet was manufactured under the condition of finish rolling and coiling presented in the following Table 12. In this steel, Ar-. temperature, maximum temperature under ferrite phase was 910°C, and thickness of hot rolled sheet was 2.0 mm. The hot rolled sheet which, finish rolling was conducted as listed in the following Table 12, was coiled in the air and pickled in HCl solution. Measurement of Ar-, was made by electric resistance measuring instrument. In case of putting on concurrent heating cover during coiling and cooling of hot rolled coil, cooling speed was 5-10°C per hour on the basis of room temperature 25° C. Then-, the hot rolled sheet was cold rolled by one time cold rolling method with the thickness of 0.50 mm.

As for the sheet which was cold rolled as mentioned above, a rolling lubrication was removed from alkaline solution and high-temperature annealing was conducted at the temperature presented in the following Table 12. The high-temperature annealing time was 2 minutes and atmosphere during high-temperature annealing was the drying atmosphere of mixed gas of 30 % hydrogen and 70 % nitrogen. Residual C after high-temperature annealing was 0.003 %. The high-temperature annealing sheet was cut after insulation coating with organic and nonorganic combined coating, and annealing with stress relieving was conducted at 800° C during 2 hours. After that, magnetic properties and grain size were measured and the measured results were indicated in the following Table 12. The grain size in the following Table 12 was measured by line segment method. Table 12

(*)^L5/5θO"/kδ) ^: C°^re l°^ss ""hen magnetized from 50Hz to 1.5 Tesla

B5Q (Tesla) : Magnetic flux density inducing ωhen magnetized to 5000 A/m μ-i c ' Permeability uihen magnetized at 50Hz to obtain 1.5 Tesla As indicated in the above Table 12, it can be seen that the present invention product(1-4) has the grain size of 85-98 μm and superior magnetic properties, whereas comparative product(l) was hot rolled under ferrite phase, but finish rolling temperature and coiling temperature were low and final percentage reduction in thickness was low, whereby magnetic properties deteriorate, and comparative product(2) has low finishing percentage reduction in thickness but is hot rolled at the higher temperature than Arl, a boundary point of 100 % ferrite phase, and thus grain is grown little and magnetic properties deteriorate.

Example 9

A steel slab comprising, in the unit of weight percentage, C:0.003 %, Si:l.l %, Mn:0.20 %, P:0.06 %, S:0.03 %, Al.0.35 %, N.0.002 %, Sn.0.11 %, Sb:0.05 %, Ni:0.09 %, Cu:0.21 % and residual Fe was reheated at 1150° C and manufactured by fully-process as indicated in the following Table 13.

In this steel, Ar,, a boundary temperature of ferrite phase was 940°C and hot rolling with the finishing percentage reduction in thickness of 30 % was conducted to make the thickness of 2.3 mm after hot rolling. The hot rolled sheet which finish rolling was conducted at the temperature presented in the following Table 13 was coiled and cooled, and was pickled in acid solution. The invention product(δ) and invention product(δ) of the following Table 13, on which concurrent heating cover was put, were coiled and cooled in the nitrogen atmosphere. The cooling speed was 10-lδ°C per hour, and comparative product(3) was coiled and cooled in the air.

As for the pickled hot rolled sheet, a first-order cold rolling was conducted with 1.0 mm and intermediate annealing was conducted at 900°C in the mixed atmosphere of hydrogen and nitrogen for 2 minutes. As for intermediate annealing aheet , a second-order cold rolling was conducted with 0.47 mm and high-temperature annealing was conducted with the annealing condition presented in the following Table 13. The high-temperature annealing was conducted at the drying atmosphere of 40 % hydrogen and 60 % nitrogen.

High-temperature annealing sheet was cut after insulation coating and annealing with stress relieving was conducted at 820° C in the drying atmosphere of 100 % nitrogen during 90 minutes. After that, magnetic properties and size of grain were measured and the measured results were indicated in the following Table 13. Table 13

As indicated in the above Table 13, it ^"can be seen that the present invention product(δ) and (6) has grain sufficiently grown and superior magnetic properties, while comparative product(3) has grain which is not grown δ sufficiently due to low coiling temperature and short annealing time during high-temperature annealing, and thus magnetic properties deteriorate.

