RU2398894C1 - Sheet of high strength electro-technical steel and procedure for its production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: sheet is produced out of steel containing wt %, C- 0.060 or less, Si - from 0.2 to 6.5, Mn - from 0.05 to 3.0, P - 0.30 or less, S or Se - 0.040 or less, Al - 2.50 or less and N - 0.040 or less, not necessarily - one or more ingredients additionally from group: Cu - from 0.001 to 30.0, Nb - from 0.03 to 8.0, Ti - 1.0 or less, V - 1.0 or less, Zr - 1.0 or less, B - 0.010 or less, Ni - 15.0 or less, Cr - 15.0 or less, Bi, Mo, W, Sn, Sb, Mg, Ca, Ce, La, and Co - in sum 0.5 or less, Fe - the rest and unavoidable impurities, and with deformed structures left inside steel sheet. The procedure consists in a stage of production of average dimension of d crystal grain in a steel sheet directly before the stage of forming deformed structures left in the steeel sheet with dimension 20 micro-metres or bigger.

EFFECT: production of sheet with tensile strength 500 MPA or more, of high wear resistance and super magnetic properties.

11 cl, 3 ex, 4 tbl, 1 dwg

Description

FIELD OF THE INVENTION

The present invention relates to a sheet of high strength electrical steel, and more particularly to a sheet of high strength non-textured electrical steel, and relates to magnetic material for a high speed rotary machine with low steel loss, high magnetic induction and high strength, magnetic material for an electromagnetic switch, excellent in wear resistance , and the method of its production.

State of the art

In the past, a laminated sheet of electrical steel was used as a material for rotors, but recently, in applications where high speed rotation and a larger rotor size are required, there is a chance that the centrifugal force exerted on the rotors will exceed the strength of electrical steel sheets. In addition, there are also many electric motors with structures in which magnets are built into the rotors. Even if the rotation speed is not so high, the load applied to the rotor material itself becomes large during rotation of the rotor. And in terms of fatigue strength, material strength also becomes a problem in an increasing number of cases.

In addition, electromagnetic switches wear on contact surfaces when used, thus requiring a magnetic material that is excellent not only in its electromagnetic properties, but also in its wear resistance.

To meet these needs, a sheet of high-strength, non-textured electrical steel has recently been studied and several suggestions have been made. For example, Japanese Patent Publication (A) No. 1-162748 and Japanese Patent Publication (A) No. 61-84360 suggest using a slab with a high Si content and, in addition, containing one or more elements from among Mn, Ni, Mo , Cr, and other solid solution hardening ingredients, but sheet rolling often occurs during rolling. This causes a decrease in productivity and a decrease in the yield of finished products, so there is still room for improvement. In addition, since Ni, Mo, and Cr are introduced in large quantities, the material becomes extremely expensive. Japanese Patent Publication (A) No. 2005-113185 and Japanese Patent Publication (A) No. 2006-070348 disclose a non-textured electrical steel sheet in which deformed structures are retained, while Japanese Patent Publication (A) No. 2006-009048 and Japanese Patent Publication (A) No. 2006-070296 discloses a sheet of non-textured electrical steel in which Nb, etc., is further included in the solid solution. to suppress recrystallization. However, they do not pay much attention to the size of the crystalline grain before the formation of deformed structures, thus there is the problem that stable losses in steel cannot be obtained.

In addition, Japanese Patent Publication (A) No. 2004-84053 and Japanese Patent Publication (A) No. 2004-99926 disclose a technology related to an electrical steel sheet including a large amount of copper, but due to the fact that the steel Cu phase precipitates; reduction of eddy current loss cannot be considered sufficient. There is room for improvement for applications where high-frequency characteristics become a problem.

Disclosure of invention

As explained above, various proposals have been made regarding a sheet of high-strength electrical steel, but in fact an industrially stable production using conventional plants for the production of electrical steel sheet while ensuring the necessary magnetic properties has not yet been achieved. The inventors earlier in the Japanese patent application, having the number 2003-347084, filed an application relating to a sheet of high-strength electrical steel with deformed structures left.

This technology was created on the basis of the fact that, even if deformed structures are left in the crystal structure, the magnetic properties do not deteriorate so much that, if we consider the effect on the increase in strength, the result is in no way worse than that of a material hardened by traditional elements of solid solution or precipitated phases, and not only this, if we consider the performance and planar anisotropy of magnetic properties, in particular magnetic induction, this is an extremely useful technology. However, a clear picture of metallurgy with regard to how to improve the balance of magnetic properties and mechanical properties for a sheet of electrical steel having deformed structures has not been established. In this regard, no evidence has been obtained that this technology is optimal.

The inventors participated in detailed experiments clarifying this aspect, in particular regarding the effects of influences exerted by the structure before rolling, and found that in the sheet of electrical steel having deformed structures there is an optimal region for achieving both good magnetic properties and mechanical properties, and, therefore, have succeeded in establishing an industrially optimal range taking into account further productivity, in particular machinability of steel strips.

The present invention has as its objective a stable computer-controlled production of a sheet of high-strength non-textured electrical steel having high strength: tensile strength (TS) of, for example, 500 MPA or more, and wear resistance, and having excellent magnetic properties: magnetic induction (B50), losses in steel, etc., especially when used in conditions of a high-frequency magnetic field, such as in an electric motor rotating at a high speed, without, for example, It’s about cold rolling, annealing operation efficiency, etc. from an ordinary sheet of electrical steel. The present invention was made in order to solve the above problem, and has as its essence the following:

(1) A method for producing a sheet of high strength electrical steel containing, in weight percent, C: 0.060% or less, Si: 0.2 to 6.5%, Mn: 0.05 to 3.0%, P: 0 , 30% or less, S or Se: 0.040% or less, Al: 2.50% or less and N: 0.040% or less, the rest is Fe and unavoidable impurities, and having deformed structures remaining inside the steel sheet, wherein The method for producing a sheet of high-strength electrical steel is characterized by a stage in which the average size d of the crystalline grain of the steel sheet is made immediately before the stage of processing mations deformed structures which ultimately must remain in the steel sheet components 20 micrometers or more.

(2) A method for producing a sheet of high-strength electrical steel containing, in weight percent, C: 0.060% or less, Si: 0.2 to 6.5%, Mn: 0.05 to 3.0%, P: 0 , 30% or less, S or Se: 0.040% or less, Al: 2.50% or less and N: 0.040% or less, the rest is Fe and unavoidable impurities, and having deformed structures remaining inside the steel sheet, wherein The method for producing a sheet of high-strength electrical steel is characterized by a stage in which the average size d (in micrometers) of the crystalline grain of the steel sheet is directly Ed formation step deformed structures which ultimately must remain inside the steel sheet constituting d≥ (220-50 × Si% -50 × Al%).

(3) A method for producing a sheet of high-strength electrical steel as set forth in paragraph (1) or (2), characterized in that the average size d (in micrometers) of the crystalline grain of the steel sheet is made immediately before the stage of formation of deformed structures, which ultimately must remain inside the steel sheet, comprising:

d≤ (400-50 × Si%) and

d≤ (820-200 × Si%)

(4) A method for producing a sheet of high-strength electrical steel, as set forth in any one of paragraphs (1) to (3), characterized by the stage at which the degree of recrystallization of the steel sheet is made immediately before the stage of formation of deformed structures, which, ultimately, must remain inside a steel sheet constituting 50% or more.

(5) A method for producing a sheet of high-strength electrical steel as set forth in any one of paragraphs (1) to (4), characterized in that the steel ingredients further comprise, in mass percent, one or both of the following: Cu: from 0.001 to 30.0% and Nb: 0.03 to 8.0%.

(6) A method for producing a sheet of high-strength electrical steel as set forth in any one of paragraphs (1) to (5), characterized in that the steel ingredients further comprise, in mass percent, one or more types of ingredients from: Ti: 1, 0% or less, V: 1.0% or less, Zr: 1.0% or less, B: 0.010% or less, Ni: 15.0% or less, and Cr: 15.0% or less.

(7) A method for producing a sheet of high-strength electrical steel, as set forth in any one of paragraphs (1) to (6), characterized in that the steel ingredients additionally contain, in mass percent, one or more types of ingredients from among: Bi, Mo, W, Sn, Sb, Mg, Ca, Ce, La, and Co — a total of 0.5% or less.

(8) A method of manufacturing a sheet of high-strength electrical steel, as set forth in any one of paragraphs (1) to (7), characterized in that the deformed structures present inside the steel sheet occupy 1% or more in relative area, if we consider its cross section .

(9) A method for producing a sheet of high-strength electrical steel as set forth in any one of paragraphs (1) to (8), characterized in that the average dislocation density in the deformed structures inside the steel sheet is 1 × 10 ¹³ / m ² or more.

(10) The high-strength electrical steel sheet described in paragraphs (1) to (9), characterized in that it is the only ferrite phase in the temperature range from room temperature to 1150 ° C and satisfies, in mass percent, the following ratio,

980-400 × C + 50 × Si-30 × Mn + 400 × P + 100 × Al-20 × Cu-15 × Ni-10 × Cr> 900

(11) The high-strength electrical steel sheet described in paragraph (10), characterized in that in order to make a tensile strength of 100 MPA or more, heat treatment is used at 450 ° C. for 30 minutes.

