Non-Oriented Electrical Steel Sheet Having Superior Magnetic Properties and a Production Method Therefor
A non-oriented electrical steel sheet having outstanding magnetic properties and i, as percentages by weight, from 0.7˜3.02.5% of Al, 0.2˜32.5% of Si, 0.2˜2.01.5% of Mn, 0.001 0005˜0.004% of N, 0.0005˜0.004% of S, 0.003% or less of C, and a balance of Fe and other unavoidably incorporated impurities, wherein the Al, Mn, N and S are included so as to satisfy the compositional formulae 1≤{[Al]+[Mn]}≤3.5, 0.002≤{[N]+[S]}≤0.006, 300250≤{([Al]+[Mn])/([N]+[S])}≤1,400, 1.4≤{[Al]+[Si]+[Mn]/2}≤5.5, 1 [Al]/[Si]≤7.5, 1≤[Al]/[Mn]≤3.7; and a production method therefor. By optimising the Al, Si, Mn, N and S added components, the distribution density of coarse inclusions is increased, thereby improving the crystal-grain growth properties and domain wall motility and producing the highest grade of non-oriented electrical steel sheet having superior magnetic properties, low hardness, and superior customer workability and productivity.
This application is a continuation-in-part of U.S. application Ser. No. 13/514,312 filed on Jun. 7, 2012, which is the United States national phase of International Application No. PCT/KR2010/009380 filed Dec. 28, 2010, which claims priority to Korean Patent Application No. 10-2009-0131990 filed Dec. 28, 2009, Korean Patent Application No. 10-2009-0131992 filed Dec. 28, 2009, Korean Patent Application No. 10-2010-0135003 filed Dec. 24, 2010, Korean Patent Application No. 10-2010-0135004 filed Dec. 24, 2010, and Korean Patent Application No. 10-2010-0135943 filed Dec. 27, 2010, the disclosures of which are hereby incorporated in their entirety by reference.
BACKGROUND OF THE INVENTION Technical FieldThe present invention relates to the production of a non-oriented electrical steel sheet, and particularly to a non-oriented electrical steel sheet of the highest quality, wherein the components of steel are optimally designed to increase the distribution density of coarse inclusions in steel and to improve growth of grains and mobility of domain walls, so that magnetic properties are enhanced, and low hardness is ensured, thus improving productivity and punchability, and to a method of producing the same.
Background ArtThe present invention pertains to the production of a non-oriented electrical steel sheet useful as a material for iron cores of rotation devices. This non-oriented electrical steel sheet is essential in terms of converting electrical energy into mechanical energy, and thus the magnetic properties thereof are regarded as very important. The magnetic properties mainly include core loss and magnetic flux density. Because the core loss is energy that disappears in the form of heat in the course of converting energy, it is good for it to be as low as possible. The magnetic flux density is a power source of a rotator. The higher the magnetic flux density, the more favorable the energy efficiency.
Typically, a non-oriented electrical steel sheet is composed mainly of Si in order to reduce core loss. When the amount of Si increases, the magnetic flux density decreases. If the amount of Si is excessively increased, processability is decreased making it difficult to perform cold rolling. Furthermore, the lifetime of a mold may decrease upon punching by the customer. Hence, attempts are made to decrease the amount of Si and increase the amount of Al so as to improve magnetic properties and mechanical properties. However, the magnetic properties of non-oriented electrical steel sheet of the highest quality are not obtained, and such sheets have not yet been actually produced because of difficulties in mass producing them.
Meanwhile, to obtain a non-oriented electrical steel sheet with good magnetic properties, impurities including C, S, N, Ti and so on such as fine inclusions present in steel are controlled to be minimal and thus the growth of grains needs to be increased. However, the control of impurities to the minimum is not easy in a typical production process of electrical steel sheets, and the cost of a steel making process may undesirably increase.
The impurities which were not removed in the steel making process are present in the form of nitrides or sulfides in a slab upon continuous casting. As the slab is re-heated to 1,100° C. or higher for hot rolling, inclusions such as nitrides or sulfides may be re-dissolved and then finely precipitated again upon termination of hot rolling.
The inclusions that are precipitated in typical non-oriented electrical steel sheets include MnS and AlN, which are observed to have a small average size of about 50 nm, and such fine inclusions may hinder the growth of grains upon annealing thus increasing hysteresis loss and obstructing the movement of domain walls upon magnetization, undesirably lowering permeability.
Therefore, in the process of producing the non-oriented electrical steel sheet, impurities are appropriately controlled from the steel making process so that such fine inclusions are not present, and the residual inclusions should be prevented from being more finely precipitated via re-dissolution upon hot rolling.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a non-oriented electrical steel sheet of the highest quality, wherein the proportions of Al, Si and Mn which are alloy elements of steel and N and S which are impurity elements of steel are optimally controlled so that the distribution density of coarse inclusions in steel is increased and the formation of fine inclusions is decreased, thus enhancing the growth of grains and the mobility of domain walls to thereby manifest excellent magnetic properties, and also superior productivity and punchability because of low hardness.