Example 10

A steel slab comprising the composition presented in the following Table 14 was manufactured with the steel which Ca or REM was added to melted steel outputted from steel manufacturing process, and with the steel which Ca or REM was not added thereto. REM of invention steel(b) .in the following Table 14 is Nd, and REM of invention steel(d) is Ce.

The steel slab constructed as mentioned above was heated a 1210°C, was hot rolled with the finish rolling temperature of 870°C and the thickness of 2.0 mm, and was coiled at 720°C, annealing of .hot rolled sheet was conducted at 900°C during 5 minutes, was pickled, and was cold rolled with the thickness of 0.47 mm. Then, as for the steel sheet which was cold rolled as mentioned above, high-temperature annealing was conducted in the mixed gas atmosphere having. ixture ratio of 20 % hydrogen and 80 % nitrogen under the condition presented in the following Table 15. But, in case of invention product(4) in the following Table 15, hot rolled sheet is not annealed. The steel sheet which high-temperature annealing was conducted was cut and annealing with stress relieving was conducted at 800° C during 1.5 hours. After that, magnetic properties were measured and strength of (111) plane disadvantageous to magnetic properties among textures was observed. The results were indicated in the following Table 15. Measurement of magnetic properties in the following Table Iδ was made by single sheet tester.

Table 14

Table 15

(*) i5/5o( /kg) : Core loss when magnetized from 50 Hz to 1.5 Tesla B5ø(Tesla) : Magnetic flux density inducing when magnetized to 5000 A/m PI.5 : Permeability when magnetized at 50 Hz to obtain 1.5 Tesla

As indicated in the above Table lδ, it can be seen that in case of the present invention product( 1-δ ) , texture coefficient of (111) plane detrimental to magnetic properties appears low whereby magnetic properties become superior, in comparison with comparative product(l) .

Example 11 A steel slab comprising, in the unit of weight percentage, C:0.003 %, Si:2.2 %, Mn:0.3δ %, P:0.04 %, S:0.002 %, Al:0.3 %, N: 0.002 %, Sn:0.15 % , Ni;0.2δ %, Cu:0.13 % and Ca:0.009 % was reheated at 1140°C, was hot δ rolled with the finish rolling final temperature of 850° C and the thickness of 2 mm, and was coiled at 720° C.

As for the coiled hot rolled sheet, box annealing was conducted at 900°C during 2 hours, pickling was conducted, 0 a first-stage cold rolling was conducted to make the thickness of 1.0 mm, intermediate annealing was conducted at 900° C for 3 minutes, a second-order cold rolling was conducted to make the thickness of 0.50 mm, and then final coled rolled sheet was made by double cold rolling method.

As for coled rolled sheet, high-temperature annealing was conducted at 1000°C in the atmosphere of 30 % hydrogen and 70 % nitrogen during 3 minutes, cutting was conducted, and then magnetic properties were measured by single sheet tester after annealing with stress relieving was conducted at 790° C. The measured results were indicated in the following Table 16. This measurement revealed that grain size was 105 μm and texture parameter by Horta formula was 0.57. Table 16

As indicated in the above Table 16, it can be seen that 0 nonoriented electrical steel sheets manufactured according to the present in-vention has low iron loss and high magnetic flux density and permeability.

5 Example 12

The steel slab comprising the composition presented in the following Table 17, manufactured under the steel manufacturing process was heated at 1200°C, hot rolling 0 was conducted with the final temperature of 8δO°C during hot finish rolling to make the thickness of 2.0 mm, and then was coiled at 600°C. Hot rolled sheet was pickled under the condition presented in the following Table 18 with or without annealing, and then cold rolling was δ conducted with the thickness of 0.5 mm. Where box annealing was conducted as for hot rolled sheet, surface oxide was inhibited by 100 % nitrogen atmosphere. Continuous annealing was conducted with the atmospheric atmosphere. As for the sheet which was cold rolled as mentioned above, decarburization annealing was conducted in the mixed gas atmosphere of 30 % hydrogen and 70 % nitrogen with the dew point of 40° C during 3 minutes as described 5 in the following Table 18, and high-temperature annealing was conducted.

