JP4469268B2 - Manufacturing method of high strength electrical steel sheet - Google Patents

Description

  The present invention relates to a high-strength electrical steel sheet, particularly a high-strength non-oriented electrical steel sheet, and is excellent in low iron loss for high-speed rotating machines, high magnetic material with high magnetic flux density and high wear resistance for electromagnetic switches. The present invention relates to a magnetic material and a manufacturing method thereof.

  Conventionally, laminated electromagnetic steel sheets have been used for rotor (rotor) materials. Recently, in applications where high-speed rotation or an increase in rotor diameter is required, the centrifugal force applied to the rotor is reduced. The possibility of exceeding the strength has come out. In addition, there are many motors with a structure that incorporates magnets in the rotor, and even if the rotation speed is not so high, the load applied to the rotor material itself during rotation of the rotor is large, and the strength of the material is also in terms of fatigue strength Is becoming a problem.

  In addition, because the contact surface of the electromagnetic switch is worn as it is used, a magnetic material having excellent wear resistance as well as electromagnetic characteristics is desired.

  In response to such needs, recently, non-oriented electrical steel sheets with high strength have been studied and several proposals have been made. For example, in Patent Document 1 and Patent Document 2, it is proposed to use a slab having a high Si content and further containing one or more solid solution strengthening components such as Mn, Ni, Mo, and Cr. However, there is a risk that sheet breakage may occur frequently during rolling, and there is room for improvement such as a decrease in productivity and a decrease in yield, and since it contains a large amount of Ni, Mo, and Cr, it is extremely It becomes an expensive material.

JP-A-1-162748 JP-A-61-84360

  As described above, many proposals have been made for high-strength electrical steel sheets, but it has been necessary to achieve stable industrial production using ordinary electrical steel sheet manufacturing equipment while ensuring necessary magnetic properties. The fact is that it is not. Under such circumstances, the present inventor has filed a patent application in Japanese Patent Application No. 2003-347084 for a high-strength electrical steel sheet in which a processed structure remains in the steel sheet.

  Even if the processed structure remains in the crystal structure, this technology does not deteriorate the magnetic characteristics so much, and considering the effect of increasing the strength, it is inferior to the conventional material strengthened with solid solution elements and precipitates. Not only that, but it has been found out that it is a very useful technique in consideration of productivity and magnetic characteristics, particularly in-plane anisotropy of magnetic flux density. However, no clear metallurgy has been established for how to improve the balance between magnetic properties and mechanical properties for electrical steel sheets having a processed structure, and this technology is optimal in this respect. No confirmation has been obtained.

  In order to clarify this point, the present inventor conducted detailed experiments especially on the influence of the structure before rolling, and in an electrical steel sheet having a processed structure, there is an optimum region for achieving both magnetic properties and mechanical properties. As a result, we have succeeded in setting an industrially optimal range in consideration of productivity, especially the steel plate threadability.

The present invention has a high tensile strength (TS) of, for example, 500 MPa or more, wear resistance, and magnetic flux density (B ₅₀ ) or iron when used in a high frequency magnetic field such as a motor that rotates at high speed. It is an object of the present invention to stably manufacture a high-strength non-oriented electrical steel sheet having excellent magnetic properties such as loss and on-line without changing from a normal electrical steel sheet such as cold rolling property and annealing workability.

The present invention has been made to solve the above-mentioned problems, and the gist thereof is as follows.
(1) By mass%, C: 0.060% or less, Si: 0.2-4.0%, Mn: 0.05-3.0%, P: 0.30% or less, S: 0.040 % Or less, Al: 2.50% or less, N: 0.020% or less, consisting of the remainder Fe and inevitable impurities, and further processing the region or recrystallized structure that is not eroded by the recrystallized structure inside the steel plate In the method for manufacturing a high-strength electrical steel sheet in which the processed structure that is the structure obtained by the process is left, the average crystal grain size d of the steel sheet immediately before the step of forming the processed structure finally remaining inside the steel sheet is 20 μm or more. And the recrystallization rate of the steel sheet is 100%, and the processed structure is 20% or more in terms of the area ratio in cross-sectional observation.
(2) By mass%, C: 0.060% or less, Si: 0.2-4.0%, Mn: 0.05-3.0%, P: 0.30% or less, S: 0.040 % Or less, Al: 2.50% or less, N: 0.020% or less, consisting of the remainder Fe and inevitable impurities, and further processing the region or recrystallized structure that is not eroded by the recrystallized structure inside the steel plate In the method for producing a high-strength electrical steel sheet in which the processed structure that is the structure obtained by the process is left, the average crystal grain size d (μm) of the steel sheet immediately before the step of forming the processed structure finally remaining inside the steel sheet D ≧ (220-50 × Si%) , and the recrystallization rate of the steel sheet is 100%, and the processed structure is 20% or more in terms of the area ratio in cross-sectional observation. Production method.
(3) The average crystal grain size d (μm) of the steel plate immediately before the step of forming the processed structure finally remaining inside the steel plate is d ≦ (400−50 × Si%) and d ≦ (820). -200 * Si%), The manufacturing method of the electrical steel sheet as described in (1) or (2) characterized by the above-mentioned.
( 4 ) The steel component is mass%, and further contains one or more of Cu: 0.1 to 8.0% and Nb: 0.03 to 8.0% (1) to ( 3 The manufacturing method of the electromagnetic steel sheet as described in any one of the items).
( 5 ) Steel component is mass%, and further, Ti: 1.0% or less, B: 0.010% or less, Ni: 5.0% or less, Cr: 15.0% or less The method for producing an electrical steel sheet according to any one of (1) to ( 4 ), comprising:
( 6 ) In any one of the items (1) to ( 5 ), the steel component is contained by mass% and further contains one or more of Sn and Ce in a total amount of 0.5% or less. The manufacturing method of the electromagnetic steel plate as described.
( 7 ) The method for producing an electrical steel sheet according to any one of (1) to ( 6 ), wherein an average dislocation density in the processed structure inside the steel sheet is 1 exp13 / m ² or more.