(12) A method for producing a sheet of high-strength electrical steel, characterized by the production of a steel sheet described in paragraph (10), during which the steps are performed in which the final heat treatment is performed after cold rolling, heat treatment in which the sheet is held in a temperature range of 800 ° C or more for 5 seconds or more and do not allow the formation of an austenitic phase in the steel material even at the maximum temperature in this heat treatment.

(13) A method of manufacturing a sheet of high-strength electrical steel, characterized in the production of a steel sheet described in paragraph (10), during which the cooling step is performed after holding the sheet in a temperature region of 800 ° C or more for 5 seconds or more, cooling at a cooling rate component 40 ° C / sec or more up to 300 ° C or less.

(14) A method for producing a sheet of high-strength electrical steel described in paragraph (10), characterized in a step in which the residence time of the sheet in the range from 700 to 400 ° C. at said cooling step is 5 seconds or less.

Brief Description of the Drawings

The drawing is a view showing a balance of "strength - loss in steel", depending on the grain size before processing.

The implementation of the invention

To solve this problem, the inventors took part in various experiments and studies. Thus, the present invention provides a steel sheet containing C: 0.060% or less, Si: 0.5 to 6.5%, Mn: 0.05 to 3.0%, P: 0.30% or less, S or Se: 0.040% or less, Al: 2.50% or less, and N: 0.040% or less, and further comprising, as required, one or both of Cu elements: from 0.001 to 30.0 % and Nb: from 0.05 to 8.0%, while (1) to increase the strength, the structure of the steel sheet is endowed with deformed structures and dislocation hardening is used, (2) the crystal structure immediately before the formation of deformed structures which ultimately remain in the steel sheet are subjected to grain coarsening, and (3) the aforementioned crystal structure is limited in terms of the amount of Si, which improves machinability, so that a sheet of electrical steel is provided in which deformed structures are left and formed while the balance of strength and magnetic properties is improved at high performance without causing a decrease in performance, etc.

Ingredients Composition

First, the composition of the ingredients of a high-strength electrical steel sheet according to the present invention will be considered.

C causes a deterioration in magnetic properties, therefore its content is made 0.060% or less. On the other hand, it effectively affects the improvement of texture and has an effect that suppresses the development of the {111} orientation, which is not preferable for magnetic properties, and contributes to the development of the preferred {110}, {100}, {114} and other orientations. In addition, from the point of view of increasing the strength, in particular, increasing the yield strength, increasing the thermal strength and the creep limit and improving the characteristics of warm fatigue, in the case of niobium-containing steel due to the effect of retardation of recrystallization by NbC, it is preferable that this content is from 0.0031 to 0.0301%, more preferably from 0.0051 to 0.0221%, more preferably from 0.0071 to 0.0181%, more preferably from 0.0081 to 0.0151%.

When such an effect of C described above is especially pronounced or when the issue of magnetic aging is especially acute, from the point of view of deoxidation efficiency, a higher content of C can be introduced to the slab stage and the amount of C can be reduced by decarburization annealing after the formation of the roll. Reducing the content to 0.010% or so or less, from the point of view of production costs, it is advantageous to reduce the amount of C through degassing plants at the stage of molten steel. In particular, if it is made 0.0020% o or less, then there is a remarkable effect of reducing losses in steel. In the steel of the invention, which does not require, to increase the strength of carbides or other non-metallic precipitated phases, even 0.0015% or less make it possible to increase the strength, while additionally even 0.0010% or less make it possible to sufficiently increase the strength.

Si increases the intrinsic resistance of steel, reducing eddy currents and reducing losses in steel, and increases the tensile strength, but if the input amount is less than 0.2%, this effect is small. Preferably, this content is 1.0% or more, more preferably 1.5% or more, more preferably 2.0% or more, more preferably 2.5% or more. In general, when used under conditions of a high-frequency magnetic field, the losses due to eddy currents become larger, but even in the steel according to the invention containing deformed structures, in order to suppress this loss from eddy currents, it is useful to increase the Si content. However, if it is more than 6.5%, the steel becomes noticeably brittle. Further reducing the magnetic induction of the product, this content is made 6.5% or less, preferably 4.0% or less. The optimum range of amounts of Si, which is explained above, is also determined taking into account the crystal structure immediately before the formation of deformed structures, which, ultimately, must remain in the steel sheet, an important factor of the present invention. Given this crystalline structure, in order to reduce concerns regarding brittleness, 3.7% or less is preferred. If 3.2% or less, while there is also an equilibrium with the number of other elements, it will no longer be necessary to take fragility into account at all. In addition, this content can be made less than 2.0%, less than 1.5% and less than 1.0%.

Note that in the case of using the Cu, Si solid solution explained below, it is effective for suppressing the formation of the austenitic phase at high temperature, stabilizing the ferrite phase even at high temperature, and makes the effect of reducing eddy current losses through Cu solid solution noticeable, but with an input amount of less than 1.5%, this effect is small. In particular, in steel with a low Si content, the effect of reducing eddy current losses through solid solution C tends to become weaker, so that it is preferable that Si is 2.1% or more, more preferably 2.6% or more.

Mn can be directly introduced in order to increase the strength of the steel, but is not particularly required for the purposes of the steel of the present invention using deformed structures as the main means of increasing strength. It is introduced in order to increase its own resistance or increase the amount of sulfides and promote the growth of crystalline grain and, thus, reduce eddy current losses and steel losses, but its excessive introduction not only causes a decrease in magnetic induction, but also contributes to the formation of an austenitic phase during high temperature, so that its content is made from 0.05 to 3.0%, preferably from 0.5% to 2.5%, preferably from 0.5% to 2.0%, more preferably from 0, 8% to 1.2%.

P is an element that has a remarkable effect on tensile strength and contributes to the stabilization of the ferrite phase at high temperature, but in the same way as the aforementioned Mn, its introduction is not really required in the steel of the present invention. If it is more than 0.3%, then the brittleness becomes large and industrially performed hot rolling, cold rolling and other processing became difficult, so the upper limit is made 0.30%. Preferably, the amount is 0.20% about or less, more preferably 0.15% or less.

S easily forms a bond with Cu, introduced in the steels according to the invention in accordance with need, affects the behavior during the formation of the metal phase, mainly consisting of Cu, is important for the introduction of Cu and sometimes causes a decrease in strength characteristics, therefore, when introduced into large quantities require caution. In addition, depending on the heat treatment conditions, thin Cu sulfides can be formed directly and higher strengths can be promoted. The sulfides formed sometimes cause a deterioration in magnetic properties, in particular loss in steel. In particular, when the supported steel loss value is strictly set, it is preferable that the S content is low and limited to 0.040% or less. Preferably, the content is 0.020% or less, more preferably 0.010% or less. Se also has essentially the same effect as S.

Al is usually introduced as a deoxidizer, but the introduction of Al can be reduced and used to deoxidize Si. In steel deoxidized by Si with an Al amount of 0.005% or so or less, AlN is not formed, so this also has the effect of reducing steel loss. On the contrary, it is also possible to directly introduce it in order to promote the growth of AlN grains and use the increase in intrinsic resistance in order to reduce steel losses, but if it is more than 2.50%, it becomes a problem of brittleness, so that the content is made from 2.50% to less than 2.0% or less than 1.8%.

Note that when using Cu solid solution as a strengthening element, from the point of deoxidation and the formation of nitrides, Al solid solution is directly introduced in order to stabilize the ferrite phase at high temperature and suppress eddy current losses due to an increase in electric resistance. In addition, it also has the effect of contributing to the remarkable effect of reducing eddy current losses through Cu solid solution. In the same manner as in the case of Si, it is preferable to introduce it directly. Preferably, the content is 0.3% or more, more preferably 0.6% or more, more preferably 1.1% or more, more preferably 1.6% or more, more preferably 2.1% or more. However, if it is more than 2.50%, then fluidity and brittleness become problems, so that the content is made 2.50% or less.

N, like C, causes a deterioration in magnetic properties, so that its content is made 0.040% or less. In steel deoxidized by Si with an Al content of 0.005% or so or less, like C, it is an element having the effects of increasing strength, in particular, increasing yield strength, improving thermal strength and creep strength, and improving the characteristics of warm fatigue, and in the case of niobium-containing steel - retardation of recrystallization by NbN, and also effective in terms of improving the structure. From this point of view, it is preferable that this content is from 0.0031 to 0.0301%, more preferably from 0.0051 to 0.0221%, more preferably from 0.0061 to 0.0200%, more preferably from 0.0081 to 0.0151%. When Al is 0.010% or so or more, the introduction of a large amount of N makes it possible to form thin AlN and enhance the effect of retardation of recrystallization, but the efficiency of retardation of recrystallization is low, and the harmful effect on magnetic properties is also relatively large, so there is a real need for introducing this item is missing. In steel deoxidized by Al, N must be 0.0040% or less. When no increase in strength is required due to nitrides or the effect of retardation of recrystallization, it is preferable that the N content be as low as possible. If it is made 0.0027% or less, the effect of suppressing magnetic aging or deterioration of AlN characteristics in aluminum-containing steel is noticeable. More preferably, this content is 0.0022%, more preferably 0.0015% or less.