High-temperature annealing was conducted in the atmosphere of 20 % hydrogen and 80 % nitrogen during 3 10 minutes. After cutting the annealing sheet which high- temperature was conducted as mentioned above, permeability was measure and the measured results were indicated in the following Table 18.

Iδ

Table 17

(Unit : Weight %)

Table 18

(*) i.5 : Permeability mhen magnetized at 50 Hz to obtain 1.5 Tesla

As indicated in the above Table 18, it can be seen that the invention product (1-9) which was made of the invention steel (a, b and c) having the composition range of the present invention in accordance with the manufacturing condition which accords to the present invention has higher permeability in comparison with comparative product(1-8) deviating from the composition range and/or 5 manufacturing- condition of the present invention.

As for the invention product(1-3) of the above Table 18, texture was observed and the observation results revealed that texture coefficient (110) plane and (200)

10 plane was in the range of 1.2-1.7, but observation of texture for comparative product(6, 7) revealed that index of the aforesaid texture was in the range of 0.6-1.0. Herein, index of texture represents Horta texture coefficient. And the results of observing residual C after lδ decarburization annealing, it was in the range of 0.001- 0.003 % in case of the present invention product( 1-9 ) .

Example 13.

20

A steel comprising the composition system presented in the following Table 19 was reheated at 1230° C, hot finish rolling was conducted at 850° C, and the steel coil was coiled at 7δO°C. δ

After restricting the hot rolled sheet which was coiled as mentioned above, under the manufacturing condition presented in the following Table 20, permeability was measured and the measured characteristic results were indicated in the following Table 20.

Comparative product(l-2) and invention product(l-o) presented in the following Table 20 were manufactured by δ fully-process. In case of the invention product( 1-3 ) , decarburization annealing of coled rolled sheet was conducted at respective temperature in the mixed atmosphere of 20 % hydrogen and 80 % nitrogen with the dew point of 45°C for 4 minutes, and high-temperature

10 annealing was conducted at respective temperature in the atmosphere of 30 % hydrogen and 70 % nitrogen for 3 minutes. In case of the comparative product(1) and (2), decarburization annealing was conducted in the furnace atmosphere of 50 % hydrogen and 50 % nitrogen with the dew lδ point of 80° C.

In case of the comparative product(2), content of residual C was 0.006 % and in case of the invention product(2), the content of residual C was 0.0023 %. 0

Comparative product(3-4) and invention product(4-6) were manufactured by semi-process. In case of the comparative product(3) and the invention product(4-5 ) , decarburization annealing was conducted at respective δ temperature in the mixed atmosphere of 70 % nitrogen and 30 % hydrogen with the dew point of 40° C for 2 hours during annealing with stress relieving after intermediate annealing, and furnace cooling was conducted. In case of the comparative product(4), decarburization -annealing was conducted in the mixed atmosphere of 40 % nitrogen and 60 % hydrogen with the dew point of 10° C for 2 hours. In case of the invention product(δ), decarburization annealing was conducted in the atmosphere of 20 % nitrogen and 80 % hydrogen with the dew point of 4δ % during intermediate annealin .

It was revealed that decarburization annealing can be conducted at the time of intermediate annealing process and of annealing with stress relieving.

Table 19

(Unit Weight

Table 20

As indicated in the above Table 20, it can be seen that the invention product(l-δ) which accords to composition range and manufacturing condition of the present invention has quite superior permeability in comparison with the comparative product(1-6) which accords to composition range of the present invention but deviates from the manufacturing condition of the present invention.

Further, in case of the comparative product(3) and (4) manufactured by semi-process, grain size was 80 μm and 75 μm, respectively and texture parameter was 0.40 and 0.25, respectively. Meanwhile, in case of the invention product(4), grain size was 120 μm and texture parameter was 0.68.

In case of the invention product(1_.) manufactured by fully-process, grain size was 75 μm and texture parameter was 0. δ .