  According to the present invention, a high-strength electrical steel sheet that is hard and excellent in magnetic properties can be stably manufactured. That is, the present invention can obtain the intended strength even if the additive element used for solid solution strengthening and precipitation strengthening is relatively low, so that the cold rolling property is improved and the productivity of the cold rolling process is improved. At the same time, since annealing within the normal operating range is possible, the workability of the annealing process is also improved. In addition, by performing re-cold rolling after annealing, it becomes possible to easily produce an ultrathin material that has been difficult to manufacture.

  As a result, strength, fatigue strength, and wear resistance can be ensured. Therefore, high-speed rotating motors, motors incorporating magnets in rotors, and electromagnetic switch materials can be made more efficient, smaller, and have a longer life. Achieved.

The present inventors have conducted various experiments and studies in order to achieve the above object. That is, the present invention is C: 0.060% or less, Si: 0.5-4.0%, Mn: 0.05-3.0%, P: 0.30% or less, S: 0.040% or less , Al: 2.50% or less, N: 0.020% or less, and further, if necessary, Cu: 0.1-8.0%, or Nb: 0.05-8.0 In steel materials containing one or more of
(1) A processed structure is present in the steel sheet structure to increase the strength by strengthening dislocations.
(2) finally coarsening the crystal structure immediately before forming the processed structure remaining in the steel sheet;
(3) Improve the plate-passability by limiting the above crystal structure in terms of the amount of Si.
As a result, the strength-magnetic property balance can be improved with high productivity without causing troubles such as workability in the steel sheet in which the processed structure remains in the electromagnetic steel sheet.

  First, the component composition of the high strength electrical steel sheet according to the present invention will be described.

  Since C deteriorates the magnetic characteristics, it is set to 0.060% or less. From the standpoint of increasing strength, particularly increasing yield stress, improving warm strength and creep strength, and improving fatigue properties in warm conditions, and in the case of Nb-containing steels, NbC also has the effect of delaying recrystallization. Therefore, it is preferably 0.0031 to 0.0301%, more preferably 0.0051 to 0.0221%, still more preferably 0.0071 to 0.0181%, and still more preferably 0.0081 to 0.0151%. .

  When the above-mentioned effects by C are not particularly regarded as important, higher C is contained from the viewpoint of deoxidation efficiency until the slab stage, and C may be reduced by decarburization annealing after forming the coil. Is possible. When the content is reduced to about 0.010% or less, it is advantageous to reduce the amount of C by degassing equipment at the molten steel stage from the viewpoint of manufacturing cost. In particular, if it is 0.0020% or less, the effect of reducing iron loss is remarkable, and in the steel of the present invention that does not require non-metallic precipitates such as carbides for high strength, the strength can be increased even if it is 0.0015% or less. It is possible, and even if it is 0.0010% or less, sufficient strength can be increased.

  Si increases the specific resistance of steel, reduces eddy currents, lowers iron loss, and increases tensile strength, but the effect is small when the amount added is less than 0.2%. Preferably it is 1.0% or more, More preferably, it is 1.5% or more, More preferably, it is 2.0% or more, More preferably, you may be 2.5% or more. Generally, when used under a high-frequency magnetic field, the loss due to eddy current increases. However, in the steel of the present invention containing a processed structure, it is effective to increase the Si content particularly in order to suppress this eddy current loss. However, if it exceeds 4.0%, the steel is remarkably embrittled and the magnetic flux density of the product is further reduced, so the content is made 4.0% or less. As will be described later, the optimum Si amount range is determined in consideration of the crystal structure immediately before forming the processed structure finally remaining in the steel sheet, which is an important factor of the present invention. Although it depends on this crystal structure, it is preferably 3.7% or less to reduce the fear of embrittlement. If it is 3.2% or less, there is a balance with the amount of other elements. There is no need.

  Mn may be positively added to increase the strength of the steel, but it is not particularly necessary for this purpose in the steel of the present invention that utilizes the processed structure as the main means for increasing the strength. Although it adds for the purpose of reducing a core loss by raising a specific resistance and reducing an eddy current loss, since excessive addition reduces a magnetic flux density, it is made 0.05 to 3.0%. 0.05 to 3.0%. Preferably they are 0.5%-2.5%, More preferably, they are 0.8%-2.0%.