Cu is introduced in the present invention according to need. Cu, if present in the form of a solid solution of Cu, has the effect of increasing the degree of recrystallization of the steel sheet and slowing down the recrystallization of the steel sheet. When hardening the preform of the present invention, such an effect appears from 0.001% or so. Depending on the amount of impurities, this effect of Cu can be obtained without even directly introducing Cu, but it is preferable to make the Cu content of 0.002% or more, 0.003% or more, 0.005% or more, 0.007% or more, 0.01% or more, 0.02% or more, 0.03% or more, 0.04% or more, 0.05% or more, in addition, 0.1% or more, 0.5% or more, 1.0 % or more, or 2.0% or more. In this case, the effect is more pronounced. If the Cu content is low, then the effect of retardation of recrystallization becomes small, the heat treatment conditions to obtain the effect of retardation of recrystallization are limited to a narrow range, and in some cases the freedom to control the conditions of production and adjust production is reduced. On the other hand, if the Cu content is excessively high, the effect on the magnetic properties becomes large, and, in particular, in some cases, the increase in steel loss becomes noticeable, so that the upper limit from this point of view is 8.0%, particularly preferably 5.5% or less. From a cost point of view, the introduction of this content can be made less than 0.1%, in addition, less than 0.01.

In traditional steel, in the region of such a low content of Cu, almost no influence of Cu is noticeable, but in the steel of the present invention, even with such a small amount of Cu, a good effect on improving the balance "yield strength - loss in steel" is seen. This mechanism is not clear, but is believed to be as follows. It can be said that the high density dislocations present in steel, such as the steel of the invention, are necessary to provide strength and at least to increase the loss in steel. The increase in yield strength is associated with the interaction between the dislocations remaining in the steel and the dislocations reintroduced during the deformation of the steel sheet, and the ease of activity of the dislocations remaining in the steel. The stronger the interactions or the activity of existing dislocations is hindered, the more the yield strength increases. On the other hand, losses in steel are associated with the interaction between the dislocations remaining in the steel and the domain walls moving during the application of a magnetic field. The smaller this interaction, the more the increase in steel loss is suppressed. As a result, the interaction with dislocations becomes larger (or the remaining dislocations themselves become less active). If there remains a large number of dislocations with little interaction with the domain walls, then the balance of "yield strength - loss in steel" improves. The magnitude of the interaction is generally considered to be related to the stress fields around the dislocations (with the deformation of the crystal lattice). It is believed that a small amount of Cu is released around the remaining dislocations and forms stress fields that are optimal for improving the "yield strength - steel loss" balance, preferred dislocations selectively propagate during the formation of the remaining dislocations, or preferred dislocations are selectively forced to remain in the annealing process. At what stage the influence of a small amount of Cu is manifested is not clear, but the change in the stress field caused by the difference in the atomic radius between Cu and Fe can be called one factor.

On the other hand, the inventors have already filed an application for a technology to form a metal phase in a sheet of electrical steel, mainly consisting of Cu (hereinafter referred to as the “metal phase of Cu”), in order to try to achieve a higher durability. When it comes to the phase of the Cu metal, the combination with this application in no way detracts from the results of the present invention. Preferably, although not a particular limitation, the size of the phase of the Cu metal or precipitated Nb phases present in the steel of the invention is 0.20 micrometers or less. If the size exceeds this, then the efficiency of slowing down the recrystallization decreases, a large amount of the metal phase becomes necessary and also the harmful effect on the magnetic properties easily becomes large. In addition, although not by way of particular limitation, the numerically expressed density of the phase of the Cu metal or the precipitated Nb phases is limited by the range suitable due to the content of Cu, Nb or C and the size of the precipitated phase, it is desirable that it is 20 / micrometers ³ or more or so. This effect is achieved in the aforementioned concentration range of Cu.

In addition, when using the Cu solid solution explained below as a reinforcing element, the range of Cu content to achieve good high-frequency properties can be made from 2.0 to 30.0%. If the Cu content is low, then the effect of reducing eddy current loss becomes small. On the other hand, if the Cu content is too high, then suppressing the creation of metal phases, consisting mainly of Cu, becomes difficult, and the effect of reducing eddy current losses becomes smaller. In addition, when relatively large phases of the Cu metal are formed, the hysteresis losses tend to increase significantly, and cracks and defects in the steel sheet during rolling tend to deteriorate.

Therefore, it is preferable that the Cu content in this case is 2.1% or more, more preferably 2.6% or more, more preferably 3.1% or more, more preferably 3.6% or more, more preferably - 4.1% or more, more preferably 4.6% or more. Preferably, the upper limit, taking into account also the cost of introducing Cu itself and the cost of introducing Ni, introduced in order to suppress surface defects during hot rolling caused by Cu (Cu defects), is 20.0%, more preferably 15.0%, more preferably 12.0%, more preferably 10.0%. Note that if Cu, introduced in this case into a steel with a high Si content, is in a solid solution state, then it will not cause brittleness of the steel or a deterioration in cold rolling like Si or Al. Rather, it will have a beneficial effect on suppressing brittleness caused by Si, etc. In addition, it does not cause a significant deterioration in magnetic induction, like Cr mentioned below, and has a small detrimental effect, even when introduced in a relatively large amount.

Nb in the present invention is administered as required. Depending on the amounts of C, N, and S contained, it forms large quantities of carbides, nitrides, sulfides, and other thin precipitated phases in the steel sheet and causes an alternative deterioration in steel losses, contributes to the growth of the {111} texture after cold rolling and annealing, and reduces magnetic induction, so it should not actually be introduced into the steel of the present invention. For this reason, when the upper limit of Nb is set to 8% or less, preferably 0.02% or less, more preferably 0.0050% or less, even more preferably 0.0030% or less, it becomes possible to obtain good steel losses.

However, Nb carbides and nitrides (hereinafter referred to as "precipitated Nb phases" in this description) have an effect of slowing down the recrystallization of the steel sheet, so that this can be actively used in the present invention. In addition, the thin precipitated Nb phases also have the effect of increasing strength in a range that does not adversely affect magnetic properties. In addition, Nb can also be used for hardening as a solid solution of Nb. This range is limited to a range of 0.05 to 8.0%. Preferably, this content is from 0.08 to 2.0%.

In addition to this, almost all the elements used to increase the strength of a sheet of high-strength electrical steel in the prior art are considered not only as representing problems in terms of the cost of their introduction, but also have some harmful effect on the magnetic properties, so that really should not be introduced. When introduced directly, based on the balance of the effect of slowing down recrystallization, the effect of increasing strength, increasing costs and deteriorating magnetic properties, one or more elements from among Ti, Zr, V, B, Ni and Cr are added, but the amounts entered are made as follows: Ti: 1.0% or less; Zr: 1.0% or less; V: 1.0% or less; B: 0.010% or less; Ni: 15.0% or less; and Cr: 15.0% or less.

Ti, Zr, and V are elements that form thin precipitated phases of carbides, nitrides, sulfides, etc. in the steel sheet. and also have the effect of increasing strength, but compared to Nb, these effects are small, although the tendency to cause a deterioration in steel losses is stronger. In addition, when a partial recrystallized structure is formed during the annealing stage after cold rolling, there is a strong alignment stimulation effect in the {111} orientation, which is unfavorable for improving magnetic induction, so that they could become harmful elements in the steel of the present invention. For this reason, if hardening by precipitated phases is not intended, it is preferable to make this content 1.0% or less. By making the content preferably 0.50% or less, more preferably 0.30% or less, even more preferably 0.010% or less, in addition, 0.0050% or less, good steel losses can be obtained.

Note that in the present invention, the release of Nb, Zr, Ti, V and other carbide, nitride, and sulfide-forming elements should be prevented, provided that the above-explained effects from the isolation of these elements are not used. The content of Nb + Zr + Ti + V is less than 0.1%, preferably less than 0.08%, more preferably 0.002 to 0.05%.

B is released at the boundaries of crystalline grains and has the effect of suppressing brittleness caused by the release of P along the grain boundaries, but in the steel of the present invention, brittleness is not a particular problem, as is the case with a sheet of traditional hardened, mainly by means of a solid solution of high-strength electrical steel, that an introduction for this purpose is not important. Rather, 0.0002% or more should be introduced in order to retard recrystallization caused by the effects of solid solution B on the degree of recrystallization. If more than 0.010% is introduced, then noticeable brittleness occurs, so that an upper limit of 0.010% is made.

Ni is also recognized to have an effect of increasing the degree of recrystallization when it contains from about 0.001%. Even with a content of 0.01% or less, it has a certain effect on fixing dislocations, but is preferably contained in amounts of 0.05%, 0.1%, 0.5%, 1.0%, 2.0% or, in addition , 3.0%, due to which its effects are more pronounced. In addition, it is known that Ni is effective in preventing surface defects during hot rolling caused by Cu as an element driven in accordance with the need for steel of the invention (Cu defects). And for this purpose, it can also be entered directly. In addition, its harmful effects on magnetic properties are relatively small and it has the effect of improving magnetic induction and, in addition, is recognized as effective for increasing strength, so it is an element often used in high-strength electrical steel sheet. When using Ni in order to prevent Cu defects, it is introduced in the order of a crude standard in an amount of from 1/8 to 1/2 or so on the amount of Cu.