SUMMARY OF THE INVENTIONIn order to accomplish the above object, an aspect of the present invention provides a non-oriented electrical steel sheet having superior magnetic properties, comprising 0.7˜2.5% of Al, 0.2˜2.5% of Si, 0.2˜1.5% of Mn, 0.0005˜0.004% of N, 0.0005˜0.004% of S, 0.003% or less of C, and a balance of Fe and other inevitable impurities by wt %, and satisfying the conditions below:
Conditions: 1.0≤[Al]≤3.0, 0.5≤[Si]≤2.5, 0.5≤[Mn]2.0, 1≤{[Al]+[Mn]}≤3.5, 0.002≤{[N]+[S]}≤0.006, 300250≤{([Al]+[Mn])/([N]+[S])}≤1,400, 1.4≤{[Al]+[Si]+[Mn]/2}≤5.5, 1≤[Al]/[Si]≤7.5, 1≤[Al]/[Mn]≤3.7, wherein [Al], [Si], [Mn], [N] and [S] indicate amounts (wt %) of Al, Si, Mn, N and S, respectively.
The non-oriented electrical steel sheet may further comprise 0.2% or less of P.
The non-oriented electrical steel sheet may further comprise at least one of 0.005˜0.2% of Sn and 0.005˜0.1% of Sb.
The non-oriented electrical steel sheet may further comprise 0.004% or less of Ti.
The non-oriented electrical steel sheet which satisfies Condition may have inclusions comprising nitrides and sulfides alone or combinations thereof formed in the steel sheet.
The nitride may comprise aluminum nitride and the sulfide may comprise magnesium sulfide.
The inclusion may have an average size of 300 nm or more.
A distribution density of the inclusion may having an size of 300 nm or more may be equal to or greater than 0.02 number/mm2
A cross-sectional Vickers hardness (Hv1) may be 190 or less.
According to the present invention, the proportions of alloy elements such as Al, Si and Mn and of impurity elements such as N and S can be appropriately controlled so as to increase the distribution density of coarse inclusions, thus enhancing the growth of grains and the mobility of domain walls. Thereby, a non-oriented electrical steel sheet of the highest quality having excellent magnetic properties and very low hardness can be stably produced. Also customer workability and productivity are superior, and the unit cost of production of products can be decreased, thus reducing the cost.
To solve the technical problems as mentioned above, the present inventors have examined the effects of alloy elements and impurity elements in steel and of the relation between respective elements on forming the inclusions and also the effects thereof on magnetic properties and processability, resulted in the finding that among alloy elements of steel, the amounts of Al, Si and Mn and the amounts of impurity elements such as N and S may be appropriately adjusted and Al/Si and Al/Mn, Al+Si+Mn/2, Al+Mn, N+S and (Al+Mn)/(N+S) may be optimally controlled so that the hardness of a steel sheet is decreased and the distribution density of coarse composite inclusions having an average size of 300 nm or more in the steel sheet is increased, thereby drastically enhancing magnetic properties and improving productivity and punchability, which culminates in the present invention.
The present invention is directed to a non-oriented electrical steel sheet of the highest quality, comprising 0.7˜2.5% of Al, 0.2˜2.5% of Si, 0.2˜1.5% of Mn, 0.0005˜0.004% of N, 0.0005˜0.004% of S, 0.003% or less of C, and a balance of Fe and other inevitable impurities by wt %, wherein Al, Si, Mn, N and S are contained so as to satisfy the following Condition and thus the distribution density of 300 nm or more sized coarse inclusions having combinations of nitrides and sulfides is increased to be equal to or greater than 0.02 number/mm2, resulting in high magnetic properties and low hardness.
Condition: 1≤{[Al]+[Mn]}≤3.5, 0.002≤{[N]+[S]}≤0.006, 250≤{([Al]+[Mn])/([N]+[S])}≤1,400, 1.4≤{[Al]+[Si]+[Mn]/2}≤5.5, 1≤[Al]/[Si]≤7.5, 1≤[Al]/[Mn]≤3.7
As such, [Al], [Si], [Mn], [N] and [S] indicate the amounts (wt %) of Al, Si, Mn, N and S, respectively.
In addition, the present invention is directed to the production of the non-oriented electrical steel sheet which is superior in both magnetic properties and processability, by adding 0.3˜0.5% of Al to molten steel to perform deoxidation in a steel making process, adding remaining alloy elements, and then maintaining the temperature of the molten steel at 1,500˜1,600° C. thus manufacturing a slab having the composition that satisfies Condition, followed by heating the slab to 1,100˜1,250° C. and then performing hot rolling wherein finish hot rolling is conducted at 800° C. or higher, carrying out cold rolling, and then finally annealing the cold rolled sheet at 750˜1,100° C.
The alloy elements of steel, namely, Al, Si and Mn are described below. These alloy elements are added to reduce the core loss of an electrical steel sheet. As the amounts thereof increase, the magnetic flux density may decrease and the processability of a material may deteriorate. Hence, the amounts of such alloy components are appropriately designed to improve not only the core loss but also the magnetic flux density, and also hardness needs to be maintained to an appropriate level or less.
Furthermore, Al and Mn combine with N and S which are impurity elements to form inclusions such as nitrides or sulfides. Such inclusions greatly affect magnetic properties and thus the formation of inclusions that minimize the deterioration of magnetic properties should be increased.