Claims

1. A nonoriented electrical steel sheet with superior magnetic properties comprising, in the unit of weight percentage, Crless than 0.02 56, Sir1.0-3.5 56, Mnrless than 1.0 5., Pr less than 0.10 56, Srless than 0.01 56, : less than 0.008 56, Ai less than 0.756, Ni: 0.05-1.0 56, Cur0.02- O.δ 56, sum of one kind or two kinds of Sn and Sb:0.02-0.2 56, residual Fe and other inevitably containing impurity.

2. A nonoriented electrical steel sheet with superior magnetic properties as recited in claim 1, wherein grain size is 30-200 μm and texture parameter calculated by Horta formula is more than 0.2

3. A nonoriented electrical steel sheet with superior magnetic properties comprising, in the unit of weight percentage, Crless than 0.02 56, Si:less than 1.0 56, Mnrless than 0.5 56, Prless than 0.15 56, Srless than 0.01 56, Nrless than 0.008 56, Orless than 0.005 %, Al:less than 0.7 56, Ni:0.05-1.0 56, Cur0.02-0.5 56, sum of one kind or two kinds of Sn and Sb 0.02-0.3 56, residual Fe and other inevitably containing impurity.

4. A nonoriented electrical steel sheet with superior magnetic properties as recited in claim 3, wherein grain size is 20-200 μm and texture parameter calculated by Horta formula is more than 0.2. δ. A nonoriented electrical steel sheet with superior magnetic properties comprising, in the unit of weight percentage, C:less than 0.02 56, Si: less than 3.δ 56, Mn:less than O.δ 56, P:less than O.lδ 56, S:less than 0.015 56, Al: less than 0.7 56, 0:less than O.OOδ 56, Nrless than 0.008 56, sum of one kind or two kinds of Sn and Sb:0.02- 0.3 56, Ni:0.02-1.0 56, Cu:0.02-0.4 56, residual Fe and other inevitably containing impurity.

6. A nonoriented electrical steel sheet with superior magnetic properties as recited in claim 5, wherein grain size is 25-200 μm and texture parameter calculated by Horta formula is more than 0.2.

7. A nonoriented electrical steel sheet with superior magnetic properties comprising, in the unit of weight percentage, C:less than 0.02 56, Si:less than 3.5 56, Mn:less than 0.5 56, P:less than 0.15 56, S:less than 0.01 56, N.less than 0.008%, Al:less than 0.7 56, Ni:0.02-1.0 56, Cu: 0.02-0.5 56, sum of one kind or two kinds of Sn and Sb:0.02-0.2 56, Ca: 0.001-0.02 56 and/or rare earth element(REM) :0.003-0.03 56, residual Fe and other inevitably containing impurity.

8. A nonoriented electrical steel sheet with superior magnetic properties as recited in claim 7, wherein grain size is 30-200 μm and texture parameter calculated by Horta formula is more than 0.2. 9. A nonoriented electrical steel sheet with superior magnetic properties as recited in claim 7 or claim 8, wherein rare earth element consists of one kind or more than two kinds. δ

10. A nonoriented electrical steel sheet with superior magnetic properties comprising, in the unit of weight percentage, Cr0.02-0.06 56, Si less than 3.5 56, Mnrless than 0.5 56, Prless than 0.15 56, Srless than 0.01 56, Nrless 0 than 0.008 56, Airless than 0.7 56, 0:less than 0.005 56, NirO.02-1.0 56, Cur-0.02-0. Oδ 56, sum of one kind or two kinds of Sn and Sbr0.02-0.2 56, residual Fe and other inevitably containing impurity.

5 11. A nonoriented electrical steel sheet with superior magnetic properties as recited in claim 10, wherein grain size is 20-180 μm and texture parameter calculated by Horta formula is more than 0.3.

0 12. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties by fully- process, wherein a steel slab comprising, in the unit of weight percentage, Crless than 0.02 56, Si:less than 1.0- 3.δ 56, Mn:less than 1.0 56, P:less than 0.10 56, S:less than δ 0.01 56, Nrless than 0.008 56, Airless than 0.7 56, Ni:0.0ό- 1.0 56, Cu:0.02-0.5 56, sum of one kind or two kinds of Sn and Sbr0.02-0.2 56, residual Fe and other inevitably containing impuritj^r is hot rolled, hot rolled sheet is annealed, is pickled, is cold rolled with one stage cold rolling method or double cold rolling method, coled rolled sheet is high-temperature annealed or is annealed with stress relieving.