  P is an element having a remarkable effect of increasing the tensile strength, but like the above Mn, it is not necessary to add it to the steel of the present invention. If it exceeds 0.3%, the embrittlement is severe and processing such as hot rolling and cold rolling on an industrial scale becomes difficult, so the upper limit is made 0.30%. Preferably it is 0.20% or less, More preferably, it is 0.15% or less.

  S is easy to combine with the Cu added if necessary in the steel of the present invention, affects the formation behavior of the metal phase mainly composed of Cu, which is important for the purpose of Cu addition, and may reduce the strengthening efficiency. Care must be taken when it is contained in the. In addition, depending on the heat treatment conditions, it is possible to actively form fine Cu sulfide to promote high strength. The produced sulfide may degrade the magnetic properties, particularly the iron loss. In particular, when the control value of iron loss is strict, the S content is preferably low, and is limited to 0.040% or less. Preferably it is 0.020% or less, More preferably, it is 0.010% or less. Se also has almost the same effect as S.

  Al is usually added as a deoxidizing agent, but it is also possible to suppress the addition of Al and deoxidize with Si. Since SiN deoxidized steel with an Al content of about 0.005% or less does not produce AlN, it also has an effect of reducing iron loss. On the contrary, it can be actively added to promote the coarsening of AlN and the iron loss can be reduced by increasing the specific resistance. However, if it exceeds 2.50%, embrittlement becomes a problem. To do.

  N, like C, degrades the magnetic properties, so it is set to 0.040% or less. Si deoxidized steel with an Al content of about 0.005% or less increases strength like C, especially increases yield stress, improves warm strength and creep strength, improves warm fatigue properties, and contains Nb. In the case of steel, it has an effect of delaying recrystallization by NbN, and is an effective element from the viewpoint of texture improvement. From this viewpoint, preferably 0.0031 to 0.0301%, more preferably 0.0051 to 0.0221%, more preferably 0.0071 to 0.0181%, and still more preferably 0.0081 to 0.0151%. It is. When Al is about 0.010% or more, it is possible to form a fine AlN by adding a large amount of N to enhance the recrystallization delay effect, but in the Cu metal phase which is the main mechanism of the present invention. In comparison, the recrystallization delay efficiency is poor and the adverse effect on the magnetic properties is relatively large, so there is no need to add it. In Al deoxidized steel, it should be 0.0040% or less. The lower the steel of the present invention which does not expect the strength increase and recrystallization delay effect due to nitride, the lower the content, 0.0027% or less is preferable. The effect of suppressing deterioration of characteristics due to AlN in steel is remarkable, more preferably 0.0022%, and further preferably 0.0015% or less.

  In the present invention, Cu is added as necessary. It is used not only as solute Cu but also for forming a metal phase mainly composed of Cu in the steel sheet (hereinafter referred to as “Cu metal phase” in this specification) and delaying recrystallization of the steel sheet. In addition, the fine Cu metal phase has the effect of increasing the strength within a range that does not adversely affect the magnetic properties. This range is limited to 0.1 to 8.0%. Preferably it is 1.0 to 6.0%. When the Cu content is low, the recrystallization delay effect is reduced, and the heat treatment conditions for obtaining the recrystallization delay effect are limited to a narrow range, and the degree of freedom in management of production conditions and production adjustment may be reduced. On the other hand, if the Cu content is excessively high, the magnetic properties are greatly affected, and the iron loss may be particularly increased. A particularly preferable range is 2.0 to 5.5%.

  Nb is added as necessary in the present invention, as is Cu. It is used not only as solute Nb but also to form mainly Nb charcoal / nitrides (hereinafter referred to as “Nb precipitates” in the present specification) in the steel sheet and delay the recrystallization of the steel sheet. In addition, the fine Nb precipitate has the effect of increasing the strength within a range that does not adversely affect the magnetic properties. This range is limited to 0.05 to 8.0%. Preferably it is 0.08 to 2.0%.

The present inventor has already applied for a technique for forming a Cu metal phase in a magnetic steel sheet to increase the strength. However, combining the Cu metal phase with this application has no effect on the present invention. There is no loss. Although not particularly limited, the diameter of the Cu metal phase or Nb precipitate present in the steel of the present invention is preferably about 0.20 μm or less. Beyond this, the recrystallization delay efficiency is reduced, and not only a large amount of metal phase is required, but also the adverse effect on the magnetic properties tends to increase. Similarly, although not particularly limited, the number density of the Cu metal phase or Nb precipitate is limited in the range that can be taken depending on the relationship between the Cu, Nb or C content and the size of the precipitated phase, and is 20 / μm ^3. The above degree is preferable.

  In addition, most of the elements used to increase the strength of conventional high-strength electrical steel sheets are not only problematic in terms of the cost of addition, but also have a detrimental effect on magnetic properties. There is no. In the case of positive addition, one or more of Ti, B, Ni, and Cr are added in consideration of recrystallization delay effect, strengthening effect, cost increase and magnetic property deterioration. The amounts are Ti: 1.0% or less, B: 0.010% or less, Ni: 5.0% or less, and Cr: 15.0% or less.