The present inventors were the first to discover that coarse composite inclusions comprising combinations of nitrides or sulfides may be formed when the amounts of Al, Mn, Si, N and S are adapted for specific conditions, and have found the fact that the distribution density of such composite inclusions to a predetermined level or more is ensured, and thereby magnetic properties may be drastically improved despite the addition of minimum amounts of alloy elements that deteriorate processability, and thus devised the present invention.
The reason why the ranges of component elements of the present invention and the amount ratios of the component elements are limited is described below.
[Al: 0.7˜2.5 wt %]
Al functions to increase resistivity of a material to reduce core loss and to form a nitride, and is added in an amount of 0.7˜2.5% so as to form a coarse nitride. If the amount of Al is less than 0.7%, inclusions may not be sufficiently grown. In contrast, if the amount thereof exceeds 2.5%, processability may deteriorate and all processes including steel making, continuous casting and so on may be problematic, making it impossible to produce a steel sheet in the typical manner.
[Si: 0.2˜2.5 wt %]
Si functions to increase resistivity of a material to reduce core loss. If the amount of Si is less than 0.2%, it is difficult to expect reduction effects of core loss. In contrast, if the amount thereof exceeds 2.5%, the hardness of a material may increase, undesirably deteriorating productivity and punchability.
[Mn: 0.2˜1.5 wt %]
Mn functions to increase resistivity of a material to reduce core loss and to form a sulfide, and is added in an amount of 0.2% or more. If the amount thereof exceeds 1.5%, the formation of [111] texture that is unfavorable for magnetic properties may be facilitated. Hence, the amount of Mn is preferably limited to 0.5˜1.5%.
[Sn: 0.005˜0.2 wt %]
Sn is preferentially segregated on the surface and the grain boundaries and may reduce accumulated strain energy upon hot rolling and cold rolling, so that the strength in {100} orientation that is favorable for magnetic properties may increase whereas the strength in {111} orientation that is unfavorable for magnetic properties may decrease, thus achieving improvements in texture. Hence, Sn is added in the range of 0.2% or less. Furthermore, Sn is preferentially formed on the surface during welding to thus suppress surface oxidation and enhance the weld properties thereby increasing productivity of continuous lines. Also, the formation of Al-based oxides and nitrides on the surface or the layer under the surface may be suppressed during heat treatment, thus enhancing magnetic properties. Upon punching by a customer, the increase in hardness of the layer under the surface due to nitrides may be inhibited to improve punchability.
Hence, Sn is preferably added in the range of 0.005% or more. In contrast, if the amount of Sn exceeds 0.2%, improvements in magnetic properties based on such an additional use thereof are insignificant, and fine inclusions and deposits may be formed in steel, rather than preferential segregation on the surface and the grain boundaries, negatively affecting the magnetic properties. Also, cold rollability and punchability may decrease and the Erichsen number that represents the weld properties is 5 mm or less, making it impossible to perform welding of the same species. Thus, a low-graded material having the sum of Si and Al of less than 2 should be undesirably used as a connection material for continuous line working. Hence, the amount of Sn is preferably limited to 0.005˜0.2%.
[Sb: 0.005˜0.1 wt %]
Sb is preferentially segregated on the surface and the grain boundaries and may reduce accumulated strain energy upon hot rolling and cold rolling, so that the strength in {100} orientation that is favorable for magnetic properties may increase and the strength in {111} orientation that is unfavorable for magnetic properties may decrease, thus attaining improvements in texture. Hence, Sb is added in the range of 0.1% or less. Furthermore, Sb is preferentially formed on the surface during welding to thus suppress surface oxidation and enhance weld properties thereby increasing productivity of continuous lines. Also, the formation of Al-based oxides and nitrides on the surface or the layer under the surface may be suppressed during heat treatment, thus improving magnetic properties. Upon punching by the customer, the increase in hardness of the layer under the surface due to nitrides may be inhibited to improve punchability.
Hence, Sb is preferably added in the range of 0.005% or more. In contrast, if the amount of Sb exceeds 0.1%, improvements in magnetic properties based on such an additional use thereof are insignificant, and fine inclusions and deposits may be formed in steel, rather than preferential segregation on the surface and the grain boundaries, undesirably aggravating the magnetic properties. Also, cold rollability and punchability may decrease and the Erichsen number that represents the weld properties is 5 mm or less, making it impossible to perform welding of the same species. Thus, a low-graded material having the sum of Si and Al of less than 2 should be undesirably used as a connection material for continuous line working. Hence, the amount of Sb is preferably limited to 0.005˜0.1%.
[P: 0.2 wt % or less]
When P is added in the range of 0.2% or less, texture that is favorable for magnetic properties may be formed, and in-plane anisotropy and processability are improved. If the amount thereof exceeds 0.2%, cold rollability may decrease and processability may deteriorate. Hence, the amount of P is limited to 0.2% or less.