5 13. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties as recited in claim 12, wherein annealing of said hot rolled sheet is conducted by continuous annealing _. method within temperature range of 700-1000° C during 10 seconds-20 10 minutes.

14. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties as recited in claim 12, wherein annealing of said hot rolled sheet is lδ conducted by box annealing method within temperature range of 600-1000° C during 30 minutes-10 hours.

15. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties by semi- 0 process, wherein a steel slab comprising, in the unit of weight percentage, C:less than 0.02 56, Si:less than 1.0 56, Mn:less than 0.5 56, P:less than O.lδ 56, S:less than 0.01 56, N:less than 0.008 56, 0: less than O.OOδ 56, Al:less than 0.7 56, Ni:0.05-1.0 56, Cu:0.02-0.5 56, sum of one kind or 5 two kinds of Sn and Sb:0.02-0.2 56, residual Fe and other inevitably containing impurity is hot rolled, hot rolled sheet is annealed, is pickled, is cold rolled, intermediate annealing is conducted, and skin pass rolling and annealing with stree relieving are conducted. 16. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties as recited in claim lδ, wherein finish hot rolling is completed at temperature range of 7δO°C-Arl point under ferrite phase.

17. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties as recited in claim 15 or claim 16, wherein annealing of said hot rolled sheet is conducted by continuous annealing method within temperature range of 700-1000°C during 10 seconds- 20 minutes.

18. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties as recited in claim 15 or claim 16, wherein annealing of said hot rolled sheet Is conducted by box annealing method within temperature range of 600-950°C during 30 minutes-10 hours.

19. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties by fully- process, wherein a steel slab comprising, in the unit of weight percentage, Crless than 0.0256, Sirless than 1.056, Mnrless than 0.5 56, P:less than 0.15 56, Srless than 0.01 56, Nrless than 0.008 56, 0:less than 0.005 56, Airless than 0.7 56, NirO.05-1.0 %, Cu:0.02-0.5 56, sum of one kind or two kinds of Sn and Sb: 0.02-0.2 56, residual Fe and other inevitably containing impurity is hot rolled, hot rolled sheet is annealed, is pickled, is cold rolled, and coled rolled sheet is annealed. 20. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties as recited in claim 19, wherein finish hot rolling is completed at temperature range of 750°C-Arl point under ferrite phase. δ

21. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties as recited in claim 19 or claim 20, wherein annealing of said hot rolled sheet is conducted by continuous annealing method

10 within temperature range of 700-1000°C during 10 seconds- 20 minutes.

22. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties as recited lδ in claim 19 or claim 20, wherein annealing of said hot rolled sheet is conducted by box annealing method with temperature range of 600-9δO°C during 30 minutes-10 hours.

23. A method for manufacturing nonoriented electrical 20 steel sheets with superior magnetic properties, wherein a steel slab comprising, in the unit of weight percentage,^' Crless than 0.02 56, Si :less than 3.δ 56, Mnrless than 0.5 56, P:less than 0.15 56, Al : less than 0.7 56, 0:less than O.OOδ 56, N:0.02-1.0 56, Cu:0.02-0.4 56, residual Fe and δ other inevitably containing impurity is heated, is hot rolled whereby finish rolling is conducted under ferrite phase of higher than 800° C with percentage reduction in thickness of more than 7 56, hot rolled sheet is coiled at temperature of higher than 600° C, is cooled in the air, is pickled, is cold rolled with one stage cold rolling method or double cold rolling method, and high-temperature annealing is conducted within temperature range of 700- 1100°C during 10 seconds-10 minutes.

24. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties as recited in claim 23, wherein after coiling of said hot rolled sheet, cooling speed during cooling is 30°C/hour.