When using Cu solid solution to increase strength, as explained below, the introduction of Ni in the composition of the composition demonstrated a noticeable effect of reducing eddy current losses, which was never noted in the past. The reason for this is not clear, but it could be the influence of the positions occupied by the Cu solid solution and the Ni solid solution in the Fe crystal lattice, and to some extent the formation of a regular lattice related to Ni and Cu.

In addition, Ni is also effective in improving corrosion resistance, but given the cost of introduction and the detrimental effect on magnetic properties, it is preferable to make an upper limit of 15%, in addition, 10%, in addition, and in addition to this, 5.0%.

Cr is an element introduced to improve corrosion resistance and improve magnetic properties in the high frequency range, but here, given the cost of introduction and the harmful effects on magnetic properties, it is preferable to make an upper limit of 15.0%.

In particular, when using a solid solution of Cu, as explained below, these functions are sufficiently performed by Cu (or other elements such as Ni), so that there is no need to introduce Cr for this purpose. When using a solid solution, Cu Cr is rather introduced in order to regulate the stability of the ferritic phase at high temperature, but the decrease in magnetic induction caused by this introduction is noticeable, and this element is likely to be harmful. In addition, the effect of reducing eddy current losses caused by the Cu solid solution is noticeably pronounced in steel with a low Cr content, so that if there is no kind of need, Cr is preferably not introduced. The reason is not clear, but this effect of Cu solid solution is believed to become noticeable due to the interaction not only with the aforementioned Si, Al and Ni, but also other elements, including Cr. From this point of view, also taking into account the cost of introduction, the upper limit of the Cr content is 15%, preferably 8.0%, more preferably 4.9%, more preferably 2.9%, more preferably 1.9%, more preferably 0.9% and more preferably 0.4%.

In addition, with regard to other elements with a negligible amount in addition to quantities inevitably transferred from ore, scrap, etc., even if they are introduced by various known methods, the result of the present invention is in no way violated. In addition, even if their amounts are small, they are elements that form thin carbides, sulfides, nitrides, oxides, etc. and showing not insignificant effects of slowing down recrystallization or increasing strength, but these thin precipitated phases also have great harmful effects on magnetic properties. In addition, in the steel of the present invention, the residual deformed and reduced structures make it possible to obtain a sufficient effect of retarding crystallization, so that these elements should not actually be introduced.

The inevitable content of these elements with a negligible amount is usually 0.005% or less for each element, but also for various purposes not described in this description, it is possible to introduce 0.01% or so or more. And in this case, also, based on the balance with magnetic properties, the content of one or more types of elements from among Bi, Mo, W, Sn, Sb, Mg, Ca, Ce and Co is made up to a total of 0.5% or less.

Steel, including the above ingredients, is melted by the converter in the same way as a sheet of ordinary electrical steel, continuously cast into a slab, then hot rolled. The sheet subjected to hot rolling during annealing is annealed, subjected to cold rolling, final annealing, etc. The passage in addition to these stages of the stages of formation of an insulating coating or decarburization, etc. in no way detracts from the results of the present invention. In addition, there is also no problem even if the production is carried out not through the usual steps, but through the steps of producing the strip with rapid cooling and solidification, continuous casting of thin slabs without any hot rolling step, etc.

Deformed structures

In the present invention, it is necessary to form special structures in the steel sheet, referred to in the present invention as “deformed structures”. The "deformed structures" of the present invention are different from the "recrystallized structures" that make up almost the entire steel sheet in an ordinary sheet of electrical steel. In general, this refers to structures where the deformation accumulated in the steel sheet due to cold rolling, etc., has not completely disappeared. More specifically, during the annealing of the cold rolled steel sheet, structures with a cold rolling and containing a high dislocation density are invaded by structures with a low dislocation density formed when the steel is held at a high temperature during the annealing step (“recrystallized structures”), which leads to the progression of recrystallization. The areas into which these “recrystallized structures” do not intrude are defined as “deformed structures”. In deformed structures, generally speaking, during annealing, the dislocation density becomes lower due to the so-called “recovery”, etc., but does not become as low as in recrystallized structures. During the propagation of deformation, there is some inhomogeneous state between the "deformed structures" and the "recrystallized structures". In addition, "deformed structures" can be obtained by further processing of the recrystallized structures. In this case, when viewed as a whole, this state becomes a state in which a uniform deformation remains in the structure. In the present invention, deformed structures are used to achieve the desired higher strength.

Grain size before processing

Next, we will consider the average size d of the crystalline grain of the steel sheet immediately before the stage of formation of deformed structures, which, ultimately, must remain inside the steel sheet, which serve as a hallmark of the present invention. Below, this grain size will be referred to as the "grain size before processing." The present invention basically enlarges the "grain size before processing" in order to significantly improve the properties after processing, in particular the balance of "strength - loss in steel". The "grain size before processing" becomes the grain size at the time point of the hot rolled sheet when the cold rolled sheet is cold rolled, then recrystallization is suppressed during subsequent annealing in order to leave deformed structures in the final product. At this time, if the hot-rolled sheet is annealed, as is usually done in an electrical steel sheet, the grain size after the hot-rolled sheet is annealed becomes "grain size before processing." In addition, when the cold rolled steel sheet is again cold rolled and then recrystallized so as to leave deformed structures in the final product, this size becomes the grain size at the time of the annealed sheet. Further, when, for example, cold rolling of a sheet is carried out, then its cold rolling again while leaving the deformed structures at the annealing stage, the effect of processing by repeated cold rolling may be large, but the deformed structures formed during cold rolling will not disappear completely and will remain until the end of repeated cold rolling during repeated cold rolling, so that the grain size before cold rolling, that is, if we take the usual steps, the grain size of the hot rolled sheet becomes rum grain prior to processing. "

In the present invention, this “grain size before processing" d (in micrometers) is defined as a particular range in relation to the amount of Si and the amount of Al. Thus, satisfying the following formula (1) or (2) and then (3) and (4), it is possible to obtain an excellent characteristic of the balance "strength - loss in steel", according to the present invention is achieved:

и

and

Formula (1) simply shows the case in which the "grain size before processing" is larger than some specific size. The crystalline grain size of a conventional steel sheet is maintained in the range from several micrometers to several hundred times 100 micrometers each, but to obtain the effect of the present invention, it should be made 20 micrometers or more. Preferably, this size is 50 micrometers or more, more preferably 100 micrometers or more, more preferably 150 micrometers or more, more preferably 200 micrometers or more, more preferably 250 micrometers or more.

Formula (2) defines the "grain size before processing" obtained as a result of the invention in relation to the amount of Si and the amount of Al. In general, the higher the amount of Si and the amount of Al in the steel sheet, the better the balance is “strength - loss in steel”, so the higher the Si content and the higher the A1 content in the material, the easier it is to obtain an excellent balance of “strength - loss in steel "even if the" grain size before processing "is small. The ratios d> (200-50 × Si% -50 × Al%), d> (180-50 × Si% -50 × Al%) are possible; moreover, d> (150-50 × Si% -50 × Al% ) On the other hand, it is also possible d> (220-50 × Si%).

Formula (3) and Formula (4) provide rough guidelines for the upper limit of "grain size before processing." In general, the higher the Si content in the material, the more brittle the material, but if the “grain size before processing” becomes excessively large, it becomes even more brittle and cold rolling and other processing becomes difficult, so sometimes an upper limit becomes necessary. This upper limit depends not only on the ingredients of the steel, other than the amount of Si, and the heating history up to the processing, but also on the method of processing the steel sheet and the properties to be obtained.

The specific conditions for maintaining the "grain size before processing" in the aforementioned range also depend on the ingredients of the steel and the history of heating prior to processing, therefore it cannot be limited to specific ranges, but it will not be difficult for a person skilled in the art having ordinary knowledge in it determine suitable conditions by conducting several heat treatment tests on a steel sheet with ingredients and a heating history corresponding to the steel sheet to be obtained. The purpose of this is to confirm the recrystallization of the steel sheet and grain growth behavior and to correctly adjust the heating history so that the desired structure is obtained.

As for the ingredients of steel, an increase in their purity promotes the formation of large grains. In particular, it is effective to reduce the content of C, N, and P. In addition, the production of steel from a single ferritic steel due to the ingredients and the suppression of the phase transition during hot rolling makes coarsening of grains of the hot rolled sheet easier to achieve.

In addition, if the goal is larger grains in the hot rolled sheet, then you can consider: increasing the heating temperature during hot rolling, increasing the final temperature of hot rolling, reducing the degree of compression after the end of hot rolling, slow cooling after the final rolling, rolling into a roll when high temperature, high temperature annealing of the hot rolled sheet for a long period of time, etc. In addition, if the target is larger grains in the annealed sheet, high-temperature annealing for a long period of time is simple, but it is also possible to make the precipitated phases larger and improve grain growth during annealing by low-temperature heating of the slab or coiling into a roll at a high temperature in during hot rolling or high temperature annealing of the hot rolled sheet. In particular, for example, it is preferable to make the annealing step immediately before the formation of the deformed structures any step from among the following steps in which.

(1) In the case where cold rolling is performed two or more times with intermediate annealing between them, intermediate annealing is performed immediately before the final cold rolling at temperatures above 850 ° C (preferably 860 ° C or more) or for a period of time over 30 seconds (preferably 35 seconds or more).