[N: 0.0005˜0.004 wt %]
N is an impurity element, and may form a fine nitride during the production process to suppress the growth of grains undesirably deteriorating core loss. Although the formation of nitrides is suppressed, an additional high cost and long process time are required, and thus monetary benefits are negatively affected. Therefore, it is preferred that an element having high affinity for the impurity element N is positively utilized to coarsely grow inclusions so as to reduce an influence on the growth of grains. To coarsely grow the inclusions in this way, the amount of N is essentially controlled in the range of 0.0005˜0.004%. If the amount of N exceeds 0.004%, the inclusions may not be coarsely formed undesirably increasing core loss. More preferably, the amount of N is limited to 0.003% or less.
[S: 0.0005˜0.004 wt %]
S is an impurity element, and may form a fine sulfide during the production process to thus suppress the growth of grains and deteriorate core loss. Although the formation of sulfides is suppressed, an additional high cost and long process time are required, and thus monetary benefits are negatively affected. Thus, it is preferred that an element having high affinity for the impurity element S is positively utilized to coarsely grow inclusions so as to reduce the influence on the growth of grains. To coarsely grow the inclusions in this way, the amount of S is essentially controlled in the range of 0.0005˜0.004%. If the amount of S exceeds 0.004%, the inclusions may not be coarsely formed undesirably increasing core loss. More preferably, the amount of S is limited to 0.003% or less.
In addition to the above impurity elements, inevitable impurities such as C, Ti may be incorporated. C may cause magnetic aging, and the amount thereof is thus limited in the range of 0.003% or less. Ti may promote the growth of [111] texture that is unfavorable for a non-oriented electrical steel sheet, and the amount thereof is thus limited in the range of 0.004% or less, and preferably 0.002% or less.
In the non-oriented electrical steel sheet that satisfies Condition, the sum ([Al]+[Mn]) of Al and Mn by wt % is limited to 3.5% or less. If the sum of Al and Mn exceeds 3.5% in steel comprising 0.7˜2.5% of Al, 0.2˜2.5% of Si and 0.2˜1.5% of Mn, the fraction of [111] texture that is unfavorable for magnetic properties may increase undesirably deteriorating the magnetic properties. In the non-oriented electrical steel sheet that satisfies Condition, if the sum of Al and Mn is less than 1%, nitrides, sulfides or composite inclusions of these two are not coarsely formed, thus deteriorating the magnetic properties.
In the present invention, the sum ([N]+[S]) of N and S is limited to 0.002˜0.006%. This is because inclusions are coarsely formed in the above range. If the sum of N and S exceeds 0.006%, the fraction of fine inclusions may be increased, undesirably deteriorating the magnetic properties.
Also in the present invention, the ratio of the sum ([Al]+[Mn]) of Al and Mn by wt % to the sum ([N]+[S]) of N and S by wt % is regarded as important.
The present inventors have appreciated that, in order for the distribution density of 300 nm or more sized coarse composite inclusions of nitrides and sulfides to increase and become equal to or greater than 0.02 number/mm2, ([Al]+[Mn])/([N]+[S]) should be appropriately adjusted, and the proper range of ([Al]+[Mn])/([N]+[S]) may vary depending on the amounts of Si, Al and Mn.
In the case where the amounts of Al, Si and Mn are given as in Condition, when the ratio of ([Al]+[Mn])/([N]+[S]) is 250˜1400, the formation of composite inclusions may be effectively increased. Specifically, when the ratio of ([Al]+[Mn])/([N]+[S]) falls in the range of 250˜1400 under Condition, inclusions may be coarsely formed thus increasing the distribution density of coarse composite inclusions. In contrast, when the ratio thereof falls outside the above range, the inclusions are not coarsely formed and the formation of coarse composite inclusions is low and texture that is unfavorable for magnetic properties is formed.
The accurate mechanism for forming such coarse composite inclusions has not yet been revealed, but is assumed to take place in the steel making process. Specifically upon initial addition of Al in the steel making process, Al-based oxides and nitrides may be formed due to deoxidation, and in the composition that additionally includes the alloy elements such as Al and Mn and satisfies the amounts of Al, Mn, Si, N and S as designed in the present invention upon bubbling, Al-based oxides and nitrides are grown and Mn-based sulfides may also be precipitated thereon.
In the range of the present invention that satisfies Condition, namely, wherein the sum ([Al]+[Mn]) of Al and Mn by wt % is 3.5% or less and the sum ([N]+[S]) of N and S by wt % is 0.002˜0.006 and the ratio of the sum of Al and Mn to the sum of N and S ([Al]+[Mn])/([N]+[S]) falls in the range of 250˜1,400, inclusions are coarsely formed and the distribution density of coarse composite inclusions having an average size of 300 nm or more is greater than 0.02 number/mm2, thus exhibiting superior magnetic properties. However, in the range falling outside the present invention (outside the thick line), coarse inclusions are not formed and the distribution density of coarse composite inclusions having an average size of 300 nm or more is less than 0.02 number/mm2, thus deteriorating texture and magnetic properties.
Although the coarse inclusions are mainly observed to be combinations of nitrides and sulfides having an average size of 300 nm or more, the examples thereof may include combinations of a plurality of nitrides or combinations of a plurality of sulfides having an average size of 300 nm or more, and those having nitrides or sulfides alone having a size of 300 nm or more. Herein, the average size of the inclusions is determined by measuring the longest length and the shortest length of the inclusions when viewed in the cross-section of the steel sheet and averaging the measured values.