  Ti is an element that forms fine precipitates such as carbides, nitrides or sulfides in the steel sheet and is effective in increasing the strength. However, compared with Nb, the effect is small, but iron loss is degraded. The tendency is strong. Further, when a partially recrystallized structure is used in the annealing process after cold rolling, it has a strong effect of promoting accumulation in the {111} orientation, which is disadvantageous for improving the magnetic flux density. . Therefore, the upper limit is set to 1.0%. Preferably it is 0.50% or less, more preferably 0.30% or less, and good iron loss can be obtained by setting it to 0.0050% or less, which is inevitably mixed without any addition.

  B is bent at the crystal grain boundary and has the effect of suppressing embrittlement due to the P grain boundary deflection. The addition for this purpose is not important. Rather, it is added for the purpose of delaying the recrystallization due to the influence of the solid solution B on the recrystallization temperature. If it exceeds 0.010%, the material is significantly brittle, so the upper limit is made 0.010%.

  Ni is known to be effective in preventing surface roughness (Cu hege) during hot rolling by Cu, which is an element added as necessary in the steel of the present invention, and is actively added for this purpose. You can also. Further, since it has a relatively small adverse effect on magnetic properties, has an effect of improving magnetic flux density, and is also effective in increasing strength, it is an element often used in high-strength electrical steel sheets. Moreover, although it is effective also in improving corrosion resistance, it is preferable to set the upper limit to 5.0% in consideration of the adverse effect on the addition cost and magnetic properties.

  Cr is an element added for improving the corrosion resistance and improving the magnetic characteristics in the high frequency range. However, the upper limit is preferably made 15.0% in consideration of the adverse effect on the addition cost and the magnetic characteristics.

  Moreover, about the other trace element, in addition to the quantity contained inevitably from an ore or a scrap, even if it adds for a well-known various objective, the effect of this invention is not impaired at all. In addition, there are some elements that form at least fine carbides, sulfides, nitrides, oxides, etc., and have a considerable recrystallization delay effect and strengthening effect. In addition, the steel of the present invention can provide a sufficient recrystallization delay effect due to the remaining processed / recovered structure, so that it is not necessary to add these elements.

  The steel containing the above components is melted in a converter in the same manner as a normal electromagnetic steel sheet, is made into a slab by continuous casting, and then manufactured by processes such as hot rolling, hot rolled sheet annealing, cold rolling, and finish annealing. The In addition to these steps, the formation of an insulating film and a decarburization step do not impair the effects of the present invention. Moreover, there is no problem even if it is manufactured not by a normal process but by a process such as a thin slab or a continuous casting process in which the production of a ribbon by the rapid solidification method or the hot rolling process is omitted.

  In the present invention, it is necessary to form a special structure called “processed structure” in the steel sheet in the present invention. The “processed structure” in the present invention is distinguished from a “recrystallized structure” that occupies almost the entire amount of steel sheet with a normal electromagnetic steel sheet. Generally, it refers to a structure in which the strain accumulated in the steel sheet due to cold rolling or the like has not sufficiently disappeared. More specifically, in the process of annealing a cold-rolled steel sheet, a structure that is deformed by cold rolling and contains high-density dislocations is a structure having a low dislocation density generated by holding at a high temperature in the annealing process (“recrystallized structure”). The region that is not engulfed by this “recrystallized structure” is defined as “processed structure”. This processed structure generally has a dislocation density that is low during annealing because of so-called recovery, but it is not as low as the recrystallized structure. The crystal structure is uneven. The “processed structure” can also be obtained by further processing the recrystallized structure. In this case, uniform strain remains in the tissue as a whole. In the present invention, this processed structure is utilized to increase the intended strength.

  Next, the average crystal grain size d of the steel sheet immediately before the step of forming a processed structure finally remaining inside the steel sheet, which is a characteristic of the present invention, will be described. Hereinafter, this particle diameter is referred to as “particle diameter before processing”. In the present invention, by basically increasing the “particle diameter before processing”, the characteristics after processing, particularly the strength-iron loss balance, is greatly improved. “Pre-process grain size” refers to the grain size at the time of hot-rolling when cold-rolling the hot-rolled sheet and suppressing the recrystallization during subsequent annealing to leave the processed structure in the final product. It becomes the diameter. At this time, if the hot-rolled sheet annealing generally performed on the electromagnetic steel sheet is performed, the particle diameter after the hot-rolled sheet annealing becomes the “particle diameter before processing”. Further, when the recrystallized steel sheet is re-cold rolled after cold rolling to leave the processed structure in the final product, the grain size at the time of annealing plate is obtained. Furthermore, for example, when re-rolling is performed with the processed structure remaining in the annealing process after cold rolling, the effect of processing in the re-rolling may be substantially large, but it was formed by cold rolling. Since the processed structure does not completely disappear and remains after re-rolling after re-rolling, the grain size before cold rolling, that is, the diameter of hot-rolled sheet is the usual process. It becomes “particle diameter before processing”.