(2) In the case where cold rolling is performed only once, when the hot rolled sheet is annealed, the hot rolled sheet is annealed at a temperature above 1100 ° C (preferably 1110 ° C or more) or for a period of time over 30 seconds (preferably 35 seconds or more).

(3) In the case where neither the aforementioned paragraph (1) nor (2) applies, coiling is carried out during hot rolling at temperatures above 700 ° C (preferably 710 ° C or more).

The degree of recrystallization in the structure before processing

Note that depending on the conditions, sometimes deformed structures remain in the steel sheet immediately before the stage of formation of deformed structures, which, ultimately, must remain in the steel sheet. In this case, to obtain the effect of the present invention, it is preferable not to allow the deformed structures to remain immediately before the step of forming the deformed structures as much as possible. It is preferable to make the degree of (r) recrystallization immediately before the stage of formation of deformed structures

.

.

More preferably, r is 90% or more. It goes without saying that immediately before the step of formation of the deformed structures, completely recrystallized structures that satisfy the above formulas (1) to (4) are preferred. In addition, when in the structure immediately before the stage of formation of the deformed structures there are still partially recrystallized regions, it is possible to obtain the effect according to the invention, satisfying the above formula (5), but when the grain size of the recrystallized parts is large, even if the unrecrystallized parts exceed 50 %, the effects of the present invention will sometimes appear. Moreover, assuming that the parts not yet recrystallized are small crystalline grains with a grain size of 5 micrometers, and having found the average grain size, one can judge the effect of the invention by formulas (1) and (2). This case is also included in the present invention.

The method of measuring grain size before processing

Note that the size of the crystalline grain and the degree of recrystallization are determined by observing the structure of the cross section of the sheet during etching in the same way as is usually done when observing the structure of ferrous metals. The grain size is the diameter determined based on the observed crystalline grain area under the assumption that the grain cross-sectional area is a circle, while the degree of recrystallization is determined based on the relative area of the unrecrystallized parts in the observed region. It goes without saying that this measurement should be performed for a reasonably middle area without segregation.

Effect of grain size before processing

The mechanism of influence of “grain size before processing” is not indisputable, but one can consider the effects of changes in the dislocation structure, changes in texture, in addition, changes in the dislocation structure after processing, due to differences in texture before processing, etc. While the details are not clear, it is assumed that, ultimately, dislocation structures in deformed structures turn into structures that act as powerful obstacles to dislocations trying to move due to external stress, and do not easily act as barriers for domain walls trying move due to an external magnetic field.

Tensile strength

The steel sheet covered by the present invention has a tensile strength of 500 MPA or more. If a steel sheet has a tensile strength lower than this value, even in the case of a steel sheet hardened mainly by ordinary Si, Mn and other elements of the solid solution and structurally completely occupied by recrystallized structures, it becomes possible to produce it without such a severe decrease in performance. This is due to the fact that such a material makes the sheet noticeably better in its magnetic properties. The present invention is limited to high-strength materials that are hardened mainly through conventional hardening of a solid solution and which cannot be produced without compromising performance. To further benefit from the present invention, the invention should preferably be applied to a steel sheet with a tensile strength of 600 MPA or more, more preferably 700 MPA or more, more preferably to a steel sheet with a tensile strength of 800 MPA or more . It is even possible to produce a steel sheet with a tensile strength of 900 MPA or more, which is currently not being produced at all. In addition, even a steel sheet with a tensile strength of 1000 MPA or more, not even intended for future production, can be produced with high productivity.

Note that when using a rotor of an electric motor, a slight deformation means the end of the service life of this part, so that not tensile strength, but yield strength should be used for evaluation. The steels according to the invention have deformed structures remaining in them, so that in comparison with steel hardened by solid solution or dispersion hardened steel, the yield strength is higher at the same strength, and they exhibit more desirable properties compared to these traditional materials. That is, the ratio of stress at yield strength to tensile strength becomes a relatively high value, component from 0.7 to 1.0 or so. The correlation between yield strength and tensile strength becomes extremely strong in this material. For this reason, even if the yield strength is used to evaluate the superiority of the steels according to the invention does not change at all. The effect of the invention is demonstrated without problems even for applications like the rotor, where the yield strength becomes a problem.

The relative area of the deformed structures

Deformed structures are present when observing the structure in a section of a steel sheet on a relative area of 1% or more. The cross-sectional area in the present invention is observed as a cross-section in which one side of the cross-section becomes the rolling direction of the steel sheet and the other side becomes the direction of the thickness of the steel sheet. A method is used that is performed on ordinary steel sheets, consisting of using nital or another chemical to etch and expose the structure, but the invention is not particularly limited to the observation method. Any technology can be used to distinguish between a recrystallized structure and deformed structures.

If the relative area of the deformed structures is 1% or less, then the effect of increasing the strength becomes less. When the deformed structures are substantially 0%, the result is a sheet of ordinary steel as such. By adjusting the relative area in the range from 0 to 1%, the effect of increasing the strength is less, although it is necessary to strictly regulate the annealing temperature, so this is not practical. To obtain the actually required level of strength, it is preferable to maintain the relative area of the deformed structures of 5% or more, more preferably 10% or more, more preferably 20% or more, more preferably 30% or more, more preferably 50% or more, more preferably 70% or more. There are no problems, even if you make 100% deformed structures, where essentially no recrystallized structures are observed at all. In this case, the result is the so-called “completely solid” state, which is not annealed at all, or the state in which annealing is performed, but the structure is restored to the state preceding the onset of recrystallization.

Note that even if the deformed structures are less than 95%, 90%, 85%, 80%, or, in addition, 75%, the effect of the present invention is obtained.

The formation of deformed structures

In the steel sheet of the present invention, the structure is adjusted in accordance with the required strength and magnetic properties, but this adjustment can be made due to the ingredients of the steel, history of hot rolling, cold rolling speed, heating temperature during annealing, duration of annealing or heating rate, cooling rate and etc. One of ordinary skill in the art can accomplish this without any problems by retrying. Alternatively, a steel sheet subjected to such annealing so that the crystallized structures occupy its entire mass can be deformed by repeated cold rolling, etc. in order to form deformed structures. In this case, deformation is usually performed macroscopically uniformly, so that the entire amount of the structure becomes deformed structures or corresponds to 100% of the deformed structures. In this case, the ingredients of the steel, heating history, properties, etc., are taken into account before processing, and the amount of treatment is used to adjust strength and magnetic properties. It is also possible without problems for a person skilled in the art in several attempts.

As a rough guideline, in the case of a sheet of so-called ordinary low-grade electrical steel with an amount of Si 1% or so or less or less, the temperature does not exceed 700 ° C, while even in the case of a sheet of so-called ordinary high-grade electrical steel with an amount of Si of 3% or the temperature does not exceed 800 ° C or so, but, for example, with the introduction of appropriate quantities of Cu, Nb, etc. it is possible to obtain steels according to the invention with completely reduced structures that do not recrystallize at all, even at a temperature of 900 ° C or about or more. On the other hand, annealing at a temperature very different from the temperature for a sheet of ordinary electrical steel requires a large change in furnace temperature and not only entails a decrease in operating efficiency, but also, along with the aforementioned, causes safety problems due to the formation of unburned gas. The lower limit of the heating temperature during annealing in order to avoid these problems due to the extremely low-temperature annealing is 400 ° C or so or more.

The rough standard for determining the duration of annealing also depends on temperature, but it takes at least 5 seconds or so to create an annealing effect. The duration of annealing cannot be clearly indicated, since it depends on the ingredients, the history of production before heat treatment, etc., but the rough standard is: if 850 ° C, then within 5 minutes, if 750 ° C, then within one hour , and if 600 ° C, then over 10 hours. As explained above, the conditions of temperature and duration, making it possible to take advantage of the effect according to the invention, can be found without problems by a person skilled in the art, in several attempts. The main thing is to confirm the behavior during recrystallization of the considered steel sheet.

In the case when the deformed structures are formed anew by repeated cold rolling, etc., if the amount of processing is small, it is sometimes difficult to clearly determine the existence of deformed structures by the aforementioned method of observing the structure, but as a rough norm in order to sufficiently obtain effect according to the invention, when observing the cross-sectional structure, it is possible to use the ratio: (size of crystalline grains in the direction of sheet thickness) / (size of crystalline grains in the direction of pellets) c. This value is made to be 0.9 or less. If it is 0.8 or less, then the effect of increasing strength is clearly obtained. Preferably, this value is 0.7 or less, more preferably 0.6 or less, more preferably 0.5 or less, more preferably 0.3 or less. However, if this value is excessively low, deterioration in magnetic properties becomes noticeable, so caution is required.

The above processing is usually carried out by cold rolling, but there is no need to insist on it, provided that there is a change in the amount of deformation or quality of the material in accordance with the requirements of the present invention. Can be used: warm rolling, hot rolling to the extent that the deformed structures do not disappear, tensile deformation by applying tensile force, bending deformation by a straightening machine, etc., shot blasting, forging or other method. On the contrary, due to the method of creating the deformation, the dislocation structure is forced to turn into the structure preferred for the present invention, explained below, so that it becomes possible to further improve the properties.