Also in the non-oriented electrical steel sheet that satisfies Condition, the amount ratio of Al to Si ([Al]/[Si]) is limited to 1˜7.5. In the case where the amount ratio of Al to Si is 1˜7.5, the grains may effectively grow and the hardness of a material may decrease thus improving productivity and punchability. If the ratio of [Al]/[Si] is less than 1, inclusions do not greatly grow undesirably decreasing the growth of grains and deteriorating magnetic properties. Furthermore, the amount of Si may increase, undesirably enhancing hardness. If the ratio of [Al]/[Si] exceeds 7.5, texture of a material may become poor undesirably deteriorating the magnetic flux density.
In the present invention, the ratio of Al to Mn ([Al]/[Mn]) is preferably limited to 1˜3.7. When the ratio of Al to Mn is 1˜3.7, the inclusions may effectively grow thus exhibiting superior core loss properties. In contrast, if the ratio thereof falls outside the above range, the growth of inclusions may decrease and the fraction of texture that is favorable for magnetic properties may decrease.
The limited ratio of alloy components related to resistivity is described below. Recently, as the demand for environmentally friendly automobiles drastically increases, there is a high need for non-oriented electrical steel sheets usable for highly rotatable motors. The motors used in the environmentally friendly automobiles should greatly increase their number of rotations. When the number of rotations of the motor is increased, the fraction of eddy current loss in the inner core loss may be drastically increased. To reduce such eddy current loss, resistivity should increase.
The relation between the amounts of alloy elements of the non-oriented electrical steel sheet and the intrinsic resistance is represented below.
ρ=13.25+11.3([Al]+[Si]+[Mn]/2)(ρ:resistivity,Ω·m)
In the present invention that satisfies Condition, [Al]+[Si]+[Mn]/2 is limited to 1.7 or more so as to ensure the resistivity of 32 or more. Furthermore, in the present invention that satisfies Condition, [Al]+[Si]+[Mn]/2 is controlled to 5.5% or less so that resistivity (intrinsic resistance) is maintained to 75 or less and Vickers hardness (Hv1) is 190 or less.
Also the demand for high magnetic flux density products is drastically increasing these days to achieve high efficiency of motors. Accordingly, there is an urgent requirement for non-oriented electrical steel sheets having lowered resistivity and improved magnetic flux density. In the case where magnetic flux density properties are regarded as important, resistivity (intrinsic resistance) is decreased to 36 or less to increase the magnetic flux density. Moreover to correspond to high-speed rotations, the resistivity should be controlled to at least 25.
Below is a description of a method of producing the non-oriented electrical steel sheet according to the present invention. The method of producing the non-oriented electrical steel sheet preferably includes adding 0.3˜0.5% of Al, corresponding to a portion of the total amount of added Al, in the steel making process, so that deoxidation of steel sufficiently occurs, and adding the remaining alloy elements. Subsequently, the temperature of molten steel is maintained at 1,500˜1,600° C. so that inclusions in steel are sufficiently grown, after which the resultant steel is solidified in a continuous casting process thus manufacturing a slab.
Subsequently, the slab is placed in a furnace so that it is re-heated to 1,100˜1,250° C. If the slab is heated to a temperature exceeding 1,250° C., deposits that negatively affect the magnetic properties may be re-dissolved, hot rolled and then finely deposited, and thus the slab is heated to 1,250° C. or less.
Subsequently, the heated slab is hot rolled. Upon hot rolling, finish hot rolling is preferably carried out at 800° C. or more. The hot rolled sheet is annealed at 850˜1,100° C. If the annealing temperature of the hot rolled sheet is lower than 850° C., texture does not grow or finally grows, and thus the extent of increasing the magnetic flux density is low. In contrast, if the annealing temperature of the hot rolled sheet is higher than 1,100° C., magnetic properties may deteriorate instead, and rolling workability may decrease due to plate transformation. Hence, the temperature range thereof is limited to 850˜1,100° C. More preferably the annealing temperature of the hot rolled sheet is 950˜1,100° C. The annealing of the hot rolled sheet may be carried out to increase the grain orientation favorable for magnetic properties, as necessary, but may be omitted.
Subsequently, the hot rolled sheet which was annealed or not is pickled, and cold rolled to a reduction of 70˜95% to obtain a predetermined sheet thickness.
The amounts of added Si, Mn and Al alloy elements that affect cold rollability are appropriately controlled thus attaining superior cold rollability and high reduction. Thus, one cold rolling makes it possible to form a thin sheet having a thickness of about 0.15 mm. Upon cold rolling, two cold rolling operations including intermediate annealing may be conducted, as necessary, or two annealing operations may be applied.
Subsequently, the cold rolled sheet is subjected to final annealing. If the final annealing temperature is lower than 750° C., recrystallization does not sufficiently occur. In contrast, if the final annealing temperature exceeds 1,100° C., the surface oxide layer is deeply formed, undesirably deteriorating magnetic properties. Hence, final annealing is preferably conducted at 750˜1,100° C.