  In the present invention, this “particle diameter before processing” d (μm) is defined in a specific range in relation to the amount of Si. That is, by satisfying the following formula (1) or (2) and further (3) and (4), an excellent strength-iron loss balance that is a feature of the present invention is achieved.

d ≧ 20 μm (1)
d ≧ (220-50 × Si%) (2)
d ≦ (400-50 × Si%) (3)
And,
d ≦ (820−200 × Si%) (4)
Formula (1) simply indicates a case where the “particle diameter before processing” is coarser than a specific size. The crystal grain size of a normal steel sheet is controlled in the range of several μm to several hundred μm, but it is necessary to be 20 μm or more in order to obtain the effect of the present invention. Preferably they are 50 micrometers or more, More preferably, they are 100 micrometers or more, More preferably, they are 150 micrometers or more, More preferably, they are 200 micrometers or more, More preferably, they are 250 micrometers or more.

  Formula (2) defines the “particle diameter before processing” at which the effect of the invention can be obtained in relation to the amount of Si. This is because, generally, the steel sheet having a higher Si content has a higher strength-iron loss balance, and the higher the Si material, the easier it is to obtain a good strength-iron loss balance even if the “particle diameter before processing” is smaller.

  Equations (3) and (4) give an upper limit of the “particle diameter before processing”. In general, the higher the Si material, the more fragile the material is. However, when the “particle diameter before processing” is excessively coarse, the material becomes more fragile and difficult to process such as cold rolling, so an upper limit may be required. This upper limit depends on the steel component other than the Si amount and the heat history up to processing, as well as the processing method of the steel sheet and the target characteristics.

  Specific conditions for controlling the “particle diameter before processing” within the above-mentioned range depend on the steel composition and the heat history until processing, and thus cannot be limited to a specific range, but those skilled in the art having ordinary knowledge If so, it is not difficult to determine appropriate conditions by performing several heat treatment tests on the steel sheet that has the component corresponding to the target steel sheet and the thermal history. In short, it is only necessary to confirm the recrystallization and grain growth behavior of the steel sheet and to control the thermal history so as to obtain a target structure.

Depending on the conditions, the processed structure may remain on the steel sheet immediately before the step of forming the processed structure finally remaining inside the steel sheet. In such a case, in order to obtain the effect of the present invention, it is preferable not to leave the processed structure as much as possible.
r ≧ 50% (5)
It is preferable that Further, it is needless to say that it is preferable that r is 90% or more, a completely recrystallized structure, and satisfy the above expressions (1) to (4).
In the present invention, the recrystallization rate of the steel sheet immediately before the step of forming the processed structure finally remaining inside the steel sheet is set to 100% at which a more preferable complete recrystallization structure is obtained.

The crystal grain size and the recrystallization rate are usually determined by observing the structure of the cross section of the plate by etching, which is performed by observing the structure of the steel material. The grain size is obtained from the area per observed crystal grain, the diameter when the cross-sectional area of the grain is assumed to be a circle, and the recrystallization rate is obtained from the area ratio of the unrecrystallized portion in the observed area. Needless to say, measurements need to be made on a sufficiently average area without bias.

  The mechanism for the effect of “grain size before processing” is not clear, but the effects of changes in dislocation structure, changes in texture, and changes in dislocation structure after processing due to differences in texture before processing are considered. It is done. Details are unknown, but eventually the dislocation structure in the processed structure acts as a powerful obstacle to dislocations that are going to move due to external stress, and against domain walls that are going to move due to an external magnetic field. This is expected to change to a structure that hardly acts as an obstacle.

  The steel plate targeted by the present invention shall have a tensile strength of 500 MPa or more. If the steel sheet has a lower tensile strength than this, it is strengthened mainly by solid solution elements such as ordinary Si and Mn, and even in steel sheets that are completely occupied by a recrystallized structure, the productivity deteriorates so much. This is because it is possible to manufacture without using the material, and the material is significantly superior in terms of magnetic properties. The present invention is limited to a high-strength material that cannot be manufactured without deteriorating productivity, mainly with normal solid solution strengthening. In order to enjoy the merits of the present invention to a greater extent, it should preferably be applied to a steel plate of 600 MPa or more, more preferably 700 MPa or more, more preferably 800 MPa or more. It is possible to manufacture a steel plate of 900 MPa or higher, and even a steel plate of 1000 MPa or higher, which has not been imagined in the past, can be manufactured with high productivity.

  When used as a motor rotor, slight deformation means the end of the service life of the part, so it should be evaluated by yield stress rather than tensile strength. Since the steel of the present invention has a processed structure remaining, the yield stress is high if the strength is the same as that of solid solution reinforced steel and precipitation reinforced steel, and more favorable characteristics are exhibited in comparison with these conventional materials. . That is, the yield ratio is a relatively high value of about 0.7 to 1.0, and the material has a very strong correlation between the yield stress and the tensile strength. For this reason, even if it evaluates with a yield stress, the predominance of this invention steel does not change at all, and the effect of the invention is exhibited without a problem also for the use which yield stress becomes a problem like a rotor.

  This processed structure is assumed to be 1% or more in terms of the area ratio in the cross-sectional structure observation of the steel sheet. In the present invention, the cross-sectional structure observation is performed in a cross section in which one side of the cross section is the steel plate rolling direction and the other side is the steel plate thickness direction. Uses chemicals such as Nital, which are performed on ordinary steel plates, and uses a method of revealing the structure by etching. However, the method is not particularly limited to the observation method, and any technique that can distinguish the recrystallized structure and the processed structure is acceptable. .