In the case of performing this processing by cold rolling, the rough norm of the degree of compression can be easily estimated by the ratio of the size of the crystalline grains, but from 10 to 70% or so. When the material is subsequently cold-rolled again, softened to some extent at such an annealing step, in order to increase its hardness, the material can be easily made thinner, and the productivity of releasing a very thin sheet of electrical steel that was difficult to produce in the past also increases. Such a very thin sheet of electrical steel according to the present invention makes it possible to suppress eddy current losses when used in a high-frequency magnetic field, so it also has the advantage of being effective in reducing losses in steel.

Note that now there is even a sheet of electrical steel shipped after rolling a steel sheet subjected to recrystallization annealing performed by rolling 1-20% or so in a temper mill as with the other method of the present invention, i.e., the so-called semi-finished sheet of electrical steel . This sheet, which has been rolled in a training stand, is shipped as products, processed by electric motor manufacturers on electric motor parts, and then annealed under conditions under which recrystallization will occur sufficiently to cause grain-induced deformation to grow and thus produce large recrystallized structures. This method is a means of improving magnetic properties and is also sometimes called the skipping method in a training stand. In this method, during use as a structural member, there are never any deformed structures.

Heat treatment after the formation of deformed structures

The present invention is essentially different from this steel sheet and method. It basically does not perform any heat treatment after processing the sheet into a piece of electrical equipment. Even when performing a kind of heat treatment when welding a steel sheet or surface treatment, etc. the deformed structures provided by the present invention will not disappear and remain in the range provided by the present invention. This is because if the deformed structures disappear or deviate from the intended range of the present invention, then the strength of the steel sheet, which is required in the state of use in a real electric motor, will become insufficient. The rough standard for the temperature of this heat treatment is the same as the temperature conditions at the aforementioned step of annealing the steel sheet.

The optimal conditions for using the effect of the invention can be found in cooperation with or even without specialists in the field of steel sheet production, without any problems by several attempts by the ordinary manufacturer of electrical equipment.

Dislocation density

The effect of “deformed structures” explained above can also be estimated from the density of dislocations in “deformed structures”. The average dislocation density in the deformed structures is 1 × 10 ¹³ / m ² or more, more preferably 3 × 10 ¹³ / m ² or more, more preferably -1 × 10 ¹⁴ / m ² or more, more preferably 3 × 10 ¹⁴ / m ² or more. This dislocation density is measured by a transmission electron microscope. In an ordinary sheet of electrical steel, where the entire amount of the steel sheet is constituted by crystallized structures, the average dislocation density is 1 × 10 ¹² / m ² or so or less, so that there is a tenfold or greater difference sufficient to distinguish the deformed structures.

Note that, strictly speaking, in order to use even an ordinary sheet of electrical steel as various structural elements, manufacturers, etc. cut, crimped and otherwise processed. It is known that as a result of this, some deformations remain introduced into the steel sheet and that this affects the properties of structural elements. This type of deformation is introduced only in the machined places of the steel sheet and differs from the deformation deliberately created over the entire surface of the steel sheet in the present invention, so that they do not make such a big contribution to achieving high strength of the structural element as a whole.

The reason magnetic properties can be maintained

The reason that good magnetic properties can be maintained even if deformed structures remain in the material, as in the present invention, is not clear, but is believed to be something like the following. In the past, it was believed that deformed structures caused a significant deterioration in magnetic properties and were not considered as a means to achieve high material strength. High strength was achieved by grinding crystalline grains, hardening of a solid solution, dispersion hardening, etc. However, the need for higher strength materials has steadily increased. Traditional means to achieve high strength are now forced to deal even with areas of conditions that noticeably worsen magnetic properties. When considering the means to achieve high strength, using deformed structures again under such conditions, it turns out that in a sense it can no longer be called such a disadvantageous method.

In addition, the effect of deformed structures during the cold rolling of materials, where the strain was relatively small in amplitude, was traditionally studied. It is believed that under such conditions, dislocation structures in the material are relatively heterogeneous and relatively stable distribution of dislocations, such as the so-called cellular structures or reduced structures, are not formed. This degree of processing was not at all attractive as a means of achieving high strength. In addition, with such dislocation structures, dislocations became only obstacles to the movement of domain walls. The magnetic properties were remarkably deteriorating, so obviously this was never put into practice.

On the other hand, during cold processing with a relatively high strain, as in the present invention or in deformed structures restored by annealing, dislocations form relatively stable cellular structures. Cells typically have a diameter of 1 micrometer to 0.1 micrometer or so. Except for the fact that the cell boundaries are formed by dislocations, and the difference in the orientations of the crystal with adjacent cells is small, they have structures similar to ordinary crystalline grains. They can be considered as one type of ultrafine crystalline grains and are not believed to easily interfere with the movement of domain walls. In addition, such ultrafine crystalline grains have high strength and have appropriate ductility when processing is required. If we consider the balance of strength and magnetic properties, then it is believed to be at a level sufficient to make practical use possible. In addition, even in steels according to the invention, where deformed structures are present in applications, such as use in a high-frequency magnetic field, where the contribution of eddy current loss to steel loss is especially large, it is important to introduce Si, Mn, Al, Cr, Ni etc. This has a great influence on the behavior during mechanical hardening, behavior during recrystallization, etc., therefore, the development of steel with dislocation hardening based on a sheet of electrical steel is completely different from the development of the so-called ordinary steel for industrial use, used for automobiles, containers and etc.

Using Cu Solid Solution

Note that in the present invention, apart from Si and other conventionally known solid solution strengthening elements, it is also possible to introduce a Cu solid solution and obtain an electrical steel sheet excellent in high frequency magnetic properties without causing a deterioration in the magnetic properties or performance associated with the introduction of traditional alloying elements (below, this is referred to as “Cu solidification hardening”). In this case, thanks to the following activities:

1) the introduction of more Cu than ever before,

2) suppressing the formation of the austenitic phase in the high temperature region,

3) performing high temperature heat treatment in the ferritic region in order to cause a large amount of Cu to enter the solid solution, and

4) controlling the cooling so that supersaturated Cu is not released during cooling,

the introduced Cu will be present in the form of a Cu solid solution even in the final product, the effect of suppressing eddy current losses, which had never been thought of in the past, is pronounced, good high-frequency losses in steel can be obtained, and the effect on the deterioration of magnetic induction can be made relatively small.

Cu solid solution hardening is an effect independent of the aforementioned mechanical hardening, and can be performed independently, even without being accompanied by mechanical hardening. In this case, for example, a sheet of electrical steel is made containing, in mass percent: C: 0.06% or less, Si: from 1.5 to 6.5%, Mn: from 0.05 to 3.0%, P : 0.30% or less, S or Se: 0.040% or less, Al: 2.50% or less, Cu: 2.0 to 30.0% and N: 0.0400% or less, the rest is Fe and inevitable impurities, and not containing any metal phase with Cu inside it. In some cases, it may also contain one or more elements from among: Nb: 8% or less, Ti: 1.0% or less, B: 0.010% or less, Ni: 15.0% or less, and Cr : 15.0% or less.

On the other hand, when using this sheet for mechanical hardening, a synergistic hardening effect is obtained together with the effect of increasing the degree of recrystallization by means of a Cu solid solution.

The effect of reducing eddy current losses and the effect of brittleness with an increase in the amount of Cu solid solution are not explained solely by the amount of solid solution element. As explained above, an interconnected effect is observed. Therefore, it is also considered when prescribing a preferred range of ingredients. In addition, during the use of hardening with Cu solid solution, it is ultimately preferable to apply heat treatment causing recrystallization and grain growth, so it is necessary to determine the ingredients, taking into account also the change in the amount of Cu solid solution due to the formation of precipitated phases during this heat treatment, containing Cu. In particular, the phase transition of the main phase of the steel during heat treatment not only leads to a large change in the solubility of Cu, but also leads to the disappearance of structures preferred for magnetic induction, so that when using hardening with Cu solid solution, avoid phase transition during heat treatment. In particular, a single ferrite phase is preferred in the temperature range from room temperature to 1150 ° C., or in order to satisfy the following ratio, in mass percent,

980-400 × C + 50 × Si-30 × Mn + 400 × P + 100 × Al-20 × Cu-15 × Ni-10 × Cr> 900 ... formula 1

Out of this range, an undesirable phase transition occurs during the heat treatment and the likelihood of the effect of hardening hardening with Cu solid solution increases.

The features of hardening with Cu solid solution can be clearly shown even when comparing properties with conventional materials. Compared to a steel sheet in which the ingredients of the steel other than Cu are the same, the Cu content is 0.1% and the crystalline grain size is the same, a steel sheet hardened by Cu solid solution having losses (W _10/400 ) in steel, components of 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, more preferably 0.30 or less.

In addition, in a steel sheet hardened by a solid solution of Cu, the tensile strength is 2.0 times or less higher than that of steel taken for comparison. In general, if the amount of the solid solution element increases, then hardening of the solid solution causes an increase in strength. If the amount of solid solution is large, as in the case of hardening with Cu solid solution, then depending on the element, the increase in strength also becomes noticeable, but the Cu solid solution in steel with a high Si content, which is characteristic of steel hardened with Cu solid solution, does not the material is so hard. It is more preferable to reduce this ratio to 1.7 or less, more preferably to 1.5 or less.

If the amount of Cu in the solid solution is increased, then, despite the fact that the result can be called steel, hardened with a solid solution of Cu, the strength becomes higher. Not that the smaller the increase in strength, the better, but when compared with Si, Cr, etc. used as a solid solution element, the increase in strength is small, and fragility is also suppressed.