The finally annealed steel sheet is subjected to insulation coating treatment using typical methods and is then discharged to customers. Upon insulation coating, the application of a typical coating material is possible, and either Cr-type or Cr-free type may be used without limitation.
Below, the present invention is described by the following examples. Unless otherwise stated, the amounts of components are represented by wt % in the following examples.
Example 1Vacuum melting was performed in a laboratory, thus preparing steel ingots having the components shown in Table 1 below. As such, the amount of each of impurity elements C, S, N, Ti was controlled to 0.002%, and 0.3˜0.5% of Al was added to molten steel to facilitate the formation of inclusions, after which the remainder of Al, and Si and Mn were added thus making steel ingots. Each of the ingots was heated to 1,150° C., and finish hot rolled at 850° C. thus manufacturing a hot rolled sheet having a thickness of 2.0 mm. The hot rolled sheet was annealed at 1,050° C. for 4 min and then pickled. Subsequently, cold rolling was conducted so that the thickness of the sheet was 0.35 mm, followed by carrying out final annealing at 1,050° C. for 38 sec.
The size and distribution density of inclusions of respective sheets, the core loss, the magnetic flux density and hardness were measured. The results are shown in Table 2 below. A sample for use in observing the inclusions was manufactured using a replica method that is typical in the steel industry, and a transmission electron microscope was used therefor. As such, the acceleration voltage of 200 kV was applied.
As is apparent from Table 2, steels A3, A5, A6, A9, A10, and A14 were inventive examples that satisfy Condition, wherein coarse composite inclusions having a size of 300 nm or more were observed, and the distribution density thereof was greater than 0.02(1/mm2) thus exhibiting superior magnetic properties. The Vickers hardness (Hv1) was as low as 190 or less thus obtaining superior productivity and customer punchability.
Whereas in steel A1, the ratio of Al+Mn did not satisfy Condition, and thus inclusions having a size of 300 nm or more were not observed, and core loss and magnetic flux density were deteriorated. Also, in steel A15, the ratio of Al/Si did not satisfy Condition, and thus inclusions having a size of 300 nm or more were not observed, and core loss and magnetic flux density were deteriorated. Also in steels A4, A8, A11 and A13, Al+Mn did not satisfy Condition, and thus inclusions having a size of 300 nm or more were not observed, and core loss and magnetic flux density were deteriorated. Also in steel A7, the ratio of Al/Si and the ratio of Al/Mn did not satisfy Condition), and thus inclusions having a size of 300 nm or more were not observed, and core loss and magnetic flux density were deteriorated.
Example 2Vacuum melting was performed in a laboratory, thus preparing steel ingots having the components shown in Table 3 below. As such, the components of steel were controlled while variously adjusting the amounts of impurity elements N and S, and 0.3˜0.5% of Al was added to molten steel to facilitate the formation of inclusions, after which the remainder of Al, and Si and Mn were added thus making steel ingots. Each of the ingots was heated to 1,150° C., and finish hot rolled at 850° C. thus manufacturing a hot rolled sheet having a thickness of 2.0 mm. The hot rolled sheet was annealed at 1,050° C. for 4 min and then pickled. Subsequently, cold rolling was conducted so that the thickness of the sheet was 0.35 mm, followed by carrying out final annealing at 1,050° C. for 38 sec.
The size and distribution density of inclusions of respective sheets, the core loss, the magnetic flux density and hardness were measured. The results are shown in Table 4 below. A sample for observing the inclusions was manufactured using a replica method that is typical in the steel industry, and a transmission electron microscope was used therefor. As such, the acceleration voltage of 200 kV was applied.
As is apparent from Table 4, steels B1, B4, B5, B7, B9, B10, B13 and B14 were inventive examples that satisfy Condition, wherein coarse composite inclusions having a size of 300 nm or more were observed, and the distribution density thereof was greater than 0.02(1/mm2) thus manifesting excellent magnetic properties. The hardness was low thus obtaining superior productivity and customer punchability.
However in steels B3, B6, B11 and B15, N+S fell outside Condition, and thus inclusions having a size of 300 nm or more were not observed, and core loss and magnetic flux density were deteriorated. Also in steel B8, Al+Mn fell outside Condition, and in steel B12, the ratio of (Al+Mn)/(N+S) fell outside Condition, and thus inclusions having a size of 300 nm or more were not observed, and core loss and magnetic flux density were deteriorated.
Example 3Vacuum melting was performed in a laboratory, thus preparing steel ingots having the components shown in Table 5 below. As such, 0.3˜0.5% of Al was added to molten steel to facilitate the formation of inclusions, after which the remainder of Al, and Si, Mn and P were added thus making steel ingots. Each of the ingots was heated to 1,150° C., and finish hot rolled at 850° C. thus manufacturing a hot rolled sheet having a thickness of 2.0 mm. The hot rolled sheet was annealed at 1,050° C. for 4 min and then pickled. Subsequently, cold rolling was conducted so as to form sheets having different thicknesses in the range of 0.15˜0.35 mm, followed by carrying out final annealing at 1,050° C. for 38 sec. The core loss and magnetic flux density of respective sheets having different thicknesses were measured. The results are shown in Table 6 below. A sample for observing the inclusions was manufactured using a replica method that is typical in the steel industry, and a transmission electron microscope was used therefor. As such, the acceleration voltage of 200 kV was applied.