  When the area ratio of the processed structure is 1% or less, the effect of increasing the strength is reduced. When the processed structure is substantially 0%, it is a normal steel plate itself, and controlling within the range of 0 to 1% makes the temperature control of annealing very strict for the effect of increasing the strength is small. Needed and not realistic. In practice, the area ratio of the processed structure is controlled so as to obtain the required strength level, but preferably 5% or more, more preferably 10% or more, more preferably 20% or more, more preferably 30% or more, Preferably it is 50% or more, more preferably 70% or more. There is no problem even if the processed structure is 100% in which substantially no recrystallized structure is observed. In this case, the state is a so-called full-hard state in which annealing is not performed at all, or a state of a recovery structure in which annealing is performed but before recrystallization starts.

  In the steel sheet of the present invention, the structure is adjusted according to the required strength and magnetic properties, and this adjustment is made by the steel composition, hot rolling history, cold rolling rate, annealing temperature, annealing time, heating rate, cooling rate, etc. It is possible for those skilled in the art to do this without any problems after several trials. Alternatively, it is possible to form a processed structure by imparting strain to a steel sheet that has been annealed to occupy the entire amount of the recrystallized structure by recold rolling or the like. In this case, since strain is generally applied uniformly macroscopically, the entire amount of the tissue becomes a processed structure, which corresponds to 100% of the processed structure. In this case, the strength and magnetic properties are controlled by the amount of processing in consideration of the steel composition, heat history, characteristics, etc. before processing, but those skilled in the art can also perform this without any problems by several trials. Is.

  As a guideline, the so-called ordinary low-grade electrical steel sheet having a Si content of about 1% or less does not exceed 700 ° C., and the so-called normal high-grade electrical steel sheet having a Si content of about 3% does not exceed 800 ° C. For example, by adding an appropriate amount of Cu, Nb or the like, it is possible to obtain an invented steel having a complete recovery structure that does not recrystallize at all even at a temperature of about 900 ° C. or higher. On the other hand, annealing at a temperature significantly different from that of normal electrical steel sheets requires a significant change in furnace temperature, which not only reduces workability but also improves safety as described above due to the generation of unburned gas. May also cause problems. The lower limit of the annealing temperature for avoiding these problems caused by cryogenic annealing is about 400 ° C. or higher.

  The standard of the annealing time depends on the temperature, but at least about 5 seconds is necessary to exert the effect of annealing. The annealing time depends on the components and the manufacturing history up to the heat treatment and cannot be clearly specified. However, the standard is within 5 minutes at 850 ° C, within 1 hour at 750 ° C, and 10 hours at 600 ° C. Is within. As described above, these temperature and time conditions can be found by those skilled in the art through a few trials and can find out the conditions for enjoying the effects of the invention without any problems. It is to confirm the recrystallization behavior of the steel sheet.

  When a new processed structure is formed by re-cold rolling, etc., if the processing amount is low, it may be difficult to clearly show the presence of the processed structure by the above-described structure observation method, but it is a guideline that sufficiently obtains the effects of the invention. As (crystal grain size in the plate thickness direction) / (crystal grain size in the rolling direction) in cross-sectional structure observation may be used, and this value is set to 0.9 or less. If it is 0.8 or less, the effect of increasing the strength is clearly obtained, preferably 0.7 or less, more preferably 0.6 or less, more preferably 0.5 or less, and further preferably 0.3 or less. . However, it should be noted that if this value becomes excessively low, the magnetic characteristics will deteriorate significantly.

  The above processing is usually performed by cold rolling, but it is not necessary to stick to this as long as the amount of strain or material change is within the rules of the present invention, warm rolling, hot rolling to such an extent that the work structure is not lost. Furthermore, any method such as tensile deformation by applying tension, bending deformation by a leveler, shot blasting, forging, etc. may be used. Rather, since the dislocation structure is changed to a preferable one for the present invention described later by the method of imparting strain, further improvement in characteristics can be achieved.

  When this processing is performed by cold rolling, the rolling reduction can be easily estimated from the above-described ratio of crystal grain sizes, but is approximately 10 to 70%. In this way, when the material softened to some extent in the annealing process is further hardened by re-cooling, the material can be easily thinned, and the productivity of the ultra-thin electrical steel sheet, which was conventionally difficult to manufacture, is also improved. . Such an ultra-thin electromagnetic steel sheet according to the present invention can suppress eddy current loss particularly when used under a high-frequency magnetic field, and thus has an advantage of being effective in reducing iron loss.

  At present, there is an electrical steel sheet, so-called semi-process electrical steel sheet, which is shipped as a product by performing skin pass rolling of about 1 to 20% on a recrystallized annealed steel sheet as in the method of the present invention. This is because a skin-passed plate is shipped as a product, processed as a motor part by a motor manufacturer, and then annealed under conditions that cause sufficient recrystallization to cause strain-induced grain growth. A means for obtaining a recrystallized structure and improving magnetic properties is sometimes referred to as a skin pass method, but in this method, the processed structure is not left at the time of use as a member.