25. A method for ^"manufacturing nonoriented electrical steel sheets with superior magnetic properties by fully- process, wherein a steel slab comprising, in the unit of weight percentage, C:less than 0.02 56, Si:less than 3.5 56, Mn:less than 0.5 56, P:less than 0.15 56, S:less than 0.01 56, Nrless than 0.00856, Airless than 0.756, NirO.02-1.0 56, Cu: 0.02- 0.5%, Ca:0.001-0.02% or rare earth element: 0.003-0.03%, residual Fe and other inevitably containing impurity is hot rolled, is coiled, is pickled as said hot rolled sheet is or after the hot rolled sheet Is annealed, is cold rolled with one stage cold rolling method or double cold rolling method, and high-temperature annealing is conducted.

26. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties by semi- process, wherein a steel slab comprising, in the unit of weight percentage, C:less than 0.0256, Si:less than 3.5 56, Mnrless than 0.5 56, Prless than O.lδ 56, Srless than 0.01 7δ 56, N:less than 0.008 56, Airless than 0.7 56, Ni:0.02-1.0 56, Cu:0.02-0.δ 56, sum of one kind or two kinds of Sn and Sb:0.02-0.2 56, Ca: 0.001-0.02 56 and/or rare earth element: 0.003-0.03 56, residual Fe and other inevitably δ containing impurity is hot rolled, is coiled, is pickled as said hot rolled sheet is or after the hot rolled sheet is annealed, a first-order annealing and intermediate annealing are conducted, and skin pass rolling is conducted. 10

27. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties by fully- process, wherein a steel slab comprising, in the unit of weight percentage, C:0.02-0.06 56, Si:less than 3.5 56, lδ Mn:less than O.δ 56, P;less than O.lδ 56, S:less than 0.01 56, Nrless than 0.008 56, Airless than 0.7 56, Orless than O.OOδ56, sum of one kind or two kinds os Sn and Sb:0.02-0.2 56, Ni;0.02-1.0 56, Cu:0.02-0.05 56, residual Fe and other inevitably containing impurity is hot rolled, is pickled,

20 is cold rolled with one stage cold rolling method or double cold rolling method, decarburization annealing of said coled rolled sheet is conducted within temperature range of 7δO-900°C in the mixed atmosphere of 60-90 56 nitrogen and 40-10 56 hydrogen with dew point of 30-60° C,

2δ and final high-temperature annealing is conducted.

28. A method for manuf cturing nonoriented electrical steel sheets with superior magnetic properties as recited in claim 27, wherein with respect to said hot rolled sheet, continuous annealing or box annealing in non- oxidizing atmosphere is conducted.

29. A method for manufacturing nonoriented electrical δ steel sheets with superior magnetic properties by semi- process, wherein a steel slab comprising, in the unit of weight percentage, Cr0.02-0.06 56, Sir less than 3.δ 56, Mnrless than O.δ 56, Prless than O.lδ 56, Srless than 0.01- 56, Nrless than 0.008 56, Airless than 0.7 56, Orless than 0 0.00556, sum of one kind or two kinds of Sn and Sbr0.02- 0.2 56, Nir 0.02-1.0 56, Cu:0.02-0.05 56, residual Fe and other inevitably containing impurity is hot rolled, is pickled, is cold rolled as a first-order cold rolling, intermediate annealing and skin pass rolling are 5 conducted, and annealing with stress relieving is conducted after processing by consumers, so to speak, the electric apparatus manufacturers.

30. A method for manufacturing nonoriented electrical 0 steel sheets with superior magnetic properties as recited in claim 29, wherein during intermediate annealing, decarburization annealing of said coled rolled sheet is conducted within temperature range of 750-900° C in the mixed atmosphere of 60-90 56 nitrogen and 40-10 56 hydrogen δ with dew point of 30-60° C during 1-10 minutes.

31. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties as recited in claim 29, wherein at the time of annealing with stress relieving, decarburization annealing is conducted within temperature range of 750-850° C in the mixed atmosphere of 60-90 % nitrogen and 40-10 56 hydrogen with dew point of 30-60°C.

32. A method for manufacturing nonoriented electrical steel sheets with superior magnetic properties as recited in claim 29 or claim 31, wherein with respect to said hot rolled sheet, continuous annealing or box annealing in non-oxidizing atmosphere is conducted.