As is apparent from Table 6, steels C2˜C4, C6, C7 were inventive examples that satisfy Condition, wherein the magnetic flux density was high and the core loss was low. This is considered to be because the composition according to the present invention had coarsely grown inclusions and the distribution density of coarse composite inclusions was greater than 0.02(1/mm2), and also the texture was stable. The radio-frequency core loss (W10/400) is surely correlated with the thickness of steel sheet. Specifically, as the thickness of the steel sheet decreases, the properties thereof may be improved. Compared to the steel sheet having a thickness of 0.35 mm, the core loss of the steel sheet having a thickness of 0.15 mm was improved by about 50%. In steel C1, Al/Mn did not satisfy Condition, and thus core loss (W10/400) and magnetic flux density (B50) were deteriorated.
Example 4Vacuum melting was performed in a laboratory, thus preparing steel ingots having the components shown in Table 7 below. As such, 0.3˜0.5% of Al was added to molten steel to facilitate the formation of inclusions, after which the remainder of Al, and Si, Mn and P were added thus making steel ingots. Each of the ingots was heated to 1,150° C., and finish hot rolled at 850° C. thus manufacturing a hot rolled sheet having a thickness of 2.0 mm. The hot rolled sheet was annealed at 1,050° C. for 4 min and then pickled. Subsequently, cold rolling was conducted so that the thickness of the sheet was 0.35 mm, followed by carrying out final annealing at 1,050° C. for 38 sec.
The size and distribution density of inclusions of respective sheets, the core loss, the magnetic flux density, the Erichsen number and hardness were measured. The results are shown in Table 8 below. A sample for observing the inclusions was manufactured using a replica method that is typical in the steel industry, and a transmission electron microscope was used therefor. As such, the acceleration voltage of 200 kV was applied.
While the welding part of the hot rolled sheet was pushed-up using a steel ball having a diameter of 20 mm at room temperature, the height until the sheet broken was determined, which is referred to as the Erichsen number. The case where the Erichsen number is typically 5 mm or more makes it possible to produce continuous lines via welding of the same species.
As is apparent from Table 8, steels D2˜6, D8˜12, D15 and D17 were inventive examples which satisfy Condition and in which 0.005˜0.2% of Sn or 0.005˜0.1% of Sb is added, and thus, the distribution density of coarse inclusions having a size of 300 nm or more was greater than 0.02(1/mm2), and upon final annealing, the oxide layer and the nitride layer of the surface were reduced thus improving core loss and magnetic flux density. Also, the Erichsen number was high and the Vickers hardness (Hv1) was low, thus exhibiting superior weldability, productivity and customer punchability.
Whereas in steel D1, the ratio of Al/Si fell outside Condition, and thus inclusions having a size of 300 nm or more were not observed, and core loss and magnetic flux density were deteriorated. Also because Sn and Sb were not added, the Erichsen number was low and weldability was decreased and hardness was high undesirably deteriorating processability.
Example 5Vacuum melting was performed in a laboratory, thus preparing steel ingots having the components shown in Table 9 below. As such, 0.3˜0.5% of Al was added to molten steel to facilitate the formation of inclusions, after which the remainder of Al, and Si and Mn were added thus making steel ingots. Each of the ingots was heated to 1,150° C., and finish hot rolled at 850° C. thus manufacturing a hot rolled sheet having a thickness of 2.3 mm. The hot rolled sheet was annealed at 1,050° C. for 4 min and then pickled. Subsequently, cold rolling was conducted so that the thickness of the sheet was 0.50 mm, followed by carrying out final annealing at 900° C. for 30 sec.
The size and distribution density of inclusions of respective sheets, the core loss, the magnetic flux density and hardness were measured. The results are shown in Table 10 below. A sample for observing the inclusions was manufactured using a replica method that is typical in the steel industry, and a transmission electron microscope was used therefor. As such, the acceleration voltage of 200 kV was applied.
As is apparent from Table 10, steels E2, E3, E6, E16, E20 and E21 were inventive examples that satisfy Condition, wherein the coarse inclusions having a size of 300 nm or more were observed, and the distribution density thereof was greater than 0.02(1/mm2) thus exhibiting superior magnetic properties, and the Vickers hardness (Hv1) was 140 or less, resulting in good productivity and customer punchability.
Whereas in steels E4, E5, E9, E11, E14, E15 and E19, the ratio of Al/Mn and the amount of Al+Mn fell outside Condition and thus inclusions having a size of 300 nm or more were not observed, and core loss and magnetic flux density were deteriorated.
Example 6Vacuum melting was performed in a laboratory, thus preparing steel ingots having the components shown in Table 11 below. As such, 0.3˜0.5% of Al was added to molten steel to facilitate the formation of inclusions, after which the remainder of Al, and Si and Mn were added thus making steel ingots. Each of the ingots was heated to 1,150° C., and finish hot rolled at 850° C. thus manufacturing a hot rolled sheet having a thickness of 2.3 mm. The hot rolled sheet was annealed at 1,050° C. for 4 min and then pickled. Subsequently, cold rolling was conducted so that the thickness of the sheet was 0.50 mm, followed by carrying out final annealing at 900° C. for 30 sec.