  The present invention is essentially different from the steel plate and method, and basically no heat treatment is performed after being processed as a part of an electrical device. Even when any heat treatment is performed for adhesion or surface control of a steel plate, the processed structure defined in the present invention is not lost, and the present invention is limited to those that remain within the definition of the present invention. This is because when the processed structure disappears or deviates from the specified range of the present invention, the strength of the steel sheet required in the situation where it is used as an actual motor will be insufficient. The standard of the temperature of this heat processing is the same as the temperature conditions in the above-mentioned steel plate annealing process. Optimal conditions are those with the cooperation of those skilled in the art of manufacturing steel sheets, or those who are ordinary electrical equipment manufacturers without cooperation can find the conditions that can enjoy the effects of the invention without any problems after several trials. It is possible.

The effect of the “processed structure” described above can also be evaluated by the dislocation density in the “processed structure”. The average dislocation density in the processed structure is 1 exp13 / m ² or more, more preferably 3 exp13 / m ² or more, more preferably 1 exp14 / m ² or more, and further preferably 3 exp14 / m ² or more. This dislocation density is measured by a transmission electron microscope or the like. In an ordinary electrical steel sheet in which the total amount of the steel sheet is a recrystallized structure, the average dislocation density is about 1 exp12 / m ² or less, and therefore, the difference is set to 10 times or more as a sufficient difference for sorting the processed structures.

  Strictly speaking, in order to use various members in ordinary electromagnetic steel sheets, processing such as shearing and caulking is performed by a manufacturer or the like, so that a considerable amount of distortion introduced into the steel sheets remains, and the characteristics of the members are reduced. It is known to affect. Such strains enter only the processed portion of the steel sheet, and unlike the strain that consciously remains on the entire surface of the steel sheet in the present invention, it hardly contributes to increasing the strength of the entire member.

  The reason why good magnetic characteristics can be maintained even if the processed structure remains in the material as in the present invention is not clear, but is considered as follows. Conventionally, the processed structure is not considered as a means for increasing the strength of the material because it greatly deteriorates the magnetic properties, and the increase in the strength has been performed by crystal grain refinement, solid solution strengthening, precipitation strengthening and the like. However, the demand for higher strength of materials is increasing, and conventional strength enhancement means have to step into the area of conditions that significantly deteriorates magnetic properties. If we look at the means for strengthening using the processed structure again, it seems to be one aspect that it is no longer a disadvantageous method.

  In addition, what has been studied in the past is that the effect of the processed structure is cold working on the material and the strain amount is only in a relatively small range. Under such conditions, the dislocation structure in the material is relatively uniform, It is expected that a relatively stable dislocation arrangement such as a so-called cell structure or recovery structure was not formed. In this amount of processing, it was not attractive at all as a means of increasing the strength, and in such a dislocation structure, the dislocation only became an obstacle to the domain wall movement and the deterioration of the magnetic properties was remarkable and was not put into practical use. I think that the.

  On the other hand, dislocations form a relatively stable cell structure when a relatively high strain amount of cold working is performed as in the present invention, or in a processed structure recovered by annealing. The size of the cell is usually less than 1 μm in diameter and is about 0.1 μm, and the cell boundary is formed by dislocations, except that the crystal orientation difference between adjacent cells is small. It has a similar structure, and can be regarded as a kind of ultrafine crystal grains, and is considered to be less likely to be an obstacle to domain wall movement. Further, such ultrafine crystal grains have high strength and have a certain degree of ductility when processing is necessary. Considering the balance between strength and magnetism, the ultrafine crystal grains are considered to be sufficiently practical.

  In addition, in the steel of the present invention in which a processed structure exists, addition of Si, Mn, Al, Cr, Ni, etc. is not necessary in applications where the iron loss is used in a high-frequency magnetic field where the contribution of eddy current loss is particularly large The development of dislocation strengthened steels based on electrical steel sheets has become important for so-called ordinary steels for processing used in automobiles and containers, because they are important and have a great influence on dislocation behavior such as work hardening behavior and recrystallization behavior. It has a completely different meaning.

  The effect of the present invention can be applied to a non-oriented or directional electrical steel sheet because it does not depend on the manufacturing process, regardless of the presence and type of a surface film usually formed on the surface of the electrical steel sheet. In particular, the steel according to the present invention can impart characteristics that are greatly different from those of steel sheets having a conventional recrystallization structure in the in-plane anisotropy of characteristics. Looking at the magnetic flux density, the characteristics in the 45 ° direction (D direction) from the coil rolling direction are higher than the characteristics in the rolling direction (L direction) or the coil width direction (C direction) in the fully hard state as cold rolled. It has become. In most cases of electrical steel sheets having a normal recrystallized structure, the characteristics in the D direction are lower than those in the L or C direction. By controlling to the crystallization stage, it is possible to easily obtain a steel sheet having almost no in-plane anisotropy. The fact that there is almost no in-plane anisotropy is a steel sheet having a feature that can exhibit very favorable characteristics depending on applications such as a rotating machine.