In addition, in steel hardened by a solid solution of Cu, with the introduction of excess Cu, in some cases, a noticeable precipitation of metal phases of Cu is observed. In addition, in terms of properties, along with the precipitation of metallic phases of Cu, a large increase in strength is observed. In addition, in this case, at the same time, there is an increase in losses in steel, in particular losses from eddy currents. In particular, due to heat treatment at 450 ° C for 30 minutes, the density of a number of metal phases, consisting mainly of Cu, having a size of 0.02 micrometers or less, in steel increases to 20 / micrometer ³ or more or tensile strength at tensile rises to 100 MPA or more. As explained above, this heat treatment significantly increases eddy current loss and degrades the high-frequency magnetic properties that are strengthened by Cu solidification, so that this is not done to control the quality of the steel sheet, but it can be done to evaluate the steels according to the invention such in the same way as, for example, analysis of ingredients.

To introduce a large amount of Cu solid solution, characteristic of hardening with Cu solid solution, it is effective to use the following heating history. During the final heat treatment during the production of sheet products, usually during recrystallization annealing after cold rolling, the sheet is held in the temperature range of 800 ° C or more for 5 seconds or more and the conditions are set so that during this heat treatment no austenitic phase is created in steel material even at maximum temperature. Preferably, the temperature is 900 ° C or more, more preferably 1000 ° C or more, more preferably 1050 ° C or more. In addition, it is preferable that the duration is 10 seconds or more, more preferably 30 seconds or more, more preferably 60 seconds or more, but if it is the temperature and duration at which there is sufficient solubility of Cu in balance with the content of Cu, then the characteristic effect of the present invention can be obtained sufficiently. However, of course, it is necessary to regulate this, taking into account the aspect of regulating the size of crystalline grains, which also have a great influence on magnetic properties.

If the crystalline grain size is too small or too large, then the magnetic properties will sometimes be degraded. It is well known that there is an optimal grain size under conditions of use. In addition, the maximum temperature should be set in the temperature region where the austenitic phase does not form. If a small amount is formed, then the harmful effect on the properties will be small, but it is preferable to perform annealing at the fully ferritic phase. The temperature depends mainly on the ingredients of the steel, so no specific temperature can be indicated, but the above formula (1) is a general standard. In addition, a specialist in metal science would be able, without any difficulty, to establish a suitable temperature range using commonly performed experiments on heat treatment and observing the structure or recent remarkable advances in thermodynamic calculations.

In addition, the cooling rate during the heat treatment step also becomes an important regulatory factor. The reason for this is that Cu, sufficiently dissolved by keeping the steel at high temperature, becomes oversaturated during cooling, and thus, depending on the cooling rate, it ultimately precipitates as the metallic phase of Cu and sometimes reduces the effect of the present invention. In the present invention, preferred conditions are made as follows: a cooling step after keeping the steel in a temperature range of 800 ° C. or more for 5 seconds or more, consisting of cooling at a cooling rate of 40 ° C./sec or more to 300 ° C. or less. From the point of view of the object of the present invention, there is nothing better than a high cooling rate, but when cooling is too fast, the properties sometimes deteriorate due to a history of heating, etc., so caution is required. Preferably, the rate is 60 ° C / sec or more, more preferably 80 ° C / sec or more, more preferably 100 ° C / sec or more.

In particular, in the present invention, attention should be paid to cooling in the temperature region where the metal phase of Cu is precipitated. The importance of staying at temperatures from 700 to 400 ° C. At 700 ° C or more, the degree of Cu supersaturation is small and it is difficult to isolate Cu, while at 400 ° C or less Cu diffusion is suppressed, so that Cu is more difficult to isolate. If a duration of 5 seconds or less is made, preferably 3 seconds or less, more preferably 2 seconds or less, the evolution of the metal phase of Cu can be suppressed and a sufficient amount of Cu in the solid solution can be provided in order to obtain the effect of the invention.

In addition, after this heat treatment, it is preferable to withstand steel in a temperature region above 400 ° C for 30 seconds or more. This is explained by the fact that during such a heat treatment, the precipitation of the Cu metal phase is stimulated, and the eddy current losses increase.

Thanks to the above ingredients and steps, the effect of reducing eddy current loss by a characteristic large amount of Cu in the solid solution is effectively expressed, and the production of a sheet of electrical steel with a high Cu content becomes possible without causing any harm to the fluidity or rolling. On the other hand, in the production with conventional ingredients and heat treatment conditions that do not take into account the conservation of the amount of Cu in the solid solution, the parts where the amount of introduced Cu becomes small are present as Cu metal phases or Cu sulfides with small effects of reducing eddy current losses, brittleness becomes noticeable, and normal production is hampered.

Note that in the case of also using mechanical hardening according to the present invention, the aforementioned heat treatment may be annealing in the range of 350 to 700 ° C. for 10 seconds to 360 minutes, so that the Cu metal phase finely precipitates while recrystallization is suppressed . It goes without saying that the metal phase of Cu ultimately coarsens by annealing at high temperature for a long time and the hardening ability decreases. At high temperatures, care should be taken to ensure that the annealing time does not become too long. The lower the temperature, the more prolonged annealing is possible.

The present invention is characterized by the absence of any metallic phases of Cu in the steel material. This can be determined and confirmed by the diffraction pattern of an electron microscope, etc. or an attached radiographic analysis device. Of course, confirmation is also possible in a way different from this, such as chemical analysis. In the present invention, the term "metal phase, mainly consisting of Cu" covers phases with a diameter of 0.010 micrometers or more. The reason for this is that if it is less than 0.005 micrometers, then it is too small, so even using the most modern high-precision analytical equipment, it would be difficult to recognize the Cu metal phases covered by the present invention. In addition, no matter what treatment is carried out, in steels according to the invention containing large quantities of Cu, there are locally separated phases containing Cu in one form or another, so that it is impossible to completely eliminate the metallic phases of Cu. The present invention is limited to a sheet of electrical steel containing a significant amount of Cu and hardened or made with a large number of metal phases of Cu through significant heat treatment described in the present invention. An essential feature of the present invention, of course, is the large amount of Cu in the solid solution.

Application options

Note that the effects of the present invention are independent of the presence or type of protective coating formed on the surface of a sheet of ordinary electrical steel, or, in addition, of the manufacturing steps, so that the invention can be applied to a sheet of non-textured or textured electrical steel. In particular, the steel according to the invention can exhibit characteristics very different from a steel sheet with traditional recrystallized structures with planar anisotropy properties. If we consider the magnetic induction in the past completely cold rolled solid state, the properties in the direction of 45 ° to the direction of rolling of the roll (D direction) are higher than the properties in the direction of rolling (L direction) or the direction of the width of the roll (C direction). An electrical steel sheet having ordinary recrystallized structures in almost all cases has properties in the D direction lower than properties in the L or C direction. Given this, by properly adjusting the degrees of recrystallization and reduction and adjusting the structure at the intermediate stage of recrystallization, it is easy to obtain steel a sheet with almost no planar anisotropy. The almost absent planar anisotropy means that a steel sheet having characteristics making it possible to exhibit extremely preferred properties depending on applications such as rotating machines.

The applications are not particularly limited. In addition to applications for rotors of electric motors used in home electrical appliances, automobiles, etc., the invention can also be applied to all applications in which strength and magnetic properties are important.

EXAMPLES

Example 1

A 200 mm thick slab having the ingredients: 0.002% C - 3.0% Si - 0.5% Mn - 0.03% P - 0.001% S - 0.3% Al - 0.002% N, was hot rolled at a temperature heating the slab 1100 ° C and the temperature of the strip winding into a roll of 700 ° C. The hot rolled sheets were annealed to 800, 950 and 1050 ° C in order to change the grain size to 10, 100, and 200 micrometers. These hot rolled sheets were cold rolled, then either not annealed or annealed at a temperature of 400 to 1000 ° C for 30 seconds to produce sheets of products with a sheet thickness of 0.5 mm, differing in the degree of recrystallization and strength. They were evaluated for their mechanical properties using test specimens according to JIS No. 5 (Japanese Industrial Standard No. 5) and the loss properties (W _10/400 ) in steel using SST tests for a 55 mm square. The average values of the mechanical properties and magnetic properties for the direction of rolling the roll, the direction at an angle of 45 ° and the direction perpendicular to it, were determined by the following formula:

X = (X ₀ + 2 × X ₄₅ + X ₉₀ ) / 4

where X ₀ , X ₄₅ and X ₉₀ are properties in the rolling direction of the roll, the direction at an angle of 45 ° and the direction perpendicular to it.

The results are shown in the drawing. As is clear from the results, materials with large grain sizes of the hot rolled sheet, that is, materials produced under the conditions of the present invention, are excellent in the strength-loss in steel balance.