The size and distribution density of inclusions of respective sheets, the core loss, the magnetic flux density and hardness were measured. The results are shown in Table 12 below. A sample for observing the inclusions was manufactured using a replica method that is typical in the steel industry, and a transmission electron microscope was used therefor. As such, the acceleration voltage of 200 kV was applied.
As is apparent from Table 12, steels F1, F4, F6, F8, F9, F11 and F12 were inventive examples that satisfy Condition, wherein the coarse inclusions having a size of 300 nm or more were observed, and the distribution density thereof was greater than 0.02(1/mm2) thus exhibiting superior magnetic properties, and hardness was low, resulting in good productivity and customer punchability.
Whereas in steels F5, F10 and F13, the amount of N+S fell outside Condition and thus inclusions having a size of 300 nm or more were not observed, and core loss and magnetic flux density were deteriorated.
Example 7Vacuum melting was performed in a laboratory, thus preparing steel ingots having the components shown in Table 13 below. As such, 0.3˜0.5% of Al was added to molten steel to facilitate the formation of inclusions, after which the remainder of Al, and Si and Mn were added thus making steel ingots. Each of the ingots was heated to 1,150° C., and finish hot rolled at 850° C. thus manufacturing a hot rolled sheet having a thickness of 2.0 mm. The hot rolled sheet was annealed at 1,050° C. for 4 min and then pickled. Subsequently, cold rolling was conducted so that the thickness of the sheet was 0.35 mm, followed by carrying out final annealing at 1,050° C. for 38 sec.
The size and distribution density of inclusions of respective sheets, the core loss, the magnetic flux density and hardness were measured. The results are shown in Table 14 below. A sample for observing the inclusions was manufactured using a replica method that is typical in the steel industry, and a transmission electron microscope was used therefor. As such, the acceleration voltage of 200 kV was applied.
As is apparent from Table 14, steel G14 was inventive examples that satisfy Condition wherein the coarse inclusions having a size of 300 nm or more were observed, and the distribution density thereof was greater than 0.02(1/mm2) thus exhibiting superior magnetic properties, and the Vickers hardness was as low as 225 or less.
Whereas in steels G1, G8, G11 and G13, the amount of Al+Mn fell outside Condition and thus inclusions having a size of 300 nm or more were not observed, and core loss and magnetic flux density were deteriorated. In steel G7, Al/Si, Al/Mn, did not satisfy Condition, and thus inclusions having a size of 300 nm or more were not observed, and core loss and magnetic flux density were deteriorated. In steels G8 and G11, Al+Mn did not satisfy Condition, and thus hardness was high, thereby deteriorating productivity and punchability.
Claims
1. A non-oriented electrical steel, comprising 0.7˜2.5% of Al, 0.2˜2.5% of Si, 0.2˜1.5% of Mn, 0.0005˜0.004% of N, 0.0005˜0.004% of S, 0.003% or less of C, and a balance of Fe and other inevitable impurities by wt %, and satisfying the conditions below:
- Conditions:
- 1≤{[Al]+[Mn]}≤3.5
- 0.002≤{[N]+[S]}≤0.006,
- 250≤{([Al]+[Mn])/([N]+[S])}≤1,400,
- 1.4≤{[Al]+[Si]+[Mn]/2}≤5.5,
- 1≤[Al]/[Si]≤7.5, and
- 1≤[Al]/[Mn]≤3.7,
- wherein [Al], [Si], [Mn], [N] and [S] indicate amounts (wt %) of Al, Si, Mn, N and S, respectively.
2. The non-oriented electrical steel sheet of claim 1, further comprising 0.2% or less of P.
3. The non-oriented electrical steel sheet of claim 1, further comprising at least one of 0.005˜0.2% of Sn and 0.005˜0.1% of Sb.
4. The non-oriented electrical steel sheet of claim 1, further comprising 0.004% or less of Ti.
5. The non-oriented electrical steel sheet of claim 1, wherein an inclusion comprising a nitride and a sulfide alone or a combination thereof is formed in the steel sheet.
6. The non-oriented electrical steel sheet of claim 5, wherein the nitride comprises aluminum nitride and the sulfide comprises magnesium sulfide.
7. The non-oriented electrical steel sheet of claim 5, wherein the inclusion having an average size of 300 nm or more.
8. The non-oriented electrical steel sheet of claim 5, wherein a distribution density of the inclusion having a size of 300 nm or more is equal to or greater than 0.02 number/mm2.
9. The non-oriented electrical steel sheet of claim 1, wherein a cross-sectional Vickers hardness (Hv1) is 190 or less.
Type: Application
Filed: Apr 6, 2018
Publication Date: Aug 9, 2018
Inventors: Jae-Hoon Kim (Pohang-si), Jae-Kwan Kim (Pohang-si), Yong-Soo Kim (Pohang-si), Won-Seog Bong (Pohang-si)
Application Number: 15/947,340