The use is not particularly limited, and the present invention is applicable to all uses where strength and magnetic properties are required in addition to the use of a rotor of a motor used in home appliances or automobiles.
[ Reference example ]

200 mm thick steel slab having a component of 0.002% C-3.0% Si-0.5% Mn-0.03% P-0.001% S-0.3% Al-0.002% N Then, hot rolling at a slab heating temperature of 1100 ° C. and a coiling temperature of 700 ° C. was performed, the hot-rolled sheet annealing was changed to 800, 950, and 1050 ° C., and the particle size was changed to 10, 100, and 200 μm. Each hot-rolled sheet was cold-rolled and then annealed at 400 to 1000 ° C. for 30 seconds to produce a product sheet having a thickness of 0.5 mm with different recrystallization rate and strength. About these, the mechanical characteristic by a _JIS5 test piece and the iron loss _{W10 / 400} by the SST test of a 55 mm square were evaluated. For both the mechanical characteristics and the magnetic characteristics, the average value was determined by the following formula for the rolling direction of the coil, the 45 ° direction, and the direction perpendicular thereto.
X = (X ₀ + 2 × X ₄₅ + X ₉₀ ) / 4
Here, X ₀ , X ₄₅ , and X ₉₀ are characteristics of the coil rolling direction, 45 ° direction, and its perpendicular direction.

The results are shown in FIG. As is clear from the results, the material having a large hot-rolled plate particle size has a good strength-iron loss balance.

Product plates were produced from the 200 mm thick steel pieces having the components shown in Table 1 under the production conditions shown in Table 2. Some materials were heat-treated (user annealed) assuming heat treatment at the motor manufacturer. These characteristics were evaluated in mechanical properties, and 55mm angle iron loss W _10/400 and the magnetic flux density B ₂₅ by SST test by JIS5 No. specimen. For both the mechanical characteristics and the magnetic characteristics, the average value was determined by the following formula for the rolling direction of the coil, the 45 ° direction, and the direction perpendicular thereto.
X = (X ₀ + 2 × X ₄₅ + X ₉₀ ) / 4
Here, X ₀ , X ₄₅ , and X ₉₀ are characteristics of the coil rolling direction, 45 ° direction, and its perpendicular direction.

  The results are shown in Table 2. As is apparent from the results, the material produced under the conditions of the present invention is hard and has excellent magnetic properties. It should be noted that, in general, electrical steel sheets have different characteristics depending on the amount of Si so that grades are sold according to the amount of Si contained. The iron loss varies greatly depending on the plate thickness. The high Si material has a significantly reduced iron loss due to the difference in Si content compared to the low Si material, and the iron loss is also reduced in the case of a thin plate, so when evaluating the effect of the present invention, Si In consideration of the difference in the amount and thickness, it is necessary to compare with the same amount of Si and thickness.

It is a figure which shows the intensity | strength-iron loss balance depending on the particle size before cold rolling.

Claims (7)

In mass%, C: 0.060% or less, Si: 0.2-4.0%, Mn: 0.05-3.0%, P: 0.30% or less, S: 0.040% or less, By further processing a region or recrystallized structure containing Al: 2.50% or less, N: 0.020% or less, consisting of the remainder Fe and unavoidable impurities and not eroded by the recrystallized structure inside the steel sheet. in the method of producing a high strength electrical steel sheet is obtained tissue processing tissue remains, the average crystal grain size d of the steel sheet immediately before the step of forming the worked structure to finally remain inside the steel sheet with a higher 20μm A method for producing an electrical steel sheet, wherein a recrystallization rate of the steel sheet is 100%, and the processed structure is 20% or more in terms of an area ratio in cross-sectional observation. In mass%, C: 0.060% or less, Si: 0.2-4.0%, Mn: 0.05-3.0%, P: 0.30% or less, S: 0.040% or less, By further processing a region or recrystallized structure containing Al: 2.50% or less, N: 0.020% or less, consisting of the remainder Fe and unavoidable impurities and not eroded by the recrystallized structure inside the steel sheet. In the method for producing a high-strength electrical steel sheet in which the processed structure that is the resulting structure remains,
The average crystal grain size d (μm) of the steel sheet immediately before the step of forming the processed structure finally remaining inside the steel sheet,
d ≧ (220-50 × Si%) ,
And the recrystallization rate of the steel sheet is 100%, and the processed structure is 20% or more in terms of the area ratio in cross-sectional observation. The average crystal grain size d (μm) of the steel sheet immediately before the step of forming the processed structure finally remaining inside the steel sheet,
d ≦ (400-50 × Si%),
And,
d ≦ (820−200 × Si%),
The method for producing an electrical steel sheet according to claim 1 or 2, wherein: In mass% steel composition, further, Cu: 0.1~8.0%, Nb: 0.03~8.0% of any of claims 1-3, characterized in that it contains one or more The manufacturing method of the electromagnetic steel sheet as described in a term. Steel component is mass%, and further contains one or more of Ti: 1.0% or less, B: 0.010% or less, Ni: 5.0% or less, Cr: 15.0% or less. The method for producing an electrical steel sheet according to any one of claims 1 to 4 , wherein: In steel ingredients by weight%, further, Sn, the electrical steel sheet according to any one of claims 1-5, characterized in that it contains less than 0.5% in total of one or more of Ce Production method. The method for producing an electrical steel sheet according to any one of claims 1 to 6 , wherein an average dislocation density in the processed structure inside the steel sheet is 1 exp13 / m ² or more.

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