Table 1 room Ingredients (in mass percent) FROM Si Mn R S Al N Cu Nb Other one 0.0010 3.0 0.8 0,0 0,0005 1,64 0.0019 - - - 2 0.0010 3.0 0.8 0.010 0,0005 1,64 0.0019 - - - 3 0.0010 3.0 0.8 0.010 0,0005 1,64 0.0019 - - - four 0.0025 0.7 0.21 0,090 0.0025 0.001 0.0024 - - - 5 0.0025 0.7 0.21 0,090 0.0025 0.001 0.0024 - - - 6 0.0025 0.7 0.21 0,090 0.0025 0.001 0.0024 - - - 7 0.0025 0.7 0.21 0,090 0.0025 0.001 0.0024 - - - 8 0.0019 2.1 0.20 0,060 0.0012 0.22 0.0026 - - - 9 0.0019 2.1 0.20 0,060 0.0012 0.22 0.0026 - - - 10 0.0019 2.1 0.20 0,060 0.0012 0.22 0.0026 - - - eleven 0.0038 3,1 0.20 0,044 0.0018 1,0 0.0020 - - - 12 0.0012 2.9 0.40 0,030 0,0005 0.5 0.0013 3.9 - Ni: 1.8 13 0.0012 2.9 0.40 0,030 0,0005 0.5 0.0013 3.9 - Ni: 1.8 fourteen 0,0006 3,1 0.30 0.008 0,0009 0.15 0.0025 Ni: 2.0 Cr: 5.0 fifteen 0,0230 2.5 1.20 0,022 0,0006 0.06 0.0036 0.11 B: 0.008 16 0,0230 2.5 1.20 0,022 0,0006 0.06 0.0036 0.11 B: 0.008 17 0,0008 3.4 0.53 0,041 0,0004 0.02 0.0024 037 Ti: 0.35 eighteen 0,0008 3.4 0.53 0,041 0,0004 0.02 0.0024 037 Ti: 0.35 19 0,0322 3,1 0.50 0.016 0,0002 1,2 0.0011 - 1.3 - twenty 0,0322 3,1 0.50 0.016 0,0002 1,2 0.0011 - 1.3 - 21 0.0077 2.9 0.29 0,023 0.0015 0.8 0.0022 2.1 - - 22 0.0021 3,7 0.05 0.002 0,0009 0.24 0.0026 Sn: 0.09 Ce: 0.002 (The rest is Fe and inevitable impurities)

Example 2

From 200 mm thick slabs having the ingredients shown in Table 1, sheets of products were produced under the production conditions shown in Table 2. Some of the materials were heat-treated, including heat treatment by electric motor manufacturers (user annealing). They were evaluated for their mechanical properties using test samples according to JIS No. 5 and the loss properties (W _10/400 ) in steel and magnetic induction B ₂₅ using SST tests for a square of 55 mm. The average values of the mechanical properties and magnetic properties for the direction of rolling the roll, the direction at an angle of 45 ° and the direction perpendicular to it, were determined by the following formula:

X = (X _o + 2 × X ₄₅ + X ₉₀ ) / 4

where X ₀ , X ₄₅ and X ₉₀ are properties in the rolling direction of the roll, the direction at an angle of 45 ° and the direction perpendicular to it.

The results are shown in Table 2. As is clear from the results, the materials produced under the conditions of the present invention are solid and, in addition, excellent in magnetic properties. Care must be taken that usually an electrical steel sheet is significantly different in properties depending on the amount of Si, therefore it is sorted and sold according to the amount of Si contained therein. In addition, steel losses vary significantly depending on the thickness of the sheet. A material with a high Si content compared to a material with a low Si content, due to differences in the Si content, has significantly lower losses in steel. In addition, even sheets with thin sheet thicknesses have reduced steel losses, so when evaluating the effect of the present invention, it is necessary to take into account differences in the amounts of Si and sheet thicknesses and compare the sheets with equivalent amounts of Si sheet thicknesses.

Example 3

Slabs of steels with the ingredients shown in Table 3, 250 mm thick, were used to produce sheets of products under the conditions shown in Tables 3 and 4. To measure B1O magnetic induction and losses (W _10/400 ), SST tests were used in steel square 55 mm. The average values of magnetic properties in the direction of rolling the roll, the direction at an angle of 45 ° and the direction perpendicular to it, were determined by the following formula:

X = (X ₀ + 2 × X ₄₅ + X ₉₀ ) / 4

Here, X ₀ , X ₄₅ and X ₉₀ are characteristics in the direction of rolling the roll, the direction at an angle of 45 ° and the direction perpendicular to it.

As is clear from the results shown in Table 4, samples produced under the conditions of the present invention are good in rolling ability during the cold rolling step and excellent in magnetic properties. Note that it was confirmed that the good steel losses in the steels according to the invention were mainly due to a decrease in eddy current losses.

According to the present invention, it is possible to stably produce a sheet of solid high-strength electrical steel, excellent in its magnetic properties. That is, the present invention makes it possible to obtain a predetermined strength even with relatively small amounts of input elements used for hardening the solid solution and dispersion hardening, thus improving cold rolling, improving the performance of the cold rolling step, and it becomes possible to anneal in the normal operating range, so that the efficiency processing at the annealing stage is also improved. In addition, thanks to repeated cold rolling after annealing, it is possible to easily produce extremely thin materials that were difficult to produce in the past.

In addition, if Cu solid solution is used, it becomes possible to suppress brittleness and stably produce a sheet of electrical steel that is excellent in its high-frequency magnetic properties using high alloy alloy ingredients that provide low eddy current loss, without problems with cold rolling, etc.

Based on the foregoing, strength, fatigue strength and abrasion resistance can be provided, so that increased efficiency, smaller size, longer service life, etc. are achieved. ultra-high-speed electric motors, electric motors with magnets integrated in the rotors, and materials for electromagnetic switches.

Claims (11)

1. A method of manufacturing a sheet of high-strength electrical steel, containing, wt.%: C - 0.060 or less, Si - from 0.2 to 6.5, Mn - from 0.05 to 3.0, P - 0.30 or less, S or Se - 0,040 or less, Al - 2,50 or less and N - 0,040 or less, optionally one or more additional ingredients from the group: Cu - from 0.001 to 30.0, Nb - from 0.03 to 8 , 0, Ti - 1.0 or less, V - 1.0 or less, Zr - 1.0 or less, B - 0.010 or less, Ni - 15.0 or less, Cr - 15.0 or less, Bi , Mo, W, Sn, Sb, Mg, Ca, Ce, La, and Co - in the sum of 0.5 or less, the rest is Fe and inevitable impurities, and having deformed structures that remain inside sheet ceiling elements, comprising the step of obtaining the average crystal grain size d of the steel sheet immediately before the step of formation of the deformed structures, which remain in the steel sheet is 20 m or more. 2. A method of manufacturing a sheet of high-strength electrical steel containing, wt.%: C - 0.060 or less, Si - from 0.2 to 6.5, Mn - from 0.05 to 3.0, P - 0.30 or less, S or Se - 0,040 or less, Al - 2,50 or less and N - 0,040 or less, optionally one or more additional ingredients from the group: Cu - from 0.001 to 30.0, Nb - from 0.03 to 8 , 0, Ti — 1.0 or less, V — 1.0 or less, Zr — 1.0 or less, B — 0.010 or less, Ni — 15.0 or less, and Cr — 15.0 or less, Bi, Mo, W, Sn, Sb, Mg, Ca, Ce, La, and Co — a total of 0.5 or less; the rest is Fe and unavoidable impurities, and having deformed structures remaining inside the steel sheet, including the step of obtaining the average size d of the crystalline grain of the steel sheet immediately before the stage of formation of deformed structures that remain in the steel sheet of d≥ (220-50 · Si% - 50 · Al%) microns. 3. The method according to claim 1 or 2, characterized in that it includes a stage in which the average size d of the crystalline grain of the steel sheet is obtained immediately before the stage of formation of deformed structures that remain in the steel sheet, comprising:
d≤ (400-50 · Si%) or
d≤ (820-200 · Si%), microns. 4. The method according to claim 1 or 2, characterized in that it includes a stage in which the degree of recrystallization of the steel sheet is obtained immediately before the stage of formation of deformed structures that remain in the steel sheet, comprising 50% or more. 5. The method according to claim 1 or 2, characterized in that the deformed structures remaining in the steel sheet are 1% or more relative to the cross-sectional area of the sheet. 6. The method according to claim 1 or 2, characterized in that the average dislocation density in the deformed structures in the steel sheet is 1 · 10 ¹³ / m ² or more. 7. The method according to claim 1 or 2, characterized in that a steel sheet with a single ferrite phase is obtained in the temperature range from room temperature to 1150 ° C in the following ratio:
980-400 · C + 50 · Si-30 · Mn + 400 · P + 100 · Al-20 · Cu-15 · Ni-10 · Cr> 900. 8. The method according to claim 1 or 2, characterized in that the sheet is heat treated at 450 ° C for 30 minutes to obtain a tensile strength of 100 MPa or more. 9. The method according to claim 7, characterized in that the stages are performed, which produce the final heat treatment after cold rolling, the heat treatment at which the sheet is held in the temperature range of 800 ° C or more for 5 s or more without the formation of an austenitic phase in steel sheet even at maximum temperature in this heat treatment. 10. The method according to claim 7, characterized in that they perform the cooling step after holding the sheet in a temperature range of 800 ° C or more for 5 s or more with a cooling rate of 40 ° C / s or more to 300 ° C or less . 11. The method according to claim 7, characterized in that at the stage of cooling the sheet in the range from 700 to 400 ° C, the cooling time is 5 s or less.

Images